全文获取类型
收费全文 | 2905篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 20篇 |
化学工业 | 206篇 |
金属工艺 | 11篇 |
机械仪表 | 25篇 |
建筑科学 | 134篇 |
矿业工程 | 1篇 |
能源动力 | 54篇 |
轻工业 | 125篇 |
水利工程 | 14篇 |
石油天然气 | 4篇 |
无线电 | 136篇 |
一般工业技术 | 148篇 |
冶金工业 | 1939篇 |
原子能技术 | 13篇 |
自动化技术 | 91篇 |
出版年
2022年 | 9篇 |
2021年 | 9篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 20篇 |
2013年 | 49篇 |
2012年 | 25篇 |
2011年 | 42篇 |
2010年 | 27篇 |
2009年 | 26篇 |
2008年 | 31篇 |
2007年 | 28篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 31篇 |
2003年 | 23篇 |
2002年 | 22篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 78篇 |
1998年 | 662篇 |
1997年 | 339篇 |
1996年 | 255篇 |
1995年 | 130篇 |
1994年 | 113篇 |
1993年 | 143篇 |
1992年 | 42篇 |
1991年 | 43篇 |
1990年 | 31篇 |
1989年 | 40篇 |
1988年 | 37篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 32篇 |
1982年 | 23篇 |
1981年 | 27篇 |
1980年 | 37篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 56篇 |
1976年 | 78篇 |
1975年 | 14篇 |
1974年 | 6篇 |
1973年 | 16篇 |
1969年 | 6篇 |
排序方式: 共有2921条查询结果,搜索用时 21 毫秒
31.
Multilevel-spiral inductors using VLSI interconnect technology 总被引:1,自引:0,他引:1
A multilevel-spiral (MLS) inductor structure for implementation in VLSI interconnect technology is presented. Inductances of 8.8 and 32 nH and maximum quality-factors (Q) of ~6.8 and 3.0, respectively, are achieved in a four-level metal BiCMOS technology, with four turns at each of the two or four stacked spiral coils and with an area of 226×226 μm2. The comparison of the MLS inductors to different single-level-spiral (SLS) control devices shows that a MLS inductor provides the same inductance at ~50% dc resistance, but the maximum Q is typically measured at a lower frequency and the self-resonance frequency is reduced due to a high inter-wire capacitance 相似文献
32.
Greenhut S.E. Jenkins J.M. MacDonald R.S. 《IEEE transactions on bio-medical engineering》1993,40(9):845-858
In order to study heart-pacemaker interaction (HPI), a computer model of the cardiac conduction system has been developed which includes the effects of artificial pacemaker function and failure. The stochastic network model of cardiac conduction consists of five vertices, each representing a functional electrophysiologic element. Electrophysiologic multidimensional conditional probability functions determine the depolarization status of each vertex. The atrioventricular (AV) node is emulated using a mathematical model which includes the influence of past cycle lengths on AV nodal conduction time. Twenty-three classes of arrhythmias may be simulated and, for pacing simulation, one of 12 antibradycardia pacing modes may be chosen. Random effects of pacemaker malfunction including oversensing, undersensing, or failure-to-capture may be simulated through the use of probability distribution functions. This model should prove useful in the development of pacemaker algorithms, determining patient-specific pacemaker therapy, and predicting causes for apparent pacemaker malfunction. The model has been used in the development of an expert system to analyze paced ECGs for pacemaker function and malfunction 相似文献
33.
虽然无线通信技术一直都在不断发展,但当前却处于一个前所未有的变革期,新兴的4G空中接口如WiMAX、LTE、UMB、802.20、WiBRo以及下一代PHS等等都有一个共同的特点:即都是基于正交频分多址接入(OFDMA)、都采用MIMo(多入多出)技术、都具有“扁平化架构”且均基于IP(互联网协议)。 相似文献
34.
Multilevel monolithic inductors in silicon technology 总被引:5,自引:0,他引:5
Soyuer M. Burghartz J.N. Jenkins K.A. Ponnapalli S. Ewen J.F. Pence W.E. 《Electronics letters》1995,31(5):359-360
Multilevel monolithic inductors implemented in standard BiCMOS technology are presented. Use of top metal layers shunted with vias provides Q values approaching 10 at 2.4 GHz and above 6 at 900 MHz for a 2 nH inductor. There is no modification to the conventional wiring metallurgy and no need for extra processing steps 相似文献
35.
Soyuer M. Burghartz J.N. Ainspan H.A. Jenkins K.A. Xiao P. Shahani A.R. Dolan M.S. Harame D.L. 《Solid-State Circuits, IEEE Journal of》1997,32(9):1451-1454
A 10.5- to 11-GHz fully monolithic voltage controlled oscillator circuit implemented in a standard SiGe bipolar technology is presented. An oscillator phase noise of -78 to -87 dBc/Hz is achieved at 100-kHz offset. The tuning range is close to 5% with an on-chip varactor-tuned resonator and for a control voltage of 0 to 3 V. The circuit draws less than 8 mA from a 3-V supply including the reference branch bias current 相似文献
36.
