全文获取类型
收费全文 | 4661篇 |
免费 | 844篇 |
国内免费 | 516篇 |
专业分类
化学 | 1649篇 |
晶体学 | 99篇 |
力学 | 646篇 |
综合类 | 100篇 |
数学 | 1238篇 |
物理学 | 2289篇 |
出版年
2024年 | 5篇 |
2023年 | 36篇 |
2022年 | 68篇 |
2021年 | 83篇 |
2020年 | 119篇 |
2019年 | 102篇 |
2018年 | 122篇 |
2017年 | 185篇 |
2016年 | 197篇 |
2015年 | 152篇 |
2014年 | 230篇 |
2013年 | 466篇 |
2012年 | 300篇 |
2011年 | 325篇 |
2010年 | 249篇 |
2009年 | 311篇 |
2008年 | 275篇 |
2007年 | 319篇 |
2006年 | 286篇 |
2005年 | 220篇 |
2004年 | 230篇 |
2003年 | 232篇 |
2002年 | 190篇 |
2001年 | 157篇 |
2000年 | 151篇 |
1999年 | 152篇 |
1998年 | 126篇 |
1997年 | 77篇 |
1996年 | 82篇 |
1995年 | 78篇 |
1994年 | 77篇 |
1993年 | 68篇 |
1992年 | 54篇 |
1991年 | 45篇 |
1990年 | 40篇 |
1989年 | 30篇 |
1988年 | 28篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1957年 | 3篇 |
排序方式: 共有6021条查询结果,搜索用时 406 毫秒
11.
Teresa Regińska 《BIT Numerical Mathematics》2004,44(1):119-133
The paper concerns conditioning aspects of finite-dimensional problems arising when the Tikhonov regularization is applied
to discrete ill-posed problems. A relation between the regularization parameter and the sensitivity of the regularized solution
is investigated. The main conclusion is that the condition number can be decreased only to the square root of that for the
nonregularized problem. The convergence of solutions of regularized discrete problems to the exact generalized solution is
analyzed just in the case when the regularization corresponds to the minimal condition number. The convergence theorem is
proved under the assumption of the suitable relation between the discretization level and the data error. As an example the
method of truncated singular value decomposition with regularization is considered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
13.
建立了相变热力学理论和场论的关系. 强调在量子场论中必须引进序参量场, 则相变的讨论就类似于Goldstone bosons 的产生. 如果只讨论一级相变, Goldstone bosons场就足够了; 如果要讨论二级相变, 则必须讨论一系列的场, 这些场构成一个对称群的表示. 另外, 也将这一思想用到色超导中. In this paper we built a relation between the thermodynamical theory of the phase transition and field theory. We emphasized that in the quantum field theory we have to introduce the order parameter fields. Then the discussion of the phase transition is closed to the creation of the Goldstone bosons. If we only discuss the first order transition, the Goldstone bosons fields are sufficient. If we want to discuss the second order transition, we have to discuss a set of fields that constructs a representation of a symmetry group. We also apply this concept to color superconductivity. 相似文献
14.
L. A. Utracki 《Journal of Polymer Science.Polymer Physics》2004,42(15):2909-2915
The Simha and Somcynsky (S–S) statistical thermodynamics theory was used to compute the solubility parameters as a function of temperature and pressure [δ = δ(T, P)], for a series of polymer melts. The characteristic scaling parameters required for this task, P*, T*, and V*, were extracted from the pressure–temperature–volume (PVT) data. To determine the potential polymer–polymer miscibility, the dependence of δ versus T (at ambient pressure) was computed for 17 polymers. Close proximity of the δ versus T curves for four miscible polymer pairs: PPE/PS, PS/PVME, and PC/PMMA signaled the usefulness of this approach. It is noteworthy, that the tabulated solubility parameters (derived from the solution data under ambient conditions) propounded the immiscibility of the PVC/PVAc pair. The computed values of δ also suggested miscibility for polymer pairs of unknown miscibility, namely PPE/PVC, PPE/PVAc, and PET/PSF. In recognizing the limitations of the solubility parameter approach (the omission of several thermodynamic contributions), these preliminary results are auspicious because they indicate a new route for estimating the miscibility of any polymeric material at a given temperature and pressure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2909–2915, 2004 相似文献
15.
报导了Yb :FAP和Yb :C3S2 _FAP晶体在不同温度下的吸收光谱和荧光光谱实验结果 ,研究发现由于电子_声子近共振耦合作用 ,Yb :FAP和Yb :C3S2 _FAP晶体均存在有明显的振动谱 ,Yb :FAP晶体的零声子线在低温下还劈裂为相差 10cm- 1 的两条线 .采用激光选择激发技术研究了Yb3 离子在FAP和C3S2 _FAP晶体中的格位特征 ,结果表明Yb3 离子在这两种基质中都只占据Ca(Ⅱ )格位 ,但由于CaF2 的挥发 ,导致了Ca(Ⅱ )格位的局部畸变 . 相似文献
16.
I. Peshko G. Galich M. Lopiychuk A. Khizhnyak V. Nakvasuk 《Optics & Laser Technology》1997,29(4):211-215
A laser system containing four CW Nd:YAG double-rod lasers, transforming optics and a fibre with input-output optics has been designed and investigated. It is shown that reduction of the beam parameter product of the non-Gaussian beams in the image space of the lens has made it possible to collect the emission of four lasers to the same fibre. Independent laser operation has provided the output power control in the range of 10–900 W with a stable light spot size on the input end of the fibre. 相似文献
17.
Identification of nonlinear elliptic equations 总被引:1,自引:0,他引:1
An optimization theoretic approach and algorithm for the estimation of state-dependent coefficients in nonlinear elliptic equation is presented. It is based on a splitting method combined with convex analysis techniques. Convergence of the algorithm is established and numerical examples are included.The research of K. Kunisch was supported in part by a grant from the Bundesministerium für Wissenschaft und Forschung, Austria. 相似文献
18.
In this work two non-local problems for the parabolic-hyperbolic type equation with non-characteristic line of changing type
are considered. Unique solvability of these problems is proven. The uniqueness of the solution is proven by the method of
energy integrals and the existence is proven by the method of integral equations. 相似文献
19.
A. B. Vasil’eva A. A. Plotnikov 《Computational Mathematics and Mathematical Physics》2006,46(5):762-767
A singularly perturbed parabolic equation with a nonlinear right-hand side of a special form is examined. A numerical analytical study of such equations is performed. 相似文献
20.