全文获取类型
收费全文 | 12672篇 |
免费 | 1581篇 |
国内免费 | 1025篇 |
专业分类
化学 | 3526篇 |
晶体学 | 63篇 |
力学 | 4317篇 |
综合类 | 308篇 |
数学 | 2975篇 |
物理学 | 4089篇 |
出版年
2024年 | 38篇 |
2023年 | 128篇 |
2022年 | 377篇 |
2021年 | 367篇 |
2020年 | 437篇 |
2019年 | 358篇 |
2018年 | 354篇 |
2017年 | 449篇 |
2016年 | 555篇 |
2015年 | 444篇 |
2014年 | 553篇 |
2013年 | 933篇 |
2012年 | 721篇 |
2011年 | 722篇 |
2010年 | 600篇 |
2009年 | 672篇 |
2008年 | 697篇 |
2007年 | 646篇 |
2006年 | 717篇 |
2005年 | 583篇 |
2004年 | 575篇 |
2003年 | 524篇 |
2002年 | 441篇 |
2001年 | 426篇 |
2000年 | 395篇 |
1999年 | 353篇 |
1998年 | 289篇 |
1997年 | 265篇 |
1996年 | 248篇 |
1995年 | 220篇 |
1994年 | 167篇 |
1993年 | 154篇 |
1992年 | 141篇 |
1991年 | 116篇 |
1990年 | 111篇 |
1989年 | 82篇 |
1988年 | 74篇 |
1987年 | 60篇 |
1986年 | 45篇 |
1985年 | 44篇 |
1984年 | 37篇 |
1983年 | 17篇 |
1982年 | 35篇 |
1981年 | 29篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1975年 | 6篇 |
1957年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Xiao‐Dong Pan 《Journal of Polymer Science.Polymer Physics》2004,42(13):2467-2478
For properly chosen elastomer compounds, thermorheological characterization is combined with an examination of the variation of the wet sliding friction with temperature. A conceptual argument leads to the assumption that the wet sliding friction should maximize at the energy dissipation peak associated with the dynamic softening transition at a characteristic frequency determined by the sliding speed and the effective smallest surface asperity scale. The dynamic softening transition is characterized with the peak in tan δ/G′n, where tan δ is the loss tangent, G′ is the elastic modulus, and n is a constant between 0 and 1. The William–Landel–Ferry transform is uncritically applied for extrapolating the position of the peak in tan δ/G′n at high frequencies. Even based on the criterion of tan δ, the results obtained on a concrete surface indicate that the effective smallest asperity scale is of order of 100 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2467–2478, 2004 相似文献
12.
13.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls. 相似文献
14.
Mari Grobbelaar‐Van Dalsen 《Mathematical Methods in the Applied Sciences》2004,27(11):1301-1315
This paper is concerned with well‐posedness results for a mathematical model for the transversal vibrations of a two‐dimensional hybrid elastic structure consisting of a rectangular Reissner–Mindlin plate with a Timoshenko beam attached to its free edge. The model incorporates linear dynamic feedback controls along the interface between the plate and the beam. Classical semigroup methods are employed to show the unique solvability of the coupled initial‐boundary‐value problem. We also show that the energy associated with the system exhibits the property of strong stability. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
15.
探讨了设计负动量压缩因子(αp<0)的正负电子对撞机储存环磁聚焦结构的可行性及方法.作为应用实例,说明了设计αp<0的τ–粲工厂磁聚焦结构的可能性. 相似文献
16.
We develop a production policy that controls work-in-process (WIP) levels and satisfies demand in a multistage manufacturing system with significant uncertainty in yield, rework, and demand. The problem addressed in this paper is more general than those in the literature in three aspects: (i) multiple products are processed at multiple workstations, and the capacity of each workstation is limited and shared by multiple operations; (ii) the behavior of a production policy is investigated over an infinite-time horizon, and thus the system stability can be evaluated; (iii) the representation of yield and rework uncertainty is generalized. Generalizing both the system structure and the nature of uncertainty requires a new mathematical development in the theory of infinite-horizon stochastic dynamic programming. The theoretical contributions of this paper are the existence proofs of the optimal stationary control for a stochastic dynamic programming problem and the finite covariances of WIP and production levels under the general expression of uncertainty. We develop a simple and explicit sufficient condition that guarantees the existence of both the optimal stationary control and the system stability. We describe how a production policy can be constructed for the manufacturing system based on the propositions derived. 相似文献
17.
Y. Yavin 《Journal of Optimization Theory and Applications》1993,78(1):77-91
Stochastic optimal control techniques are applied to compare the performance of identical medium-range air-to-air missiles which have different thrust-mass profiles. The measure of the performance is the probability of reaching a lock-on-point with a favorable range of guidance and flight parameters, during a fixed time interval [0,t
f
], given that, during the flight, the trajectories of the missile are subjected to a variety of constraints including dynamic pressure constraints. 相似文献
18.
臧忠卿 《数学的实践与认识》2006,36(10):132-136
运用中学生男性性别角色期望调查表和因子分析方法对贵阳市中学生进行男性性别角色期望调查和定性与定量分析,为中学生树立适宜的性别角色观,促进其心理健康发展提供量化依据.分析显示:传统的男性角色并不被现代中学生完全接受,无论是男中学生还是女中学生都在力图探求一种新的男性性别角色模式,且两性中学生对这一新的男性性别角色模式的期望和把握是有一定差异的. 相似文献
19.
In this paper, we first reduce the problem of finding a minimum parity (g,f)-factor of a graph G into the problem of finding a minimum perfect matching in a weighted simple graph G*. Using the structure of G*, a necessary and sufficient condition for the existence of an even factor is derived.
This paper was accomplished while the second author was visiting the Center for Combinatorics, Nankai University.
The research is supported by NSFC 相似文献
20.
C. Vaca‐Garcia G. Gozzelino W. G. Glasser M. E. Borredon 《Journal of Polymer Science.Polymer Physics》2003,41(3):281-288
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