全文获取类型
收费全文 | 149931篇 |
免费 | 1343篇 |
国内免费 | 409篇 |
专业分类
化学 | 81803篇 |
晶体学 | 2409篇 |
力学 | 6124篇 |
综合类 | 3篇 |
数学 | 14002篇 |
物理学 | 47342篇 |
出版年
2021年 | 1056篇 |
2020年 | 1228篇 |
2019年 | 1273篇 |
2018年 | 1656篇 |
2017年 | 1722篇 |
2016年 | 2593篇 |
2015年 | 1604篇 |
2014年 | 2406篇 |
2013年 | 6141篇 |
2012年 | 4938篇 |
2011年 | 6047篇 |
2010年 | 4249篇 |
2009年 | 4284篇 |
2008年 | 5797篇 |
2007年 | 5608篇 |
2006年 | 5465篇 |
2005年 | 5027篇 |
2004年 | 4520篇 |
2003年 | 4179篇 |
2002年 | 4070篇 |
2001年 | 5581篇 |
2000年 | 4031篇 |
1999年 | 3128篇 |
1998年 | 2142篇 |
1997年 | 2237篇 |
1996年 | 2109篇 |
1995年 | 1965篇 |
1994年 | 1967篇 |
1993年 | 1782篇 |
1992年 | 2284篇 |
1991年 | 2356篇 |
1990年 | 2179篇 |
1989年 | 2135篇 |
1988年 | 2110篇 |
1987年 | 2129篇 |
1986年 | 1945篇 |
1985年 | 2431篇 |
1984年 | 2438篇 |
1983年 | 1965篇 |
1982年 | 1965篇 |
1981年 | 1799篇 |
1980年 | 1789篇 |
1979年 | 2076篇 |
1978年 | 2140篇 |
1977年 | 2091篇 |
1976年 | 2007篇 |
1975年 | 1889篇 |
1974年 | 1886篇 |
1973年 | 1922篇 |
1972年 | 1256篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Egorova L. A. Radishevskaya N. I. Izaak T. I. 《Russian Journal of Applied Chemistry》2003,76(2):328-329
The possibility of using synthesized iron(III) and cobalt(II) molybdophosphates as dyes in dyeing of copolymers and polymeric formulations based on methacrylic acid and methyl methacrylate and also as pigments deposited onto natural and inorganic supports for heterogeneous dyeing of polymeric materials was studied. 相似文献
992.
A systematic study has been carried out on the characteristic changes in the fluorescence spectra of 1-naphthol doped in the
sol-gel-xerogel transition systems comprised of tetraethyl orthosilicate and diisobutoxyaluminium triethylsilicate catalyzed
by a small amount of HCl, NH4OH, as well as under uncatalyzed conditions. In the systems containing large amounts of silicon, the fluorescence of 1-naphthol
shifts to the red (a predominant emission from the 1La state) during the first stage of the reaction. This red shift indicates an increase in the polarity of the matrix surrounding
1-naphthol. In the second stage of the reaction, the spectrum shifts to the blue (a predominant emission from the 1Lb state), reflecting an increase in the micro-viscosity around 1-naphthol. In the systems containing relatively large amounts
of aluminum, however, the spectrum just after mixing shows a larger red shift than that originating from the 1L2 emission. This large red-shifted fluorescence reflects the formation of a complex between 1-naphthol and the −O−Al−O−Si−O-network.
The spectrum then shifted to the blue. The spectral behaviours observed indicate that there is a large and dynamic molecular-level
change in the physicochemical properties of the matrix surrounding the 1-naphthol molecules during the sol-gel-xerogel transitions
of the systems while the gelation phenomenon reflects macroscopic inflexibility although it is completely different from the
restriction of movement at the molecular level. 相似文献
993.
T. M. Gairbekov Ya. S. Yakhyaev S. N. Khadzhiev 《Reaction Kinetics and Catalysis Letters》1986,31(1):127-131
Regularities in n-hexane conversion on decationized Y zeolites under cracking and aromatization conditions have been studied. Possible formation of lower olefins and benzenes in parallel reactions following different mechanisms at low conversion degrees is suggested. The effect of thermosteam treatment on the activity and selectivity of Y zeolites in n-hexane conversion has been examined.
- Y . , . Y -.相似文献
994.
