全文获取类型
收费全文 | 13099篇 |
免费 | 870篇 |
国内免费 | 2篇 |
学科分类
农业科学 | 13971篇 |
出版年
2023年 | 98篇 |
2022年 | 128篇 |
2021年 | 300篇 |
2020年 | 275篇 |
2019年 | 234篇 |
2018年 | 524篇 |
2017年 | 567篇 |
2016年 | 535篇 |
2015年 | 407篇 |
2014年 | 522篇 |
2013年 | 748篇 |
2012年 | 898篇 |
2011年 | 822篇 |
2010年 | 460篇 |
2009年 | 448篇 |
2008年 | 668篇 |
2007年 | 610篇 |
2006年 | 523篇 |
2005年 | 547篇 |
2004年 | 450篇 |
2003年 | 428篇 |
2002年 | 364篇 |
2001年 | 278篇 |
2000年 | 263篇 |
1999年 | 241篇 |
1998年 | 65篇 |
1997年 | 52篇 |
1996年 | 55篇 |
1992年 | 141篇 |
1991年 | 119篇 |
1990年 | 116篇 |
1989年 | 135篇 |
1988年 | 124篇 |
1987年 | 125篇 |
1986年 | 121篇 |
1985年 | 114篇 |
1984年 | 86篇 |
1983年 | 81篇 |
1982年 | 50篇 |
1981年 | 68篇 |
1980年 | 58篇 |
1979年 | 111篇 |
1978年 | 99篇 |
1977年 | 93篇 |
1976年 | 60篇 |
1975年 | 49篇 |
1974年 | 102篇 |
1973年 | 74篇 |
1972年 | 96篇 |
1971年 | 97篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Pavel Šamonil Martin Valtera Stanislav Bek Barbora Šebková Tomáš Vrška Jakub Houška 《European Journal of Forest Research》2011,130(6):1075-1091
Soil variability was assessed in a 74.2-ha area within the Žofínsky prales natural forest. Parameters evaluated for 1765 soil
profiles inside 353 graticule plots were as follows: (1) thickness of organic horizons, (2) thickness and form of mineral
horizons, (3) humus form (HF), (4) soil taxonomic unit (STU) and (5) anomalies. In addition, soil reaction (pHKCl) and oxidizable carbon content (Cox) were measured in the laboratory for 734 samples from the upper mineral (A) and lower mineral (B) horizons. The most frequently
occurring humus form was mor followed by moder, hydromor and peaty T-horizon. Entic Podzols, Dystric Cambisols, Haplic Cambisols,
Albic Podzols, Histic (or Haplic) Gleysols, Endogleyic Stagnosols, Fibric or Hemic or Sapric Histosols and Stagnic Gleysols
were all present at the site despite its homogeneous geological bedrock. Overall coefficient of variance (CV) was lower in
terrestrial soils compared with (semi-)hydromorphic soils. Overall variance decreased in both soil groups with increasing
depth, as did CV differences between the fine (up to 10 m) and the locality scales. The lowest CV values occurred for Cox and pHKCl. The CV values differed between STUs as well. Compared to lower horizons, variograms of upper horizons showed greater autocorrelation
at the intermediate spatial scale (10–320 m)—ranging from 50 to 150 m. Semivariance values, however, reached 70–80% of sill
already at a distance of 10 m. The most significant factor of variability at all studied spatial scales is presumably the
soil disturbance regime, followed by terrain micro-topography and the effect of tree species. 相似文献
992.
Reyes Tárrega Leonor Calvo Ángela Taboada Elena Marcos José Antonio Marcos 《European Journal of Forest Research》2011,130(6):949-957
We compared the structure of the arboreal layer and the diversity and species composition of the understory vegetation of
three types of mature forest communities: oak (Quercus pyrenaica) and beech (Fagus sylvatica) forests and Scots pine (Pinus sylvestris) plantations. Our main aim was to determine whether differences in these variables existed and were due to the identity of
the dominant tree species. We selected four stands or replicates per forest type located geographically close and with relatively
similar conditions. We found no differences in the arboreal structure of oak and beech forests, which were characterised by
great variability in tree size, while in case of plantations, this variability was lower at both the intra-stand (estimated
by the coefficient of variation) and inter-stand (i.e. the four replicates harboured trees of similar sizes) scales. However,
the highest variability in the canopy layer of natural forests was not consistently linked to greater understory species richness.
