全文获取类型
收费全文 | 486918篇 |
免费 | 4948篇 |
国内免费 | 1656篇 |
专业分类
化学 | 264994篇 |
晶体学 | 7147篇 |
力学 | 20101篇 |
综合类 | 12篇 |
数学 | 57035篇 |
物理学 | 144233篇 |
出版年
2020年 | 3737篇 |
2019年 | 4008篇 |
2018年 | 4933篇 |
2017年 | 4751篇 |
2016年 | 7652篇 |
2015年 | 5237篇 |
2014年 | 7731篇 |
2013年 | 21661篇 |
2012年 | 16256篇 |
2011年 | 20034篇 |
2010年 | 13380篇 |
2009年 | 13244篇 |
2008年 | 18760篇 |
2007年 | 19057篇 |
2006年 | 18101篇 |
2005年 | 16414篇 |
2004年 | 14744篇 |
2003年 | 13258篇 |
2002年 | 13013篇 |
2001年 | 14390篇 |
2000年 | 11178篇 |
1999年 | 8690篇 |
1998年 | 7231篇 |
1997年 | 7107篇 |
1996年 | 6963篇 |
1995年 | 6172篇 |
1994年 | 6003篇 |
1993年 | 5862篇 |
1992年 | 6399篇 |
1991年 | 6341篇 |
1990年 | 6025篇 |
1989年 | 5789篇 |
1988年 | 6015篇 |
1987年 | 5708篇 |
1986年 | 5465篇 |
1985年 | 7630篇 |
1984年 | 7832篇 |
1983年 | 6382篇 |
1982年 | 6941篇 |
1981年 | 6880篇 |
1980年 | 6510篇 |
1979年 | 6774篇 |
1978年 | 6897篇 |
1977年 | 6885篇 |
1976年 | 6852篇 |
1975年 | 6595篇 |
1974年 | 6466篇 |
1973年 | 6754篇 |
1972年 | 4139篇 |
1971年 | 3333篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
The Wheeler–DeWitt equation of arbitrary Hartle–Hawking factor ordering for several minisuperspace universe models, such as the pure gravity Friedmann–Robertson–Walker and Taub ones, is mapped onto the dynamics of corresponding classical oscillators. The latter ones are studied by the classical Ermakov invariant method, which is a natural approach in this context. For the more realistic case of a minimally coupled massive scalar field, one can study, within the same type of approach, the corresponding squeezing features as a possible means of describing cosmological evolution. Finally, we comment on the analogy with the accelerator physics. 相似文献
32.
Yu. K. Voron'ko A. B. Kudryavtsev V. V. Osiko E. V. Sorokin 《Journal of Applied Spectroscopy》1991,55(4):953-957
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 535–540, October, 1991. 相似文献
33.
R. J. Vanderbei 《Mathematical Programming》1989,43(1-3):31-44
The affine-scaling modification of Karmarkar's algorithm is extended to solve problems with free variables. This extended primal algorithm is used to prove two important results. First the geometrically elegant feasibility algorithm proposed by Chandru and Kochar is the same algorithm as the one obtained by appending a single column of residuals to the constraint matrix. Second the dual algorithm as first described by Adler et al., is the same as the extended primal algorithm applied to the dual. 相似文献
34.
A new geometrical method to determine the surface damage threshold for ultrashort pulses is presented. It consists in the formation of a surface damage profile by a movement of the sample across the laser beam focus. A single measurement of the maximum transversal dimension of this damage profile, which depends solely on the laser beam power, is used to calculate the local damage threshold intensity. It is also theoretically shown that the damage in the transverse dimension can be controlled under the diffraction-limited spot. 相似文献
35.
A piecewise linearization method based on the linearization of nonlinear ordinary differential equations in small intervals, that provides piecewise analytical solutions in each interval and smooth solutions everywhere, is developed for the study of the limit cycles of smooth and non-smooth, conservative and non-conservative, nonlinear oscillators. It is shown that this method provides nonlinear maps for the displacement and velocity which depend on the previous values through the nonlinearity and its partial derivatives with respect to time, displacement and velocity, and yields non-standard finite difference formulae. It is also shown by means of five examples that the piecewise linearization method presented here is more robust and yields more accurate (in terms of displacement, energy and frequency) solutions than the harmonic balance procedure, the method of slowly varying amplitude and phase, and other non-standard finite difference equations. 相似文献
36.
I. J. Tchoupaeva 《Journal of Mathematical Sciences》2006,135(5):3409-3419
Some geometric theorems can be stated in coordinate-free form as polynomials in Grassman algebra and can be proven by the anticommutative Gröbner basis method. In this article, we analyze some properties of both sets of hypotheses and conclusions of the theorem. 相似文献
37.
R. J. Hinde 《Few-Body Systems》2006,38(2-4):187-191
We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2-H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set
for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster
theory and find that a fully iterative treatment of connected triples may be required to estimate the H2-H2 vibrational coupling accurately using coupled cluster theory. 相似文献
38.
J. M. Rubi 《Journal of statistical physics》2006,123(2):497-498
39.
In this paper we study root system generalizations of the quantum Bose-gas on the circle with pair-wise delta-function interactions.
The underlying symmetry structures are shown to be governed by the associated graded algebra of Cherednik's (suitably filtered)
degenerate double affine Hecke algebra, acting by Dunkl-type differential-reflection operators. We use Gutkin's generalization
of the equivalence between the impenetrable Bose-gas and the free Fermi-gas to derive the Bethe ansatz equations and the Bethe
ansatz eigenfunctions. 相似文献
40.
We study oscillation in a gyrotron with allowance for reflections from an output horn. Regions with different system behaviors,
such as stationary oscillation, self-modulation, and complex-dynamics regimes are found in the parameter plane. The scenarios
of appearance of chaotic oscillations are considered. It is shown that they can emerge via either a sequence of period-doubling
bifurcations or destruction of quasiperiodic motion. For chaotic attractors, Lyapunov exponents are calculated and their dimensions
are estimated on the basis of the Kaplan-Yorke formula. The dimension values turn out to be anomalously large, which is stipulated
by the presence of a large number of high-Q eigenmodes in the gyrotron cavity due to operation near the cutoff frequency of
an electrodynamic system.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 10, pp. 887–899, October 2006. 相似文献