全文获取类型
收费全文 | 263976篇 |
免费 | 17334篇 |
国内免费 | 12129篇 |
专业分类
化学 | 134593篇 |
晶体学 | 3624篇 |
力学 | 16045篇 |
综合类 | 673篇 |
数学 | 42204篇 |
物理学 | 96300篇 |
出版年
2023年 | 2159篇 |
2022年 | 4099篇 |
2021年 | 4292篇 |
2020年 | 4581篇 |
2019年 | 4351篇 |
2018年 | 13640篇 |
2017年 | 14184篇 |
2016年 | 10135篇 |
2015年 | 6447篇 |
2014年 | 7065篇 |
2013年 | 10230篇 |
2012年 | 15844篇 |
2011年 | 25260篇 |
2010年 | 16166篇 |
2009年 | 16079篇 |
2008年 | 20466篇 |
2007年 | 23408篇 |
2006年 | 8020篇 |
2005年 | 14106篇 |
2004年 | 9278篇 |
2003年 | 8216篇 |
2002年 | 5729篇 |
2001年 | 5212篇 |
2000年 | 4282篇 |
1999年 | 3550篇 |
1998年 | 2794篇 |
1997年 | 2568篇 |
1996年 | 2573篇 |
1995年 | 2226篇 |
1994年 | 2008篇 |
1993年 | 1693篇 |
1992年 | 1892篇 |
1991年 | 1774篇 |
1990年 | 1550篇 |
1989年 | 1321篇 |
1988年 | 1195篇 |
1987年 | 1211篇 |
1986年 | 1067篇 |
1985年 | 1240篇 |
1984年 | 1126篇 |
1983年 | 821篇 |
1982年 | 781篇 |
1981年 | 704篇 |
1980年 | 648篇 |
1979年 | 761篇 |
1978年 | 791篇 |
1977年 | 709篇 |
1976年 | 664篇 |
1974年 | 581篇 |
1973年 | 559篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The existence of linear nonstationary optical resonances in a diatomic nanostructural object with a dipole-dipole atomic interaction has been proved. A new solution to the joint system of modified Bloch optical equations and nonlocal field equations is obtained for time intervals much shorter than the times of phase and energy relaxation. Formulas for effective polarizabilities of the object’s atoms, which have a set of dimensional resonances, are derived. The frequencies of these resonances significantly differ from the eigenfrequencies of the object’s atoms, and their properties depend on the interatomic distance, light-pulse duration, initial atomic inversions, and the orientation of the object’s axis relative to the direction of incidence of the external light wave. 相似文献
42.
The results of laser induced deposition of copper on polyimide substrate from copper electrolyte solution are reported. Unlike most work reported in the literatures where CW Ar+ lasers were used, a second harmonic (532 nm wavelength) Q-switch Nd:YAG laser was used for our experiments. The deposition process was conducted by laser-catalyzing of the polyimide surface and subsequent photothermal-accelerated reduction of copper-complex ions in an alkaline reducing environment. The characteristics of the deposited copper line were investigated in terms of laser beam scanning speed, and the number of scans. The surface morphology and chemical composition of the deposited copper were analyzed using field emission scanning electron microscope (FESEM) and energy dispersive spectrometer (EDX). The optimum processing conditions have been identified. The copper deposit was found to adhere well to the substrate. 相似文献
43.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献
44.
J. Kobayashi Y. Izumi M. Kumakura Y. Takahashi 《Applied physics. B, Lasers and optics》2006,83(1):21-25
By stabilizing the beam pointing of optical trapping beams, we have succeeded in stable formation of Bose–Einstein condensate
(BEC) of 87Rb with all-optical method. The thermal effect of acousto-optic modulator (AOM) is usually one of the most serious problems
to induce beam-pointing instability, especially for high power CO2 laser. By passing the beam through AOM twice, we have improved the beam pointing from about 4.8 mrad to less than 0.4 mrad,
which has been experimentally confirmed to be small enough to stably form BEC at the crossed region of CO2 lasers as well as to perform experiments using an optical lattice which might have been affected by beam-pointing instability.
PACS 32.80.Pj; 42.79.Jq; 03.75.Mn 相似文献
45.
46.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献
47.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
48.
X-ray diffraction patterns of nanocrystalline Fe-Cu-Nb-Si-B (FINEMET) alloys reveal that bcc α-Fe/α-FeSi crystallites with
the average grain size of 20(5) nm are dispersed in amorphous matrix. Enhanced electron—electron interaction (EEI) and quantum
interference (QI) effects as well as electron-magnon (and/or electron-spin fluctuation) scattering turn out to be the main
mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon
scattering is the most effective mechanism to destroy phase coherence of electron wave functions. The diffusion constant,
density of states at the Fermi level and the inelastic scattering time have been estimated, for the first time, for the alloys
in question
Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and
Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India. 相似文献
49.
A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes. 相似文献
50.