全文获取类型
收费全文 | 2038篇 |
免费 | 123篇 |
国内免费 | 9篇 |
学科分类
农业科学 | 2170篇 |
出版年
2023年 | 19篇 |
2022年 | 57篇 |
2021年 | 79篇 |
2020年 | 96篇 |
2019年 | 127篇 |
2018年 | 150篇 |
2017年 | 134篇 |
2016年 | 133篇 |
2015年 | 72篇 |
2014年 | 86篇 |
2013年 | 216篇 |
2012年 | 114篇 |
2011年 | 133篇 |
2010年 | 107篇 |
2009年 | 69篇 |
2008年 | 125篇 |
2007年 | 58篇 |
2006年 | 45篇 |
2005年 | 38篇 |
2004年 | 34篇 |
2003年 | 32篇 |
2002年 | 25篇 |
2001年 | 17篇 |
2000年 | 27篇 |
1999年 | 16篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1967年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有2170条查询结果,搜索用时 15 毫秒
101.
Shahbaz Khan Muhammad Nadeem Asghar Tariq Rana 《Water, air, and soil pollution》2007,182(1-4):131-148
Automated synoptic weather typing and robust orthogonal stepwise regression analysis (via principal components analysis) were applied together to develop within-weather-type air pollution prediction models for a variety of pollutants (specifically, carbon monoxide – CO, nitrogen dioxide – NO2, ozone – O3, sulphur dioxide – SO2, and suspended particles – SP) for the period 1974–2000 in south-central Canada. The SAS robust regression procedure was used to limit the influence of outliers on air pollution prediction algorithms. Six-hourly Environment Canada surface observed meteorological data and 6-hourly US National Centers for Environmental Prediction (NCEP) reanalysis data of various weather elements were used in the analysis. The models were developed using two-thirds of the total years for meteorological and air pollution data; the remaining one-third (randomly selected) was used for model validation. Robust stepwise regression analysis was performed to analytically determine the meteorological variables that might be used to predict air pollution concentrations. There was a significant correlation between observed daily mean air pollution concentrations and model predictions. About 20, 50, and 80% of the 80 prediction models across the study area possessed R 2 values ≥ 0.7, 0.6, and 0.5, respectively. The results of model validation were similar to those of model development, with slightly smaller model R 2 values. 相似文献
102.
Assessing soil erosion and control factors by the radiometric technique in the Boussouab catchment,Eastern Rif,Morocco 总被引:1,自引:0,他引:1
In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the 137Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m− 2). All the sampling sites were eroded and 137Cs inventories varied widely (between 245 and 3670 Bq m− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha− 1 yr− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha− 1 yr− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha− 1 yr− 1 and reaching a maximum of 48.8 t ha− 1 yr− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha− 1 yr− 1) to 25° (40. 8 t ha− 1 yr− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha− 1 yr− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha− 1 yr− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area. 相似文献
103.
M. B. Halitligil Ali Akın Nesteren Bilgin Yusuf Deniz Karani Öğretir Bülent Altınel Yusuf Işık 《Biology and Fertility of Soils》2000,31(2):175-182
In order to evaluate the influence of different N rates on percent N derived from fertilizer (%Ndff) at different growth stages, on yields and the percent N use efficiency (%NUE) values of two winter wheat varieties (durum and bread), field experiments on fallow were carried out at four different locations in Central Anatolia, in the 1991–1992 and 1992–1993 growing seasons. At each site the rates of N (0, 40, 80 and 120?kg N/ha) were applied as ammonium sulphate [(NH4)2SO4] using a Latin Square experimental design with four replicates. The total amounts of N fertilizer were applied once after seedling emergence at all experimental sites. Labelled (15NH4)2SO4 fertilizer was applied to sub-plots from which %Ndff values were determined at tillering, booting, grain filling, and harvest stages. Yield sub-plots received unlabelled (NH4)2SO4 from which total dry matter (seed and straw) and N yields were determined. Also the %NUE values were calculated by the 15N and "difference" methods at the harvest stage. Stored soil moisture at 0–90?cm depth, evapotranspiration and water use efficiency values were calculated as well. The results obtained showed that (1) Gerek-79 variety used both the applied N fertilizer and the available soil moisture more efficiently, (2) the percent NUE values obtained overall were generally less than 20 for both varieties and (3) with the 15N method, less variable %NUE values were obtained in comparison to the difference method. 相似文献
104.
105.
Mohamed R. Lasheen Salwa A. Shehata Gamila H. Ali 《Water, air, and soil pollution》1990,50(1-2):19-30
The Algal Assay Procedure Bottle Test was used to investigate the effect of Cd, Cu, and Cr (VI) on the growth of Nile water algae. The results of this investigation indicated that Cd has slight inhibitory effects on algal growth at low concentration (0.05 mg L?1), while it was inhibiting algal growth at higher concentration (> 1.0 mg L?1). In contrast, Cu and Cr did not affect algal growth in all investigated concentrations. Combinations of Cd with Cu and Cr seemed to interact synergistically. The synergism between Cd and Cu was more pronounced than between Cd and Cr. Clear changes in the diversity and redundancy of algal structure took place after metal addition. The inhibitory effect of the studied metals was in the following order: Cd-Cu > Cd - Cr > Cd > Cu > Cr. 相似文献
106.
