全文获取类型
收费全文 | 508873篇 |
免费 | 6778篇 |
国内免费 | 1629篇 |
专业分类
电工技术 | 9449篇 |
综合类 | 739篇 |
化学工业 | 75929篇 |
金属工艺 | 16878篇 |
机械仪表 | 14490篇 |
建筑科学 | 13445篇 |
矿业工程 | 1315篇 |
能源动力 | 14439篇 |
轻工业 | 52359篇 |
水利工程 | 4182篇 |
石油天然气 | 5306篇 |
武器工业 | 13篇 |
无线电 | 65205篇 |
一般工业技术 | 94159篇 |
冶金工业 | 95430篇 |
原子能技术 | 7844篇 |
自动化技术 | 46098篇 |
出版年
2021年 | 3682篇 |
2020年 | 2763篇 |
2019年 | 3449篇 |
2018年 | 5613篇 |
2017年 | 5493篇 |
2016年 | 5899篇 |
2015年 | 4309篇 |
2014年 | 7359篇 |
2013年 | 23990篇 |
2012年 | 12670篇 |
2011年 | 17891篇 |
2010年 | 13918篇 |
2009年 | 15896篇 |
2008年 | 16732篇 |
2007年 | 16732篇 |
2006年 | 15095篇 |
2005年 | 13806篇 |
2004年 | 13447篇 |
2003年 | 13130篇 |
2002年 | 12541篇 |
2001年 | 13014篇 |
2000年 | 12109篇 |
1999年 | 13004篇 |
1998年 | 31020篇 |
1997年 | 21975篇 |
1996年 | 16958篇 |
1995年 | 13073篇 |
1994年 | 11646篇 |
1993年 | 11343篇 |
1992年 | 8299篇 |
1991年 | 7913篇 |
1990年 | 7616篇 |
1989年 | 7365篇 |
1988年 | 7127篇 |
1987年 | 5908篇 |
1986年 | 5918篇 |
1985年 | 7109篇 |
1984年 | 6406篇 |
1983年 | 5955篇 |
1982年 | 5408篇 |
1981年 | 5589篇 |
1980年 | 5168篇 |
1979年 | 4966篇 |
1978年 | 4617篇 |
1977年 | 5506篇 |
1976年 | 7033篇 |
1975年 | 3961篇 |
1974年 | 3748篇 |
1973年 | 3814篇 |
1972年 | 3044篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Chan C.C. Zheng Ming Zhao Qian C. Meng S. 《Industrial Electronics, IEEE Transactions on》2002,49(6):1342-1344
Based on the concepts of cascade multilevel converters and one-cycle technique, comparisons are conducted to characterize the distortion of the pulsewidth modulation (PWM) and one-cycle control methods that were applied to converters. Simulation results for the different control schemes are obtained in PSIM software initially to see the effect of one-cycle control different from that of PWM control. Through the comparisons, the advantages and disadvantages are identified for each method. The one-cycle scheme is better than PWM control in reducing undesirable harmonics and tracing dynamic waveforms. Simulation and experimental results are also provided to verify the conclusions. 相似文献
993.
Malyshev S.A. Galwas B.A. Piotrowski J. Chizh A.L. Szczepaniak Z.R. 《Microwave and Wireless Components Letters, IEEE》2002,12(6):201-203
A photovaractor for the remote optical control of microwave circuits was studied. The photovaractor was fabricated as a p-i-n photodiode placed in a pigtailed fiber optical module. The study of the impedance in the frequency range up to 3 GHz in darkness and under illumination has shown that the photovaractor capacitance strongly depends on the incident optical power. The capacitance variation of the photovaractor diode under illumination is discussed 相似文献
994.
Relation between abrasion resistance and flexural strength of high volume fly ash concrete 总被引:2,自引:0,他引:2
In this paper, abrasion of high volume fly ash (HVFA) concretes made with 50% and 70% of cement replacement with fly ash was
assessed in terms of its relation to flexural tensile strength. Comparisons were made between normal Portland cement (NPC)
concrete and fly ash concrete. Comparisons were also made between fly ash concretes. Investigation results have shown that
the abrasion resistance increased as flexural tensile strength increased. Analysis of the results showed that, for concrete
with tensile strength of greater than 4–5 MPa, the abrasion resistance of HVFA concrete with 70% replacement with cement was
found to be higher than that of counterpart control NPC concrete and concrete made with 50% fly ash. The comparison between
the relation of abrasion to compressive strength and abrasion to flexural tensile strength made in terms of R2 of the linear regression showed that a stronger relation existed between abrasion and flexural tensile strength than that
of abrasion to compressive strength of the concrete studied.
Résumé L'étude a pour but d'estimer la relation entre la résistance à l'usure avec la résistance à la traction en flexion des bétons contenant de 50% et 70% de cendres volantes. On a comparé le béton pur au béton contenant des cendres volantes. Des comparaisons ont été faites également entre les différents bétons contenant des cendres volantes. Les resultats de la recherche ont montré que la résistance à l'usure augmente à mesure que la résistance à la traction en flexion de 4∼5 MPa ont une résistance à l'usure plus grande s'ils contienneint 70% de cendres volantes que s'ils étaient purs ou contenaient 50% de cendres volantes. La comparaison entre les relation de la résistance à l'usure en compression et de la résistance à l'usure en traction a été établie en termes de R2 de la régression linéaire. On a prouvé qu'une relation plus forte a été obtenue entre la résistance à l'usure et la résistance à la traction en flexion par rapport à la résistance à l'usure en compression du béton étudié.相似文献
995.
Vilar Moreno C. Amaris Duarte H. Usaola Garcia J. 《Energy Conversion, IEEE Transaction on》2002,17(2):267-272
Wind energy conversion systems (WECS) produce fluctuating output power, which may cause voltage fluctuations and flicker. Flicker assessment in networks may be difficult since its evaluation requires long computing time and special procedures to calculate the flicker severity index, Pst. In this paper, a frequency domain method to study flicker propagation is presented. This method is based on propagation of frequency components from WECS output currents throughout the grid. In this way, a fast flicker analysis in a network of any size can be performed. Also, an algorithm for flicker measurement in the frequency domain, which allows Pst calculation, is proposed. Several study cases have been performed, and results have been compared with time domain simulations, showing good agreement between them 相似文献
996.
An analytical expression for both band-to-band and band-trap-band indirect tunnelings is used to study the gate-induced drain leakage (GIDL) current of MOSFETs measured before and after hot-carrier stress. The voltage and temperature dependence of GIDL are characterized. Both results show that interface traps situated near the midgap participate in the conduction of GIDL, and band-trap-band indirect tunneling could be the major mechanism. This is further supported by the fact that the percentage increase in GIDL induced by hot-carrier stress is about the same as the corresponding increase in interface-trap density. On the other hand, under low-field conditions, trap-assisted Poole–Frenkle emission dominates over tunneling for temperatures even well below room temperature. 相似文献
997.
This article presents the data collected from 128 court appointed psychiatric evaluations (CAPEs) and their analysis. Issues addressed are: the link between type of criminal offence and mental disorder; rate of recidivism; efficacy of the early detection and follow-up systems; inherent psychiatric dilemmas; unacceptable lacuna in information recorded in the CAPEs; and the babel of legal and psychiatric terms. We advocate that a combined effort be made by the legal and psychiatric fraternities to create a uniform and standardized CAPE. 相似文献
998.
999.
1000.