Indeed, the lowest plant species richness was found in beech forests, while oak forests harboured the highest value at either
the sampling unit (per m2) or stand scales. The greatest negative correlation between plant diversity and the environmental variables measured was
found for litter depth, which was the highest in beech forests. The results obtained by the CCA indicated that the four replicates
of each forest type clustered together, due to the presence of characteristic species. We concluded that pine plantations
did not approach the environmental conditions of native forests, as plantations were characterised by singular understory
species composition and low arboreal layer variability, compared to natural woodlands. 相似文献
993.
Jaime A. Ocampo-Hernández Patricia Tamez-Guerra Samuel Pineda Fernando Tamayo-Mejía Ariel Guzmán-Franco José I. Figueroa de la Rosa Ana Mabel Martínez 《Journal of pest science》2011,84(4):471-477
Entomopathogenic fungi represent excellent candidates for biological insecticides. Among the many entomopathogenic fungi, Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae) is one of the most promising species. Here, we report the results of infection studies performed using four B. bassiana native isolates (Bb37, Bb38, Bb40, and Bb45) compared with the commercial product Mycotrol® (strain GHA) on adult Mexican bean beetle Epilachna varivestis Mulsant (Coleoptera: Coccinellidae), one of the most important pests of bean production in Mexico. First, single concentration (1 × 108 conidia mL?1) assays were carried out using all isolates applied using an immersion method. Examinations at 10 days after inoculation indicated that isolates Bb37, Bb38, and Bb40 significantly reduced adult survival, causing 60–75% mortality compared to the commercial strain GHA (33%) and control (29%). Second, using two selected isolates (Bb37 and Bb40), the mean lethal concentration values (LC50) were estimated for third instar larvae and adult E. varivestis. The LC50 values for Bb37 and Bb40 isolates decreased 5.26-fold and 3.19-fold, respectively, in third instars compared with adults. However, such difference for Bb40 isolate was not significant. Finally, an experiment, to compare the median survival time (MST) values between third instar and adult E. varivestis, was conducted using Bb37 and Bb40 at 1 × 109 conidia mL?1. MST values were significantly reduced against larvae (87 and 100 h) compared with adults (130 and 134 h) by Bb37 and Bb40, respectively. We conclude that native isolates of B. bassiana represent an important alternative for the control of E. varivestis. However, to demonstrate its effectiveness under field conditions, detailed studies are needed. 相似文献
994.
In laboratory tests, the toxicity of acaricides targeted against house dust mites was tested on five species of stored product
mites (Acarus siro, Aleuroglyphus ovatus, Carpoglyphus lactis, Lepidoglyphus destructor, and Tyroborus lini). The formulations of benzyl-benzoate, benzyl-benzoate/permethrin/pyriproxyfen, and neem were diluted in water and applied
to filter paper in an unventilated chamber. The mortality of mites was observed after 24 h of exposure to acaricide-impregnated
filter paper. All of the tested acaricides were toxic to all of the mite species. There were significant differences in mortality
among the species and the acaricides. Benzyl-benzoate/permethrin/pyriproxyfen was the most effective, followed by benzyl-benzoate
and neem. L. destructor (LD50 0.01–0.11 μg) was the most sensitive mite species, followed by A. siro (LD50 0.04–0.12 μg), T. lini (LD50 2–21 μg), A. ovatus (LD50 3–18 μg), and C. lactis (LD50 4–64 μg). Based on the highly toxic effects of the tested acaricides against the stored product mites, the acaricides should
be considered as a potential tool in the control of stored product mites, although next screening is necessary. 相似文献
995.
