全文获取类型
收费全文 | 44615篇 |
免费 | 698篇 |
国内免费 | 134篇 |
专业分类
系统科学 | 1239篇 |
丛书文集 | 740篇 |
教育与普及 | 96篇 |
理论与方法论 | 471篇 |
现状及发展 | 18574篇 |
研究方法 | 1579篇 |
综合类 | 22277篇 |
自然研究 | 471篇 |
出版年
2018年 | 762篇 |
2017年 | 775篇 |
2016年 | 525篇 |
2012年 | 785篇 |
2011年 | 1936篇 |
2010年 | 1034篇 |
2009年 | 635篇 |
2008年 | 1147篇 |
2007年 | 1444篇 |
2006年 | 742篇 |
2005年 | 778篇 |
2004年 | 762篇 |
2003年 | 833篇 |
2002年 | 784篇 |
2001年 | 1193篇 |
2000年 | 1105篇 |
1999年 | 733篇 |
1992年 | 711篇 |
1991年 | 576篇 |
1990年 | 610篇 |
1989年 | 616篇 |
1988年 | 612篇 |
1987年 | 628篇 |
1986年 | 629篇 |
1985年 | 770篇 |
1984年 | 655篇 |
1983年 | 531篇 |
1982年 | 475篇 |
1981年 | 484篇 |
1980年 | 570篇 |
1979年 | 1275篇 |
1978年 | 1119篇 |
1977年 | 1034篇 |
1976年 | 798篇 |
1975年 | 838篇 |
1974年 | 1143篇 |
1973年 | 980篇 |
1972年 | 1000篇 |
1971年 | 1260篇 |
1970年 | 1606篇 |
1969年 | 1202篇 |
1968年 | 1183篇 |
1967年 | 1208篇 |
1966年 | 1031篇 |
1965年 | 764篇 |
1959年 | 433篇 |
1958年 | 649篇 |
1957年 | 514篇 |
1956年 | 438篇 |
1954年 | 421篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
WANG Xibo ZHOU Benhai YU Gei LI Qian 《武汉大学学报:自然科学英文版》2007,12(5):946-950
μC/OS-Ⅱ is an open source real-time kernel adopting priority preemptive schedule strategy. Aiming at the problem of μC/OS-Ⅱ failing to support homology priority tasks scheduling, an approach for solution is proposed. The basic idea is adding round-robin scheduling strategy in its original scheduler in order to schedule homology priority tasks through time slice roundrobin. Implementation approach is given in detail. Firstly, the Task Control Block (TCB) is extended. And then, a new priority index table is created, in which each index pointer points to a set of homology priority tasks. Eventually, on the basis of reconstructing μC/OS-Ⅱ real-time kernel, task scheduling module is rewritten. Otherwise, schedulability of homology task supported by modified kernel had been analyzed, and deadline formula of created homology tasks is given. By theoretical analysis and experiment verification, the modified kernel can support homology priority tasks scheduling, meanwhile, it also remains preemptive property of original μC/OS-Ⅱ. 相似文献
42.
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
43.
Numerous microRNAs (miRNAs) have been discovered in the genomes of higher eukaryotes, and functional studies indicate that they are important during development. However, little is known concerning the function of individual miRNAs. We approached this problem in zebrafish by combining identification of miRNA expression, functional analyses and experimental validation of potential targets. We show that miR-214 is expressed during early segmentation stages in somites and that varying its expression alters the expression of genes regulated by Hedgehog signaling. Inhibition of miR-214 results in a reduction or loss of slow-muscle cell types. We show that su(fu) mRNA, encoding a negative regulator of Hedgehog signaling, is targeted by miR-214. Through regulation of su(fu), miR-214 enables precise specification of muscle cell types by sharpening cellular responses to Hedgehog. 相似文献
44.
45.
46.
47.
48.
49.
50.