全文获取类型
收费全文 | 309559篇 |
免费 | 5247篇 |
国内免费 | 2240篇 |
专业分类
化学 | 166496篇 |
晶体学 | 5199篇 |
力学 | 13423篇 |
综合类 | 111篇 |
数学 | 33344篇 |
物理学 | 98473篇 |
出版年
2021年 | 2639篇 |
2020年 | 2907篇 |
2019年 | 3155篇 |
2018年 | 3806篇 |
2017年 | 3930篇 |
2016年 | 5961篇 |
2015年 | 3836篇 |
2014年 | 5842篇 |
2013年 | 13784篇 |
2012年 | 10914篇 |
2011年 | 12918篇 |
2010年 | 9346篇 |
2009年 | 9327篇 |
2008年 | 12075篇 |
2007年 | 11727篇 |
2006年 | 11278篇 |
2005年 | 10242篇 |
2004年 | 9204篇 |
2003年 | 8384篇 |
2002年 | 8138篇 |
2001年 | 10156篇 |
2000年 | 7499篇 |
1999年 | 5879篇 |
1998年 | 4480篇 |
1997年 | 4521篇 |
1996年 | 4227篇 |
1995年 | 3961篇 |
1994年 | 3878篇 |
1993年 | 3603篇 |
1992年 | 4333篇 |
1991年 | 4339篇 |
1990年 | 4153篇 |
1989年 | 4026篇 |
1988年 | 4013篇 |
1987年 | 3982篇 |
1986年 | 3733篇 |
1985年 | 4772篇 |
1984年 | 4821篇 |
1983年 | 4099篇 |
1982年 | 4150篇 |
1981年 | 3837篇 |
1980年 | 3808篇 |
1979年 | 4215篇 |
1978年 | 4314篇 |
1977年 | 4188篇 |
1976年 | 4188篇 |
1975年 | 3978篇 |
1974年 | 3958篇 |
1973年 | 4163篇 |
1972年 | 2744篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
261.
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
262.
263.
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
264.
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
265.
P. P. Kirpichok N. B. Voronina A. F. Sitnikov V. Ya. Garmash 《Russian Physics Journal》1989,32(1):26-30
The effect of rare-earth oxides on the properties of anisotropic barium ferrites has been studied by x-ray structural and Mössbauer methods. Additions of SrCO3, as well as SrCO3 and La2O3, SrCO3 and Pr6O11, SrCO3 and Nd2O3, SrCO3 and Sm2O3 in amounts of 7.5 mole % Sr and 10 mole % rare-earth element to grade-A barium powder results in the substitution of barium ions by Sr and rare-earth ions; consequently, the energy of magnetic anisotropy changes and the technically important parameters Br and (BH)max increase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–39, January, 1989. 相似文献
266.
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
267.
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
268.
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
269.
D. B. Kayumova Yu. P. Syrnikov N. V. Penkina M. N. Rodnikova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(10):1634-1635
The structural relaxation time for series of various liquids (alkanes, aliphatic alcohols, and diols) are calculated from published data on the shear viscosity and the heat of evaporation per unit volume. Liquids having a 3D H-bond network (diols) are characterized by relaxation times one to two orders of magnitudes longer than those typical of liquids without such a network (alkanes and aliphatic alcohols). 相似文献
270.
Operators on manifolds with corners that have base configurations with geometric singularities can be analysed in the frame of a conormal symbolic structure which is in spirit similar to the one for conical singularities of Kondrat'ev's work. Solvability of elliptic equations and asymptotics of solutions are determined by meromorphic conormal symbols. We study the case when the base has edge singularities which is a natural assumption in a number of applications. There are new phenomena, caused by a specific kind of higher degeneracy of the underlying symbols. We introduce an algebra of meromorphic edge operators that depend on complex parameters and investigate meromorphic inverses in the parameter-dependent elliptic case. Among the examples are resolvents of elliptic differential operators on manifolds with edges. 相似文献