全文获取类型
收费全文 | 736篇 |
免费 | 51篇 |
国内免费 | 1篇 |
专业分类
林业 | 29篇 |
农学 | 45篇 |
基础科学 | 4篇 |
114篇 | |
综合类 | 115篇 |
农作物 | 21篇 |
水产渔业 | 39篇 |
畜牧兽医 | 382篇 |
园艺 | 6篇 |
植物保护 | 33篇 |
出版年
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 20篇 |
2019年 | 18篇 |
2018年 | 18篇 |
2017年 | 23篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 35篇 |
2012年 | 36篇 |
2011年 | 52篇 |
2010年 | 27篇 |
2009年 | 23篇 |
2008年 | 46篇 |
2007年 | 45篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 34篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 14篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1970年 | 6篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 5篇 |
排序方式: 共有788条查询结果,搜索用时 296 毫秒
51.
Wang Dechun Prato Tony Qiu Zeyuan Kitchen Newell R. Sudduth Kenneth A. 《Precision Agriculture》2003,4(1):35-52
Variable Rate Technology (VRT) has the potential to increase crop yields and improve water quality relative to Uniform Rate Technology (URT). The effects on profitability and water quality of adopting VRT for nitrogen (N) and lime were evaluated for corn production on four claypan soil fields in north central Missouri under average to better than average weather conditions. Variable N and lime rates were based on measured topsoil depth and soil pH, respectively. VRT rates were compared to two different uniform N applications (URT-Nl based on the topsoil depth within these claypan soil fields, and URT-N2 based on a typical N rate for corn production in this area). Expected corn yield was predicted based on topsoil depth, soil pH, N rate, and lime rate. Water quality benefits of VRT relative to URT were evaluated based on potential leachable N. Sensitivity analyses were performed using simulated topsoil data for topsoil depth and soil pH. Results showed that VRT was more profitable than URT in the four sample fields under URT-N1, and in two of the four fields under URT-N2. Greater variation in topsoil depth and soil pH resulted in higher profitability and greater water quality benefits with VRT. Results support adoption of VRT for N and lime application for other claypan soil fields with characteristics similar to those in the fields used in this study. 相似文献
52.
Bakal C Linding R Llense F Heffern E Martin-Blanco E Pawson T Perrimon N 《Science (New York, N.Y.)》2008,322(5900):453-456
Cellular signaling networks have evolved to enable swift and accurate responses, even in the face of genetic or environmental perturbation. Thus, genetic screens may not identify all the genes that regulate different biological processes. Moreover, although classical screening approaches have succeeded in providing parts lists of the essential components of signaling networks, they typically do not provide much insight into the hierarchical and functional relations that exist among these components. We describe a high-throughput screen in which we used RNA interference to systematically inhibit two genes simultaneously in 17,724 combinations to identify regulators of Drosophila JUN NH(2)-terminal kinase (JNK). Using both genetic and phosphoproteomics data, we then implemented an integrative network algorithm to construct a JNK phosphorylation network, which provides structural and mechanistic insights into the systems architecture of JNK signaling. 相似文献
53.
Frudakis T 《Science (New York, N.Y.)》2008,319(5866):1039-40; author reply 1039-40
54.
Sutton T Baumann U Hayes J Collins NC Shi BJ Schnurbusch T Hay A Mayo G Pallotta M Tester M Langridge P 《Science (New York, N.Y.)》2007,318(5855):1446-1449
55.
Extension of day length by artificial light in selected field plots in the fall prevented 76 percent of European corn borer [Ostrinia nubilalis (Hübner)] larvae and 70 percent of codling moth [Laspeyresia pomonella (L.)] larvae from entering diapause. Nondiapausing insects cannot survive rigorous winter conditions. 相似文献
56.
Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change 总被引:3,自引:0,他引:3
Searchinger T Heimlich R Houghton RA Dong F Elobeid A Fabiosa J Tokgoz S Hayes D Yu TH 《Science (New York, N.Y.)》2008,319(5867):1238-1240
Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products. 相似文献
57.
Femtosecond laser irradiation is used to excite adsorbed CO molecules on a Cu110 surface; the ensuing motion of individual molecules across the surface is characterized on a site-to-site basis by in situ scanning tunneling microscopy. Adsorbate motion both along and perpendicular to the rows of the Cu110 surface occurs readily, in marked contrast to the behavior seen for equilibrium diffusion processes. The experimental findings for the probability and direction of the molecular motion can be understood as a manifestation of strong coupling between the adsorbates' lateral degrees of freedom and the substrate electronic excitation produced by the femtosecond laser radiation. 相似文献
58.
59.
60.