全文获取类型
收费全文 | 1071篇 |
免费 | 22篇 |
国内免费 | 4篇 |
专业分类
化学 | 789篇 |
晶体学 | 11篇 |
力学 | 17篇 |
数学 | 86篇 |
物理学 | 194篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 13篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 22篇 |
2013年 | 38篇 |
2012年 | 59篇 |
2011年 | 63篇 |
2010年 | 41篇 |
2009年 | 27篇 |
2008年 | 87篇 |
2007年 | 74篇 |
2006年 | 77篇 |
2005年 | 78篇 |
2004年 | 80篇 |
2003年 | 45篇 |
2002年 | 50篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 11篇 |
1974年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有1097条查询结果,搜索用时 15 毫秒
81.
We have used a density-functional theory based on the interaction site model to predict the liquid-vapor coexistence curve of nitrogen fluid. The pressure and chemical potential were calculated from thermodynamic integrations. The different paths of thermodynamic integration provide slightly different predictions for the liquid-vapor coexistence curve. However, these critical points and coexistence curves evaluated by the theory are in qualitative agreement with the experimental data. The theoretical coexistence curves scaled to critical constants agree with the experimental data quantitatively. 相似文献
82.
The photodecarboxylation of chiral mesityl alkanoate to mesitylalkane has been studied experimentally/theoretically, and it has been found that the photodecarboxylation proceeds to give the product in > 99% enantiomeric excesses under a variety of conditions, indicating no involvement of any radical intermediates, but that the reaction proceeds through the concerted cheletropic extrusion of CO2 from the energetically less-favored s-cis conformation. 相似文献
83.
Otsuka H Kijima H Hirata E Shinzato T Takushi A Bando M Takeda Y 《Chemical & pharmaceutical bulletin》2003,51(3):286-290
Five megastigmane glucosides were isolated from the leaves of Glochidion zeylanicum. One of them was a known compound, blumenol C O-beta-D-glucopyranoside (1), and the structures of the four new compounds, glochidionionosides A-D (2-5), were mainly elucidated by spectroscopic methods, including a modified Mosher's method. The absolute configurations of the six-membered ring of glochidionionoside D (5) were deduced by beta-D-glucopyranosylation-induced shift trends in the (13)C-NMR spectra and confirmed by X-ray analysis as its p-bromobenzoate (5b), and the axis chirality of C-7 was determined to be R. 相似文献
84.
Ishii A Kawai T Tekura K Oshida H Nakayama J 《Angewandte Chemie (International ed. in English)》2001,40(10):1924-1926
85.
A theoretical framework is demonstrated to evaluate the degree of entanglement of bit states in quantum computing. Separability
of general superposition of Hilbert space unit vectors is discussed, and criteria in amplitude as well as in phase are derived.
By these criteria the possibility of different quantum gates such as controlled not (CN), controlled controlled not (CCN),
controlled rotation (CR), and controlled phase shift (CPS), to create the entanglement is examined. Furthermore, the selection
of measurement mode external to the quantum system is incorporated in the formula using Kronecker delta (δ
kx
), introducing the concept of dynamic entanglement. With this the process of wavefunction collapse upon measurement is understood as the result of the activation of the dynamic
entanglement. A firefly in a box model is used to show a pure state of ontological uncertainty, which is in a dynamically
entangled state in Hilbert space. 相似文献
86.
Balance equations are derived from Enskog’s kinetic equation for a two-dimensional system of hard disks using Grad’s moment
expansion method. This set of equations constitute an extended hydrodynamics for moderately dense bi-dimensional fluids. The
set of independent hydrodynamic fields in the present formulations are: density, velocity, temperature and also—following Grad’s original idea—the symmetric and traceless pressure tensor p
ij
and the heat flux vector q
k
. An approximation scheme similar in spirit to one made by Grad in his original work is made. Once the hydrodynamics is derived
it is used to discuss the nature of a simple one-dimensional heat conduction problem. It is shown that, not too far from equilibrium,
the nonequilibrium pressure in this case only depends on the density, temperature and heat flux vector.
PACS: 51.10.+y, 05.20.Jj, 44.10.+i, 05.70.Ln 相似文献
87.
A new butenolide, designated odoratinolide (1), was isolated from the bark of the Vietnamese medicinal plant Machilus odoratissima. Its structure was determined by spectroscopic analyses. 相似文献
88.
89.
Turbulent flow in a rectangular duct with a sharp 180‐degree turn is difficult to predict numerically because the flow behavior is influenced by several types of forces, including centrifugal force, pressure‐driven force, and shear stress generated by anisotropic turbulence. In particular, this type of flow is characterized by a large‐scale separated flow, and it is difficult to predict the reattachment point of a separated flow. Numerical analysis has been performed for a turbulent flow in a rectangular duct with a sharp 180‐degree turn using the algebraic Reynolds stress model. A boundary‐fitted coordinate system is introduced as a method for coordinate transformation to set the boundary conditions next to complicated shapes. The calculated results are compared with the experimental data, as measured by a laser‐Doppler anemometer, in order to examine the validity of the proposed numerical method and turbulent model. In addition, the possibility of improving the wall function method in the separated flow region is examined by replacing the log‐law velocity profile for a smooth wall with that for a rough wall. The analysis results indicated that the proposed algebraic Reynolds stress model can be used to reasonably predict the turbulent flow in a rectangular duct with a sharp 180‐degree turn. In particular, the calculated reattachment point of a separated flow, which is difficult to predict in a turbulent flow, agrees well with the experimental results. In addition, the calculation results suggest that the wall function method using the log‐law velocity profile for a rough wall over a separated flow region has some potential for improving the prediction accuracy. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
90.