全文获取类型
收费全文 | 653篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 505篇 |
晶体学 | 6篇 |
力学 | 20篇 |
数学 | 16篇 |
物理学 | 128篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 47篇 |
2012年 | 21篇 |
2011年 | 23篇 |
2010年 | 15篇 |
2009年 | 11篇 |
2008年 | 43篇 |
2007年 | 42篇 |
2006年 | 18篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 37篇 |
2002年 | 35篇 |
2001年 | 33篇 |
2000年 | 27篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1932年 | 5篇 |
1906年 | 2篇 |
1903年 | 2篇 |
1898年 | 2篇 |
1886年 | 2篇 |
排序方式: 共有675条查询结果,搜索用时 0 毫秒
141.
Dr. Vonika Ka-Man Au Shuk Ying Kwan Mio Nga Lai Dr. Kam-Hung Low 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(35):9174-9179
By using tritopic and ditopic organic linkers derived from the same 2,4,6-triphenylpyridine core, copper(II) metal-organic frameworks with different three-dimensional structures have been successfully synthesized under ambient conditions. The crystalline framework, PTB MOF ([Cu3(PTB)2(H2O)3]n, where H3PTB=4,4′,4′′-(pyridine-2,4,6-triyl)tribenzoic acid, was observed to be mesoporous in nature and exhibited dual functionality in the removal of organic dyes. While cationic dyes such as methylene blue and malachite green, which are of different sizes, were adsorbed by PTB MOF ; anionic dyes such as tartrazine could be effectively degraded in a photo-Fenton-like reaction catalyzed by the MOFs under irradiation with visible light. 相似文献
142.
143.
144.
145.
Minimizing the makespan in a single machine scheduling problems with flexible and periodic maintenance 总被引:1,自引:0,他引:1
This paper deals with a single machine scheduling problems with availability constraints. The unavailability of machine results from periodic maintenance activities. In our research, a periodic maintenance consists of several maintenance periods. We consider a machine should stop to maintain after a periodic time interval or to change tools after a fixed amount of jobs processed simultaneously. Each maintenance period is scheduled after a periodic time interval. We study the problems under deterministic environment and flexible maintenance considerations. Preemptive operation is not allowed. In addition, we propose a more reasonable flexible model for the real production settings. The objective is to minimize the makespan. The proposed problem is NP-hard in the strong sense and some heuristic algorithms are provided. The purpose is to present an efficient and effective heuristic algorithm so that it will be straightforward and easy to implement. Computational results show that the proposed algorithm first fit decreasing (DFF) performs well. 相似文献
146.
147.
Symmetries in quantum mechanics are realized by the projective representations of the Lie group as physical states are defined only up to a phase. A cornerstone theorem shows that these representations are equivalent to the unitary representations of the central extension of the group. The formulation of the inertial states of special relativistic quantum mechanics as the projective representations of the inhomogeneous Lorentz group, and its nonrelativistic limit in terms of the Galilei group, are fundamental examples. Interestingly, neither of these symmetries include the Weyl–Heisenberg group; the hermitian representations of its algebra are the Heisenberg commutation relations that are a foundation of quantum mechanics. The Weyl–Heisenberg group is a one dimensional central extension of the abelian group and its unitary representations are therefore a particular projective representation of the abelian group of translations on phase space. A theorem involving the automorphism group shows that the maximal symmetry that leaves the Heisenberg commutation relations invariant is essentially a projective representation of the inhomogeneous symplectic group. In the nonrelativistic domain, we must also have invariance of Newtonian time. This reduces the symmetry group to the inhomogeneous Hamilton group that is a local noninertial symmetry of the Hamilton equations. The projective representations of these groups are calculated using the Mackey theorems for the general case of a nonabelian normal subgroup. 相似文献
148.
Solange M. S. V. Wardell James L. Wardell Mark F. Ward John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):865-867
Crystals of the title compound, C18H20N4O4, contain equal numbers of (R,R) and (S,S) molecules, but these are not precise enantiomorphs, neither are they related by crystallographic symmetry; in addition, each molecule exhibits approximate, but not exact, twofold rotational symmetry. There are intramolecular N—H?O hydrogen bonds [N?O 2.609 (4)–2.638 (5) Å; N—H?O 125–132°] and the molecules are linked into molecular ladders by C—H?O hydrogen bonds [C?O 3.306 (6)–3.386 (6) Å; C—H?O 146–160°]. 相似文献
149.
Kh.S.Karimov Khaulah Sulaiman Zubair Ahmad Khakim M.Akhmedov A.Mateen 《中国物理 B》2015,24(1):18801-018801
We report newly designed pressure and displacement capacitive sensors based on a flexible paper–CNT structure.The carbon nanotube(CNT)powder was deposited on a thin paper substrate and was pressed at an elevated temperature.The sheet resistance of the paper–CNT films was in the range of 2–4 kΩ/cm2.The paper–CNT films were used to fabricate pressure and displacement sensors.The sensitivities of the pressure and the displacement sensors were found to be17.3 p F·m2/k N and 0.93 10-3p F/μm,respectively.The experimental results were compared with the simulated data and they found good agreement with each other. 相似文献
150.
Andreasson-Ochsner M Fu Z May S Xiu LY Nallani M Sinner EK 《Langmuir : the ACS journal of surfaces and colloids》2012,28(4):2044-2048
To improve the stability of cell membrane mimics, there has been growing interest in the use of block copolymers. Here, we present an easy approach to create an array of planar polymeric matrices capable of hosting membrane proteins. The array of polymeric matrices was formed by the selective deposition of triblock copolymers onto an array of hydrophilic islands situated within a hydrophobic background. The thickness of these matrices corresponds to the length of a single polymer chain. These polymeric matrices were used to host cell-free expressed membrane proteins, and offers a prototype from which a membrane protein array can be created for diagnostics or drug discovery purposes. 相似文献