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   448279篇
  免费   11364篇
  国内免费   6676篇
化学   227248篇
晶体学   6906篇
力学   22750篇
综合类   338篇
数学   61891篇
物理学   147186篇
  2022年   3546篇
  2021年   4209篇
  2020年   4596篇
  2019年   4646篇
  2018年   13004篇
  2017年   13674篇
  2016年   11080篇
  2015年   6552篇
  2014年   7896篇
  2013年   17123篇
  2012年   18643篇
  2011年   28207篇
  2010年   18147篇
  2009年   17742篇
  2008年   24056篇
  2007年   27066篇
  2006年   13636篇
  2005年   18612篇
  2004年   13998篇
  2003年   12616篇
  2002年   10473篇
  2001年   10108篇
  2000年   8122篇
  1999年   6536篇
  1998年   5390篇
  1997年   5325篇
  1996年   5199篇
  1995年   4866篇
  1994年   4396篇
  1993年   4206篇
  1992年   4589篇
  1991年   4495篇
  1990年   4349篇
  1989年   4076篇
  1988年   4073篇
  1987年   4053篇
  1986年   3794篇
  1985年   4965篇
  1984年   5226篇
  1983年   4372篇
  1982年   4720篇
  1981年   4537篇
  1980年   4414篇
  1979年   4525篇
  1978年   4703篇
  1977年   4593篇
  1976年   4711篇
  1975年   4423篇
  1974年   4272篇
  1973年   4596篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  相似文献   
2.
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined.  相似文献   
3.
The γcmc values of CTAB-SDS decrease from 63.67 mN/m at 10‡C to 36.38 mN/m at 90‡C, slightly lower than those of either CTAB or SDS. Correspondingly, the CMC of CTAB-SDS decreases almost by half. The increase of surface activity of CTAB-SDS can be attributed to the relatively weak electrostatic interaction at high temperature, which is supported by the increase of solubility of CTAB-SDS with rise in temperature. Catalytic effect on oxidation of toluene derivatives with potassium permanganate follows the order CTAB-SDS > SDS > CTAB. This is not caused by the dissociative effect of CTAB-SDS with low surface activity at low temperature, as seen from the fact that almost all oxidative products can be retrieved for different toluene derivatives and surfactants by mimicking the conditions of reaction. In the emulsifications of toluene derivatives at 90‡C, the time that turbid water layers of surfactant solutions take to become clear is the same as that of the catalytic effect on oxidation of toluene derivatives. Thus, it can be inferred that surfactants can improve the oxidation yields of toluene derivatives by increasing the contact between two reacting phases.  相似文献   
4.
Kinetic, sorption and selectivity properties of commercial adsorbents are improved by adding petroleum residues (tar asphaltene concentrates) 13% of whole mass. Obtained adsorbents can be used for selective extraction of nobel metals from multicomponent polymetallic solutions of heavy metals and fro sewages purification for removing arsenic.  相似文献   
5.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron...  相似文献   
6.
7.
We investigate theoretically the effects of optical absorption and saturation of the non-linear index of refraction on the bistability of non-linear distributed feedback structures (NLDFBs). By assuming that the Kerr non-linearity saturates in an exponential fashion, we obtain for the first time closed-form expressions for the so-called self-phase and cross-phase modulation terms. Our investigation shows that both absorption and, in particular, saturation significantly affect the bistable properties of this structure and in many cases eliminate this response completely. In some cases, however, saturation alters the NLDFB's transfer characteristics in a potentially useful manner. We find that weak levels of saturation may increase the contrast ratio between the intensities of the high and low bistable states. At increasing levels of saturation, where bistability is no longer observed, we find regimes where the NLDFB structure could possibly be used for optical amplification. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
8.
The interaction of isotactic polypropylene with ethylene propylene diene terpolymer in their blends has been investigated by use of differential scanning calorimetry, dynamic mechanical analysis, wide- and small-angle x-ray scattering, and by investigating the nucleation and kinetics of crystallization of the iPP component under the polarization microscope. It is found, that the dispersion of the EPDM component in the iPP matrix is dependent on blend composition and is maximal at 10% EPDM content. An interface layer between the two components is formed by migration of iPP molecules into the EPDM phase. A model for this interface is proposed.  相似文献   
9.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as hydroxyl (OH) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place. In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996  相似文献   
10.
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