全文获取类型
收费全文 | 669篇 |
免费 | 63篇 |
专业分类
林业 | 16篇 |
农学 | 8篇 |
基础科学 | 4篇 |
83篇 | |
综合类 | 133篇 |
农作物 | 26篇 |
水产渔业 | 9篇 |
畜牧兽医 | 357篇 |
园艺 | 7篇 |
植物保护 | 89篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 10篇 |
2014年 | 16篇 |
2013年 | 22篇 |
2012年 | 29篇 |
2011年 | 38篇 |
2010年 | 17篇 |
2009年 | 15篇 |
2008年 | 30篇 |
2007年 | 41篇 |
2006年 | 37篇 |
2005年 | 18篇 |
2004年 | 24篇 |
2003年 | 27篇 |
2002年 | 25篇 |
2001年 | 27篇 |
2000年 | 28篇 |
1999年 | 13篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1980年 | 5篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1974年 | 4篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1963年 | 4篇 |
1955年 | 4篇 |
1927年 | 3篇 |
1917年 | 3篇 |
排序方式: 共有732条查询结果,搜索用时 218 毫秒
41.
42.
43.
44.
45.
Shaw SR 《Science (New York, N.Y.)》1969,165(3888):88-90
The extent to which light can escape from one ommatidium into its neighbors in the compound eye has been examined by recording from single receptors during stimulation of single facets. In the "apposition" eye of the drone honeybee and locust, optical interaction is extremely small. In the "superposition" eye of the crayfish, more than half the light captured by the average cell gets in through neighboring facets, even when screening pigments are in the fully lightadapted position. 相似文献
46.
Shaw EB 《Science (New York, N.Y.)》1932,76(1981):566-567
47.
Genetic variation in HTLV-III/LAV over time in patients with AIDS or at risk for AIDS 总被引:89,自引:0,他引:89
B H Hahn G M Shaw M E Taylor R R Redfield P D Markham S Z Salahuddin F Wong-Staal R C Gallo E S Parks W P Parks 《Science (New York, N.Y.)》1986,232(4757):1548-1553
In a study of genetic variation in the AIDS virus, HTLV-III/LAV, sequential virus isolates from persistently infected individuals were examined by Southern blot genomic analysis, molecular cloning, and nucleotide sequencing. Four to six virus isolates were obtained from each of three individuals over a 1-year or 2-year period. Changes were detected throughout the viral genomes and consisted of isolated and clustered nucleotide point mutations as well as short deletions or insertions. Results from genomic restriction mapping and nucleotide sequence comparisons indicated that viruses isolated sequentially had evolved in parallel from a common progenitor virus. The rate of evolution of HTLV-III/LAV was estimated to be at least 10(-3) nucleotide substitutions per site per year for the env gene and 10(-4) for the gag gene, values a millionfold greater than for most DNA genomes. Despite this relatively rapid rate of sequence divergence, virus isolates from any one patient were all much more related to each other than to viruses from other individuals. In view of the substantial heterogeneity among most independent HTLV-III/LAV isolates, the repeated isolation from a given individual of only highly related viruses raises the possibility that some type of interference mechanism may prevent simultaneous infection by more than one major genotypic form of the virus. 相似文献
48.
Lopatto D Alvarez C Barnard D Chandrasekaran C Chung HM Du C Eckdahl T Goodman AL Hauser C Jones CJ Kopp OR Kuleck GA McNeil G Morris R Myka JL Nagengast A Overvoorde PJ Poet JL Reed K Regisford G Revie D Rosenwald A Saville K Shaw M Skuse GR Smith C Smith M Spratt M Stamm J Thompson JS Wilson BA Witkowski C Youngblom J Leung W Shaffer CD Buhler J Mardis E Elgin SC 《Science (New York, N.Y.)》2008,322(5902):684-685
49.
Identification of a putative regulator of early T cell activation genes 总被引:98,自引:0,他引:98
J P Shaw P J Utz D B Durand J J Toole E A Emmel G R Crabtree 《Science (New York, N.Y.)》1988,241(4862):202-205
Molecules involved in the antigen receptor-dependent regulation of early T cell activation genes were investigated with the use of functional sequences of the T cell activation-specific enhancer of interleukin-2 (IL-2). One of these sequences forms a protein complex, NFAT-1, specifically with nuclear extracts of activated T cells. This complex appeared 10 to 25 minutes before the activation of the IL-2 gene. Studies with inhibitors of protein synthesis indicated that the time of synthesis of the activator of the IL-2 gene in Jurkat T cells corresponds to the time of appearance of NFAT-1. NFAT-1, or a very similar protein, bound functional sequences of the long terminal repeat (LTR) of the human immunodeficiency virus type 1; the LTR of this virus is known to be stimulated during early T cell activation. The binding site for this complex activated a linked promoter after transfection into antigen receptor-activated T cells but not other cell types. These characteristics suggest that NFAT-1 transmits signals initiated at the T cell antigen receptor. 相似文献
50.
Russell CA Jones TC Barr IG Cox NJ Garten RJ Gregory V Gust ID Hampson AW Hay AJ Hurt AC de Jong JC Kelso A Klimov AI Kageyama T Komadina N Lapedes AS Lin YP Mosterin A Obuchi M Odagiri T Osterhaus AD Rimmelzwaan GF Shaw MW Skepner E Stohr K Tashiro M Fouchier RA Smith DJ 《Science (New York, N.Y.)》2008,320(5874):340-346
Antigenic and genetic analysis of the hemagglutinin of approximately 13,000 human influenza A (H3N2) viruses from six continents during 2002-2007 revealed that there was continuous circulation in east and Southeast Asia (E-SE Asia) via a region-wide network of temporally overlapping epidemics and that epidemics in the temperate regions were seeded from this network each year. Seed strains generally first reached Oceania, North America, and Europe, and later South America. This evidence suggests that once A (H3N2) viruses leave E-SE Asia, they are unlikely to contribute to long-term viral evolution. If the trends observed during this period are an accurate representation of overall patterns of spread, then the antigenic characteristics of A (H3N2) viruses outside E-SE Asia may be forecast each year based on surveillance within E-SE Asia, with consequent improvements to vaccine strain selection. 相似文献