全文获取类型
收费全文 | 83583篇 |
免费 | 8504篇 |
国内免费 | 4860篇 |
专业分类
电工技术 | 6115篇 |
技术理论 | 7篇 |
综合类 | 6963篇 |
化学工业 | 13161篇 |
金属工艺 | 4399篇 |
机械仪表 | 5178篇 |
建筑科学 | 7260篇 |
矿业工程 | 2536篇 |
能源动力 | 2603篇 |
轻工业 | 6920篇 |
水利工程 | 1868篇 |
石油天然气 | 3716篇 |
武器工业 | 894篇 |
无线电 | 9409篇 |
一般工业技术 | 9165篇 |
冶金工业 | 3550篇 |
原子能技术 | 986篇 |
自动化技术 | 12217篇 |
出版年
2024年 | 435篇 |
2023年 | 1524篇 |
2022年 | 2819篇 |
2021年 | 3764篇 |
2020年 | 2876篇 |
2019年 | 2386篇 |
2018年 | 2562篇 |
2017年 | 2874篇 |
2016年 | 2550篇 |
2015年 | 3602篇 |
2014年 | 4480篇 |
2013年 | 5199篇 |
2012年 | 5781篇 |
2011年 | 5976篇 |
2010年 | 5650篇 |
2009年 | 5339篇 |
2008年 | 5403篇 |
2007年 | 4857篇 |
2006年 | 4729篇 |
2005年 | 3654篇 |
2004年 | 2825篇 |
2003年 | 2507篇 |
2002年 | 2889篇 |
2001年 | 2541篇 |
2000年 | 1915篇 |
1999年 | 1684篇 |
1998年 | 1140篇 |
1997年 | 990篇 |
1996年 | 909篇 |
1995年 | 708篇 |
1994年 | 594篇 |
1993年 | 390篇 |
1992年 | 357篇 |
1991年 | 254篇 |
1990年 | 180篇 |
1989年 | 166篇 |
1988年 | 110篇 |
1987年 | 73篇 |
1986年 | 60篇 |
1985年 | 32篇 |
1984年 | 27篇 |
1983年 | 18篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 41篇 |
1979年 | 11篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1959年 | 4篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Tian Xiao Qing Huo Liu 《Antennas and Propagation, IEEE Transactions on》2008,56(3):765-773
In this paper, we present an enlarged cell technique (ECT) to avoid the time step reduction encountered in the conformal finite-difference time-domain (CFDTD) method due to small irregular cells truncated by metallic boundaries. We focus our efforts on the discussion of the accuracy and stability of the ECT and its comparison with other conformal methods, especially the one called the uniformly stable conformal (USC) method. We also provide a simplified ECT, which is much easier to implement. In the ECT, a stability criterion is first constructed to identify instable irregular cells, i.e., those having so small an area to cause instability. Those instable cells are then enlarged into their adjacent cells to obtain a large, stable area. Careful treatment is performed on the communication between the intruding and intruded cells in terms of electromotive force by keeping the total electromotive force conservative. This technique is verified by several 3-D numerical experiments. Results show that the ECT is second-order accurate and numerically stable at the regular Courant time step limit. 相似文献
32.
高白度漂白商品浆的白度已从通常的88%~90%提高到更高的水平,达到92%.这种高白度的要求导致了纸厂使用高价格光学漂白剂,以及过量使用这种添加剂的环境风险. 相似文献
33.
34.
Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays 总被引:5,自引:0,他引:5
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results. 相似文献
35.
36.
