全文获取类型
收费全文 | 2641篇 |
免费 | 29篇 |
国内免费 | 13篇 |
专业分类
化学 | 1780篇 |
晶体学 | 6篇 |
力学 | 26篇 |
数学 | 539篇 |
物理学 | 332篇 |
出版年
2016年 | 23篇 |
2015年 | 17篇 |
2014年 | 35篇 |
2013年 | 79篇 |
2012年 | 62篇 |
2011年 | 61篇 |
2010年 | 47篇 |
2009年 | 38篇 |
2008年 | 57篇 |
2007年 | 59篇 |
2006年 | 73篇 |
2005年 | 65篇 |
2004年 | 59篇 |
2003年 | 50篇 |
2002年 | 47篇 |
2001年 | 19篇 |
2000年 | 35篇 |
1999年 | 37篇 |
1998年 | 27篇 |
1997年 | 35篇 |
1996年 | 56篇 |
1995年 | 40篇 |
1994年 | 38篇 |
1993年 | 49篇 |
1992年 | 42篇 |
1991年 | 40篇 |
1990年 | 31篇 |
1989年 | 31篇 |
1988年 | 23篇 |
1987年 | 30篇 |
1986年 | 37篇 |
1985年 | 58篇 |
1984年 | 32篇 |
1983年 | 35篇 |
1982年 | 45篇 |
1981年 | 37篇 |
1980年 | 58篇 |
1979年 | 54篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1976年 | 48篇 |
1975年 | 31篇 |
1974年 | 34篇 |
1973年 | 38篇 |
1972年 | 26篇 |
1971年 | 24篇 |
1970年 | 27篇 |
1967年 | 17篇 |
1930年 | 18篇 |
1929年 | 15篇 |
排序方式: 共有2683条查询结果,搜索用时 328 毫秒
141.
142.
The thermodynamics approach has been developed to describe the self-diffusion in nano-sized solids. It has been established that identical homologous temperatures of metal nanoparticles with their fixed characteristic size give the identical coefficients of diffusion under different pressures. The dependence of the activation enthalpy of diffusion on pressure and on the characteristic size of nanoparticles is first obtained. 相似文献
143.
William A. Roughead Donald P. Miller Alfred D. French 《Journal of Macromolecular Science: Physics》2013,52(1-4):229-245
The previous Polymer Diffraction Symposium saw the use of x-ray film data array calculations to obtain diffraction intensities with computed accuracies. Subsequently, methods for geometrical deconvolution of overlapped diffraction spots have been developed. The techniques have now been applied to data arrays from films of Fortisan. Severely overlapped reflection arcs were splined and transformed into polar coordinate space, yielding orthogonalized diffraction spot groups. Spots were then identified 相似文献
144.
Analysis of mechanical cochlear responses to wide bands of random noise clarifies many effects of cochlear nonlinearity. The previous paper [de Boer and Nuttall, J. Acoust. Soc. Am. 107, 1497-1507 (2000)] illustrates how closely results of computations in a nonlinear cochlear model agree with responses from physiological experiments. In the present paper results for tone stimuli are reported. It was found that the measured frequency response for pure tones differs little from the frequency response associated with a noise signal. For strong stimuli, well into the nonlinear region, tones have to be presented at a specific level with respect to the noise for this to be true. In this report the nonlinear cochlear model originally developed for noise analysis was modified to accommodate pure tones. For this purpose the efficiency with which outer hair cells modify the basilar-membrane response was made into a function of cochlear location based on local excitation. For each experiment, the modified model is able to account for the experimental findings, within 1 or 2 dB. Therefore, the model explains why the type of filtering that tones undergo in the cochlea is essentially the same as that for noise signals (provided the tones are presented at the appropriate level). 相似文献
145.
Simal F Delfosse S Demonceau A Noels AF Denk K Kohl FJ Weskamp T Herrmann WA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(13):3047-3052
Air-stable and readily available ruthenium benzylidene complexes of the general type [RuCl2(=CHPh)(L)(L')] (L, L' = PCy3 and/or N-heterocyclic carbene) constitute a new class of catalyst precursors for atom-transfer radical polymerization (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the polymerization of various monomers with good to excellent yields, and in a controlled way with methyl methacrylate and styrene. Variations of their basic structural motif provide insights into the essential parameters responsible for catalytic activity. The ligands L (PCy3 and/or N-heterocyclic carbene) turned out to play a particularly important role in determining the rate of the polymerizations. A similarly pronounced influence is exerted by the substituents on the N-heterocyclic carbene. Our results indicate that the catalysts decompose quickly under ATRP conditions, and polymerizations are mediated by both [RuCl2(=CHPh)(L)(L')] complexes and ruthenium species bereft of the benzylidene moiety, through a pathway in which both tricyclohexylphosphane and/or N-heterocyclic carbene ligands remain bound to the metal center. Polymerization of n-butyl acrylate and vinyl acetate is not controlled and most probably takes place through a redox-initiated free-radical process. 相似文献
146.
Diels-Alder-type cycloaddition of an electronically matched pair of saccharide-linked conjugated dienes and a dienophile-equipped protein gives neoglycoproteins at ambient temperature in pure water with a reaction half-life of approximately 2 h. Uncoupled saccharides can be recovered by diafiltration with complete conservation of the diene moiety, thus allowing their repeated use. The procedure described is the first for creating a carbon-carbon covalent bond in the bioconjugation step between a saccharide and a protein. 相似文献
147.
Weisshoff H Preiss A Nehls I Win T Mügge C 《Analytical and bioanalytical chemistry》2002,373(8):810-819
A hyphenated HPLC-(1)H NMR method for the identification and quantification of PAHs in soil samples has been developed and applied to a PAH reference sample provided by the Federal Institute for Materials Research and Testing (BAM, Berlin, Germany). The results were compared with those obtained by HPLC-DAD, HPLC-F, and GC-MS analyses of the same sample. 相似文献
148.
149.
150.
Stéphane Chalais Alfred Delville Christian Detellier André Gerstmans Pierre Laszlo 《Journal of solution chemistry》1983,12(1):33-40
Intrinsic formation constants for complexes of Na+ ions with a series of polyamines have been determined from23Na NMR measurements in binary mixtures of tetrahydrofuran (THF) and amines. The results show in a totally unambiguous manner a regular decrease in the magnitude of the chelate effect with the number of atoms intervening between the nitrogen ligators. The key assumption, tetracoordination of the cation, is critically examined, and experimental evidence is adduced in its support. 相似文献