全文获取类型
收费全文 | 15101篇 |
免费 | 1738篇 |
国内免费 | 1188篇 |
专业分类
化学 | 2270篇 |
晶体学 | 27篇 |
力学 | 1462篇 |
综合类 | 353篇 |
数学 | 10258篇 |
物理学 | 3657篇 |
出版年
2024年 | 26篇 |
2023年 | 143篇 |
2022年 | 169篇 |
2021年 | 291篇 |
2020年 | 397篇 |
2019年 | 391篇 |
2018年 | 400篇 |
2017年 | 470篇 |
2016年 | 598篇 |
2015年 | 372篇 |
2014年 | 688篇 |
2013年 | 1275篇 |
2012年 | 681篇 |
2011年 | 905篇 |
2010年 | 823篇 |
2009年 | 905篇 |
2008年 | 970篇 |
2007年 | 986篇 |
2006年 | 905篇 |
2005年 | 827篇 |
2004年 | 725篇 |
2003年 | 673篇 |
2002年 | 636篇 |
2001年 | 500篇 |
2000年 | 501篇 |
1999年 | 403篇 |
1998年 | 363篇 |
1997年 | 310篇 |
1996年 | 258篇 |
1995年 | 247篇 |
1994年 | 163篇 |
1993年 | 160篇 |
1992年 | 138篇 |
1991年 | 114篇 |
1990年 | 85篇 |
1989年 | 70篇 |
1988年 | 54篇 |
1987年 | 41篇 |
1986年 | 50篇 |
1985年 | 42篇 |
1984年 | 43篇 |
1983年 | 21篇 |
1982年 | 30篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 27篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1974年 | 11篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 450 毫秒
51.
52.
Based on the beam coherence-polarization (BCP) matrix, the polarization property of coherent and incoherent Gaussian beam combinations is studied in detail. The general expressions for the degree of polarization P of the resulting beam in case of incoherent and coherent combinations are derived. It is shown that P is dependent on the incoherent or coherent combination, propagation distance, separation, azimuth of the polarization plane and numbers of beamlets in general. The irradiance distribution of the resulting beam for the coherent cases depends on the azimuth of the polarization plane of beamlets. However, for the incoherent case it does not. 相似文献
53.
We study initial boundary value problems for linear scalar evolutionpartial differential equations, with spatial derivatives ofarbitrary order, posed on the domain {t > 0, 0 < x <L}. We show that the solution can be expressed as an integralin the complex k-plane. This integral is defined in terms ofan x-transform of the initial condition and a t-transform ofthe boundary conditions. The derivation of this integral representationrelies on the analysis of the global relation, which is an algebraicrelation defined in the complex k-plane coupling all boundaryvalues of the solution. For particular cases, such as the case of periodic boundaryconditions, or the case of boundary value problems for even-orderPDEs, it is possible to obtain directly from the global relationan alternative representation for the solution, in the formof an infinite series. We stress, however, that there existinitial boundary value problems for which the only representationis an integral which cannot be written as an infinite series.An example of such a problem is provided by the linearized versionof the KdV equation. Similarly, in general the solution of odd-orderlinear initial boundary value problems on a finite intervalcannot be expressed in terms of an infinite series. 相似文献
54.
55.
A solution to the phase problem in optics is considered within the context of the analysis of signals changing in time and of the effect of an object under investigation on the probing radiation. The solution is based on the use of a twin-wave interferometer with phase modulation in one of the channels and a spectrometer. The analysis is concerned, in particular, with signals and processes of ultrashort duration. To shift the frequency in the interferometer channel, an electrooptical crystal of ferroelectric perovskite is used as the modulator. Errors of amplitude and phase structures determined are analyzed. 相似文献
56.
57.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions. 相似文献
58.
Marko Nedeljkov 《Mathematical Methods in the Applied Sciences》2004,27(8):931-955
This work gives a condition for existence of singular and delta shock wave solutions to Riemann problem for 2×2 systems of conservation laws. For a fixed left‐hand side value of Riemann data, the condition obtained in the paper describes a set of possible right‐hand side values. The procedure is similar to the standard one of finding the Hugoniot locus. Fluxes of the considered systems are globally Lipschitz with respect to one of the dependent variables. The association in a Colombeau‐type algebra is used as a solution concept. Copyright © 2004 John Wiley &Sons, Ltd. 相似文献
59.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
60.
本文给出了 n阶 r-不可分矩阵的本原指数的上界 ,即任 n阶 r—不可分矩阵 A的本原指数 (A)≤n+(r- ) 2r (1≤ r相似文献