全文获取类型
收费全文 | 147375篇 |
免费 | 1469篇 |
国内免费 | 400篇 |
专业分类
化学 | 80622篇 |
晶体学 | 2392篇 |
力学 | 6071篇 |
综合类 | 3篇 |
数学 | 13579篇 |
物理学 | 46577篇 |
出版年
2021年 | 1040篇 |
2020年 | 1187篇 |
2019年 | 1255篇 |
2018年 | 1642篇 |
2017年 | 1690篇 |
2016年 | 2548篇 |
2015年 | 1572篇 |
2014年 | 2359篇 |
2013年 | 6073篇 |
2012年 | 4860篇 |
2011年 | 5953篇 |
2010年 | 4194篇 |
2009年 | 4212篇 |
2008年 | 5764篇 |
2007年 | 5544篇 |
2006年 | 5389篇 |
2005年 | 4953篇 |
2004年 | 4463篇 |
2003年 | 4149篇 |
2002年 | 4039篇 |
2001年 | 5574篇 |
2000年 | 3997篇 |
1999年 | 3088篇 |
1998年 | 2122篇 |
1997年 | 2211篇 |
1996年 | 2081篇 |
1995年 | 1919篇 |
1994年 | 1922篇 |
1993年 | 1728篇 |
1992年 | 2218篇 |
1991年 | 2299篇 |
1990年 | 2147篇 |
1989年 | 2110篇 |
1988年 | 2083篇 |
1987年 | 2092篇 |
1986年 | 1922篇 |
1985年 | 2380篇 |
1984年 | 2399篇 |
1983年 | 1915篇 |
1982年 | 1918篇 |
1981年 | 1753篇 |
1980年 | 1740篇 |
1979年 | 2026篇 |
1978年 | 2101篇 |
1977年 | 2052篇 |
1976年 | 1977篇 |
1975年 | 1863篇 |
1974年 | 1844篇 |
1973年 | 1876篇 |
1972年 | 1237篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
T. T. Vasil'eva V. A. Kochetkova V. I. Dostovalova B. V. Nelyubin R. Kh. Freidlina 《Russian Chemical Bulletin》1989,38(11):2346-2349
The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)5 + DMF, telomers of CHBr2(CH52CHCF3)nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr2CH2CH(CF3)CH3CHCF3 radicals to CBr2CH2CH(CF3)CH2CH2CF3 radicals.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2558–2562, November, 1989. 相似文献
122.
123.
Ultrasonic longitudinal velocity and adsorption have been measured in ceramic superconductors YBa2Cu3Oy with various porosity and also in BiSrCaCu2Oy. A velocity drop of about 400 ppm was found at Tc only in the measurements on cooling. The magnitude of the velocity drop is anomalously large compared with the value expected from the thermodynamics. A hysteresis of velocity with respect to temperature was observed in all the samples studied. It is suggested that some structural change at pore size level is responsible for this phenomenon. 相似文献
124.
This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated 3-dB modulation bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of conventional electrode structures that are limited by phase velocity mismatch.This work was supported by the U.S. Army Research Office under contract DAAL-03-88-K-0005 and the Texas Advanced Technology Program. 相似文献
125.
Z.J. Yang T.H. Johansen H. Bratsberg G. Helgesen A.T. Skjeltorp 《Physica C: Superconductivity and its Applications》1989,160(5-6):461-465
Based on a dipole-dipole interaction model, we discuss the levitation force and related vibration problems to understand the effects of flux pinning in type-II superconductors, and the applications of levitation in superconducting systems. 相似文献
126.
J. Giroire T. Ha‐Duong V. Moumas 《Mathematical Methods in the Applied Sciences》2005,28(13):1527-1552
This article deals with a boundary value problem for Laplace equation with a non‐linear and non‐local boundary condition. This problem comes from petroleum engineering and is used to obtain an estimation of well productivity. The non‐linear and non‐local boundary condition is written on the well boundary. On the outer reservoir boundaries, we have both Dirichlet and Neumann conditions. In this paper, we prove the existence and uniqueness of a solution to this problem. The existence is proved by Schauder theorem and the uniqueness is obtained under more restricted conditions, when the involved operator is a contraction. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
127.
A brief review of the potential functions used in the molecular dynamics modeling of liquid benzene is presented. The structural characteristics of liquid benzene obtained from the correlation distribution functions are discussed. It is demonstrated that, within the framework of this approach, the predicted structure of liquid benzene is virtually independent of the form of the potential used. 相似文献
128.
The room temperature structure of perovskite CeAlO3 has been reinvestigated by X-ray powder diffraction. The Rietveld refinement has confirmed the tetragonal symmetry; but revealed a super cell, a=5.32489(6) Å and c=7.58976(10) Å, with the space group I4/mcm. In CeAlO3, the distortion from the ideal cubic perovskite is caused by the cooperative tilting of the AlO6 octahedra around the primitive cubic [001]p-axis. 相似文献
129.
130.
Chemisorption at interfaces between organic semiconductors and metals: role of the electron affinity
Chemisorption is a well-known phenomenon for many interfaces between organic semiconductors and metals. It is shown that many published data indicate that the occurrence of chemisorption can be rationalized upon the consideration of the metal work function versus the electron affinity of the organic semiconductor. 相似文献