全文获取类型
收费全文 | 417篇 |
免费 | 65篇 |
国内免费 | 12篇 |
专业分类
化学 | 114篇 |
晶体学 | 1篇 |
力学 | 129篇 |
综合类 | 3篇 |
数学 | 91篇 |
物理学 | 156篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 29篇 |
2019年 | 14篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 26篇 |
2012年 | 13篇 |
2011年 | 19篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 27篇 |
2007年 | 38篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 22篇 |
2003年 | 20篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 15 毫秒
151.
Zhisheng Lin Zhengmi Du Shener Chen 《International Journal of Infrared and Millimeter Waves》1996,17(10):1749-1760
A 4MM-Wave composite mode multimode conical feedhorn has been developed. Its mode-ratios are calculated and its formulas of the radiation patterns are derived. The measurement results of one and two dimension radiation patterns, measured by the automatic measurement system which we had researched, and the properties of band width and sidelobe are given. Theoretical analyses and measurements show that at the centre frequency 69.1GHZ, down to -23dB, the radiation pattern is rotationally symmetric, in this range there is not any sidelobe existing, the band width is 4.5 GHZ. The multimode feedhorn is thus of certain practical using value. 相似文献
152.
153.
The solution of the problem of impulsive minimization of a weighted sum of characteristic velocities of a spacecraft subject to linear equations of motion is presented without the use of calculus of variations or optimal control theory. The geometric structure of the set of boundary points associated with an optimal primer vector is found to be a simplex composed of convex conical sets. Eachk-dimensional open face of the simplex consists of boundary points having nondegeneratek-impulse solutions. This geometric structure leads to a simple proof that at mostn-impulses are required to solve a problem inn-dimensional space. This work is applied to the problem of planar rendezvous of a spacecraft with a satellite in Keplerian orbit using the Tschauner-Hempel equations of motion, with special emphasis on four-impulse solutions. Primer vectors representing four-impulse solutions are sought out and found for elliptical orbits, but none were found for orbits of higher eccentricity. For highly eccentric elliptical orbits, degenerate fiveimpulse solutions were found. In this situation, computer simulations reveal vastly different optimal trajectories having identical boundary conditions and cost. 相似文献
154.
The paper describes a method for solving numerically two-dimensional or axisymmetric, and three-dimensional turbulent internal flow problems. The method is based on an implicit upwinding relaxation scheme with an arbitrarily shaped conservative control volume. The compressible Reynolds-averaged Navier-Stokes equations are solved with a two-equation turbulence model. All these equations are expressed by using a non-orthogonal curvilinear co-ordinate system. The method is applied to study the compressible internal flow in modern power installations. It has been observed that predictions for two-dimensional and three-dimensional channels show very good agreement with experimental results. 相似文献
155.
Using the equations of a non-isothermal thin layer of viscous fluid with an exponential dependence of the viscosity on temperature, a family of hydrodynamic models of a cooling lava flow over a conical surface in the presence of mass supply is constructed. These models correspond to asymptotically different rates of heat exchange with the ambient medium. The evolution of the free-surface shape and the temperature fields is investigated numerically for a stationary mass supply. Using the matched asymptotic expansions method, solutions valid both near and very far from the mass supply region are constructed. The solutions obtained are compared with known analytical solutions for isothermal flow.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 62–75.Original Russian Text Copyright © 2005 by Osiptsov. 相似文献
156.
How Photoisomerization Drives Peptide Folding and Unfolding: Insights from QM/MM and MM Dynamics Simulations 下载免费PDF全文
Dr. Shu‐Hua Xia Prof. Dr. Ganglong Cui Prof. Dr. Wei‐Hai Fang Prof. Dr. Walter Thiel 《Angewandte Chemie (International ed. in English)》2016,55(6):2067-2072
Photoswitchable azobenzene cross‐linkers can control the folding and unfolding of peptides by photoisomerization and can thus regulate peptide affinities and enzyme activities. Using quantum mechanics/molecular mechanics (QM/MM) methods and classical MM force fields, we report the first molecular dynamics simulations of the photoinduced folding and unfolding processes in the azobenzene cross‐linked FK‐11 peptide. We find that the interactions between the peptide and the azobenzene cross‐linker are crucial for controlling the evolution of the secondary structure of the peptide and responsible for accelerating the folding and unfolding events. They also modify the photoisomerization mechanism of the azobenzene cross‐linker compared with the situation in vacuo or in solution. 相似文献
157.
The potential surfaces of the ground and lowest excited states of the [RuCl5NO]2? complex ion were studied by density functional theory. The conical intersections between the potential surfaces of the ground and lowest excited states were found and characterized. The possible routes from the conical intersection points to the ground state and metastable bond isomers were traced. A preliminary scheme, describing photoisomerizations in the complex, was suggested. 相似文献
158.
159.
160.
Prof. Dr. Joonghan Kim Dakyeung Oh Eunji Park Jeongmin Park Jungyoon Kim Prof. Dr. Jeong Sik Lim 《Chemphyschem》2023,24(13):e202300048
The photochemical reaction mechanism underlying the intramolecular H-transfer of the H2C3O+⋅ radical cation to the H2CCCO+⋅ methylene ketene cation was elucidated using time-dependent density functional theory and high-level ab initio methods. Once the D1 state of H2C3O+⋅ is populated, the reaction proceeds to form an intermediate (IM) in the D1 state (IM4D1). The molecular structure of the conical intersection (CI) was optimized using a multiconfigurational ab initio method. The CI is readily accessible because it lies slightly above the IM4D1 in energy. In addition, the gradient difference vector of the CI is almost parallel to the intramolecular H-transfer reaction coordinate. Once the vibration mode of IM4D1 which is parallel to the reaction coordinate is populated, the degeneracy of the CI is readily lifted and H2CCCO+⋅ was formed via a relaxation pathway in the D0 state. Our calculated results clearly describe the photochemical intramolecular H transfer reaction reported in a recent study. 相似文献