全文获取类型
收费全文 | 11734篇 |
免费 | 970篇 |
国内免费 | 40篇 |
专业分类
电工技术 | 144篇 |
综合类 | 27篇 |
化学工业 | 2919篇 |
金属工艺 | 475篇 |
机械仪表 | 728篇 |
建筑科学 | 197篇 |
矿业工程 | 12篇 |
能源动力 | 542篇 |
轻工业 | 864篇 |
水利工程 | 31篇 |
石油天然气 | 22篇 |
武器工业 | 1篇 |
无线电 | 2117篇 |
一般工业技术 | 2547篇 |
冶金工业 | 677篇 |
原子能技术 | 112篇 |
自动化技术 | 1329篇 |
出版年
2024年 | 10篇 |
2023年 | 149篇 |
2022年 | 205篇 |
2021年 | 327篇 |
2020年 | 256篇 |
2019年 | 313篇 |
2018年 | 410篇 |
2017年 | 382篇 |
2016年 | 436篇 |
2015年 | 369篇 |
2014年 | 575篇 |
2013年 | 800篇 |
2012年 | 795篇 |
2011年 | 919篇 |
2010年 | 699篇 |
2009年 | 748篇 |
2008年 | 644篇 |
2007年 | 543篇 |
2006年 | 482篇 |
2005年 | 418篇 |
2004年 | 379篇 |
2003年 | 384篇 |
2002年 | 337篇 |
2001年 | 250篇 |
2000年 | 222篇 |
1999年 | 216篇 |
1998年 | 312篇 |
1997年 | 202篇 |
1996年 | 164篇 |
1995年 | 117篇 |
1994年 | 106篇 |
1993年 | 79篇 |
1992年 | 66篇 |
1991年 | 44篇 |
1990年 | 46篇 |
1989年 | 51篇 |
1988年 | 37篇 |
1987年 | 36篇 |
1986年 | 29篇 |
1985年 | 19篇 |
1984年 | 29篇 |
1983年 | 23篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1975年 | 7篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Jooyoung Jeon Youngwoo Kwon Hong-Shick Min 《Microwave and Wireless Components Letters, IEEE》2002,12(9):342-344
A new physics-based noise model of a GaAs PHEMT is developed using the characteristic potential method (CPM). The model calculates the intrinsic noise current sources using CPM. Combined with the extrinsic noise parameters extracted from the measured S-parameters, the model reproduces four noise parameters of the device accurately under low drain bias voltages without using any fitting parameters. The model is verified with a 0.2-/spl mu/m GaAs PHEMT and shows excellent agreement with the measurements for all the noise parameters up to a drain voltage of 1 V Also, the proposed method allows the simulation of the microscopic noise distribution and thus allows one to obtain a physical understanding of noise mechanisms inside the device. 相似文献
72.
Joon Sik LeeIn Sung Jung 《International Journal of Heat and Mass Transfer》2002,45(1):113-123
Experiments are conducted to investigate the effects of bulk flow pulsations on film cooling with compound angle holes. A row of five film cooling holes is considered with orientation angles of 0°, 30°, 60°, and 90° at a fixed inclination angle of 35°. Static pressure pulsations are produced by an array of six rotating shutter blades, which extend across the span of the exit of the wind tunnel test section. The pulsation frequency is fixed at 36 Hz, but changes in the time-averaged blowing ratios of 0.5, 1.0 and 2.0 produce three different coolant Strouhal numbers, 3.6, 1.8 and 0.9, respectively. Detailed film cooled boundary layer temperature distributions are measured by a cold wire and the adiabatic film cooling effectiveness by thermochromic liquid crystal (TLC). The boundary layer temperature surveys show that pulsations induce large disruptions to the boundary layer temperature distribution and the film coverage. As the orientation angle increases, the injectant concentration spreads further into the spanwise direction because of pulsations than the steady case. With pulsations the adiabatic film cooling effectiveness value decreases regardless of the orientation angle. The amount of reduction, however, depends on the orientation angle in such a way that the larger the orientation angle is, the smaller the reduction is. 相似文献
73.
Hayat M.M. Sakoglu U. Oh-Hyun Kwon Shuling Wang Campbell J.C. Saleh B.E.A. Teich M.C. 《Quantum Electronics, IEEE Journal of》2003,39(1):179-185
The recurrence theory for the breakdown probability in avalanche photodiodes (APDs) is generalized to heterostructure APDs that may have multiple multiplication layers. The generalization addresses layer-boundary effects such as the initial energy of injected carriers as well as the layer-dependent profile of the dead space in the multiplication region. Reducing the width of the multiplication layer serves to both downshift and sharpen the breakdown probability curve as a function of the applied reverse-bias voltage. In structures where the injected carriers have an initial energy that is comparable to the ionization threshold energy, the transition from linear mode to Geiger-mode is more abrupt than in structures in which such initial energy is negligible. The theory is applied to two recently fabricated Al/sub 0.6/Ga/sub 0.4/As-GaAs heterostructure APDs and to other homostructure thin GaAs APDs and the predictions of the breakdown-voltage thresholds are verified. 相似文献
74.
