全文获取类型
收费全文 | 6226篇 |
免费 | 217篇 |
国内免费 | 33篇 |
专业分类
化学 | 4243篇 |
晶体学 | 19篇 |
力学 | 276篇 |
数学 | 924篇 |
物理学 | 1014篇 |
出版年
2023年 | 38篇 |
2022年 | 103篇 |
2021年 | 108篇 |
2020年 | 130篇 |
2019年 | 123篇 |
2018年 | 81篇 |
2017年 | 73篇 |
2016年 | 199篇 |
2015年 | 183篇 |
2014年 | 227篇 |
2013年 | 340篇 |
2012年 | 460篇 |
2011年 | 549篇 |
2010年 | 282篇 |
2009年 | 287篇 |
2008年 | 370篇 |
2007年 | 404篇 |
2006年 | 391篇 |
2005年 | 358篇 |
2004年 | 281篇 |
2003年 | 253篇 |
2002年 | 231篇 |
2001年 | 82篇 |
2000年 | 87篇 |
1999年 | 56篇 |
1998年 | 64篇 |
1997年 | 70篇 |
1996年 | 72篇 |
1995年 | 50篇 |
1994年 | 60篇 |
1993年 | 36篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 29篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 24篇 |
1978年 | 18篇 |
1977年 | 11篇 |
1976年 | 19篇 |
1975年 | 13篇 |
1974年 | 13篇 |
排序方式: 共有6476条查询结果,搜索用时 15 毫秒
131.
Prof. Donald G. Truhlar Prof. Philippe C. Hiberty Prof. Sason Shaik Prof. Mark S. Gordon Dr. David Danovich 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(36):12460-12466
Electron momentum spectroscopy, scanning tunneling microscopy, and photoelectron spectroscopy provide unique information about electronic structure, but their interpretation has been controversial. This essay discusses a framework for interpretation. Although this interpretation is not new, we believe it is important to present this framework in light of recent publications. The key point is that these experiments provide information about how the electron distribution changes upon ionization, not how electrons behave in the pre‐ionized state. Therefore, these experiments do not lead to a “selection of the correct orbitals” in chemistry and do not overturn the well‐known conclusion that both delocalized molecular orbitals and localized molecular orbitals are useful for interpreting chemical structure and dynamics. The two types of orbitals can produce identical total molecular electron densities and therefore molecular properties. Different types of orbitals are useful for different purposes. 相似文献
132.
Mathilde Pantin Florent Bodinier Jordan Saillour Yassine M. Youssouf Fabien Boeda Morwenna S.M. Pearson-Long Philippe Bertus 《Tetrahedron》2019,75(33):4657-4662
A convenient access to 2-hydroxycyclopentenones was designed from acylcyanohydrins, by using titanacyclopropane complexes as nucleophilic partners and an intramolecular aldol condensation in basic conditions. The development of a one-pot procedure allows a step- and atom-economic process, and the use of Grignard reagents other than ethylmagnesium bromide provided valuable 3,4-disubstituted 2-hydroxycyclopentenones. The utility of the hydroxy group was illustrated by further functionalization of the α-position using palladium-mediated cross-coupling reactions. 相似文献
133.
A highly stereoselective synthesis of (E)-1,5-syn-diols 6 is described. The kinetically controlled hydroboration of allenyltrifluoroborate 8 with Soderquist borane 2 provides the (Z)-allylic trifluoroborate 9, which undergoes sequential allylboration with two different aldehydes to provide (E)-1,5-syn-diols 6 in 72-98% yields with >95% ee and >20:1 dr. Application of this method to the synthesis of the tetrafibricin C(23)-C(40) fragment 19 is described. 相似文献
134.
Stéphanie Rat Michael Bosco Marie-Laure Tavernier Philippe Michaud Anne Wadouachi José Kovensky 《Comptes Rendus Chimie》2011,14(2-3):307-312
Substitution of a glucuronic acid trisaccharide was easily performed in one step under microwave irradiation, affording a product resulting from simultaneous glycosylation, esterification and a butyl ether formation. 相似文献
135.
