全文获取类型
收费全文 | 778篇 |
免费 | 37篇 |
学科分类
农业科学 | 815篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 15篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 60篇 |
2012年 | 36篇 |
2011年 | 48篇 |
2010年 | 26篇 |
2009年 | 23篇 |
2008年 | 43篇 |
2007年 | 47篇 |
2006年 | 36篇 |
2005年 | 36篇 |
2004年 | 36篇 |
2003年 | 37篇 |
2002年 | 32篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1991年 | 6篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 8篇 |
1971年 | 3篇 |
1970年 | 5篇 |
1969年 | 5篇 |
1967年 | 6篇 |
1966年 | 5篇 |
1965年 | 6篇 |
1963年 | 4篇 |
排序方式: 共有815条查询结果,搜索用时 15 毫秒
1.
2.
3.
The orchard of the Institute of Fruit Breeding of the German Federal Centre of Breeding Research on Cultivated Plants in Dresden-Pillnitz was highly affected by fire blight in 2003. Infected pomefruit trees were observed over a period of nearly 3 months. The first symptoms on pear trees were found on May 19th. The pathogen Erwinia amylovora was confirmed officially on May 26, and the last infected apple trees were detected the 11th of August. The infected trees had to be grubbed at the decision of the Phytopathological Authority. In total, 1164 apple and 478 pear trees were grubbed, including the entire pear collection of the gene bank. Of 35 wild species of pear, 49 accessions, eight accessions of six species each, showed infections. The apple collection of the gene bank included 33 wild species, with 365 accessions, and 845 cultivars and clones. Ten accessions of nine wild apple species and 81 cultivars/clones of these collections showed fire blight infection. The source of infection was the pear collection, and the distance from that source was important for the occurrence of infection. Field plots close to the pear collection had tree losses of 10–34%, while more distant plots had losses of 0–6%. Around 80% of the lost apple trees were detected and grubbed from 27th May to 11th June. Some of the cultivars bred in Dresden-Pillnitz, e.g. ‘Pilot’ and ‘Rekarda’, were affected by fire blight in most field plots, whereas most others were affected mainly only in plots adjacent to the infection source. A correlation of r=?0.72 could be calculated for rating in artificial shoot inoculations and percentage of trees of resistant cultivars lost. The cultivars ‘Pirol’, ‘Reanda’, ‘Remo’, ‘Rene’, ‘Renora’, ‘Resi’, and ‘Retina’ showed only a very low numbers of infected trees. No tree of ‘Rewena’ showed symptoms of fire blight. Despite a tendency to postblooming, only 8.9% of ‘Pinova’ trees had to be grubbed. 相似文献
4.
从本期起我们将陆续向读者推出核苷酸的营养作用。本期首先介绍核苷酸是怎样促进年轻动物的生长发育的。 相似文献
5.
6.
Pharmacokinetics of xylazine after 2-, 4-, and 6-hr durations of continuous rate infusions in horses
Klaus Hopster Lawrence R. Soma Xiaoqing Li Charlotte Hopster-Iversen Raymond C. Boston Bernd Driessen 《Journal of veterinary pharmacology and therapeutics》2020,43(6):557-564
Intravenous (i.v.) bolus administration of xylazine (XYL) (0.5 mg/kg) immediately followed by a continuous rate infusion (CRI) of 1 mg kg−1 hr−1 for 2, 4, and 6 hr produced immediate sedation, which lasted throughout the duration of the CRI. Heart rate decreased and blood pressure increased significantly (p > .05) in all horses during the first 15 min of infusion, both returned to and then remained at baseline during the duration of the infusion. Compartmental models were used to investigate the pharmacokinetics of XYL administration. Plasma concentration–time curves following bolus and CRI were best described by a one-compartment model. No differences were found between pharmacokinetic estimates of the CRIs for the fractional elimination rate constant (Ke), half-life (t1/2e), volume of distribution (Vd), and clearance (Cl). Median and range were 0.42 (0.15–0.97)/hr, 1.68 (0.87–4.52) hr, 5.85 (2.10–19.34) L/kg, and 28.7 (19.6–39.5) ml min−1 kg−1, respectively. Significant differences were seen for area under the curve ( ) (p < .0002) and maximum concentration (Cmax) (p < .04). This indicates that with increasing duration of infusion, XYL may not accumulate in a clinically relevant way and hence no adjustments are required in a longer XYL CRI to maintain a constant level of sedation and a rapid recovery. 相似文献
7.
