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   1029640篇
  免费   112527篇
  国内免费   700篇
  2018年   9518篇
  2017年   8941篇
  2016年   12954篇
  2015年   17918篇
  2014年   20924篇
  2013年   29775篇
  2012年   33328篇
  2011年   33690篇
  2010年   22951篇
  2009年   20846篇
  2008年   29793篇
  2007年   30733篇
  2006年   28923篇
  2005年   27841篇
  2004年   27461篇
  2003年   26446篇
  2002年   25776篇
  2001年   48085篇
  2000年   48469篇
  1999年   38472篇
  1998年   13443篇
  1997年   14003篇
  1996年   13210篇
  1995年   12343篇
  1994年   12063篇
  1993年   11809篇
  1992年   31711篇
  1991年   30908篇
  1990年   30009篇
  1989年   29149篇
  1988年   27069篇
  1987年   25390篇
  1986年   23581篇
  1985年   23443篇
  1984年   19379篇
  1983年   16374篇
  1982年   12408篇
  1981年   11128篇
  1980年   10425篇
  1979年   17940篇
  1978年   13833篇
  1977年   12534篇
  1976年   11359篇
  1975年   12750篇
  1974年   13538篇
  1973年   13379篇
  1972年   12061篇
  1971年   10873篇
  1970年   9439篇
  1969年   9068篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
A casein-phosvitin-Sepharose chromatography column allows separation of nuclear protein kinases from their chromosomal phosphoprotein substrates and from at least some protein kinase inhibitors in a single step. The additional step of passing the eluted material through a partially hydrolyzed, dephosphorylated casein-Sepharose column separates the two protein kinases, NI and NII, from each other.  相似文献   
972.
The pericarp of Chinese gooseberries is green due to the presenceof low concentrations of chlorophylls. On a f. wt basis thereis about 1.5 times more tetrapyrollic pigments (chlorophyllsand related compounds) in the outer pericarp than in the innerpericarp, whereas the carotenoid pigment values only showed1.25 times more in the outer than in the inner part of the fruit.The drying of Chinese gooseberries at 40 °C for 40 h resultedin the loss of at least half the tetrapyrollic pigments andof carotenoids. Chlorophylls a and b were converted to chlorophyllides,pheophytins and pheophorbides. Chloroplasts in the outer pericarp are clustered closely aroundthe nucleus and have a well-defined grana and inter-granal membranesystem. In the inner pericarp the chloroplasts are again clusteredaround the nucleus and there is a proliferation of inter-granalmembranes. In dried tissue the limiting membrane of chloroplastswas completely dispersed whereas some of the internal membranesremained intact. Actinidia chinensis Planch., Chinese gooseberry, Kiwi fruit, pigments, chloroplast structure  相似文献   
973.
974.
The effect of prey species and the different stages of prey on the predatory efficiency and biology of the phytoseiid mites,Amblyseius gossipi Elbadry andTyphlodromus mangiferus sp. n. was studied. It was found that feeding either predator onTetranychus cucurbitacearum (Sayed) promoted faster development and a higher rate of oviposition than rearing on the twospotted spider mite,T. urticae (Koch). Different stages of both prey species also produced different responses in the biological activities of these predaceous mites.
Résumé On a étudié l'effet de l'espèce de la proie et de ses différents stades sur l'efficacité et la biologie des acariens phytoseiides,Amblyseius gossipi Elbadry etTyphlodromus mangiferus sp. n. Il a été constaté que l'alimentation des 2 prédateurs avecTetranychus cucurbitacearus (Sayed) assure un dévelopment plus rapide et une fécondité plus élevée que leur élevage surT. urticae (Koch). Les différents stades de ces 2 proies produisent des réponses différentes dans les activités biologiques des 2 acariens prédateurs.
  相似文献   
975.
976.
The metabolism of N-nitrosodiethanolamine (NDELA) was studied to assess whether the formation of the beta-oxidated metabolites N-(2-hydroxyethyl)-N-(formylmethyl)nitrosamine (EFMN) and N-(2-hydroxyethyl)-N-(carboxymethyl)nitrosamine (ECMN) is involved in the mechanism of tumor induction in various animal species with different susceptibility to NDELA carcinogenicity. In vitro studies using liver S9 fractions from rats, hamster, B6C3F1 and CD-1 mice and rabbits showed that all the animal species metabolize NDELA through the beta-oxidation pathway, although to different extents. Urinary excretion of NDELA and its metabolite ECMN in rats, hamsters and mice after 5 mg X kg-1 NDELA i.p. confirmed these findings. The results suggest there is no correlation between carcinogenesis by NDELA and its beta-oxidation. The possibility that ECMN formation might represent a detoxifying metabolic pathway for NDELA is discussed.  相似文献   
977.
A sensitive and specific radioimmunoassay (RIA) for the measurement of urinary total chenodeoxycholic acid-3-sulfate (SCDCA) was developed and the accuracy was confirmed. SCDCA bound to bovine serum albumin as the antigen and emulsified with Freund's complete adjuvant was injected into rabbits. The antiserum obtained was capable of binding 75% of [11,12-3H]SCDCA at 1:1000 dilution. The percentage of bound radioactivity decreased linearly with logarithmic increases in unlabeled SCDCA, from 8 to 200 pmol/ml. The antiserum showed an extremely high specificity for SCDCA (free and conjugated), and the values determined by RIA indicated a close correlation with those found by gas-liquid chromatography. The daily urinary SCDCA level was determined using SCDCA-RIA in 12 disease-free humans and 74 patients with chronic liver diseases. In the normal subjects the daily urinary SCDCA level was 0.74 +/- 0.83 mg/day and increased levels were evident in all groups with chronic liver diseases. The daily urinary SCDCA level corresponds closely with the extent of hepatic dysfunction.  相似文献   
978.
A total of 2,377 C 57 Bl/6M mice were assigned to control groups and experimental groups exposed to tritiated water administered as a pulse injection or in drinking water, at a dose of 1.0 microCi per injection or per ml of drinking water. Weanlings were observed for the duration of life span. Data analysis was based on two coefficient estimates (1) individual carcinogenic induction coefficient and (2) specific tumorigenic induction coefficient. The carcinogenic potency of tritium was found to be dual in nature in enhancing the absolute induction of lymphocytic lymphomas in both sexes as well as their relative induction in competition with reticulo-endothelial tumors of other types.  相似文献   
979.
980.
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