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   17129篇
  免费   41篇
  国内免费   41篇
系统科学   82篇
丛书文集   108篇
教育与普及   30篇
理论与方法论   74篇
现状及发展   6196篇
研究方法   885篇
综合类   9512篇
自然研究   324篇
  2013年   196篇
  2012年   277篇
  2011年   627篇
  2010年   124篇
  2008年   295篇
  2007年   382篇
  2006年   380篇
  2005年   358篇
  2004年   324篇
  2003年   305篇
  2002年   320篇
  2001年   715篇
  2000年   703篇
  1999年   399篇
  1992年   365篇
  1991年   280篇
  1990年   302篇
  1989年   323篇
  1988年   293篇
  1987年   285篇
  1986年   305篇
  1985年   331篇
  1984年   283篇
  1983年   250篇
  1982年   211篇
  1981年   193篇
  1980年   219篇
  1979年   523篇
  1978年   408篇
  1977年   377篇
  1976年   309篇
  1975年   358篇
  1974年   504篇
  1973年   388篇
  1972年   404篇
  1971年   509篇
  1970年   620篇
  1969年   425篇
  1968年   466篇
  1967年   391篇
  1966年   391篇
  1965年   266篇
  1964年   54篇
  1959年   137篇
  1958年   227篇
  1957年   165篇
  1956年   121篇
  1955年   116篇
  1954年   111篇
  1948年   91篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
String theorists are certain that they are practicing physicists. Yet, some of their recent critics deny this. This paper argues that this conflict is really about who holds authority in making rational judgment in theoretical physics. At bottom, the conflict centers on the question: who is a proper physicist? To illustrate and understand the differing opinions about proper practice and identity, we discuss different appreciations of epistemic virtues and explanation among string theorists and their critics, and how these have been sourced in accounts of Einstein's biography. Just as Einstein is claimed by both sides, historiography offers examples of both successful and unsuccessful non-empirical science. History of science also teaches that times of conflict are often times of innovation, in which novel scholarly identities may come into being. At the same time, since the contributions of Thomas Kuhn historians have developed a critical attitude towards formal attempts and methodological recipes for epistemic demarcation and justification of scientific practice. These are now, however, being considered in the debate on non-empirical physics.  相似文献   
2.
3.
Genera assigned to the cheilostome bryozoan family Onychocellidae are revised based on the skeletal morphology of the type species and, when possible, the type material of these species. All genera are illustrated using scanning electron micrographs, some for the first time. Onychocellidae, which ranges from the Cenomanian stage of the Cretaceous to the Recent, has been a particularly troublesome family because of poorly defined generic concepts correlating at least in part with a paucity of morphological characters. Thirty-five genera are described in this review. Of these, two are recognised as subjective synonyms of other onychocellid genera (Rhebasia and Semieschara), one cannot be sufficiently characterised from the type material (Collura), and two are new: Aechmellina gen. nov. (type species Aechmella falcifera) and Kamilocella gen. nov. (type species Eschara latilabris). A neotype is chosen for Rhagasostoma hexagonum, the type species of Rhagasostoma. A key is provided to assist in the identification of onychocellid genera. Phylogenetic relationships between genera remain obscure and are unlikely to be fully resolved based on skeletal morphology alone. The family as an entity is loosely circumscribed and almost certainly paraphyletic, containing stem genera of other anascan familes such as Lunulitidae, Coscinopleuridae and Aspidostomatidae.

www.zoobank.org/urn:lsid:org:pub:63A31AD2-F049-42CB-A45B-557014DC286E  相似文献   

4.
5.
6.
以具体工程为例,介绍了建筑物地基处理的设计、施工中遵循的原则,施工中遇到特殊情况时采取的处理方法和必要的检测方法,对几种桩基的设计要求、施工工艺及过程、质量控制等情况进行了简单阐述。  相似文献   
7.
8.
9.
Opitz-Kaveggia syndrome (also known as FG syndrome) is an X-linked disorder characterized by mental retardation, relative macrocephaly, hypotonia and constipation. We report here that the original family for whom the condition is named and five other families have a recurrent mutation (2881C>T, leading to R961W) in MED12 (also called TRAP230 or HOPA), a gene located at Xq13 that functions as a thyroid receptor-associated protein in the Mediator complex.  相似文献   
10.
We tested 310,605 SNPs for association in 778 individuals with celiac disease and 1,422 controls. Outside the HLA region, the most significant finding (rs13119723; P = 2.0 x 10(-7)) was in the KIAA1109-TENR-IL2-IL21 linkage disequilibrium block. We independently confirmed association in two further collections (strongest association at rs6822844, 24 kb 5' of IL21; meta-analysis P = 1.3 x 10(-14), odds ratio = 0.63), suggesting that genetic variation in this region predisposes to celiac disease.  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