全文获取类型
收费全文 | 23458篇 |
免费 | 965篇 |
国内免费 | 164篇 |
专业分类
电工技术 | 393篇 |
综合类 | 39篇 |
化学工业 | 5034篇 |
金属工艺 | 728篇 |
机械仪表 | 731篇 |
建筑科学 | 416篇 |
矿业工程 | 60篇 |
能源动力 | 1630篇 |
轻工业 | 1341篇 |
水利工程 | 182篇 |
石油天然气 | 103篇 |
武器工业 | 1篇 |
无线电 | 2944篇 |
一般工业技术 | 5367篇 |
冶金工业 | 2118篇 |
原子能技术 | 205篇 |
自动化技术 | 3295篇 |
出版年
2024年 | 106篇 |
2023年 | 463篇 |
2022年 | 1068篇 |
2021年 | 1288篇 |
2020年 | 1013篇 |
2019年 | 1029篇 |
2018年 | 1337篇 |
2017年 | 1074篇 |
2016年 | 1071篇 |
2015年 | 693篇 |
2014年 | 991篇 |
2013年 | 1874篇 |
2012年 | 1069篇 |
2011年 | 1281篇 |
2010年 | 1030篇 |
2009年 | 1056篇 |
2008年 | 875篇 |
2007年 | 686篇 |
2006年 | 590篇 |
2005年 | 465篇 |
2004年 | 361篇 |
2003年 | 333篇 |
2002年 | 268篇 |
2001年 | 240篇 |
2000年 | 233篇 |
1999年 | 231篇 |
1998年 | 432篇 |
1997年 | 345篇 |
1996年 | 339篇 |
1995年 | 249篇 |
1994年 | 238篇 |
1993年 | 229篇 |
1992年 | 160篇 |
1991年 | 199篇 |
1990年 | 165篇 |
1989年 | 141篇 |
1988年 | 124篇 |
1987年 | 132篇 |
1986年 | 116篇 |
1985年 | 132篇 |
1984年 | 106篇 |
1983年 | 95篇 |
1982年 | 85篇 |
1981年 | 105篇 |
1980年 | 70篇 |
1979年 | 64篇 |
1978年 | 56篇 |
1977年 | 53篇 |
1976年 | 68篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Exploiting information theory for adaptive mobility and resource management in future cellular networks 总被引:2,自引:0,他引:2
We utilize tools from information theory to develop adaptive algorithms for two key problems in cellular networks: location tracking and resource management. The use of information theory is motivated by the fundamental observation that overheads in many aspects of mobile computing can be traced to the randomness or uncertainty in an individual user's movement behavior. We present a model-independent information-theoretic approach for estimating and managing this uncertainty, and relate it to the entropy or information content of the user's movement process. Information-theoretic mobility management algorithms are very simple, yet reduce overhead by /spl sim/80 percent in simulated scenarios by optimally adapting to each individual's movement. These algorithms also allow for flexible tradeoff between location update and paging costs. Simulation results demonstrate how an information-theory-motivated resource provisioning strategy can meet QoS bounds with very small wastage of resources, thus dramatically reducing the overall blocking rate. 相似文献
52.
In the modeling of the gas metal-arc (GMA) welding process, heat inputs to the workpiece by the arc and the metal transfers
have been considered separately. The heat energy delivered due to the metal transfer has been approximated in the form of
a cylindrical volumetric heat source, whose dimensions of the radius and the height are dependent on the molten metal droplet
characteristics. The pinch instability theory (PIT) and the static force balance theory (SFBT) of drop detachment have independently
been used to obtain the expressions for various characteristics of the drop,i.e., the drop radius, the drop velocity, and the drop frequency at various welding parameters. The occurrence or the nonoccurrence
of finger penetration, routinely found in the GMA welding at high welding currents, has been satisfactorily explained by the
cylindrical heat source model. The effect of various welding parameters,e.g., the welding current, the wire radiusetc., on the weld bead penetration characteristics has been investigated. In this modeling effort, the heat conduction equation
has been solved in three dimensions. 相似文献
53.
In the present work Taguchi's approach has been applied to the V-process castings of Al-11 per cent Si alloy to acertain the most influential control factors which will provide better and consistent surface finish to the castings regardless of the noise factors present. The control factors of the V-process that may affect the quality of the castings are the molding sand, vibration frequency, vibrating time, degree of vacuum imposed, and pouring temperature. In order to understand how these factors affect the surface roughness of the V-process castings, response surface methodology has been applied, and to obtain the optimal setting of the control factors Taguchi's method has been used. It is found that the pouring temperature has a significant effect on the surface roughness of Al-11 per cent Si alloy castings made by a V-process. Thus the pouring temperature must be kept at the lower level. All other factors are insignificant. Therefore, any setting of the insignificant factors/variables that give the minimum cost can be used. 相似文献
54.
55.
In vertical co-current gas-liquid flow, the transition from annular to intermittent flow occurs when gas core becomes interrupted by liquid bridges due to the instability of the interfacial capillary waves. An analytical model is formulated to explain the liquid bridging in terms of the growth of finite amplitude interfacial capillary waves. Experimental results show that the longest wave length, which is associated with the transition, is about eight times the wave length of waves moving with the velocity of the liquid film. 相似文献
56.
57.
S Kasiviswanathan P S Asoka Kumar B K Mathur K L Chopra 《Bulletin of Materials Science》1996,19(2):411-416
Surface structure of thin silver films (200 Å) on two technologically important films, indium tin oxide (ITO) and aluminium oxide, has been studied using scanning tunneling microscope. ITO films were prepared by reactive electron beam evaporation. Aluminium oxide films were prepared by oxidizing 2000 Å thick aluminium films evaporated on to H2 terminated single crystal silicon substrates. The surface structure of silver on ITO and aluminium oxide appeared to be same and was characteristic of Stranski-Krastanov type. The observed asymmetry in the island shape was attributed to the anisotropic nature of the strain fields surrounding the nucleation centres. 相似文献
58.
59.
60.
A simple method (based on Floquet theory) for obtaining the characteristic equation (and hence stability) of periodic discrete-time systems is presented. Using this method it is shown that 2-periodic controllers can be used to relocate the zeros of SISO plants. Some examples are considered to illustrate the use of 2-periodic controllers for robust control of finite gain margin problems 相似文献