全文获取类型
收费全文 | 1908篇 |
免费 | 62篇 |
国内免费 | 8篇 |
专业分类
化学 | 1431篇 |
晶体学 | 6篇 |
力学 | 44篇 |
数学 | 327篇 |
物理学 | 170篇 |
出版年
2023年 | 16篇 |
2022年 | 76篇 |
2021年 | 91篇 |
2020年 | 76篇 |
2019年 | 56篇 |
2018年 | 39篇 |
2017年 | 32篇 |
2016年 | 64篇 |
2015年 | 74篇 |
2014年 | 47篇 |
2013年 | 116篇 |
2012年 | 125篇 |
2011年 | 161篇 |
2010年 | 87篇 |
2009年 | 77篇 |
2008年 | 129篇 |
2007年 | 138篇 |
2006年 | 107篇 |
2005年 | 103篇 |
2004年 | 83篇 |
2003年 | 77篇 |
2002年 | 73篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 3篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1978条查询结果,搜索用时 531 毫秒
991.
The mechanochemistry of the disulfide bridge--that is, the influence of an externally applied force on the reactivity of the sulfur-sulfur bond--is investigated by unrestricted Kohn-Sham theory. Specifically, we apply the COGEF (constrained geometry simulates external force) approach to characterize the mechanochemistry of the disulfide bond in three different chemical environments: dimethyl disulfide, cystine, and a 102-atom model of the I27 domain in the titin protein. Furthermore, the mechanism of the thiol-disulfide reduction reaction under the effect of an external force is investigated by considering the COGEF potential for the adduct and transition-state clusters. With the unrestricted Becke-three-parameter-Lee-Yang-Parr (UB3LYP) exchange-correlation functional in the 6-311++G(3df,3pd) orbital basis, the rupture force of dimethyl disulfide is 3.8 nN at a disulfide bond elongation of 35 pm. The interaction with neighboring groups and the effect of conformational rigidity of the protein environment have little influence on the mechanochemical characteristics. Upon stretching, we make the following observations: the diradical character of the disulfide bridge increases; the energy difference between the singlet ground state and low-lying triplet state decreases; and the disulfide reduction is promoted by an external force in the range 0.1-0.4 nN. Our model of the interplay between force and reaction mechanism is in qualitative agreement with experimental observations. 相似文献
992.
Eilertsen EA Giordanino F Lamberti C Bordiga S Damin A Bonino F Olsbye U Lillerud KP 《Chemical communications (Cambridge, England)》2011,47(43):11867-11869
A new zeotype titanium silicate oxidation catalyst with the STT topology has been synthesized from direct synthesis. Ti-STT has a microporous structure with small pore openings, allowing shape selective oxidation catalysis. The isomorphous substitution of Si by Ti in the framework has been confirmed by Raman, FT-IR, UV-VIS and XANES spectroscopies. 相似文献
993.
Haywood J Stokes FA Less RJ McPartlin M Wheatley AE Wright DS 《Chemical communications (Cambridge, England)》2011,47(14):4120-4122
The reaction of chromocene, Cp(2)Cr, with dilithiated 2,3-diphenylguanidine [(PhNH)(2)C=NH = L(2)H(3)] gives the novel, quadruply-bonded tetraanion [Cr(2)(L(2)H)(4)](4-). 相似文献
994.
Francesca Caterina Izzo Elisabetta Zendri Guido Biscontin Eleonora Balliana 《Journal of Thermal Analysis and Calorimetry》2011,104(2):541-546
Thermogravimetry coupled with differential scanning calorimetry (TG–DSC) has been commonly used in the field of conservation
of Cultural Heritage for the study of art objects, especially for the characterisation of inorganic matrixes. In recent years,
thermal analyses have been applied to the study of organic painting materials. The advantages of performing TG–DSC are linked
to the fact that it is micro-destructive technique which does not require any treatment prior the analysis and provide useful
information in relatively short time. The aim of this study is to describe the application of TG–DSC on the study of oil binders
used in contemporary paints. Even if synthetic binders have become increasingly popular in the 20th century, many contemporary
artists still prefer the more traditional media: drying oils. Although the wish of recalling traditional methods, much practical
knowledge in paint preparation by mixing drying oil and pigments and in the behaviour of the mixture has been lost. This is
mainly due to the different composition of contemporary materials in comparison with the traditional ones and may sometimes
lead to different drying properties of the oil paint formulations and consequent problems in the art creation and conservation.
For answer to this artistic need and in particular to the difficulties outlined by artists themselves in producing and employing
oil paints, unpigmented and pigmented oil films were studied after a week, 1 and 2 years of natural drying under laboratory
conditions. Thermal analyses were performed in air flow: the focus of this research was, in fact, to study the thermal and
oxidative behaviours of young films for better understanding the very first processes leading to the formation of the film. 相似文献
995.
Singh P Lamanna G Ménard-Moyon C Toma FM Magnano E Bondino F Prato M Verma S Bianco A 《Angewandte Chemie (International ed. in English)》2011,50(42):9893-9897
Stuck together: Adenine/carbon nanotube hybrids trigger the formation of controlled-size catalytic silver nanoparticles on the nanotube surface. The catalytic efficiency of the resulting species was assessed in the oxidation of 2-methylhydroquinone to its corresponding benzoquinone, with complete recovery and without loss of activity of the catalyst. 相似文献
996.
