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   11519篇
  免费   1402篇
  国内免费   1272篇
化学   3851篇
晶体学   118篇
力学   1256篇
综合类   166篇
数学   2936篇
物理学   5866篇
  2024年   23篇
  2023年   113篇
  2022年   229篇
  2021年   245篇
  2020年   231篇
  2019年   283篇
  2018年   249篇
  2017年   375篇
  2016年   436篇
  2015年   376篇
  2014年   598篇
  2013年   868篇
  2012年   608篇
  2011年   745篇
  2010年   634篇
  2009年   724篇
  2008年   744篇
  2007年   770篇
  2006年   626篇
  2005年   634篇
  2004年   559篇
  2003年   481篇
  2002年   469篇
  2001年   345篇
  2000年   337篇
  1999年   292篇
  1998年   268篇
  1997年   240篇
  1996年   185篇
  1995年   161篇
  1994年   160篇
  1993年   136篇
  1992年   106篇
  1991年   99篇
  1990年   84篇
  1989年   79篇
  1988年   61篇
  1987年   49篇
  1986年   46篇
  1985年   70篇
  1984年   48篇
  1983年   22篇
  1982年   68篇
  1981年   66篇
  1980年   53篇
  1979年   33篇
  1978年   30篇
  1977年   29篇
  1976年   41篇
  1973年   18篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
Based on the non-Markovian quantum Langevin equations, we obtain time-dependent transport coefficients for an inverted oscillator coupled linearly in the coordinate to a thermostat. We comparatively analyze the diffusion coefficients for harmonic and inverted oscillators and study the role of quantum statistical effects in the passage through a parabolic barrier. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 156, No. 3, pp. 425–443, September, 2008.  相似文献   
872.
The influence of poly(ethylene glycol) on the partition of a charged long chain spin probe between membranes and an external phase is studied. The partition coefficient is derived from the ESR spectra. Membranes of different properties are used (egg lecithin liposomes, erythrocytes) to differentiate between the influence of the external phase and the specific properties of the membrane.The partition coefficient is decreased in an exponential manner on increasing the PEG concentration, which indicates a lowering of the thermodynamic stability of the membranes. The determination of the change in the difference of the chemical potential is dependent on the PEG concentration.The membrane destabilization induced by PEG is caused in an indirect manner by a change of the chemical potential difference as result of the changed water structure and the osmotic pressure, surface tension and hydration of the membrane. This destabilization could be connected with the high fusogenic activity of PEG.  相似文献   
873.
通过引入带参数的指数积分并利用Bernoulli不等式以及改进了的Hlder不等式,对Hardy-Hilbert积分不等式作了有意义改进.特别,当p=2时,得到了经典的Hilbert积分不等式的一个很强的结果.  相似文献   
874.
偶氮类化合物热相变动态过程的二维相关拉曼光谱研究   总被引:1,自引:0,他引:1  
利用变温傅里叶变换拉曼光谱(FT-Raman)研究含偶氮苯基长链脂肪酸化合物8A5H固体的热相变。二维相关光谱分析技术被应用到以温度为变量的同步和异步相关计算,目的在于研究该化合物中不同基团在热相变过程中取向变化过程以及变化趋势、步骤等一系列的动态结构变化。展示了研究偶氮类化合物热致相变过程中结构动态新的研究方法,同时也为二维相关光谱的应用拓宽了新的研究领域。  相似文献   
875.
We consider in a new statement the inverse problem of the theory of vibrational spectra of molecules, in which a theoretical spectral curve directly gets closer to the experimental one. A coefficient of correlation between the curves is used as a criterion of the closeness of the curves and as a functional of the inverse problem. The procedure developed for solving the inverse problem makes it possible to dispense with the preliminary referencing of frequencies in an experimental spectrum and with its expansion into elementary absorption bands.  相似文献   
876.
The quantum-statistical generalization of the well-known classical, linear revised Enskog equation is derived for spatially uniform systems. This new quantum kinetic equation allows the study of equilibrium time correlation functions and their associated transport coefficients of normal quantum fluids where static correlations and degeneracy effects due to particle statistics (both are treated exactly) are important. Furthermore, we derive the quantum-statistical analog of the classical ring operator. These microscopic and systematic derivations are based on a recently developed superoperator formalism (including cluster expansion techniques) that, as a main feature, allows a clear distinction between static and dynamic correlations, which is crucial in the discussion of the Enskog approximation.  相似文献   
877.
878.
We report the effects of guest particles on the swelling properties of bulk polyacrylamide gels. The guest particles were the spheres of poly(N‐isopropylacrylamide) gel with submicrometer diameter, which were synthesized by an emulsion‐polymerized reaction in water. Polyacrylamide gels were prepared by a free radical polymerization reaction, immobilizing the gel microparticles with different concentrations at gelation. The macroscopic swelling ratio of this hybrid gel in a cylindrical shape was measured as functions of temperature and acetone concentration. The presence of guest particles was found to strongly affect the swelling behavior in the bulk gels when the concentration of incorporated particles exceeded a threshold. The experimental results indicated that the macroscopic volume in response to the temperature change should be determined by the guest particles above the threshold. On the other hand, the hybrid gel could not evidently shrink by adding acetone when the concentration of guest particles exceeded the threshold. To make clear the distribution of guest particles in the bulk networks, the fractured surfaces of dried gels were imaged by tapping mode atomic force microscopy. The guest particles were found to aggregate in the bulk homogeneous networks to form microdomains with densely connected structure, which became larger with increasing particle concentration. The roles of bulk networks as well as guest particles on the swelling behavior of hybrid gels were qualitatively discussed on the basis of the incorporated structure of guest particles, depending on the concentration of guest particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1696–1704, 2005  相似文献   
879.
880.
We designed and fabricated a fully automatic fast face recognition optical parallel correlator [E. Watanabe and K. Kodate: Appl. Opt. 44 (2005) 5666] based on the VanderLugt principle. The implementation of an as-yet unattained ultra high-speed system was aided by reconfiguring the system to make it suitable for easier parallel processing, as well as by composing a higher accuracy correlation filter and high-speed ferroelectric liquid crystal-spatial light modulator (FLC-SLM). In running trial experiments using this system (dubbed FARCO), we succeeded in acquiring remarkably low error rates of 1.3% for false match rate (FMR) and 2.6% for false non-match rate (FNMR). Given the results of our experiments, the aim of this paper is to examine methods of designing correlation filters and arranging database image arrays for even faster parallel correlation, underlining the issues of calculation technique, quantization bit rate, pixel size and shift from optical axis. The correlation filter has proved its excellent performance and higher precision than classical correlation and joint transform correlator (JTC). Moreover, arrangement of multi-object reference images leads to 10-channel correlation signals, as sharply marked as those of a single channel. This experiment result demonstrates great potential for achieving the process speed of 10000 face/s.  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