全文获取类型
收费全文 | 253147篇 |
免费 | 2910篇 |
国内免费 | 446篇 |
专业分类
电工技术 | 4459篇 |
综合类 | 268篇 |
化学工业 | 41832篇 |
金属工艺 | 9573篇 |
机械仪表 | 7638篇 |
建筑科学 | 6014篇 |
矿业工程 | 1483篇 |
能源动力 | 5506篇 |
轻工业 | 25649篇 |
水利工程 | 2586篇 |
石油天然气 | 5248篇 |
武器工业 | 33篇 |
无线电 | 25776篇 |
一般工业技术 | 46555篇 |
冶金工业 | 48212篇 |
原子能技术 | 6058篇 |
自动化技术 | 19613篇 |
出版年
2021年 | 2252篇 |
2019年 | 2154篇 |
2018年 | 3650篇 |
2017年 | 3582篇 |
2016年 | 3871篇 |
2015年 | 2377篇 |
2014年 | 4104篇 |
2013年 | 10905篇 |
2012年 | 6532篇 |
2011年 | 8845篇 |
2010年 | 6897篇 |
2009年 | 7616篇 |
2008年 | 8078篇 |
2007年 | 8181篇 |
2006年 | 7364篇 |
2005年 | 6424篇 |
2004年 | 6117篇 |
2003年 | 5899篇 |
2002年 | 5992篇 |
2001年 | 5764篇 |
2000年 | 5577篇 |
1999年 | 5514篇 |
1998年 | 12761篇 |
1997年 | 9100篇 |
1996年 | 7055篇 |
1995年 | 5530篇 |
1994年 | 4948篇 |
1993年 | 4874篇 |
1992年 | 3876篇 |
1991年 | 3548篇 |
1990年 | 3775篇 |
1989年 | 3668篇 |
1988年 | 3459篇 |
1987年 | 3083篇 |
1986年 | 3106篇 |
1985年 | 3587篇 |
1984年 | 3403篇 |
1983年 | 3068篇 |
1982年 | 2886篇 |
1981年 | 2985篇 |
1980年 | 2860篇 |
1979年 | 2780篇 |
1978年 | 2838篇 |
1977年 | 3065篇 |
1976年 | 3924篇 |
1975年 | 2514篇 |
1974年 | 2357篇 |
1973年 | 2488篇 |
1972年 | 2031篇 |
1971年 | 1916篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
861.
862.
W. Klas U. Herpers M. Reich R. Michel R. Droste R. Holm E.-M. Horn G. Müller 《工业材料与腐蚀》1991,42(11):570-575
The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10?6 to 5 · 10?4 mm/y, for tantalum: 10?8 to 4 · 10?6 mm/y, and for the Ta-40Nb alloy: 2 · 10?7 to 8 · 10?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F? and at a temperature of 108°C, corrosion rates between 5.3 · 10?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10?3 mm/y at 50°C/280 ppm F? and 1.4 · 10?2 mm/y at 110°C/320 ppm F?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing. 相似文献
863.
A non-linear behaviour in the resistance of tellurium as a function of pressure has been observed. At each pressure the resistance
shows a time variation. At lower pressures, the normalized resistance increases with time, and at higher pressures, the normalized
resistance decreases exponentially as a function of time. This change in behaviour with respect to time occurs in the region
of the steepest descent in the resistance versus pressure plot. However, the magnitude of the change in the resistance with
time is small compared to a change in the resistance with pressure. The origin of this behaviour is suggested to be linked
with the generation and annealing of localized charged defects.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
864.
