全文获取类型
收费全文 | 235905篇 |
免费 | 2882篇 |
国内免费 | 1068篇 |
专业分类
电工技术 | 3903篇 |
综合类 | 2495篇 |
化学工业 | 35899篇 |
金属工艺 | 10493篇 |
机械仪表 | 7968篇 |
建筑科学 | 6582篇 |
矿业工程 | 945篇 |
能源动力 | 5106篇 |
轻工业 | 20985篇 |
水利工程 | 2386篇 |
石油天然气 | 962篇 |
武器工业 | 8篇 |
无线电 | 29739篇 |
一般工业技术 | 45032篇 |
冶金工业 | 26358篇 |
原子能技术 | 2603篇 |
自动化技术 | 38391篇 |
出版年
2021年 | 886篇 |
2018年 | 15424篇 |
2017年 | 14395篇 |
2016年 | 11193篇 |
2015年 | 1709篇 |
2014年 | 2100篇 |
2013年 | 6902篇 |
2012年 | 6364篇 |
2011年 | 13924篇 |
2010年 | 11814篇 |
2009年 | 9653篇 |
2008年 | 11354篇 |
2007年 | 12558篇 |
2006年 | 4510篇 |
2005年 | 5338篇 |
2004年 | 5145篇 |
2003年 | 5079篇 |
2002年 | 4489篇 |
2001年 | 4105篇 |
2000年 | 3932篇 |
1999年 | 3769篇 |
1998年 | 6697篇 |
1997年 | 5275篇 |
1996年 | 4527篇 |
1995年 | 3734篇 |
1994年 | 3392篇 |
1993年 | 3210篇 |
1992年 | 2804篇 |
1991年 | 2730篇 |
1990年 | 2648篇 |
1989年 | 2625篇 |
1988年 | 2488篇 |
1987年 | 2185篇 |
1986年 | 2130篇 |
1985年 | 2570篇 |
1984年 | 2338篇 |
1983年 | 2218篇 |
1982年 | 2085篇 |
1981年 | 2011篇 |
1980年 | 1874篇 |
1979年 | 1887篇 |
1978年 | 1779篇 |
1977年 | 2094篇 |
1976年 | 2565篇 |
1975年 | 1590篇 |
1974年 | 1434篇 |
1973年 | 1455篇 |
1972年 | 1196篇 |
1971年 | 1115篇 |
1970年 | 949篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Ahn Jaeshin Stromsmoe Keith A. Lawson Ronald P. W. 《Industrial Electronics, IEEE Transactions on》1985,(4):405-409
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films. 相似文献
33.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献
34.
P.W. Hawkes 《Ultramicroscopy》1985,17(2):151-156
Modifications of solid water and their transitions are described as they relate to cryo electron microscopy. In particular, the various amorphous states (amorphous polymorphs) as they exist below 100 K are extensively investigated. The “high-density” midification exhibits a lower viscosity than the “low-density” form. Differences are also observed in the mechanism of void formation due to electron irradiation: in the high-density form, voids are formed — not, however, in the low-density form. Together with the reaction to radiation damage, the physical properties of amorphous solid water are discussed with respect to embedding of organic specimens. Finally, the conditions and pitfalls associated with preparation of thin and entirely vitrified ice layers by shock-freezing are described. 相似文献
35.
36.
Tipton C.W. Bayne S.B. Griffin T.E. Scozzie C.J. Geil B. Agarwal A.K. Richmond J. 《Electron Device Letters, IEEE》2002,23(4):194-196
This paper reports on the first demonstration of a half-bridge power inverter constructed from silicon carbide gate turn-off thyristors (GTOs) operated in the conventional GTO mode. This circuit was characterized with input bus voltages of up to 600 VDC and 2 A (peak current density of 540 A/cm2) with resistive loads using a pulse-width modulated switching frequency of 2 kHz. We discuss the implications of the thyristor's electrical characteristics and the circuit topology on the overall operation of the half-bridge circuit. This work has determined the conservative critical rate of rise value of the off-state voltage to be 200 V/μs in these devices 相似文献
37.
Chlorogenic acid at 5° published threshold concentration (100 mg/ L) in aqueous 0.2% potassium acid tartrate was not significantly more bitter than aqueous 0.2% potassium tartrate alone when evaluated by taste panel. 相似文献
38.
Third generation mobile radio systems are currently being deployed in different regions of the world. Future systems beyond the third generation are already under discussion in international bodies and forums such as ITU, WWRF and R&D programmes of the European Union and in other regions. These systems will determine the research and standardisation activities in mobile and wireless communication in the next years. Based on experience of the third generation, future systems will be developed mainly from the user perspective with respect to potential services and applications including traffic demands. Therefore, the Wireless World Research Forum was launched in 2001 as a global and open initiative of manufacturers, network operators, SMEs, R&D centres and the academic domain. WWRF is focused on the vision of such systems - the Wireless World-and potential key technologies. This paper describes the international context of activities on systems beyond third generation, the goals, objectives and structure of WWRF, the user perspective as the starting point for a future system design and the key enabling technologies for the Wireless World. 相似文献
39.
40.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献