全文获取类型
收费全文 | 25902篇 |
免费 | 1647篇 |
国内免费 | 965篇 |
专业分类
电工技术 | 1674篇 |
技术理论 | 1篇 |
综合类 | 1478篇 |
化学工业 | 1917篇 |
金属工艺 | 1702篇 |
机械仪表 | 3172篇 |
建筑科学 | 1463篇 |
矿业工程 | 567篇 |
能源动力 | 1028篇 |
轻工业 | 221篇 |
水利工程 | 377篇 |
石油天然气 | 1237篇 |
武器工业 | 516篇 |
无线电 | 2693篇 |
一般工业技术 | 1499篇 |
冶金工业 | 847篇 |
原子能技术 | 226篇 |
自动化技术 | 7896篇 |
出版年
2024年 | 63篇 |
2023年 | 267篇 |
2022年 | 522篇 |
2021年 | 732篇 |
2020年 | 683篇 |
2019年 | 419篇 |
2018年 | 478篇 |
2017年 | 615篇 |
2016年 | 725篇 |
2015年 | 981篇 |
2014年 | 1873篇 |
2013年 | 1544篇 |
2012年 | 1916篇 |
2011年 | 2190篇 |
2010年 | 1420篇 |
2009年 | 1488篇 |
2008年 | 1490篇 |
2007年 | 1936篇 |
2006年 | 1728篇 |
2005年 | 1568篇 |
2004年 | 1227篇 |
2003年 | 1123篇 |
2002年 | 750篇 |
2001年 | 534篇 |
2000年 | 430篇 |
1999年 | 340篇 |
1998年 | 259篇 |
1997年 | 207篇 |
1996年 | 204篇 |
1995年 | 156篇 |
1994年 | 128篇 |
1993年 | 85篇 |
1992年 | 62篇 |
1991年 | 74篇 |
1990年 | 49篇 |
1989年 | 49篇 |
1988年 | 40篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 12篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
陈海 《中国海上油气(工程)》2002,(4)
海上无人驻守简易平台设计是降低原油成本的重要手段之一,密闭循环涡轮发电机组(Closed Cycle Vapor Turbogenerator)是海上无人驻守平台上应用最可靠且低维护的远程发电系统。介绍CCVT这种发电机组,并讨论了在海上工程设计中需要考虑的问题,为今后简易平台上电站的选择设计提供参考。 相似文献
82.
83.
对低温器件计算机模拟方法作了具体的考虑。从求解变量和半导体物理意义出发,数值计算结果事先有一个定性范围,如果每一次循环的迭代初值都修正到这个数值范围内,那么选代过程将以更快的速度接近真解。提出了适用于低温半导体器件计算机模拟的增量限制方法,并且将该方法插入MINIMOS4.0进行了数值实验。结果表明,设置增量限制能保证低温半导体器件模拟的数值收敛性,并巨有较快的收敛速度。 相似文献
84.
带FPGA的PCI接口应用 总被引:2,自引:1,他引:1
文章介绍了一种带FPGA的PCI接口的应用及设计方法。该方法将PCI接口和PCI用户逻辑集成在一片FPGA里,可以对整个逻辑进行仿真测试,大大缩短了开发周期,提高了系统集成度和性能。文章重点叙述了Quicklogic公司提供的32wug TARGET接口芯片QL5030的原理和结构,分析了时序设计要点,给出了典型应用的逻辑框图和注意事项。 相似文献
85.
水下物体运动引起扰动,会在海面产生尾迹。这种尾迹特征同运动物体的参数和下潜的深度以及海况有关。研究这种尾迹特征及其合成孔径雷达(SAR)成像,就有可能利用SAR来检测这个水下运动物体。本文给出了一种水下运动物体的伴流尾迹的快速模拟方法及其合成孔径雷达(SAR)成像仿真方法,并对模拟仿真的结果进行了讨论。 相似文献
86.
Evaluation of a two-temperature control structure for a two-reactant/two-product type of reactive distillation column 总被引:1,自引:0,他引:1
Devrim B. Kaymak 《Chemical engineering science》2006,61(13):4432-4450
Several different control structures have been proposed for reactive distillation columns. The appropriate control structure depends on the flowsheet and on the type of reactions occurring in the column. If two reactants are involved and if it is desirable to operate the process without any excess of reactant, it is necessary to manage the fresh feed streams so that the stoichiometry is exactly balanced. A composition analyzer that measures an internal composition in the column is often required. However, if two products are produced, it is possible to avoid the use of an analyzer by using two temperatures in the column to adjust the two feed streams. This type of structure was proposed by Roat et al. [Roat, S., Downs. J., Vogel, E., Doss, J., 1986. Integration of rigorous dynamic modeling and control system synthesis for distillation columns. In: Chemical Process Control—CPC III. Elsevier, Amsterdam.] for the ideal reaction A+B↔C+D in one of the earliest papers dealing with reactive distillation control.The purpose of this paper is to explore the effectiveness of this two-temperature control structure for various column designs (number of reactive stages) to quantify the impact of design on controllability. We also discuss the issues of the selection of the trays whose temperatures are to be controlled and the tuning of the two interacting temperature controllers. Disturbances in production rate and fresh feed compositions are made to examine the rangeability of this control structure. Both an ideal reaction system and the methyl acetate system are studied. One of the main conclusions is that the locations of the temperature control trays should be made such that the two temperature controllers both have direct action (an increase in temperature increases feed), which requires negative openloop process gains for both loops. 相似文献
87.
本文提出了一种快速远场近似(FAFFA)加速的混合物理光学矩量法(POMM),利用FAFFA加速计算矩阵方程中的矩阵矢量积,明显提高了计算效率.对物体表面上的远场组之间的耦合作用推导出了一组简洁的计算公式,并分析了计算复杂度.复杂金属组合体上线天线输入导纳、互导纳和方向性图的计算结果与文献结果一致.利用该方法分析计算了一个舰船模型上线天线的电磁特性.数值结果表明了这种方法的正确性和工程应用中的有效性. 相似文献
88.
To provide responsive information services in a ubiquitous computing environment, service software and system development are indispensable. A component-based ubiquitous information system with a JAIN (Java APIs for Integrated Networks) platform to achieve seamless transmissions and reach-everywhere communications was designed in our research. In this development, numerous ubiquitous service modules were identified: location management, roaming, mobile IP and WAP networking. These component-based network modules were constructed using a component composition language with component specification and interface definition, running on top of a distributed service architecture using a JAIN platform to distribute the ubiquitous information services to mobile users. Two applications, Wireless-Application-Protocol (WAP) Mail and Video-on-Demand (VoD) services, show that the JAIN-like platform with the developed networking components effectively fills the gap for application developers between mobile appliances and various kinds of ubiquitous information services. 相似文献
89.
90.
Giovanni Giambene Enrico Zoli 《International Journal of Satellite Communications and Networking》2003,21(2):199-225
In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time‐Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot‐code resource. This protocol is named Adaptive Time Code‐Packet Reservation Multiple Access (ATC‐PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)‐Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High‐Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC‐PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC‐PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献