全文获取类型
收费全文 | 30157篇 |
免费 | 4073篇 |
国内免费 | 2736篇 |
专业分类
化学 | 20535篇 |
晶体学 | 284篇 |
力学 | 1947篇 |
综合类 | 273篇 |
数学 | 3285篇 |
物理学 | 10642篇 |
出版年
2024年 | 105篇 |
2023年 | 591篇 |
2022年 | 907篇 |
2021年 | 1011篇 |
2020年 | 1112篇 |
2019年 | 1082篇 |
2018年 | 913篇 |
2017年 | 813篇 |
2016年 | 1279篇 |
2015年 | 1270篇 |
2014年 | 1537篇 |
2013年 | 2050篇 |
2012年 | 2630篇 |
2011年 | 2658篇 |
2010年 | 1647篇 |
2009年 | 1634篇 |
2008年 | 1743篇 |
2007年 | 1663篇 |
2006年 | 1491篇 |
2005年 | 1232篇 |
2004年 | 944篇 |
2003年 | 794篇 |
2002年 | 758篇 |
2001年 | 562篇 |
2000年 | 561篇 |
1999年 | 653篇 |
1998年 | 580篇 |
1997年 | 575篇 |
1996年 | 663篇 |
1995年 | 507篇 |
1994年 | 465篇 |
1993年 | 391篇 |
1992年 | 371篇 |
1991年 | 322篇 |
1990年 | 255篇 |
1989年 | 202篇 |
1988年 | 157篇 |
1987年 | 136篇 |
1986年 | 127篇 |
1985年 | 118篇 |
1984年 | 88篇 |
1983年 | 61篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
931.
Feimin Huang 《应用数学年刊》2019,(3)
The usual heat flow moves along the direction from high temperature place to the low one, as often observed in the daily life. However, when the gas is very rarefied, the gas may move along a different way, that is, the so-called thermal creep flow moves along the direction from the low temperature place to the high one. In this note, we will survey our recent mathematical works on this topic, mainly based on [27] and [25]. 相似文献
932.
改革物理实验教学,培养学生创新能力 总被引:7,自引:0,他引:7
改革传统的物理实验教学内容,增加综合性、设计性、障碍性实验,开放实验室,培养学生的创新能力。 相似文献
933.
关于宇宙常数问题是个至今没有解决的问题, 它的来源至今还没有一个共识. 从额外维的流形出发, 给出了宇宙常数的,bulk,流形起源的理论, 得到了不同情况下宇宙常数的取值和宇宙常数随时间演化的函数, 并且得到了可拟合现代天文观测的宇宙常数. 相似文献
934.
Wenjie Li Lihong Huang Jinchen Ji 《Mathematical Methods in the Applied Sciences》2019,42(13):4498-4515
This paper investigates the periodic solution of a delayed Beddington‐DeAngelis (BD) type predator‐prey model with discontinuous control strategy. Firstly, the regularity and visibility analysis of the delayed predator‐prey model is carried out by using the principle of differential inclusion. Secondly, the positiveness and boundeness of the solution is discussed by employing the comparison theorem. Based on the boundary conditions of the model and the Mawhin‐like coincidence theorem, it is shown that the solution of the delayed BD system is asymptotically stable in finite time. Furthermore, it is found that there exists at least one periodic solution of the nonautonomous delayed predator‐prey model by using the principle of topological degree and set value mapping. Specially, when the nonautonomous delayed BD system degenerates into an autonomous system, some criteria are obtained to guarantee the convergence behavior of the harvesting solutions for the corresponding autonomous delayed BD system. Finally, numerical examples are given to demonstrate the applicability and effectiveness of main results. It is worthy to point out that the discontinuous control strategy is superior to the continuous harvesting policies adopted in existing literature. 相似文献
935.
The line-integrated optical measurement of impurity radiation profiles for the study of light impurity transport is performed in the HT-7 tokamak. The carbon impurity line emissivity is obtained by Abel inversion. The radial transport behaviours of carbon impurities at different central line averaged electron densities ne are investigated in ohmic discharges. The diffusion coefficient Dk(r), the convection velocity Wk(r) and the total flux of the impurity ions Fk decrease with the increase of ne, which shows a reduction in the impurity particle transport at higher electron densities. 相似文献
936.
This paper mainly concerns a tuple of multiplication operators
defined on the weighted and unweighted multi-variable Bergman
spaces, their joint reducing subspaces and the von Neumann algebra
generated by the orthogonal projections onto these subspaces. It is
found that the weights play an important role in the structures of
lattices of joint reducing subspaces and of associated von Neumann
algebras. Also, a class of special weights is taken into account.
Under a mild condition it is proved that if those multiplication
operators are defined by the same symbols, then the corresponding
von Neumann algebras are $*$-isomorphic to the one defined on the
unweighted Bergman space. 相似文献
937.
We study the effective second-harmonic generation (SHG) susceptibility in graded metallic films by invoking the local field effects exactly and further numerically demonstrate that graded metallic films can serve as a novel optical material for producing a broad structure in both the linear and the SHG response and an enhancement in the SHG signal. 相似文献
938.
Given two graphs and , a graph is -free if it contains no induced subgraph isomorphic to or . Let and be the path on vertices and the cycle on vertices, respectively. In this paper we show that for any -free graph it holds that , where and are the chromatic number and clique number of , respectively. Our bound is attained by several graphs, for instance, the 5-cycle, the Petersen graph, the Petersen graph with an additional universal vertex, and all -critical -free graphs other than (see Hell and Huang [Discrete Appl. Math. 216 (2017), pp. 211–232]). The new result unifies previously known results on the existence of linear -binding functions for several graph classes. Our proof is based on a novel structure theorem on -free graphs that do not contain clique cutsets. Using this structure theorem we also design a polynomial time -approximation algorithm for coloring -free graphs. Our algorithm computes a coloring with colors for any -free graph in time. 相似文献
939.
We describe a novel scheme for obtaining a superhigh numerical aperture gradient-index (SHNA GRIN) lens from multiple thin layers of two or more materials with large refractive-index contrast. Design procedures for the lens are described, including variation of the layer thickness to achieve focusing and of the thickness limit to reduce scattering loss. We use an exact numerical solution by the finite-difference time-domain method to evaluate the lens's performance. Specific examples of a SHNA GRIN lens with a SiO2-TiO2 material system designed for fiber coupling to a nanowaveguide are shown to have focusing FWHM spot sizes of 0.53-0.7 microm at lambda =1.55 microm (corresponding to a NA of approximately 1.6-1.1) with 2.7-2.4% more loss than an ideal continuous index profile GRIN lens. With this approach, a SHNA GRIN lens with a NA of > 1.5 and a length of <20 microm can be achieved with currently available thin-film deposition techniques. 相似文献
940.