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   17287篇
  免费   26篇
  国内免费   67篇
系统科学   123篇
丛书文集   288篇
教育与普及   43篇
理论与方法论   63篇
现状及发展   7398篇
研究方法   908篇
综合类   8294篇
自然研究   263篇
  2013年   113篇
  2012年   298篇
  2011年   566篇
  2010年   104篇
  2009年   99篇
  2008年   316篇
  2007年   360篇
  2006年   376篇
  2005年   376篇
  2004年   376篇
  2003年   323篇
  2002年   320篇
  2001年   609篇
  2000年   571篇
  1999年   388篇
  1992年   325篇
  1991年   264篇
  1990年   279篇
  1989年   253篇
  1988年   235篇
  1987年   280篇
  1986年   291篇
  1985年   319篇
  1984年   280篇
  1983年   222篇
  1982年   182篇
  1981年   195篇
  1980年   249篇
  1979年   566篇
  1978年   432篇
  1977年   425篇
  1976年   314篇
  1975年   349篇
  1974年   515篇
  1973年   437篇
  1972年   428篇
  1971年   519篇
  1970年   688篇
  1969年   484篇
  1968年   399篇
  1967年   487篇
  1966年   398篇
  1965年   282篇
  1959年   162篇
  1958年   268篇
  1957年   207篇
  1956年   180篇
  1955年   144篇
  1954年   150篇
  1948年   126篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
The new, presumably extinct species, Chrysothamnus pulchelloides, is formally described and illustrated. The plant materials came from Holocene packrat middens. Anatomical and phyletic relationships of the fossil species to extant taxa are discussed.  相似文献   
192.
An expression of Centaurium namophilum (Gentianaceae), long confused with C. exaltatum in the Great Basin of the western United States, is described and designated as var. nevadense. It may be separated from the Death Valley region endemic, var. namophilum, by its broader leaves, its diffuse corymbose cyme, the ultimate peduncles that are longer than the flowers, its medium to deep rose pink corolla, and its stamens that equal or exceed the style and are only slightly exserted from the corolla-tube. The var. nevadense occurs from eastern California to western Utah, and from southeastern Oregon and adjacent Idaho south to the northern Mojave Desert of southeastern California. Centaurium exaltatum may be distinguished from the new variety by its broader, more elliptical leaves, dichotomous peduncles, paler pink or bluish and generally four-merous flowers, shorter and more blunt corolla lobes, and a thicker, more included style and stigma.  相似文献   
193.
Reproduction in L. pyromelana infralabialis Tanner is reported. Eggs were measured and weighed and incubation time and hatching reported. Hatchlings were measured and weighed, and feeding was observed.  相似文献   
194.
195.
We developed a series of interrelated locus-specific databases to store all published and unpublished genetic variation related to hemoglobinopathies and thalassemia and implemented microattribution to encourage submission of unpublished observations of genetic variation to these public repositories. A total of 1,941 unique genetic variants in 37 genes, encoding globins and other erythroid proteins, are currently documented in these databases, with reciprocal attribution of microcitations to data contributors. Our project provides the first example of implementing microattribution to incentivise submission of all known genetic variation in a defined system. It has demonstrably increased the reporting of human variants, leading to a comprehensive online resource for systematically describing human genetic variation in the globin genes and other genes contributing to hemoglobinopathies and thalassemias. The principles established here will serve as a model for other systems and for the analysis of other common and/or complex human genetic diseases.  相似文献   
196.
The Alzheimer Disease Genetics Consortium (ADGC) performed a genome-wide association study of late-onset Alzheimer disease using a three-stage design consisting of a discovery stage (stage 1) and two replication stages (stages 2 and 3). Both joint analysis and meta-analysis approaches were used. We obtained genome-wide significant results at MS4A4A (rs4938933; stages 1 and 2, meta-analysis P (P(M)) = 1.7 × 10(-9), joint analysis P (P(J)) = 1.7 × 10(-9); stages 1, 2 and 3, P(M) = 8.2 × 10(-12)), CD2AP (rs9349407; stages 1, 2 and 3, P(M) = 8.6 × 10(-9)), EPHA1 (rs11767557; stages 1, 2 and 3, P(M) = 6.0 × 10(-10)) and CD33 (rs3865444; stages 1, 2 and 3, P(M) = 1.6 × 10(-9)). We also replicated previous associations at CR1 (rs6701713; P(M) = 4.6 × 10(-10), P(J) = 5.2 × 10(-11)), CLU (rs1532278; P(M) = 8.3 × 10(-8), P(J) = 1.9 × 10(-8)), BIN1 (rs7561528; P(M) = 4.0 × 10(-14), P(J) = 5.2 × 10(-14)) and PICALM (rs561655; P(M) = 7.0 × 10(-11), P(J) = 1.0 × 10(-10)), but not at EXOC3L2, to late-onset Alzheimer's disease susceptibility.  相似文献   
197.
Hajdu-Cheney syndrome is a rare autosomal dominant skeletal disorder with facial anomalies, osteoporosis and acro-osteolysis. We sequenced the exomes of six unrelated individuals with this syndrome and identified heterozygous nonsense and frameshift mutations in NOTCH2 in five of them. All mutations cluster to the last coding exon of the gene, suggesting that the mutant mRNA products escape nonsense-mediated decay and that the resulting truncated NOTCH2 proteins act in a gain-of-function manner.  相似文献   
198.
We report a genome-wide association study for open-angle glaucoma (OAG) blindness using a discovery cohort of 590 individuals with severe visual field loss (cases) and 3,956 controls. We identified associated loci at TMCO1 (rs4656461[G] odds ratio (OR) = 1.68, P = 6.1 × 10(-10)) and CDKN2B-AS1 (rs4977756[A] OR = 1.50, P = 4.7 × 10(-9)). We replicated these associations in an independent cohort of cases with advanced OAG (rs4656461 P = 0.010; rs4977756 P = 0.042) and two additional cohorts of less severe OAG (rs4656461 combined discovery and replication P = 6.00 × 10(-14), OR = 1.51, 95% CI 1.35-1.68; rs4977756 combined P = 1.35 × 10(-14), OR = 1.39, 95% CI 1.28-1.51). We show retinal expression of genes at both loci in human ocular tissues. We also show that CDKN2A and CDKN2B are upregulated in the retina of a rat model of glaucoma.  相似文献   
199.
Synthesis of methyl-mercury compounds by extracts of a methanogenic bacterium   总被引:24,自引:0,他引:24  
J M Wood  F S Kennedy  C G Rosen 《Nature》1968,220(5163):173-174
  相似文献   
200.
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