González-Sarrías A Gromek S Niesen D Seeram NP Henry GE 《Journal of agricultural and food chemistry》2011,59(16):8632-8638
Research has shown that members of the Carex genus produce biologically active stilbenoids including resveratrol oligomers. This is of great interest to the nutraceutical industry given that resveratrol, a constituent of grape and red wine, has attracted immense research attention due to its potential human health benefits. In the current study, five resveratrol oligomers (isolated from Carex folliculata and Carex gynandra ), along with resveratrol, were evaluated for antiproliferative effects against human colon cancer (HCT-116, HT-29, Caco-2) and normal human colon (CCD-18Co) cells. The resveratrol oligomers included one dimer, two trimers, and two tetramers: pallidol (1); α-viniferin (2) and trans-miyabenol C (3); and kobophenols A (4) and B (5), respectively. Although not cytotoxic, the resveratrol oligomers (1-5), as well as resveratrol, inhibited growth of the human colon cancer cells. Among the six stilbenoids, α-viniferin (2) was most active against the colon cancer cells with IC(50) values of 6-32 μM (>2-fold compared to normal colon cells). Moreover, α-viniferin (at 20 μM) did not induce apoptosis but arrested cell cycle (in the S-phase) for the colon cancer but not the normal colon cells. This study adds to the growing body of knowledge supporting the anticancer effects of resveratrol and its oligomers. Furthermore, Carex species should be investigated for their nutraceutical potential given that they produce biologically active stilbenoids such as α-viniferin. 相似文献
996.
Del Barrio-Galán R Pérez-Magariño S Ortega-Heras M Williams P Doco T 《Journal of agricultural and food chemistry》2011,59(23):12433-12442
A study was made of the effect of aging on lees and of three different commercial yeast derivative products of different composition and degree of purification on the phenolic compounds, color, proteins, polysaccharides, and sensorial characteristics of white wines. The results obtained showed that the lees and yeast derivative products can interact or adsorb some of the phenolic compounds present in wines, reducing their concentration. This reduction depends on the treatment applied, the phenolic compound analyzed, and the stage of vinification or aging process. The use of lees and yeast derivative products can reduce the color intensity and the browning of the wines immediately following treatment. The monosaccharide and polysaccharide content of yeast derivative products depends on the manufacturing process and degree of purification of the product, both of which have an influence on wine treatments. After 6 months in the bottle, both the aging on lees and the treatment with commercial yeast derivative products gave rise to wines with better sensorial characteristics than in the case of the control wines. 相似文献
997.
Risalde MA Gómez-Villamandos JC Pedrera M Molina V Cerón JJ Martínez-Subiela S Sánchez-Cordón PJ 《Veterinary journal (London, England : 1997)》2011,190(2):e110-e116
Eight colostrum-deprived calves aged 8-12 weeks were inoculated intranasally with a non-cytopathic strain of bovine viral diarrhoea virus (BVDV) genotype-1 and the effects on the hepatic immune response were studied. Two calves were sacrificed at each of 3, 6, 9 and 14 days post-inoculation (dpi) and two uninoculated animals were used as negative controls. BVDV was detected in hepatic macrophages and monocytes from 3 to 14dpi and in Küpffer cells (KCs) from 6 to 14dpi. Increases in the numbers of MAC387(+) KCs and monocytes, but not interstitial macrophages, differentiated by morphological features, were evident in the liver following inoculation with BVDV. There was a substantial increase in the number of monocytes positive for tumour necrosis factor (TNF)-α, but only small increases in the numbers of TNF-α(+) KCs and interstitial macrophages and interleukin (IL)-6(+) monocytes, KCs and interstitial macrophages. There was an increase in the number of interstitial CD3(+) T lymphocytes in the liver, but no substantial changes in the numbers of circulating CD3(+) T lymphocytes, interstitial or circulating CD4(+) or CD8(+) T lymphocytes, or CD79αcy(+) B lymphocytes. Serum haptoglobin and serum amyloid A increased transiently at 12dpi. Upregulation of some pro-inflammatory cytokines by hepatic macrophages is evident in subclinical acute BVDV type 1 infection in calves. 相似文献
998.
