全文获取类型
收费全文 | 44258篇 |
免费 | 2475篇 |
国内免费 | 1086篇 |
学科分类
工业技术 | 47819篇 |
出版年
2024年 | 38篇 |
2023年 | 418篇 |
2022年 | 622篇 |
2021年 | 1138篇 |
2020年 | 905篇 |
2019年 | 793篇 |
2018年 | 888篇 |
2017年 | 923篇 |
2016年 | 852篇 |
2015年 | 1062篇 |
2014年 | 1612篇 |
2013年 | 2282篇 |
2012年 | 2742篇 |
2011年 | 5344篇 |
2010年 | 2948篇 |
2009年 | 2867篇 |
2008年 | 2587篇 |
2007年 | 2305篇 |
2006年 | 2001篇 |
2005年 | 1818篇 |
2004年 | 1622篇 |
2003年 | 1761篇 |
2002年 | 1666篇 |
2001年 | 1180篇 |
2000年 | 813篇 |
1999年 | 655篇 |
1998年 | 1033篇 |
1997年 | 690篇 |
1996年 | 558篇 |
1995年 | 475篇 |
1994年 | 392篇 |
1993年 | 334篇 |
1992年 | 248篇 |
1991年 | 226篇 |
1990年 | 234篇 |
1989年 | 204篇 |
1988年 | 177篇 |
1987年 | 153篇 |
1986年 | 136篇 |
1985年 | 130篇 |
1984年 | 130篇 |
1983年 | 85篇 |
1982年 | 75篇 |
1981年 | 65篇 |
1980年 | 81篇 |
1979年 | 49篇 |
1978年 | 60篇 |
1977年 | 58篇 |
1976年 | 76篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Pengfei Chen Honggang Chang Tao Peng Yongfan Tang Youquan Liu Chao Xiang 《应用聚合物科学杂志》2021,138(30):50314
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters. 相似文献
4.
针对在我国各大矿区广泛应用的EBZ160悬臂式掘进机,基于声发射原理及技术,设计一套掘进机故障诊断声发射检测系统,获得各种故障的声发射数据样本,同时借助小波神经网络的迭代收敛性质,对故障数据样本的精确度进行验证,正确率较高,能够较好地应用于井下掘进机的故障诊断. 相似文献
5.
Jincheng Yu Yabin Chang Ewa Jakubczyk Bing Wang Feridoon Azough Robert Dorey Robert Freer 《Journal of the European Ceramic Society》2021,41(9):4859-4869
Ca3Co4O9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca2.7Bi0.3Co4O9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm?1 K-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm?1 K-2 at 673 K through microstructure control. 相似文献
6.
Patil Rupesh C. Jagdale Ashutosh A. Patil Uttam P. Ghodake Jeevan S. Mali Sawanta S. Hong Chang K. Patil Suresh S. 《Catalysis Letters》2021,151(12):3617-3631
Catalysis Letters - We converted agro-waste Custard Apple Peels (CAP) to ash via thermal treatment, on which Pd(OAc)2 was immobilized easily that produced a low-cost, highly efficient Pd/CAP-ash... 相似文献
8.
Wireless Personal Communications - The purpose of this study is to construct a structural equation model of shared bicycle added psychological factors proceeding from the theory of planned... 相似文献
9.
10.
Jiangpeng Lin Tsangyao Chang 《Energy Sources, Part B: Economics, Planning, and Policy》2018,13(5):269-280
This study revisits whether CO2 emissions converge in G18 countries over the period of 1950–2013. To work on this empirical analysis, we employ a more powerful quantile unit root test with per capita CO2 emissions. While conventional unit root tests fail to reject convergence in CO2 emissions in these G18 countries, quantile unit root test results demonstrate CO2 emissions converged in 5 of these G18 countries (i.e., Australia, Brazil, Canada, Germany, and India). Our empirical results have important policy implications for the governments of G18 countries to direct efficient and effective energy policies to reduce the CO2 emissions. 相似文献