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   342514篇
  免费   2092篇
  国内免费   812篇
化学   131241篇
晶体学   3895篇
力学   18512篇
综合类   7篇
数学   65658篇
物理学   92294篇
无线电   33811篇
  2019年   1255篇
  2018年   20363篇
  2017年   20818篇
  2016年   12356篇
  2015年   3245篇
  2014年   3065篇
  2013年   7084篇
  2012年   12733篇
  2011年   28141篇
  2010年   17595篇
  2009年   17832篇
  2008年   22816篇
  2007年   28447篇
  2006年   6683篇
  2005年   14437篇
  2004年   10472篇
  2003年   10139篇
  2002年   7058篇
  2001年   5516篇
  2000年   4634篇
  1999年   3460篇
  1998年   3160篇
  1997年   3040篇
  1996年   2889篇
  1995年   2682篇
  1994年   2598篇
  1993年   2395篇
  1992年   2600篇
  1991年   2721篇
  1990年   2480篇
  1989年   2476篇
  1988年   2400篇
  1987年   2074篇
  1986年   2022篇
  1985年   2511篇
  1984年   2624篇
  1983年   2213篇
  1982年   2355篇
  1981年   2239篇
  1980年   2173篇
  1979年   2283篇
  1978年   2447篇
  1977年   2230篇
  1976年   2304篇
  1975年   2180篇
  1974年   2210篇
  1973年   2262篇
  1972年   1487篇
  1971年   1320篇
  1968年   1257篇
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
931.
In this paper, we apply a three-stage-DEA model to the Spanish Professional Football League, which means separating the teams’ economic behaviour into three components: operating efficiency—of the offence and defence—athletic or operating effectiveness, and social effectiveness. The results showed that the technical inefficiency of the defence is greater than that of the offence, both being caused by aspects linked to the poor management of players’ abilities and by the football team’s size. Teams showed a favourable evolution of their offensive and defensive efficiency during the 2004/2005 season and to a lesser extent in the season before. The point system assigned by the professional football league regulations evaluates the teams’ athletic effectiveness, but we detected that the teams with the most experience perform athletically in a more effective manner. Their social effectiveness is strongly related to the level of play in itself and to factors linked to their PFL ranking: participation in international competitions for important football teams; or the struggle of minor football teams to stay in the first division.  相似文献   
932.
This paper discusses an analytical method to study the effects of the vane-parameters on the gain-frequency response of an azimuthally periodic vane-loaded cylindrical waveguide interaction structure for the gyro-traveling wave tube (gyro-TWT) amplifier in the small-orbit TE01 waveguide mode configuration. The vane-loaded gyro-TWT enables the higher gain than that of the smooth-wall device. An optimum choice of the vane dimensions causes a change in the frequency corresponding to the peak-gain.  相似文献   
933.
934.
935.
Arguello  F. 《Electronics letters》2006,42(5):270-271
An algorithm for computing multiplicative inverses in Galois fields GF(2/sup m/) is presented. It is based on Lehmer's algorithm for computing the greatest common divisor of two integers. The algorithm is designed to be advantageous for Galois fields of large size.  相似文献   
936.
It has been found that by the addition of low concentrations of an amphiphilic block copolymer to an epoxy resin, novel disordered morphologies can be formed and preserved through curing. This article will focus on characterizing the influence of the block copolymer and casting solvent on the templated morphology achieved in the thermoset sample. The ultimate goal of this work is to determine the parameters that would control the microphase morphology produced. Epoxy resins blended with a series of amphiphilic block copolymers based on hydrogenated polyisoprene (polyethylene-alt-propylene or PEP) and polyethylene oxide (PEO), specifically, were investigated. In this article, the cure-induced order–order phase transition from the spherical to wormlike micelle morphology will also be discussed. It is proposed that the formation of the wormlike micelle structure from the spherical micelle structure is similar to the phase transition behavior that occurs in dilute block copolymer solutions as a function of the influence of the solvent on micelle morphology. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3338–3348, 2007  相似文献   
937.
The interactive two-state model of cell membrane ion channels in an electric field is formulated on the Bethe lattice by means of the exact recursion relations. The probability of channel opening or maximum fractions of open potassium and sodium channels are obtained by solving a non-linear algebraic equation. Using known parameters for the conventional mean-field theory the model gives a good agreement with the experiment both at low and high trans-membrane potential values. For intermediate voltages, the numerical results imply that collective effects are introduced by trans-membrane voltage.  相似文献   
938.
We propose a model-based automated approach to extracting microtubules from noisy electron tomography volume. Our approach consists of volume enhancement, microtubule localization, and boundary segmentation to exploit the unique geometric and photometric properties of microtubules. The enhancement starts with an anisotropic invariant wavelet transform to enhance the microtubules globally, followed by a three-dimensional (3-D) tube-enhancing filter based on Weingarten matrix to further accentuate the tubular structures locally. The enhancement ends with a modified coherence-enhancing diffusion to complete the interruptions along the microtubules. The microtubules are then localized with a centerline extraction algorithm adapted for tubular objects. To perform segmentation, we novelly modify and extend active shape model method. We first use 3-D local surface enhancement to characterize the microtubule boundary and improve shape searching by relating the boundary strength with the weight matrix of the searching error. We then integrate the active shape model with Kalman filtering to utilize the longitudinal smoothness along the microtubules. The segmentation improved in this way is robust against missing boundaries and outliers that are often present in the tomography volume. Experimental results demonstrate that our automated method produces results close to those by manual process and uses only a fraction of the time of the latter.  相似文献   
939.
In a recent paper Conway and Kochen, Found. Phys. 36, 2006, claim to have established that theories of the Ghirardi-Rimini-Weber (RW) type, i.e., of spontaneous wave function collapse, cannot be made relativistic. On the other hand, relativistic GRW-type theories have already been presented, in my recent paper, J. Stat. Phys. 125, 2006, and by Dowker and Henson, J. Stat. Phys. 115, 2004. Here, I elucidate why these are not excluded by the arguments of Conway and Kochen.   相似文献   
940.
We introduce a random perturbed version of the classical fidelity and we show that it converges with the same rate of decay of correlations, but not uniformly in the noise. This makes the classical fidelity unstable in the zero-noise limit.  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