全文获取类型
收费全文 | 496424篇 |
免费 | 7125篇 |
国内免费 | 1509篇 |
专业分类
化学 | 265955篇 |
晶体学 | 6864篇 |
力学 | 21217篇 |
综合类 | 25篇 |
数学 | 64809篇 |
物理学 | 146188篇 |
出版年
2021年 | 4193篇 |
2020年 | 4730篇 |
2019年 | 5048篇 |
2018年 | 7762篇 |
2017年 | 7730篇 |
2016年 | 10657篇 |
2015年 | 7167篇 |
2014年 | 10063篇 |
2013年 | 23088篇 |
2012年 | 20839篇 |
2011年 | 23968篇 |
2010年 | 16350篇 |
2009年 | 15749篇 |
2008年 | 20414篇 |
2007年 | 20355篇 |
2006年 | 18775篇 |
2005年 | 20342篇 |
2004年 | 18510篇 |
2003年 | 15226篇 |
2002年 | 13275篇 |
2001年 | 14090篇 |
2000年 | 10609篇 |
1999年 | 8332篇 |
1998年 | 6922篇 |
1997年 | 6619篇 |
1996年 | 6480篇 |
1995年 | 5714篇 |
1994年 | 5687篇 |
1993年 | 5492篇 |
1992年 | 6228篇 |
1991年 | 6254篇 |
1990年 | 5971篇 |
1989年 | 5750篇 |
1988年 | 5732篇 |
1987年 | 5598篇 |
1986年 | 5273篇 |
1985年 | 6862篇 |
1984年 | 6971篇 |
1983年 | 5493篇 |
1982年 | 5651篇 |
1981年 | 5621篇 |
1980年 | 5191篇 |
1979年 | 5565篇 |
1978年 | 5707篇 |
1977年 | 5555篇 |
1976年 | 5574篇 |
1975年 | 5112篇 |
1974年 | 5105篇 |
1973年 | 5095篇 |
1972年 | 3559篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels. 相似文献
962.
963.
1D-nanostructural zinc oxide (ZnO) with different shapes have been synthesized on p-type Si(1 0 0) and glass substrates via vapor phase growth by heating pure zinc powder at temperatures between 480 and 570 °C. The different ZnO nanostructures depend on the substrates and the growth temperatures. Scanning electron microscopy and X-ray diffraction revealed that a well-aligned nanowires array, which are vertical to the substrate of Si(1 0 0) with 18 sides on their heads, but six sides on their stems, has been formed at 480 °C. Raman study on the ZnO nanostructures shows that the coupling strength between electron and phonon determined by the ratio of the second- to the first-order Raman scattering cross-sections declines with decreasing diameter of the nanowires. However, a little changes of the coupling strength in terms of the width of the nanobelts have been observed. 相似文献
964.
965.
966.
M. De Falco F. De Giovanni C. Musella R. Schmidt 《Rendiconti del Circolo Matematico di Palermo》2003,52(1):70-76
A subgroupH of a groupG is said to bepermutable ifHX=XH for every subgroupX ofG. In this paper the structure of groups in which every subgroup either is abelian or permutable is investigated.
This work was done while the last author was visiting the University of Napoli Federico II. He thanks the “Dipartimento di
Matematica e Applicazioni” for its financial support. 相似文献
967.
968.
Pre—Separation Axioms in Fuzzifying Topology 总被引:1,自引:0,他引:1
K.M.AbdEl-Hakeim F.M.Zeyada 《模糊系统与数学》2003,17(1):28-36
1 IntroductionYing[5,6 ] introduced and elementally developed so called fuzzifying topology with the semanticmethod of continuous valued L ogic.Shen[7] introduced and studied T0 -,T1-,T2 (Hausdorff) -,T3(regularity) -,T4 (normality) -separation axioms in fuzzifying topology.In [3 ]the concepts of thefamily of fuzzifying pre-open sets,fuzzifying pre-neighbourhood structure of a point and fuzzifyingpre-closure are introduced and studied.It is worth to mention that pre-separation axioms are … 相似文献
969.
970.
The projection approach is applied to construct and investigate an operator-difference scheme for fluid dynamics in Lagrangean variables which has first-order local approximation in the axisymmetric case near the symmetry axis. The scheme also has operator properties that make it suitable for rederiving and substantiating previous results, methods, and algorithms. 相似文献