全文获取类型
收费全文 | 154026篇 |
免费 | 2364篇 |
国内免费 | 658篇 |
专业分类
电工技术 | 3153篇 |
综合类 | 187篇 |
化学工业 | 24529篇 |
金属工艺 | 5896篇 |
机械仪表 | 5034篇 |
建筑科学 | 4403篇 |
矿业工程 | 393篇 |
能源动力 | 4082篇 |
轻工业 | 17646篇 |
水利工程 | 1150篇 |
石油天然气 | 620篇 |
武器工业 | 6篇 |
无线电 | 20651篇 |
一般工业技术 | 29450篇 |
冶金工业 | 23822篇 |
原子能技术 | 2354篇 |
自动化技术 | 13672篇 |
出版年
2021年 | 989篇 |
2019年 | 979篇 |
2018年 | 1288篇 |
2017年 | 1320篇 |
2016年 | 1488篇 |
2015年 | 1243篇 |
2014年 | 2033篇 |
2013年 | 6967篇 |
2012年 | 3431篇 |
2011年 | 4804篇 |
2010年 | 3749篇 |
2009年 | 4335篇 |
2008年 | 4780篇 |
2007年 | 5032篇 |
2006年 | 4428篇 |
2005年 | 4164篇 |
2004年 | 4060篇 |
2003年 | 3957篇 |
2002年 | 3974篇 |
2001年 | 4007篇 |
2000年 | 3772篇 |
1999年 | 3710篇 |
1998年 | 6654篇 |
1997年 | 5243篇 |
1996年 | 4469篇 |
1995年 | 3724篇 |
1994年 | 3367篇 |
1993年 | 3193篇 |
1992年 | 2789篇 |
1991年 | 2694篇 |
1990年 | 2647篇 |
1989年 | 2623篇 |
1988年 | 2425篇 |
1987年 | 2107篇 |
1986年 | 2080篇 |
1985年 | 2519篇 |
1984年 | 2301篇 |
1983年 | 2169篇 |
1982年 | 2038篇 |
1981年 | 1966篇 |
1980年 | 1829篇 |
1979年 | 1857篇 |
1978年 | 1736篇 |
1977年 | 2045篇 |
1976年 | 2533篇 |
1975年 | 1545篇 |
1974年 | 1394篇 |
1973年 | 1441篇 |
1972年 | 1177篇 |
1971年 | 1084篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The multihop optical network is the most appropriate solution to satisfy the increasing applications of Internet services. This paper extends the regular Kautz graph to one with multiple layers in order to produce more architectural variations. The connectivity between adjacent layers utilizes the systematic connection patterns of a regular Kautz graph. A routing algorithm based on its property is presented. Optical passive star (OPS) couplers are adopted to implement our new topologies. Three scheduling criteria that can solve the contention problem in the intermediate nodes are evaluated and compared in terms of their capability to improve the accessibility. 相似文献
102.
Inerfield M. Skones W. Nelson S. Ching D. Cheng P. Wong C. 《Solid-State Circuits, IEEE Journal of》2003,38(9):1524-1532
To date, the development of multifunction multicarrier digital receivers for cellular base station and military communications applications has been limited by the demanding dynamic range requirements for the analog-to-digital converter (ADC). The use of oversampling delta-sigma modulators provides a promising approach to overcoming the dynamic range barriers Nyquist-rate converters face in the same applications. This paper discusses issues involved in the design of high-speed high dynamic range wide-band delta-sigma ADCs for such communications applications. Test results of prototype designs are also presented. The delta-sigma modulators described in this paper operate at sampling frequencies ranging from 1 to 2.5 GHz with center frequencies ranging from dc to 100 MHz, providing between 74 and 84.2 dB signal-to-noise ratio (12 and 13.7 bits) for bandwidths of 25 and 12.5 MHz, respectively. The loop filters are continuous-time low-pass and bandpass implementations of order 6 and 10, and were fabricated in an InP heterojunction bipolar (HBT) technology. A typical tenth-order design consumes 6 W of power and occupies a die area of 23.5 mm/sup 2/. 相似文献
103.
