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   1663409篇
  免费   156085篇
  国内免费   1770篇
  1821264篇
  2021年   18616篇
  2019年   16518篇
  2018年   19622篇
  2017年   18395篇
  2016年   29752篇
  2015年   43977篇
  2014年   52235篇
  2013年   78552篇
  2012年   50603篇
  2011年   42105篇
  2010年   48474篇
  2009年   48326篇
  2008年   38451篇
  2007年   37225篇
  2006年   40086篇
  2005年   41055篇
  2004年   39986篇
  2003年   37261篇
  2002年   34974篇
  2001年   52049篇
  2000年   49819篇
  1999年   45097篇
  1998年   27801篇
  1997年   27542篇
  1996年   26660篇
  1995年   24828篇
  1994年   24433篇
  1993年   23662篇
  1992年   37905篇
  1991年   35980篇
  1990年   34598篇
  1989年   35033篇
  1988年   32296篇
  1987年   30308篇
  1986年   28679篇
  1985年   30122篇
  1984年   28274篇
  1983年   24462篇
  1982年   23238篇
  1981年   22088篇
  1980年   20581篇
  1979年   23849篇
  1978年   21332篇
  1977年   20200篇
  1976年   18944篇
  1975年   18972篇
  1974年   19771篇
  1973年   20023篇
  1972年   17161篇
  1971年   15687篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
1. High mol. wt kininogen (HMW kininogen) was purified to a homogeneous state from porcine plasma. 2. The protein exhibited a strong inhibitory activity for thiol proteinases such as ficin, papain and calpain I, whereas it did not inhibit serine proteinases, trypsin and chymotrypsin. 3. The mol. wt, isoelectric point, amino acid and carbohydrate compositions, stabilities to temperature and pH, kinetic constants, and immunological properties of the porcine HMW kininogen were determined and compared with those of human HMW kininogen.  相似文献   
42.
Female BALB/c mice were immunized with human melanoma (Mewo) cells containing ganglioside GD3 as a surface antigen. Immune splenocytes were fused with syngeneic P3-X63.Ag 8 myeloma cells. Antibodies produced by hybrid clones were analyzed by solid phase immunoassay. B, C, D and Q clones producing antibodies against Raja clavata brain gangliosides were obtained. Monoclonal B and C antibodies bound monosialogangliosides. Monoclonal D antibody bound a number of gangliosides but reacted predominantly with GD1a. Monoclonal Q antibody reacted selectively with GQ1c. It is assumed that ganglioside GQ1c is expressed on the melanoma cell surface and may be found only in the early stage of ontogenesis of high vertebrates.  相似文献   
43.
44.
The degree of serotiny (i.e. the proportion of follicles remaining closed in each year's crop of cones since the last fire) was measured in Bank-sia attenuata, B. menziesii and B. prionotes at five sites along a climatic gradient extending 500 km north of Perth, Western Australia. The decrease in annual rainfall and increase in average temperature along the gradient paralleled a decrease in plant height and an increase in the degree of serotiny of all species. Extreme serotiny was recorded in the scrub-heath at the xeric end of the gradient whereas two species were essentially non-serotinous in the low woodland at the most mesic site. It is concluded that degree of serotiny is related to the fire characteristics of the site which depend on plant height. In xeric scrub-heath, the entire canopies of the Banksia spp. are consumed by fire which promotes massive release of seed. This facilitates recruitment in an otherwise unpredictable and unreliable seedbed. In mesic woodland, where cones rarely come into contact With flames, seeds are released spontaneously and site conditions are more conducive to recruitment in the inter-fire period.  相似文献   
45.
46.
Exposure of male Syrian hamsters (Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10 hr light: 14 hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T4) levels and free T4 index (FT4I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). C57bl male house mice (Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T3 uptake (T3U) values. Male gerbils (Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T3U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T4 and triiodothyronine (T3) values nor the FT4I and free T3 index (FT3I). White-footed male mice (Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T4 and T3 levels were unaffected. Snell strain house mice (Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T3 and in the FT3I in the SP animals.  相似文献   
47.
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