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   24170篇
  免费   751篇
  国内免费   231篇
系统科学   1456篇
丛书文集   381篇
教育与普及   74篇
理论与方法论   356篇
现状及发展   7463篇
研究方法   848篇
综合类   13985篇
自然研究   589篇
  2018年   769篇
  2017年   781篇
  2016年   526篇
  2013年   290篇
  2012年   766篇
  2011年   2061篇
  2010年   1188篇
  2009年   794篇
  2008年   1065篇
  2007年   1588篇
  2006年   652篇
  2005年   627篇
  2004年   564篇
  2003年   572篇
  2002年   465篇
  2001年   510篇
  2000年   570篇
  1999年   417篇
  1992年   289篇
  1991年   260篇
  1990年   256篇
  1989年   230篇
  1988年   213篇
  1987年   227篇
  1986年   204篇
  1985年   251篇
  1984年   242篇
  1983年   160篇
  1982年   174篇
  1981年   157篇
  1980年   203篇
  1979年   446篇
  1978年   342篇
  1977年   368篇
  1976年   266篇
  1975年   323篇
  1974年   446篇
  1973年   379篇
  1972年   361篇
  1971年   424篇
  1970年   486篇
  1969年   427篇
  1968年   407篇
  1967年   444篇
  1966年   384篇
  1965年   302篇
  1959年   156篇
  1958年   231篇
  1957年   179篇
  1955年   154篇
排序方式: 共有10000条查询结果,搜索用时 374 毫秒
51.
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   
52.
Summary The disappearance of thrombin—formed in the blood, or added to serum-follows a manomolecular reaction-type. Heparin increases the reaction-velocity of this thrombin-inactivating process.Our investigation established that toluidine blue or kinase, which, according to the literature, bind heparin, strongly reduce the speed of thrombin-inactivation too. Therefore the heparin-binding capacity of these substances is also manifested in the decrease of thrombin-inactivation.  相似文献   
53.
54.
PAULING L 《Nature》1948,161(4104):1019
  相似文献   
55.
56.
Infection of bacteria triggers innate immune defense reactions in Drosophila. So far, the only bacterial component known to be recognized by the insect innate immune system is peptidoglycan, one of the most abundant constituents of the bacterial cell wall. Insects use peptidoglycan recognition proteins to detect peptidoglycan and to activate innate immune responses. Such specialized peptidoglycan receptors appear to have evolved from phage enzymes that hydrolyze bacterial cell walls. They are able to bind specific peptidoglycan molecules with distinct chemical moieties and activate innate immune pathways by interacting with other signaling proteins. Recent X-ray crystallographic studies of the peptidoglycan recognition proteins LCa, and LCx bound to peptidoglycan have provided structural insights into recognition of peptidoglycan and activation of innate immunity in insects. Received 28 December 2006; received after revision 2 February 2007; accepted 21 February 2007  相似文献   
57.
58.
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   
59.
Today, liver transplantation (LT) is the only established treatment for end-stage liver diseases. The de- velopment of LT, including OLT, cadaveric LT, split LT, living donor LT (LDLT), brings hopes to patients with these diseases. However, increasing donor shortage, rejection and life-long immunosuppression with its side effects are the major limitations of this therapy strategy. Bone marrow-derived stem cells (BMDSCs) are capable of differentiating into hepatocyte-like cells and contribute to liver injury repair. The microenvironment of liver injury caused by rejection, ischemia/reperfusion, loss of liver mass, recurrence of HCV and "small-for-size syndrome" after LT can attract a variety of bone marrow-derived stem cell population to the peripheral circulation and then migration to the injury liver to promote the hepatic function restoration. Additionally, BMDSCs can also take part in the functional regeneration of living donor liver after LDLT. This participation in liver regeneration may be associated to the interac- tion between SDF-1and its receptor CXCR4, involving HGF, IL-8, MMP9, and VEGF/VEGFR-2. BMDSC with its bio-characteristics could maintain the allograft tolerance from different angles and in different ways. In conclusion, BMDSCs transplantation, as a new assistant therapeutic method for LT, will ex- pand the space of LT, and provide more survival opportunities for the patients suffering liver diseases in the future.  相似文献   
60.
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