全文获取类型
收费全文 | 61243篇 |
免费 | 7101篇 |
国内免费 | 4631篇 |
专业分类
电工技术 | 5374篇 |
技术理论 | 4篇 |
综合类 | 5556篇 |
化学工业 | 10697篇 |
金属工艺 | 2337篇 |
机械仪表 | 4528篇 |
建筑科学 | 3260篇 |
矿业工程 | 1781篇 |
能源动力 | 6291篇 |
轻工业 | 1746篇 |
水利工程 | 5268篇 |
石油天然气 | 4058篇 |
武器工业 | 737篇 |
无线电 | 3718篇 |
一般工业技术 | 5683篇 |
冶金工业 | 3164篇 |
原子能技术 | 3136篇 |
自动化技术 | 5637篇 |
出版年
2024年 | 295篇 |
2023年 | 911篇 |
2022年 | 1762篇 |
2021年 | 2074篇 |
2020年 | 2089篇 |
2019年 | 1829篇 |
2018年 | 1649篇 |
2017年 | 2150篇 |
2016年 | 2415篇 |
2015年 | 2406篇 |
2014年 | 3318篇 |
2013年 | 4355篇 |
2012年 | 4021篇 |
2011年 | 4694篇 |
2010年 | 3257篇 |
2009年 | 3601篇 |
2008年 | 3272篇 |
2007年 | 3944篇 |
2006年 | 3719篇 |
2005年 | 3295篇 |
2004年 | 2775篇 |
2003年 | 2505篇 |
2002年 | 2014篇 |
2001年 | 1681篇 |
2000年 | 1433篇 |
1999年 | 1234篇 |
1998年 | 1029篇 |
1997年 | 851篇 |
1996年 | 806篇 |
1995年 | 711篇 |
1994年 | 601篇 |
1993年 | 457篇 |
1992年 | 409篇 |
1991年 | 267篇 |
1990年 | 264篇 |
1989年 | 189篇 |
1988年 | 158篇 |
1987年 | 122篇 |
1986年 | 84篇 |
1985年 | 60篇 |
1984年 | 67篇 |
1983年 | 46篇 |
1982年 | 36篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1979年 | 17篇 |
1978年 | 6篇 |
1974年 | 4篇 |
1959年 | 31篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
H. M. Park M. C. Sung 《International journal for numerical methods in engineering》2004,60(12):1949-1968
The Karhunen–Loève Galerkin procedure is employed to solve an inverse radiation problem of determining the time‐varying strength of a heat source, which mimics flames in a furnace, from temperature measurements in three‐dimensional participating media where radiation and conduction occur simultaneously. The inverse radiation problem is solved through the minimization of a performance function, which is expressed by the sum of square residuals between calculated and observed temperature, using a conjugate gradient method. Through the Karhunen–Loève Galerkin procedure, one can represent the system dynamics with a minimum degree of freedom, and consequently the amount of computation required in the solution of the inverse problem is reduced drastically when the present technique is adopted. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
102.
A. Aryshev S. Araki P. Karataev T. Naito N. Terunuma J. Urakawa 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2007,580(3):1544-1551
A fast room temperature microwave detection system based on the Schottky Barrier-diode detector was created at the KEK ATF (Accelerator Test Facility). It was tested using Coherent Synchrotron Radiation (CSR) generated by the 1.28 GeV electron beam in the damping ring. The speed performance of the detection system was checked by observing the CSR from a multi-bunch (2.8 ns bunch separation time) beam. The theoretical estimations of CSR power yield from an edge of bending magnet as well as new injection tuning method are presented. A very high sensitivity of CSR power yield to the longitudinal electron distribution in a bunch is discussed. 相似文献
103.
Sezen Curgul 《Polymer》2005,46(1):275-281
An elongational flow field is imposed on a solution of block copolymers consisting of semirigid macromolecules with rigid, rodlike sequences of units in combination with random coil (flexible) units. The problem is formulated according to the lattice treatment of Matheson and Flory. In this formulation, the system consists of rigid blocks whose lengths and locations are fixed by the structure within each macromolecule. These blocks are separated by random coiled units. An excess free energy other than the equilibrium Gibbs free energy of the quiescent solution has to be considered due to the flow field that tends to align the rods. This excess free energy is calculated from the potential energy of rods when a steady-state, homogeneous and irrotational flow field is applied to the solution. The effects of composition, polymer-solvent interaction, size of the co-polymer and flow rates are investigated. Depending on the size and number of rods, some of the chains studied exhibit a biphasic region at equilibrium that shifts to lower concentrations with increasing flow. Longer chains with shorter rods that are isotropic at equilibrium, exhibit a biphasic region at finite values of flow. The degree of orientation increases sharply when the system is biphasic. For larger flows, the orientation function is very close to unity which is perfect orientation. 相似文献
104.
