全文获取类型
收费全文 | 6601篇 |
免费 | 808篇 |
国内免费 | 730篇 |
专业分类
化学 | 745篇 |
晶体学 | 19篇 |
力学 | 562篇 |
综合类 | 189篇 |
数学 | 5437篇 |
物理学 | 1187篇 |
出版年
2024年 | 12篇 |
2023年 | 39篇 |
2022年 | 75篇 |
2021年 | 112篇 |
2020年 | 160篇 |
2019年 | 157篇 |
2018年 | 170篇 |
2017年 | 200篇 |
2016年 | 207篇 |
2015年 | 140篇 |
2014年 | 273篇 |
2013年 | 583篇 |
2012年 | 287篇 |
2011年 | 360篇 |
2010年 | 347篇 |
2009年 | 425篇 |
2008年 | 484篇 |
2007年 | 478篇 |
2006年 | 418篇 |
2005年 | 407篇 |
2004年 | 351篇 |
2003年 | 379篇 |
2002年 | 322篇 |
2001年 | 262篇 |
2000年 | 220篇 |
1999年 | 236篇 |
1998年 | 196篇 |
1997年 | 168篇 |
1996年 | 120篇 |
1995年 | 77篇 |
1994年 | 85篇 |
1993年 | 55篇 |
1992年 | 39篇 |
1991年 | 25篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 28篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 30篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1936年 | 3篇 |
排序方式: 共有8139条查询结果,搜索用时 46 毫秒
31.
H. R. Ebrahimi-Vishki M. A. Pourabdollah 《Proceedings of the American Mathematical Society》1997,125(7):2171-2174
The purpose of this paper is to introduce an algebra of functions on a semitopological semigroup and to study these functions from the point of view of universal semigroup compactification. We show that the corresponding semigroup compactification of this algebra is universal with respect to the property of being a nilpotent group.
32.
For given a graph H, a graphic sequence π = (d
1, d
2,..., d
n) is said to be potentially H-graphic if there is a realization of π containing H as a subgraph. In this paper, we characterize the potentially (K
5 − e)-positive graphic sequences and give two simple necessary and sufficient conditions for a positive graphic sequence π to
be potentially K
5-graphic, where K
r is a complete graph on r vertices and K
r-e is a graph obtained from K
r by deleting one edge. Moreover, we also give a simple necessary and sufficient condition for a positive graphic sequence
π to be potentially K
6-graphic.
Project supported by National Natural Science Foundation of China (No. 10401010). 相似文献
33.
Let λ and μ be solid sequence spaces. For a sequence of modulus functions Φ = (ϕ k) let λ(Φ) = {x = (x
k
): (ϕk(|x
k
|)) ∈ λ}. Given another sequence of modulus functions Ψ = (ψk), we characterize the continuity of the superposition operators P
f
from λ(Φ) into μ (Ψ) for some Banach sequence spaces λ and μ under the assumptions that the moduli ϕk (k ∈ ℕ) are unbounded and the topologies on the sequence spaces λ(Φ) and μ(Ψ) are given by certain F-norms. As applications
we consider superposition operators on some multiplier sequence spaces of Maddox type.
This research was supported by Estonian Science Foundation Grant 5376. 相似文献
34.
The purpose of this work is to investigate the weakened Ambrosetti–Prodi type multiplicity results for weak doubly periodic solutions of damped beam equations. By using the topological degree theory, the author obtains a result which is similar to the result for damped wave equations in the literature. 相似文献
35.
In this paper, we consider questions related to the structure of inverse matrices of linear bounded operators acting in infinite-dimensional complex Banach spaces. We obtain specific estimates of elements of inverse matrices for bounded operators whose matrices have a special structure. Matrices are introduced as special operator-valued functions on an index set. The matrix structure is described by the behavior of the given function on elements of a special partition of the index set. The method used for deriving the estimates is based on an analysis of Fourier series of strongly continuous periodic functions. 相似文献
36.
In this paper, we establish the existence of upper and lower solutions for a periodic boundary value problems (PBVP for short) of impulsive differential equations. which guarantees the existence of at least one solution for the problem. As an application, these results are applied to PBVP of ODE and some examples are given to illustrate our results. 相似文献
37.
Héctor J. Sussmann 《Set-Valued Analysis》2002,10(2-3):233-285
It is shown that the construction of needle variations can be carried out for almost lower semicontinuous differential inclusions rather than for the case of ordinary single-valued continuously differentiable vector fields usually considered in the literature. The construction leads to needle variations whose flows are in general set-valued but still have good differentiability properties. The variations are constructed by using single-valued selections that are not necessarily continuous with respect to the state variable, but have instead a much weaker 'integral continuity' property, somewhat more general that the 'directional continuity' considered in previous work by A. Cambini and S. Querci, A. Pucci, and A. Bressan. The existence of many such selections is proved by slightly adapting an argument due to Bressan, extending it from the lower semicontinuous to the almost lower semicontinuous case, and strengthening it to yield not only directional continuity at all points but also full continuity at a specified point. 相似文献
38.
An infinite row of periodically spaced, identical rigid circularcylinders is excited by an acoustic line source which is parallelto the generators of the cylinders. A method for calculatingthe scattered field accurately and efficiently is presented.When the cylinders are sufficiently close together, Rayleigh–Blochsurface waves that propagate energy to infinity along the arrayare excited. An expression is derived which enables the amplitudesof these surface waves to be computed without requiring thesolution to the full scattering problem. 相似文献
39.
In this paper, the impact of optical beat noise on the performance of optical fast frequency-hopping code-division multiple-access (FFH OCDMA) networks is analyzed. BCH/FFH-OCDMA to reduce the impact of optical beat noise is proposed. It is shown that, BCH/FFH-OCDMA has much better performance under the same bit rate, same chip time and same number of available wavelengths. Another advantage for BCH/FFH-OCDMA is that the code length of one-coincidence sequence will be shorter, which can greatly reduce the difficulty of fabrication for fiber gratings. 相似文献
40.
YAN Zhen-Ya 《理论物理通讯》2002,38(10)
Recently, we obtained thirteen families of Jacobian elliptic function solutions of mKdV equation by usingour extended Jacobian elliptic function expansion method. In this note, the mKdV equation is investigated and anotherthree families of new doubly periodic solutions (Jacobian elliptic function solutions) are fbund again by using a newtransformation, which and our extended Jacobian elliptic function expansion method form a new method still called theextended Jacobian elliptic function expansion method. The new method can be more powertul to be applied to othernonlinear differential equations. 相似文献