Static energy reduction techniques for microprocessor caches 总被引:1,自引:0,他引:1
Hanson H. Hrishikesh M.S. Agarwal V. Keckler S.W. Burger D. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2003,11(3):303-313
Microprocessor performance has been improved by increasing the capacity of on-chip caches. However, the performance gain comes at the price of static energy consumption due to subthreshold leakage current in cache memory arrays. This paper compares three techniques for reducing static energy consumption in on-chip level-1 and level-2 caches. One technique employs low-leakage transistors in the memory cell. Another technique, power supply switching, can be used to turn off memory cells and discard their contents. A third alternative is dynamic threshold modulation, which places memory cells in a standby state that preserves cell contents. In our experiments, we explore the energy and performance tradeoffs of these techniques. We also investigate the sensitivity of microprocessor performance and energy consumption to additional cache latency caused by leakage-reduction techniques. 相似文献
104.
This paper extends an analysis developed for tubular permanent-magnet machines to account for the effect of fringing associated with the finite length of the ferromagnetic armature core. The magnetic field distribution, established by using an analytical technique formulated in the cylindrical coordinate system, provides an accurate means of evaluating the effect of the fringing flux on the thrust force and the back-electromotive force. Finite-element calculations confirm the analytically derived results. In Part II of the paper, the analysis is used to predict the cogging force that results from end effects and to facilitate minimization of the force. 相似文献
105.
106.
Anaerobic co-digestion of organic wastes from households, slaughterhouses and meat processing industries was optimised in a half technical scale plant. The plant was operated for 130 days using two different substrates under organic loading rates of 10 and 12 kgCOD.m(-3).d(-1). Since the substrates were rich in fat and protein components (TKN: 12 g.kg(-1) the treatment was challenging. The process was monitored on-line and in the laboratory. It was demonstrated that an intensive and stable co-digestion of partly hydrolysed organic waste and protein rich slaughterhouse waste can be achieved in the balance of inconsistent pH and buffering NH4-N. In the first experimental period the reduction of the substrate COD was almost complete in an overall stable process (COD reduction >82%). In the second period methane productivity increased, but certain intermediate products accumulated constantly. Process design options for a second digestion phase for advanced degradation were investigated. Potential causes for slow and reduced propionic and valeric acid degradation were assessed. Recommendations for full-scale process implementation can be made from the experimental results reported. The highly loaded and stable codigestion of these substrates may be a good technical and economic treatment alternative. 相似文献
107.
H.W. Choi C.W. Jeon M.D. Dawson 《Photonics Technology Letters, IEEE》2004,16(1):33-35
The fabrication and performance of an InGaN light-emitting diode (LED) array based on a microring device geometry is reported. This design has been adopted in order to increase the surface area for light extraction and to minimize losses due to internal reflections and reabsorption. Electrical characteristics of these devices are similar to those of a conventional large-area LED, while the directed light extraction proves to be superior. In fact, these devices are found to be more efficient when operated at higher currents. This may be attributed to improved heat sinking due to the large surface area to volume ratio. The potential applications of these devices are also discussed. 相似文献
108.
109.
Ostojic R. Catalan Lasheras N. Lucas J. Venturini Delsolaro W. Landgrebe D. 《Applied Superconductivity, IEEE Transactions on》2004,14(2):199-202
The LHC insertions will be equipped with individually powered MQM superconducting quadrupoles, produced in three versions with magnetic lengths of 2.4 m, 3.4 m, and 4.8 m. The quadrupoles feature a 56 mm aperture coil, designed on the basis of an 8.8 mm wide Rutherford-type NbTi cable for a nominal gradient of 200 T/m at 1.9 K and 5390 A. A total of 96 quadrupoles are in production in Tesla Engineering, UK. In this report we describe the construction of the pre-series MQM quadrupoles and present the results of the qualification tests. 相似文献
110.
On the capacities of bipartite Hamiltonians and unitary gates 总被引:2,自引:0,他引:2
Bennett C.H. Harrow A.W. Leung D.W. Smolin J.A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(8):1895-1911
We consider interactions as bidirectional channels. We investigate the capacities for interaction Hamiltonians and nonlocal unitary gates to generate entanglement and transmit classical information. We give analytic expressions for the entanglement generating capacity and entanglement-assisted one-way classical communication capacity of interactions, and show that these quantities are additive, so that the asymptotic capacities equal the corresponding 1-shot capacities. We give general bounds on other capacities, discuss some examples, and conclude with some open questions. 相似文献