全文获取类型
收费全文 | 289864篇 |
免费 | 1946篇 |
国内免费 | 858篇 |
专业分类
化学 | 122618篇 |
晶体学 | 4057篇 |
力学 | 17092篇 |
综合类 | 5篇 |
数学 | 63407篇 |
物理学 | 85489篇 |
出版年
2018年 | 18092篇 |
2017年 | 18717篇 |
2016年 | 10267篇 |
2015年 | 2651篇 |
2014年 | 1792篇 |
2013年 | 5295篇 |
2012年 | 10847篇 |
2011年 | 25342篇 |
2010年 | 14606篇 |
2009年 | 14837篇 |
2008年 | 20112篇 |
2007年 | 25473篇 |
2006年 | 4640篇 |
2005年 | 12531篇 |
2004年 | 8525篇 |
2003年 | 8440篇 |
2002年 | 5515篇 |
2001年 | 3983篇 |
2000年 | 3273篇 |
1999年 | 2391篇 |
1998年 | 2117篇 |
1997年 | 2031篇 |
1996年 | 2125篇 |
1995年 | 1971篇 |
1994年 | 1702篇 |
1993年 | 1700篇 |
1992年 | 1862篇 |
1991年 | 1870篇 |
1990年 | 1790篇 |
1989年 | 1805篇 |
1988年 | 1819篇 |
1987年 | 1803篇 |
1986年 | 1709篇 |
1985年 | 2263篇 |
1984年 | 2392篇 |
1983年 | 2014篇 |
1982年 | 2332篇 |
1981年 | 2142篇 |
1980年 | 2194篇 |
1979年 | 2194篇 |
1978年 | 2322篇 |
1977年 | 2141篇 |
1976年 | 2192篇 |
1975年 | 2116篇 |
1974年 | 1951篇 |
1973年 | 2209篇 |
1972年 | 1337篇 |
1971年 | 1007篇 |
1968年 | 1161篇 |
1967年 | 1139篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Lasing and discharge in mixtures of SF6 with hydrogen and hydrocarbons are investigated. If the chemical reaction is initiated by a self-sustained discharge (a generator
with both an inductive and capacitive energy storage can be used), the maximum lasing efficiency is attained at high values
of the ratio E/p (where E is the electric field intensity and p is the pressure in the mixture) if shaped electrodes and preionization of the discharge gap are employed. For the first time,
the lasing efficiency obtained in a nonchain HF laser is as high as 10% of the energy deposit and 4.5% of the stored energy
for a specific radiation energy of ≈140 J/(l atm). At high efficiencies, the emission spectrum of the nonchain HF laser significantly
broadens and cascade lasing at P(3-2) → P(2-1) → P(1-0) vibrational transitions for several rotational lines is realized. 相似文献
992.
Massoud Pourmahdian 《Archive for Mathematical Logic》2003,42(5):415-421
We prove that for any simple theory which is constructed via Fr?issé-Hrushovski method, if the forking independence is the
same as the d-independence then the stable forking property holds.
Received: 22 January 2001 /
Published online: 19 December 2002
This article is part of the author's D-Phil thesis, written at the University of Oxford and supported by the Ministry of
Higher Education of Iran. The author would like to thank the Institute for Studies in Theoretical Physics and Mathematics
(IPM), Tehran, Iran, for its financial support whilst working on this article.
Mathematics Subject Classification (2000): 03C45
Key words or phrases: Generic structures – Fr?issé-Hrushovski method – Predimension – Simple theories – Stable theories – Stable forking conjecture 相似文献
993.
R. M. Sardarly O. A. Samedov I. Sh. Sadykhov V. A. Aliev 《Physics of the Solid State》2003,45(6):1118-1121
The relaxor properties of Fe-doped TlInS2 crystals are investigated. It is shown that Fe-doped TlInS2 compounds exhibit all features inherent in relaxor ferroelectric materials. The temperature range of existence of the microdomain (relaxor) state and the temperature of the transition from this state to a macro-domain state are determined. 相似文献
994.