J. T. Glass J. F. McCann D. S. F. Crothers 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(2):119-124
Starting with the impulse approximation, we analyse second-order effects in relativistic electron capture. The relation of this model with relativistic distorted-wave approximations is clarified. In particular it is shown that the second-order spin-coupling terms in the RCDW theory are consistent with the correct form given by perturbation theory. In the semirelativistic limit, the RCDW results are shown to accord with the formulae of Moiseiwitsch for flip and nonflip transitions in the ultra-relativistic limit. This confirms that the continuum-distorted-wave model generalises to relativistic spinors, and highlights the defects of scalar models. We also present a new symmetric eikonal theory which gives reliable results for capture without change of spin, but leads to a divergent total cross section for spin-flip transitions in the second-order term. This effect, which is quite distinct from the spurious spin-flip amplitudes of the scalar symmetric eikonal theory, is taken as further evidence that the eikonal approximation is not valid for magnetic transitions. 相似文献
995.
996.
997.
A. Dávid G. Horváth Z. Mészáros T. Meisel Z. Halmos 《Journal of Thermal Analysis and Calorimetry》1974,6(1-2):59-66
The thermal behaviour of tetrahydroperparine (THP) and its derivatives with various acids has been investigated. The acid is liberated from the formate derivative basically in two steps, while the other aliphatic acids are released quantitatively before the thermal decomposition of the THP molecule. The thermoanalytical curves, electrical conductivity data measured in the molten phase, and infrared spectra prove that while part of the formic acid is hydrogen-bonded the other part is bound ionically in the molecule. It may be assumed that the marked biological activity of the compound can be explained by this difference in the nature of the bonds. 相似文献
998.
J R J Delben D R Chaves P D Candelorio A A S T Delben 《Journal of Thermal Analysis and Calorimetry》2006,83(2):411-414
New glasses have been synthesized in the system ZrF46BaF26PrF3. Glasses were prepared by conventional fusion method and the
vitreous domain was established. For vitreous samples the thermal stability
parameters were determined, so that the best compositions could be selected
according to a compromise between high glass forming ability and thermal stability
vs. crystallization. 相似文献
999.
A system was designed to automate the determination of three image dyes in an instant photographic material. The method involves extracting negative samples with dimethylsulfoxide and filtering the extract, followed by quantitating the dye coverage (dye per unit area of negative) through a spectrophotometric flow-injection procedure. Significant spectral overlap exists among the dyes, and as a result calculation of coverage requires solving three simultaneous equations. A microcomputer and data acquisition system were employed for controlling the detector and flow-injection system, acquiring and integrating the detector response, calculating coverage, producing and displaying control charts, and automatically transferring results to a VAX based corporate database. In addition to automating sample preparation and measurement steps as much as possible, the goal of this project was to automate the data manipulation and transfer steps. 相似文献
1000.
Martin B. Hocking David T. Syme David E. Axelson Kirk H. Michaelian 《Journal of polymer science. Part A, Polymer chemistry》1990,28(11):2969-2982
The comonomer required, p-maleimidobenzoic acid (MBA) was first prepared in good yield by refinements of published methods. p-Carboxysuccinanilic acid (CSA), and p-succinimidobenzoic acid (SBA), were also prepared to provide models useful for IR and NMR for spectroscopic assignments of the new copolymers. Polymerization of MBA with acrylamide in glacial acetic acid at 60°C gave copolymers with estimated viscosity average molecular weights of 60,000 to 90,000. Yields and viscosity average molecular weights decreased as the MBA to acrylamide monomer feed ratio was increased. The rate of incorporation of MBA into the copolymer rose from 7 to 23% when the mole ratio in the feed was raised from 5 to 20%. Decreasing the initiator concentration increased molecular weights by less than predicted and reduced the yield of copolymer for any given feed ratio of MBA to acrylamide. In all cases about 30–40% of the MBA units in the purified copolymers were hydrolyzed. A change to dimethyl sulfoxide solvent gave good, and poor yields of copolymer at 5 and 10 mol % MBA, respectively, and no copolymer at 20 mol % MBA. Viscosity average molecular weights of the copolymer products prepared in DMSO were somewhat lower than obtained for the copolymers prepared in acetic acid. Polymerization in a DMSO-water mixture gave a negligible yield of polymeric product. Instead, only hydrolysates of MBA precipitated when the coloured polymerization solutions were added to methanol. 相似文献