全文获取类型
收费全文 | 8347篇 |
免费 | 1378篇 |
国内免费 | 683篇 |
专业分类
化学 | 5681篇 |
晶体学 | 87篇 |
力学 | 491篇 |
综合类 | 36篇 |
数学 | 999篇 |
物理学 | 3114篇 |
出版年
2024年 | 12篇 |
2023年 | 160篇 |
2022年 | 242篇 |
2021年 | 265篇 |
2020年 | 357篇 |
2019年 | 300篇 |
2018年 | 269篇 |
2017年 | 250篇 |
2016年 | 417篇 |
2015年 | 407篇 |
2014年 | 459篇 |
2013年 | 582篇 |
2012年 | 777篇 |
2011年 | 758篇 |
2010年 | 535篇 |
2009年 | 491篇 |
2008年 | 558篇 |
2007年 | 425篇 |
2006年 | 461篇 |
2005年 | 335篇 |
2004年 | 266篇 |
2003年 | 218篇 |
2002年 | 173篇 |
2001年 | 139篇 |
2000年 | 147篇 |
1999年 | 174篇 |
1998年 | 154篇 |
1997年 | 127篇 |
1996年 | 131篇 |
1995年 | 112篇 |
1994年 | 98篇 |
1993年 | 80篇 |
1992年 | 80篇 |
1991年 | 78篇 |
1990年 | 45篇 |
1989年 | 39篇 |
1988年 | 39篇 |
1987年 | 35篇 |
1986年 | 30篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
901.
Ying Liu Chong‐an Di Dr. Chunyan Du Yunqi Liu Prof. Kun Lu Wenfeng Qiu Dr. Gui Yu Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(7):2231-2239
A series of fused thiophenes composed of fused α‐oligothiophene units as building blocks, end‐capped with either styrene or 1‐pentyl‐4‐vinylbenzene groups, has been synthesized through Stille coupling reactions. The compounds have been fully characterized by means of 1H NMR spectrometry, high‐resolution mass spectrometry, and elemental analysis. The molecules present a trans–trans configuration between their double bonds, which has been verified and confirmed by Fourier‐transform infrared spectroscopy and single‐crystal X‐ray diffraction analysis. The X‐ray crystal structures showed π–π overlap and sulfur–sulfur interactions between the adjacent molecules. The decomposition temperatures were all found to be above 300 °C, indicating that compounds of this series possess excellent thermal stability. The fact that no phase transition occurs at low temperature indicates that they should be well‐suited for application in devices. Moreover, they possess low HOMO energy levels, based on cyclic voltammetry measurements, and suitable energy gaps, as determined from their thin‐film UV/Vis spectra. Thin‐film X‐ray diffraction analysis and atomic force microscopy revealed high crystallinity on supporting substrates. In addition, as the substrate temperature has a significant influence on the morphology and the degree of crystallinity, the device performance could be optimized by varying the substrate temperature. These materials were found to exhibit optimal field‐effect performance, with a mobility of 0.17 cm2 V?1 s?1 and an on/off ratio of 105, at a substrate temperature of 70 °C. 相似文献
902.
A method for characterizing and identifying firing patterns of neural spike trains is presented. Three characteristic variables defined at sequential moments, including two formal derivatives and the integration of the counting process, are introduced to reflect the temporal patterns of a spike train. This paper also examines how noise interacts with encoding mechanisms of neuronal stimulus in a cold receptor. From ISI series and bifurcation diagrams it is shown that there are considerable differences in interval distributions and impulse patterns caused by purely deterministic simulations and noisy simulations. The ISI-distance can be used as an effective and powerful way to measure the noise effects on spike trains quantitatively. It is found that spike trains observed in cold receptors can be more strongly affected by noise for low temperatures than for high temperatures in some aspects; meanwhile, spike train has greater variability with the noise intensity increasing. 相似文献
903.
