全文获取类型
收费全文 | 82563篇 |
免费 | 10816篇 |
国内免费 | 6124篇 |
专业分类
电工技术 | 14125篇 |
技术理论 | 1篇 |
综合类 | 8778篇 |
化学工业 | 9047篇 |
金属工艺 | 2403篇 |
机械仪表 | 4092篇 |
建筑科学 | 6310篇 |
矿业工程 | 2418篇 |
能源动力 | 3006篇 |
轻工业 | 3531篇 |
水利工程 | 2501篇 |
石油天然气 | 4374篇 |
武器工业 | 1092篇 |
无线电 | 9185篇 |
一般工业技术 | 7473篇 |
冶金工业 | 3387篇 |
原子能技术 | 1476篇 |
自动化技术 | 16304篇 |
出版年
2024年 | 435篇 |
2023年 | 1193篇 |
2022年 | 2280篇 |
2021年 | 2711篇 |
2020年 | 3209篇 |
2019年 | 2897篇 |
2018年 | 2641篇 |
2017年 | 3336篇 |
2016年 | 3536篇 |
2015年 | 3728篇 |
2014年 | 5241篇 |
2013年 | 5860篇 |
2012年 | 5965篇 |
2011年 | 6230篇 |
2010年 | 4554篇 |
2009年 | 4838篇 |
2008年 | 4638篇 |
2007年 | 5355篇 |
2006年 | 4961篇 |
2005年 | 4034篇 |
2004年 | 3460篇 |
2003年 | 3102篇 |
2002年 | 2626篇 |
2001年 | 2185篇 |
2000年 | 1902篇 |
1999年 | 1522篇 |
1998年 | 1231篇 |
1997年 | 1011篇 |
1996年 | 814篇 |
1995年 | 710篇 |
1994年 | 662篇 |
1993年 | 485篇 |
1992年 | 365篇 |
1991年 | 331篇 |
1990年 | 259篇 |
1989年 | 225篇 |
1988年 | 162篇 |
1987年 | 136篇 |
1986年 | 97篇 |
1985年 | 101篇 |
1984年 | 73篇 |
1983年 | 53篇 |
1982年 | 60篇 |
1981年 | 36篇 |
1980年 | 39篇 |
1979年 | 29篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1959年 | 17篇 |
1956年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased. 相似文献
53.
单元系T—p相图的数学结构 总被引:1,自引:0,他引:1
作者以化学元素的稳定单质为基准,推演出了任意物质M_i(相态Ω)的热力学生成活度{相态Ω)的函数形式:?D_Ω数值的大小体现着相态Ω的热力学相对稳定性.根据集合论原理沿D(稳定性)座标取极大值的方法把物理性质互不连续的各个异相态连结在一起,建立了单元系在T-p面上的优势分布方程(PSDE):■作者以H_2O为实例,计算了T-p相图,与实验相图基本一致. 相似文献
54.
55.
56.
Zhen Wang 《Applied Composite Materials》1995,2(4):257-264
A bimodal Weibull distribution function was applied to analyse the strength distribution of glass fibre bundles under tensile impact. The simulation was performed using a one-dimensional damage constitutive model. The results show that there were two concurrent flaw populations in the fracture process. The regression analysis using the bimodal Weibull distribution function was in good agreement with experiment. 相似文献
57.
Learning a sequence of target locations when the sequence is uncorrelated with a sequence of responses and target location is not the response dimension (pure perceptual-based sequence learning) was examined. Using probabilistic sequences of target locations, the author shows that such learning can be implicit, is unaffected by distance between target locations, and is mostly limited to first-order transition probabilities. Moreover, the mechanism underlying learning affords processing of information at anticipated target locations and appears to be attention based. Implications for hypotheses of implicit sequence learning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
58.
A semi-Markov model is constructed that describes an arbitrarily structured multicomponent technological system and takes
into account its calendar maintenance. Using an aggregation algorithm, approximate values of stationary reliability characteristics
and an optimal term of maintenance work are determined for the system.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 69–86, March–April 2006. 相似文献
59.
We study epidemic schemes in the context of collaborative data delivery. In this context, multiple chunks of data reside at different nodes, and the challenge is to simultaneously deliver all chunks to all nodes. 相似文献
60.
Klaus G. Johannsen 《International Journal of Satellite Communications and Networking》1987,5(3):233-247
Several domestic satellite systems have been more than 10 years in operation. During this time, the world has experienced a dramatic growth in communication. While the demand for more telephony and data circuits and television channels is still on the rise, new methods of signal transmission and circuit compression have been developed which may balance or reduce the need for more satellite trunk capacity. And while whole national networks are converting to digital transmission, new transmission media like optical fibre, are finding application, and may take over some of the heavy traffic routes previously carried by satellite. On the other side, business data communication between roof-top terminals, thin route traffic to remote users, television distribution by direct satellite broadcasting are becoming more popular and satellite land mobile communication may soon be a reality. Thus the domestic satellite's role appears to be slowly changing towards thin route and mobile traffic and DBS-type distribution and perhaps even radio position determination. System planners are adapting to the new trends in satellite communication and are trying to accommodate the various service payloads on a single satellite. This article discusses some aspects of the emerging multi-purpose domestic satellite, which carries fixed and mobile services, TV direct broadcasting and radio position determination, in view of network digitalization, network expansion, circuit compression, synchronization. The discussion centres on transponder supply and demand, satellite replenishment, Ku-band vs. C-band for TV direct satellite broadcasting, choice of modulation/multiple access for mobile communication, and expected accuracy in radio position determination. 相似文献