全文获取类型
收费全文 | 78612篇 |
免费 | 16047篇 |
国内免费 | 6972篇 |
专业分类
化学 | 70872篇 |
晶体学 | 776篇 |
力学 | 3233篇 |
综合类 | 445篇 |
数学 | 7514篇 |
物理学 | 18791篇 |
出版年
2024年 | 102篇 |
2023年 | 919篇 |
2022年 | 1473篇 |
2021年 | 1690篇 |
2020年 | 2882篇 |
2019年 | 3994篇 |
2018年 | 2411篇 |
2017年 | 1958篇 |
2016年 | 5110篇 |
2015年 | 5268篇 |
2014年 | 5708篇 |
2013年 | 6951篇 |
2012年 | 6757篇 |
2011年 | 6044篇 |
2010年 | 5550篇 |
2009年 | 5319篇 |
2008年 | 5035篇 |
2007年 | 4201篇 |
2006年 | 3773篇 |
2005年 | 3548篇 |
2004年 | 3117篇 |
2003年 | 2624篇 |
2002年 | 3361篇 |
2001年 | 2451篇 |
2000年 | 2252篇 |
1999年 | 1489篇 |
1998年 | 932篇 |
1997年 | 813篇 |
1996年 | 843篇 |
1995年 | 722篇 |
1994年 | 643篇 |
1993年 | 534篇 |
1992年 | 513篇 |
1991年 | 433篇 |
1990年 | 379篇 |
1989年 | 267篇 |
1988年 | 247篇 |
1987年 | 219篇 |
1986年 | 165篇 |
1985年 | 180篇 |
1984年 | 145篇 |
1983年 | 124篇 |
1982年 | 87篇 |
1981年 | 65篇 |
1980年 | 51篇 |
1979年 | 37篇 |
1978年 | 27篇 |
1976年 | 27篇 |
1975年 | 33篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Guofen Yu Yuanci Gao Shenggang Liu Wenxiang Wang Jin Wu 《International Journal of Infrared and Millimeter Waves》2002,23(8):1261-1269
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources. 相似文献
102.
提出了一种基于微悬臂梁传感技术研究大分子折叠/构象转变的新方法.通过分子自组装的方法将热敏性的聚N-异丙基丙烯酰胺(PNIPAM)分子链修饰到微悬臂梁的单侧表面,用光杠杆技术检测温度在20-40 ℃之间变化时由于微悬臂梁上的PNIPAM分子在水中的构象转变所引起的微悬臂梁变形.实验结果显示:在升温过程中,微悬臂梁的表面应力发生了变化并且导致微悬臂梁产生了弯曲变形,这个过程对应着微悬臂梁上的PNIPAM分子从无规线团构象到塌缩小球构象的构象转变.在降温过程中,微悬臂梁发生了反方向的弯曲变形,这对应着PNIPAM分子从塌缩小球构象向无规线团构象的构象转变.整个温度变化过程中构象转变是连续进行的,而在低临界溶解温度(约32 ℃)附近转变幅度较大,这与自由水溶液中PNIPAM分子的无规线团-塌缩小球构象转变相对应.实验结果还显示:由于PNIPAM分子在塌缩过程中氢键的形成和链段间可能的缠结效应,整个温度循环过程中微悬臂梁的变形是不可逆的且有明显的迟滞效应. 相似文献
103.
104.
利用国家同步辐射实验室合肥光源的真空紫外同步辐射,使NO分子和Ar原子混合物的超声分子束发生光电离,测量了Ar,NO和异类团簇Ar·NO的光电离效率谱. 在谱中,在与Ar原子的共振线对应的能量区域(11.5—12.0 eV)观察到一个强的类共振结构. 这个结果表明,在异类团簇Ar·NO的内部,稀有气体Ar原子的激发能转移到与它接触的分子NO上,使分子NO发生电离.
关键词:
Ar·NO团簇
同步辐射
光电离
能量转移 相似文献
105.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
106.
107.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
108.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献
109.
C.J. Wu 《Applied Acoustics》2002,63(10):1143-1154
This work formulates the double-layer structural-acoustic coupling problem for cylindrical shell by using a combination of the wave-number domain approach (WDA) and the boundary integral equation (BIE). Expressions for the spectral radial velocity of the outer surface of a finite fluid-filled/submerged (FFS) cylindrical thin shell are formulated by means of the transfer matrix equation in wave-number domain. It is shown that the spectral variables on the inner surface of the shell are related to those on the outer surface of the shell. The far field sound radiation from this kind of shell is numerically evaluated for various fluid cases. An experimental verification is performed, and a good correlation between the theoretical results and the experimental results shows that the theoretical study work in this paper is correct. 相似文献
110.
Bond covalency and valence of elements in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with Tc was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest Tc sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher Tc. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples. 相似文献