全文获取类型
收费全文 | 2071篇 |
免费 | 418篇 |
国内免费 | 510篇 |
专业分类
化学 | 2052篇 |
晶体学 | 25篇 |
力学 | 8篇 |
综合类 | 11篇 |
数学 | 29篇 |
物理学 | 874篇 |
出版年
2024年 | 5篇 |
2023年 | 14篇 |
2022年 | 56篇 |
2021年 | 93篇 |
2020年 | 79篇 |
2019年 | 80篇 |
2018年 | 59篇 |
2017年 | 75篇 |
2016年 | 71篇 |
2015年 | 139篇 |
2014年 | 129篇 |
2013年 | 184篇 |
2012年 | 161篇 |
2011年 | 180篇 |
2010年 | 166篇 |
2009年 | 175篇 |
2008年 | 150篇 |
2007年 | 194篇 |
2006年 | 130篇 |
2005年 | 140篇 |
2004年 | 142篇 |
2003年 | 122篇 |
2002年 | 82篇 |
2001年 | 47篇 |
2000年 | 51篇 |
1999年 | 45篇 |
1998年 | 41篇 |
1997年 | 19篇 |
1996年 | 33篇 |
1995年 | 19篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有2999条查询结果,搜索用时 156 毫秒
41.
We present a theoretical study of dissociative photoionization of H2 via the 1Πu symmetry in the photon energy range 30–43 eV. Our results explain the various peaks observed in the experiments below 40 eV and illustrate, in particular, the important role of the 2Πu(2pπu) ionization threshold. At higher photon energies, they suggest the existence of new resonance structures that may be associated with doubly excited states of H2 lying above the third and fourth ionization thresholds (the Q3 and Q4 resonance series). From the calculated resonance parameters, we conclude that the dominant mechanism at high photon energies should involve the Q4 (and probably higher) doubly excited states of H2. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2002 相似文献
42.
本文报道新的Tweezer(1)的合成,用^1HNMR研究了新的Tweezer分子和对硝基苯甲酸盐的配位效应,结果表明它兴通过氢键,静电引力和芳环夹心堆叠作用而自动缔合。 相似文献
43.
This article examines the current status of Markov processes in single molecule fluorescence. For molecular dynamics to be described by a Markov process, the Markov process must include all states involved in the dynamics and the first-passage time (FPT) distributions out of those states must be describable by a simple exponential law. The observation of non-exponential FPT distributions or other evidence of non-Markovian dynamics is common in single molecule studies and offers an opportunity to expand the Markov model to include new dynamics or states that improve understanding of the system. 相似文献
44.
本文设计合成了一系列以咔唑(CZ)和吡咯并吡咯二酮(DPP)为基本结构单元的D-A结构的新型小分子材料,并对其进行了一系列的性能表征.合成的材料以咔唑作为给电子单元,吡咯并吡咯二酮作为吸电子单元,采用三键作为π桥,并引入4-氟苯基、4-氰基苯基和4-甲氧基苯基作为末端取代基团对材料进行修饰.其中材料CZBTDPPF和CZBTDPPO因分别具有1.85和1.79 eV的较窄带隙而分别获得了相对较高的的光电转化效率(1.97%和1.91%).由此可见,引入4-氟苯基和4-甲氧基苯基作为末端取代基团对于延长材料共轭结构、拓宽材料吸收从而实现材料光伏性能的提升具有重要的作用. 相似文献
45.
R. Centoducatte E. P. Muniz F. E. Jorge M. T. Barreto 《Journal of Molecular Structure》2004,680(1-3):143-147
The molecular improved generator coordinate Hartree–Fock (MIGCHF) method is used to generate accurate basis sets of primitive Gaussian-type functions for the H2O molecule. Sequences of increasing size atom centered basis sets are employed to explore the accuracy that can be achieved with this method. Using the O(24s14p8d5f2g1h);H(22s9p5d2f1g) basis set, the HF and second-order electron correlation energies of the H2O ground state at the experimental geometry are computed as −76.0674680 and −0.3491935 hartree, respectively. The HF energy is in error by 20 μhartree and the second-order correlation energy corresponds to 96.5% of an estimate of the limiting value. The relevance of the present calculations is to show the accuracy that can be achieved in studies of small polyatomic molecules with the MIGCHF method. 相似文献
46.
This review aims to provide a summary of the progress in TP small molecule fluorescent probes for enzymes in recent years and displays the main fluorescent mechanisms that have been applied to design probes. 相似文献
47.
A new and more precise method is proposed for calculating van der Waals atomic and molecular volumes of organic compounds. The method provides for intersections of three or more spheres at one point of space. Such a possibility is essential for calculating the volumes of sterically overcrowded molecules and of molecules with intramolecular hydrogen bonds. A computer program for IBM PC/AT(XT) is developed. Depending on the atomic environment in the molecule, the average values of the volume increments for atoms C, N, O, H, F, Cl, and S are obtained using the data from the Cambridge Structural Database.N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow 117071. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 922–931, April, 1992. 相似文献
48.
We employ dissipative particle dynamics (DPD) to examine the self‐assembly behavior of A2‐star‐(B‐alt‐C) molecules. We successfully observe various types of hierarchical structure‐within‐structures, such as A‐formed spheres in the matrix formed by B and C alternating layers, hexagonally packed A‐formed cylinders in the matrix with B and C segregated layers, B and C alternating layers‐within‐lamellae, coaxial B and C alternating domains within hexagonally packed BC‐formed cylinders in the A‐matrix, and co‐centric BC‐alternating domains within BC‐formed spheres in the A‐matrix, by increasing the A composition. Generally speaking, the small length‐scale B and C segregated domains are in parallel to the large length‐scale structures. This hierarchical periodicity along the same axis as well as the various characteristic structures, that the A2‐star‐(B‐alt‐C) copolymers display, are quite different from those in A‐block‐(B‐graft‐C) coil‐comb copolymers. Moreover, it is interesting to find that when the copolymer chain length increases, though the hierarchical structure type is maintained, the number of small length‐scale lamellae that can form within the large length‐scale structure increases. These hierarchical structures under various compositions are reported theoretically for the first time in the copolymer systems consisting of the alternating blocks, and are in good agreement with the most recent experimental work by Matsushita and co‐workers (Macromolecules 2007 , 40, 4023). 相似文献
49.
50.
《Chemphyschem》2004,5(2):175-182
The selectins are Ca2+‐dependent cell adhesion molecules that facilitate the initial attachment of leukocytes to the vascular endothelium by binding to a carbohydrate moiety as exemplified by the tetrasaccharide, sialyl Lewis X (sLeX). An important property of the selectin‐sLeX interaction is its ability to withstand the hydrodynamic force of the blood flow. Herein, we used single‐molecule dynamic force spectroscopy (DFS) to identify the molecular determinants within sLeX that give rise to the dynamic properties of the selectin/sLeX interaction. Our atomic force microscopy (AFM) measurements revealed that the unbinding of the selectin/sLeX complexes involves overcoming at least two activation barriers. The inner barrier, which determines the dynamic response of the complex at high forces, is governed by the interaction between the Fuc residue of sLeX and a Ca2+ ion chelated to the lectin domain of the selectin molecule, whereas the outer activation barrier can be attributed to interactions involving the sialic acid residue of sLeX. Due to their steep inner activation barriers, the selectin‐sLeX complexes are less sensitive to high pulling forces. Hence, besides its contribution to the bond energy, the Ca2+ ion also grants the selectin–sLeX complexes a tensile strength that is crucial for the selectin‐mediated rolling of leukocytes. 相似文献