全文获取类型
收费全文 | 1941篇 |
免费 | 178篇 |
国内免费 | 166篇 |
专业分类
电工技术 | 69篇 |
综合类 | 153篇 |
化学工业 | 238篇 |
金属工艺 | 58篇 |
机械仪表 | 51篇 |
建筑科学 | 83篇 |
矿业工程 | 17篇 |
能源动力 | 69篇 |
轻工业 | 22篇 |
水利工程 | 16篇 |
石油天然气 | 13篇 |
武器工业 | 9篇 |
无线电 | 495篇 |
一般工业技术 | 503篇 |
冶金工业 | 154篇 |
原子能技术 | 47篇 |
自动化技术 | 288篇 |
出版年
2024年 | 3篇 |
2023年 | 57篇 |
2022年 | 21篇 |
2021年 | 48篇 |
2020年 | 55篇 |
2019年 | 57篇 |
2018年 | 52篇 |
2017年 | 57篇 |
2016年 | 61篇 |
2015年 | 81篇 |
2014年 | 91篇 |
2013年 | 152篇 |
2012年 | 73篇 |
2011年 | 126篇 |
2010年 | 54篇 |
2009年 | 108篇 |
2008年 | 116篇 |
2007年 | 108篇 |
2006年 | 85篇 |
2005年 | 102篇 |
2004年 | 103篇 |
2003年 | 84篇 |
2002年 | 73篇 |
2001年 | 67篇 |
2000年 | 66篇 |
1999年 | 55篇 |
1998年 | 38篇 |
1997年 | 30篇 |
1996年 | 27篇 |
1995年 | 28篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1964年 | 2篇 |
1959年 | 1篇 |
1958年 | 2篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2285条查询结果,搜索用时 62 毫秒
21.
22.
23.
本文着重于辐射作用于物质最初生成的产物,包括激发态的离子与分子,能量超过热能的次级电子等的反应以及电荷和激发能的转移,并试图论述它们的最新发展。 相似文献
24.
D. L. Wakefield 《International Journal of Thermophysics》1988,9(3):365-381
This paper is the final in a series of three viscosity and density studies of pure n-alkanes and selected binary and quaternary mixtures. A standard U-tube viscometer was used for viscosity measurements, and a Pyrex flask-type pycnometer was used for density determinations. Results are given here for pure alkane and selected binary mixtures of n-tetradecane + n-octane, for selected quaternary mixtures of n-hexadecane + n-dodecane + n-decane + n-hexane, and for pure and selected quaternary mixtures of n-hexadecane + n-dodecane + n-nonane + n-heptane at 303.16 and 308.16 K. The principle of congruence was tested, as was the Grunberg and Nissan equation, as they have been shown to be useful as prediction techniques for other n-alkane binary mixtures. Comparisons were made between the two groups of quaternary alkane mixtures and the binary n-tetradecane + n-octane mixtures of the same pseudo composition to understand better the dependence of mixture viscosities on the composition parameter. 相似文献
25.
A new method has been developed for predicting liquid activity coefficients in ternary mixtures from group contributions. In this method, activity coefficients are obtained from the excess Gibbs free energy of mixing at constant temperature and pressure. In calculating this excess function, the constituent and mixture Gibbs free energies are each represented by an expansion about a pure reference fluid in powers of ratios of hard-sphere diameters and molecular attraction parameters. When the pure component differs from the reference by a single structural group, these ratios represent, respectively, the size contribution and the attraction contribution of this group to the thermodynamic property of the pure fluid. Contributions of intermolecular repulsion to the excess Gibbs free energy are calculated directly from hard-sphere equations of state for the mixture and pure components. The effect of polar contributions calculated by a Padé approximant is also examined. Results indicate that the method developed from the hard-sphere expansion corresponding-states theory is useful for predicting activity coefficients in ternary mixtures when unlike-pair interaction parameters are fitted to binary activity coefficient data. Furthermore, the method shows promise in providing a theoretical basis for applying group contributions to activity coefficients.Nomenclature
A
Residual Helmholtz free energy
-
C
p
Constant-pressure heat capacity
- H
vap
Heat of vaporization
-
P
s
Saturated vapor pressure
-
R
Gas constant
-
T
Temperature
-
U
HS
Hard-sphere internal energy
-
V
c
Critical volume
-
V
L
Liquid volume
-
x
Dimensionless residual thermodynamic property
-
Z
Compressibility factor
-
d
Center-to-center distance between two touching molecules
-
k
Boltzmann constant
-
n
Moles
-
x
Liquid mole fraction
-
y
Vapor mole fraction
-
Volume expansivity
-
Liquid activity coefficient
-
Minimum molecular attraction potential
-
Isothermal compressibility
-
Permanent dipole moment
-
3.14159...
