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   4661篇
  免费   149篇
  国内免费   33篇
化学   3258篇
晶体学   37篇
力学   76篇
数学   622篇
物理学   850篇
  2023年   27篇
  2022年   87篇
  2021年   108篇
  2020年   107篇
  2019年   98篇
  2018年   94篇
  2017年   59篇
  2016年   159篇
  2015年   130篇
  2014年   152篇
  2013年   251篇
  2012年   316篇
  2011年   398篇
  2010年   190篇
  2009年   164篇
  2008年   280篇
  2007年   261篇
  2006年   262篇
  2005年   227篇
  2004年   180篇
  2003年   162篇
  2002年   143篇
  2001年   56篇
  2000年   67篇
  1999年   42篇
  1998年   30篇
  1997年   41篇
  1996年   66篇
  1995年   52篇
  1994年   25篇
  1993年   36篇
  1992年   37篇
  1991年   33篇
  1990年   24篇
  1989年   21篇
  1988年   26篇
  1987年   16篇
  1986年   20篇
  1985年   31篇
  1984年   23篇
  1983年   21篇
  1982年   34篇
  1981年   29篇
  1980年   29篇
  1979年   24篇
  1978年   27篇
  1977年   14篇
  1975年   17篇
  1974年   13篇
  1973年   17篇
排序方式: 共有4843条查询结果,搜索用时 15 毫秒
21.
Epilobium angustifolium L. (EA) has been used as a topical agent since ancient times. There has been an increasing interest in applying EA as a raw material used topically in recent years. However, in the literature, there are not many reports on the comprehensive application of this plant to skin care and treatment. EA contains many valuable secondary metabolites, which determine antioxidant, anti-inflammatory, anti-aging, and antiproliferative activity effects. One of the most important active compounds found in EA is oenothein B (OeB), which increases the level of ROS and protects cells from oxidative damage. OeB also influences wound healing and reduces inflammation by strongly inhibiting hyaluronidase enzymes and inhibiting COX-1 and COX-2 cyclooxygenases. Other compounds that play a key role in the context of application to the skin are flavonoids, which inhibit collagenase and hyaluronidase enzymes, showing anti-aging and anti-inflammatory properties. While terpenes in EA play an important role in fighting bacterial skin infections, causing, among other things cell membrane, permeability increase as well as the modification of the lipid profiles and the alteration of the adhesion of the pathogen to the animal cells. The available scientific information on the biological potential of natural compounds can be the basis for the wider use of EA in skin care and treatment. The aim of the article is to review the existing literature on the dermocosmetic use of E. angustifolium.  相似文献   
22.
The effect of laser irradiation on the optical properties of thermally evaporated Se100?x Te x (x=8, 12, 16) chalcogenide thin films has been studied. The result shows that the irradiation causes a shift in the optical gap. The results have been analyzed on the basis of laser irradiation-induced defects in the film. The width of the tail of localized state in the band gap has been evaluated using the Urbach edge method. As the irradiation time increases, the values of the optical energy gap for all compositions decrease, while tail energy width increases. It is also observed that the optical energy gap decreases with increasing Te content in the alloy. These changes are a consequence of an increment in disorder produced by laser irradiation in the amorphous structure of thin film.  相似文献   
23.
The hydroxyalkylation reaction has been used to condense benzocrown ethers with various aldehydes and ketones. The condensation reactions are catalyzed by triflic or sulfuric acid. The products from the reactions are bis(benzocrown ethers) and they are formed in good yields (42-98%, 13 examples).  相似文献   
24.
The paper provides the complete list of local models forZ 2 l -invariant generic germs of Lagrangian submanifolds of dimension ≦3. Classification is done directly for genrating functions of Lagrangian submanifolds and contains both elementary singularities and non-elementary ones with continuous moduli. The results demonstrate, in particular, that in contrast to the non-equivariant case the classification of equivariant Lagrangian singularities is not subordinated to the classification of symmetric functions up to the right equivariant equivalences.  相似文献   
25.
26.
Using data collected at the psi(3770) resonance with the CLEO-c detector at the Cornell e+e- storage ring, we present searches for 25 charmless decay modes of the psi(3770), mostly multibody final states. No evidence for charmless decays is found.  相似文献   
27.
28.
The excitation and the relaxation of the plasma waves and ion acoustic waves (IAW), respectively, driven by stimulated Raman (SRS) and Brillouin (SBS) backscatterings have been experimentally investigated with short-pulse lasers. The spectra have been obtained with a 0.3 ps time resolution. It is shown that SRS develops before SBS and suddenly decays around the peak of the pump, as the IAW reaches saturation. On this short time scale, electron kinetic effects play a major role for SRS saturation, contrary to ion dynamics. These results are supported by particle-in-cell simulations.  相似文献   
29.
We describe new measurements of the inclusive and exclusive branching fractions for psi(2S) transitions to J/psi using e(+)e(-) collision data collected with the CLEO detector operating at CESR. All branching fractions and ratios of branching fractions reported here represent either the most precise measurements to date or the first direct measurements. Indirectly and in combination with other CLEO measurements, we determine B(chi(cJ) --> gamma(J/psi)) and B[psi(2S) --> light hadrons].  相似文献   
30.
We present a definition of Riemannian manifold in noncommutative geometry. Using products of unbounded Kasparov modules, we show one can obtain such Riemannian manifolds from noncommutative spincc manifolds; and conversely, in the presence of a spincc structure. We also show how to obtain an analogue of Kasparov’s fundamental class for a Riemannian manifold, and the associated notion of Poincaré duality. Along the way we clarify the bimodule and first-order conditions for spectral triples.  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