首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1362篇
  免费   85篇
  国内免费   2篇
林业   27篇
农学   24篇
基础科学   2篇
  76篇
综合类   288篇
农作物   44篇
水产渔业   43篇
畜牧兽医   875篇
园艺   12篇
植物保护   58篇
  2021年   15篇
  2020年   14篇
  2019年   16篇
  2018年   22篇
  2017年   16篇
  2016年   20篇
  2015年   23篇
  2014年   24篇
  2013年   44篇
  2012年   55篇
  2011年   59篇
  2010年   25篇
  2009年   39篇
  2008年   52篇
  2007年   56篇
  2006年   34篇
  2005年   34篇
  2004年   38篇
  2003年   35篇
  2002年   45篇
  2001年   32篇
  2000年   47篇
  1999年   42篇
  1998年   16篇
  1997年   18篇
  1996年   15篇
  1993年   13篇
  1992年   19篇
  1991年   27篇
  1990年   37篇
  1989年   33篇
  1988年   19篇
  1987年   22篇
  1986年   22篇
  1985年   22篇
  1984年   21篇
  1983年   20篇
  1982年   11篇
  1980年   10篇
  1979年   12篇
  1978年   14篇
  1977年   12篇
  1975年   12篇
  1974年   25篇
  1973年   18篇
  1972年   26篇
  1971年   16篇
  1970年   15篇
  1969年   10篇
  1966年   11篇
排序方式: 共有1449条查询结果,搜索用时 437 毫秒
111.
A passage line of a spontaneous hamster fibrosarcoma is contaminated by the virus. of lymphocytic choriomeningitis. Tumors from animals receiving implants when newborn contain high titers of infectious lymphocytic-choriomeningitis virus and complement-fixing antigen, and hamsters receiving implants when weanlings develop high titers of complement-fixing antibody against lymphocytic-choriomeningitis virus. In contrast with the specific reactions of tumorous hamsters to the initiating virus in virus-induced tumors, the development of complement-fixing antibody to lymphocytic-choriomeningitis virus does not depend on the development of tumors. Infant hamsters bearing the tumor have a generalized subclinical infection and seem able to spread virus to other hamsters and to humans.  相似文献   
112.
Human infants aged I to 7 months were exposed to modifications of the normal spatial relationship between their mothers' face and voice. There was no evidence that such modifications were experienced by the infants as violations of a preexisting expectancy for face and voice to occupy the same spatial location.  相似文献   
113.
Stishovite, a dense phase of silica, has become widely accepted as an indicator of terrestrial impact events. Stishovite occurs at several impact structures but has not been found at volcanic sites. Solid-state silicon-29 magic-angle spinning nuclear magnetic resonance (silicon-29 MAS NMR) and X-ray diffraction of samples from the Cretaceous-Tertiary boundary layer at Raton, New Mexico, indicate that stishovite occurs in crystalline mineral grains. Stishovite was indicated by a single, sharp resonance with a chemical shift value of -191.3 ppm, characteristic of silicon in octahedral coordination, that disappeared after heating the sample at 850 degrees Celsius for 30 minutes. An X-ray diffraction pattern of HF residuals from the unheated sample displayed more than 120 peaks, most of which correspond to quartz, zircon, rutile, and anatase. Eight unambiguous weak to moderate reflections could be ascribed to d-spacings characteristic of stishovite.  相似文献   
114.
115.
116.
An age of 3.33+/-0.05x10(9) years was obtained for Apollo 15 sample 15555 by argon40-argon-39 dating. The age of rock 15555, a basalt from the rim of Hadley Rille, establishes an upper limit to the age of the rille. The basalt flows filling the Hadley Rille section of the Imbrium basin postdate the formation of the basin-as measured by the Apollo 14 samples of the Fra Mauro formation-by at least 500x10(6) years. Therefore, the mare basalts cannot be simple impact melts but rather must result from some igneous activity on the moon.  相似文献   
117.
甜瓜属野生种及其与黄瓜种间杂交后代抗根结线虫初步研究   总被引:15,自引:2,他引:15  
为了鉴定甜瓜属野生种酸黄瓜 (CucumishystrixChakr.)对南方根结线虫 [Meloidogyneincognit(Kofoid&White)Chit wood]的抗性 ,进而评估抗性向酸黄瓜与栽培黄瓜种间杂种的转移 ,选用了酸黄瓜、 4个栽培黄瓜材料、两种倍性水平的 3个正反交杂种F1和 1个回交后代作为试材 ,在温室中进行抗性鉴定和筛选。结果表明 ,酸黄瓜对南方根结线虫具有高度抗性 ,而 4个栽培黄瓜材料均为高度敏感。酸黄瓜平均每株根系形成约 3个根结 ,栽培黄瓜材料每株根系的根结数超过 10 0个。酸黄瓜通过与栽培黄瓜的正反交 ,其抗性已被部分转移到杂种之中。当杂种作为供体亲本与栽培黄瓜进行回交时 ,抗性又被进一步转移到回交一代 (BCF1)中  相似文献   
118.
Activating mutations of NOTCH1 in human T cell acute lymphoblastic leukemia   总被引:1,自引:0,他引:1  
Very rare cases of human T cell acute lymphoblastic leukemia (T-ALL) harbor chromosomal translocations that involve NOTCH1, a gene encoding a transmembrane receptor that regulates normal T cell development. Here, we report that more than 50% of human T-ALLs, including tumors from all major molecular oncogenic subtypes, have activating mutations that involve the extracellular heterodimerization domain and/or the C-terminal PEST domain of NOTCH1. These findings greatly expand the role of activated NOTCH1 in the molecular pathogenesis of human T-ALL and provide a strong rationale for targeted therapies that interfere with NOTCH signaling.  相似文献   
119.
Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder characterized by multiple clinical features that include pigmentary retinal dystrophy, polydactyly, obesity, developmental delay, and renal defects. BBS is considered an autosomal recessive disorder, and recent positional cloning efforts have identified two BBS genes (BBS2 and BBS6). We screened our cohort of 163 BBS families for mutations in both BBS2 and BBS6 and report the presence of three mutant alleles in affected individuals in four pedigrees. In addition, we detected unaffected individuals in two pedigrees who carry two BBS2 mutations but not a BBS6 mutation. We therefore propose that BBS may not be a single-gene recessive disease but a complex trait requiring three mutant alleles to manifest the phenotype. This triallelic model of disease transmission may be important in the study of both Mendelian and multifactorial disorders.  相似文献   
120.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号