全文获取类型
收费全文 | 107034篇 |
免费 | 10614篇 |
国内免费 | 5934篇 |
专业分类
电工技术 | 7567篇 |
技术理论 | 9篇 |
综合类 | 7390篇 |
化学工业 | 16102篇 |
金属工艺 | 5791篇 |
机械仪表 | 6664篇 |
建筑科学 | 7819篇 |
矿业工程 | 3306篇 |
能源动力 | 3351篇 |
轻工业 | 7528篇 |
水利工程 | 2232篇 |
石油天然气 | 4402篇 |
武器工业 | 1065篇 |
无线电 | 14684篇 |
一般工业技术 | 12282篇 |
冶金工业 | 5434篇 |
原子能技术 | 1411篇 |
自动化技术 | 16545篇 |
出版年
2024年 | 567篇 |
2023年 | 1833篇 |
2022年 | 3739篇 |
2021年 | 5242篇 |
2020年 | 3943篇 |
2019年 | 3048篇 |
2018年 | 3395篇 |
2017年 | 3735篇 |
2016年 | 3303篇 |
2015年 | 4818篇 |
2014年 | 6083篇 |
2013年 | 7472篇 |
2012年 | 8339篇 |
2011年 | 8849篇 |
2010年 | 7650篇 |
2009年 | 7262篇 |
2008年 | 7005篇 |
2007年 | 6245篇 |
2006年 | 5398篇 |
2005年 | 4316篇 |
2004年 | 3108篇 |
2003年 | 2501篇 |
2002年 | 2569篇 |
2001年 | 2071篇 |
2000年 | 1579篇 |
1999年 | 1393篇 |
1998年 | 1401篇 |
1997年 | 1060篇 |
1996年 | 895篇 |
1995年 | 745篇 |
1994年 | 603篇 |
1993年 | 478篇 |
1992年 | 351篇 |
1991年 | 320篇 |
1990年 | 288篇 |
1989年 | 248篇 |
1988年 | 217篇 |
1987年 | 180篇 |
1986年 | 151篇 |
1985年 | 136篇 |
1984年 | 121篇 |
1983年 | 78篇 |
1982年 | 81篇 |
1981年 | 70篇 |
1980年 | 102篇 |
1979年 | 64篇 |
1978年 | 60篇 |
1977年 | 59篇 |
1976年 | 78篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
T. H. Chang K. F. Pao S. H. Chen K. R. Chu 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(9):1415-1420
Self-consistent effects on the starting current of gyrotron oscillators are examined. Field profiles in the open cavity are shown to be sensitive to the interaction dynamics. This can either significantly raise or lower the oscillation threshold, particularly for the low-Q modes. The transition from resonant-mode oscillations at the low magnetic field to backward-wave oscillations at the high magnetic field is demonstrated. 相似文献
82.
Chia-Sheng Chang Kwang-Cheng Chen 《Wireless Communications, IEEE Transactions on》2003,2(6):1159-1167
To enable multimedia real-time applications over next-generation wireless code-division multiple access (CDMA) packet-switching networks, previous efforts show a proper scheduling policy is the key to provide delay-guaranteed access services to various traffic types with different bit error rate (BER) requirements. Considering the support of the prevailing Internet protocol (IP) with variable-length packets in future mobile networks, we develop a mathematically delay-optimal medium access control (MAC) protocol over multicode CDMA (MC-CDMA) environments under the continuous-time assumption. From our investigations, we suggest that a good MAC protocol should be designed by using a proper single-server scheduling policy to guarantee packet-delay, and controlling the maximal number of simultaneous spreading-code transmissions to maintain the required BER. We further evaluate the performance of some MC-CDMA MAC protocols supporting QoS on BER and packet-delay, and show that MAC schemes conforming to our design rules give better performance on packet-delay when maintaining acceptable BER of various traffic types. 相似文献
83.
杨雷 《石油化工管理干部学院学报》2006,(1):40-41,45
运用薪酬、绩效管理等相关理论,结合工作实际,讨论中石化直属企事业在实施经营者年薪制时,如何解决好年薪制对象、模式、总额、结构;经营者业绩考核评价;风险收入计算;额外收入和职务消费控制等关键问题。 相似文献
84.
焊接方法对双相不锈钢焊接接头力学性能的影响 总被引:2,自引:0,他引:2
研究了不同焊接方法对SAF2205双相不锈钢板焊接接头金相组织和力学性能的影响,结果表明,采用不同焊接方法得到的焊接接头的铁素体与奥氏体两相比例不同,使焊接接头的力学性能存在较大差异,对实际生产中SAF2205双相不锈钢的焊接具有一定的指导意义。 相似文献
85.
Min-Seok Park Vladislav P. Vislovskiy Jong-San Chang Yong-Gun Shul Jin S. Yoo Sang-Eon Park 《Catalysis Today》2003,87(1-4):205-212
Alumina-supported vanadium oxide, VOx/Al2O3, and binary vanadium–antimony oxides, VSbOx/Al2O3, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by SBET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO2 pulse methods. VSbOx/Al2O3 exhibited enhanced catalytic activity and especially on-stream stability compared to VOx/Al2O3 catalyst. Incorporation of antimony into VOx/Al2O3 increased dispersion of active VOx species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V0.43Sb0.57Ox/Al2O3 system. 相似文献
86.
87.
A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths.<> 相似文献
88.
A design-for-testability scheme for detecting CMOS analog faults was reported by Favalli et al. (see ibid., vol.25, no.5, p.1239-46, 1990). The authors propose two alternative designs, one for small circuits and another for large circuits, which require significantly less area overhead (about 1/4 to 1/3) than that of Favalli's design. With the proposed modification in the first design, the untestable problem, which occurred in Favalli's design, can be alleviated. Furthermore, the proposed schemes are also fit to be implemented in VLSI circuits 相似文献
89.
文章详细分析了静电产生的机理,指出积聚静电电荷的多少与材料的电阻率和介电常数有关。讨论了静电火灾发生的条件,指出静电火灾的发生具有隐蔽性、复杂性和突发性。但只要对其规律进行深入地研究,可以找到有效地防止静电火灾发生的办法。 相似文献
90.
The authors derive and verify the concept of antenna focusing by a planar 'microstrip reflectarray' antenna. Experimental results from schematically distributed patch radiators with microstrip delay lines are consistent with the simulation results. The advantages and disadvantages of such an antenna are described. The measured overall antenna efficiency is approximately 48% at scan angles up to 30 degrees . These results demonstrate the feasibility of such an antenna.<> 相似文献