The photonic quantum ring (PQR) laser is a three dimensional whispering gallery (WG) mode laser and has anomalous quantum wire properties, such as microampere to nanoampere range threshold currents and √T‐dependent thermal red shifts. We observed uniform bottom emissions from a 1‐kb smart pixel chip of a 32×32 InGaAs PQR laser array flip‐chip bonded to a 0.35 µm CMOS‐based PQR laser driver. The PQR‐CMOS smart pixel array, now operating at 30 MHz, will be improved to the GHz frequency range through device and circuit optimization. 相似文献
75.
To provide responsive information services in a ubiquitous computing environment, service software and system development are indispensable. A component-based ubiquitous information system with a JAIN (Java APIs for Integrated Networks) platform to achieve seamless transmissions and reach-everywhere communications was designed in our research. In this development, numerous ubiquitous service modules were identified: location management, roaming, mobile IP and WAP networking. These component-based network modules were constructed using a component composition language with component specification and interface definition, running on top of a distributed service architecture using a JAIN platform to distribute the ubiquitous information services to mobile users. Two applications, Wireless-Application-Protocol (WAP) Mail and Video-on-Demand (VoD) services, show that the JAIN-like platform with the developed networking components effectively fills the gap for application developers between mobile appliances and various kinds of ubiquitous information services. 相似文献
76.
Sungmoon Jung Jamshid Ghaboussi Soon-Duck Kwon 《Canadian Metallurgical Quarterly》2004,130(11):1356-1364
A new method of estimating flutter derivatives using artificial neural networks is proposed. Unlike other computational fluid dynamics based numerical analyses, the proposed method estimates flutter derivatives utilizing previously measured experimental data. One of the advantages of the neural networks approach is that they can approximate a function of many dimensions. An efficient method has been developed to quantify the geometry of deck sections for neural network input. The output of the neural network is flutter derivatives. The flutter derivatives estimation network, which has been trained by the proposed methodology, is tested both for training sets and novel testing sets. The network shows reasonable performance for the novel sets, as well as outstanding performance for the training sets. Two variations of the proposed network are also presented, along with their estimation capability. The paper shows the potential of applying neural networks to wind force approximations. 相似文献
77.
An improved method for the preparation of cross-sectional thin foils of coated WC-Co samples for studies by analytical electron microscopy is described. A braze alloy is used to join the sections of the sample together and the resulting sample is stable during subsequent grinding, dimpling, and milling operations. Cross-sectional micrographs provide examples of the efficacy of this method. No microstructural alteration associated with the brazing operation was observed. 相似文献
78.
79.
Traditional Korean soysauce samples were collected from households in Chinju, Gyeongnam, Korea and analysed for volatile N-nitrosamines. Five of 24 samples contained NDMA (range = 1.6-10.4 micrograms/l) which was the only volatile N-nitroso compound found. Soysauce made from well water contained NDMA more often (4 of 6 samples) than soysauce made from tap water (1 of 18). This suggests that the water source is a determinate in the NDMA content of soysauce, probably due to a higher nitrate content of well water. The source of salt used did not clearly influence NDMA content. Soysauce was prepared in the laboratory using traditional methods but with 0 to 400 mg/l nitrate and in some cases made 6.5 to 65 mM in ascorbic acid and fermented for 120 days. The NDMA content of the samples was positively correlated with increasing nitrate concentration. Nitrate at 400 mg/l resulted in an NDMA content of 203 micrograms/l. Ascorbic acid substantially inhibited NDMA formation. All samples contained large numbers of nitrate reductase-containing organisms (greater than 1 x 10(7) CFU/ml). 相似文献
80.
Sung Ho Jeong Joon Jeong Yi Jong Keun Kim Man Yeong Ha 《Journal of Mechanical Science and Technology》1991,5(1):16-21
A computer program to calculate the strip temperature heated in the continuous annealing furnace was developed, using the
zone method for radiative heat transfer analysis with the measured gas temperature in the furnace. Using theF
E Operator, the present study considered the effects of soot and transient species, in addition to the H2O−CO2 gas mixture on the gas radiative heat transfer. The predicted strip temperature distribution forF
E=1.05 represented well the measured data. The maximum difference in the heat flux transfered to the strip from the combustion
gas forF
E=1.0 (without soot and transient species gas radiation) and 1.05 (with soot and transient species gas radiation) was about
15%. The present study also investigated the effects of line speed and thickness variations on the strip temperature, establishing
the bases for the on-line computer model. 相似文献