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   48538篇
  免费   4158篇
  国内免费   6篇
  2023年   238篇
  2021年   375篇
  2020年   333篇
  2019年   330篇
  2018年   931篇
  2017年   959篇
  2016年   1066篇
  2015年   984篇
  2014年   1152篇
  2013年   1994篇
  2012年   3187篇
  2011年   3520篇
  2010年   1838篇
  2009年   1230篇
  2008年   2890篇
  2007年   2947篇
  2006年   2743篇
  2005年   2512篇
  2004年   2408篇
  2003年   2244篇
  2002年   2239篇
  2001年   1594篇
  2000年   1792篇
  1999年   1040篇
  1998年   495篇
  1997年   405篇
  1996年   464篇
  1995年   405篇
  1994年   430篇
  1993年   380篇
  1992年   525篇
  1991年   442篇
  1990年   425篇
  1989年   400篇
  1988年   371篇
  1987年   379篇
  1986年   337篇
  1985年   405篇
  1984年   455篇
  1983年   401篇
  1982年   367篇
  1981年   335篇
  1980年   303篇
  1979年   313篇
  1978年   303篇
  1977年   288篇
  1976年   279篇
  1975年   336篇
  1974年   273篇
  1973年   256篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterised by tumours of the parathyroids, pancreas and anterior pituitary. The MEN1 gene has been localised to a 2-Mb region of chromosome 11q13 by meiotic mapping studies in MEN1 families. Such studies may have a limited resolution of approximately 1 cM (i.e. 1 Mb) and we have therefore investigated 96 MEN1 families (40 British, 17 French, 12 Finnish, 7 Swedish, 7 Dutch, 7 North American, 2 Australian, 1 New Zealand, 1 German, 1 Spanish and 1 Danish) for linkage disequilibrium, in order to facilitate a finer mapping resolution. We have utilised five microsatellite DNA sequence polymorphisms from the candidate region and have accurately determined their allele sizes, which ranged from 161 bp to 272 bp. The heterozygosity and number of alleles (given in brackets), respectively, at the loci were: D11S1883 (76%, 11), D11S457 (55%, 5), PYGM (94%, 18), D11S1783 (10%, 4) and D11S449 (87%, 16). Allelic association was assessed by Chi-square 2 ×n contingency tables, by Fisher exact 2 ×n contingency tables and by a likelihood-based approach. The results of haplotype analysis revealed 91 different affected haplotypes in the 96 families, an identical affected haplotype being observed in no more than two families. These results indicate the absence of an ancestral affected haplotype. Significant linkage disequilibrium (P < 0.005) could be established amongst the microsatellite loci but not between the loci and MEN1 in either the total population or in any of the geographical sub-populations. The absence of linkage disequilibrium between MEN1 and the polymorphic loci is probably the result of the occurrence of multiple different disease-causing mutations in MEN1. Received: 1 April 1997 / Accepted: 25 June 1997  相似文献   
5.
Throughout Central Europe, foxes have taken over urban areas as their habitat. In Southern Germany, these foxes are also carriers of the small fox tapeworm, which causes a serious zoonotic infection in humans. Therefore, a survey was carried out in a suburb of the city of Munich. A postal questionnaire was used to analyse the attitudes, opinions and fears of these participants towards their urban foxes and the background to these attitudes. Questionnaires were sent to all households with gardens and collected in again via the community council. Seven hundred and seventy-nine or 31% of questionnaires were returned. Only a few people are afraid of the fox itself; however, 55% are afraid of the fox tapeworm. Worming the animals is the preferred counter-measure, with 81% in favour. The majority of inhabitants are pleased to see a fox in the community and feel the animals have a right to live. People are afraid of the tapeworm either because they have children in the household or because of increased knowledge of the subject or because it has increasingly become an issue. On the basis of the results of this study, it is to be expected that radical solutions such as killing the foxes are unlikely to be accepted among the population. Worming of the foxes does, however, meet with general approval.  相似文献   
6.
7.
8.
Saturated fatty acids like palmitate induce endoplasmic reticulum (ER) stress in pancreatic beta‐cells, an event linked to apoptotic loss of β‐cells in type 2 diabetes. Sustained activation of the ER stress response leads to expression of growth arrest and DNA damage‐inducible protein 34 (GADD34), a regulatory subunit of protein phosphatase 1. In the present study, we have used small interfering RNA in order to knockdown GADD34 expression in insulin‐producing MIN6 cells prior to induction of ER stress by palmitate and evaluated its consequences on RNA‐activated protein kinase‐like ER‐localized eIF2alpha kinase (PERK) signalling and apoptosis. Salubrinal, a specific inhibitor of eukaryotic initiation factor 2α (eIF2α) dephosphorylation, was used as a comparison. Salubrinal treatment augmented palmitate‐induced ER stress and increased GADD34 levels. Both GADD34 knockdown and salubrinal treatment potentiated the cytotoxic effects of palmitate as evidenced by increased DNA fragmentation and activation of caspase 3, with the fundamental difference that the former did not involve enhanced levels of GADD34. The data from this study suggest that sustained activation of PERK signalling and eIF2α phosphorylation sensitizes insulin‐producing MIN6 cells to lipoapoptosis independently of GADD34 expression levels. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
9.
The database systems PaleoTax and GONIAT provide detailed information on literature, taxonomy, morphology and occurrence of fossil invertebrate groups. PaleoTax is designed for Mesozoic corals, GONIAT for Paleozoic ammonoids, but both can be modified to cover other fossil groups. Both systems use dBASE format, but with different database structures. PaleoTax aims at the complete storage of all available objective data, GONIAT provides determinations based upon morphologic criteria, and includes information on geographic distribution and stratigraphic range of every taxon. A combination of both systems could lead to the establishment of a comprehensive paleontological information system useful for research and practical stratigraphic applications.  相似文献   
10.
From the Upper Liassic of Dobbertin (Mecklenburg, Germany) the first stoneflyDobbertiniopteryx capniomimus gen. et sp. nov. is described. It is probably a representative of the Capniidae (Plecoptera: Nemouroidea) or of its stemgroup. Slowly running fresh water streams and stagnant water bodies in coastal regions are considered an ecological cause of the rarity of Plecoptera in European Jurassic sediments.  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