The classical economic order quantity (EOQ) model assumes that items produced are of perfect quality and that the unit cost of production is independent of demand. However, in realistic situations, product quality is never perfect, but is directly affected by the reliability of the production process. In this paper, we consider an EOQ model with imperfect production process and the unit production cost is directly related to process reliability and inversely related to the demand rate. In addition, a numerical example is given to illustrate the developed model. Sensitivity analysis is also performed and discussed. 相似文献
995.
Terminal alkynes undergo mild and efficient aminomethylation with aqueous formaldehyde and secondary amines under CuI catalysis. In most cases high to nearly quantitative yields of tertiary propargylamines are obtained in DMSO solution at room temperature. Aromatic, aliphatic and silylated acetylenes as well as alkynols can be used. Primary amines are less reactive and satisfactory yields of secondary propargylamines are obtained only with phenylacetylene. 相似文献
996.
V. L. Tsymbalenko 《JETP Letters》2003,78(8):493-496
The kinetics of formation of an anomalous phase from a solution with a small 3He impurity was studied in the temperature range 0.2–0.7 K up to a supersaturation of ~30 mbar. The phase diagram was determined for normal and anomalous growths. It is found that, in the presence of impurities, the formation of a fast-growing state is retarded. This experimental fact indicates that the dissipative processes in fluids have an appreciable effect on the phase formation kinetics. The retardation is, possibly, caused by the direct interaction of an impurity with the crystal surface. 相似文献
997.
998.
G. M. Maksimova A. L. Chuvilin E. M. Moroz V. A. Likholobov K. I. Matveev 《Kinetics and Catalysis》2004,45(6):870-878
Conditions for the preparation of stable aqueous monometallic and bimetallic colloidal solutions (sols) of noble metals (Ru, Rh, Pd, Pt, Ir, Ag, and Au) in the presence of polyoxometalates containing W, Mo, V, and Nb were found. The stability of sols against coagulation at room temperature was studied. The metal/C samples prepared by metal adsorption from sols were studied by powder X-ray diffraction analysis and transmission electron microscopy. The following factors of importance for the preparation of a stable sol are discussed: (1) the formation of a sol of a metal polyhydroxo complex stabilized by a polyoxometalate (preliminary stage) and (2) the formation of polyoxometalate-metal clusters in the course of reduction of polyhydroxo complexes.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 921–929.Original Russian Text Copyright © 2004 by Maksimova, Chuvilin, Moroz, Likholobov, Matveev. 相似文献
999.
Summary. We consider the spline collocation method for a class of parabolic pseudodifferential operators. We show optimal order convergence
results in a large scale of anisotropic Sobolev spaces. The results cover the classical boundary integral equations for the
heat equation in the general case where the spatial domain has a smooth boundary in the plane. Our proof is based on a localization
technique for which we use our recent results proved for parabolic pseudodifferential operators. For the localization we need
also some special spline approximation results in anisotropic Sobolev spaces.
Received May 17, 2001 / Revised version received February 19, 2002 / Published online April 17, 2002 相似文献
1000.
E. A. Bogdanov A. A. Kudryavtsev L. D. Tsendin R. R. Arslanbekov V. I. Kolobov V. V. Kudryavtsev 《Technical Physics》2003,48(9):1151-1158
Comprehensive self-consistent simulations of the positive column plasma of a dc oxygen discharge are performed with the help
of commercial CFDRC software (), which enables one to carry out computations in an arbitrary 3D geometry using fluid equations for heavy components and
a kinetic equation for electrons. The main scaling laws for the spatial distributions of charged particles are determined.
These scaling laws are found to be quite different in the parameter ranges that are dominated by different physical processes.
At low pressures, both the electrons and negative ions in the inner discharge region obey a Boltzmann distribution; as a result,
a flat profile of the electron density and a parabolic profile of the ion density are established there. In the ion balance,
transport processes prevail, so that ion heating in an electric field dramatically affects the spatial distribution of the
charged particles. At elevated pressures, the volume processes prevail in the balance of negative ions and the profiles of
the charged particle densities in the inner region turn out to be similar to each other. 相似文献