全文获取类型
收费全文 | 346724篇 |
免费 | 1677篇 |
国内免费 | 834篇 |
专业分类
化学 | 147783篇 |
晶体学 | 4900篇 |
力学 | 21788篇 |
综合类 | 10篇 |
数学 | 71051篇 |
物理学 | 103703篇 |
出版年
2021年 | 2012篇 |
2020年 | 2090篇 |
2019年 | 2621篇 |
2018年 | 19068篇 |
2017年 | 19422篇 |
2016年 | 13039篇 |
2015年 | 3750篇 |
2014年 | 4752篇 |
2013年 | 9090篇 |
2012年 | 13372篇 |
2011年 | 26444篇 |
2010年 | 16737篇 |
2009年 | 17417篇 |
2008年 | 21663篇 |
2007年 | 26235篇 |
2006年 | 7102篇 |
2005年 | 12421篇 |
2004年 | 9663篇 |
2003年 | 9794篇 |
2002年 | 7324篇 |
2001年 | 5975篇 |
2000年 | 4703篇 |
1999年 | 3307篇 |
1998年 | 2917篇 |
1997年 | 2909篇 |
1996年 | 2850篇 |
1995年 | 2401篇 |
1994年 | 2471篇 |
1993年 | 2379篇 |
1992年 | 2635篇 |
1991年 | 2771篇 |
1990年 | 2661篇 |
1989年 | 2743篇 |
1988年 | 2667篇 |
1987年 | 2688篇 |
1986年 | 2537篇 |
1985年 | 3162篇 |
1984年 | 3245篇 |
1983年 | 2727篇 |
1982年 | 2690篇 |
1981年 | 2653篇 |
1980年 | 2462篇 |
1979年 | 2851篇 |
1978年 | 2825篇 |
1977年 | 2920篇 |
1976年 | 2945篇 |
1975年 | 2732篇 |
1974年 | 2665篇 |
1973年 | 2822篇 |
1972年 | 2140篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The finite-difference method is a numerical technique for obtaining approximate solutions to differential equations. The main
objective of the present study is to give a new aspect to the finite-difference method by using a variational derivative.
By applying this formulation, accurate values of the buckling loads of beams and frames with various end supports are obtained.
The performance of this formulation is verified by comparison with numerical examples in the literature
__________
Published in Prikladnaya Mekhanika, Vol. 41, No. 7, pp. 139–144, July 2005. 相似文献
112.
L. B. Beinenson 《Journal of Mathematical Sciences》2005,129(2):3730-3756
For an arbitrary poset H and measure ρ on H × R (where R is the real axis), we construct a monotone decreasing stochastic field ηρ and compute its finite-dimensional distributions. In the case where H is a Λ-semilattice and the measure ρ satisfies additional conditions, we compute various characteristics of the field ηρ such as the expectation of the field value at a point, variance of the field value at a point, and correlation function of the field. The described construction of random fields gives a new method for constructing positive definite functions on posets. Bibliography: 6 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 301, 2003, pp. 92–143. 相似文献
113.
Andrew Barton 《The Journal of the Operational Research Society》1987,38(10):965-974
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area. 相似文献
114.
115.
116.
Morey Timothy E. Varshney Manoj Flint Jason A. Seubert Christoph N. Smith W. Brit Bjoraker David G. Shah Dinesh O. Dennis Donn M. 《Journal of nanoparticle research》2004,6(2):159-170
Background: Although microemulsion-based nanoparticles (MEs) may be useful for drug delivery or scavenging, these benefits must be balanced against potential nanotoxicological effects in biological tissue (bio-nano interface). We investigated the actions of assembled MEs and their individual components at the bio-nano interface of thrombosis and hemolysis in human blood.
Methods: Oil-in-water MEs were synthesized using ethylbutyrate, sodium caprylate, and pluronic F-68 (ME4) or F-127 (ME6) in 0.9% NaClw/v. The effects of MEs or components on thrombosis were determined using thrombo-elastography, platelet contractile force, clot elastic modulus, and platelet counting. For hemolysis, ME or components were incubated with erythrocytes, centrifuged, and washed for measurement of free hemoglobin by spectroscopy.
Results and conclusions: The mean particle diameters (polydispersity index) for ME6 and ME4 were 23.6 ± 2.5 nm (0.362) and 14.0 ± 1.0 nm (0.008), respectively. MEs (0, 0.03, 0.3, 3 mM) markedly reduced the thromboelastograph maximal amplitude in a concentration-dependent manner (49.0 ± 4.2, 39.0 ± 5.6, 15.0 ± 8.7, 3.8 ± 1.3 mm, respectively), an effect highly correlated (r2 = 0.94) with similar changes caused by pluronic surfactants (48.7 ± 10.9, 30.7 ± 15.8, 20.0 ± 11.3, 2.0 ± 0.5) alone. Neither oil nor sodium caprylate alone affected the thromboelastograph. The clot contractile force was reduced by ME (27.3 ± 11.1–6.7 ± 3.4 kdynes/cm2, P = 0.02, n = 5) whereas the platelet population not affected (175 ± 28–182 ± 23 106/ml, P = 0.12, n = 6). This data suggests that MEs reduced platelet activity due to associated pluronic surfactants, but caused minimal changes in protein function necessary for coagulation. Although pharmacological concentrations of sodium caprylate caused hemolysis (EC50 = 213 mM), MEs and pluronic surfactants did not disrupt erythrocytes. Knowledge of nanoparticle activity and potential associated nanotoxicity at this bio-nano interface enables rational ME design for in vivo applications. 相似文献
117.
V. S. Berezinsky 《Physics of Atomic Nuclei》2003,66(3):423-434
About 400 years have passed since the great discoveries by Galileo, Kepler, and Newton, but astronomy still remains an important source of discoveries in physics. They start with puzzles, with phenomena difficult to explain, and phenomena which in fact need new physics for explanation. Do such puzzles exist now? There are at least three candidates: absence of absorption of TeV gamma radiation in extragalactic space (violation of Lorentz invariance?), absence of GZK cutoff in the spectrum of ultrahigh-energy cosmic rays (new particle physics?), tremendous energy (up to 1054 erg) released in gamma ray bursts on a time scale of a second (collapsing stars or sources of a new type?). Do these puzzles really exist? A critical review of these phenomena is given. 相似文献
118.
119.
120.
Chris Hope 《The Journal of the Operational Research Society》2003,54(11):1167-1176
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points. 相似文献