Naglaa Abdel Megid Gomaa BVSc MVSc Gábor Köller Dr rer nat Gerald Fritz Schusser Dr vet med DECEIM 《Journal of Veterinary Emergency and Critical Care》2011,21(3):242-252
Objectives – To measure serum alcohol dehydrogenase (ADH) activity in horses with acute intestinal obstruction and to determine the diagnostic and prognostic utility of this analyte. Design – Prospective observational study. Setting – University Veterinary Hospital. Animals – Thirty healthy horses (control group) and 77 horses with acute intestinal obstruction, including 36 horses with nonstrangulating obstruction (23 with left ventral colon impaction and 13 with left dorsal displacement [G1], 22 with small intestinal strangulation [G2], and 19 with colon torsion [G3]). Interventions – Serum ADH activity was assayed spectrophotometerically in all horses. Serum lactate concentration and hepatic enzyme (aspartate aminotransferase, gamma‐glutamyl transferase, glutamate dehydrogenase) activities were measured using an automatic analyzer. Measurements and Main Results – The median [interquartile range] serum ADH activity in healthy horses was 10.5 [8.7 – 11 U/L]. ADH activity was significantly increased (P<0.05) in G1=16.5 [13.8 – 18 U/L], G2=40 [20 – 74.9 U/L], and G3=63.2 [40 – 78 U/L] compared with healthy controls. Aspartate aminotransferase and glutamate dehydrogenase activities were also significantly increased in G3 in comparison with controls. ADH activity was correlated with serum lactate concentration in G1 and G3, respectively (P<0.01, r=0.55 and 0.8). Other liver enzymes did not show any significant correlation with lactate. ADH activity was directly related to the probability of strangulation; odds ratio=1.11. ADH activity >20 U/L had 80.6% specificity and 80.5% sensitivity for discriminating horses with strangulating obstruction. Twelve horses euthanized before surgery were excluded from the outcome analysis. Increasing ADH activity was associated with nonsurvival; odds ratio=1.03. ADH activity <80 U/L had 94.44% specificity and 66.67% sensitivity for survival. Conclusion – Serum ADH activity may be a useful clinical parameter in detecting intestinal strangulation in horses and may provide some prognostic value in horses with acute intestinal obstruction. 相似文献
999.
da Cruz CE de Oliveira LG Boabaid FM Zimermann FC Stein G Marks F Cerva C Lieberknecht C Canal CW Driemeier D 《Journal of zoo and wildlife medicine》2011,42(3):451-459
Pekin robins (Leiothrix lutea) were once the most widely kept softbills in captivity. As a result of the Convention on the International Trade of Endangered Species of Fauna and Flora (CITES-1997), the worldwide trade of wild-caught pekin robins has been prohibited due to the depletion of native populations of this species. In Brazil, as in other countries, pekin robins imported prior to the enactment of the CITES have disappeared from aviaries because the end of the birds' natural life span has passed, and only very few captive-bred pekin robins now exist. While captive propagation fails to address the primary causes of wild bird population decline, it might help the recovery of populations of this species. This article presents records made over a 10-yr period of a captive colony of pekin robins. Emphasis is placed on the management of the flock, the ailments affecting the birds, and the findings associated with bird losses. The main causes of bird losses included rearing management failures and age-related disorders. 相似文献
1000.
Suárez-Bonnet A Herráez P Martín de las Mulas J Rodríguez F Déniz JM Espinosa de los Monteros A 《Veterinary journal (London, England : 1997)》2011,(3):345-351
14-3-3 σ protein is a negative cell cycle regulator, with both reduced and elevated levels associated with cancer in humans. This study assessed the expression of this protein in canine mammary tissues using immunohistochemistry and Western blotting. 14-3-3 σ was detected in 97% of the mammary tissue samples examined and was found in both myoepithelial (MECs) and epithelial (ECs) cells. Expression levels were elevated and reduced in neoplastic ECs and MECs, respectively (P < 0.001). Intense expression of 14-3-3 σ was detected in neoplastic ECs infiltrating blood vessels and lymph nodes and suggests a possible role for this protein in the malignant transformation of mammary neoplasms. Moreover, double immunostaining for 14-3-3 σ and the MEC – specific marker p63, confirmed that 14-3-3 σ is a highly sensitive marker of MECs since all p63 – positive cells were also positive for 14-3-3 σ. However, this protein is not exclusive to MECs as ECs also labelled positively. 相似文献