全文获取类型
收费全文 | 15553篇 |
免费 | 248篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 192篇 |
综合类 | 3篇 |
化学工业 | 2101篇 |
金属工艺 | 363篇 |
机械仪表 | 342篇 |
建筑科学 | 531篇 |
矿业工程 | 60篇 |
能源动力 | 319篇 |
轻工业 | 1260篇 |
水利工程 | 89篇 |
石油天然气 | 121篇 |
无线电 | 1525篇 |
一般工业技术 | 2390篇 |
冶金工业 | 4902篇 |
原子能技术 | 161篇 |
自动化技术 | 1465篇 |
出版年
2022年 | 88篇 |
2021年 | 111篇 |
2019年 | 116篇 |
2018年 | 141篇 |
2017年 | 104篇 |
2016年 | 97篇 |
2015年 | 117篇 |
2014年 | 234篇 |
2013年 | 592篇 |
2012年 | 321篇 |
2011年 | 427篇 |
2010年 | 353篇 |
2009年 | 353篇 |
2008年 | 468篇 |
2007年 | 463篇 |
2006年 | 447篇 |
2005年 | 404篇 |
2004年 | 339篇 |
2003年 | 377篇 |
2002年 | 323篇 |
2001年 | 329篇 |
2000年 | 321篇 |
1999年 | 390篇 |
1998年 | 1332篇 |
1997年 | 844篇 |
1996年 | 614篇 |
1995年 | 432篇 |
1994年 | 386篇 |
1993年 | 400篇 |
1992年 | 279篇 |
1991年 | 246篇 |
1990年 | 266篇 |
1989年 | 220篇 |
1988年 | 224篇 |
1987年 | 207篇 |
1986年 | 199篇 |
1985年 | 252篇 |
1984年 | 214篇 |
1983年 | 216篇 |
1982年 | 209篇 |
1981年 | 185篇 |
1980年 | 196篇 |
1979年 | 135篇 |
1978年 | 137篇 |
1977年 | 242篇 |
1976年 | 322篇 |
1975年 | 136篇 |
1974年 | 127篇 |
1973年 | 109篇 |
1970年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Prospective memory is remembering to perform an action in the future. The authors introduce the 1st formal model of event-based prospective memory, namely, a multinomial model that includes 2 separate parameters related to prospective memory processes. The 1st measures preparatory attentional processes, and the 2nd measures retrospective memory processes. The model was validated in 4 experiments. Manipulations of instructions to place importance on either the prospective memory task or the background task (Experiments 1 and 2) and manipulations of distinctiveness of prospective memory targets (Experiment 2) had expected effects on model parameters, as did a manipulation of the difficulty of prospective memory target encoding (Experiments 3 and 4). An alternative model was also evaluated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
72.
The authors present a theory for understanding risk for problem drinking among reservation-dwelling American Indians. The theory offers an overall framework for understanding the risk process for this group. It considers the distinction between factors that influence mean levels of American Indian problem drinking and factors that influence individual differences in American Indian drinking. It proposes important contextual differences between reservation-dwelling American Indians and Caucasians that may help explain the higher mean levels of American Indian problem drinking. The theory further holds that, within the high mean level of problem drinking characteristic of many American Indian reservations, individual differences in problem drinking can be explained by very similar personality and learning factors as those that influence problem-drinking levels for other ethnic groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
73.
GD Ruth S Smith M Bronson AT Davis RM Wilcox 《Canadian Metallurgical Quarterly》2003,24(5):318-21; discussion 317
Nationally, approximately 10% of child abuse cases involve burning, and up to 20% of pediatric burn admissions involve abuse or neglect. Historically, these cases have been more difficult to prosecute than nonburn cases for multiple reasons. Between 1995 and 1999, there were 285 pediatric (under 18) patients admitted to the Spectrum Health Regional Burn Center. Of these cases, 18 of the alleged perpetrators were legally investigated for suspicion of child abuse, and 7 received punitive sentences. We found that men tended to be prosecuted and convicted more often than women and that cases involving multiple instances of injury tended to be prosecuted more frequently. Similarly, we found that cases involving more severe injuries tended to be prosecuted more successfully. There are many psychological and social factors involved in handling burn abuse cases. However, by successful prosecution of these crimes, victims tend to fare better both socially and psychologically. 相似文献
74.
