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   23211篇
  免费   695篇
  国内免费   39篇
系统科学   1175篇
丛书文集   263篇
教育与普及   30篇
理论与方法论   357篇
现状及发展   9569篇
研究方法   737篇
综合类   11601篇
自然研究   213篇
  2018年   761篇
  2017年   770篇
  2016年   503篇
  2012年   474篇
  2011年   1364篇
  2010年   903篇
  2009年   535篇
  2008年   748篇
  2007年   1208篇
  2006年   307篇
  2005年   334篇
  2004年   518篇
  2003年   499篇
  2002年   385篇
  2001年   487篇
  2000年   454篇
  1999年   335篇
  1992年   294篇
  1991年   225篇
  1990年   240篇
  1989年   238篇
  1988年   204篇
  1987年   242篇
  1986年   280篇
  1985年   337篇
  1984年   236篇
  1983年   229篇
  1982年   215篇
  1981年   223篇
  1980年   228篇
  1979年   582篇
  1978年   486篇
  1977年   451篇
  1976年   356篇
  1975年   413篇
  1974年   577篇
  1973年   471篇
  1972年   481篇
  1971年   562篇
  1970年   717篇
  1969年   553篇
  1968年   557篇
  1967年   552篇
  1966年   440篇
  1965年   377篇
  1959年   198篇
  1958年   334篇
  1957年   248篇
  1956年   191篇
  1955年   192篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
23.
In this experiment, using the methods of drought-stress in the pot and PEG simulative drought-stress, three native rocky-slope grasses Pogonatherum panideum(Lam.) Hack, Erioophorum comosum nees and Cynodon dactylon cultivated in the pots were selected as materials to study their drought-resistance by analyzing the indexes such as the leaf area index, the drying roots accumulation, the holding water ability of leaf, the relative conductance of leaf, the soluble protein, chlorophyll. At the same time, by comparing with membership function value of each index, the order of each grass drought-resistance was decided. The results showed that the drought-resistance of Erioophorum comosum nees was stronger than Cynodon dactylon and drought-resistance of Cynodon dactylon was stronger than Pogonatherum panideum (Lam.) Hack. The purpose of the experimental results was to find theoretical foundations for selecting and cultivating native protecting-slope vegetations to adapt to rocky slopes.  相似文献   
24.
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   
25.
26.
27.
28.
29.
30.
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   
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