全文获取类型
收费全文 | 37978篇 |
免费 | 4379篇 |
国内免费 | 4099篇 |
专业分类
化学 | 12955篇 |
晶体学 | 85篇 |
力学 | 2921篇 |
综合类 | 347篇 |
数学 | 22120篇 |
物理学 | 8028篇 |
出版年
2024年 | 111篇 |
2023年 | 462篇 |
2022年 | 718篇 |
2021年 | 864篇 |
2020年 | 1265篇 |
2019年 | 1290篇 |
2018年 | 1110篇 |
2017年 | 1179篇 |
2016年 | 1553篇 |
2015年 | 1413篇 |
2014年 | 2026篇 |
2013年 | 3748篇 |
2012年 | 2054篇 |
2011年 | 2395篇 |
2010年 | 2048篇 |
2009年 | 2594篇 |
2008年 | 2552篇 |
2007年 | 2621篇 |
2006年 | 2330篇 |
2005年 | 1845篇 |
2004年 | 1591篇 |
2003年 | 1551篇 |
2002年 | 1315篇 |
2001年 | 1075篇 |
2000年 | 1063篇 |
1999年 | 929篇 |
1998年 | 786篇 |
1997年 | 721篇 |
1996年 | 503篇 |
1995年 | 348篇 |
1994年 | 322篇 |
1993年 | 228篇 |
1992年 | 223篇 |
1991年 | 161篇 |
1990年 | 146篇 |
1989年 | 112篇 |
1988年 | 103篇 |
1987年 | 81篇 |
1986年 | 73篇 |
1985年 | 120篇 |
1984年 | 137篇 |
1983年 | 71篇 |
1982年 | 108篇 |
1981年 | 97篇 |
1980年 | 92篇 |
1979年 | 78篇 |
1978年 | 72篇 |
1977年 | 49篇 |
1976年 | 50篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Alexandros A. Skordos Ivana K. Partridge 《Journal of Polymer Science.Polymer Physics》2004,42(1):146-154
This article presents a new methodology for the quantitative determination of the progress of the curing reaction of a thermosetting resin, using the results of electrical impedance spectroscopy. The method is an extension of the use of the imaginary impedance maximum as a reaction progress indicator and is based on the demonstration of a close correlation between the reaction rate, as measured by conventional differential scanning calorimetry, and the rate of change of the value of the imaginary impedance spectrum maximum. Tests on a commercial aerospace epoxy resin under both isothermal and dynamic heating conditions with calorimetry and impedance spectroscopy have demonstrated the validity of the method and set the accuracy limits involved. This technique can be used as a real-time online control tool for thermoset composite manufacturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 146–154, 2004 相似文献
42.
Differential game formulations provide an adequate basis for a guidance law synthesis against highly maneuvering targets. This paper deals with a guidance law based on a linear-quadratic differential game formulation. This guidance law has many attractive properties: it is continuous, linear with respect to the state variables, and its gain coefficients can be precalculated offline. Nevertheless, due to the lack of hard control constraints in the formulation, the magnitude of the control can exceed the admissible level imposed by the nature of the problem. In this paper, the upper bound of the interceptor control is obtained depending on the system parameters and the penalty coefficients of the game performance index. It is shown that the interceptor can guarantee an arbitrarily small miss distance without exceeding the control constraints if it has sufficient maneuverability and if the penalty coefficients are chosen properly. By manipulating the penalty coefficients, it is possible to reduce significantly the maneuverability requirements compared to the case of zero interceptor penalty coefficient. 相似文献
43.
Defining speed of diffusion as the amount of time it takes to get from one penetration level to a higher one, we introduce a dynamic model in which we study the link between pricing policy, speed of diffusion, and number of competitors in the market. Our analysis shows that, in the case of strategic (oligopolistic) competition, the speed of diffusion has an important influence on the optimal pricing policy. In particular, we find that higher speeds of diffusion create an incentive to strategically interacting firms to lower their prices. 相似文献
44.
Quan Sen JIU Department of Mathematics Capital Normal University Beijing P.R.China Cheng HE Institute of Applied Mathematics Academy of Mathematics System Sciences Chinese Academy of Sciences Beijing P.R.China 《应用数学学报(英文版)》2004,(4)
In this paper we are interested in the sufficient conditions which guarantee the regularityof solutions of 3-D ideal magnetohydrodynamic equations in the arbitrary time interval [0,T].Fivesufficient conditions are given.Our results are motivated by two main ideas:one is to control theaccumulation of vorticity alone;the other is to generalize the corresponding geometric conditions of3-D Euler equations to 3-D ideal magnetohydrodynamic equations. 相似文献
45.
Continuous dependence on a modelling parameter is established for solutions of a problem for a complex Ginzburg–Landau equation. A homogenizing boundary condition is also used to discuss the continuous dependence results. We derive a priori estimates that indicate that solutions depend continuously on a parameter in the governing differential equation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
46.
通过对非饱和土非线性本构方程和场方程的线性化,推导出了非饱和土的线性本构方程和场方程,把线性方程表示为与Biot饱和多孔介质方程相似的形式;证明了Darcy定律对非饱和土的适用性;说明了Biot饱和多孔介质方程是这些线性方程的特征。所有这些都表明用混合理论处理非饱和土本构问题的正确性。 相似文献
47.
48.
Modular and quasimodular solutions of a specific second order differential equation in the upper-half plane, which originates from a study of supersingular j-invariants in the first author's work with Don Zagier, are given explicitly. Positivity of Fourier coefficients of some of the solutions as well as a characterization of the differential equation are also discussed. 相似文献
49.
Zhu Yongliang; Pagilla Prabhakar R. 《IMA Journal of Mathematical Control and Information》2005,22(2):181-186
We derive some useful and easily computable necessary conditionsfor the existence of a positive semi-definite solution to thealgebraic Ricatti equation (ARE). A motivating example is givento highlight the usefulness of the conditions for controllerand observer designs for nonlinear systems. Further, an upperbound on the trace of the solution to the ARE is also derived. 相似文献
50.