全文获取类型
收费全文 | 29565篇 |
免费 | 2641篇 |
国内免费 | 5670篇 |
专业分类
电工技术 | 558篇 |
综合类 | 2564篇 |
化学工业 | 5644篇 |
金属工艺 | 881篇 |
机械仪表 | 2117篇 |
建筑科学 | 5794篇 |
矿业工程 | 1269篇 |
能源动力 | 1547篇 |
轻工业 | 1012篇 |
水利工程 | 661篇 |
石油天然气 | 6556篇 |
武器工业 | 1259篇 |
无线电 | 542篇 |
一般工业技术 | 4022篇 |
冶金工业 | 845篇 |
原子能技术 | 309篇 |
自动化技术 | 2296篇 |
出版年
2024年 | 112篇 |
2023年 | 424篇 |
2022年 | 732篇 |
2021年 | 861篇 |
2020年 | 869篇 |
2019年 | 879篇 |
2018年 | 807篇 |
2017年 | 1096篇 |
2016年 | 1277篇 |
2015年 | 1346篇 |
2014年 | 1680篇 |
2013年 | 2117篇 |
2012年 | 2074篇 |
2011年 | 2409篇 |
2010年 | 1852篇 |
2009年 | 1816篇 |
2008年 | 1655篇 |
2007年 | 2079篇 |
2006年 | 2169篇 |
2005年 | 2159篇 |
2004年 | 1871篇 |
2003年 | 1423篇 |
2002年 | 1083篇 |
2001年 | 805篇 |
2000年 | 734篇 |
1999年 | 634篇 |
1998年 | 561篇 |
1997年 | 444篇 |
1996年 | 381篇 |
1995年 | 346篇 |
1994年 | 235篇 |
1993年 | 172篇 |
1992年 | 126篇 |
1991年 | 108篇 |
1990年 | 105篇 |
1989年 | 77篇 |
1988年 | 59篇 |
1987年 | 45篇 |
1986年 | 41篇 |
1985年 | 23篇 |
1984年 | 29篇 |
1983年 | 25篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 25篇 |
1979年 | 21篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1959年 | 7篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
采用流动和反应耦合模型模拟ZSM5-Y复配催化剂体系在提升管反应器内的催化裂化过程。结果表明,重油催化裂化反应主要发生在喷嘴附近,该处有45%的重油转化为汽油和柴油。对于ZSM5-Y型复配催化剂体系,ZSM5加入沸石催化剂的显然影响着汽油和液化气的产率,反应产物中柴油馏分及重油馏分的产率基本上不受影响。加入少量择形催化剂便大大降低提升管反应器汽油馏分收率,并提高液化气收率,但汽油与液化气产率显著变化仅发生在择形催化剂加量较小的时候,一旦超过10%以后,对气油和液化气的产率影响反而较小。 相似文献
142.
Jerry L. Trahan Mingxian Jin Wittaya Chantamas Johnnie W. Baker 《Journal of Parallel and Distributed Computing》2010
The MASC (Multiple ASsociative Computing) model is a multi-SIMD model that uses control parallelism to coordinate the interaction of data parallel threads and supports associative SIMD computing on each of its threads. There have been a wide range of algorithms developed for this model. Research on using this model in real-time system applications and building a scalable MASC architecture is currently quite active. In this paper, we present simulations between MASC and reconfigurable bus-based models, e.g., various versions of the Reconfigurable Multiple Bus Machine (RMBM). Constant time simulations of the basic RMBM by MASC and vice versa are obtained. Simulations of the segmenting RMBM, fusing RMBM, and extended RMBM by MASC in non-constant time are also discussed. By taking advantage of previously established relationships between RMBM and two other popular parallel computational models, namely, the Reconfigurable Mesh (RM) and the Parallel Random Access Machine (PRAM), we extend our simulation results to further categorize the power of the MASC model in relation to RM and PRAM. 相似文献
143.
