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   30668篇
  免费   70篇
  国内免费   85篇
系统科学   318篇
丛书文集   661篇
教育与普及   64篇
理论与方法论   117篇
现状及发展   14596篇
研究方法   1149篇
综合类   13617篇
自然研究   301篇
  2012年   342篇
  2011年   700篇
  2010年   153篇
  2009年   152篇
  2008年   428篇
  2007年   514篇
  2006年   496篇
  2005年   506篇
  2004年   575篇
  2003年   520篇
  2002年   458篇
  2001年   896篇
  2000年   905篇
  1999年   560篇
  1992年   527篇
  1991年   420篇
  1990年   485篇
  1989年   460篇
  1988年   408篇
  1987年   445篇
  1986年   481篇
  1985年   596篇
  1984年   426篇
  1983年   387篇
  1982年   360篇
  1981年   408篇
  1980年   431篇
  1979年   1029篇
  1978年   839篇
  1977年   822篇
  1976年   625篇
  1975年   701篇
  1974年   1044篇
  1973年   823篇
  1972年   806篇
  1971年   983篇
  1970年   1231篇
  1969年   1032篇
  1968年   960篇
  1967年   978篇
  1966年   816篇
  1965年   647篇
  1964年   196篇
  1959年   369篇
  1958年   575篇
  1957年   411篇
  1956年   347篇
  1955年   341篇
  1954年   334篇
  1948年   206篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Summary The toxic effect of trimethylphosphate on rat testes was investigated after oral dosing with 250 mg/kg for either 5 days/week for 30 days or 6 days/week for 60 days. After these prolonged treatments azoospermia resulted.Acknowledgments. The authors wish to thank Ms M. Michelles, Ms A. Murray and Ms R. Peake for their technical support.  相似文献   
993.
P Liedholm  B Astedt 《Experientia》1976,32(2):226-227
The fibrinolytic activity of the endometrium of the two uterine horns in the rat was histochemically determined. One of the horns contained a plastic-IUD, the other served as control. The endometrium of the control horn was almost inactive in contrast with that of the IUD-horn in which fibrinolytic activity was apparent. The fibrinolytic activity induced by the IUD might be involved in the prevention of ova implantation.  相似文献   
994.
Summary Brush border sucrase and alkaline phosphatase activities are considerably enhanced in the intestine of ascorbic acid deficient guinea-pigs. Similar increase in the uptake of D-glucose and L-alanine also occurs in chronic vitamin C deficiency. However the permeability of D-glucose and L-alanine in the intestine of animals fed with large doses of vitamin C is severely depressed, with a reduction in the levels of sucrase and alkaline phosphatase activities.  相似文献   
995.
Summary An apparently transient elevation of basal morning (08.00 h) plasma corticosterone levels in male mice was found 48 h after bilateral electrolytic lesions of the brainstem locus coeruleus complex but was not observed 6 weeks after lesioning.Supported by Alfred P. Sloan Foundation research fellowships awarded to W.G. Luttge and S.F. Zornetzer.  相似文献   
996.
Summary 125I-Insulin initially localizes to the plasma membrane of isolated rat hepatocytes but is subsequently internalized and preferentially associates with lysosomal structures. In the present study, we show that this preferential association to lysosomes occurs in regions of the cell rich in lysosomal and Golgi structures.This work was performed while Dr Gorden was visiting professor of the Institute of Histology and Embryology, University of Geneva, Geneva, Switzerland.This work was supported by grant No. 3.120.77 from Swiss National Science Foundation. We thank M.M. Sidler-Ansermet, O. Jerotic and N. Maalaoui for their valuable help.  相似文献   
997.
Riassunto Vengono riportati i dati relativi allo sviluppo in funzione dell'età, della reatività immunologica primaria nel topo con nanismo ereditario preipofisario e nel corrispondente fratello normale. Mentre in quest'ultimo si è notato un graduale incremento della reattività immunitaria di tipo primario soprattutto a partire dalla fine del periodo di allattamento, nel topo nano la reattività immunitaria primaria è rimasta costante nel tempo su bassi livelli anche dopo lo svezzamento. Alla luce dei dati sperimentali riportati viene ipotizzata l'esistenza di un controllo ipofisario della reattività immunitaria primaria.  相似文献   
998.
Riassunto Il dodecilsolfato di sodio causa la dissociazione dell'urease (massa molecolare 480,000) in una maniera che dipende fortemente sulla concentrazione relativa dei reagenti. Il prodotto ottenuto con un sufficiente eccesso di detergente ha una massa molecolare di 50,000–60,000.

This work was supported by Grant No. 11,573 and Career Award No. 5K3 GM 13,489 (to G.G.) from the National Institutes of Health, Department of Health, Education and Welfare.  相似文献   
999.
Zusammenfassung Pregnenolon-20-14C wird von roten Meerzwiebeln als Vorstufe für herzwirksame Glykoside verwendet, dagegen kannBufo paracnemis diese Produkte, subkutan appliziert, nicht in die üblichen Krötengifte überführen.  相似文献   
1000.
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