全文获取类型
收费全文 | 308078篇 |
免费 | 3612篇 |
国内免费 | 908篇 |
专业分类
化学 | 170214篇 |
晶体学 | 5354篇 |
力学 | 12381篇 |
综合类 | 16篇 |
数学 | 30392篇 |
物理学 | 94241篇 |
出版年
2019年 | 2466篇 |
2018年 | 2796篇 |
2017年 | 2846篇 |
2016年 | 4618篇 |
2015年 | 3068篇 |
2014年 | 4702篇 |
2013年 | 13281篇 |
2012年 | 9392篇 |
2011年 | 11757篇 |
2010年 | 8014篇 |
2009年 | 7778篇 |
2008年 | 10449篇 |
2007年 | 10385篇 |
2006年 | 10016篇 |
2005年 | 9336篇 |
2004年 | 8408篇 |
2003年 | 7723篇 |
2002年 | 7414篇 |
2001年 | 8950篇 |
2000年 | 6788篇 |
1999年 | 5371篇 |
1998年 | 4327篇 |
1997年 | 4254篇 |
1996年 | 4144篇 |
1995年 | 3941篇 |
1994年 | 3619篇 |
1993年 | 3469篇 |
1992年 | 4302篇 |
1991年 | 4195篇 |
1990年 | 4064篇 |
1989年 | 4103篇 |
1988年 | 4113篇 |
1987年 | 4149篇 |
1986年 | 3940篇 |
1985年 | 5163篇 |
1984年 | 5225篇 |
1983年 | 4213篇 |
1982年 | 4585篇 |
1981年 | 4495篇 |
1980年 | 4312篇 |
1979年 | 4643篇 |
1978年 | 4740篇 |
1977年 | 4768篇 |
1976年 | 4644篇 |
1975年 | 4337篇 |
1974年 | 4159篇 |
1973年 | 4334篇 |
1972年 | 2855篇 |
1968年 | 2647篇 |
1967年 | 2601篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
951.
952.
E. S. Moskalenko M. Larsson K. F. Karlsson P. O. Holtz B. Monemar W. V. Schoenfeld P. M. Petroff 《Physics of the Solid State》2007,49(10):1995-1998
We report on low-temperature microphotoluminescence (μ-PL) measurements of InAs/GaAs quantum dots (QDs) exposed to a lateral
external electric field. It is demonstrated that the QDs’ PL signal could be increased severalfold by altering the external
and/or the internal electric field, which could be changed by an additional infrared laser. A model which accounts for a substantially
faster lateral transport of the photoexcited carriers achieved in an external electric field is employed to explain the observed
effects. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity
measured in our experiment—a finding which could be used to tailor the properties of QD-based optoelectronic applications.
The text was submitted by the authors in English. 相似文献
953.
N. B. Voznesensky E. V. Gavrilov A. P. Zhevlakov V. K. Kirillovskiĭ P. V. Orlov 《Technical Physics》2007,52(2):271-275
Methods and schemes to inspect the EUV mirror shape are developed on the basis of a point diffraction interferometer with computer processing of interferograms. A measurement accuracy to within 0.001 of a wavelength in the visual range is achieved. 相似文献
954.
The effect of an applied magnetic field on an inhomogeneous superconductor is studied and the value of the upper critical magnetic field Hc3 at which superconductivity can nucleate is estimated. In addition, the authors locate the concentration of the order parameter, which depends on the inhomogeneous term a(x). Unlikely to the homogeneous case, the order parameter may concentrate in the interior of the superconducting material, due to the influence of the inhomogeneous term a(x). 相似文献
955.
We investigate two families of Lorenz-like three-dimensional nonlinear dynamical systems (i) the generalized Lorenz system and (ii) the Burke–Shaw system. Analytical investigation of the former system is possible under the assumption (I) which in fact concerns four different systems corresponding to = ±1, m = 0, 1. The fixed points and stability characteristics of the Lorenz system under the assumption (I) are also classified. Parametric and temporal (t → ∞) asymptotes are also studied in connection to the memory of both the systems. We calculate the Lyapunov exponents and Lyapunov dimension for the chaotic attractors in order to study the influence of the parameters of the Lorenz system on the attractors obtained not only when the assumption (I) is satisfied but also for other values of the parameters σ, r, b, ω and m. 相似文献
956.
