全文获取类型
收费全文 | 925篇 |
免费 | 17篇 |
国内免费 | 4篇 |
专业分类
化学 | 556篇 |
晶体学 | 15篇 |
力学 | 38篇 |
数学 | 105篇 |
物理学 | 232篇 |
出版年
2022年 | 18篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 26篇 |
2017年 | 13篇 |
2016年 | 35篇 |
2015年 | 5篇 |
2014年 | 20篇 |
2013年 | 35篇 |
2012年 | 33篇 |
2011年 | 49篇 |
2010年 | 22篇 |
2009年 | 25篇 |
2008年 | 45篇 |
2007年 | 40篇 |
2006年 | 39篇 |
2005年 | 44篇 |
2004年 | 35篇 |
2003年 | 30篇 |
2002年 | 28篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1988年 | 7篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 29篇 |
1984年 | 18篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 4篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1933年 | 4篇 |
排序方式: 共有946条查询结果,搜索用时 46 毫秒
1.
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
2.
Ariel M. Sarotti 《Tetrahedron letters》2004,45(44):8203-8206
A two-step general approach to a new chiral auxiliary starting from levoglucosenone is reported. The compound is obtained by a [4+2] cycloaddition reaction with anthracene followed by a diastereoselective reduction of the C-2 keto function in high overall yield. The auxiliary has been used as chiral template in an asymmetric Diels-Alder reaction of the corresponding acrylic ester derivative with cyclopentadiene and shown to be efficient for asymmetric induction. 相似文献
3.
Experiments concerning the properties of soap films have recently been carried out and these systems have been proposed as experimental versions of theoretical two‐dimensional liquids. A silk filament introduced into a flowing soap film, was seen to demonstrate various stable modes, and these were, namely, a mode in which the filament oscillates and one in which the filament is stationary and aligns with the flow of the liquid. The system could be forced from the oscillatory mode into the non‐ oscillatory mode by varying the length of the filament. In this article we use numerical and computational techniques in order to simulate the strongly coupled behaviour of the filament and the fluid. Preliminary results are presented for the specific case in which the filament is seen to oscillate continuously for the duration of our simulation. We also find that the filament oscillations are strongly suppressed when we reduce the effective length of the filament. We believe that these results are reminiscent of the different oscillatory and non‐oscillatory modes observed in experiment. The numerical solutions show that, in contrast to experiment, vortices are created at the leading edge of the filament and are preferentially grown in the curvature of the filament and are eventually released from the trailing edge of the filament. In a similar manner to oscillating hydrofoils, it seems that the oscillating filaments are in a minimal energy state, extracting sufficient energy from the fluid to oscillate. In comparing numerical and experimental results it is possible that the soap film does have an effect on the fluid flow especially in the boundary layer where surface tension forces are large. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
Danny E. Akin W. Herbert Morrison III Luanne L. Rigsby Franklin E. Barton II David S. Himmelsbach Kevin B. Hicks 《Applied biochemistry and biotechnology》2006,129(1-3):104-116
Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion
to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment
significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf
fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave
up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those
more suitable as residues for soil erosion control. 相似文献
5.
6.
This paper develops a theory for the global solution of nonconvex optimization problems with parameter-embedded linear dynamic systems. A quite general problem formulation is introduced and a solution is shown to exists. A convexity theory for integrals is then developed to construct convex relaxations for utilization in a branch-and-bound framework to calculate a global minimum. Interval analysis is employed to generate bounds on the state variables implied by the bounds on the embedded parameters. These bounds, along with basic integration theory, are used to prove convergence of the branch-and-bound algorithm to the global minimum of the optimization problem. The implementation of the algorithm is then considered and several numerical case studies are examined thoroughly 相似文献
7.
Ariel Fernández 《International Journal of Theoretical Physics》1991,30(2):129-136
We establish a mechanism for energy localization in regions of the sugar-phosphate RNA backbone which leads to the formation of transesterification or hydrolysis hot spots. In particular, our results account for the site specificity of the covalent cyclization and cycle reopening in the catalytic intervening sequence (IVS) of a ribosomal RNA. 相似文献
8.
In this paper we study the 2-dimension of a finite poset from the topological point of view. We use homotopy theory of finite
topological spaces and the concept of a beat point to improve the classical results on 2-dimension, giving a more complete answer to the problem of all possible 2-dimensions
of an n-point poset.
相似文献
9.
After administration of [3H] cortisol, the specific radioactivity of the urinary cortisol metabolites is determined by chemical conversion of the 17-hydroxycorticosteroid conjugates to 17-ketosteroids, extraction with Sep-Pak C18 cartridges, derivatisation with 2,4-dinitrophenylhydrazine and isocratic reversed-phase high-performance liquid chromatography. This allows on-line measurement of ultra-violet absorbance; fractions are collected and 3H is measured by scintillation counting. Alternatively extraction and chromatography are done after enzymic hydrolysis of the steroid conjugates, and the major metabolites are determined colorimetrically in the fractions. The results from the two methods were consistent with each other and with published data. 相似文献
10.