107.
Hela Chikh-Rouhou Rafael González-Torres Ali Oumouloud José M. Alvarez 《Euphytica》2011,182(2):177-186
The resistance to Fusarium oxysporum f.sp. melonis (Fom) race 1.2 has been studied in melons, such as the Portuguese accession ‘BG-5384’ and in the Japanese ‘Shiro Uri Okayama’,
‘Kogane Nashi Makuwa’, and ‘C-211’, since a good characterization of the resistance is necessary before its introgression
into commercial varieties. These four melon accessions showed a high level of resistance to races 0, 1, and 2 of Fom, indicating that the partial resistance to the race 1.2 previously detected may not have been race specific. To determine
the mode of inheritance of the resistance to Fom race 1.2, the F1, F2, BCPR, and BCPS generations from the crosses between the four resistant accessions above and ‘Piel de Sapo’, a Fom race 1.2 susceptible melon, were developed. They were subsequently inoculated with two Fom isolates, one from the pathotype 1.2Y and the other from the pathotype 1.2W. The area under the disease progress curve was
determined for each inoculated plant, and the data were analyzed. We show that the resistance seen in these accessions is
polygenically inherited with a complex genetic control because many epistatic interactions were detected. The three epistatic
effects; additivity × additivity, dominance × dominance, and dominance × additivity are present and significant, with differing
magnitudes from one cross to the next. The relatively low heritabilities, and these epistatic effects make difficult the improvement
of the resistance, from these sources, through a standard selection procedure. 相似文献
108.
长枝木霉TICC鉴定及其生物学特性研究 总被引:2,自引:0,他引:2
从土壤中分离得到1株木霉T1CC,为明确其分类地位及其生物学特性,对该菌进行形态学鉴定和分子鉴定,并对其生长培养基、光照、温度、碳源、氮源、微量元素和pH等生物学特性进行研究.鉴定结果显示,该菌株为长枝木霉(Trichoderm longibrachiatum).生物学特性结果表明:菌株T1CC在PDA上生长量最大,查氏培养基和基本培养基上生长量最小;不同光照条件下,菌丝生长无明显差异,但在连续光照条件下可明显促进孢子产生;在15~40℃范围能够生长产孢,在35℃时菌丝生长最快,但产孢量在25~35℃最大;果糖最能促进菌丝生长,果糖、可溶性淀粉最有利于产孢;谷氨酸对菌丝生长和孢子产生都有促进作用;Cu最能促进菌丝生长,而zn、K和Mg则对菌丝生长有一定抑制作用,Cu最有利于产孢,zn对产孢明显抑制;在pH/值在2~10范围内均可生长,在pH为5时为生长最佳,在pH值3~7范围内最有利于产孢. 相似文献
109.
Lyeo HK Khajetoorians AA Shi L Pipe KP Ram RJ Shakouri A Shih CK 《Science (New York, N.Y.)》2004,303(5659):816-818
We have probed the local thermoelectric power of semiconductor nanostructures with the use of ultrahigh-vacuum scanning thermoelectric microscopy. When applied to a p-n junction, this method reveals that the thermoelectric power changes its sign abruptly within 2 nanometers across the junction. Because thermoelectric power correlates with electronic structure, we can profile with nanometer spatial resolution the thermoelectric power, band structures, and carrier concentrations of semiconductor junctions that constitute the building blocks of thermoelectric, electronic, and optoelectronic devices. 相似文献
110.
Shahzad Ali Amanullah Jan Jia Zhikuan Amir Sohail Cai Tie Wei Ting Zhang Peng Manzoor Irshad Ahmad Mati Ur Rahman Ren Xiaolong Liu Xiaoli Xu Yue Yue 《Russian Agricultural Sciences》2016,42(3-4):224-229
A field experiment was conducted on silty clay loam soil in the years 2011–2012. Two sesame (Sesamum indicum L.) cultivars (Local Black and Local White) were evaluated using various 3 different sowing dates (20th June, 10th and 30th July) and four agrotechnical level (0, 40, 80 and 120 kg N ha–1) at New Developmental Farm The University of Agriculture, Peshawar, Pakistan. The objective of this study was to evaluate the effects of sowing dates on growth, yield and oil fatty acid composition of two sesame cultivars grown under different nitrogen fertilization. Results showed that cv. Local Black was characterized by significantly higher content of oil (47%), seed yield (696 kg ha–1) and oil yield (335 kg ha–1) while cv. Local White had higher palmitic acid (8%) and linoleic acid (38.7%). Yield and its main components were positively affected by the earlier sowing date. With regard to fatty acid composition, a decrease in oleic and stearic acid and an increase in linoleic and palmitic acid were observed. At early sowing, oleic and palmitic acid decreased whereas linoleic and stearic acid increased. The decrease in the oleic/linoleic acid ratio observed at early sowing, suggests a possible role of temperature on the activity of oleate desaturase in the developing seeds. Intensive technology of cultivation (120 kg N ha–1), compared to the economical technology (40 kg N ha–1), significantly increased the seed yield of both sesame cultivars. This was due to higher number of branches, Capsules m–2, capsules plant–1, seeds capsule–1 and 1000 seed weight (g). The intensive technology of cultivation had a beneficial effect on the content of palmitic acid, linolenic acid and oleic acid in sesame seed. 相似文献