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   261140篇
  免费   2562篇
  国内免费   812篇
化学   141910篇
晶体学   3878篇
力学   11099篇
综合类   12篇
数学   26700篇
物理学   80915篇
  2018年   2033篇
  2017年   1946篇
  2016年   3597篇
  2015年   2420篇
  2014年   3583篇
  2013年   10612篇
  2012年   7846篇
  2011年   10039篇
  2010年   6669篇
  2009年   6483篇
  2008年   9092篇
  2007年   9199篇
  2006年   8894篇
  2005年   8398篇
  2004年   7402篇
  2003年   6618篇
  2002年   6553篇
  2001年   7327篇
  2000年   5614篇
  1999年   4508篇
  1998年   3927篇
  1997年   3822篇
  1996年   3585篇
  1995年   3461篇
  1994年   3257篇
  1993年   3086篇
  1992年   3552篇
  1991年   3608篇
  1990年   3363篇
  1989年   3368篇
  1988年   3318篇
  1987年   3226篇
  1986年   3075篇
  1985年   4095篇
  1984年   4304篇
  1983年   3557篇
  1982年   4005篇
  1981年   3728篇
  1980年   3730篇
  1979年   3840篇
  1978年   4095篇
  1977年   3914篇
  1976年   3979篇
  1975年   3812篇
  1974年   3738篇
  1973年   3944篇
  1972年   2489篇
  1971年   2065篇
  1968年   2030篇
  1967年   2087篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The purpose of this note is to describe a procedure for transferring familiar estimates for transition probabilities on RN to transition probabilities on compact manifolds.  相似文献   
52.
The behavior of real disperse systems with organic impurities was examined under conditions of destabilization by inorganic coagulants. A number of physicochemical methods of analysis and a simulation method were used to identify the character and type of the complexes formed and to calculate their stability constants.  相似文献   
53.
The electro-optic response of ferroelectric smectic C* liquid crystals has been studied. Anomalous switching behaviour of such materials which possess a negative dielectric anisotropy has been reported. These materials show a minimum in response time at a sufficiently high field. We present results showing the dependency of this minimum upon spontaneous polarisation and the effect of AC bias. Calculations based upon the equation of motion of the director around the cone are presented which describe this effect and its dependence on the relative magnitudes of the spontaneous polarization and dielectric anisotropy of the material. Good agreement with the experimental results is found.  相似文献   
54.
55.
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003  相似文献   
56.
The results of optical study and quantum-chemical simulation of a conjugated organic system, 2-cyclooctylamino-5-nitropyridine (COANP)-fullerene, performed to determine its potential for application as a limiter of visible and near-IR laser radiation and as a material for diffraction elements in systems for reversible recording of optical information, are presented. Complexation between a COANP molecule and fullerene is considered as one of the main mechanisms responsible for the corresponding properties of this system. For the first time, nonlinear optical characteristics of COANP-C60 and COANP-C70 systems are comparatively studied and the intermolecular interaction between a COANP molecule and fullerene is analyzed on the quantum-chemical level.  相似文献   
57.
We construct an integral Newton-type interpolation polynomial with a continual set of nodes. This interpolant is unique and preserves an operator polynomial of the corresponding degree.  相似文献   
58.
59.
We studied the low speed fracture regime (10−4-10−9 m s−1) in different glassy materials (soda-lime glass, glass ceramics) with variable but controlled length scale of heterogeneity. The chosen mechanical system enabled us to work in pure mode I (tensile) and at a fixed load on double cleavage drilled compression specimen. The internal residual stresses of studied samples were carefully relaxed by appropriate thermal treatment. By means of optical and atomic force microscopy techniques fracture surfaces have been examined. We have shown for the first time that the crack front line underwent an out-of-plane oscillating behavior as a result of a reproducible sequence of instabilities. The wavelength of such a phenomenon is in the micrometer range and its amplitude in the nanometer range. These features were observed for different glassy materials providing that a typical length scale characterizing internal heterogeneities was lower than a threshold limit estimated to few nanometers. This effect is the first clear experimental evidence of crack path instabilities in the low speed regime in a uniaxial loading experiment. This phenomenon has been interpreted by referring to the stability criterion for a straight crack propagation as presented by Adda-Bedia et al. [Phys. Rev. Lett. 76 (1996) 1497].  相似文献   
60.
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