全文获取类型
收费全文 | 1267篇 |
免费 | 115篇 |
国内免费 | 97篇 |
专业分类
化学 | 627篇 |
晶体学 | 8篇 |
力学 | 330篇 |
综合类 | 11篇 |
数学 | 138篇 |
物理学 | 365篇 |
出版年
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 31篇 |
2020年 | 37篇 |
2019年 | 28篇 |
2018年 | 36篇 |
2017年 | 37篇 |
2016年 | 43篇 |
2015年 | 37篇 |
2014年 | 49篇 |
2013年 | 69篇 |
2012年 | 60篇 |
2011年 | 57篇 |
2010年 | 54篇 |
2009年 | 77篇 |
2008年 | 91篇 |
2007年 | 84篇 |
2006年 | 86篇 |
2005年 | 51篇 |
2004年 | 64篇 |
2003年 | 47篇 |
2002年 | 49篇 |
2001年 | 27篇 |
2000年 | 43篇 |
1999年 | 35篇 |
1998年 | 34篇 |
1997年 | 26篇 |
1996年 | 23篇 |
1995年 | 27篇 |
1994年 | 33篇 |
1993年 | 37篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有1479条查询结果,搜索用时 8 毫秒
101.
K. Jagadeeswara Pillai S. Vijaya Kumar Varma M. Syam Babu 《Proceedings Mathematical Sciences》1987,96(1):61-69
The aligned magnetic effects on a steady laminar, viscous, incompressible, conducting fluid down an open inclined channel
bounded below by a bed of varying permeability has been studied when the free surface is exposed to atmospheric pressure.
Beavers and Joseph slip condition at the interface of the free flow region and the fluid flow in the porous bed and the Darcy’s
law in the porous medium have been used. The expressions for velocity, magnetic strength and the mass flow across the cross-section
of the channel are obtained. 相似文献
102.
以左手材料中产生负磁导率的开口谐振环结构模型为例,从磁导率的定义出发,借助于电磁感应定律,推导了负磁导率的产生过程. 相似文献
103.
Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction,which limits their capability for increased predictive accuracy relative to experimental data.This is partly because of the nature of slug flow pneumatic conveying system,which,as a dynamic system,never becomes stable.By utilising conservation of mass (airflow),a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour.The rate of air permeation through slug,one of the important factors in the conservation model,is expressed as a function of a slug permeability factor.Other factors such as slug velocity,slug length and the fraction of stationary layer were also considered.Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model,showing good agreement between the model and experimental results. 相似文献
104.
James J. Sheng 《Transport in Porous Media》2009,77(3):507-527
To determine the permeabilities from a vertical interference test, earlier investigators proposed correlations or type curves
based on point source solutions or partially penetrated well solutions. However, it is impossible for these correlations or
type curves to cover all possible scenarios in the real world. In more recent years, people use regression analysis to simultaneously
match the pressure responses at the source interval and the observation point. With regression analysis, we face the problem
of non-unique solutions. Sometimes, estimated permeability could be outside a reasonable range when analyzing noisy data from
real tests. In this paper, a new technique is presented to estimate horizontal and vertical permeabilities from the time-delayed
response in a wireline vertical interference test. In a vertical test, a pressure drawdown test period is followed by a pressure
buildup test period. Because of the delay in response, the pressure at the observation probe continues to drop for some time
while the pressure at the source interval is being built up. The maximum pressure drop at the observation probe with regard
to the maximum pressure drop in the source interval is time-delayed. Using this time delay and the maximum pressure drop at
the observation probe, vertical and horizontal permeabilities can be estimated. A novel numerical scheme is used. The new
technique is compared with the previous methods, and it shows its superiority in accuracy. In addition, it can be used in
different test configurations. Application issues in real testing conditions are discussed. Finally, two field tests are analyzed
using this technique, while an earlier effort to analyze the tests using a conventional method was not successful due to poor
data quality. 相似文献
105.
Masahiro Yoshida Tsutomu Matsui Yasuo Hatate Takayuki Takei Koichiro Shiomori Shiro Kiyoyama 《Journal of polymer science. Part A, Polymer chemistry》2008,46(5):1749-1757
Nylon‐polystyrene microcapsules with immobilized ferroelectric liquid crystalline segments were prepared, and permeability control of an encapsulated core material was investigated under an external electric field. A ferroelectric liquid crystal monomer possessing both mesogenicity and chirality responded effectively to the external electrical field. Permeation of the material (oxprenolol) contained in the inner aqueous core of the microcapsules was enhanced under a weak electric field (2 V). Furthermore, the permeability of oxprenolol did not depend on the external electric field in the absence of the ferroelectric liquid crystal segments. To clarify the controlled‐release mechanism of the core material, the light transmittance of the polymer membranes was quantitatively evaluated under an external electric field using a handmade polarized light transmittance apparatus. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1749–1757, 2008 相似文献
106.
E. Rudnik I. Resiak C. Wojciechowski Z. Dobkowski 《Journal of Thermal Analysis and Calorimetry》2001,64(2):495-500
Laboratory-made asymmetric polyurethane membranes designed for immunoisolation were investigated. Two types of EK and ES membranes
were prepared in different spinning conditions.
The membrane structure was characterised by the skin pore radius measurements using differential scanning calorimetry (DSC).
Diffusive transport properties of membranes were determined by in vitro method for albumin and creatinine. The scanning electron
microscopy (SEM) was applied to study the morphology of membranes.
It has been found that the DSC technique is a useful tool for the evaluation of pore radii in the skin layer for PU membranes.
Calculated pore radii were in the range from 1.95 to 2.47 nm for the EK and ES types. A correlation between the skin pore
radii and the transport properties was not found in this case of investigated membranes. However, the transport properties
data can serve for the estimation of selectivity of membranes. Thus, the selectivity of membranes for solutes of various molecular
size was estimated from the D
m/D
w ratio of diffusion coefficients for albumin and creatinine. The SEM micrographs reveal the finger-like internal structure
of capillary membranes, as well as various skin thickness.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
107.
A result on pure shear provides the motivation for the determination of some new general results relating real second order
Cartesian tensors.
相似文献
108.
109.
O. N. Soboleva 《Journal of Applied Mechanics and Technical Physics》2005,46(6):891-900
Equations for the effective coefficients of random permeability fields for fluid flow through a porous medium with log-stable
distributions are derived using the Wilson renormalization group approach. Results of the theoretical modeling are compared
with data of numerical modeling.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 146–158, November–December, 2005. 相似文献
110.