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   15136篇
  免费   28篇
  国内免费   47篇
系统科学   63篇
丛书文集   181篇
教育与普及   32篇
理论与方法论   73篇
现状及发展   6180篇
研究方法   786篇
综合类   7611篇
自然研究   285篇
  2013年   105篇
  2012年   264篇
  2011年   544篇
  2010年   105篇
  2008年   321篇
  2007年   304篇
  2006年   321篇
  2005年   329篇
  2004年   319篇
  2003年   280篇
  2002年   260篇
  2001年   458篇
  2000年   442篇
  1999年   310篇
  1992年   267篇
  1991年   197篇
  1990年   224篇
  1989年   219篇
  1988年   223篇
  1987年   218篇
  1986年   205篇
  1985年   293篇
  1984年   229篇
  1983年   158篇
  1982年   167篇
  1981年   152篇
  1980年   181篇
  1979年   418篇
  1978年   309篇
  1977年   307篇
  1976年   289篇
  1975年   323篇
  1974年   385篇
  1973年   363篇
  1972年   379篇
  1971年   434篇
  1970年   550篇
  1969年   462篇
  1968年   469篇
  1967年   431篇
  1966年   383篇
  1965年   285篇
  1964年   87篇
  1959年   169篇
  1958年   297篇
  1957年   199篇
  1956年   185篇
  1955年   150篇
  1954年   185篇
  1948年   138篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
181.
Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Past observations and ongoing population surveys indicate daily and yearly vertical movement of the Devil’s Hole pupfish, Cyprinodon diabolis Wales, within the upper 27 m of the water column in Devil’s Hole, Nevada. This movement involves occupying and leaving a 5 by 3.5 m rock shelf during daily and yearly periods of maximum light intensity.    相似文献   
182.
Lenski RE 《Nature genetics》2011,43(12):1174-1176
The combination of genomic, epidemiological and evolutionary analyses provides a powerful toolbox for understanding how pathogens adapt to their human hosts. By sequencing 112 Burkholderia dolosa genomes from an outbreak among patients with cystic fibrosis, a new study documents evolution in action and identifies a set of genes that contributed to the pathogen's adaptation.  相似文献   
183.
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   
184.
The evolutionarily conserved SLX4 protein, a key regulator of nucleases, is critical for DNA damage response. SLX4 nuclease complexes mediate repair during replication and can also resolve Holliday junctions formed during homologous recombination. Here we describe the phenotype of the Btbd12 knockout mouse, the mouse ortholog of SLX4, which recapitulates many key features of the human genetic illness Fanconi anemia. Btbd12-deficient animals are born at sub-Mendelian ratios, have greatly reduced fertility, are developmentally compromised and are prone to blood cytopenias. Btbd12(-/-) cells prematurely senesce, spontaneously accumulate damaged chromosomes and are particularly sensitive to DNA crosslinking agents. Genetic complementation reveals a crucial requirement for Btbd12 (also known as Slx4) to interact with the structure-specific endonuclease Xpf-Ercc1 to promote crosslink repair. The Btbd12 knockout mouse therefore establishes a disease model for Fanconi anemia and genetically links a regulator of nuclease incision complexes to the Fanconi anemia DNA crosslink repair pathway.  相似文献   
185.
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   
186.
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   
187.
A B Cachelin  J E de Peyer  S Kokubun  H Reuter 《Nature》1983,304(5925):462-464
Modulation of ion channels is of increasing interest as it is an important step in the regulation of cellular functions. We have analysed the effect of 8-bromocyclic AMP on Ca2+ channels in cultured cardiac cells by the patch-clamp method and report here that there was a large increase in the probability of opening of the channels. On the basis of a recently proposed kinetic reaction scheme we suggest that cyclic AMP-dependent phosphorylation of Ca2+ channels primarily promotes the forward rate constants which lead to the open state of a Ca2+ channel during depolarization.  相似文献   
188.
189.
190.
Translation initiation is a critical step in protein synthesis. Previously, two major mechanisms of initiation were considered as essential: prokaryotic, based on SD interaction; and eukaryotic, requiring cap structure and ribosomal scanning. Although discovered decades ago, cap-independent translation has recently been acknowledged as a widely spread mechanism in viruses, which may take place in some cellular mRNA translations. Moreover, it has become evident that translation can be initiated on the leaderless mRNA in all three domains of life. New findings demonstrate that other distinguishable types of initiation exist, including SD-independent in Bacteria and Archaea, and various modifications of 5′ end-dependent and internal initiation mechanisms in Eukarya. Since translation initiation has developed through the loss, acquisition, and modification of functional elements, all of which have been elevated by competition with viral translation in a large number of organisms of different complexity, more variation in initiation mechanisms can be anticipated.  相似文献   
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