The non-uniformity of the air temperatures and the slow flow rate at the plane collector exit constitute the main cause of the limitations of the solar drying systems. In order to obtain an uniform and a variable flow rate for different uses, a hot air generator using concentrated solar radiation is proposed. To improve the thermal efficiency of the generator, a study of the influence of different shape parameters is realized. The generator is simulated in the laboratory while investigating the flow induced by a circular disc heated uniformly by Joule effect at constant temperature. This disc is placed at the entrance of an open ended vertical cylinder of a larger diameter. Thermal radiation emitted by the hot disc heats the cylinder wall. The heating of the fluid at the cylinder-inlet generates a thermosiphon flow around the one created by the hot disc. The comparison of the velocity and the temperature profiles of the resulting flow permits to determine the influence of the cylinder height, the vertical source-cylinder spacing and the radius ratio, on the resulting flow at the system exit. Thus, a judicious choice of the shape parameters entails an improvement of the flow rate as well as the thermal flux absorbed by the air and a good homogenization of the air temperature at the generator exit. 相似文献
105.
Giulio Croce Paola Dagaro Carlo Nonino 《International Journal of Heat and Mass Transfer》2007,50(25-26):5249-5259
106.
Arash Sarhangi Fard Navid M. Famili Patrick D. Anderson 《Computers & Chemical Engineering》2008,32(7):1471-1481
The main objective of the present work is to modify the traditional mapping method for the simulation of distributive mixing of multiphase flows in geometries involving moving parts such as, internal mixers or twin-screw extruders without a limitation on their geometrical periodicity. The periodicity condition, limits the results of traditional mapping method to tracking mapping mesh between specific discrete time intervals or distances for that geometry is repeated, hence, result is only for fixed orientation of rotors. Imaginary domain method is introduced to track mapping mesh from one state to the next free of geometrical periodicity limitations. In this work the method is introduced and its applicability and accuracy is discussed in details. A two-dimensional (2D) simulation of mixing of two Newtonian fluids with different viscosities in an intermeshing internal mixer is used as a test case study. In this example the key issues of ability to predict mixing state in details for all orientations of rotors is presented. To reduce diffusion errors of mapping method in the boundaries of the rotors, mapping mesh refinement technique that relies upon one single reference mesh is also presented. 相似文献
107.
Jaber Almedeij 《Powder Technology》2008,186(3):218-223
An empirical relationship of drag coefficient of flow around a sphere is developed for the entire range of Particle Reynolds numbers reported in the literature from Stokes regime to the condition when turbulent boundary layer prevails. The relationship is obtained using an approach to match asymptotically the wide trend of drag coefficient. The matching approach, which relies on dividing the wide trend into smaller segments that can be combined into an overall relationship, employs regression techniques and thus warrants the best-fit accuracy results. The relationship is calibrated with experimental data available in the literature covering the entire range for Reynolds numbers up to ~ 106. For Reynolds values greater than 106, the relationship renders a drag coefficient of 0.2. The performance of the relationship is tested and compared with other suitable models found in the literature. This relationship is also transformed into an explicit expression for settling velocity calculations. 相似文献
108.
J. L. Barron R. E. Mercer X. Chen P. Joe 《International journal of imaging systems and technology》2005,15(3):189-198
We present local least squares and regularization frameworks for computing 3D velocity (3D optical flow) from 3D radial velocity measured by a Doppler radar. We demonstrate the performance of our algorithms quantitatively on synthetic radial velocity data and qualitatively on real radial velocity data, obtained from the Doppler radar at Kurnell Radar station, Botany Bay, New South Wales, Australia. Radial velocity can be used to predict the future positions of storms in sequences of Doppler radar datasets.© 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 189–198, 2005 相似文献
109.
本文应用NOPD技术设计了一种复合多层板,按照四边固定薄板结构的模态振型,对不同的NOPD填充形式,进行声学实验,来评价不同填充形式在降低板类结构声辐射方面的效果,分析了该类板结构声振耦合的关系并验证了NOPD技术对声辐射控制的作用。 相似文献
110.