全文获取类型
收费全文 | 16430篇 |
免费 | 225篇 |
国内免费 | 582篇 |
专业分类
系统科学 | 1461篇 |
丛书文集 | 824篇 |
教育与普及 | 1942篇 |
理论与方法论 | 134篇 |
现状及发展 | 1070篇 |
研究方法 | 1409篇 |
综合类 | 10354篇 |
自然研究 | 43篇 |
出版年
2018年 | 50篇 |
2017年 | 68篇 |
2016年 | 65篇 |
2015年 | 73篇 |
2014年 | 154篇 |
2013年 | 94篇 |
2012年 | 734篇 |
2011年 | 952篇 |
2010年 | 275篇 |
2009年 | 106篇 |
2008年 | 829篇 |
2007年 | 1025篇 |
2006年 | 1141篇 |
2005年 | 1349篇 |
2004年 | 1032篇 |
2003年 | 1085篇 |
2002年 | 839篇 |
2001年 | 771篇 |
2000年 | 1008篇 |
1999年 | 421篇 |
1998年 | 151篇 |
1997年 | 91篇 |
1996年 | 83篇 |
1995年 | 73篇 |
1994年 | 96篇 |
1993年 | 145篇 |
1992年 | 128篇 |
1991年 | 137篇 |
1990年 | 130篇 |
1989年 | 138篇 |
1988年 | 181篇 |
1987年 | 196篇 |
1986年 | 232篇 |
1985年 | 221篇 |
1984年 | 234篇 |
1983年 | 221篇 |
1982年 | 215篇 |
1981年 | 180篇 |
1980年 | 152篇 |
1979年 | 82篇 |
1970年 | 57篇 |
1964年 | 35篇 |
1959年 | 238篇 |
1958年 | 354篇 |
1957年 | 258篇 |
1956年 | 250篇 |
1955年 | 247篇 |
1954年 | 206篇 |
1948年 | 46篇 |
1946年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
留驻在柏林,我們的政府每天就要花掉我們很多的钱。留駐在柏林,我們的政府就要準備把该城的行政机构变成一个吵嚷的场所。据某些报纸和某些政客所说,留驻在柏林,我們的政府就要準備對俄国每一個农人饗以原子彈。我走到各處,都听见有人问起关于這种奇異局勢的問題,英国人民对于他們的官吏和士兵留驻在别人的城市里,並且佔为已有,而他们又不是在戰爭中由於战鬥的結果而進入該城的,都认为是极其激动的。 相似文献
23.
24.
25.
26.
Schlesinger Y Straussman R Keshet I Farkash S Hecht M Zimmerman J Eden E Yakhini Z Ben-Shushan E Reubinoff BE Bergman Y Simon I Cedar H 《Nature genetics》2007,39(2):232-236
Many genes associated with CpG islands undergo de novo methylation in cancer. Studies have suggested that the pattern of this modification may be partially determined by an instructive mechanism that recognizes specifically marked regions of the genome. Using chromatin immunoprecipitation analysis, here we show that genes methylated in cancer cells are specifically packaged with nucleosomes containing histone H3 trimethylated on Lys27. This chromatin mark is established on these unmethylated CpG island genes early in development and then maintained in differentiated cell types by the presence of an EZH2-containing Polycomb complex. In cancer cells, as opposed to normal cells, the presence of this complex brings about the recruitment of DNA methyl transferases, leading to de novo methylation. These results suggest that tumor-specific targeting of de novo methylation is pre-programmed by an established epigenetic system that normally has a role in marking embryonic genes for repression. 相似文献
27.
Association scan of 14,500 nonsynonymous SNPs in four diseases identifies autoimmunity variants 总被引:2,自引:0,他引:2
Wellcome Trust Case Control Consortium;Australo-Anglo-American Spondylitis Consortium 《Nature genetics》2007,39(11):1329-1337
We have genotyped 14,436 nonsynonymous SNPs (nsSNPs) and 897 major histocompatibility complex (MHC) tag SNPs from 1,000 independent cases of ankylosing spondylitis (AS), autoimmune thyroid disease (AITD), multiple sclerosis (MS) and breast cancer (BC). Comparing these data against a common control dataset derived from 1,500 randomly selected healthy British individuals, we report initial association and independent replication in a North American sample of two new loci related to ankylosing spondylitis, ARTS1 and IL23R, and confirmation of the previously reported association of AITD with TSHR and FCRL3. These findings, enabled in part by increased statistical power resulting from the expansion of the control reference group to include individuals from the other disease groups, highlight notable new possibilities for autoimmune regulation and suggest that IL23R may be a common susceptibility factor for the major 'seronegative' diseases. 相似文献
28.
29.
Prof. Zhu Zuoyan Vice President of NSFC met with the National Institute of Agricultural Research 《中国科学基金(英文版)》2007,15(1):33
Prof. Zhu Zuoyan, Vice President of NSFC, met with the National Institute of Agricultural Research (INRA) delegation led by its Deputy Director General, Prof. Guy Riba on Jan. 18, 2007. 相似文献
30.