Ivan Poto?ňák Michal Dunaj-Jur?o Du?an Miklo? Lothar J?ger 《Monatshefte für Chemie / Chemical Monthly》2001,22(6):315-327
The structure of the new compound [Cu(bpy)2N(CN)2]C(CN)3 (6) is compared with thestructures of six copper(II) coordination compounds with phenanthroline or bipyridine ligands and N-donor pseudohalide anions: [Cu(phen)2NCS]C(CN)3 (1), [Cu(bpy)2NCS]C(CN)3 (2), [Cu(phen)2NCS]ONC(CN)2 (3), [Cu(phen)2N(CN)2]C(CN)3 (4), [Cu(bpy)2C(CN)3]C(CN)3 (5), and [Cu(bpy)2NCO]C(CN)3 (7). The Cu(II) atoms in all above compounds are five-coordinated with an N-donor atom of the pseudohalide anion located in the equatorial plane of a deformed trigonal bipyramid. The shape of the coordination polyhedra and the degree of trigonal bipyramidal distortion towards a tetragonal pyramid are discussed and described using one electronic and several structural criteria which are discussed and compared. 相似文献
904.
905.
A Mössbauer absorber was made by simultaneous evaporation of copper and implantation of119Sn, and postimplantation of F. A large fraction of Sn4+ was formed, assigned to the formation of SnF4. 相似文献
906.
Measurement of the mode coherence coefficients 总被引:3,自引:0,他引:3
Based on average intensity distributions at two axial positions, an experimental approach to determine the mode coherence coefficients was developed. Using this approach, investigations were carried out for a CO2 laser with a stripe resonator. The power partitions of, and cross-correlations between, modes at different aperture widths and the dependence of the beam quality on the aperture width were studied. The measuring principle, an iterative fit method, and some experimental results are presented and discussed. 相似文献
907.
用硝酸盐分解法(N-法)和柠檬酸络合法(L-法)合成了La-Sr-Ni-O系复合氧化物.用XRD技术考察了样品组成、制备条件及灼烧气氛等对产物结构的影响.结果表明:按La_(1-x)Sr_xNiO_3计量比,用N-法合成只能形成四方体心K_2NiF_4结构的A_2BO_4型复合氧化物.而采用L-法,通过改变条件,在0.0≤x≤0.2范围内可形成菱形晶系钙钛矿结构的复合氧化物.另外,用L-法合成La_(2-x)Sr_xNiO_4系列样时发现,制备条件及灼烧温度、气氛对样品结晶态存在较大的影响,高温、空气氛下可形成高结晶态的K_2NiF_4结构复合氧化物.La_(2-x)Sr_xNiO_4体系CO催化氧化活性研究表明,随x(Sr~(2+)取代量)增加,CO的转化率增加. 相似文献
908.
Ji‐Min Du Hui‐Yi Zeng Zhen‐Chao Dong Guo‐Cong Guo Jin‐Shun Huang 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):m396-m397
The title compound, {[Cu4(C3H4NS2)4]·2H2O}n, was produced by diffusing a solution of 2‐mercaptothiazoline in tetrahydrofuran into a solution of CuCl in CH3CN at room temperature. The structure is characterized by self‐assembled one‐dimensional chains that are condensed from butterfly‐like [Cu(C3H4NS2)]4 tetrameric units via double S‐bridging at opposite ends. The Cu—Cu distances within the Cu4 butterfly cluster are in the range 2.7103 (10)–2.9764 (10) Å, while the shortest Cu?Cu intercluster distance is 3.468 (1) Å, much longer than the sum of the van der Waals radii. 相似文献
909.
910.
Quasi-hereditary algebras can be viewed as a Lie theory approach to the theory of finite dimensional algebras. Motivated by the existence of certain nice bases for representations of semisimple Lie algebras and algebraic groups, we will construct in this paper nice bases for (split) quasi-hereditary algebras and characterize them using these bases. We first introduce the notion of a standardly based algebra, which is a generalized version of a cellular algebra introduced by Graham and Lehrer, and discuss their representation theory. The main result is that an algebra over a commutative local noetherian ring with finite rank is split quasi-hereditary if and only if it is standardly full-based. As an application, we will give an elementary proof of the fact that split symmetric algebras are not quasi-hereditary unless they are semisimple. Finally, some relations between standardly based algebras and cellular algebras are also discussed. 相似文献