全文获取类型
收费全文 | 843篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 484篇 |
晶体学 | 19篇 |
力学 | 24篇 |
数学 | 65篇 |
物理学 | 262篇 |
出版年
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 33篇 |
2013年 | 63篇 |
2012年 | 38篇 |
2011年 | 49篇 |
2010年 | 28篇 |
2009年 | 20篇 |
2008年 | 34篇 |
2007年 | 23篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 16篇 |
2002年 | 26篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 12篇 |
1972年 | 5篇 |
排序方式: 共有854条查询结果,搜索用时 15 毫秒
101.
102.
R.C. Mehta 《Shock Waves》2002,11(6):431-440
The pressure oscillations over a forward facing spike attached to an axisymmetric blunt body are simulated by solving time-dependent
compressible Navier–Stokes equations. The governing fluid flow equations are discretized in spatial coordinates employing
a finite volume approach which reduces the equations to semidiscretized ordinary differential equations. Temporal integration
is performed using the two-stage Runge–Kutta time stepping scheme. A global time step is used to obtain a time-accurate numerical
solution. The numerical computation is carried out for a freestream Mach number of 6.80 and for spike length to hemispherical
diameter ratios of 0.5, 1.0 and 2.0. The flow features around the spiked blunt body are characterized by a conical shock wave
emanating from the spike tip, a region of separated flow in front of the hemispherical cap, and the resulting reattachment
shock wave. Comparisons of the numerical results are made with the available experimental results, such as schlieren pictures
and the surface pressure distribution along the spiked blunt body. They are found to be in good agreement. Spectral analysis
of the computed pressure oscillations are performed employing fast Fourier transforms. The surface pressure oscillations over
the spike and phase plots exhibit a behaviour analogous to that of the Van der Pol equation for a self-sustained oscillatory
flow.
Received 28 February 2001 / Accepted 17 January 2002 相似文献
103.
104.
A reliable Pd-catalyzed amination protocol is described for the synthesis of N-alkyltacrines and analogs. The Josiphos ligand CyPFtBu was found to provide optimum yields: 16 examples are given. Compared to the typical high-temperature nucleophilic aromatic substitution (NAS) routes, Pd-catalyzed aminations proceed at significantly lower reaction temperatures, and enable the synthesis of otherwise inaccessible products. 相似文献
105.
Anil Kumar Sharma Abhilasha Singh R. K. Mehta Sudhanshu Sharma S. P. Bansal K. S. Gupta 《国际化学动力学杂志》2011,43(7):379-392
To understand the chemistry of Cu(II)–NH3–S(IV)–O2 system, the kinetics of the oxidation of sulfur(IV) catalyzed by amminecopper(II) complexes has been studied in the ammonia‐buffered solutions. Sulfur(IV) is oxidized to sulfate. The complexes, Cu(NH3)2+, Cu(NH3)22+, and Cu(NH3)2+3 appear to be equally reactive and Cu(NH3)42+ appears to be unreactive. The kinetics obey the rate law: where α1 and γ1 are the rate constants for O2‐dependent and O2‐independent pathways, respectively, for Cu(NH3)2+, Cu(NH3)2+2, and Cu(N H3)32+ complexes, which appear to be equally reactive. The values of α1 and γ1 were found to be (1.32 ± 0.21) × 106 L2 mol?2 s?1 (1.74 ± 0.40) × 109 L3 mol?3 s?1respectively at 30°C. The reaction rate is not influenced by the presence of ethanol—a free radical scavenger, so a nonradical mechanism has been proposed. The results of this study are useful in understanding the atmospheric chemistry of aqueous phase autoxidation of dissolved sulfur dioxide in copper(II)–ammonia–sulfur(IV)–oxygen system at high pH. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 379–392, 2011 相似文献
106.
Goverdhan Mehta Raja MohanraoSreenivas Katukojvala Yannick LandaisSaikat Sen 《Tetrahedron letters》2011,52(22):2893-2897
A stereocontrolled synthesis of nine-membered aminocarbasugar analogs (amino-cyclononanoses) from a rigid bicyclo[4.3.1]deca-2,4-dien-10-one platform, harboring a latent functionalized cyclononane ring, is described. 相似文献
107.
Monodispersed PEG-coated ZnS (P-ZnS) nanoparticles (NPs) were synthesized by facile microwave process and utilized as efficient electron mediators for the fabrication of highly sensitive hydrazine chemical sensor. The detailed morphological and structural properties revealed the monodispersity and good crystallinity for synthesized P-ZnS NPs. A high-sensitivity of ∼89.3 μA cm−2 μM and low limit of detection of 1.07 μM, based on S/N ratio, were obtained for the fabrication of hydrazine chemical sensor based on P-ZnS NPs. To the best of our knowledge, this is the first report which demonstrates the utilization of P-ZnS NPs for the fabrication of efficient hydrazine chemical sensor. By this work, it could be concluded that simply synthesized ZnS NPs can be used as efficient electron mediators for the fabrication of effective hydrazine chemical sensors. 相似文献
108.
Mehta VP Sharma Ak Modha SG Sharma S Meganathan T Parmar VS Van der Eycken E 《The Journal of organic chemistry》2011,76(8):2920-2925
The N-heterocyclic carbene catalyzed chemoselective C3-aroylation of 3,5-dichloro-2(1H)-pyrazinones with various aldehydes is reported. We herein describe results of this remarkable mild and efficient procedure. 相似文献
109.
110.
Short synthetic routes to the title compounds 1,–3, from readily available Diels-Alder adduct 5 of 6,6-dimethylfulvene and acrylonitrile are described. 相似文献