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   267954篇
  免费   2057篇
  国内免费   625篇
化学   142136篇
晶体学   4164篇
力学   11931篇
综合类   9篇
数学   29512篇
物理学   82884篇
  2019年   2298篇
  2018年   3120篇
  2017年   3115篇
  2016年   4492篇
  2015年   2662篇
  2014年   4286篇
  2013年   10696篇
  2012年   8079篇
  2011年   9920篇
  2010年   7095篇
  2009年   6888篇
  2008年   9324篇
  2007年   9517篇
  2006年   8884篇
  2005年   8076篇
  2004年   7425篇
  2003年   6737篇
  2002年   6664篇
  2001年   7326篇
  2000年   5659篇
  1999年   4361篇
  1998年   3861篇
  1997年   3847篇
  1996年   3585篇
  1995年   3332篇
  1994年   3490篇
  1993年   3189篇
  1992年   3664篇
  1991年   3666篇
  1990年   3599篇
  1989年   3458篇
  1988年   3568篇
  1987年   3463篇
  1986年   3285篇
  1985年   4360篇
  1984年   4633篇
  1983年   3873篇
  1982年   4006篇
  1981年   3932篇
  1980年   3909篇
  1979年   3881篇
  1978年   4191篇
  1977年   4109篇
  1976年   4174篇
  1975年   3849篇
  1974年   3895篇
  1973年   4050篇
  1972年   2851篇
  1971年   2378篇
  1970年   2177篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
Translated from Vychislitel'nye Kompleksy i Modelirovanie Slozhnykh Sistem, pp. 98–106, Moscow State University, 1989.  相似文献   
153.
154.
155.
A cluster mechanism is considered for the detachment of particles when the surface of a high-temperature superconducting target absorbs laser pulses. By proposing a fractal nature for the surface, one can model it as an assembly of a large number of nonlinear oscillators (clusters). Utilizing the method of sudden perturbations, a calculation was made of the probability of dissociation of these oscillators, i.e., of the detachment of clusters from the surface. The calculated probability decreases rapidly as the power density of the laser radiation is reduced to some limiting value. This is in agreement with experiments. State Institute of Sensory Microelectronics. Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 73–77, June, 1997.  相似文献   
156.
We investigate some issues of minimax estimation of spectral intensity of acoustic sources in cases when the noise and the spectral amplitudes satisfy quadratic constraints. Recursive minimax filters are obtained.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 58, pp. 116–119, 1986.  相似文献   
157.
A theoretical temperature-electric field phase diagram is constructed for thiourea SC(ND2)2 using a phenomenological approach based on the representation of the thermodynamic potentials for all phases. The theoretical diagram is compared with the experimental diagram. Fiz. Tverd. Tela (St. Petersburg) 39, 1282–1286 (July 1997)  相似文献   
158.
The electronic and structural characteristics of CrF5, CrF4, RuF5 and RuF4 were studied. Ab initio (SCF-CI) calculations were performed with different structures and spin states for each complex. The favored conformation always corresponds to the highest multiplicity: doublet for CrF5 in D3h, triplet for CrF4 in Td, quadruplet for RuF5 in C4v and quintuplet for RuF4 in D4h symmetry.  相似文献   
159.
A two-dimensional self consistent model of the Beam-Plasma-Discharge (BPD) has been developed to calculate the discharge ignition of a bandlike electron beam in a discharge chamber. The discharge was considered in Argon with an initial concentration of 1014 cm?3. The model allows calculation of the time evolution of perpendicular profiles of electron density, temperature and the potential.  相似文献   
160.
Polymer packing density can be conveniently measured by either density-based measurements (direct or estimated free volume) or wide-angle X-ray diffraction (WAXD) spectra. Previously reported diffusivity and permeability values for various polyarylates and polyimides are examined on the basis of the packing density measured by these different techniques. It is shown that in these rigid glassy polymers, the mean intersegmental distance, the d-spacing, obtained from WAXD provides a better measure of the effect of polymer packing on diffusivity than either direct density measurements or estimated free volumes. It has been possible to correlate previously reported diffusivity and sorption data for various polyarylates and polycarbonate on the basis of the WAXD investigation, using the d-spacing and the amorphous peak width, respectively. The effect of polyarylate structure on d-spacing has been studied. A series of polyarylates have been synthesized with different substituents on the bridge carbon. In this series the d-spacing remains constant while the carbonyl group density and the glass transition temperatures are varied. However, small substituents on the aromatic ring cause significant changes in the d-spacing. These results can be used to tailor polyarylates with desired intersegmental distances and chain flexibility.  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