全文获取类型
收费全文 | 8994篇 |
免费 | 481篇 |
国内免费 | 69篇 |
专业分类
化学 | 6602篇 |
晶体学 | 77篇 |
力学 | 202篇 |
数学 | 823篇 |
物理学 | 1840篇 |
出版年
2023年 | 36篇 |
2022年 | 113篇 |
2021年 | 168篇 |
2020年 | 146篇 |
2019年 | 168篇 |
2018年 | 135篇 |
2017年 | 136篇 |
2016年 | 291篇 |
2015年 | 265篇 |
2014年 | 325篇 |
2013年 | 567篇 |
2012年 | 679篇 |
2011年 | 734篇 |
2010年 | 469篇 |
2009年 | 360篇 |
2008年 | 611篇 |
2007年 | 550篇 |
2006年 | 547篇 |
2005年 | 460篇 |
2004年 | 408篇 |
2003年 | 354篇 |
2002年 | 324篇 |
2001年 | 172篇 |
2000年 | 163篇 |
1999年 | 104篇 |
1998年 | 87篇 |
1997年 | 74篇 |
1996年 | 92篇 |
1995年 | 87篇 |
1994年 | 62篇 |
1993年 | 52篇 |
1992年 | 42篇 |
1991年 | 37篇 |
1990年 | 46篇 |
1989年 | 48篇 |
1988年 | 32篇 |
1987年 | 30篇 |
1986年 | 25篇 |
1985年 | 45篇 |
1984年 | 31篇 |
1983年 | 30篇 |
1982年 | 30篇 |
1981年 | 33篇 |
1979年 | 36篇 |
1978年 | 23篇 |
1977年 | 27篇 |
1976年 | 29篇 |
1975年 | 21篇 |
1974年 | 21篇 |
1973年 | 33篇 |
排序方式: 共有9544条查询结果,搜索用时 296 毫秒
41.
On the harmonic Bergman space of the half-space, we give characterizations for an arbitrary positive Toeplitz operator to
be a Schatten (or Schatten-Herz) class operator in terms of averaging functions and Berezin transforms. Examples are provided
to show that various results are sharp.
This research was supported by KOSEF(R01-2003-000-10243-0). 相似文献
42.
Ju Yeon Woo Eun Hee Kim Byung Kyu Kim 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5590-5596
Doping of conductive fullerene particles to the formulation of conventional holographic polymer dispersed liquid crystal‐induced dual effects of reducing both droplet coalescence and operating voltage. Fullerene induced an induction period which otherwise does not exist, followed by a gradual increase of diffraction efficiency to a saturation value being increased with increasing fullerene content. The increased diffraction efficiency was caused by the decreased droplet coalescence which was due to the hindered migration of LC by the fullerene particles. On the other hand, doped fullerene particles augmented the conductivity of polymer phase and hence the local electrical field imposed on LC droplet, which overcome the threshold for driving and reduced operating voltage and response times. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5590–5596, 2007 相似文献
43.
Based on the matrix-analytic approach to fluid flows initiated by Ramaswami, we develop an efficient time dependent analysis
for a general Markov modulated fluid flow model with a finite buffer and an arbitrary initial fluid level at time 0. We also
apply this to an insurance risk model with a dividend barrier and a general Markovian arrival process of claims with possible
dependencies in successive inter-claim intervals and in claim sizes. We demonstrate the implementability and accuracy of our
algorithms through a set of numerical examples that could also serve as test cases for comparing other solution approaches.
相似文献
44.
Nusselt number correlations for heat transfer to small spheres in thermal plasma flows 总被引:1,自引:0,他引:1
Seven different equations predicting heat transfer rates to small spheres in plasma flows are examined considering argon and nitrogan as plasma gases from 300 to 21,000 K at 1 atm. For argon there is a general consensus up to 9000 K, beyond which wide deviations in behavior occur. For nitrogen, the seven correlations are in good agreement up to 4000 K, but show substantial deviations beyond this value. Comparisons with the sparsely available experimental data are made for argon from 300 to 17,000 K and for nitrogen up to 5500 K. Disagreement between the various correlations and experiment can exceed one order of magnitude. 相似文献
45.
Young Wook Kim Seong-Deog Yang 《Proceedings of the American Mathematical Society》2006,134(11):3379-3390
We prove the existence of an infinite family of complete spacelike maximal surfaces with singularities in Lorentz-Minkowski three-space and study their properties. These surfaces are distinguished by their number of handles and have two elliptic catenoidal ends.
46.
Mary Cheung Alex B. Young Alex G. Harrison 《Journal of the American Society for Mass Spectrometry》1994,5(6):553-557
O? and OH? react with fatty acid methyl esters (FAMES) under chemical ionization conditions both as Bronsted bases to form [M - H]? and as nucleophiles to form the carboxylate ion RCOO?. O? shows a much greater tendency to react as a nucleophile than does OH?. The [M - H]? ions fragment by elimination of CH3OH, with unsaturation in certain positions in the fatty acid hydrocarbon chain promoting this elimination for unknown reasons. The reaction of O? and OH? with triacylglycerols leads to [M - H]?, characteristic of the molecular mass, and to carboxylate ions characteristic of the fatty acid(s) present in the lipid. The presence of the three ester functions in the lipids greatly enhances the formation of carboxylate ions compared to the FAMES. 相似文献
47.
Ranked-set sampling is useful when measurements are destructive or costly to obtain but ranking of the observations is relatively easy. The Wilcoxon signed rank test statistic based on the ranked-set sample is considered. We compared the asymptotic relative efficiencies of the RSS Wilcoxon signed rank test statistic with respect to the SRS Wilcoxon signed rank test statistic and the RSS sign test statistic. Throughout the ARE’s, the proposed test statistic is superior to the SRS Wilcoxon signed rank test statistic and the RSS sign test statistic. 相似文献
48.
A numerical model is presented to calculate V(z) and V(x, z) curves for a line focus acoustic microscope and a specimen containing a subsurface crack. In this model, a Gaussian beam which is tracked through the lens into the coupling fluid and into the specimen, interacts with the crack. The numerical approach is based on the solution of singular integral equations by the boundary element method. The system of singular integral equations follows from the conditions at the interface of the coupling fluid and the specimen and on the faces of the crack. An electromechanical reciprocity relation is used to express the voltage at the terminals of the microscope's transducer in terms of the calculated incident and back-scattered fields. V(z) and V(x, z) curves are presented for various locations and orientations of the crack. The characteristic features of the V(z) and particularly the V(x, z) curves, as they relate to crack configuration, are discussed in some detail. 相似文献
49.
50.
Do Young Kim Ji Sim Jung Young Rae Jang Kun Ho Yoo Jin Jang 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):400
We studied the growth of nanocrystalline silicon (nc-Si) thin film exhibiting a strong room temperature photoluminescence (PL) at 1.81–2.003 eV. The amorphous silicon was crystallized by Ni silicide mediated crystallization (Ni SMC) and then Secco-etched to exhibit the PL. The PL peak energy and intensity increase with increasing the metal density on the a-Si because of the reduction in the grain size down to 2 nm. The photoluminescence energy and peak intensity depend strongly on the Secco etch time because the grain size is reduced by etching the grain boundaries. 相似文献