全文获取类型
收费全文 | 745600篇 |
免费 | 8998篇 |
国内免费 | 1705篇 |
专业分类
电工技术 | 14001篇 |
综合类 | 625篇 |
化学工业 | 115104篇 |
金属工艺 | 29631篇 |
机械仪表 | 23470篇 |
建筑科学 | 17334篇 |
矿业工程 | 4817篇 |
能源动力 | 19717篇 |
轻工业 | 60419篇 |
水利工程 | 8421篇 |
石油天然气 | 16393篇 |
武器工业 | 49篇 |
无线电 | 84807篇 |
一般工业技术 | 150244篇 |
冶金工业 | 132723篇 |
原子能技术 | 17535篇 |
自动化技术 | 61013篇 |
出版年
2021年 | 6918篇 |
2020年 | 5092篇 |
2019年 | 6524篇 |
2018年 | 11174篇 |
2017年 | 11433篇 |
2016年 | 11914篇 |
2015年 | 7522篇 |
2014年 | 12824篇 |
2013年 | 34240篇 |
2012年 | 19936篇 |
2011年 | 27053篇 |
2010年 | 21771篇 |
2009年 | 24304篇 |
2008年 | 24872篇 |
2007年 | 24583篇 |
2006年 | 21421篇 |
2005年 | 19254篇 |
2004年 | 18428篇 |
2003年 | 18308篇 |
2002年 | 17516篇 |
2001年 | 17452篇 |
2000年 | 16494篇 |
1999年 | 16677篇 |
1998年 | 40140篇 |
1997年 | 28590篇 |
1996年 | 22255篇 |
1995年 | 16929篇 |
1994年 | 15270篇 |
1993年 | 15018篇 |
1992年 | 11278篇 |
1991年 | 10996篇 |
1990年 | 10773篇 |
1989年 | 10350篇 |
1988年 | 10016篇 |
1987年 | 8912篇 |
1986年 | 8685篇 |
1985年 | 9751篇 |
1984年 | 8809篇 |
1983年 | 8504篇 |
1982年 | 7701篇 |
1981年 | 7766篇 |
1980年 | 7481篇 |
1979年 | 7368篇 |
1978年 | 7135篇 |
1977年 | 8145篇 |
1976年 | 10478篇 |
1975年 | 6343篇 |
1974年 | 6140篇 |
1973年 | 6114篇 |
1972年 | 5303篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
811.
Steroidal glycoalkaloids, found in species of the Solanaceae, elicit bursting activity in galeal and tarsal chemosensilla of adult Colorado potato beetles. The effect has an average latency of 6–12 sec, depending on the sensillum/alkaloid combination. A 20-sec alkaloid treatment is often suffficient to render galeal sensilla unresponsive to gamma-aminobutyric acid, normally an effective stimulant. The alkaloids have similar effects on galeal sensilla of larval Colorado potato beetles and on labellar chemosensilla of the blowfly. It is concluded that these compounds act independently of any specialized chemoreceptor in the Colorado potato beetle, and that association of the Colorado potato beetle with solanaceous plants has not led to evolution of a specific receptor forSolanum glycoalkaloids. 相似文献
812.
813.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed. 相似文献
814.
815.
The stereausis model of biological auditory processing is proposed as a representation that encodes both binaural and spectral information in a unified framework. A working analog VLSI chip that implements this model of early auditory processing in the brain is described. The chip is a 100000-transistor integrated circuit that computes the stereausis representation in real time, using continuous-time analog processing. The chip receives two audio inputs, representing sound entering the two ears, computes the stereausis representation, and generates output signals that can directly drive a color CRT display. Outputs from the chips for a variety of artificial and speech stimuli are shown. 相似文献
816.
E. A. Timofeev 《Cybernetics and Systems Analysis》1991,27(4):540-548
The generating function of the number of customers in a GI|HM2|1 queue is derived for a service discipline which is a stochastic mixture of absolute and relative priorities.Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 75–84, July–August, 1991. 相似文献
817.
Kunkel Mark A.; Hector Mark A.; Góngora Coronado Elías; Castillo Vales Victor 《Canadian Metallurgical Quarterly》1989,36(3):322
Conducted a study of client expectations of psychological services in Yucatán, Mexico, under the sponsorship of a grant from the Organization of American States. The Expectations about Counseling–Brief form (EAC-B) questionnaire was translated and administered to 488 subjects across age, sex, and experience with psychological services. Subsequent analyses supported the reliability and robustness of the Spanish EAC-B, with factor structure similar to the EAC-B in English. Some relation was found among age, sex, prior counseling experience, and expectations about counseling. Implications of these data for future research and comparison with U.S. subjects are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
818.
819.
This paper contains several new results concerning covariant quantum channels in d ≥ 2 dimensions. The first part, Sec. 3, based on [4], is devoted to unitarily covariant channels, namely depolarizing and transpose-depolarizing channels. The second part, Sec. 4, based on [10], studies Weyl-covariant channels. These results are preceded by Sec. 2 in which we discuss various representations of general completely positive maps and channels. In the first part of the paper we compute complementary channels for depolarizing and transpose-depolarizing channels. This method easily yields minimal Kraus representations from non-minimal ones. We also study properties of the output purity of the tensor product of a channel and its complementary. In the second part, the formalism of discrete noncommutative Fourier transform is developed and applied to the study of Weyl-covariant maps and channels. We then extend a result in [16] concerning a bound for the maximal output 2-norm of a Weyl-covariant channel. A class of maps which attain the bound is introduced, for which the multiplicativity of the maximal output 2-norm is proven. The complementary channels are described which have the same multiplicativity properties as the Weyl-covariant channels. 相似文献
820.
Tipton C.W. Bayne S.B. Griffin T.E. Scozzie C.J. Geil B. Agarwal A.K. Richmond J. 《Electron Device Letters, IEEE》2002,23(4):194-196
This paper reports on the first demonstration of a half-bridge power inverter constructed from silicon carbide gate turn-off thyristors (GTOs) operated in the conventional GTO mode. This circuit was characterized with input bus voltages of up to 600 VDC and 2 A (peak current density of 540 A/cm2) with resistive loads using a pulse-width modulated switching frequency of 2 kHz. We discuss the implications of the thyristor's electrical characteristics and the circuit topology on the overall operation of the half-bridge circuit. This work has determined the conservative critical rate of rise value of the off-state voltage to be 200 V/μs in these devices 相似文献