全文获取类型
收费全文 | 13331篇 |
免费 | 1585篇 |
国内免费 | 1667篇 |
专业分类
化学 | 5468篇 |
晶体学 | 106篇 |
力学 | 2067篇 |
综合类 | 214篇 |
数学 | 6235篇 |
物理学 | 2493篇 |
出版年
2024年 | 38篇 |
2023年 | 155篇 |
2022年 | 221篇 |
2021年 | 390篇 |
2020年 | 480篇 |
2019年 | 422篇 |
2018年 | 418篇 |
2017年 | 501篇 |
2016年 | 598篇 |
2015年 | 395篇 |
2014年 | 616篇 |
2013年 | 1202篇 |
2012年 | 745篇 |
2011年 | 742篇 |
2010年 | 643篇 |
2009年 | 809篇 |
2008年 | 852篇 |
2007年 | 893篇 |
2006年 | 734篇 |
2005年 | 642篇 |
2004年 | 611篇 |
2003年 | 526篇 |
2002年 | 521篇 |
2001年 | 437篇 |
2000年 | 413篇 |
1999年 | 405篇 |
1998年 | 329篇 |
1997年 | 276篇 |
1996年 | 240篇 |
1995年 | 230篇 |
1994年 | 180篇 |
1993年 | 160篇 |
1992年 | 111篇 |
1991年 | 121篇 |
1990年 | 81篇 |
1989年 | 62篇 |
1988年 | 49篇 |
1987年 | 47篇 |
1986年 | 37篇 |
1985年 | 42篇 |
1984年 | 40篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1979年 | 23篇 |
1978年 | 8篇 |
1977年 | 15篇 |
1976年 | 7篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 68 毫秒
81.
简要叙述了稠密等离子体聚焦装置作为中子发生器的工作原理,对影响稠密等离子体聚焦装置放电出中子产额及其稳定性的一些因素和改进措施进行了简单讨论.通过使用不同电极形状的场畸变开关很好地提高了焦点装置的运行,使装置输出中子的起伏得到明显的改善.通过对腔内电极的清洁,在不更换气体的条件下,聚焦装置放电出中子产额稳定.The principle of dense plasma focus(DPF) as neutron generator has been investigated in this paper. We have stated briefly some factors that mainly influnce the DPF s neutron yield and some methods improving the stability of neutron yields on the dense plasma focus. It is showed that the fluctuation of DPF output neutron becomes smaller by using different types of field-distortion elements. Over 100 consecutive shots without purging the test gas the neutron yields has no obvious change. 相似文献
82.
We consider the problem of determining the dielectric permittivity for a nonconducting and nonmagnetic medium. As information we take the traces of the tangential components of the electromagnetic field on the lateral surface of a cylindrical domain. These traces correspond to a solution to some direct problem for the Maxwell system. The impulse source of the current flux lies outside the domain in which the coefficient is sought. The main result of the article is a stability estimate for a solution to the inverse problem in question. 相似文献
83.
森林发展系统的一个非线性半离散模型 总被引:2,自引:2,他引:0
王定江 《数学的实践与认识》2003,33(2):86-90
本文建立了森林发展系统的一类非线性林龄面积结构的半离散模型 ,并讨论了半离散系统解的存在唯一性 ,给出了线性半离散系统稳定的一些充分条件 相似文献
84.
A. Budhiraja 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2003,39(6):2318-941
In this work we study connections between various asymptotic properties of the nonlinear filter. It is assumed that the signal has a unique invariant probability measure. The key property of interest is expressed in terms of a relationship between the observation σ field and the tail σ field of the signal, in the stationary filtering problem. This property can be viewed as the permissibility of the interchange of the order of the operations of maximum and countable intersection for certain σ-fields. Under suitable conditions, it is shown that the above property is equivalent to various desirable properties of the filter such as
- (a) uniqueness of invariant measure for the signal,
- (b) uniqueness of invariant measure for the pair (signal, filter),
- (c) a finite memory property of the filter,
- (d) a property of finite time dependence between the signal and observation σ fields and
- (e) asymptotic stability of the filter.
85.
86.
本文就欧氏空间和球面中紧致子流形的Yang-Mills场进行了讨论.得到了一类不稳定性结果. 相似文献
87.
We show that the tensor product B-spline basis and the triangular Bernstein basis are in some sense best conditioned among all nonnegative bases for the spaces of tensor product splines and multivariate polynomials, respectively. We also introduce some new condition numbers which are analogs of component-wise condition numbers for linear systems introduced by Skeel. 相似文献
88.
A Stability Estimate for a Solution to a Three-Dimensional Inverse Problem for the Maxwell Equations
We consider the problem of determining dielectric permittivity and conductivity in the Maxwell equations. As additional information we prescribe the traces of the tangential components of the electromagnetic field on the lateral surface of a cylindric domain. We establish a stability estimate for a solution to the inverse problem and a uniqueness theorem. 相似文献
89.
V. V. Struzhanov V. V. Bashurov 《Journal of Applied Mechanics and Technical Physics》2003,44(4):549-556
Some iterative methods for calculating self-balanced stresses under shrinkage of a ball inclusion enclosed in a spherical matrix of a physically nonlinear damageable material. The stability of this system was studied using methods of catastrophe theory. It has been established that the beginning of divergence of the proposed iterative processes coincides with the moment of transition of the system to an unstable position of equilibrium. 相似文献
90.
In this paper, we study the linearization of the Cauchy problem and the mixed problem for the system of Grad--Hermite moments in nonequilibrium thermodynamics in the neighborhood of the equilibrium state. Stability conditions for solutions of the Cauchy problem are proved as a generalization of the classical Hermite--Biller theorem on stable polynomials. For the mixed problem, we prove an analog of the Vishik--Lyusternik theorem on small singular perturbations of general elliptic problems. The last observation allows us to introduce the Shapiro--Lopatinskii condition, which implies the well-posedness of the mixed problem. 相似文献