全文获取类型
收费全文 | 1441篇 |
免费 | 53篇 |
国内免费 | 11篇 |
专业分类
化学 | 939篇 |
晶体学 | 40篇 |
力学 | 40篇 |
数学 | 192篇 |
物理学 | 294篇 |
出版年
2023年 | 11篇 |
2022年 | 31篇 |
2021年 | 35篇 |
2020年 | 41篇 |
2019年 | 27篇 |
2018年 | 31篇 |
2017年 | 36篇 |
2016年 | 52篇 |
2015年 | 32篇 |
2014年 | 50篇 |
2013年 | 103篇 |
2012年 | 87篇 |
2011年 | 98篇 |
2010年 | 52篇 |
2009年 | 44篇 |
2008年 | 52篇 |
2007年 | 67篇 |
2006年 | 66篇 |
2005年 | 55篇 |
2004年 | 48篇 |
2003年 | 43篇 |
2002年 | 31篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 7篇 |
1974年 | 7篇 |
排序方式: 共有1505条查询结果,搜索用时 15 毫秒
121.
122.
123.
The purpose of this note is to generalize a theorem of Tamura’s [3] providing a self-contained and, we think, more elementary
proof than Tamura’s in that it avoids using the theory of contents. Tamura’s result states that a semigroup S satisfies an
identify xy=f(x,y) with f(x,y) a word of length greater than 2 which starts with y and ends in x if and only if S is an inflation
of a semilattice of groups satisfying the same identity. We investigate semigroups as in Tamura’s Theorem, except that we
permit f(x,y) to vary with x and y. 相似文献
124.
125.
A new bis-andrographolide ether from Andrographis paniculata nees and evaluation of anti-HIV activity 总被引:3,自引:0,他引:3
Reddy VL Reddy SM Ravikanth V Krishnaiah P Goud TV Rao TP Ram TS Gonnade RG Bhadbhade M Venkateswarlu Y 《Natural product research》2005,19(3):223-230
Novel bis-andrographolide ether (1) and six known compounds andrographolide, 14-deoxy-11,12-didehydroandrographolide, andrograpanin, 14-deoxyandrographolide, (+/-)-5-hydroxy-7,8-dimethoxyflavanone, and 5-hydroxy-7,8-dimethoxyflavone have been isolated from the aerial parts of Andrographis paniculata and their structures were established by spectral data. All the isolates were tested for the anti-HIV and cytotoxic activity. 相似文献
126.
Estimation of frequency-averaged loss factors by the power injection and the impulse response decay methods 总被引:2,自引:0,他引:2
This paper describes a comparison, both analytically and experimentally, between two widely used loss factor estimation techniques frequently used in statistical energy analysis. Analytical models of simple spring/mass/damper systems were created to compare frequency-averaged loss factor values from the single subsystem power injection method and the impulse response decay method. The parameters of the analytical models were varied to study the effects of the total number of modes, amount of damping, location of modes within frequency bands, and the width of the frequency bands on loss factor estimation. The analytical study shows that both methods give accurate loss factor values as long as the damping values remain realistic for linear systems and at least one modal resonance is present in each frequency band. These analytical results were verified experimentally by measuring the loss factors of simple steel plates, with and without damping treatments applied. 相似文献
127.
A data-processing technique is proposed for use with conventional frequency-chirped absorption spectroscopy to ensure accurate mapping of spectral features into time-domain signatures with arbitrarily fast readout chirp rates. This technique recovers the spectrum from a signal that is distorted owing to the fast chirp rate and therefore facilitates fast measurement of the spectral features over a broad spectral range with high resolution. Both numerical simulations and experimental results are presented. 相似文献
128.
[reaction: see text] Lewis acid-promoted addition of allyltri-n-butylstannane to o-quinonediimines afforded tetrahydroquinoxaline derivatives or allylated amides depending on the nature of the substituent on imine nitrogen. 相似文献
129.
Prakash TP Püschl A Lesnik E Mohan V Tereshko V Egli M Manoharan M 《Organic letters》2004,6(12):1971-1974
[structure: see text] Oligonucleotides with a novel 2'-O-[2-(guanidinium)ethyl] (2'-O-GE) modification have been synthesized using a novel protecting group strategy for the guanidinium group. This modification enhances the binding affinity of oligonucleotides to RNA as well as duplex DNA (DeltaT(m) 3.2 degrees C per modification). The 2'-O-GE modified oligonucleotides exhibited exceptional resistance to nuclease degradation. The crystal structure of a palindromic duplex formed by a DNA oligonucleotide with a single 2'-O-GE modification was solved at 1.16 A resolution. 相似文献
130.
Bruhat-Chevalley Order in Reductive Monoids 总被引:1,自引:1,他引:0
Mohan S. Putcha 《Journal of Algebraic Combinatorics》2004,20(1):33-53