全文获取类型
收费全文 | 2040篇 |
免费 | 111篇 |
国内免费 | 12篇 |
专业分类
林业 | 168篇 |
农学 | 107篇 |
基础科学 | 25篇 |
519篇 | |
综合类 | 163篇 |
农作物 | 90篇 |
水产渔业 | 149篇 |
畜牧兽医 | 753篇 |
园艺 | 47篇 |
植物保护 | 142篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 21篇 |
2021年 | 39篇 |
2020年 | 60篇 |
2019年 | 56篇 |
2018年 | 64篇 |
2017年 | 64篇 |
2016年 | 73篇 |
2015年 | 52篇 |
2014年 | 84篇 |
2013年 | 128篇 |
2012年 | 122篇 |
2011年 | 141篇 |
2010年 | 104篇 |
2009年 | 103篇 |
2008年 | 145篇 |
2007年 | 127篇 |
2006年 | 102篇 |
2005年 | 91篇 |
2004年 | 91篇 |
2003年 | 83篇 |
2002年 | 102篇 |
2001年 | 34篇 |
2000年 | 20篇 |
1999年 | 16篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 27篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1971年 | 6篇 |
1970年 | 4篇 |
排序方式: 共有2163条查询结果,搜索用时 406 毫秒
141.
Wind erosion is not as significant or a widespread problem in Europe as in dryer parts of the world, but it can cause major damage in small areas. The hazard is greatest in the lowlands of northwestern Europe with more than 3 million ha at high-potential wind erosion risk. Crop damage and off-site damage have prompted farmers and policymakers to pay more attention to wind erosion control. A great variety of measures have been developed in the last decades. Most farmers, however, only use measures to protect their high value crops. In existing policies, little attention is paid to the off-site effects and long-term effects of wind erosion. There are no direct policy measures at a European level to control soil erosion, and few measures exist in individual Member States. Agricultural or environmental EC policies offer different policy tools to approach the wind erosion problems related to agricultural practices. Tools like subsidies for the re-afforestation of arable land can help regional policy makers with the implementation of wind erosion control measures. A case study concerning the ‘Code of Good Agricultural Practice’ shows that regional differences result in different control measures that fits best given the physical, social and economic context. The formulation of the practical details of such code should therefore remain a task of the local or regional government. The main objectives of a Code of Good Agricultural Practice could be formulated at national or European level. 相似文献
142.
Jan Peter van der Hoek Wim F. van der Hoek Abraham Klapwijk 《Water, air, and soil pollution》1988,37(1-2):41-53
A new, strong base, macro-porous anion exchange resin, Amberlite IRA 996, appeared to be more nitrate selective than sulfate selective in treating high nitrate concentrations (18 mg NO inf3 sup? -N L?1) in potable water. When regeneration is carried out in a closed circuit in which a biological denitrification reactor is incorporated to remove nitrate from the regenerant, regeneration salt requirement and brine production can be minimized. In this combination of ion exchange and biological denitrification, regeneration with 30 g NaHCO3 L?1) is possible in 6 hr at a flow rate of 11 BV hr?1. Accumulation of sulfate in the closed regeneration circuit does not affect the nitrate capacity of the resin. 相似文献
143.
Loska Krzysztof Cebula Jan Pelczar Jacek Wiechuła Danuta Kwapuliński Jerzy 《Water, air, and soil pollution》1997,93(1-4):347-365
In this paper, the contamination degree of the Rybnik Reservoir with cadmium, copper and nickel was analyzed. Quality of the water from the reservoir was determined by drawing comparisons between the metal content in the water and both the officially permitted levels (contamination factor) and levels of metals occurring in the water of non-contaminated areas (enrichment factor). Contamination of bottom sediment with chosen metals was analyzed with reference to the metal content in mudstone (geoaccumulation index, enrichment factor, contamination factor). Trends towards changing the metal content in the bottom sediment was analyzed by determining the enrichment factor of the surface layer of the bottom sediments in relation to a deeper layer. Enrichment of the bottom sediments with metals coming from the water was also determined. 相似文献
144.
145.
Identification and characterization of a neuron-specific nuclear antigen in Drosophila 总被引:7,自引:0,他引:7
An antigen found only in neuronal nuclei of Drosophila melanogaster is revealed by staining with a monoclonal antibody (Mab44C11). This antigen appears early in development, before neurons show any other signs of antigenic or morphologic differentiation, and persists throughout development. This nuclear staining permits reliable detection of neurons in developmental studies of wild-type and mutant flies. Protein immunoblot analyses and immune precipitation experiments show that the neuronal nuclear antigen is a 50-kilodalton polypeptide. 相似文献
146.
CENH3 is a centromere-specific histone H3 variant essential for kinetochore assembly. Despite its central role in centromere function, there has been no conclusive evidence supporting CENH3 as sufficient to determine centromere identity. To address this question, we artificially targeted Drosophila CENH3 (CENP-A/CID) as a CID-GFP-LacI fusion protein to stably integrated lac operator (lacO) arrays. This ectopic CID focus assembles a functional kinetochore and directs incorporation of CID molecules without the LacI-anchor, providing evidence for the self-propagation of the epigenetic mark. CID-GFP-LacI-bound extrachromosomal lacO plasmids can assemble kinetochore proteins and bind microtubules, resulting in their stable transmission for several cell generations even after eliminating CID-GFP-LacI. We conclude that CID is both necessary and sufficient to serve as an epigenetic centromere mark and nucleate heritable centromere function. 相似文献
147.
148.
149.
Siemens J 《Science (New York, N.Y.)》2003,302(5651):1681; author reply 1681
150.
CX3CR1-mediated dendritic cell access to the intestinal lumen and bacterial clearance 总被引:3,自引:0,他引:3
Niess JH Brand S Gu X Landsman L Jung S McCormick BA Vyas JM Boes M Ploegh HL Fox JG Littman DR Reinecker HC 《Science (New York, N.Y.)》2005,307(5707):254-258
Dendritic cells (DCs) and macrophages are critical to innate and adaptive immunity to the intestinal bacterial microbiota. Here, we identify a myeloid-derived mucosal DC in mice, which populates the entire lamina propria of the small intestine. Lamina propria DCs were found to depend on the chemokine receptor CX3CR1 to form transepithelial dendrites, which enable the cells to directly sample luminal antigens. CX3CR1 was also found to control the clearance of entero-invasive pathogens by DCs. Thus, CX3CR1-dependent processes, which control host interactions of specialized DCs with commensal and pathogenic bacteria, may regulate immunological tolerance and inflammation. 相似文献