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   42662篇
  免费   75篇
  国内免费   98篇
系统科学   207篇
丛书文集   909篇
教育与普及   101篇
理论与方法论   263篇
现状及发展   19477篇
研究方法   1609篇
综合类   19761篇
自然研究   508篇
  2013年   242篇
  2012年   523篇
  2011年   1061篇
  2010年   227篇
  2008年   678篇
  2007年   687篇
  2006年   754篇
  2005年   750篇
  2004年   779篇
  2003年   733篇
  2002年   725篇
  2001年   1210篇
  2000年   1104篇
  1999年   752篇
  1992年   728篇
  1991年   587篇
  1990年   632篇
  1989年   633篇
  1988年   611篇
  1987年   636篇
  1986年   660篇
  1985年   799篇
  1984年   633篇
  1983年   550篇
  1982年   492篇
  1981年   493篇
  1980年   580篇
  1979年   1352篇
  1978年   1142篇
  1977年   1163篇
  1976年   803篇
  1975年   926篇
  1974年   1323篇
  1973年   1103篇
  1972年   1151篇
  1971年   1424篇
  1970年   1841篇
  1969年   1393篇
  1968年   1322篇
  1967年   1377篇
  1966年   1161篇
  1965年   874篇
  1964年   250篇
  1959年   506篇
  1958年   780篇
  1957年   632篇
  1956年   512篇
  1955年   471篇
  1954年   519篇
  1948年   300篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
11.
12.
13.
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   
14.
The corrosion cast technique provided for the first time an excellent three-dimensional visualization of the vascular pattern of the choroid and iris in the newt eye. The results show the presence of a single arterial afference to the choroidal and iris capillaries: the ophthalmic artery is the origin fo both ciliary arteries and the long posterior ciliary artery. Slightly behind the equatorial circumference of the eyeball the venous drainage consists of a single vessel on the dorsal side and two distinct vessels on the ventral one. It receives blood from both iris and choroid. The surface of the plastic endocasts shows some details of fine luminal structures of the endothelial cells. Shallow depressions may be regarded as imprints of endothelial cell nuclei, and they are distinctly different for arteries and capillaries. The angioarchitecture of the newt eye differs from that of brain in that hairpin-shaped capillary loops are not observed at all.  相似文献   
15.
16.
17.
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   
18.
19.
A linear regression model with random walk coefficients is extended to allow for linear restrictions between the coefficients to be satisfied at each point in time. Estimation in this model is shown to be no more involved than estimation in the standard model. It is also demonstrated how, after a slight modification to the testing problem, classical test procedures may be applied to the problem of testing for such restrictions. The performance of the Lagrange Multiplier test for a variety of different restrictions is then investigated via simulation. An empirical application involving testing for homogeneity in a random walk coefficient version of the AIDS model is given.  相似文献   
20.
We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium-induced attacks of skeletal muscle paralysis. HYPP co-segregated with the equine adult skeletal muscle sodium channel alpha subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS3 which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition.  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