全文获取类型
收费全文 | 13229篇 |
免费 | 95篇 |
国内免费 | 159篇 |
专业分类
系统科学 | 198篇 |
丛书文集 | 275篇 |
教育与普及 | 82篇 |
理论与方法论 | 58篇 |
现状及发展 | 5296篇 |
研究方法 | 502篇 |
综合类 | 6940篇 |
自然研究 | 132篇 |
出版年
2015年 | 129篇 |
2014年 | 149篇 |
2013年 | 218篇 |
2012年 | 310篇 |
2011年 | 434篇 |
2010年 | 212篇 |
2009年 | 178篇 |
2008年 | 318篇 |
2007年 | 327篇 |
2006年 | 325篇 |
2005年 | 307篇 |
2004年 | 255篇 |
2003年 | 243篇 |
2002年 | 263篇 |
2001年 | 343篇 |
2000年 | 336篇 |
1999年 | 221篇 |
1992年 | 196篇 |
1991年 | 164篇 |
1990年 | 169篇 |
1989年 | 173篇 |
1988年 | 175篇 |
1987年 | 162篇 |
1986年 | 170篇 |
1985年 | 235篇 |
1984年 | 141篇 |
1983年 | 141篇 |
1981年 | 120篇 |
1980年 | 155篇 |
1979年 | 384篇 |
1978年 | 286篇 |
1977年 | 309篇 |
1976年 | 219篇 |
1975年 | 220篇 |
1974年 | 341篇 |
1973年 | 281篇 |
1972年 | 302篇 |
1971年 | 309篇 |
1970年 | 424篇 |
1969年 | 365篇 |
1968年 | 368篇 |
1967年 | 338篇 |
1966年 | 293篇 |
1965年 | 214篇 |
1959年 | 117篇 |
1958年 | 212篇 |
1957年 | 169篇 |
1956年 | 161篇 |
1955年 | 132篇 |
1954年 | 132篇 |
排序方式: 共有10000条查询结果,搜索用时 670 毫秒
11.
Strell C Lang K Niggemann B Zaenker KS Entschladen F 《Cellular and molecular life sciences : CMLS》2007,64(24):3306-3316
The extravasation of leukocytes and tumor cells is a multi-step process with the involvement of various adhesion molecules
depending on the three steps rolling, adhesion, and diapedesis. We have developed an in vitro model, by which we investigated the rolling and adhesion of neutrophil granulocytes and MDA-MB-468 human breast carcinoma
cells to lung endothelial cells under physiological flow-conditions. We found that norepinephrine had an inhibitory function
on the fMLP-promoted adhesion of neutrophil granulocytes due to a down-regulation of β2-integrin. Furthermore, neutrophil
granulocytes serve as linking cells for the interaction of the MDA-MB-468 cells with the endothelium, which are both β2-integrin
negative, but express the β2-integrin ligand ICAM-1. In addition, we show here that N-cadherin is up-regulated on the endothelial
cells and on neutrophil granulocytes in response to fMLP. This up-regulation resulted in a significant increase of adherent
MDA-MB-468 cells, which are also N-cadherin positive.
Received 3 September 2007; received after revision 17 October 2007; accepted 22 October 2007 相似文献
12.
Advances in our understanding of cardiac development have fuelled research into cellular approaches to myocardial repair of
the damaged heart. In this collection of reviews we present recent advances into the basic mechanisms of heart development
and the resident and non-resident progenitor cell populations that are currently being investigated as potential mediators
of cardiac repair. Together these reviews illustrate that despite our current knowledge about how the heart is constructed,
caution and much more research in this exciting field is essential. The current momentum to evaluate the potential for cardiac
repair will in turn accelerate research into fundamental aspects of myocardial biology. 相似文献
13.
Summary Intravenous or subcutaneous administration of pyribenzamine and other antihistaminics is able to decrease, and to delay the appearance of chemosis produced by mustard oils in the eye of the rabbit. Simultaneously occurring vascular reactions, on the other hand, are but slightly affected by antihistaminics. Intravenous or subcutaneous administration of rutin has no clear-cut effect on chemosis; it is however able to inhibit the vascular reaction. 相似文献
14.
15.
16.
17.
The C-banding pattern and nucleolar organizer regions of the metaphase chromosomes of Cynoglossus semilaevis are reported. The interstitial regions in all chromosomes including the pair of sex chromosomes had positive C-bands, and the 6th and 12th pairs of chromosomes were entirely stained in most cases. Some chromosomes such as the 1st, 2nd, 7th, 8th, 9th and 10th pairs showed C-bands at centromeric or distal ends. The C-banding heretochromatin occupies 30.03% of the total chromosome surface in C. semilaevis,which is similar to that of amphibians such as Mixophyes fasciolatus (30.2%) and M. schevilli (20.7%), but is rather lower than that of cephalochordate Branchiostoma belcheri (54.3%). Silver staining revealed a single pair of nucleolar organizer regions (NORs) located in the telomeric regions of Chromosome 2. The association of NORs with heterochromatin observed in vertebrates also occurs in C. semilaevis as the telomeric regions of Chromosome 2 are always stained positively with C-banding. 相似文献
18.
19.
20.