全文获取类型
收费全文 | 1746篇 |
免费 | 63篇 |
国内免费 | 3篇 |
专业分类
林业 | 141篇 |
农学 | 56篇 |
基础科学 | 13篇 |
327篇 | |
综合类 | 279篇 |
农作物 | 107篇 |
水产渔业 | 151篇 |
畜牧兽医 | 544篇 |
园艺 | 49篇 |
植物保护 | 145篇 |
出版年
2023年 | 13篇 |
2022年 | 25篇 |
2021年 | 33篇 |
2020年 | 30篇 |
2019年 | 49篇 |
2018年 | 53篇 |
2017年 | 55篇 |
2016年 | 39篇 |
2015年 | 47篇 |
2014年 | 47篇 |
2013年 | 86篇 |
2012年 | 116篇 |
2011年 | 125篇 |
2010年 | 72篇 |
2009年 | 52篇 |
2008年 | 99篇 |
2007年 | 82篇 |
2006年 | 108篇 |
2005年 | 94篇 |
2004年 | 98篇 |
2003年 | 88篇 |
2002年 | 84篇 |
2001年 | 26篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 20篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有1812条查询结果,搜索用时 15 毫秒
161.
162.
Anatomy of a conformational change: hinged "lid" motion of the triosephosphate isomerase loop 总被引:14,自引:0,他引:14
Triosephosphate isomerase (TIM) is used as a model system for the study of how a localized conformational change in a protein structure is produced and related to enzyme reactivity. An 11-residue loop region moves more than 7 angstroms and closes over the active site when substrate binds. The loop acts like a "lid" in that it moves rigidly and is attached by two hinges to the remainder of the protein. The nature of the motion appears to be built into the loop by conserved residues; the hinge regions, in contrast, are not conserved. Results of molecular dynamics calculations confirm the structural analysis and suggest a possible ligand-induced mechanism for loop closure. 相似文献
163.
Dagdigian J 《Science (New York, N.Y.)》2003,302(5652):1893
164.
Warrick R. Nelson Tonja W. Fisher Joseph E. Munyaneza 《European journal of plant pathology / European Foundation for Plant Pathology》2011,130(1):5-12
Three haplotypes of the recently discovered bacterium species “Candidatus Liberibacter solanacearum” are described and related to geographic ranges. The first two are associated with Zebra Chip/Psyllid
Yellows of potatoes and other solanaceous plants, vectored by the tomato/potato psyllid Bactericera cockerelli in North and Central America and New Zealand. The third is associated with diseased carrots in Finland and vectored by the
carrot psyllid Trioza apicalis. The haplotypes are described by SNPs on the 16s rRNA, 16s/23s ISR and 50s rplJ and rplL ribosomal protein genes. These SNPs
are inherited as a package across the three genes. Haplotype “a” has been found primarily from Honduras and Guatemala through
western Mexico to Arizona and California, and in New Zealand. Haplotype “b” is currently known from eastern Mexico and northwards
through Texas to south central Washington. These haplotypes show some range overlap in Texas, Kansas and Nebraska. The haplotypes
are not yet known to elicit biological differences in the plant or insect hosts. These apparently stable haplotypes suggest
separate bacterial populations of long standing. 相似文献
165.
BACKGROUND: RNA interference (RNAi) is a breakthrough technology for conducting functional genomics studies and also as a potential tool for crop protection against insect pests. The major challenge for efficient pest control using RNAi in the field is the development of efficient and reliable methods for production and delivery of double‐stranded RNA (dsRNA). In this paper, the potential of feeding dsRNA expressed in bacteria or synthesized in vitro to manage populations of Colorado potato beetle, Leptinotarsa decemlineata (Say) (CPB), was investigated. RESULTS: Feeding RNAi successfully triggered the silencing of all five target genes tested and caused significant mortality and reduced body weight gain in the treated beetles. This study provides the first example of an effective RNAi response in insects after feeding dsRNA produced in bacteria. CONCLUSION: These results suggest that the efficient induction of RNAi using bacteria to deliver dsRNA is a possible method for management of CPB. This could be also a promising bioassay approach for genome‐wide screens to identify effective target genes for use as novel RNAi‐based insecticides. Copyright © 2010 Society of Chemical Industry 相似文献
166.
