全文获取类型
收费全文 | 12061篇 |
免费 | 659篇 |
国内免费 | 281篇 |
专业分类
化学 | 7102篇 |
晶体学 | 125篇 |
力学 | 323篇 |
综合类 | 15篇 |
数学 | 2170篇 |
物理学 | 3266篇 |
出版年
2023年 | 96篇 |
2022年 | 111篇 |
2021年 | 224篇 |
2020年 | 236篇 |
2019年 | 237篇 |
2018年 | 287篇 |
2017年 | 279篇 |
2016年 | 571篇 |
2015年 | 460篇 |
2014年 | 513篇 |
2013年 | 976篇 |
2012年 | 723篇 |
2011年 | 806篇 |
2010年 | 544篇 |
2009年 | 477篇 |
2008年 | 529篇 |
2007年 | 410篇 |
2006年 | 325篇 |
2005年 | 263篇 |
2004年 | 223篇 |
2003年 | 231篇 |
2002年 | 245篇 |
2001年 | 180篇 |
2000年 | 146篇 |
1999年 | 149篇 |
1998年 | 135篇 |
1997年 | 126篇 |
1996年 | 125篇 |
1995年 | 117篇 |
1994年 | 110篇 |
1993年 | 95篇 |
1992年 | 105篇 |
1991年 | 93篇 |
1990年 | 82篇 |
1988年 | 83篇 |
1987年 | 97篇 |
1986年 | 88篇 |
1985年 | 116篇 |
1984年 | 107篇 |
1983年 | 91篇 |
1982年 | 89篇 |
1981年 | 86篇 |
1980年 | 120篇 |
1979年 | 90篇 |
1978年 | 114篇 |
1977年 | 141篇 |
1976年 | 93篇 |
1975年 | 88篇 |
1974年 | 97篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
81.
82.
The existence and semiclassical limit of the solution to one-dimensional transient quantum drift-diffusion model in semiconductor
simulation are discussed. Besides the proof of existence of the weak solution, it is also obtained that the semiclassical
limit of this solution solves the classical drift-diffusion model. The key estimates rest on the entropy inequalities derived
from separation of quantum quasi-Fermi level. 相似文献
83.
Gašper Jaklič Jernej Kozak Marjeta Krajnc Vito Vitrih Emil Žagar 《Numerical Algorithms》2007,45(1-4):49-60
In this paper, three-pencil lattices on triangulations are studied. The explicit representation of a lattice, based upon barycentric
coordinates, enables us to construct lattice points in a simple and numerically stable way. Further, this representation carries
over to triangulations in a natural way. The construction is based upon group action of S
3 on triangle vertices, and it is shown that the number of degrees of freedom is equal to the number of vertices of the triangulation.
相似文献
84.
Jin Kyu Park Dong Hun Lee Bok Ju Song Jae Buem Oh Hwan Kyu Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1326-1342
We have designed and synthesized novel perfluorinated polyimides with 3D controlled structure. At first, we successfully developed the new synthetic routes to diamines with pendant bulky perfluorinated aromatic units in a multi‐step synthetic procedure. Novel perfluorinated polyimides were prepared in a two‐step reaction in N‐methyl‐2‐pyrrolidinone (NMP) solution: The first step was for the synthesis of polyamic acids (PAAs) and the second reaction was for the imidization of PAA. The polymer yield was over 89% and the inherent viscosity of PAAs was in the range of 0.24–0.36 dL/g. The thin films were prepared by spin‐coating the PAA solution in NMP onto various substrates such as a Si wafer or a KBr pellet, dried at 80 °C and further cured at 230 °C. The resultant polyimides are thermally stable over 400 °C. The refractive index and birefringence of the resultant polyimides are 1.5858–1.6452 and 0.01–0.005, respectively. The refractive index of polyimide decreases with increasing the fluorine content. The copolymerization and the ether linkages into the backbone reduce the birefringence of polyimides. Surprisingly, the pendant ether linkage is not a crucial factor in reducing the polyimide birefringence. Their birefringence is comparatively very low, compared with that of previous polyimides. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1326–1342, 2006 相似文献
85.
Abull is the (self-complementary) graph with verticesa, b, c, d, e and edgesab, ac, bc, bd, ce; a graphG is calledBerge if neitherG not its complement contains a chordless cycle whose length is odd and at least five. We prove that bull-free Berge graphs are perfect; a part of our argument relies on a new property of minimal imperfect graphs.This work was done while both authors were at the School of Computer Science, McGill University; support by NSERC is gratefully acknowledged. 相似文献
86.
The composting of organic solid waste, the mixture of fruit and vegetable leftovers enriched with night soil, was investigated
in a closed thermally insulated reactor. It was found that 80.9 % of the original substrate biodegraded after 14 days. A mathematical
model of the column reactor was proposed where the biodegradation rate of the organic solid waste was described using simple
n-thorder kinetics. A good prediction of process performance was obtained using the proposed kinetics and experimentally obtained
reaction heat.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
87.
高分子阳离子絮凝剂用于炼油废水处理研究 总被引:15,自引:0,他引:15
用聚二甲基二烯丙基氯化铵型高分子阳离子絮凝剂处理炼油废水考察了险油和化学耗氧量的动态变化规律。对产生的浮渣性质及滤饼的成份进行了研究。并且与聚合铝的处理效果进行对照。研究结果表明,HCA除油和化学耗管氧量的性能优于PAC,HCA产生的浮渣是PAC的三分之一,而浮渣中的含油量则是PAC的三倍。 相似文献
88.
叙述一种新的光电复合测量技术,它集CCD摄像显示,微机信息采集与处理,光不投影放大,显微镜目视判读为一体,可对微粒大小及其空间分布实行多通道测量,观察和分析。 相似文献
89.
A. Janušauskas 《Lithuanian Mathematical Journal》1996,36(1):22-31
Institute of Mathematics and Informatics. Akademijos 4, 2600 Vilnius, Lithuania. Translated from Lietuvos Matematikos Rinkinys.
Vol. 36, No. 1, pp. 27–38, January–March,. 1996. 相似文献
90.
Summary. The dimensional reduction method for solving boundary value problems of Helmholtz's equation in domain by replacing them with systems of equations in dimensional space are investigated. It is proved that the existence and uniqueness for the exact solution and the dimensionally reduced solution of the boundary value problem if the input data on the faces are in some class of functions. In addition, the difference
between and in is estimated as and are fixed. Finally, some numerical experiments in a domain are given in order to compare theretical results.
Received April 2, 1996 / Revised version received July 30, 1990 相似文献