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   37125篇
  免费   3144篇
  国内免费   120篇
  2022年   382篇
  2021年   717篇
  2020年   449篇
  2019年   622篇
  2018年   729篇
  2017年   599篇
  2016年   940篇
  2015年   1477篇
  2014年   1538篇
  2013年   2109篇
  2012年   2373篇
  2011年   2192篇
  2010年   1538篇
  2009年   1203篇
  2008年   1770篇
  2007年   1630篇
  2006年   1541篇
  2005年   1381篇
  2004年   1385篇
  2003年   1290篇
  2002年   1329篇
  2001年   1015篇
  2000年   906篇
  1999年   833篇
  1998年   432篇
  1997年   414篇
  1996年   327篇
  1995年   329篇
  1994年   250篇
  1993年   301篇
  1992年   551篇
  1991年   531篇
  1990年   485篇
  1989年   443篇
  1988年   364篇
  1987年   356篇
  1986年   338篇
  1985年   390篇
  1984年   368篇
  1983年   325篇
  1982年   240篇
  1981年   240篇
  1980年   218篇
  1979年   287篇
  1978年   252篇
  1977年   270篇
  1976年   255篇
  1975年   252篇
  1974年   249篇
  1973年   240篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A new species of the genusEndomycopsis is proposed. It was isolated from waste water, at Montevideo-Uruguay.By its morphological and biochemical proprieties it differs from allEndomycopsis previously described.

Este trabajo fue desarrollado en el Laboratorio de Micologia de la Facultad de Química de Montevideo, Uruguay y en uso de una beca de la Universidad Federal de Pernambuco para perfecciobamiento en el estudio de las levaduras.  相似文献   
42.
Mutants with impaired biosynthesis of unsaturated fatty acids or altered metabolism of the phospholipids were isolated at a rather high frequency from a set of temperature-sensitive lysis mutants. It is suggested that preselection for the lysis phenotype makes it possible to isolate several kinds of mutants affected in the integrity of the cytoplasmic membrane.  相似文献   
43.
The role of abscisic acid (ABA) in controlling growth and developmenthas been studied in maize (Zea mays L.) coleoptile segments.Application of ABA reduces the elongation rate by about 50%and affects ion fluxes. In particular, proton extrusion is decreasedwhile potassium efflux is greatly enhanced. Apparently, ABAdoes not: seem to influence calcium influx from the apoplastinto the cytosol, but more likely it influences its efflux.Alteration of cytosolic calcium concentration may also be obtainedby increasing its release from internal stores. This possibilitymight be sustained by the increased hydrolysis of phosphatidylinositolupon ABA application. Change in the balance of ion fluxes shouldresult from regulation of transport mechanisms at the membranelevel and should produce changes in the transmembrane electricalpotential. The H+- ATPase and the ATP-dependent calcium transportactivities are both influenced by the treatment with ABA, –55%and –40%, respectively. Under these conditions [Ca2+]cytand pHcyt can be modified and, as a consequence of their regulation,they may play an important role in mediating the physiologicaland biochemical effects of ABA, acting as second intracellularmessengers. 1Research supported by National Research Council of Italy, SpecialProject RAISA, Sub-Project N. 2, Paper n. 2782.  相似文献   
44.
45.
46.
47.
It has been proposed that ovale malaria in humans is caused by two closely related but distinct species of malaria parasites: P. ovale curtisi and P. ovale wallikeri. We have extended and optimized a Real-time PCR assay targeting the parasite’s small subunit ribosomal RNA (ssrRNA) gene to detect both these species. When the assay was applied to 31 archival blood samples from patients diagnosed with P. ovale, it was found that the infection in 20 was due to P. ovale curtisi and in the remaining 11 to P. ovale wallikeri. Thus, this assay provides a useful tool that can be applied to epidemiological investigations of the two newly recognized distinct P. ovale species, that might reveal if these species also differ in their clinical manifestation, drugs susceptibility and relapse periodicity. The results presented confirm that P. ovale wallikeri is not confined to Southeast Asia, since the majority of the patients analyzed in this study had acquired their P. ovale infection in African countries, mostly situated in West Africa.  相似文献   
48.
49.
50.
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