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   36779篇
  免费   123篇
  国内免费   121篇
系统科学   192篇
丛书文集   792篇
教育与普及   92篇
理论与方法论   214篇
现状及发展   16093篇
研究方法   1522篇
综合类   17677篇
自然研究   441篇
  2013年   217篇
  2012年   484篇
  2011年   975篇
  2010年   221篇
  2009年   182篇
  2008年   642篇
  2007年   659篇
  2006年   684篇
  2005年   679篇
  2004年   715篇
  2003年   651篇
  2002年   655篇
  2001年   1124篇
  2000年   1043篇
  1999年   722篇
  1992年   642篇
  1991年   542篇
  1990年   553篇
  1989年   553篇
  1988年   551篇
  1987年   573篇
  1986年   573篇
  1985年   708篇
  1984年   574篇
  1983年   462篇
  1982年   407篇
  1981年   438篇
  1980年   531篇
  1979年   1140篇
  1978年   1004篇
  1977年   974篇
  1976年   674篇
  1975年   760篇
  1974年   1078篇
  1973年   912篇
  1972年   952篇
  1971年   1158篇
  1970年   1529篇
  1969年   1160篇
  1968年   1097篇
  1967年   1152篇
  1966年   967篇
  1965年   733篇
  1959年   401篇
  1958年   601篇
  1957年   505篇
  1956年   423篇
  1955年   358篇
  1954年   424篇
  1948年   232篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
15.
16.
Humoral immune reactions to heat shock proteins (hsp) from microorganisms are one aspect of microbial infections in humans. The production of antibodies which are specific to epitopes present on procaryotic hsp leads also to the appearance of cross-reactive serum antibodies in the host organism that react with human hsp. This article discusses the consequences of such autoreactive antibodies for the host in context with the development of immune tolerance and autoimmune diseases, especially rheumatoid arthritis (RA), and in experimental animal models for arthritis such as adjuvant arthritis in rats. On the basis of epitope cross-reactivity between hsp and other host proteins, a hypothesis is presented for the development of autoimmune disease following the production of hsp-specific antibodies.  相似文献   
17.
Vitamin B12 (methylcobalamin) was administered orally (3 mg/day) to 9 healthy subjects for 4 weeks. Nocturnal melatonin levels after exposure to bright light (ca. 2500 lx) were determined, as well as the levels of plasma melatonin over 24 h. The timing of sleep was also recorded. Vitamin B12 was given blind to the subjects and crossed over with placebo. We found that the 24-h melatonin rhythm was significantly phase-advanced (1.1 h) in the vitamin B12 trial as compared with that in the placebo trial. In addition, the 24-h mean of plasma melatonin level was much lower in the vitamin B12 trial than with the placebo. Furthermore, the nocturnal melatonin levels during bright light exposure were significantly lower in the vitamin B12 trial than with the placebo. On the other hand, vitamin B12 did not affect the timing of sleep. These findings raise the possibility that vitamin B12 phase-advances the human circadian rhythm by increasing the light sensitivity of the circadian clock.  相似文献   
18.
19.
20.
This paper assesses the information content of two survey indicators for consumption developments in the near future for eight European countries in the period 1985–1998. Empirical work on this topic typically focuses on consumer confidence, the perceptions of buyers of consumption goods. This paper examines whether perceptions of sellers of consumption goods, measured by retail trade surveys, may also improve short‐term monitoring of consumption. We find that both consumer confidence and retailer confidence embody valuable information, when analysed in isolation. For France, Italy and Spain we conclude that adding retail confidence does not improve the indicator model once consumer confidence has been included. For the UK the reverse case is obtained. For the remaining four countries we show that combining consumer sentiment and retail trade confidence into a composite indicator leads to optimal results. Our results suggest that incorporating information from retail trade surveys may offer significant benefits for the analysis of short‐term prospects of consumption. Copyright © 2004 John Wiley & Sons, Ltd.  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