全文获取类型
收费全文 | 411994篇 |
免费 | 6552篇 |
国内免费 | 1383篇 |
专业分类
电工技术 | 7704篇 |
综合类 | 349篇 |
化学工业 | 61993篇 |
金属工艺 | 14283篇 |
机械仪表 | 11870篇 |
建筑科学 | 11636篇 |
矿业工程 | 869篇 |
能源动力 | 11117篇 |
轻工业 | 43798篇 |
水利工程 | 3312篇 |
石油天然气 | 1835篇 |
武器工业 | 13篇 |
无线电 | 55388篇 |
一般工业技术 | 76611篇 |
冶金工业 | 74951篇 |
原子能技术 | 5568篇 |
自动化技术 | 38632篇 |
出版年
2021年 | 2666篇 |
2019年 | 2435篇 |
2018年 | 3838篇 |
2017年 | 3903篇 |
2016年 | 4144篇 |
2015年 | 3426篇 |
2014年 | 5714篇 |
2013年 | 19279篇 |
2012年 | 10202篇 |
2011年 | 14680篇 |
2010年 | 11283篇 |
2009年 | 12884篇 |
2008年 | 13914篇 |
2007年 | 14285篇 |
2006年 | 12777篇 |
2005年 | 11961篇 |
2004年 | 11574篇 |
2003年 | 11279篇 |
2002年 | 10913篇 |
2001年 | 11131篇 |
2000年 | 10271篇 |
1999年 | 10769篇 |
1998年 | 24010篇 |
1997年 | 17587篇 |
1996年 | 13903篇 |
1995年 | 10979篇 |
1994年 | 9771篇 |
1993年 | 9354篇 |
1992年 | 7121篇 |
1991年 | 6790篇 |
1990年 | 6397篇 |
1989年 | 6106篇 |
1988年 | 5860篇 |
1987年 | 4884篇 |
1986年 | 4834篇 |
1985年 | 5978篇 |
1984年 | 5599篇 |
1983年 | 4832篇 |
1982年 | 4496篇 |
1981年 | 4447篇 |
1980年 | 4208篇 |
1979年 | 4080篇 |
1978年 | 3771篇 |
1977年 | 4548篇 |
1976年 | 6097篇 |
1975年 | 3115篇 |
1974年 | 3011篇 |
1973年 | 2890篇 |
1972年 | 2318篇 |
1971年 | 2003篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
891.
A unified theoretical approach is presented for the calculation of the performance of the single-phase capacitor-start permanent-magnet (PM) ac line-start motor. The earlier work of Chang and of Finch and Lawrenson on capacitor reluctance motors is extended. As far as possible, a common set of reference frame transformations for steady-state, transient, and asynchronous performance is also provided, permitting the use of all the theory developed for the analysis of the balanced polyphase PM motor. A new approximate technique is given for estimating the average asynchronous torque/speed curve from computed acceleration curves. 相似文献
892.
D.H.R. Price J.A. Sharp 《International Journal of Electrical Power & Energy Systems》1985,7(3):131-137
Peak demand forecasts obtained from six different univariate forecasting methods, under a range of conditions, were used to drive a capacity acquisition model of a large electrical supply system; and the resulting physical and financial performance of the model was observed for each set of forecasts. The results obtained are discussed in the context of their implications for the choice of load forecasting method used in capacity acquisition planning by a power supply undertaking. 相似文献
893.
Seo K. Heiblum M. Knoedler C.M. Oh J.E. Pamulapati J. Bhattacharya P. 《Electron Device Letters, IEEE》1989,10(2):73-75
A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In 0.12Ga0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In0.12Ga0.88As was estimated to be about 380 meV 相似文献
894.
The absorption of gas through the plume eye and of an injected gas in a steelmaking ladle process was investigated, using
a physical model of CO2 absorption into a NaOH solution. The results show that the inert gas escaping through the plume eye is ineffective in protecting
the bath from the atmosphere, and placing an oil layer (simulated slag) decreases the absorption rate significantly. Increasing
the flow rate of the inert gas not only exposes more of the liquid surface to the CO2 atmosphere, but also increases the mass transfer coefficient at the surface. The overall mass transfer between an injected
CO2 gas and NaOH solution includes the mass transfer through the surface of the bath as well as the mass transfer in the bubble
dispersion zone. The difference between the mass transfer in the bubble dispersion zone and the overall mass transfer was
found to be significant for relatively low gas flow rates. The mass transfer coefficient of CO2 in the bubble dispersion zone was estimated using available information regarding the bubble size and velocity. Mass transfer
coefficient estimated for the constant bubble frequency regime shows a dependence on gas flow rate. However, if a constant
characteristic size of bubbles is assumed as an alternative approach, the mass transfer coefficient is independent of the
gas flow rate. 相似文献
895.
