全文获取类型
收费全文 | 4097篇 |
免费 | 72篇 |
国内免费 | 14篇 |
专业分类
化学 | 2769篇 |
晶体学 | 21篇 |
力学 | 87篇 |
数学 | 651篇 |
物理学 | 618篇 |
综合类 | 37篇 |
出版年
2016年 | 57篇 |
2015年 | 61篇 |
2014年 | 57篇 |
2013年 | 163篇 |
2012年 | 146篇 |
2011年 | 155篇 |
2010年 | 77篇 |
2009年 | 114篇 |
2008年 | 139篇 |
2007年 | 98篇 |
2006年 | 125篇 |
2005年 | 138篇 |
2004年 | 126篇 |
2003年 | 118篇 |
2002年 | 92篇 |
2001年 | 101篇 |
2000年 | 76篇 |
1999年 | 46篇 |
1998年 | 54篇 |
1997年 | 75篇 |
1996年 | 76篇 |
1995年 | 51篇 |
1994年 | 77篇 |
1993年 | 64篇 |
1992年 | 76篇 |
1991年 | 60篇 |
1990年 | 59篇 |
1989年 | 74篇 |
1988年 | 84篇 |
1987年 | 76篇 |
1986年 | 41篇 |
1985年 | 68篇 |
1984年 | 72篇 |
1983年 | 35篇 |
1982年 | 67篇 |
1981年 | 80篇 |
1980年 | 82篇 |
1979年 | 69篇 |
1978年 | 77篇 |
1977年 | 53篇 |
1976年 | 53篇 |
1975年 | 72篇 |
1974年 | 50篇 |
1973年 | 51篇 |
1972年 | 41篇 |
1971年 | 43篇 |
1970年 | 46篇 |
1969年 | 32篇 |
1967年 | 31篇 |
1966年 | 29篇 |
排序方式: 共有4183条查询结果,搜索用时 0 毫秒
41.
Groshaus JG Dujovne I Gallais Y Hirjibehedin CF Pinczuk A Tan YW Stormer H Dennis BS Pfeiffer LN West KW 《Physical review letters》2008,100(4):046804
Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020+/-0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3. 相似文献
42.
A BaTiO3 thin-film electro-optic waveguide modulator with a low half-wave voltage-length product has been demonstrated at near-infrared wavelengths of 1-1.6 microm. Half-wave voltage-length products as small as 0.25 and 0.5 V cm were measured for a 5-mm-long device at wavelengths of 973 and 1561 nm, respectively. The effective electro-optic coefficients were calculated as 420 pm/V at 973 nm and 360 pm/V at 1561 nm. Further improvements in device performance by optimizing the ferroelectric domain structure are anticipated. 相似文献
43.
Nadine Werth Mathias S. Müller Johann Meier Alexander W. Koch 《Optics Communications》2011,284(9):2317-2322
Using Laser-based Speckle-Interferometers, the shape of optically rough surfaces can be measured precisely and contactlessly from variable measuring distances even in regions of difficult access. This work is concerned with the integration of a micromirror array (MMA) into an electronic Speckle-Pattern-Interferometer. With the adaptive optics, it is intended to adapt the phasefront of a reference wave to critical surface areas of the measurement object. Yet, due to the topography of the MMA, diffraction effects occur which affect the phase and intensity of the generated wavefront. We demonstrate how these diffraction effects can be efficiently modelled by a Fraunhofer diffraction method. We compare the results of this model to theoretical data obtained by a numerical Fresnel diffraction model and to measurement data obtained from a measurement setup incorporating a multi mirror array. 相似文献
44.
Xenon ions in the metastable state 5d 4D are excited by means of a tunable dye laser at 6051 Å. The excitation is monitored by non-resonant fluorescence at 5292 Å. 相似文献
45.
46.
47.
A. Baurichter M. Deicher S. Deubler D. Forkel J. Meier H. Wolf W. Witthuhn ISOLDE Collaboration 《Applied Surface Science》1991,50(1-4):165-168
Molecule-like defect complexes have been studied at Cd acceptors in the III–V semiconductors GaAs, GaP, InP, InAs, and InSb by PAC spectroscopy. After hydrogen plasma treatment, the formation of Cd-H complexes was observed in all these compounds. Additionally, the formation and stability of Cd-S and Cd-Se pairs in GaAs have been analyzed. 相似文献
48.
Horst Elmar Winkelnkemper 《Annals of Global Analysis and Geometry》1992,10(3):209-218
Let
t
be the flow (parametrized with respect to arc length) of a smooth unit vector field v on a closed Riemannian manifold M
n
, whose orbits are geodesics. Then the (n-1)-plane field normal to v, v, is invariant under d
t
and, for each x M, we define a smooth real function
x
(t) : (1 +
i
(t)), where the i(t) are the eigenvalues of AA
T, A being the matrix (with respect to orthonormal bases) of the non-singular linear map d2t
, restricted to v at the point x
-t M
n.Among other things, we prove the
Theorem (Theorem II, below). Assume v is also volume preserving and that
x
'
(t) 0 for all x M and real t; then, if
x
t
: M M is weakly missng for some t, it is necessary that vx 0 at all x M. 相似文献
49.
Summary Forf ( C
n() and 0 t x letJ
n
(f, t, x) = (–1)n
f(–x)f
(n)(t) +f(x)f
(n)
(–t). We prove that the only real-analytic functions satisfyingJ
n
(f, t, x) 0 for alln = 0, 1, 2, are the exponential functionsf(x) = c e
x,c, . Further we present a nontrivial class of real-analytic functions satisfying the inequalitiesJ
0
(f, x, x) 0 and
0
x
(x – t)n – 1Jn(f, t, x)dt 0 (n 1). 相似文献
50.
Global optimization of concave functions subject to quadratic constraints: An application in nonlinear bilevel programming 总被引:2,自引:0,他引:2
When the follower's optimality conditions are both necessary and sufficient, the nonlinear bilevel program can be solved as a global optimization problem. The complementary slackness condition is usually the complicating constraint in such problems. We show how this constraint can be replaced by an equivalent system of convex and separable quadratic constraints. In this paper, we propose different methods for finding the global minimum of a concave function subject to quadratic separable constraints. The first method is of the branch and bound type, and is based on rectangular partitions to obtain upper and lower bounds. Convergence of the proposed algorithm is also proved. For computational purposes, different procedures that accelerate the convergence of the proposed algorithm are analysed. The second method is based on piecewise linear approximations of the constraint functions. When the constraints are convex, the problem is reduced to global concave minimization subject to linear constraints. In the case of non-convex constraints, we use zero-one integer variables to linearize the constraints. The number of integer variables depends only on the concave parts of the constraint functions.Parts of the present paper were prepared while the second author was visiting Georgia Tech and the University of Florida. 相似文献