-
Density
-
Fugacity coefficient
Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A. 相似文献
26.
提出一种融合节点状态信息的跨社交网络用户对齐方法, 通过网络表示捕获节点的局部特征和节点状态信息得到每个账户的嵌入向量, 计算不同账户对应表示之间的相似性发现对齐用户。在2个真实数据集上的试验结果表明, 提出的方法相对于其他方法可以对齐更多的用户。在预测不同尺度的top-k时, 提出的方法在网络结构较稠密的Twitter-Foursquare数据集上能够在top-9时对齐准确率达到50%且在稀疏且大网络数据集DM-ML上相比其他方法对齐准确率提高12.06%~36.62%;在分析F1-score时, 提出的方法能够有效提高用户对齐的性能。 相似文献
27.
28.
1 INTRODUCTIONThe CSP(Corresponding States Principle)has been considered to be a useful methodfor the prediction of fluid properties from a minimum amount of information.One ofits form,the shape factor methods is developed through relating the pVT of any interestedpure fluid"a"to that of another"0"by writing 相似文献
29.
I. van der Westhuizen E. Du Toit W. Nicol 《Chemical Engineering Research and Design》2007,85(12):1604-1610
The existence of multiple hydrodynamic studies (MHS) in trickle flow is a well-known phenomenon. It is also known that different prewetting procedures result in major differences in MHS when the hydrodynamic variables pressure drop, liquid holdup and gas–liquid mass transfer are considered. Given a certain prewetting procedure one still has the option to perform flow hysteresis cycles to achieve an even wider variety of MHS. Although numerous studies have been performed on trickle flow hysteresis, none have attempted to decouple the hysteresis behaviour from the prewetting procedure followed. Accordingly there are numerous hysteresis possibilities that have not been investigated. In this work a single liquid and gas cycle were performed for four distinct prewetting procedures described here as a dry bed, a Levec type prewetted bed, Kan prewetted bed (achieved by increasing either the liquid or the gas flow rate until the pulsing flow regime is reached) and a Super prewetted bed. Pressure drop, liquid holdup and gas–liquid mass transfer are the hydrodynamic parameters studied to quantify the various MHS. It is shown that the shape and extent of the hysteresis cycle are strongly dependant on the prewetting procedure. In terms of flow structure, similar hysteresis trends on the Kan Liquid and Super prewetting modes indicate that these modes are hydrodynamically similar. The additional measurement of the hysteresis behaviour of gas–liquid mass transfer proofs that neither holdup nor pressure drop can be used as an indicator of the distribution uniformity. 相似文献
30.
Andrew J. Morris Rebecca J. Nicholls Chris J. Pickard Jonathan R. Yates 《Computer Physics Communications》2014
We present OptaDOS, a program for calculating core-electron and low-loss electron energy loss spectra (EELS) and optical spectra along with total-, projected- and joint-density of electronic states (DOS) from single-particle eigenenergies and dipole transition coefficients. Energy-loss spectroscopy is an important tool for probing bonding within a material. Interpreting these spectra can be aided by first principles calculations. The spectra are generated from the eigenenergies through integration over the Brillouin zone. An important feature of this code is that this integration is performed using a choice of adaptive or linear extrapolation broadening methods which we show produces higher accuracy spectra than standard fixed-width Gaussian broadening. OptaDOS may be straightforwardly interfaced to any electronic structure code. OptaDOS is freely available under the GNU General Public licence from http://www.optados.org. 相似文献