全文获取类型
收费全文 | 25888篇 |
免费 | 3901篇 |
国内免费 | 2431篇 |
专业分类
电工技术 | 1393篇 |
技术理论 | 5篇 |
综合类 | 2475篇 |
化学工业 | 2045篇 |
金属工艺 | 1515篇 |
机械仪表 | 771篇 |
建筑科学 | 1367篇 |
矿业工程 | 620篇 |
能源动力 | 2686篇 |
轻工业 | 351篇 |
水利工程 | 2286篇 |
石油天然气 | 1945篇 |
武器工业 | 171篇 |
无线电 | 6056篇 |
一般工业技术 | 2547篇 |
冶金工业 | 792篇 |
原子能技术 | 378篇 |
自动化技术 | 4817篇 |
出版年
2024年 | 176篇 |
2023年 | 976篇 |
2022年 | 1460篇 |
2021年 | 1496篇 |
2020年 | 1507篇 |
2019年 | 1283篇 |
2018年 | 1122篇 |
2017年 | 1275篇 |
2016年 | 1131篇 |
2015年 | 1231篇 |
2014年 | 1585篇 |
2013年 | 1669篇 |
2012年 | 1906篇 |
2011年 | 2030篇 |
2010年 | 1520篇 |
2009年 | 1413篇 |
2008年 | 1379篇 |
2007年 | 1519篇 |
2006年 | 1312篇 |
2005年 | 1146篇 |
2004年 | 910篇 |
2003年 | 797篇 |
2002年 | 686篇 |
2001年 | 493篇 |
2000年 | 415篇 |
1999年 | 338篇 |
1998年 | 267篇 |
1997年 | 218篇 |
1996年 | 194篇 |
1995年 | 154篇 |
1994年 | 169篇 |
1993年 | 78篇 |
1992年 | 81篇 |
1991年 | 42篇 |
1990年 | 42篇 |
1989年 | 42篇 |
1988年 | 32篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1970年 | 2篇 |
1959年 | 10篇 |
1958年 | 1篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Yen-Cho ChenJ.N. Chung 《Computers & Fluids》2003,32(6):795-822
This study intends to provide an increased understanding of the laminar-turbulent transition phenomena for the buoyancy-assisted heated vertical channel flow during the early transient stage. The spectral method with weak formulation is applied in the direct numerical simulation. Initial disturbances consist of the finite-amplitude two-dimensional TS wave and a pair of three-dimensional oblique waves for the K-type disturbances. The results from the harmonic energy competitions of different wave modes show that for the buoyancy-assisted heated flow, the (kx=1, kz=1) or (1,1) and (1,0) modes would gain energy immediately and start to rise at almost the same rate. This phenomenon is different from that of the buoyancy-opposed flow, where the (1,1) mode decays slowly in the beginning until other modes gain enough energy and then it begins to grow quickly and overtakes the (1,0) mode after a short time period. These different transition patterns match with the experimental results that the flow transition is supercritical and subcritical for the buoyancy-assisted and -opposed flows, respectively. Buoyancy-assisted heated flow transition follows the general trend of an isothermal flow in the beginning, but the thermal-buoyant force is crucial in accelerating the instability and also causing notable differences during the subsequent transition process. All of the results for the vortex structures development, kinetic energy budget of the disturbances, flow visualization by tagged fluid particles, and the local temperature fluctuations are consistent in pointing to a clear pattern for the buoyancy-assisted heated flow transition. 相似文献
92.
Like any other domain of human activity, psychology has its fads and fashions. One consequence of fads is an overconcentration of resources on specific problems or approaches, which leaves other important problems or approaches (holes) underappreciated and understudied. This article is primarily about different factors (such as negativity bias, polarization of positions, focus on internal causes of behavior, dedication to a narrow view of what science is) that result in holes and about explorations of some of these holes that have interested the author. Psychologists should look more in the holes left behind by current enthusiasms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
93.
研究了光纤-电缆调制解调器接入技术的上行信道调制方式,分析了离散小波多音(DWMT)调制与其它调制方式相比所具有的特点和优势,提出了DWMT调制解调器的实现模型,设计了使用DWMT调制解调器的光纤-电缆调制解调器双向传输的系统方案;并对DWMT调制的系统特性进行了计算机仿真分析。仿真结果表明,DWMT调制是一项能有效实用于光纤-电缆调制解调器系统上行信道的技术。 相似文献
94.
This paper considers the equalisation problem in Quadrature Phase-Shift Keying (QPSK) modulated signals which have been distorted by the passage through a transmission channel. The channel is modelled as a Rician fading channel to simulate the behaviour of the transmission channel in the mobile satellite context. The equalisation is treated as the generalisation of the channel behaviour, and some algorithms with the structure of an artificial neural network using the Multilayer Perceptron, Volterra Series and Radial Basis Function are described. Results for the BER performance of typical transversal equalisers, with Square-Root Kalman adaptation algorithm, and algorithms with artificial neural network structure are also reported and evaluated. Improved performance is exhibited by the artificial neural network approaches. 相似文献
95.
本文从冗余磁盘阵列的信道模型出发,研究各部分组成的理论与技术。文中在给出系统的模型描述之后,着重分析了冗余信息元生与检纠错、数据分割与同步。还研究了系统中的负荷平衡问题,指出了磁盘优化调度的方向。 相似文献
96.
本文讨论了在一条通讯通道上执行基本控制决策的信息传输问题。结果表明当且仅当第一条通道可模拟另一条通道的操作时,则第一条通道在任何情况下比另一条通道都有优势。 相似文献
97.
短模型上的明渠非恒定流试验 总被引:1,自引:0,他引:1
水工整体模型试验中,明渠非恒定流至今大多被简化为恒定流,而效果有时并不理想。本文指出,只要设置固定式曲线尾门,并有必要的动态量测设备,便可模拟原型非恒定流;即使模型偏短,也能得出比恒定流试验更接近原型的成果。在同一模型上,既做恒定流试验,又进行必要的非恒定流试验,二者相辅相成,必将有助于试验水平的提高。作为例证,本文介绍了泄洪调度导致航道水面波动的一项试验成果,并以岩基冲刷、通航水流条件、围堰过水、河床冲淤等研究课题为例,讨论了采用“短模型非恒定流试验方式”的必要性与可行性。 相似文献
98.
99.
本文对峒室爆破断面布药计算机辅助设计参数驱动方法进行了探讨围绕断面布药主要参数的变化,提出一种基于参数驱动的计算机辅助设计方法,利用windows操作系统下的动态数据交换特性,对断面布药进行布药参数优化,实现了交互调整布药,形成一套断面布的计算机软件,为工程爆破设计实现计算机提供了一种可行的方法。 相似文献
100.
Reorganisation and evolution of class hierarchies is important for object-oriented system development and has received considerable attention in the literature. The contributions of this paper are: (1) a formal study of a set of extension relations and transformations on class hierarchies; (2) a presentation of a small set of primitive transformations which form a minimal and complete basis for the extension relations; and (3) an analysis of the impact of these transformations at the object level.The study leads to a better understanding of evolution and reuse of object-oriented software and class hierarchies. It also provides a terminology and a means of classification for design reuse. The theory presented in this paper is based on the Demeter data model, which gives a concise mathematical foundation for classes and their inheritance and part-of relationships. Parts of the theory have been implemented in the Demeter System
TM
C++, a CASE tool for object-oriented design and programming. 相似文献