全文获取类型
收费全文 | 456978篇 |
免费 | 4555篇 |
国内免费 | 1936篇 |
专业分类
化学 | 251535篇 |
晶体学 | 6697篇 |
力学 | 19691篇 |
综合类 | 68篇 |
数学 | 52347篇 |
物理学 | 133131篇 |
出版年
2019年 | 3820篇 |
2018年 | 5093篇 |
2017年 | 5122篇 |
2016年 | 7431篇 |
2015年 | 4702篇 |
2014年 | 7206篇 |
2013年 | 18303篇 |
2012年 | 14317篇 |
2011年 | 17483篇 |
2010年 | 12468篇 |
2009年 | 12177篇 |
2008年 | 16456篇 |
2007年 | 16756篇 |
2006年 | 15659篇 |
2005年 | 14250篇 |
2004年 | 12919篇 |
2003年 | 11600篇 |
2002年 | 11559篇 |
2001年 | 12577篇 |
2000年 | 9754篇 |
1999年 | 7314篇 |
1998年 | 6314篇 |
1997年 | 6318篇 |
1996年 | 6062篇 |
1995年 | 5493篇 |
1994年 | 5699篇 |
1993年 | 5276篇 |
1992年 | 5938篇 |
1991年 | 5944篇 |
1990年 | 5725篇 |
1989年 | 5592篇 |
1988年 | 5670篇 |
1987年 | 5497篇 |
1986年 | 5342篇 |
1985年 | 7115篇 |
1984年 | 7402篇 |
1983年 | 6126篇 |
1982年 | 6518篇 |
1981年 | 6203篇 |
1980年 | 6178篇 |
1979年 | 6297篇 |
1978年 | 7346篇 |
1977年 | 7067篇 |
1976年 | 6734篇 |
1975年 | 6116篇 |
1974年 | 6315篇 |
1973年 | 6449篇 |
1972年 | 4862篇 |
1971年 | 3961篇 |
1968年 | 3633篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Time structure of iodine laser pulse in the free running mode of operation was studied using the power amplifier of laser system PERUN as the laser oscillator. Two characteristic shapes of laser pulse correspond to different regimes of laser operation, the existence of which is ascribed to the critical concentration of I2 molecules. Simultaneously an additional chemical pumping was proved at least in the initial phase of photodissociation and in a late-time lasing after the end of flashlamps pumping light. 相似文献
152.
153.
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
154.
In an effort to clarify the role of controlled oxygen exposure in the synthesis of LaBa2Cu3Oy samples which achieve zero resistivity above 90 K, we have prepared samples of La(1+x)Ba(2–x)Cu3Oy with x approximately equal to 0 and with y varying between 6.22 and 7.00. We find that for large values of y, 6.88相似文献
155.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as
far as the calibration of a satellite altimeter is concerned. 相似文献
156.
157.
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
158.
V. Ballarini G. Barucca E. Bennici C. F. Pirri C. Ricciardi E. Tresso F. Giorgis 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):591
All amorphous silicon-nitride planar optical microcavities operating in the visible range have been grown by plasma enhanced chemical vapor deposition. The luminescence intensity of the N-rich silicon-nitride layer from a microcavity with 6 period distributed Bragg reflectors (DBRs) is two order of magnitude higher than that of the luminescent layer without the cavity. Moreover, a strong directionality of the microcavities emission can be observed. Such results can be ascribed to the anisotropic optical density of states induced in the Fabry–Perot structure. The quality factors of the resonators are strictly correlated to the number of periods of the DBRs. 相似文献
159.
G. Lujanienë 《Czechoslovak Journal of Physics》2003,53(1):A57-A65
In order to understand better the way in which radioactive contamination may be transferred from the atmosphere to other ecological compartments it is necessary to obtain information of the deposition mechanisms of radionuclides. Concentration and speciation of 137Cs and 7Be in the atmospheric aerosol and deposition were studied. The mixed deposition velocities of water-soluble and insoluble 137Cs and 7Be were determined. The relation between activity concentrations of insoluble 7Be in the atmosphere and its amount in deposition was observed. It is supposed that in the deposition process of radiocesium the precipitation plays an important role in scavenging of water-soluble radiocesium by falling raindrops, in contrast to insoluble 137Cs where the dry deposition becomes predominant. 相似文献
160.
The method of nonlinear moments, when used to solve the Boltzmann equation, necessitates the calculation of collision integral
matrix elements. The matrix elements are hard to calculate numerically, especially at large indices. The asymptotics of the
matrix elements are constructed. In terms of the model of pseudopower particle interaction, a formula free of summation is
derived. This makes it possible to find the asymptotic behavior of linear and nonlinear elements when two indices are large.
For an arbitrary interaction cross section, asymptotic expansions of linear and nonlinear matrix elements in one index are
obtained. For Maxwellian molecules, asymptotic formulas are derived for three large indices. 相似文献