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   11631篇
  免费   44篇
  国内免费   72篇
系统科学   61篇
丛书文集   29篇
教育与普及   21篇
理论与方法论   32篇
现状及发展   5434篇
研究方法   586篇
综合类   5456篇
自然研究   128篇
  2012年   205篇
  2011年   300篇
  2010年   77篇
  2009年   74篇
  2008年   201篇
  2007年   243篇
  2006年   246篇
  2005年   233篇
  2004年   202篇
  2003年   195篇
  2002年   247篇
  2001年   435篇
  2000年   427篇
  1999年   288篇
  1992年   236篇
  1991年   194篇
  1990年   215篇
  1989年   191篇
  1988年   202篇
  1987年   219篇
  1986年   190篇
  1985年   252篇
  1984年   226篇
  1983年   171篇
  1982年   176篇
  1981年   180篇
  1980年   170篇
  1979年   403篇
  1978年   340篇
  1977年   250篇
  1976年   290篇
  1975年   260篇
  1974年   272篇
  1973年   224篇
  1972年   244篇
  1971年   308篇
  1970年   374篇
  1969年   254篇
  1968年   307篇
  1967年   292篇
  1966年   249篇
  1965年   178篇
  1964年   99篇
  1959年   88篇
  1958年   162篇
  1957年   100篇
  1956年   91篇
  1955年   85篇
  1954年   77篇
  1948年   64篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Type A and Type B women assessed by a newly developed German questionnaire 'need for control' (NC) were compared with respect to time-pressured information processing performance and to simultaneously recorded psychophysiological reactivity. The task was computer controlled, monetarily reinforced and subject paced. The physiological measurements included the cardiovascular parameters, ECG and finger plethysmographic amplitudes and the noncardiovascular parameters, EMG (frontal muscle), skin conductance reactivity, and respiration. NC-Type A and Type B women did not differ in performance, but the Type As showed stronger vasoconstrictive responses to the task than did the Type Bs. Other physiological intergroup differences were not seen. In addition, the Type As scored significantly higher in nervousness and irritability and marginally higher in depression, reactive aggressivity and neuroticism than did the Type Bs. This particular pattern of NC-Type A/B differences is discussed with regard to relevant differences observed by other studies between SI and JAS Type As and Bs.  相似文献   
993.
Summary Only 1 of 7 dogs with long-standing renovascular hypertension showed clear changes in the fundus. No distinct retinopathy was seen in the others. Ophthalmoscopy alone is thus of limited value in assessing the progress of benign hypertension in the dog.  相似文献   
994.
Soluble dipeptidyl peptidase IV (EC 3.4.14.5) was purified from the 100,000 X g supernatant fraction of pig liver homogenate. The purified enzyme had the same properties as, and immunological identity with, the membrane-bound enzyme which was described previously. However, the purified enzyme had a pattern of molecular heterogeneity different from the membrane-bound enzyme; this was shown by isoelectric focusing. Carbohydrate analysis revealed that the soluble enzyme contained glucose, which is not found in the membrane-bound one, and less fucose, mannose, and sialic acid than the latter. From these results, we conclude that the soluble form of dipeptidyl peptidase IV in pig liver is closely related to the membrane-bound enzyme, but is not simply a proteolytically solubilized product of it.  相似文献   
995.
Summary A unicellular exocrine gland possessing an epicuticular ductule occurs in grass shrimp gills. This gland displays ultrastructural changes in relation to the molt cycle. These changes include an increase in the quantity of secretory granules during late premolt, and the development of ciliary axonemes in relation to ductule formation.This investigation was supported in part by grant CR-807417 from the U.S. Environmental Protection Agency.  相似文献   
996.
997.
Summary Remarkable regional distribution patterns of some chlorinated xenobiotics in the CNS are described.We thank Dr Åke Bergman, Wallenberg Laboratory, University of Stockholm, Stockholm, for the synthesis of compounds IV and V. The studies were supported by the Swedish Work Environment Fund (grants nos 73/169 and 74/181) and by the Research Committee of the National Swedish Environment Protection Board (grant no. 7-27/79).  相似文献   
998.
P K Sasi  R Kaleysa Raj 《Experientia》1975,31(11):1261-1262
The phospholipid level in the human parasitic nematode Ascaris lumbricoides is decreased by piperazine, by partially stimulating catabolic enzymes such as phospholipase C and partially inhibiting anabolic enzymes such as choline kinase.  相似文献   
999.
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