全文获取类型
收费全文 | 418499篇 |
免费 | 17221篇 |
国内免费 | 8501篇 |
专业分类
化学 | 236465篇 |
晶体学 | 4787篇 |
力学 | 19730篇 |
综合类 | 325篇 |
数学 | 48027篇 |
物理学 | 134887篇 |
出版年
2021年 | 4465篇 |
2020年 | 5319篇 |
2019年 | 5051篇 |
2018年 | 4800篇 |
2017年 | 4449篇 |
2016年 | 7849篇 |
2015年 | 6906篇 |
2014年 | 8921篇 |
2013年 | 20763篇 |
2012年 | 18392篇 |
2011年 | 21599篇 |
2010年 | 13832篇 |
2009年 | 13637篇 |
2008年 | 18369篇 |
2007年 | 18052篇 |
2006年 | 17172篇 |
2005年 | 15420篇 |
2004年 | 13521篇 |
2003年 | 11729篇 |
2002年 | 11432篇 |
2001年 | 13308篇 |
2000年 | 10341篇 |
1999年 | 8589篇 |
1998年 | 6840篇 |
1997年 | 6678篇 |
1996年 | 6641篇 |
1995年 | 5806篇 |
1994年 | 5392篇 |
1993年 | 4989篇 |
1992年 | 5664篇 |
1991年 | 5457篇 |
1990年 | 5019篇 |
1989年 | 4670篇 |
1988年 | 4894篇 |
1987年 | 4596篇 |
1986年 | 4362篇 |
1985年 | 6143篇 |
1984年 | 6094篇 |
1983年 | 4840篇 |
1982年 | 5165篇 |
1981年 | 5191篇 |
1980年 | 4893篇 |
1979年 | 5120篇 |
1978年 | 5181篇 |
1977年 | 5167篇 |
1976年 | 5045篇 |
1975年 | 4855篇 |
1974年 | 4739篇 |
1973年 | 4860篇 |
1972年 | 2735篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Thermoelastic stress analysis was used to document the effect of composite damage on the stress distribution in three ceramic matrix composites. Composite damage was found to significantly alter the thermoelastic response of each material, with the greatest effect noted in SiC/CAS. Thermoelastic imaging of these materials affords a more complete picture of how the various damage mechanisms affect the stress distribution. In particular, a stress concentration factor computed from thermoelastic images, serves as an indicator of stress redistribution. The stress concentration factors were computed by comparing notch root to far field temperatures, and monitored after the introduction of various amounts of damage. In each material, the stress concentration factor diminished as the damaging load approached the ultimate stress. Reduction in the stress concentration is associated with local changes in modulus, mechanistically arising from combinations of fiber, matrix and interface fracture. Stress redistribution occurs as a consequence of modulus changes, leading to lower notch sensitivity in each of the tested composites. 相似文献
992.
We present some classical solutions to a gauge theory based on quadratically nonlinear Lie algebras without a central term. We observe that instanton-like and meron-like solutions force the internal fields to behave like solitons. 相似文献
993.
994.
Determination of the arc-root position in a DC plasma torch 总被引:4,自引:0,他引:4
Seungho Paik P. C. Huang J. Heberleinand E. Pfender 《Plasma Chemistry and Plasma Processing》1993,13(3):379-397
The behavior of an arc operated in the nontransferred mode with a conical-shaped cathode and a nozzle-shaped anode is studied by applying general tyro-dimensional conservation equations and auxiliary relations for the simulation of arc channel flows. The position of the arc-root attachment at the anode surface is determined by using Steenbeck's minimum principle, which postulates a minimum arc voltage for a given current and certain given boundary conditions. The overall effects of the anode-arc root on the plasma flow are, studied by comparing the results with those of the transferred mode of operation. Specific arc-channel diameters are chosen in the simulation in order to verify flit, numerical model through comparisons with experimental results. The results show that Steenbeck's minimum principle is useful for determining the position of the arc-root attachment at the anode surface. Application of this method for control of the arc-anode attachment may be valuable in the design and operation of plasma spray torches to avoid jet instabilities. 相似文献
995.
The phase behavior of binary blends of poly(ether ether ketone) (PEEK), sulfonated PEEK, and sulfamidated PEEK with aromatic polyimides is reported. PEEK was determined to be immiscible with a poly(amide imide) (TORLON 4000T). Blends of sulfonated and sulfamidated PEEK with this poly(amide imide), however, are reported here to be miscible in all proportions. Blends of sulfonated PEEK and a poly(ether imide) (ULTEM 1000) are also reported to be miscible. Spectroscopic investigations of the intermolecular interactions suggest that formation of electron donoracceptor complexes between the sulfonated/sulfamidated phenylene rings of the PEEKs and the n-phenylene units of the polyimides are responsible for this miscibility. © 1993 John Wiley & Sons, Inc. 相似文献
996.
997.
Bolian Liu 《应用数学学报(英文版)》1993,9(1):36-43
The exponent of a primitive digraph has been generalized in [2]. In this paper we obtain new parameters on generalized exponent of primitive simple graphs (symmetric primitive (0,1) matrices with zero trace) completely. 相似文献
998.
This paper provides a rigorous proof of the existence of an infinite number of black hole solutions to the Einstein-Yang/Mills equations with gauge groupSU(2), for any event horizon. It is also demonstrated that the ADM mass of each solutions is finite, and that the corresponding Einstein metric tends to the associated Schwarzschild metric at a rate 1/r
2, asr tends to infinity.Research supported in part by the NSF, Contract No. DMS-89-05205Research supported in part by the DE, Contract No. De-FG 02-88 EF 25065 相似文献
999.
In this paper we propose time-optimal convex hull algorithms for two classes of enhanced meshes. Our first algorithm computes the convex hull of an arbitrary set ofn points in the plane inO (logn) time on a mesh with multiple broadcasting of sizen×n. The second algorithm shows that the same problem can be solved inO (1) time on a reconfigurable mesh of sizen×n. Both algorithms achieve time lower bounds for their respective model of computation.This work was supported by NASA under grant NCCI-99.Additional support by the National Science Foundation under grant CCR-8909996 is gratefully acknowledged. 相似文献
1000.
High-level ab initio calculations are carried out to study the relative stability of the two hydrogen bonded structures of water-hydrogen sulfide complex, one with water as the proton donor (A) and the other with hydrogen sulfide as the proton donor (B). The results show that structure A is considerably more stable than B at the correlated level, which is in contrast with previous results obtained from Hartree-Fock calculations. 相似文献