全文获取类型
收费全文 | 910篇 |
免费 | 39篇 |
国内免费 | 2篇 |
专业分类
化学 | 558篇 |
晶体学 | 5篇 |
力学 | 17篇 |
数学 | 197篇 |
物理学 | 174篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 28篇 |
2020年 | 27篇 |
2019年 | 23篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 32篇 |
2014年 | 23篇 |
2013年 | 57篇 |
2012年 | 66篇 |
2011年 | 56篇 |
2010年 | 36篇 |
2009年 | 40篇 |
2008年 | 59篇 |
2007年 | 44篇 |
2006年 | 63篇 |
2005年 | 62篇 |
2004年 | 37篇 |
2003年 | 35篇 |
2002年 | 31篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1888年 | 1篇 |
1887年 | 1篇 |
排序方式: 共有951条查询结果,搜索用时 15 毫秒
71.
Patricio Jara 《Journal of Mathematical Analysis and Applications》2008,344(2):956-968
This paper extends the Hille-Phillips functional calculus and rational approximations results due to R. Hersh, T. Kato, P. Brenner, and V. Thomée to generators of bi-continuous semigroups. The method yields error estimates for rational time-discretization schemes for such semigroups, in particular for dual semigroups, Feller semigroups such as the Ornstein-Uhlenbeck semigroup, the heat semigroup, semigroups induced by nonlinear flows, implemented semigroups, and evolution semigroups. Furthermore, the results provide error estimates for a new class of inversion formulas for the Laplace transform. 相似文献
72.
Reyes Malavé Osuna Rocio Ponce Ortiz Mari Carmen Ruiz Delgado Valentin G Nenajdenko Viktor V Sumerin Elizabeth S Balenkova Víctor Hernández Juan Teodomiro López Navarrete 《Chemphyschem》2007,8(5):745-750
Herein, we study the conjugation properties of three different thienoacenes, each of which has three or four fused thiophene rings, by means of Fourier transform Raman spectroscopy. The B3LYP/6-31G** vibrational analysis of all of the collected spectroscopic data evidences that the selective enhancement of a limited number of Raman scatterings is related to the occurrence in the three thienoacenes of a vibronic coupling between the lowest unoccupied frontier molecular orbital (LUMO) and some Raman-active skeletal nu(C==C) stretching modes of 1600-1300 cm(-1). 相似文献
73.
We introduce the notion ofsearchability as a property of an in place merging algorithm. We show that a pair of sorted arrays can be merged in place in linear time, so that a search can be performed in logarithmic time at any point during the merging process. We apply this method to devise an implicit data structure which can support searches inO(log2
n) time in the worst case, andO(logn) on the average, and insertions inO(logn) time, in the worst case.This research was partly supported by NSERC under grant A8237 and presented in preliminary form at the 10th International Colloquium on Automata, Languages and Programming.On leave from the University of Chile. 相似文献
74.
Francisco Núñez‐Zarur Eduardo Arguello Ricardo Vivas‐Reyes 《International journal of quantum chemistry》2010,110(9):1622-1636
The electronic structure and reactivity trends of a set of tris‐(n‐methyl‐8‐quinolinolato) metal (III) (n = 0, 3, 4, 5; metal = Al+3, Ga+3) used as electron‐transport layer in organic light‐emitting diodes were studied and compared. All geometries were optimized at B3LYP/6‐31G(d,p) level of theory. The geometries of the ground state (S0) of unsubstituted molecules AlQ3 and GaQ3 were found to be slightly affected by the methyl group, which is in agreement with previous works. Methyl‐derivatives conserve largely the electronic structures of AlQ3 and GaQ3. The energies of the frontier orbitals highest occupied and lowest unoccupied molecular orbital are raised by the electron‐releasing effect of methyl group. Molecular orbital contribution analysis reveals that the orbital population is essentially the same for both MQ3 and their derivatives. Analyses of the ionization potential and electron affinity showed that MQ3 tend to be better hole‐blockers than methylated analogues and 5Me‐MQ3 have higher hole‐injection capability than the other methyl‐substituted derivatives. The global reactivity analysis showed that the electrophilicity index can be an indicator of electron‐injection capability in these complexes. Local reactivity analysis showed that atomic sites that are prone to nucleophilic/electrophilic attack are atoms C‐4 in L3/C‐5 in L1. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
75.
Fluorescence microscopy offers an important tool for the study of complex biological phenomena such as symbiosis. Here we identify a strategy that adapts the unique differences between the secondary metabolism in host and guest symbiotic species to selectively image endosymbiotic organisms. The method is demonstrated by application to the complex symbiotic relationships in toxic marine dinoflagellates. 相似文献
76.
Learning to teach is difficult for prospective teachers because of the complex nature of the work of teaching. Practicing (Lampert in J Teach Educ 61(1–2):21–34, 2010), interacting with the practice of teaching from a first-person perspective, may give them a unique experience in learning to teach. Computer-based simulators in which the apprentice teacher can interact with virtual students may be used to create that kind of experience. In this paper, we show how to apply techniques in artificial intelligence to design an intelligent learning environment. We show how to model the apprentice’s decision making and resources that can help him or her improve the practice of teaching. 相似文献
77.
Mounce AM Oh S Mukhopadhyay S Halperin WP Reyes AP Kuhns PL Fujita K Ishikado M Uchida S 《Physical review letters》2011,106(5):057003
Competition with magnetism is at the heart of high-temperature superconductivity, most intensely felt near a vortex core. To investigate vortex magnetism we have developed a spatially resolved probe based upon NMR spin-lattice-relaxation spectroscopy. With this approach we have found a spin-density wave associated with the vortex core in Bi(2)Sr(2)CaCu(2)O(8+y), similar to checkerboard patterns in the local density of electronic states reported from scanning tunneling microscope experiments. We have determined both the spin-modulation amplitude and decay length from the vortex core in fields up to H=30 T. 相似文献
78.
The synthesis of a new azacyclophane formed by two l-tyrosine units joined by two methylene bridges is presented. The structural and conformational characteristics are briefly discussed. Spectroscopic and theoretical data reveal a syn structure with two intramolecular hydrogen bonds. 相似文献
79.
In this paper, we prove a Hadamard property and Liouville type theorems for viscosity solutions of fully nonlinear elliptic partial differential equations with a gradient term, both in the whole space and in an exterior domain. 相似文献
80.
Dario Romano Efren Alberto Andablo‐Reyes Sara Ronca Sanjay Rastogi 《Journal of polymer science. Part A, Polymer chemistry》2013,51(7):1630-1635
The use of a hindered phenol to trap free trimethylaluminum (TMA) in methylaluminoxane (MAO) solutions has been reported to improve the performance of single‐site, homogeneous catalysts for olefin polymerization. In the present study, with the help of rheological analyses, we have investigated and compared the molecular weight, molecular weight distribution and entanglement density of ultrahigh molecular weight polyethylene synthesized with a single‐site catalyst activated by MAO and phenol‐modified MAO. While the number average molecular weight (Mn) of the obtained polymers remains the same for both activations, a higher yield and a higher entanglement density are found in the initial stages of polymerization on using phenol‐modified MAO as the cocatalyst. These results suggest that on using the phenol‐modified MAO as activator, a higher number of active sites are obtained. Surprisingly in the presence of untreated MAO, a tail in the higher molecular mass region is produced. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 相似文献