全文获取类型
收费全文 | 476篇 |
免费 | 15篇 |
国内免费 | 4篇 |
专业分类
化学 | 324篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 37篇 |
物理学 | 121篇 |
出版年
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 8篇 |
2013年 | 23篇 |
2012年 | 18篇 |
2011年 | 32篇 |
2010年 | 21篇 |
2009年 | 21篇 |
2008年 | 35篇 |
2007年 | 21篇 |
2006年 | 25篇 |
2005年 | 14篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 10篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1968年 | 3篇 |
排序方式: 共有495条查询结果,搜索用时 15 毫秒
21.
Absolute rate constants and approximate product distributions are presented for the reactions of He+, Ne+, Ar+, Kr+, Xe+, CO+ and CO+2 with NH3 and PH3. In all cases, electron transfer is the dominant reaction channel. Hydrogen atom transfer is observed in several systems, but only as a minor product, even when this channel is very exothermic. The magnitude of the absolute rate constants can be correlated with the Franck-Condon factors associated with the reactions in most cases. Several exceptions to this general rule are observed that could not be readily predicted a priori. It is speculated that these reactions proceed via a collision complex. 相似文献
22.
Electroosmotic flow controllable coating on a capillary surface by a sol-gel process for capillary electrophoresis 总被引:1,自引:0,他引:1
A simple coating procedure employing a sol-gel process to modify the inner surface of a bare fused-silica capillary with a positively charged quaternary ammonium group is established. Scanning electron microscopic studies reveal that a smooth coating with 1 to approximately 2 microm thickness can be obtained at optimized coating conditions. With 40 mM citrate as a running electrolyte, the plot of electroosmotic flow (EOF) versus pH shows a unique three-stage EOF pattern from negative to zero and then to positive over a pH range of 2.5 to 7.0. At pH above 5.5, the direction of the EOF is from the anode to the cathode, as is the case in a bare fused-silica capillary, and the electroosmotic mobility increases as the pH increases. However, the direction of the EOF is reversed at pH below 4.0. Over the pH range of 4.0 to 5.5, zero electroosmotic mobility is obtained. Such a three-stage EOF pattern has been used to separate six aromatic acids under suppressed EOF and to separate nitrate and nitrite with the anions migrating in the same direction as the EOF. The positively charged quaternary ammonium group on the coating was also utilized to minimize the adsorption problem during the separation of five basic drugs under suppressed EOF and during the separation of four basic proteins with the cations migrate in the opposite direction as the EOF. Also, the stability and reproducibility of this column are good. 相似文献
23.
Filter-based microfluidic device as a platform for immunofluorescent assay of microbial cells 总被引:5,自引:0,他引:5
A filter-based microfluidic device was combined with immunofluorescent labeling as a platform to rapidly detect microbial cells. The coin-sized device consisted of micro-chambers, micro-channels and filter weirs (gap = 1-2 microm), and was demonstrated to effectively trap and concentrate microbial cells (i.e., Cryptosporidium parvum and Giardia lamblia), which were larger in size than the weir gap. After sample injection, a staining solution containing fluorescently-labeled antibodies was continuously provided into the device (flow rate = 20 microl min(-1)) to flush the microbial cells toward the weirs and to accelerate the fluorescent labeling reaction. Using a staining solution that was 10 to 100 times more dilute than the recommended concentration used in a conventional glass method, those target cells with a fluorescent signal-to-noise ratio of 12 could be microscopically observed at single-cell level within 2 to 5 min prior to secondary washing. 相似文献
24.
25.
Mildred M. Maguire Huang Do Son Kim Nguyen Chau Vo Douglas Smith Grant Koher Gregg Doutt Martyn C.R. Symons 《Journal of organometallic chemistry》1984,269(2):183-189
Exposure of (C5H5)2MO(CH3)2 and (C5H5)2W(CH3)2, prepared from the corresponding dichlorides, to 20Co γ-rays at 77 K gave H2C.CML3 carbene species characterised by their ESR spectra, together with a central feature possibly due to the parent cations. Dilute solutions in CD3OD gave features assigned to the parent anions which were converted on bleaching with visible light into methyl radicals, and H2C.ML3 radicals. From the magnitude of the 1H and 183W hyperfine coupling constants, it is deduced that the SOMO for H2C.WL3 radicals is strongly localised on carbon.Dilute solutions in aqueous sulphuric acid also gave species with A(2H) = 20 G, identified as the carbene derivatives, H2C.Ml3. These were formed on annealing, as signals assigned to HSO4 · radicals were lost. 相似文献
26.
The method of similarity analysis in the study of differential equations is extended to study the variability of parameters in a physical system. The analysis provides an insight into the meaning of physical similarity, which usually means the possibility of a reduction in the number of physical parameters characterizing the system. Theorems relating similarities to groups of invariant transformations are proved and employed to show how the number of parameters can be reduced. 相似文献
27.
28.
29.
This paper deals with ultrasound medical image processing, particularly to filter the noise while preserving the edges and
structures of information. The mathematical processing consists in solving by a numerical way a nonlinear evolutive boundary
value problem. Several numerical semi-implicit time marching schemes are considered and analyzed. At each time step, parallel
synchronous or asynchronous Schwarz alternating methods are used to solve the linear system and its convergence is studied.
Lastly, the results of sequential and parallel simulations are presented.
相似文献
30.
E. Herrmann Nguyen Thi Thu Chau O. Navratil G. Ohms L. Beyer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract The new 1,1-disubstituted 3-diphenoxy(thio)phosphoryl-(thio)ureas, R1R2NC(X)NHP(0Ph)2, HA, with X,Y = O,S, were synthesized by addition of secondary mines to the corresponding P-iso(thio)cyanates. This reaction is reversible if X,Y = S. (PhO)2P(Y)Cl reacts with H2NC(X)NR2 in the presence of an HCl acceptor only if X,Y a 0. Side reactions are observed. Phosphorylated derivatives of biuret were isolated from such a reaction mixture. 相似文献