The rationale for utilizing filial therapy as a treatment intervention with child witnesses of domestic violence while residing with their mothers in a shelter facility is explored and the effectiveness of an intensive 12-session filial therapy parent training group, conducted within 2-3 weeks, is described (n=11; aged 4-10 yrs). Results of analysis of covariance revealed that child witnesses in the experimental group significantly reduced behavior problems prevalent in child witnesses and significantly increased their self-concept as compared to child witnesses in the non-treatment comparison group. In addition, t-test results showed that mothers who facilitated treatment of the experimental group scored significantly higher after training on both their attitudes of acceptance and their empathic behavior. Comparative analysis revealed that intensive filial therapy as facilitated by the children's mothers was as effective in reducing behavior problems as was intensive individual play therapy and intensive sibling group play therapy as facilitated by professionally trained therapists. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
75.
Flash-lamp annealing (FLA) on a millisecond time scale has been shown to be a promising tool in the preparation of high-quality semiconducting materials. The process imposes time varying through-thickness temperature profiles on the substrates being processed, and consequently thermal stresses. A combined thermal and optical model has been developed to predict the substrate temperature distribution and this model has been linked to a structural model to compute stresses and deflections. The paper shows how these models can be used to explore process conditions in flash lamp annealing, with particular regard to the annealing of ion implants in silicon and the crystallization of amorphous silicon layers on glass substrates. 相似文献
76.
77.
OomiG KagayamaT SmithJL LacerdaAH KajiS OhashiM 《中国稀土学报(英文版)》2004,22(1):7-12
Electrical resistance, thermal expansion, lattice constants of the intermediate valence materials, α-Ce and CeBe13, were measured at high pressure. It is found that the Grttneisen parameters of Kondo temperature TK are 13 and 42 for α-Ce and CeBe13, respectively, and it decreases with increasing pressure. The magnetoresistance of α-Ce shows H^2 dependence and its coefficient increases with pressure below 1 GPa, but becomes nearly constant above 1 GPa. The results indicate that the intermediate valence states are enhanced at high pressure indicating the enhancement of hybridization between the 4f electron and conduction band. 相似文献
78.
Ronald Smith 《Canadian Metallurgical Quarterly》2004,130(2):165-169
For longitudinally uniform stretches of waterways there is a mixing center for the across-channel location of a steady point source in steady flow, such that complete mixing is achieved as soon as possible and there is no concentration overshoot at either of the two shorelines. A mathematical definition of the mixing center is the zero of the first oscillatory cross-channel diffusion mode. With the shorelines plus four interior data points across the channel, the starting estimate for the mixing center suffices to keep peak shoreline concentrations to within 6% of optimal. For comparison, a source at mid flow gives 18% shoreline concentration overshoot in the test case. Should very high precision be required, the Appendix gives an iterative construction that converges to the first oscillatory diffusion mode. 相似文献
79.
Andre C.L. Carlin J.A. Boeckl J.J. Wilt D.M. Smith M.A. Pitera A.J. Lee M.L. Fitzgerald E.A. Ringel S.A. 《Electron Devices, IEEE Transactions on》2005,52(6):1055-1060
High-performance p/sup +//n GaAs solar cells were grown and processed on compositionally graded Ge-Si/sub 1-x/Ge/sub x/-Si (SiGe) substrates. Total area efficiencies of 18.1% under the AM1.5-G spectrum were measured for 0.0444 cm/sup 2/ solar cells. This high efficiency is attributed to the very high open-circuit voltages (980 mV (AM0) and 973 mV (AM1.5-G)) that were achieved by the reduction in threading dislocation density enabled by the SiGe buffers, and thus reduced carrier recombination losses. This is the highest independently confirmed efficiency and open-circuit voltage for a GaAs solar cell grown on a Si-based substrate to date. Larger area solar cells were also studied in order to examine the impact of device area on GaAs-on-SiGe solar cell performance; we found that an increase in device area from 0.36 to 4.0 cm/sup 2/ did not degrade the measured performance characteristics for cells processed on identical substrates. Moreover, the device performance uniformity for large area heteroepitaxial cells is consistent with that of homoepitaxial cells; thus, device growth and processing on SiGe substrates did not introduce added performance variations. These results demonstrate that using SiGe interlayers to produce "virtual" Ge substrates may provide a robust method for scaleable integration of high performance III-V photovoltaics devices with large area Si wafers. 相似文献
80.