A new pulse stabilisation scheme for a harmonically frequency modulated (FM) modelocked erbium fibre ring laser using a distributed feedback laser diode (DFBLD) is presented. More than 65 dB supermode noise suppression in the RF spectrum was obtained with the proposed method. Effective reduction of supermode noise can be accomplished as the DFBLD in the fibre laser acts not only as a fast-gain saturated medium but also as an optical bandpass filter for suppressing supermode noise in a harmonically modelocked laser system. 相似文献
896.
Kimoto T. Kosugi H. Suda J. Kanzaki Y. Matsunami H. 《Electron Devices, IEEE Transactions on》2005,52(1):112-117
Design and fabrication of lateral SiC reduced surface field (RESURF) MOSFETs have been investigated. The doping concentration (dose) of the RESURF and lightly doped drain regions has been optimized to reduce the electric field crowding at the drain edge or in the gate oxide by using device simulation. The optimum oxidation condition depends on the polytype: N/sub 2/O oxidation at 1300/spl deg/C seems to be suitable for 4H-SiC, and dry O/sub 2/ oxidation at 1250/spl deg/C for 6H-SiC. The average inversion-channel mobility is 22, 78, and 68 cm/sup 2//Vs for 4H-SiC(0001), (112~0), and 6H-SiC(0001) MOSFETs, respectively. RESURF MOSFETs have been fabricated on 10-/spl mu/m-thick p-type 4H-SiC(0001), (112~0), and 6H-SiC(0001) epilayers with an acceptor concentration of 1/spl times/10/sup 16/ cm/sup -3/. A 6H-SiC(0001) RESURF MOSFET with a 3-/spl mu/m channel length exhibits a high breakdown voltage of 1620 V and an on-resistance of 234 m/spl Omega//spl middot/cm/sup 2/. A 4H-SiC(112~0) RESURF MOSFET shows the characteristics of 1230 V-138 m/spl Omega//spl middot/cm/sup 2/. 相似文献
897.
The results of a computer simulation of the initial stages of the nucleation and growth of gold on NaCl(100) are presented. A potential energy scaling Monte Carlo model employing a 50 × 50 array, mobile monomers, dimers and trimers, and gold atom vertical “roll up” was used. The parameters in the model were obtained from the work of Robinson and Robins, other published sources and/or found by calculation. Simulations of the migration of single gold adatoms over the surface permitted the determination of the diffusion coefficient as a function of the reciprocal temperature which returned the same activation energy given by the potential field, thus indicating the consistency of the model. Initial cluster densities were determined using deposition rates of Rd = 1015cm-2s-1 and Rd = 1014cm-2s-1 over the temperature range T=200–425 K. Initial cluster growth was found to occur primarily by surface phase transport and resulted in clusters that were shaped like very thin disks. Using the equations from the work of Velfe and coworkers, calculations were made to extrapolate the computer simulation data in order to permit an indirect comparison with the data of Robinson and Robins. Good agreement was achieved. Initial condensation coefficients determined over a 250 ms interval showed that α ≈ 0 at T > 425 K and α ≈ 1 at T < 325 K for a deposition rate of Rd=1015 cm-2 s-1. 相似文献
898.
S H Yoon J H Collins D Musale S Sundararajan S P Tsai G A Hallsby J F Kong J Koppes P Cachia 《Water science and technology》2005,51(6-7):151-157
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works. 相似文献
899.
B.J.W. Waarsing M. Nuttin H. Van Brussel B. Corteville 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2005,35(1):53-65
This paper presents our approach to extend the niche of behavior-based robotics toward manipulation. We use results from neuroscience to derive some qualitative design rules for the mechanics of the manipulator, resulting in a next-generation manipulator, the "soft arm". By defining the basic behaviors of the manipulator as trajectory-producing behaviors (which is also biologically plausible), we have designed a first test case: writing on a board with a mobile manipulator. The soft arm has not yet been developed; therefore, we have emulated such a soft robot arm on an industrial robot. 相似文献
900.
Tian Yang Lipson S. O'Brien J.D. Deppe D.G. 《Photonics Technology Letters, IEEE》2005,17(11):2244-2246
We report on the demonstration of optically pumped photonic crystal lasers with InAs quantum dot active regions operating at room temperature near 1310 nm. Absorbed threshold pump powers as low as 25 /spl mu/W are observed. We also extract a characteristic temperature of 17 K, which is attributed to limitations caused by surface recombination. 相似文献