全文获取类型
收费全文 | 37627篇 |
免费 | 680篇 |
国内免费 | 167篇 |
专业分类
化学 | 20991篇 |
晶体学 | 250篇 |
力学 | 1197篇 |
综合类 | 9篇 |
数学 | 5308篇 |
物理学 | 10719篇 |
出版年
2022年 | 402篇 |
2021年 | 484篇 |
2020年 | 497篇 |
2019年 | 413篇 |
2018年 | 510篇 |
2017年 | 440篇 |
2016年 | 790篇 |
2015年 | 693篇 |
2014年 | 820篇 |
2013年 | 1433篇 |
2012年 | 1756篇 |
2011年 | 2051篇 |
2010年 | 1150篇 |
2009年 | 1070篇 |
2008年 | 1735篇 |
2007年 | 1762篇 |
2006年 | 1665篇 |
2005年 | 2104篇 |
2004年 | 2021篇 |
2003年 | 1474篇 |
2002年 | 1072篇 |
2001年 | 952篇 |
2000年 | 886篇 |
1999年 | 527篇 |
1998年 | 458篇 |
1997年 | 455篇 |
1996年 | 573篇 |
1995年 | 510篇 |
1994年 | 486篇 |
1993年 | 551篇 |
1992年 | 514篇 |
1991年 | 447篇 |
1990年 | 365篇 |
1989年 | 358篇 |
1988年 | 348篇 |
1987年 | 342篇 |
1986年 | 294篇 |
1985年 | 392篇 |
1984年 | 372篇 |
1983年 | 307篇 |
1982年 | 335篇 |
1981年 | 318篇 |
1980年 | 299篇 |
1979年 | 283篇 |
1978年 | 311篇 |
1977年 | 238篇 |
1976年 | 251篇 |
1975年 | 202篇 |
1974年 | 232篇 |
1973年 | 210篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
In intonation research, prominence-lending pitch movements have either been described on a linear or on a logarithmic frequency scale. An experiment has been carried out to check whether pitch movements in speech intonation are perceived on one of these two scales or on a psychoacoustic scale representing the frequency selectivity of the auditory system. This last scale is intermediary between the other two scales. Subjects matched the excursion size of prominence-lending pitch movements in utterances resynthesized in different pitch registers. Their task was to adjust the excursion size in a comparison stimulus in such a way that it lent equal prominence to the corresponding syllable in a fixed test stimulus. The comparison stimulus and the test stimulus had pitches running parallel on either the logarithmic frequency scale, the psychoacoustic scale, or the linear frequency scale. In one-half of the experimental sessions, the test stimulus was presented in the low register, while the comparison stimulus was presented in the high register, and, conversely, for the other half of the sessions. The result is that, in all cases, stimuli are matched in such a way that the average excursion sizes in different registers are equal on the psychoacoustic scale. 相似文献
12.
13.
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. 相似文献
14.
Robert de Levie 《The Chemical Educator》2002,7(3):132-135
Using contemporary accounts, we describe the scope of the Henderson approximation, and its relationship to the mass action law of Guldberg & Waage. The Henderson approximation, apparently written in logarithmic form by Hasselbalch, has the same form as the mass action law, but has a completely different meaning and a much more restricted range of applicability. The Guldberg-Waage law is the fundamental mass action relationship valid for all chemical equilibria, whereas the Henderson approximation is useful only within a limited range of a sufficiently concentrated two-component buffer mixture. 相似文献
15.
A Hodge structure V of weight k on which a CM field acts defines, under certain conditions, a Hodge structure of weight , its half twist. In this paper we consider hypersurfaces in projective space with a cyclic automorphism which defines an
action of a cyclotomic field on a Hodge substructure in the cohomology. We determine when the half twist exists and relate
it to the geometry and moduli of the hypersurfaces. We use our results to prove the existence of a Kuga-Satake correspondence
for certain cubic 4-folds.
Received: 25 August 2000; in final form: 8 January 2001 / Published online: 18 January 2002 相似文献
16.
Affine Arithmetic: Concepts and Applications 总被引:2,自引:0,他引:2
Affine arithmetic is a model for self-validated numerical computation that keeps track of first-order correlations between computed and input quantities. We explain the main concepts in affine arithmetic and how it handles the dependency problem in standard interval arithmetic. We also describe some of its applications. 相似文献
17.
18.
Pascher W. Den Besten J. H. Caprioli D. Leijtens X. Smit M. van Dijk R. 《Optical and Quantum Electronics》2003,35(4-5):453-464
Based on a rigorous vectorial analysis, a fast travelling-wave Mach–Zehnder modulator is modelled and designed. The cross-section of the semiconductor layer stack and the lossy electrodes are carefully modelled using the method of lines in order to investigate propagation characteristics, velocity and losses. This yields an accurate microwave and optical field distribution to explain the behaviour of the component. In order to enhance the modulation efficiency, design curves are derived and the cross-sectional dimensions for minimum microwave loss are determined. The loss of the optimized modulator agrees very well with small-signal measurements up to 40 GHz and HFSS simulations. The layerstack of the fabricated device is suitable for integration with InP multi-wavelength lasers. 相似文献
19.
Willem A.L. van Otterlo 《Tetrahedron letters》2004,45(26):5091-5094
Contrary to literature reports, bromination of 3-hydroxybenzaldehyde can afford both 2-bromo-5-hydroxybenzaldehyde and 2-bromo-3-hydroxybenzaldehyde, but 4-bromo-3-hydroxybenzaldehyde was not detected. 2-Bromo-3-hydroxybenzaldehyde was converted into 2-(benzyloxy)-1-bromo-5-methoxy-7-methylnaphthalene. X-ray crystallographic analysis supports the identity of 2-bromo-3-hydroxybenzaldehyde. 相似文献
20.