Petra Punčochářová-Pořízková Jiří Fürst Jaromír Horáček Karel Kozel 《Mathematics and computers in simulation》2010
This study deals with a numerical solution of a 2D unsteady flow of a compressible viscous fluid in a channel for low inlet airflow velocity. The unsteadiness of the flow is caused by a prescribed periodic motion of a part of the channel wall with large amplitudes, nearly closing the channel during oscillations. The channel is a simplified model of the glottal space in the human vocal tract and the flow can represent a model of airflow coming from the trachea, through the glottal region with periodically vibrating vocal folds, and to the human vocal tract. 相似文献
144.
Peter Dabnichki 《Mathematics and computers in simulation》2011,82(3):471-482
Computational fluid mechanics (CFD) has made substantial progress on modelling a variety of important problems in industry. However, there is still lack of reliable methods to model the motion of the body in water. This is a central issue in understanding animal and human propulsion in water not only to advance science but to explore the possibility of utilising such propulsion modes for man made vehicles. The presented work identified the added mass effect as the prime contributor to propulsive force generation. The use of boundary element method (BEM) proved very successful as it allowed reducing this dynamic problem to a quasi-static one without sacrificing accuracy in the model. The comparison between the experimental data and the simulation result was in the range of 95% (average accuracy) suggesting that the added mass effect and dynamic lift and drag are the most significant physical phenomena in propulsive force generation despite the fact that there is undoubtedly and the presence of turbulent effects that were not considered. 相似文献
145.
146.
A.R. Seadawy 《Computers & Mathematics with Applications》2011,62(10):3741-3755
The Korteweg-de Vries (KdV) equation with higher order nonlinearity models the wave propagation in one-dimensional nonlinear lattice. A higher-order extension of the familiar KdV equation is produced for internal solitary waves in a density and current stratified shear flow with a free surface. The variational approximation method is applied to obtain the solutions for the well-known KdV equation. Explicit solutions are presented and compared with the exact solutions. Very good agreement is achieved, demonstrating the high efficiency of variational approximation method. The existence of a Lagrangian and the invariant variational principle for the higher order KdV equation are discussed. The simplest version of the variational approximation, based on trial functions with two free parameters is demonstrated. The jost functions by quadratic, cubic and fourth order polynomials are approximated. Also, we choose the trial jost functions in the form of exponential and sinh solutions. All solutions are exact and stable, and have applications in physics. 相似文献
147.
We consider incompressible flow problems with defective boundary conditions prescribing only the net flux on some inflow and outflow sections of the boundary. As a paradigm for such problems, we simply refer to Stokes flow. After a brief review of the problem and of its well posedness, we discretize the corresponding variational formulation by means of finite elements and looking at the boundary conditions as constraints, we exploit a penalty method to account for them. We perform the analysis of the method in terms of consistency, boundedness and stability of the discrete bilinear form and we show that the application of the penalty method does not affect the optimal convergence properties of the finite element discretization. Since the additional terms introduced to account for the defective boundary conditions are non-local, we also analyze the spectral properties of the equivalent algebraic formulation and we exploit the analysis to set up an efficient solution strategy. In contrast to alternative discretization methods based on Lagrange multipliers accounting for the constraints on the boundary, the present scheme is particularly effective because it only mildly affects the structure and the computational cost of the numerical approximation. Indeed, it does not require neither multipliers nor sub-iterations or additional adjoint problems with respect to the reference problem at hand. 相似文献
148.
Alan Mehlenbacher 《Computational Economics》2009,34(2):119-143
Computational experiments with a multiagent system show that bidders use signal averaging to avoid the winner’s curse in English
auctions. The results vary with the percent of common value in a two-dimensional value signal, information levels, uncertainty,
and the number of bidders. The complexity introduced by the combinations of these factors affects the bidding strategies and
auction outcomes in interesting ways—usually nonlinearly and sometimes non-monotonically. Of main concern to a seller is the
effect of these factors on revenue. I find that revenue increases with the percent of common value in the two-dimensional
value signal, decreases with uncertainty, and increases with the number of bidders. There is very little impact of information
level on revenue when values are pure private and pure common. However, for the intermediate cases of two-dimensional value
signals, revenue decreases with increased information.
相似文献
149.
150.