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   76258篇
  免费   6563篇
  国内免费   6845篇
化学   28084篇
晶体学   359篇
力学   7008篇
综合类   1355篇
数学   28887篇
物理学   23973篇
  2023年   595篇
  2022年   1011篇
  2021年   1390篇
  2020年   1508篇
  2019年   1788篇
  2018年   1510篇
  2017年   1839篇
  2016年   2089篇
  2015年   1847篇
  2014年   2646篇
  2013年   5077篇
  2012年   3115篇
  2011年   3529篇
  2010年   3035篇
  2009年   4210篇
  2008年   4702篇
  2007年   4834篇
  2006年   4494篇
  2005年   3853篇
  2004年   3507篇
  2003年   3575篇
  2002年   3285篇
  2001年   2790篇
  2000年   2702篇
  1999年   2443篇
  1998年   2245篇
  1997年   1887篇
  1996年   1666篇
  1995年   1499篇
  1994年   1378篇
  1993年   1163篇
  1992年   1124篇
  1991年   872篇
  1990年   724篇
  1989年   629篇
  1988年   581篇
  1987年   462篇
  1986年   395篇
  1985年   478篇
  1984年   451篇
  1983年   229篇
  1982年   364篇
  1981年   416篇
  1980年   308篇
  1979年   303篇
  1978年   235篇
  1977年   215篇
  1976年   164篇
  1974年   112篇
  1973年   108篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
21.
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE.  相似文献   
22.
23.
24.
25.
The development of synthetic routes which lead to five new diisocyanide monomers with one or two phenolic groups is described. Their polymerization behavior is studied with Pd‐ and Ni‐based initiators, as well as under microwave irradiation. The polymerizability is mainly dominated by steric effects as is concluded from experiments using different protecting groups. Chiroptical properties of these new polymers are studied by CD‐spectroscopy. After deprotection, helically chiral poly(quinoxalin‐2,3‐diyl)s are obtained which display a Brønsted function attached to a stereolabile biaryl axis whose configuration should be influenced by the chiral polymer backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1320–1329  相似文献   
26.
We numerically solve the time-dependent Ginzburg–Landau equations for two-gap superconductors using the finite-element technique. The real-time simulation shows that at low magnetic field, the vortices in small-size samples tend to form clusters or other disorder structures. When the sample size is large, stripes appear in the pattern. These results are in good agreement with the previous experimental observations of the intriguing anomalous vortex pattern, providing a reliable theoretical basis for the future applications of multi-gap superconductors.  相似文献   
27.
28.
29.
Inflation of balloons provides a straightforward way of achieving large biaxial deformations. Previous studies have shown that when a balloon bursts, crack propagation occurs at very high speed – much higher than would be expected from the low strain modulus and elastic wave velocity of the rubber. The present paper is concerned with studies of the deformation and fracture of cylindrical balloons. On inflation, the deformations of such a balloon pass through an unstable region but subsequently increase monotonically with pressure. In this relatively high pressure region, the ratio of the longitudinal and circumferential extension ratios is broadly in accord with expectations from high-strain elasticity theory when the ratio of the corresponding stresses is taken into account. On bursting, crack speeds up to around 300 m/s in this region. It is shown that these speeds are in accord with large increase in incremental moduli for the highly-strained rubber. Marked changes in crack tip profile observed at very high crack speeds are consistent with control of the rate of growth by inertia rather than by the viscoelastic properties of the rubber (as is believed to be the case at lower speeds). Consistent with this, various elastomers having different glass transition temperatures show similar crack growth behaviour in the very high speed region.  相似文献   
30.
Accuracy arguments are the en vogue route in epistemic justifications of probabilism and further norms governing rational belief. These arguments often depend on the fact that the employed inaccuracy measure is strictly proper. I argue controversially that it is ill-advised to assume that the employed inaccuracy measures are strictly proper and that strictly proper statistical scoring rules are a more natural class of measures of inaccuracy. Building on work in belief elicitation I show how strictly proper statistical scoring rules can be used to give an epistemic justification of probabilism.An agent's evidence does not play any role in these justifications of probabilism. Principles demanding the maximisation of a generalised entropy depend on the agent's evidence. In the second part of the paper I show how to simultaneously justify probabilism and such a principle. I also investigate scoring rules which have traditionally been linked with entropies.  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