997.
Meyer J Wadewitz A Lokamani Toher C Gresser R Leo K Riede M Moresco F Cuniberti G 《Physical chemistry chemical physics : PCCP》2011,13(32):14421-14426
The electronic and geometrical structure of single difluoro-bora-1,3,5,7-tetraphenyl-aza-dipyrromethene (aza-BODIPY) molecules adsorbed on the Au(111) surface is investigated by low temperature scanning tunneling microscopy and spectroscopy in conjunction with ab initio density functional theory simulations of the density of states and of the interaction with the substrate. Our DFT calculations indicate that the aza-bodipy molecule forms a chemical bond with the Au(111) substrate, with distortion of the molecular geometry and significant charge transfer between the molecule and the substrate. Nevertheless, most likely due to the low corrugation of the Au(111) surface, diffusion of the molecule is observed for applied bias in excess of 1 V. 相似文献
998.
Bleken F Skistad W Barbera K Kustova M Bordiga S Beato P Lillerud KP Svelle S Olsbye U 《Physical chemistry chemical physics : PCCP》2011,13(7):2539-2549
Four 3D 10-ring zeolites, IM-5, TNU-9, ZSM-11 and ZSM-5, with Si/Al = 14-24 and crystal sizes below 2 microns, were tested as catalysts for the methanol to hydrocarbons reaction (MTH) at atmospheric pressure, 350 °C and WHSV = 9 h(-1). All catalysts gave initially full methanol conversion, and showed strikingly similar effluent product selectivities. However, their life-time duration differed significantly, and decreased in the order: ZSM-11 > ZSM-5 ? TNU-9 > IM-5. A main difference between the two groups of stability behaviour was the size of cavities formed by channel intersections; larger cavities in TNU-9 and IM-5 leading to polyaromatics formation and a more rapid deactivation compared to ZSM-5 and ZSM-11. Effluent yield-conversion plots suggested that polymethylated benzene intermediates were more important in IM-5 and TNU-9 than in ZSM-5 and ZSM-11, where alkene methylation and cracking reactions seemed to dominate product formation. However, this difference had only minor influence on effluent selectivity. 相似文献
999.
Ceraulo L Giorgi G Liveri VT Bongiorno D Indelicato S Di Gaudio F Indelicato S 《European journal of mass spectrometry (Chichester, England)》2011,17(6):525-541
In contrast with the enormous amount of literature produced during many decades in the field of surfactant aggregation in liquid, liquid crystalline and solid phases, only a few investigations concerning surfactant self- assembling in the gas phase as charged aggregates have been carried out until now. This lack of interest is disappointing in view of the remarkable theoretical and practical importance of the inherent knowledge. The absence of surfactant-solvent interactions makes it easier to study the role of surfactant-surfactant forces in determining their peculiar self-assembling features as well as the ability of these assemblies to incorporate selected solubilizate molecules. Thus, the study of gas-phase surfactant and surfactant-solubilizate aggregates is a research subject which has exciting potential, including mass and energy transport in the atmosphere, origin of life and simulation of supramolecular aggregation in interstellar space. On the other hand, the structural and dynamic properties of surfactant aggregates in the gas phase could be exploited in a number of interesting applications such as atmospheric cleaning agents, transport and protection of pulmonary drugs or biomolecules and as nanoreactors for specialized chemical reactions in confined space. Spectrometric techniques, together with molecular dynamics simulations, have been the principal investigative tools in this field and appearto be particularly suited to gaining fundamental information on the structure and stability of surfactant-based supramolecular aggregates, charge state effects, entrapment of solubilizate molecules, preferential solubilization sites and chemical reactions localized in a single organized aggregate. The main aim of this review is to present the actual state of the art in this novel and exciting research field underlining the knowledge acquired up to now as well as the aspects needing a more deep understanding. Moreover, intriguing departures of the behavior of surfactant solutions under electrospray ionization conditions from that of ionic, polar and apolar analytes will be discussed. 相似文献
1000.
Balucani N Leonori F Bergeat A Petrucci R Casavecchia P 《Physical chemistry chemical physics : PCCP》2011,13(18):8322-8330
The dynamics of the radical-radical reaction O((3)P) + CH(3), a prototypical case for the reactions of atomic oxygen with alkyl radicals of great relevance in combustion chemistry, has been investigated by means of the crossed molecular beam technique with mass spectrometric detection at a collision energy of 55.9 kJ mol(-1). The results have been examined in the light of previous kinetic and theoretical work. From product angular and velocity distribution measurements, the dynamics of the predominant H-displacement channel leading to formaldehyde formation has been characterized. This channel has been found to proceed via the formation of an osculating complex; a significant coupling between the product centre-of-mass angular and translational energy distributions has been noted. Experimental attempts to characterize the dynamics of the channel leading to HCO + H(2) have failed and it remains unclear whether HCO is formed by the reaction and/or, if formed, a part of HCO does not dissociate quickly into CO + H. 相似文献