全文获取类型
收费全文 | 41969篇 |
免费 | 88篇 |
国内免费 | 116篇 |
专业分类
系统科学 | 392篇 |
丛书文集 | 1022篇 |
教育与普及 | 107篇 |
理论与方法论 | 236篇 |
现状及发展 | 18788篇 |
研究方法 | 1598篇 |
综合类 | 19545篇 |
自然研究 | 485篇 |
出版年
2013年 | 213篇 |
2012年 | 527篇 |
2011年 | 1081篇 |
2010年 | 240篇 |
2008年 | 703篇 |
2007年 | 753篇 |
2006年 | 748篇 |
2005年 | 766篇 |
2004年 | 687篇 |
2003年 | 778篇 |
2002年 | 715篇 |
2001年 | 1286篇 |
2000年 | 1220篇 |
1999年 | 768篇 |
1992年 | 739篇 |
1991年 | 606篇 |
1990年 | 645篇 |
1989年 | 643篇 |
1988年 | 643篇 |
1987年 | 637篇 |
1986年 | 650篇 |
1985年 | 792篇 |
1984年 | 622篇 |
1983年 | 539篇 |
1982年 | 470篇 |
1981年 | 496篇 |
1980年 | 598篇 |
1979年 | 1302篇 |
1978年 | 1116篇 |
1977年 | 1114篇 |
1976年 | 825篇 |
1975年 | 872篇 |
1974年 | 1302篇 |
1973年 | 1052篇 |
1972年 | 1072篇 |
1971年 | 1326篇 |
1970年 | 1764篇 |
1969年 | 1385篇 |
1968年 | 1269篇 |
1967年 | 1329篇 |
1966年 | 1127篇 |
1965年 | 827篇 |
1964年 | 220篇 |
1959年 | 503篇 |
1958年 | 731篇 |
1957年 | 577篇 |
1956年 | 486篇 |
1955年 | 442篇 |
1954年 | 483篇 |
1948年 | 265篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
灰铸铁的应力屈服曲面及其三维热弹塑性应力解析 总被引:4,自引:0,他引:4
对原有的灰铸铁件应力屈服曲面进行了合理的简化,使其在理论上合理,工程应用上更为方便。建立了灰铸铁件三维非稳态热弹塑性应力场的有限元方法。以灰铸铁哑铃件为对象,用新屈服曲面对其应力发展过程进行了模拟,且比较了用新旧屈服面计算得到的结果。 相似文献
23.
Activation of a C. elegans Antennapedia homologue in migrating cells controls their direction of migration. 总被引:1,自引:0,他引:1
Anterior-posterior patterning in insects, vertebrates and nematodes involves members of conserved Antennapedia-class homeobox gene clusters (HOM-C) that are thought to give specific body regions their identities. The effects of these genes on region-specific body structures have been described extensively, particularly in Drosophila, but little is known about how HOM-C genes affect the behaviours of cells that migrate into their domains of function. In Caenorhabditis elegans, the Antennapedia-like HOM-C gene mab-5 not only specifies postembryonic fates of cells in a posterior body region, but also influences the migration of mesodermal and neural cells that move through this region. Here we show that as one neuroblast migrates into this posterior region, it switches on mab-5 gene expression; mab-5 then acts as a developmental switch to control the migratory behaviour of the neuroblast descendants. HOM-C genes can therefore not only direct region-specific patterns of cell division and differentiation, but can also act within migrating cells to programme region-specific migratory behaviour. 相似文献
24.
The introduction of human insulin to treat diabetics seemed straightforward. What can account for the problems that have followed? 相似文献
25.
26.
27.
28.
29.
Kang J.Y. Xu F.C. 《中国科学基金(英文版)》2004,(2):57-58,64
1 Introduction
Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].
…… 相似文献
30.
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