全文获取类型
收费全文 | 25480篇 |
免费 | 1002篇 |
国内免费 | 1370篇 |
专业分类
化学 | 7130篇 |
晶体学 | 83篇 |
力学 | 721篇 |
综合类 | 142篇 |
数学 | 2964篇 |
物理学 | 4482篇 |
综合类 | 12330篇 |
出版年
2024年 | 51篇 |
2023年 | 192篇 |
2022年 | 449篇 |
2021年 | 442篇 |
2020年 | 401篇 |
2019年 | 424篇 |
2018年 | 368篇 |
2017年 | 415篇 |
2016年 | 458篇 |
2015年 | 550篇 |
2014年 | 936篇 |
2013年 | 1269篇 |
2012年 | 1133篇 |
2011年 | 1319篇 |
2010年 | 1071篇 |
2009年 | 1444篇 |
2008年 | 1548篇 |
2007年 | 1789篇 |
2006年 | 1634篇 |
2005年 | 1325篇 |
2004年 | 1192篇 |
2003年 | 1107篇 |
2002年 | 1072篇 |
2001年 | 948篇 |
2000年 | 831篇 |
1999年 | 664篇 |
1998年 | 510篇 |
1997年 | 432篇 |
1996年 | 339篇 |
1995年 | 321篇 |
1994年 | 284篇 |
1993年 | 265篇 |
1992年 | 340篇 |
1991年 | 215篇 |
1990年 | 181篇 |
1989年 | 153篇 |
1988年 | 158篇 |
1987年 | 142篇 |
1986年 | 97篇 |
1985年 | 84篇 |
1984年 | 77篇 |
1983年 | 44篇 |
1982年 | 93篇 |
1981年 | 169篇 |
1980年 | 180篇 |
1979年 | 177篇 |
1978年 | 164篇 |
1977年 | 101篇 |
1976年 | 108篇 |
1973年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
指出了素质教育在高校实施的重要性,并结合高校素质教育的现状,指出了一些高等教育与素质教育要求相悖离的现象,就高校实施素质教育提出了几点设想。 相似文献
72.
Parking Capacity and Pricing in Park'n Ride Trips: A Continuous Equilibrium Network Design Problem 总被引:2,自引:0,他引:2
In this paper we consider the problem of designing parking facilities for park'n ride trips. We present a new continuous equilibrium network design problem to decide the capacity and fare of these parking lots at a tactical level. We assume that the parking facilities have already been located and other topological decisions have already been taken.The modeling approach proposed is mathematical programming with equilibrium constraints. In the outer optimization problem, a central Authority evaluates the performance of the transport network for each network design decision. In the inner problem a multimodal traffic assignment with combined modes, formulated as a variational inequality problem, generates the share demand for modes of transportation, and for parking facilities as a function of the design variables of the parking lots. The objective is to make optimal parking investment and pricing decisions in order to minimize the total travel cost in a subnetwork of the multimodal transportation system.We present a new development in model formulation based on the use of generalized parking link cost as a design variable.The bilevel model is solved by a simulated annealing algorithm applied to the continuous and non-negative design decision variables. Numerical tests are reported in order to illustrate the use of the model, and the ability of the approach to solve applications of moderate size. 相似文献
73.
R. S. Kaler 《Fiber and Integrated Optics》2006,25(1):41-57
In this article, the comparison of large signal theory and small signal theory has been done with dispersive propagation of optical signal with IMDD (Intensity Modulation Direct Detection) systems for semiconductor lasers with higher-order dispersion terms. The expressions for an exact large signal theory and small signal theory including higher-order dispersion terms for propagation of an optical wave with sinusoidal amplitude and frequency modulation in a dispersive fiber have been derived. It is observed that small signal theory is more sensitive compared to large signal theory in terms of intensity modulation/direct detection systems. Also, it is reported that for large signal analysis the higher-order effects of dispersion can be ignored, whereas for small signal theory, the higher-order effects can be ignored for lower modulation frequencies only. The variation in the transfer function for various values of modulation indices are greater for small signal analysis than for large signal analysis. Also, as the intensity modulation index is increased, there is a decrease in the value of transfer function. The large signal model approximates the small signal model for lower values of the intensity modulation index. 相似文献
74.
75.
In the present investigation, holographic interferometry was utilized for the first time to determine the rate change of the number of the fringe evolutions during the corrosion test of a carbon steel in blank seawater and seawater with different concentrations of a corrosion inhibitor. In other words, the anodic dissolution behaviors (corrosion) of the carbon steel were determined simultaneously by holographic interferometry, as an electromagnetic method, and by the electrochemical impedance (EI) spectroscopy, as an electronic method. So, the abrupt rate change of the number of the fringe evolutions during corrosion tests, EI spectroscopy, of the carbon steel is called electrochemical emission spectroscopy. The corrosion process of the steel samples was carried out in blank seawater and seawater with different concentrations, 5–20 ppm, of TROS C-70 corrosion inhibitor using the EI spectroscopy method, at room temperature. The electrochemical-emission spectra of the carbon steel in different solutions represent a detailed picture of the rate change of the anodic dissolution of the steel throughout the corrosion processes. Furthermore, the optical interferometry data of the carbon steel were compared to the data, which was obtained from the EI. spectroscopy. Consequently, holographic interferometry is found very useful for monitoring the anodic dissolution behaviors of metals, in which the number of the fringe evolutions of the steel samples can be determined in situ. 相似文献
76.
77.
The purpose of this paper is two-fold. First, we introduce a new asymptotic expansion in the exponent for the compound binomial
approximation of the generalized Poisson binomial distribution. The dependence of its accuracy on the symmetry and shifting
of distributions is investigated. Second, for compound binomial and compound Poisson distributions, we present new smoothness
estimates, some of which contain explicit constants. Finally, the ideas used in this paper enable us to prove new precise
bounds in the compound Poisson approximation.
Published in Lietuvos Matematikos Rinkinys, Vol. 46, No. 1, pp. 67–110, January–March, 2006. 相似文献
78.
Thomas Andreae 《Journal of Graph Theory》2002,39(4):222-229
For a graph A and a positive integer n, let nA denote the union of n disjoint copies of A; similarly, the union of ?0 disjoint copies of A is referred to as ?0A. It is shown that there exist (connected) graphs A and G such that nA is a minor of G for all n??, but ?0A is not a minor of G. This supplements previous examples showing that analogous statements are true if, instead of minors, isomorphic embeddings or topological minors are considered. The construction of A and G is based on the fact that there exist (infinite) graphs G1, G2,… such that Gi is not a minor of Gj for all i ≠ j. In contrast to previous examples concerning isomorphic embeddings and topological minors, the graphs A and G presented here are not locally finite. The following conjecture is suggested: for each locally finite connected graph A and each graph G, if nA is a minor of G for all n ? ?, then ?0A is a minor of G, too. If true, this would be a far‐reaching generalization of a classical result of R. Halin on families of disjoint one‐way infinite paths in graphs. © 2002 Wiley Periodicals, Inc. J Graph Theory 39: 222–229, 2002; DOI 10.1002/jgt.10016 相似文献
79.
介绍在IBM-PC/XT计算机上实现的曲棍球赛场统计系统的研制过程、设计思想、采用的方法、软件设计与功能、技术指标操作步骤以及使用效果。 相似文献
80.