全文获取类型
收费全文 | 23835篇 |
免费 | 3606篇 |
国内免费 | 2074篇 |
专业分类
化学 | 6777篇 |
晶体学 | 160篇 |
力学 | 904篇 |
综合类 | 280篇 |
数学 | 4648篇 |
物理学 | 9142篇 |
无线电 | 7604篇 |
出版年
2024年 | 62篇 |
2023年 | 236篇 |
2022年 | 537篇 |
2021年 | 714篇 |
2020年 | 763篇 |
2019年 | 617篇 |
2018年 | 642篇 |
2017年 | 862篇 |
2016年 | 996篇 |
2015年 | 971篇 |
2014年 | 1527篇 |
2013年 | 1682篇 |
2012年 | 1532篇 |
2011年 | 1527篇 |
2010年 | 1279篇 |
2009年 | 1356篇 |
2008年 | 1616篇 |
2007年 | 1581篇 |
2006年 | 1374篇 |
2005年 | 1235篇 |
2004年 | 1064篇 |
2003年 | 983篇 |
2002年 | 868篇 |
2001年 | 704篇 |
2000年 | 649篇 |
1999年 | 577篇 |
1998年 | 536篇 |
1997年 | 446篇 |
1996年 | 393篇 |
1995年 | 342篇 |
1994年 | 329篇 |
1993年 | 219篇 |
1992年 | 194篇 |
1991年 | 144篇 |
1990年 | 139篇 |
1989年 | 123篇 |
1988年 | 99篇 |
1987年 | 84篇 |
1986年 | 58篇 |
1985年 | 83篇 |
1984年 | 54篇 |
1983年 | 39篇 |
1982年 | 56篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 31篇 |
1978年 | 34篇 |
1977年 | 21篇 |
1976年 | 20篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Let Um be an m×m Haar unitary matrix and U[m,n] be its n×n truncation. In this paper the large deviation is proven for the empirical eigenvalue density of U[m,n] as m/n→λ and n→∞. The rate function and the limit distribution are given explicitly. U[m,n] is the random matrix model of quq, where u is a Haar unitary in a finite von Neumann algebra, q is a certain projection and they are free. The limit distribution coincides with the Brown measure of the operator quq. 相似文献
142.
燃煤烟气中AsSePb的形态分布及SCl元素对其形态分布的影响 《燃料化学学报》2003,48(11):1298-1309
基于化学热力学平衡分析方法,计算分析了燃煤烟气中重金属As、Se、Pb的形态分布规律,研究了S、Cl等元素对As、Se、Pb的形态分布规律的影响。结果表明,氧化性气氛下,As以As2O5、As4O6、AsO等氧化物的形式存在;Se主要以SeO2形式存在;Pb在1000 K以下主要是固态PbSO4,1200 K以上为气态PbO。还原性气氛下,As在较低温度时为固态As2S2,900-1400 K以As2、AsS、AsN气体共存,2000 K以上全部转化为气态AsO。Se在1100 K以下主要以气态H2Se存在,1100 K开始生成SeS和Se2气体,1800 K时主要是气态Se和少量气态SeO;Pb在中低温时主要是PbS,1800 K以上气态Pb为主要存在形态。S在还原性气氛下增大了AsS(g)、PbS(g)、SeS(g)的比例,氧化性气氛下对As、Se、Pb形态分布基本无影响;Cl无论在氧化还是还原气氛下对As、Se影响均较小,但对Pb的形态分布影响较大。 相似文献
143.
N. S. Kazak E. G. Katranji I. A. Utkin A. A. Ryzhevich A. N. Khilo 《Journal of Applied Spectroscopy》2004,71(5):697-701
The phenomenon of self-diffraction of Bessel light beams (BLB) in a nonlinear liquid medium has been studied experimentally and theoretically for the first time. Diffraction maxima which do not correspond to integer orders for an induced periodic structure have been registered. It has been shown that the appearance of these maxima is due to the initial BLB modulation, which can be caused by the departure of the axicon refracting surface from the ideal conical surface, as well as by the imperfection of the form of the Gaussian beam incident on the axicon. 相似文献
144.
Summary Our purpose is to extend results due to P. Chandra and L. Leindler concerning the order of approximation by means of Fourier series for functions belonging to generalized Lipschitz-classes. 相似文献
145.
Fabiano Severo Rodembusch Ndya Pesce da Silveira Dimitrios Samios Leandra Franciscato Campo Valter Stefani 《Journal of Polymer Science.Polymer Physics》2003,41(4):341-350
The solution behavior of new copolymers of methyl methacrylate and benzazole dyes emitting fluorescence because of an intramolecular proton‐transfer mechanism in the electronically excited state has been investigated by static light scattering, fluorescence spectroscopy, ultraviolet–visible, and gel permeation chromatography. In the dilute regime, with tetrahydrofuran (THF) and chloroform as solvents, the copolymers behave as typical polydisperse linear chains in good solvents. The analysis of the osmotic modulus for concentrated solutions in THF (c ≥ 60 g L?1) indicates the existence of an interchain association mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 341–350, 2003 相似文献
146.
In this paper, we investigate the exact distribution of the waiting time for ther-th ℓ-overlapping occurrence of success-runs of a specified length in a sequence of two state Markov dependent trials. The
probability generating functions are derived explicitly, and as asymptotic results, relationships of a negative binomial distribution
of orderk and an extended Poisson distribution of orderk are discussed. We provide further insights into the run-related problems from the viewpoint of the ℓ-overlapping enumeration
scheme. We also study the exact distribution of the number of ℓ-overlapping occurrences of success-runs in a fixed number
of trials and derive the probability generating functions. The present work extends several properties of distributions of
orderk and leads us a new type of geneses of the discrete distributions. 相似文献
147.
148.
通过数值求解一维瞬态受激布里渊散射(SBS)声光耦合波方程,从理论上分析了泵浦激光参数及光学材料参数对SBS过程发生阈值的影响。以SBS过程中建立起来的应力场抗拉(压)强度和散射场的反射率为判据,分析了激光脉宽及作用区域长度对激光超声破坏材料效果的影响,探讨了短脉冲激光(约ns)引起的激光超声对材料的破坏机理;讨论了通过参数配置有效遏制SBS过程激光超声对光学材料的破坏问题。 相似文献
149.
The dependence of emission direction of fast electrons on the laser intensity has been investigated. The experimental results show that, at nonrelativistic laser intensities, the emission of fast electrons is mainly in the polarization plane. With the increase of the laser intensity, fast electrons emit towards the laser propagation direction from laser polarization direction. At relativistic laser intensities, fast electrons move away from the laser polarization plane, closely to the reflection direction of the incident laser beam. 相似文献
150.
类比方法与光的本性的探索 总被引:2,自引:0,他引:2
简要回顾了人类对光的本性的探索历程,介绍了物理学家在研究过程中对类比方法的运用。 相似文献