Through irrigation management transfer inMexico poorly functioning governancemechanisms for maintenance were replaced.New actors, new roles, and newresponsibilities in the maintenance ofMexican irrigation systems wereestablished. This article analyzes themaintenance service delivery mechanisms inthe Alto Río Lerma Irrigation District(ARLID), to evaluate if and how theinstitutional arrangements establishedthrough management transfer ensure adequateservice provision. After presenting themain actors currently involved inirrigation maintenance, the rules andregulations underlying the servicerelationships between the actors involvedin maintenance in ARLID are analyzed. Thisis done by detailing how theserelationships are formally organized, howthey work in practice, and which incentivesexist for the service providers to providean efficient service and for the servicerecipient to pro-actively participate inservice provision. We conclude that the newinstitutional framework for maintenanceservice provision is quite coherent andthat the governance mechanisms that havebeen established work well, especiallythose between the farmers and theirorganizations. This has led to improvedmaintenance services. 相似文献
8.
Franziska R. Haunhorst Klaus Hopster Marion Schmicke Astrid Bienert-Zeit Sabine Kstner 《The Canadian veterinary journal. La revue veterinaire canadienne》2022,63(1):39
The objective of this study was to compare effects of butorphanol (BUT) or buprenorphine (BUP), in combination with detomidine and diazepam, on the sedation quality, surgical conditions, and postoperative pain control after cheek tooth extraction in horses, randomly allocated to 2 treatment groups (BUT: n = 20; BUP: n = 20). A bolus of detomidine (15 μg/kg, IV) was followed by either BUP (7.5 μg/kg, IV) or BUT (0.05 mg/kg, IV). After 20 min, diazepam (0.01 mg/kg, IV) was administered and sedation was maintained with a detomidine IV infusion (20 μg/kg/h), with rate adjusted based on scores to 5 variables. All horses received a nerve block (maxillary or mandibular), and gingival infiltration with mepivacaine. Sedation quality was assessed by the surgeon from 1 (excellent) to 10 (surgery not feasible). A pain scoring system (EQUUS-FAP) was used to assess postoperative pain. Serum cortisol concentrations and locomotor activity (pedometers) were measured.Horses in BUP and BUT required a median detomidine infusion rate of 30.2 μg/kg/h (20 to 74.4 μg/kg/h) and 32.2 μg/kg/h (20 to 48.1 μg/kg/h), respectively (P = 0.22). Horses in the BUP group had better sedation quality (P < 0.05) during surgery and higher step counts (P < 0.001) postoperatively. Buprenorphine combined with detomidine provided a more reliable sedation than butorphanol. However, the EQUUS-FAP pain scale became unreliable because of BUP-induced excitement behavior. 相似文献
9.
Environmental effects on soil NO concentrations and root N uptake in beech and spruce forests 下载免费PDF全文
Fang Dong Judy Simon Michael Rienks Jürgen Schäffer Klaus von Wilpert Heinz Rennenberg 《植物养料与土壤学杂志》2016,179(2):244-256
This study aimed to investigate the shifts in net nitrogen (N) uptake and N compounds of fine roots over the vegetation period (i.e., spring, summer, autumn) and correlate this with NO concentration in the soil. Soil NO concentration was measured using gas lysimeters for collection and a chemiluminescence analyzer for quantification. Net N uptake by the roots was determined using the 15N enrichment technique. N pools were quantified using spectrophotometric techniques. Soil NO concentrations at beech and spruce forest sites were highest in spring (June), and lowest in winter (December). Total N of the roots was similar during the seasons and between the two years under study despite considerable variation of different N compounds. Net N uptake generally increased with higher N supply. Correlation analysis revealed a positive relationship between soil NO concentration and net N uptake only for spruce trees. This relationship seemed to be modulated by environmental factors and tree species. 相似文献
10.
Putzbach K Krucker M Albert K Grusak MA Tang G Dolnikowski GG 《Journal of agricultural and food chemistry》2005,53(3):671-677
The structures of biosynthetic deuterated carotenoids in labeled vegetables were investigated: (all-E)-lutein and (all-E)-beta-carotene from spinach, and (all-E)-beta-carotene and (all-E)-alpha-carotene from carrots. The vegetables were grown hydroponically using a nutrient solution enriched with deuterium oxide (D(2)O) and were extracted using matrix solid-phase dispersion (MSPD). Deuterium enrichment in the carotenoid molecules was determined by liquid chromatography-mass spectrometry (LC-MS). (all-E)-Lutein and (all-E)-beta-carotene in spinach showed partial deuteration from (2)H(1) to (2)H(12), with the abundance maximum at (2)H(5). (all-E)-beta-Carotene and (all-E)-alpha-carotene from carrots showed partial deuteration from (2)H(1) to (2)H(17), with the abundance maximum at (2)H(11). The (1)H NMR spectra of the four deuterated carotenoids showed additional signals for all methyl groups and decreased signal intensity for the olefinic protons and the methylene protons in the ring. These differences are due to isotopic effects and are based on the substitution of protons by deuterium atoms. The deuteration was distributed randomly throughout the carotenoid molecules. 相似文献