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   101036篇
  免费   815篇
  国内免费   812篇
  2023年   42篇
  2022年   86篇
  2021年   171篇
  2020年   95篇
  2019年   158篇
  2018年   11974篇
  2017年   10773篇
  2016年   7680篇
  2015年   984篇
  2014年   739篇
  2013年   855篇
  2012年   4900篇
  2011年   13396篇
  2010年   12357篇
  2009年   8586篇
  2008年   10265篇
  2007年   11797篇
  2006年   694篇
  2005年   964篇
  2004年   1369篇
  2003年   1392篇
  2002年   1137篇
  2001年   328篇
  2000年   215篇
  1999年   99篇
  1998年   99篇
  1997年   88篇
  1996年   76篇
  1995年   45篇
  1994年   72篇
  1993年   75篇
  1992年   65篇
  1991年   73篇
  1990年   35篇
  1989年   35篇
  1988年   38篇
  1987年   28篇
  1984年   28篇
  1983年   30篇
  1982年   22篇
  1981年   16篇
  1980年   14篇
  1978年   17篇
  1977年   13篇
  1976年   14篇
  1975年   15篇
  1972年   251篇
  1971年   280篇
  1965年   15篇
  1962年   25篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
Here we report massive seed predation of Pseudobombax grandiflorum (Bombacaceae) by Botogeris versicolurus (Psittacidae) in a forest fragment in Brazil. The intensity of seed predation was very high when compared to other studies in continuous forest, perhaps resulting from a scarcity of resources in such areas. This scarcity may limit the range of parrot's diet to a few plant species. It suggests that studies of Psittacidae seed predation may be important for conservation of some plants in fragments.  相似文献   
203.
204.
205.
206.
The influence of moulded hay (Alternaria alternata, Epicoccum nigrum, Mucor racemosus, Ulocladium chartarum) and the efficiency of Vitamin B1 substitution to cope these effects on rumen protozoa was investigated using the longterm rumen simulation technique (RUSITEC) for about 25 days. Moulded hay affected medium-sized protozoa to a different extent (Alternaria alternata: ?16 %, Epicoccum nigrum: ?27 %, Mucor racemosus: ?9 %, Ulocladium chartarum: +2 %). The vitamin B1 substitution had positive effects during the feeding of Mucor racemosus and Ulocladium chartarum.  相似文献   
207.
Cells from a mouse B lymphoma were transfected by DQ alpha and DQ beta genes derived from a DR4 haplotype. Quantitatively, the resulting expression of human class II molecules was similar to that of human B lymphoblastoid cell lines. Qualitatively, the transformant class II molecules differed from normal class II molecules in their carbohydrate moiety. As for their antigenic specificity, they were shown to carry two determinants previously identified on DQ molecules controlled by DR4 haplotypes, i. e., DQw3 and DCHON. The transformant molecules did not carry a third DR4-associated specificity, DC5 (equivalent to TA10), and must possess a structure allelic to DC5. However, no corresponding alloantigenic specificity was detected by a screening of relevant alloantisera.  相似文献   
208.
An isolated rat liver was perfused with deoxynivalenol (DON) at a dose of 3 mg in a recirculating perfusion system. To identify glucuronide conjugates equal amounts of bile samples, perfusate and liver homogenates were incubated with and without (control) a β-glucuronidase preparation and analyzed by thin layer chromatography and capillary gas liquid chromatography — chemical ionization mass spectrometry. A total of 40.4% of the administered dose of DON was found to be conjugated with glucuronic acid (perfusate 20.4%, bile 19.2%, liver 0.8%), while only 1.3% of the parent DON (perfusate 1.1%, bile 0.2%) was detected. The cleavage of DON-glucuronide was demonstrated by incubating DON-glucuronide containing bile samples with intestine contents under anaerobic conditions.  相似文献   
209.
Body wall organization in enchytraeids   总被引:2,自引:2,他引:0  
The muscle organization of the body wall in some species of oligochaetes belonging to the Enchytraeus genus is described. No differences have been detected in their circular muscles, whereas longitudinal muscles show significant differences, allowing an easy identification of the various worm species. In particular, differences are noticeable in the external longitudinal layer. These observations suggest that structural and ultrastructural muscle fiber organizations can be used as a taxonomic tool.  相似文献   
210.
Summary The electrochemical behaviour of Fe(III)-protoporphyrin IX entrapped into a cellulose triacetate membrane has been investigated by cyclic voltammetry. The physical entrapment into a solid matrix does not modify the redox properties of the entrapped berries, which also act as efficient promoters in the electrochemistry of cytochromec. Such a system represents a promising example of a simple solid-state promoter, and stimulates further investigations in order to obtain more complex systems that may be of significance for basic and applied bioelectrochemistry.  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