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   26813篇
  免费   62篇
  国内免费   137篇
系统科学   147篇
丛书文集   195篇
教育与普及   63篇
理论与方法论   72篇
现状及发展   11970篇
研究方法   1179篇
综合类   13064篇
自然研究   322篇
  2013年   177篇
  2012年   409篇
  2011年   687篇
  2008年   480篇
  2007年   554篇
  2006年   563篇
  2005年   528篇
  2004年   470篇
  2003年   491篇
  2002年   487篇
  2001年   928篇
  2000年   896篇
  1999年   569篇
  1994年   350篇
  1992年   539篇
  1991年   409篇
  1990年   476篇
  1989年   417篇
  1988年   401篇
  1987年   455篇
  1986年   452篇
  1985年   558篇
  1984年   449篇
  1983年   385篇
  1982年   370篇
  1981年   357篇
  1980年   354篇
  1979年   895篇
  1978年   687篇
  1977年   593篇
  1976年   578篇
  1975年   571篇
  1974年   649篇
  1973年   570篇
  1972年   555篇
  1971年   676篇
  1970年   866篇
  1969年   643篇
  1968年   696篇
  1967年   657篇
  1966年   600篇
  1965年   421篇
  1964年   175篇
  1959年   226篇
  1958年   373篇
  1957年   247篇
  1956年   229篇
  1955年   213篇
  1954年   202篇
  1948年   173篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Zusammenfassung Vorbehandlung mit 10 mg/kg Chlorpromazin (CPZ) i.p. bewirkt bei Ratten, denen14C-Tyrosin injiziert wurde, eine Zunahme der spezifischen Radioaktivität von14C-Dopamin im Gehirn. CPZ beschleunigt bei Tieren, deren zerebrale Katecholamine durchl-214C-Dopa markiert wurden, den Abfall der spezifischen Radioaktivität von Dopamin und Noradrenalin. Daraus wird geschlossen, dass CPZ den Umsatz zerebraler Katecholamine erhöht.  相似文献   
972.
973.
    
A R Jones  K Edwards 《Experientia》1973,29(5):538-539
  相似文献   
974.
    
  相似文献   
975.
976.
Summary A comparison of the frequencies of chromosomal aberrations and the rates of SV40 transformation was made using fibroblasts obtained from 2 patients with Bloom's syndrome (BS) and from a normal individual. BS cells were found to be more susceptible to chromosome damage, in confirmation of earlier reports, but surprisingly, BS cells were distinctly less prone to transformation.Supported in part by the Michael J. Connell Foundation Medical Genetics Fund, and Health, Education and Welfare, MCH project 422.  相似文献   
977.
K Tohya  R Sugata  S Toda  M Kimura 《Experientia》1989,45(8):750-753
The in situ activity of 3 beta-hydroxysteroid dehydrogenase was detected in clustered cells which showed steroid-producing morphology, within the capsule of the paraaortic lymph node. In light and electron microscopic studies, the positive reaction products were detected on intracapsular cell clusters. This result indicates that these unique cells may have a steroid secreting function within the lymph nodes.  相似文献   
978.
    
This article studies Man and Tiao's (2006) low‐order autoregressive fractionally integrated moving‐average (ARFIMA) approximation to Tsai and Chan's (2005b) limiting aggregate structure of the long‐memory process. In matching the autocorrelations, we demonstrate that the approximation works well, especially for larger d values. In computing autocorrelations over long lags for larger d value, using the exact formula one might encounter numerical problems. The use of the ARFIMA(0, d, d?1) model provides a useful alternative to compute the autocorrelations as a really close approximation. In forecasting future aggregates, we demonstrate the close performance of using the ARFIMA(0, d, d?1) model and the exact aggregate structure. In practice, this provides a justification for the use of a low‐order ARFIMA model in predicting future aggregates of long‐memory process. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
979.
This study examined the individual and simultaneous adsorption of SOx(SO2)and NOx(NO-NO2)on activated carbon prepared from waste palm shell.The adsorption process was examined in a fixed bed reactor at low temperatures(100 300°C).For individual adsorption without any catalytic activation,SOx showed good adsorption whereas NOx was very much poor.In the simultaneous adsorption of SOx and NOx,SOx showed greater adsorption affinity than NOx.For palm shell activated carbon(PSAC)impregnated with metal catalyst(Ni and Ce)the concentration adsorbed profile showed that the amount of SOx adsorbed decreased regularly,while the amount of the adsorbed NOx increased irregularly.The properties of the pure and impregnated PSAC were analyzed by BET,SEM and EDX.These investigations indicated that PSAC impregnated with metal catalyst is the determining factor in the adsorption of SOx and NOx simultaneously.  相似文献   
980.
The antiviral activity of Shigyaku-to (TJS-109), a traditional Chinese herbal medicine, was investigated in mice infected with herpes simplex virus type 1 (HSV-1). TJS-109 is a combination of the medicinal plant extracts fromZingiberis siccatum rhizoma,Aconiti tuber andGlycyrrhizae radix in a specific proportion. Mice infected with a 10 LD50 dose of HSV-1 were treated with TJS-109 orally at doses of 1.25 to 20 mg/kg 2 days before, and 1 and 4 days after the infection. The treated groups had 80% (1.25 mg/kg), 40% (5 mg/kg) and 23% (20 mg/kg) mortality rates 25 days after the infection as compared with a 100% mortality rate in control mice treated with saline. When HSV-1 infected mice (recipients) received CD8+T cell fractions derived from spleens of mice treated with TJS-109 (donors), 70% of recipients survived, as compared with 0% survivors in the groups of mice treated with saline, B cell fractions, CD4+ T cell fractions or macrophage-enriched fractions prepared from the same donors. TJS-109 did not show any virucidal activities against HSV-1 or any virostatic activities on the growth of HSV-1 in Vero cells. These results suggest that TJS-109 protected mice exposed to lethal amounts of HSV-1 through the activation of CD8+ T cells.  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