Lu P.-F. Warnock J.D. Cressler J.D. Jenkins K.A. Toh K.-Y. 《Electron Devices, IEEE Transactions on》1991,38(6):1410-1418
The device design and performance of double-poly self-aligned p-n-p technology, featuring a low-resistivity p+ subcollector, thin p-epi, and boron-doped poly-emitter are described. Device isolation is provided by deep and shallow trenches which reduce the collector-to-substrate capacitance while maintaining a high breakdown voltage (⩾40 V). By utilizing a shallow emitter process in conjunction with an optimized arsenic-base implant, devices with emitter-base junction depths as shallow as 20 nm and base widths of less than 100 nm were obtained. Cutoff frequencies of up to 27 GHz were obtained, and the AC performance was demonstrated by an NTL-gate delay of 36 ps and an active-pull-down (APD) ECL-gate delay of 20 ps. This high-performance p-n-p technology was developed to be compatible with existing double-poly n-p-n technologies. The matching speed of p-n-p devices opens up new opportunities for high-performance complementary bipolar circuits 相似文献
37.
Four nonlactating ruminally cannulated Holstein cows were used in a 4 x 4 Latin square experiment with 4 21-d periods to determine if the effects of dietary fat would be affected by hay particle length. Treatments consisted of two levels of tallow (0 and 5%) and two hay particle lengths (short-cut and long-cut) in a 2 x 2 factorial. Diets contained alfalfa hay, corn silage, and concentrate [1:1:2, dry matter (DM) basis] fed as a total mixed ration (TMR) once per day. Samples of the 0 and 5% tallow TMR were ground and incubated in situ in polyester bags for 24 and 48 h. Ruminal samples were taken on day 21 at 0800 h and at 2-h intervals until 1600 h. The total tract digestibilities of acid detergent fiber (ADF) and neutral detergent fiber (NDF) were not affected by tallow or by hay by tallow interactions. There was a trend for tallow to improve total tract digestibility of crude protein (CP) (70.2 vs. 74.7%). After 48 h of ruminal incubation, tallow significantly decreased the digestibilities of DM, ADF, and NDF. No hay length by tallow interactions for DM, NDF, ADF or CP digestibilities occurred after 24 or 48 h. Tallow increased concentrations of propionate and decreased concentrations of acetate and valerate and the acetate-to-propionate ratio. Total volatile fatty acids increased when tallow was added to diets with short-cut hay, which suggests that when unprotected fat is added to diets with a high level of hay, a short-cut hay length may be advantageous. This result may be due to shorter rumen retention time of feed particles, which reduces the time for fatty acids to exert antimicrobial effects. Or, it may because the increased surface area of the hay particle provides more area for microbial attachment and increased fermentation. 相似文献
38.
One issue in the design and implementation of a wireless local area network is the selection of access point (AP) locations. Proper AP placement is necessary to provide adequate signal coverage and also to minimize cochannel coverage overlap. The impact of incorrect placement of APs is significant. Placing APs too far apart can lead to gaps in coverage. On the other hand, placing the units too close together leads to excessive cochannel coverage overlap, degrading system performance. Currently, AP placement involves a "trial and error" technique. When a technician tests the effect of moving an AP from one location to another, it is necessary to spend considerable time manually measuring signal strengths in order to determine how this move affects the AP's coverage area. In this letter, we describe a procedure for estimating the coverage areas of relocated APs. The procedure can be used as part of a manual design process or as part of an automated design tool. 相似文献
39.
The medial displacement osteotomy of Chiari has an established place in the management of older children and adults with severe hip dysplasia. The results claimed for the operation are, however, variable. There have also been reports of sciatic nerve lesions. In this study ten cadavers were operated upon. Chiari osteotomy was performed upon five, and five acted as controls. The hemipelvis was removed from each cadaver; each specimen was deep-frozen and sectioned transversely. The distance of the sciatic nerve from the nearest bony point was measured in each section and the results were recorded graphically. A further radiographic and photographic study was performed to determine whether apparent displacement at the osteotomy might be misleading. The conclusion was drawn that the sciatic nerve is angulated at the osteotomy and further endangered by the risk of bone splintering at the sciatic notch. The radiographic study suggested that some poor clinical results may be explained by a radiological artefact, because there is a tendency for the osteotomy to hinge posteriorly at the sciatic notch opening anteriorly like a book. Radiographs may suggest excellent medial displacement whereas in fact the femoral head is very poorly covered. 相似文献
40.