全文获取类型
收费全文 | 634篇 |
免费 | 45篇 |
国内免费 | 4篇 |
专业分类
化学 | 490篇 |
力学 | 9篇 |
数学 | 76篇 |
物理学 | 108篇 |
出版年
2024年 | 5篇 |
2023年 | 22篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 54篇 |
2019年 | 27篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 37篇 |
2015年 | 29篇 |
2014年 | 30篇 |
2013年 | 32篇 |
2012年 | 32篇 |
2011年 | 42篇 |
2010年 | 15篇 |
2009年 | 17篇 |
2008年 | 16篇 |
2007年 | 15篇 |
2006年 | 26篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 7篇 |
1985年 | 14篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1938年 | 2篇 |
1932年 | 2篇 |
1910年 | 2篇 |
1898年 | 2篇 |
1895年 | 2篇 |
1891年 | 2篇 |
排序方式: 共有683条查询结果,搜索用时 15 毫秒
51.
52.
Silvestri MA Miles D Rothwell AP Wood KV Cushman M 《Rapid communications in mass spectrometry : RCM》2003,17(15):1703-1708
Electrospray ionization (ESI) mass spectrometry was employed to obtain both molecular weight confirmation and structural information for a series of novel alkenyldiarylmethane (ADAM) analogs. The mass spectral data were intended for use during the structure elucidation of ester hydrolysis products formed during an in vitro metabolism study of a series of novel ADAM analogs. The data on the precursor molecules show the presence of the molecular ion peak, [M+H](+), as well as a peak consistent with the hydrolysis product of the original ester ([MH-ROH+H(2)O](+)). However, chemical ionization mass spectrometry, elemental analysis and (1)H NMR data indicated the presence of only the intact diester compounds, suggesting that the formation of the hydrolysis product was an instrumental artifact, i.e., in-beam hydrolysis during ESI or a result of longer ion residence times of the ion trap mass analyzer. 相似文献
53.
Stephan Klaus Maximilian W. Lehenmeier Carly E. Anderson Bernhard Rieger 《Coordination chemistry reviews》2011,255(13-14):1460-1479
The catalytic copolymerization of CO2 with epoxides has been known for over 40 years. Even though many heterogeneous and homogeneous catalyst systems have been developed, catalyst activity and selectivity still remain too low for large scale industrial application.Recent investigations have identified new copolymerization pathways with strong evidence for cooperative (bifunctional) mechanisms. At high dilutions, traditional discrete mononuclear single-site catalyst systems generally show a loss in activity. This effect can be overcome with the help of recently developed dinuclear and binary linked systems that involve cooperative mechanisms and thus permit high catalyst efficiency.This review gives an overview on the most recent advances in CO2/epoxide copolymerization, new mechanistic studies and strategies for future catalyst developments. 相似文献
54.
We analyze the time evolution describing a quantum source for non-interacting particles, either bosons or fermions. The growth
behavior of the particle number (trace of the density matrix) is investigated, leading to spectral criteria for sublinear
or linear growth in the fermionic case, but also establishing the possibility of exponential growth for bosons. We further
study the local convergence of the density matrix in the long time limit and prove the semi-classical limit. 相似文献
55.
Ohne Zusammenfassung 相似文献
56.
Markus Clemens Moritz HeliasThorsten Steinmetz Georg Wimmer 《Journal of Computational and Applied Mathematics》2008
The simulation of slowly varying transient electric high-voltage fields and magnetic fields requires the repeated and successive solution of high-dimensional linear algebraic systems of equations with identical or near-identical system matrices and different right-hand side vectors. For these solution processes which are required within implicit time integration schemes and nonlinear (quasi-)Newton–Raphson methods an iterative multiple right-hand side (mrhs) scheme is used which recycles vector subspaces resulting from previous preconditioned conjugate gradient iteration runs. The combination of this scheme with a subspace projection extrapolation start value generation scheme is discussed. Numerical results for three-dimensional electric and magnetic field simulations are presented and the efficiency of the new schemes re-using eigenvector information from previous iteration processes with different tolerance criteria are compared to those of standard conjugate gradient iterations. 相似文献
57.
J. Kunze S. Koelling M. Reich M. A. Wimmer 《Analytical and bioanalytical chemistry》2000,366(2):165-166
A technique for the determination of titanium and zirconium in human blood serum, after pressurized digestion utilizing ICP-MS coupled to an ultrasonic nebulizer (USN) and desolvating membrane is described. As no CRM for titanium is available, zirconium has been determined in order to demonstrate the accuracy of the technique, as the limits in blood are well known. Bone cement consists basically of a polymer, namely polymethylmethacrylate (PMMA). For better X-ray contrast some manufacturers use incorporated ZrO2 with a volume fraction of 10 to 15%. Thus, the zirconium present in the PMMA matrix can be used as an indicator for the PMMA particulate debris. 相似文献
58.
59.
A. L. Nielsen M. B. O. Andersen T. V. Bugge C. F. Nielsen T. B. Nielsen R. Wimmer D. Yu K. L. Larsen 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6619-6629
In this article, we present the synthesis and characterization of water‐soluble polymers with hydrophobic moieties. The polymers were synthesized in aqueous solutions utilizing β‐cyclodextrins as solubility enhancers to bring the hydrophobic monomers into solution. Polymers were made with different spacing between polymer backbone and phenyl moiety by using styrene, allylbenzene, and 4‐phenyl‐1‐butene as hydrophobic moieties, respectively. The effect of the presence of CDs during synthesis as well as this difference in spacing was investigated by rebinding free β‐CDs to the polymers. The interactions between polymers and CDs were studied by ITC and this revealed some differences between the polymers. Polymers made in the presence of CDs showed a markedly stronger binding to free CDs. The same was observed with polymers with a longer spacing between backbone and phenyl moiety. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6619–6629, 2009 相似文献
60.
Maximilian Hansinger Michael Pfitzner Vladimir A. Sabelnikov 《Proceedings of the Combustion Institute》2021,38(2):2665-2672
The Eulerian Stochastic Fields (ESF) Monte Carlo method to solve the transported PDF (TPDF) equation is extended to account for differential diffusion effects by incorporating species individual molecular diffusivities. The method has been applied in Large Eddy simulation (LES) to non-piloted oxy-fuel jet flames at different Reynolds numbers experimentally investigated by Sevault et al. [1]. Due to the high H2 content in the fuel stream and CO2 in the oxidizer these flames pose new challenges to combustion modeling as the flame structures are different compared to CH4/air flames. The simulations show very good agreement with the experiments in terms of mixture fraction conditional mean values for temperature and mayor species on the fuel lean side and the reaction zone, deviations on the fuel rich side are discussed. The trend and location of localized extinction is reproduced well in the simulations, as well as differential diffusion effects in the near field. Additionally, it is shown that a neglect of differential diffusion in the combustion model leads to a lifted flame. 相似文献