全文获取类型
收费全文 | 7684篇 |
免费 | 1095篇 |
国内免费 | 611篇 |
专业分类
化学 | 727篇 |
晶体学 | 15篇 |
力学 | 498篇 |
综合类 | 121篇 |
数学 | 4309篇 |
物理学 | 3720篇 |
出版年
2024年 | 8篇 |
2023年 | 67篇 |
2022年 | 125篇 |
2021年 | 126篇 |
2020年 | 178篇 |
2019年 | 165篇 |
2018年 | 150篇 |
2017年 | 205篇 |
2016年 | 240篇 |
2015年 | 191篇 |
2014年 | 364篇 |
2013年 | 614篇 |
2012年 | 407篇 |
2011年 | 467篇 |
2010年 | 385篇 |
2009年 | 496篇 |
2008年 | 553篇 |
2007年 | 527篇 |
2006年 | 539篇 |
2005年 | 399篇 |
2004年 | 377篇 |
2003年 | 330篇 |
2002年 | 313篇 |
2001年 | 293篇 |
2000年 | 268篇 |
1999年 | 253篇 |
1998年 | 220篇 |
1997年 | 162篇 |
1996年 | 164篇 |
1995年 | 98篇 |
1994年 | 90篇 |
1993年 | 79篇 |
1992年 | 65篇 |
1991年 | 49篇 |
1990年 | 56篇 |
1989年 | 30篇 |
1988年 | 52篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 33篇 |
1984年 | 36篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 22篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有9390条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
The aim of this paper is to present construction of finite element multiscaling function with three coefficients. In order to illuminate the result, two examples are given finally. 相似文献
35.
Browder-Petryshyn 型的严格伪压缩映射的粘滞迭代逼近方法 总被引:1,自引:0,他引:1
主要研究Browder-Petryshyn型的严格伪压缩映射的粘滞迭代逼近过程,证明了Browder-Petryshyn型的严格伪压缩映射的不动点集F(T)是闭凸集.在q-一致光滑且一致凸的Banach空间中,对于严格伪压缩映射T,利用徐洪坤在2004年引进的粘滞迭代得到的序列弱收敛于T的某个不动点.同时证明了Hilbert空间中Browder-Petryshyn型的严格伪压缩映射的相应迭代序列强收敛到T的某个不动点,其结果推广与改进了徐洪坤2004年的相应结果. 相似文献
36.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
37.
用密耦近似方法计算了He和N2体系的微分截面和总截面及转动激发分波截面,得出微分截面及总截面随入射能量变化的规律. 相似文献
38.
Silvia Vogel 《Annals of Operations Research》2006,142(1):269-282
The paper considers upper semicontinuous behavior in distribution of sequences of random closed sets. Semiconvergence in distribution
will be described via convergence in distribution of random variables with values in a suitable topological space. Convergence
statements for suitable functions of random sets are proved and the results are employed to derive stability statements for
random optimization problems where the objective function and the constraint set are approximated simultaneously.
The author is grateful to two anonymous referees for helpful suggestions. 相似文献
39.
J. J. EGOZCUE J. L. DIAZ-BARRERO V. PAWLOWSKY-GLAHN 《数学学报(英文版)》2006,22(4):1175-1182
The set of probability functions is a convex subset of L1 and it does not have a linear space structure when using ordinary sum and multiplication by real constants. Moreover, difficulties arise when dealing with distances between densities. The crucial point is that usual distances are not invariant under relevant transformations of densities. To overcome these limitations, Aitchison's ideas on compositional data analysis are used, generalizing perturbation and power transformation, as well as the Aitchison inner product, to operations on probability density functions with support on a finite interval. With these operations at hand, it is shown that the set of bounded probability density functions on finite intervals is a pre-Hilbert space. A Hilbert space of densities, whose logarithm is square-integrable, is obtained as the natural completion of the pre-Hilbert space. 相似文献
40.
We discuss the spectral lineshapes of reflectance and modulated reflectance (MR) measurements on optoelectronic device structures such as epi-layers, quantum wells (QWs), vertical-cavity surface emitting-lasers (VCSELs) and resonant-cavity light-emitting diodes (RCLEDs). We consider the various methods for the extraction of built-in electric fields and band-gap energies from Franz-Keldysh oscillations (FKO), using the example of a tensilely strained InGaAs QW system, whose InGaAsP barriers yield strong FKO. We describe how critical point transition energies can be easily obtained by eye from Kramers-Kronig (KK) transforms of low field or QW modulation spectra, using the example of the modulated transmittance spectra of dilute-nitrogen InGaAsN p-i-n structures. We also discuss how the ordinary reflectivity spectrum, usually acquired at the same time as the MR signal, may also be exploited to extract layer thicknesses and compositions, and information about the active QW absorption spectrum in VCSEL and RCLED structures. 相似文献