裂缝性油气藏采收率:100个裂缝性油气田实例的经验总结 总被引:5,自引:2,他引:3
通过对世界上100个裂缝性油气藏的综合评价,研究储集层及流体本身的性质(包括孔隙度、渗透率、黏度、可动油比例、含水饱和度、润湿性及裂缝分布特征等)和驱动机制及油藏管理战略(优化日产量和采用不同类型的提高采收率技术)对其最终采收率的影响。将裂缝性油气藏分为4类:I类的基质几乎没有孔隙度和渗透率,裂缝是储存空间和流体流动的通道;Ⅱ类的基质有较低的孔隙度和渗透率,基质提供储存空间,裂缝提供流动通道;Ⅲ类(微孔隙)的基质具有高孔隙度和低渗透率,基质提供储存空间,裂缝提供流动通道;Ⅳ类(大孔隙)的基质具有高的孔隙度和渗透率,基质提供储存空间和流动通道,裂缝仅增加渗透率。对26个Ⅱ类油气藏和20个Ⅲ类油气藏的开采历史的研究表明:Ⅱ类油气藏的采收率受水驱强度和最优日产量控制,日产量过高会很容易破坏Ⅱ类油气藏,一些Ⅱ类油气藏如果管理得当,采收率可以很高,不需要二次或三次采油;Ⅲ类油气藏的采收率主要受岩石和流体本身性质的影响,特别是基质渗透率、流体重度、润湿性以及裂缝强度等,不进行二次或三次采油不可能完全开采,往往需要采用一些提高采收率的专门技术。以往将Ⅱ类和Ⅲ类裂缝性油气藏归为一类,认识它们的区别将有助于选择更好的开发策略。 相似文献
37.
An innovative method for modelling biological processes under anaerobic conditions is presented and discussed. The method is based on titrimetric and off-gas measurements. Titrimetric data is recorded as the addition rate of hydroxyl ions or protons that is required to maintain pH in a bioreactor at a constant level. An off-gas analysis arrangement measures, among other things, the transfer rate of carbon dioxide. The integration of these signals results in a continuous signal which is solely related to the biological reactions. When coupled with a mathematical model of the biological reactions, the signal allows a detailed characterisation of these reactions, which would otherwise be difficult to achieve. Two applications of the method to the enhanced biological phosphorus removal processes are presented and discussed to demonstrate the principle and effectiveness of the method. 相似文献
38.
A systematic approach for synthesising gyrator-C active transformers using MOS transistors is presented. The topology of gyrator-C active inductors and their characteristics are briefly reviewed first. This is followed by the development of ideal gyrator-C active transformers, where only the capacitor loads of the transconductors synthesising active transformers are considered. The self and mutual inductances of both the primary and secondary windings of active transformers are investigated in detailed. Non-ideal gyrator-C active transformers are developed with the consideration of both the resistance and capacitance loads of transconductors. The intrinsic relation between the self and mutual inductances is derived. The configuration of gyrator-C active transformers with multiple primary and secondary windings is also developed. The proposed active transformers offer large and tunable self and mutual inductances with virtually no silicon area requirement. Several practical implementations of the proposed active transformers have been realised in TSMC-0.18 mum 1.8 V CMOS technology and analysed using SpectreRF with BSIM3v3 device models. Simulation results on voltage transfer characteristics, self and mutual inductances, quality factors, stability, the effect of process variations, and noise are presented. The application of the proposed active transformers is exemplified using a 1.6 GHz active transformer quadrature oscillator. 相似文献
39.
This paper studies a Kansas Department of Transportation welded plate girder bridge that developed fatigue cracks at small web gaps close to the girder top flange. Repair had been previously performed by softening the connection plate end with a slot retrofit, but cracks were recently found to have reinitiated at some of the repaired details and are again propagating. A comprehensive finite-element method study was performed to investigate the cracking behavior observed in the bridge and to recommend appropriate measures for future bridge retrofit. The analytical results show that stresses developed at the top flange web gaps could exceed yielding under the loading of an HS15 fatigue truck. The current slot repair used in the bridge was found to have introduced higher magnitude fatigue stresses in the web gap. To achieve a permanent repair of the bridge, it is recommended that a welded connection plate to flange attachment be used during future bridge retrofit. The web gap details should be able to withstand unlimited number of load cycles once this additional repair is performed. 相似文献
40.