Motivated by the central limit problem for convex bodies, we study normal approximation of linear functionals of high-dimensional
random vectors with various types of symmetries. In particular, we obtain results for distributions which are coordinatewise
symmetric, uniform in a regular simplex, or spherically symmetric. Our proofs are based on Stein’s method of exchangeable
pairs; as far as we know, this approach has not previously been used in convex geometry. The spherically symmetric case is
treated by a variation of Stein’s method which is adapted for continuous symmetries.
This work was done while at Stanford University. 相似文献
957.
Passive methods of remote analysis of waste gases of industrial enterprises and aircrafts engines and gases ejected in eruptions of volcanos, in fires, and in other processes disturbing the atmosphere are now of limited utility because of the lack of well-developed mathematical techniques for solving the inverse problems of gas analysis. However, the advantage of these methods is obvious, since the equipment is limited to a receiving device and the gas medium serves as a radiator. At the same time, in modern techniques, the interpretation of measurements of emissivities of gases is performed using a phenomenological approach such that experimental data on radiation characteristics of various objects are approximated by simple polynomial relations whose coefficients are determined by minimization methods. This approach does not allow one to investigate the mechanism of the processes occurring in a radiating medium and gives no way of solving the inverse problem of monitoring the composition and thermodynamic parameters of a medium which disturbs the atmosphere by thermal effects. In elaborating theoretical methods of gas analysis, the elaboration of the direct problem of calculation of radiating characteristics of gases is of importance, since it is not clear how the emissivity of a gas medium depends on its thermodynamic parameters. This paper is devoted to the above problem. Here, the error is estimated that arises in modeling a nonuniform gas medium with an actual temperature distribution, which linearly depends on coordinate, by a uniform gas layer. It is shown that the difference between the radiation intensities calculated for uniform and nonuniform media can be significant in the practically important case where the recording device is in a zone of normal temperatures. This implies that the error of reconstruction of the spectroscopic and molecular parameters of gaseous compounds from high-temperature measurements of the radiating and absorbing characteristics should take into account the thermodynamic nonuniformity of the medium. 相似文献
958.
959.
Frank W. Schmidt 《Linear and Multilinear Algebra》1991,30(3):229-230
This section appears from time to time. Contributions are invited, and should be submitted to R. C. Thompson, Mathematics Department, University of California, Santa Barbara, CA 93106. 相似文献
960.
Joseph Majdalani Sjoerd W. Rienstra 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(2):289-308
The bidirectional vortex refers to the bipolar, coaxial swirling motion that can be triggered, for example, in cyclone separators
and some liquid rocket engines with tangential aft-end injectors. In this study, we present an exact solution to describe
the corresponding bulk motion in spherical coordinates. To do so, we examine both linear and nonlinear solutions of the momentum
and vorticity transport equations in spherical coordinates. The assumption will be that of steady, incompressible, inviscid,
rotational, and axisymmetric flow. We further relate the vorticity to some power of the stream function. At the outset, three
possible types of similarity solutions are shown to fulfill the momentum equation. While the first type is incapable of satisfying
the conditions for the bidirectional vortex, it can be used to accommodate other physical settings such as Hill’s vortex.
This case is illustrated in the context of inviscid flow over a sphere. The second leads to a closed-form analytical expression
that satisfies the boundary conditions for the bidirectional vortex in a straight cylinder. The third type is more general
and provides multiple solutions. The spherical bidirectional vortex is derived using separation of variables and the method
of variation of parameters. The three-pronged analysis presented here increases our repertoire of general mean flow solutions
that rarely appear in spherical geometry. It is hoped that these special forms will permit extending the current approach
to other complex fluid motions that are easier to capture using spherical coordinates. 相似文献