Simbarashe Katsande Joseph J Baloyi Florence V Nherera-Chokuda Nobbert T Ngongoni Jacob Gusha Gift Matope 《African Journal of Range and Forage Science》2018,35(2):131-135
This study was conducted to determine the amino acid profiles and rumen degradability of amino acids of three cultivated forage legumes – velvet bean (Mucuna pruriens), cowpea (Vigna unguiculata) and silverleaf desmodium (Desmodium uncinatum) – using the in situ nylon-bag technique. Two Friesian cows fitted with 10-cm-diameter rumen cannulae on a complete dairy feed ration (19% crude-protein dairy meal and maize silage) were used. Silverleaf desmodium had significantly (p < 0.05) higher concentration of amino acids compared with cowpea and velvet bean. Aspartic acid showed the highest (p < 0.05) concentration in all legumes and cysteine showed the lowest concentration. Legume forage of cowpea showed the highest (p < 0.05) level of degradability of amino acid followed by silverleaf desmodium and then velvet bean. Readily and slowly degradable components in all amino acids were highest (p < 0.05) in cowpea followed by silverleaf desmodium and then velvet bean. Moreover, silverleaf and cowpea showed higher (p < 0.05) levels of effective degradability of amino acids (at outflow rates p = 0.02, 0.04 and 0.06 h?1) than velvet bean. Total amino acid disappearance was the least in velvet bean, which suggests that it can be used to supply bypass protein to the duodenum of the ruminant animal. 相似文献
167.
BACKGROUND: The potato psyllid, Bactericera cockerelli, is a vector of Candidatus Liberibacter solanacearum, causing several diseases in solanaceous crops. Laboratory and field no‐choice and choice experiments were conducted to evaluate the repellency of kaolin particle film on adults of B. cockerelli on tomato plants that had been sprayed with kaolin particle film on the upper surface only, on the lower surface only and on both leaf surfaces. RESULTS: In no‐choice tests in the laboratory, the numbers of adults on leaves were not different between the kaolin particle film and the water control, regardless of which leaf surface(s) were treated, but numbers of eggs were lower on the leaves treated with kaolin particle film than on those treated with water. In choice tests on plants treated with water/plants treated with kaolin particle film at ratios of 1:1, 6:3 or 8:1, fewer adults and eggs were found on the leaves treated with kaolin particle film than on leaves treated with water. Under field conditions, in caged no‐choice or choice tests, fewer adults, eggs and nymphs were found on plants treated with kaolin particle film than on plants treated with water. In an uncaged test under field conditions, plants sprayed with kaolin particle film had fewer psyllids than those sprayed with water. CONCLUSION: Even though potato psyllid adults could land on plants treated with kaolin particle film when no choice was given, fewer eggs were laid. When given a choice, the psyllids avoided plants treated with kaolin particle film under laboratory and field conditions. Kaolin particle film treatment may be a useful alternative for management of potato psyllids under field conditions. Copyright © 2011 Society of Chemical Industry 相似文献
168.
Ted C Schroeder Joseph Kovanda 《Veterinary Clinics of North America: Food Animal Practice》2003,19(2):397-417, vii
With their growth, it is important to consider how alliances will impact the beef industry in the future. Alliances have the potential to make sweeping changes to cattle production, live and feeder cattle marketing, food safety protocols, use of government grades and standards, ownership structure, supply chain management, wholesale and retail product marketing, risk management, and many other industry activities. In an effort to address these issues, this article addresses the following questions: What is an alliance? What has motivated their proliferation? What have we learned from alliances? What aspects of alliances affect their likelihood of success or failure? What is the future of alliances? Are they a fad or a long-term evolving industry structural change? 相似文献
169.
170.