全文获取类型
收费全文 | 110241篇 |
免费 | 10406篇 |
国内免费 | 5703篇 |
专业分类
电工技术 | 7624篇 |
技术理论 | 11篇 |
综合类 | 8078篇 |
化学工业 | 17537篇 |
金属工艺 | 6205篇 |
机械仪表 | 6710篇 |
建筑科学 | 9501篇 |
矿业工程 | 3061篇 |
能源动力 | 3442篇 |
轻工业 | 7611篇 |
水利工程 | 2106篇 |
石油天然气 | 5533篇 |
武器工业 | 1036篇 |
无线电 | 13237篇 |
一般工业技术 | 13051篇 |
冶金工业 | 4689篇 |
原子能技术 | 1354篇 |
自动化技术 | 15564篇 |
出版年
2024年 | 591篇 |
2023年 | 2073篇 |
2022年 | 3573篇 |
2021年 | 4978篇 |
2020年 | 3598篇 |
2019年 | 2992篇 |
2018年 | 3333篇 |
2017年 | 3710篇 |
2016年 | 3291篇 |
2015年 | 4553篇 |
2014年 | 5484篇 |
2013年 | 6632篇 |
2012年 | 7272篇 |
2011年 | 7583篇 |
2010年 | 7035篇 |
2009年 | 6593篇 |
2008年 | 6580篇 |
2007年 | 6071篇 |
2006年 | 6080篇 |
2005年 | 4971篇 |
2004年 | 3558篇 |
2003年 | 3103篇 |
2002年 | 3296篇 |
2001年 | 2907篇 |
2000年 | 2534篇 |
1999年 | 2672篇 |
1998年 | 1967篇 |
1997年 | 1708篇 |
1996年 | 1652篇 |
1995年 | 1299篇 |
1994年 | 1118篇 |
1993年 | 798篇 |
1992年 | 710篇 |
1991年 | 519篇 |
1990年 | 363篇 |
1989年 | 309篇 |
1988年 | 236篇 |
1987年 | 155篇 |
1986年 | 107篇 |
1985年 | 88篇 |
1984年 | 58篇 |
1983年 | 39篇 |
1982年 | 49篇 |
1981年 | 31篇 |
1980年 | 36篇 |
1979年 | 15篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1959年 | 5篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Generalized difference control of parallel streams temperatures 总被引:1,自引:0,他引:1
A furnace with multiple parallel passes and multiple burners is commonly seen in petroleum refineries. In order to maintain the furnace running in a safe, stable, and high-efficiency state it is necessary to control the outlet temperatures of the multiple passes to be the same. Due to the fact that the process of the oil heating in such furnace is nonlinear, multivariable, time varying, has serious coupling among passes, has frequent dynamic changes and a large time delay, traditional control methods have trouble in controlling these temperatures, and some advanced control methods, including predictive control, adaptive control, and robust control, are usually too complex for convenient use. In this paper, a control technique, called differences control technique (DsCT), is proposed to distribute the stream flowrates such that the stream temperatures are as identical as possible. The principle of the proposed technique is explained and demonstrated, and the results of its application to a real-life petroleum refinery furnace are also reported. The DsCT technique has the following advantages: it does not need complicated design procedures, the controller structure is simple, it is easy to apply, and it can be canonically applied to furnaces with different number of passes. 相似文献
32.
The effects of key parameters on the preparation and regeneration of protoplast from the β-carotene-producing fungus Blakeslea trispora were discussed in this paper, including the combination of various enzymes, mycelial age, digesting time and temperature,
pH value, osmotic stabilizers, pretreatment, culture medium and culture method. Under the condition of mixed enzymes in osmotic
stabilizer (0.6 M NaCl) combined with 2% lysozyme, 3% cellulase and 3% snailase, the highest protoplast yield, as high as
7.48×106 protoplasts/mL, was obtained when mycelial age was 60 h at pH 5.0–6.0 with digesting for 14–16 h at 28 °C. After
purification of the obtained protoplasts, they were regenerated in PDA regenerative medium using bilayer plate culture method.
To validate the usability of the protoplasts, a novel plasmid with green fluorescent protein (GFP) was used in transformation
for easy visual observation. The results showed that the protoplasts prepared by the optimized method were active and applicable
in further gene manipulation experiments.
This work was presented at 13
th
YABEC symposium held at Seoul, Korea, October 20–22, 2007. 相似文献
33.
34.
针对碳酸盐岩气藏部分气井生产效能低的状况,决定在长庆气田下古生界尝试开展加砂压裂重复改造试验,以期提高低产、低效气井的产量,延长气田稳产期。通过潜心研究、精细设计及现场质检监控,优选了4口老井进行加砂压裂重复改造现场试验。从试验结果来看,虽然只有1口井取得明显的改造效果,但4口井加砂压裂施工都是成功的,说明对碳酸盐岩气藏实施加砂压裂是可以实现的,但在选井思路和压裂工艺方面还有待探索和研究。 相似文献
35.
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
36.
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.
石蜡微胶囊中脲醛树脂壁材渗透性的研究 总被引:7,自引:0,他引:7
利用差示扫描量热法研究了石蜡微胶囊中脲醛树脂壁材对水及甲苯的渗透性 ,结果表明 ,水不能透过脲醛树脂壁材 ,而甲苯则易透过脲醛树脂壁材。因此 ,该石蜡微胶囊不能用于芳香族溶剂存在的场合。 相似文献