Philippe Derreumaux Grard Vergoten Philippe Lagant 《Journal of computational chemistry》1990,11(5):560-568
Normal coordinate calculations have been performed for urea and deuterated urea in the crystalline state. We have used the modified Urey–Bradley–Shimanouchi intramolecular potential energy function and a rather sophisticated intermolecular energy function to reproduce I.R. and Raman frequencies with an average error of 2 cm–1. The general agreement between the calculation and experiment suggests that intermolecular interactions must be taken into account to determine reliable intramolecular parameters of the potential energy function, mainly the barrier to internal rotation around the C? N bond. The intermolecular energy function, which consists of the Buckingham function and an explicit harmonic function for hydrogen-bonding, then has the merit to reproduce quite well the observed frequencies of lattice vibrations. 相似文献
136.
The phase behavior of mixtures formed by palmitic acid (PA), cholesterol (Chol), and sodium cholesteryl sulfate (Schol) has been characterized by differential scanning calorimetry and infrared and 2H NMR spectroscopy. It is reported that it is possible to form, with PA/sterol mixtures, fluid lamellar phases where the sterol content is very high (a sterol mole fraction of 0.7). As a consequence of the rigidifying ability of the sterols, the PA acyl chains are very ordered. The stability of these self-assembled bilayers is found to be pH-dependent. This property can be controlled by the Chol/Schol molar ratio, and it is proposed that this parameter modulates the balance between the intermolecular interactions between the constituting species. A phase-composition diagram summarizing the behavior of these mixtures as a function of pH, at room temperature, is presented. It is also shown that it is possible to produce large unilamellar vesicles (LUVs) from these mixtures, using standard extrusion techniques. The resulting LUVs display a very limited passive release of the entrapped material. In addition, these LUVs constitute a versatile vector for pH-triggered release. 相似文献
137.
Sophie Peeterbroeck Fouad Laoutid Benjamin Swoboda Jos‐Marie Lopez‐Cuesta Nicolas Moreau Janos B. Nagy Michaël Alexandre Philippe Dubois 《Macromolecular rapid communications》2007,28(3):260-264
Nanocomposites based on an ethylene–vinyl acetate copolymer (27 wt.‐% vinyl acetate) and multiwall carbon nanotubes (MWNTs) have been prepared by melt blending and their thermal degradation and flame retardant properties have been evaluated. Special attention has been paid to the influence of the nanotube nature on the flammability properties and more particularly on the time to ignition (TTI) as measured by cone calorimetry. It has been shown that there is a strong influence of the nature of carbon nanotubes on the fire behaviour of the composites, especially previous MWNTs crushing proved to substantially delay the TTI while maintaining much reduced heat release rate (HRR). Such a remarkable behaviour might be explained by the chemical reactivity of radical species present at the surface/extremities of crushed MWNTs during the combustion process.
138.
Our recent developments concerning the fabrication of polymer microchips and their applications for biochemical analyses are reviewed. We first describe two methods of fabrication of polymer microfluidic chips, namely UV-laser photoablation and plasma etching that are well suited for the prototyping and mass fabrication of microchannel networks with integrated microelectrodes. These microanalytical systems can be coupled with various detection means including mass spectrometry, and their applications in capillary electrophoresis are presented here. We also present how UV laser photoablation can be used for the patterning of biomolecules on polymer surfaces for generating two-dimensional arrays of microspots to carry out affinity assays. Finally, the use of the microchips for the development of fast affinity and immunological assays with electrochemical detection is presented, demonstrating the potential of these polymer microchips for medical diagnostics and drug discovery. 相似文献
139.
140.
Horst Schneider Gerd T. Puchta Franz A. R. Kaul Gabriele Raudaschl-Sieber Frdric Lefebvre Guillaume Saggio Dimitrios Mihalios Wolfgang A. Herrmann Jean Marie Basset 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):127-141
The modification of a mesoporous silica surface with Si(Ind)(CH3)2Cl and the immobilization of CpZr(NMe2)3 on this surface was studied via IR-spectroscopy. To reduce side reactions, the indenyl-modified silica was reacted with hexamethyldisilazane (HMDS) under IR-control before the CpZr(NMe2)3-immobilization. The role of the hydroxyl group protection with HMDS is discussed. The surface modifications have been repeated via Schlenk technique at the same conditions and the surface modifications were studied with 13C CP MAS–NMR, 1H MAS–NMR, elemental-, SEM- and BET-analysis. The surface species of the resulting catalysts are discussed. The precatalysts have been treated with methylaluminoxane (MAO) (Al:Zr (mol:mol)=500:1) and the resulting Zr contents (leaching-effect) are discussed. All catalysts have been tested in ethylene and propylene polymerization. 相似文献