全文获取类型
收费全文 | 14233篇 |
免费 | 2171篇 |
国内免费 | 692篇 |
专业分类
化学 | 1253篇 |
晶体学 | 153篇 |
力学 | 3541篇 |
综合类 | 180篇 |
数学 | 5821篇 |
物理学 | 6148篇 |
出版年
2024年 | 27篇 |
2023年 | 123篇 |
2022年 | 181篇 |
2021年 | 232篇 |
2020年 | 399篇 |
2019年 | 339篇 |
2018年 | 292篇 |
2017年 | 414篇 |
2016年 | 435篇 |
2015年 | 355篇 |
2014年 | 622篇 |
2013年 | 940篇 |
2012年 | 668篇 |
2011年 | 747篇 |
2010年 | 663篇 |
2009年 | 749篇 |
2008年 | 847篇 |
2007年 | 914篇 |
2006年 | 852篇 |
2005年 | 818篇 |
2004年 | 718篇 |
2003年 | 763篇 |
2002年 | 673篇 |
2001年 | 566篇 |
2000年 | 533篇 |
1999年 | 467篇 |
1998年 | 390篇 |
1997年 | 347篇 |
1996年 | 247篇 |
1995年 | 228篇 |
1994年 | 170篇 |
1993年 | 193篇 |
1992年 | 149篇 |
1991年 | 140篇 |
1990年 | 107篇 |
1989年 | 73篇 |
1988年 | 78篇 |
1987年 | 72篇 |
1986年 | 59篇 |
1985年 | 85篇 |
1984年 | 70篇 |
1983年 | 32篇 |
1982年 | 52篇 |
1981年 | 53篇 |
1980年 | 33篇 |
1979年 | 36篇 |
1978年 | 43篇 |
1977年 | 35篇 |
1976年 | 22篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
本文引入并研究一类新的广义集值强非线性拟变分不等式,讨论这类广义集值强非线性拟变分不等式解的存在性以及由算法所构造的迭代序列的收敛性.我们的结果改进和发展了Noor,Siddiqi和Ansari等人近期的一些主要结果. 相似文献
82.
A theoretical model of Dewangan, in which the total scattering wave function is approximated by a distorted wave containing
two Coulomb wave functions, is discussed and its relation with the Brauner-Briggs-Klar model for ionization is examined. An
important feature of the theory is that it includes a second Born amplitude naturally and in addition, contains, albeit approximately,
both real and imaginary parts of all higher order Born terms. The theory is applied to study the 1s→2s excitation of hydrogen by electrons in the energy range 54.4 to 400eV. The differential and integral cross sections predicted
by the theory are compared with the results of other theories and experimental data at 54.4eV and a good agreement is found. 相似文献
83.
本文通过使用化多时滞为单时滞的技巧,研究了一类广泛的非线性泛函微分方程解的振动性,所得结果包含和改进了Hunt,Yorke等多人的结果. 相似文献
84.
A free-piston driver that employs entropy-raising shock processes with diaphragm rupture has been constructed, which promises
significant theoretical advantages over isentropic compression. Results from a range of conditions with helium and argon driver
gases are reported. Significant performance gains were achieved in some test cases. Heat losses are shown to have a strong
effect on driver processes. Measurements compare well with predictions from a quasi-one-dimensional numerical code.
Received 7 September 1996 / Accepted 5 October 1996 相似文献
85.
Linear and nonlinear optical properties of racemic (±)2-(α-methylbenzylamino)-5-nitropyridine ((±)MBANP) single crystals have been comprehensively investigated and compared with those of the enantiomorph (–)2-(α-methylbenzylamino)-5-nitropyridine ((–)MBANP) crystals. (±)MBANP crystal exhibits very high chemical and physical stability, but relatively small nonlinear optical coefficients (d31 = 6.8 pm/V, d32 = 4.7 pm/V, d33 = 0.84 pm/V). A comparison between the nonlinear optical coefficients of (±)MBANP and (–)MBANP demonstrates the validity of the oriented-gas model in molecular crystals that neglects all the contributions from intermolecular interaction. 相似文献
86.
一类非线性单调型方程的区域分裂法 总被引:1,自引:0,他引:1
本文考虑了一类非线性单调问题的加性Schwgrz交替法和异步平行算法,并得到了在能量模意义下的收敛性结果,最后还讨论了格式的有限元离散。 相似文献
87.
L. E. Payne G. A. Philippin V. Proytcheva 《Mathematical Methods in the Applied Sciences》2007,30(15):1885-1898
In this paper, we investigate the continuous dependence on the geometry and the initial time for solutions u( x , t) of a class of nonlinear parabolic initial‐boundary value problems. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
88.
R. Centore P. Riccio S. Fusco A. Carella A. Quatela S. Schutzmann F. Stella F. De Matteis 《Journal of polymer science. Part A, Polymer chemistry》2007,45(13):2719-2725
We have prepared new polyesters containing quadratic, nonlinear optical (NLO) active chromophores covalently incorporated into the main chain. In these polymers, the sequence of the chromophore units along the main chain is rigorously head to tail. All the polyesters are processable, both in the melt and in solution. For one polyester, a full second‐order NLO characterization has been performed. An out‐of‐resonance d33 coefficient of 21 pm/V at 1368 nm has been measured. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2719–2725, 2007 相似文献
89.
We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam,
which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive
relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and
focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has
been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are
elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius
of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed
to convert a circular Gaussian beam into an elliptic Gaussian beam. 相似文献
90.
E. V. Ermanyuk 《Experiments in fluids》2002,32(2):242-251
This paper presents a study on affine similitude for the force coefficients of an arbitrary body oscillating in a uniformly
stratified fluid. A simple formula is derived that gives a relation between the force coefficients for a body oscillating
in homogeneous and uniformly stratified ideal fluids. In particular, it implies the existence of a universal nondimensional
similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by
vertical dilation of the initial coordinate system. Theoretical results are verified by experiments with a set of spheroids
having different length-to-diameter ratios. The experimental technique for evaluation of the frequency-dependent force coefficients
is based on Fourier analysis of the time-history of damped oscillation tests.
Received: 25 September 2000 / Accepted: 6 July 2001 Published online: 29 November 2001 相似文献