首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4324篇
  免费   95篇
  国内免费   7篇
电工技术   220篇
综合类   2篇
化学工业   918篇
金属工艺   137篇
机械仪表   87篇
建筑科学   69篇
能源动力   153篇
轻工业   325篇
水利工程   5篇
石油天然气   4篇
无线电   410篇
一般工业技术   809篇
冶金工业   922篇
原子能技术   123篇
自动化技术   242篇
  2023年   14篇
  2022年   43篇
  2021年   67篇
  2020年   24篇
  2019年   26篇
  2018年   50篇
  2017年   46篇
  2016年   81篇
  2015年   44篇
  2014年   86篇
  2013年   180篇
  2012年   156篇
  2011年   185篇
  2010年   146篇
  2009年   160篇
  2008年   164篇
  2007年   166篇
  2006年   153篇
  2005年   140篇
  2004年   134篇
  2003年   129篇
  2002年   124篇
  2001年   81篇
  2000年   76篇
  1999年   80篇
  1998年   392篇
  1997年   232篇
  1996年   172篇
  1995年   113篇
  1994年   134篇
  1993年   103篇
  1992年   51篇
  1991年   56篇
  1990年   62篇
  1989年   57篇
  1988年   44篇
  1987年   50篇
  1986年   42篇
  1985年   50篇
  1984年   28篇
  1983年   34篇
  1982年   37篇
  1981年   24篇
  1980年   21篇
  1979年   27篇
  1978年   18篇
  1977年   17篇
  1976年   48篇
  1975年   15篇
  1972年   9篇
排序方式: 共有4426条查询结果,搜索用时 250 毫秒
31.
A 31-year-old man came to our hospital complaining of severe voiding pain. He had inserted a fishing line made of nylon into his urethra at the age of eighteen, which was unable to be taken out and had been left there for 13 years. Preoperative ultrasonogram showed severe bilateral hydronephrosis and the serum BUN and creatinine level were as high as 45.2 mg/dl and 4.8 mg/dl, respectively. A huge bladder stone was demonstrated in X-ray film, the patient was admitted and vesicolithotomy was performed. The size of the stone was 10.5 x 7.5 x 7.5 cm and the weight was 360 grams. The fishing line was found inside the stone and the length was over 3 meters. The serum BUN and creatinine level after the operation were still high as 28.4 mg/dl and 4.1 mg/dl, respectively, and they did not improve even after six months following.  相似文献   
32.
Artificially layered Bi2Sr2Can–1CunO4+n films were synthesized by sequential sputter deposition of BiO, SrCu0.5O1.5 and CaCuO2 layers. Annealing behavior of these films which were irradiated by Ar ions was studied. Defect assisted improvement of their crystalline perfection is expected which might results in the improvement of the superconducting properties of these films. An artificial film, such as an intergrowth of 2223 and 2234 phases, and superstructure films of (2245)1(2201)1 and (2234)1(2212)1, were irradiated by Ar ions (150 keV, 2–10×1012 ions/cm2) and annealed at 730 °C. An improvement of superconducting transition temperatures were observed.  相似文献   
33.
34.
Each rat was injected intraperitoneally once with 0.9% NaCl or zinc (10, 20, 40, or 60 mg zinc/kg b.w.). The zinc content in kidney reached a maximum level of approx. 50 microgram/g kidney, corresponding to a dose (40 mg zinc/kg b.w.). The distribution profiles of the renal cytosols of zinc-injected rats on a Sephadex G-75 column showed that most of the increased zinc was attributable to metallothionein. There was a linear relationship between the zinc contents in cytosol and metallothionein. Our results demonstrated that there was a limit of zinc accumulation in kidneys of zinc-injected rats and that 57% of the increased zinc in renal cytosols was bound to metallothionein. Our results suggest that the role of metallothionein in zinc accumulation in the kidney is similar to that of zinc accumulation in liver.  相似文献   
35.
Naka  A. Saito  S. 《Electronics letters》1992,28(24):2221-2223
Numerical analysis of IM signal propagation in an optical fibre is carried out taking selfphase modulation and group-velocity dispersion into account. The transmission distance yielding a prescribed eye opening penalty, in the normal dispersion region, is shown to be inversely proportional to the square root of the signal power.<>  相似文献   
36.
A 2223 km transmission distance was achieved with a 2.5-Gb/s heterodyne detection system that used erbium-doped-fiber in-line amplifiers and dispersion-shifted single-mode fibers. Twenty-five amplifiers, placed at approximately 80-km intervals, offered a total gain of more than 440 dB. Receiver sensitivity was -42.0 dBm, with only a 4.2-dB penalty from the initial sensitivity achieved by the back-to-back configuration  相似文献   
37.
The authors have developed a modified MBE growth process to produce high-gain n-p-n GaAs-AlGaAs heterojunction bipolar transistors (HBTs) with a mean time to failure (MTTF) of 1.5×108 h at 125°C. Beryllium incorporation and diffusion are controlled through a combination of reduced substrate temperature and increased As/Ga flux ratio during MBE growth, resulting in extremely stable HBT profiles. The authors also demonstrate graded InGaAs surface layers with nonalloyed refractory metal contacts that significantly improve ohmic reliability compared to alloyed AuGe contacts. The ability to produce robust HBTs by MBE is critically important to this technology  相似文献   
38.
An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014  相似文献   
39.
The restoration of the red colour of carthamine (photo-bleached in polymeric heterosaccharide gels) was investigated using sodium salts, potassium salts, and alkali. Ca-alginate gel was stained with carthamine, and the red-dish membranes were exposed to fluorescent light for 2·5, 4·0 and 20 h (at 28°C). The resulting orange-yellow gel membranes were treated with Na- or K-citrate solution and the restoration of the red colouration was followed spectrophoto-metrically. The results indicate that the red colour of carthamine can be retained within the gel membranes, while yellow-coloured compounds were removed and/or transformed by the alkaline salt solutions.  相似文献   
40.
The mechanism of the suppression of vapor explosions by adding inversely soluble polymers in water is studied. Vapor explosion experiments and quench experiment are conducted using a silver test piece. Polymetric solution (polyethylene oxide), of concentrations from 0 to 500 wppm, whose normalized viscosity (by water) varies from 1.00 to 2.00, is used. No vapor explosion is observed in the aqueous polymer solution at a concentration higher than 200 wppm. Quench experiments using the silver test piece submerged in the polymer solution and water are performed in order to examine the stability of film boiling. The suppression of the vapor film collapse is attributed to the precipitation of polyethylene as a gel around the vapor film. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 297–306, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10037  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号