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   305135篇
  免费   1570篇
  国内免费   651篇
化学   146453篇
晶体学   4470篇
力学   15080篇
综合类   6篇
数学   46502篇
物理学   94845篇
  2020年   1972篇
  2019年   2266篇
  2018年   10955篇
  2017年   11676篇
  2016年   8000篇
  2015年   3115篇
  2014年   3936篇
  2013年   9372篇
  2012年   10883篇
  2011年   19889篇
  2010年   12523篇
  2009年   12565篇
  2008年   17835篇
  2007年   21224篇
  2006年   7830篇
  2005年   12983篇
  2004年   9279篇
  2003年   8894篇
  2002年   6854篇
  2001年   6104篇
  2000年   4999篇
  1999年   3518篇
  1998年   3061篇
  1997年   3054篇
  1996年   2995篇
  1995年   2429篇
  1994年   2504篇
  1993年   2530篇
  1992年   2667篇
  1991年   2731篇
  1990年   2635篇
  1989年   2618篇
  1988年   2557篇
  1987年   2524篇
  1986年   2437篇
  1985年   3123篇
  1984年   3301篇
  1983年   2652篇
  1982年   2917篇
  1981年   2799篇
  1980年   2596篇
  1979年   2825篇
  1978年   2954篇
  1977年   2891篇
  1976年   2899篇
  1975年   2739篇
  1974年   2715篇
  1973年   2900篇
  1972年   1912篇
  1967年   1868篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The preparation of new ring opening metathesis polymerization (ROMP) monomers using a 1,3‐dipolar cycloaddition between aryl azides and norbornadiene is described. Various norbornenetriazolines, obtained through a solvent‐and catalyst‐free reaction, can subsequently be incorporated into polymer backbones through ROMP reactions. Furthermore, thermal decomposition of the triazoline moiety can allow for further polymer functionalization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2357–2362  相似文献   
42.
43.
Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and...  相似文献   
44.
45.
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   
46.
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   
47.
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   
48.
The lidar equation for the vibrational backscattering of neodymium laser radiation and its harmonics by hydrogen molecules is solved numerically. Inclined paths in the atmosphere are investigated with the aim of selecting the transmitter wavelength for detecting the lowest concentrations of hydrogen. Zh. Tekh. Fiz. 68, 20–22 (January 1998)  相似文献   
49.
Terrestrial basalt rocks considered to be a good analogues of the Martian regolith were studied by using the Mössbauer spectroscopy and X-ray diffraction. The weathering of basalts was followed by the changes of the Fe2+/Fe3+ ratio. The basalt rock undergoes alteration from primary mineral composition (olivine+pyroxene+plagioclase) through smectite to kaolinite clay with oxides and hydroxides with the increase of the Fe2+/Fe3+ ratio.  相似文献   
50.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields.  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