You F. Embabi S.H.K. Sanchez-Sinencio E. 《Solid-State Circuits, IEEE Journal of》1997,32(12):2000-2011
This paper presents a multistage amplifier for low-voltage applications (<2 V). The amplifier consists of simple (noncascode) low gain stages and is stabilized using a nested transconductance-capacitance compensation (NGCC) scheme. The resulting topology is similar to the well known nested Miller compensation (NMC) multistage amplifier, except that the proposed topology contains extra G m feedforward stages which are used to enhance the amplifier performance. The NGCC simplifies the transfer function of the proposed multistage amplifier which, in turn, simplifies its stability conditions. A comparison between the NGCC and NMC shows that the NGCC has wider bandwidth and is easier to stabilize. A four-stage NGCC amplifier has been fabricated using a 2-μm CMOS process and is tested using a ±1.0 V power supply. A dc gain of 100 dB has been measured. A gain bandwidth product of 1 MHz with 58° of phase margin and power of 1.4 mW can be achieved. The op amp occupies an active area of 0.22 mm2. Step response shows that the op amp is stable 相似文献
865.
Anvari B. Milner T.E. Tanenbaum B.S. Nelson J.S. 《IEEE transactions on bio-medical engineering》1998,45(7):934-941
Surface cooling, in conjunction with various thermally mediated therapeutic procedures, can provide a means to protect superficial tissues from injury while achieving destruction of deeper targeted structures. We have investigated the thermal response of in-vivo human skin to: (1) contact cooling with a sapphire window (6-12°C); and (2) spray cooling with a freon substitute cryogen [tetrafluoroethane; boiling point ≈-26°C at 1 atmospheric pressure (atm)]. Measurements utilizing infrared radiometry show surface temperature reductions from 30°C to 14-19°C are obtained within approximately is in response to sapphire contact cooling. Surface temperature reductions to values between 5°C and -9°C are obtained in response to 20-100-ms cryogen spurts. Computational results, based on fitting the measured radiometric surface temperature to estimate heat transfer parameters, show: (1) temperature reductions remain localized to approximately 200 μm of superficial tissue; and (2) values of heat flux and total energy removed per unit skin surface area at least doubled when using cryogen spray cooling 相似文献
866.
Improved fully-balanced current-mode integrator 总被引:1,自引:0,他引:1
A high CMRR fully-balanced current-mode integrator structure is presented. The proposed structure improves the CMRR at low frequencies by a factor of gm/go. Moreover, the structure provides more flexibility to guarantee stability and is significantly less sensitive to process mismatches. The differential and common-mode gains and CMRR at low and high frequencies are analysed as well as verified in simulation 相似文献
867.
Gordonia amarae is a right-angled branching filament belonging to the mycolic acid-containing Actinobacteria which is commonly found in many foaming activated sludge wastewater treatment plants. Although studies on different substrates as sole carbon sources by pure cultures of G. amarae have been carried out, none have examined substrate uptake by this organism in situ. Uptake of several hydrophilic and hydrophobic substrates by G. amarae was evaluated in situ using a combination of fluorescence in situ hybridization and microautoradiography. G. amarae could assimilate a range of both hydrophilic and hydrophobic substrates. From the data, G. amarae appears to be physiologically active under aerobic, anaerobic and anoxic condition (NO2 and NO3) for some substrates. This might explain why attempts to control foaming caused by G. amarae using anoxic and anaerobic selectors have been unsuccessful. This study emphasizes that bacteria can behave differently in situ to pure cultures and that it is important to evaluate the in situ physiology of these bacteria if we are to better understand their role in the wastewater treatment process. 相似文献
868.
869.
B. E. Rytsar 《Cybernetics and Systems Analysis》2007,43(2):192-207
The paper considers the set-theoretical approach to the joint decomposition of systems of Boolean functions of variables specified
in different representation forms. The approach is based on the method of q-partitions of conjuncterms and concept of decomposition
clones. Theorems on joint decomposition of a system of full and partial functions are formulated. The approach is illustrated
by examples.
Parts I and II of this article are published in No. 5 (2001) and No. 1 (2002).
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 39–58, March–April 2007. 相似文献
870.
B. E. Nikol'skii N. L. Patratii Yu. V. Frolov 《Combustion, Explosion, and Shock Waves》1992,28(1):45-47
Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 1, pp. 51–53, January–February, 1992. 相似文献