全文获取类型
收费全文 | 37971篇 |
免费 | 2817篇 |
国内免费 | 1072篇 |
专业分类
电工技术 | 1495篇 |
技术理论 | 1篇 |
综合类 | 1360篇 |
化学工业 | 6706篇 |
金属工艺 | 1621篇 |
机械仪表 | 1760篇 |
建筑科学 | 2651篇 |
矿业工程 | 736篇 |
能源动力 | 1035篇 |
轻工业 | 2755篇 |
水利工程 | 614篇 |
石油天然气 | 1349篇 |
武器工业 | 217篇 |
无线电 | 3359篇 |
一般工业技术 | 5254篇 |
冶金工业 | 5233篇 |
原子能技术 | 508篇 |
自动化技术 | 5206篇 |
出版年
2023年 | 478篇 |
2022年 | 881篇 |
2021年 | 1188篇 |
2020年 | 968篇 |
2019年 | 895篇 |
2018年 | 965篇 |
2017年 | 1057篇 |
2016年 | 1035篇 |
2015年 | 1313篇 |
2014年 | 1694篇 |
2013年 | 2564篇 |
2012年 | 2208篇 |
2011年 | 2280篇 |
2010年 | 1960篇 |
2009年 | 1813篇 |
2008年 | 1934篇 |
2007年 | 1926篇 |
2006年 | 1699篇 |
2005年 | 1524篇 |
2004年 | 1091篇 |
2003年 | 1035篇 |
2002年 | 978篇 |
2001年 | 733篇 |
2000年 | 638篇 |
1999年 | 611篇 |
1998年 | 554篇 |
1997年 | 496篇 |
1996年 | 499篇 |
1995年 | 488篇 |
1994年 | 398篇 |
1993年 | 392篇 |
1992年 | 363篇 |
1991年 | 225篇 |
1990年 | 290篇 |
1989年 | 320篇 |
1988年 | 245篇 |
1987年 | 239篇 |
1986年 | 245篇 |
1985年 | 283篇 |
1984年 | 274篇 |
1983年 | 239篇 |
1982年 | 230篇 |
1981年 | 229篇 |
1980年 | 182篇 |
1979年 | 197篇 |
1978年 | 183篇 |
1977年 | 187篇 |
1976年 | 170篇 |
1975年 | 188篇 |
1974年 | 175篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
Evolution of the capillary network in a reactive powder concrete during hydration process 总被引:7,自引:0,他引:7
V. Morin F. Cohen-Tenoudji A. Feylessoufi P. Richard 《Cement and Concrete Research》2002,32(12):1907-1914
Ultrasonic waves in echographic mode, combined with autogenous shrinkage measurements, were used to study the evolution of the capillary network of reactive powder concrete (RPC) from the time after the mixing. Two characteristic porous classes have been identified: the first, between 10 and 20 nm, begins when the material reaches its solid hyperstatic state, and the second about 1 or 2 nm. The first class is associated with the porous space between the C-S-H hydrate clusters and the second with the internal porosity of the hydrate. The evolution of the active capillary radius as a function of the degree of hydration allows us to understand the strong interaction between the capillary network size and the chemical activity given by the dissipated calorimetric power curve. Indeed, the maximum point of the chemical activity marks the transition of the first class of pores to the second one. Finally, measurements of electrical conductivity through RPC samples show that after the maximum of the dissipated power, the curve of this electrical conductivity presents the same evolution as the capillary radius. As the electrical conductivity clearly depends on the evolution of the capillary network, the similarity between the results confirms our analysis in pore classes. 相似文献
172.
J Richard 《Canadian Metallurgical Quarterly》1997,117(9):647-650
A 47-year-old man with Hirayama's disease who developed cervical spondylotic amyotrophy (CSA) is presented. The patient had noted weakness and atrophy of hand and forearm muscles bilaterally at the age of 16. At the age of 40, he developed proximal muscle atrophy and weakness bilaterally after 20 years of a non-progressive state. Myelography and computed tomography (CT)-myelography revealed that ventral cord compression at multiple levels of C4-7 vertebral bodies was increased when the neck was extended. The clinical diagnosis was CSA associated with Hirayama's disease. To our knowledge, this is the first such case to be reported. 相似文献
173.
Diedrichsen J?rn; Ivry Richard B.; Hazeltine Eliot; Kennerley Steven; Cohen Asher 《Canadian Metallurgical Quarterly》2003,29(1):64
Four experiments were conducted to identify the locus of interference observed during the preparation of bimanual reaching movements. Target locations were specified by color, and the right-hand and left-hand targets could be either the same or a different color. Movements of different amplitudes (Experiment 1) or different directions (Experiment 2) to targets of the same color were initiated more quickly than symmetric movements to targets of different colors. These results indicate that costs observed during bimanual movements arise during target selection rather than during motor programming. Experiments 3 and 4 further examined the interference associated with target selection. Reaction time costs were found with unimanual movements when the target was presented among distractors associated with responses for the other hand. Interference observed during bimanual reaching appears to reflect difficulty in segregating the response rules assigned to each hand. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
174.
175.
Under oxygen-rich conditions in H2 + NO + O2 mixtures, Pd/V2O5/Al2O3 catalysts are active and highly selective (~80%) for NOx reduction to N2. In situ DRIFT spectroscopy and reactor data show that the system operates via formation of NHx species on the highly dispersed V2O5 component. Both NH3 and NH4 + are formed, with the latter dominant. The role of the palladium component is also discussed. 相似文献
176.
177.
龙秀兰 《石油化工设备技术》2003,24(2):11-13
阐述了全渣油催化裂化装置反应器中旋流快分系统(VQS)的工作原理,对其受力情况进行了分析。较详细介绍了放流快分系统的支撑结构形式,并就支撑梁(焊接工字钢)的选材、几何尺寸进行了详细的分析与比较。 相似文献
178.
179.
Richard D. Prosser 《Energy Economics》1985,7(1):9-12
Four models with different lag structures are used to express final energy demand in OECD from 1960–1982 as a function of real GDP and average energy price. The income and long-run price elasticities are not significantly dependent on the model specification, but the Koyck lag scheme, estimated in its distributed lag form, is found to give the most satisfactory results. The statistical properties of the data together with evidence of trends in the elasticities both suggest that the period of falling real prices prior to 1971 is not comparable to the present period. For the period after 1971, an income elsticity of 1.02 and a long-run price elasticity of -0.37 are obtained. 相似文献
180.
The electromagnetic properties of electrically thick rectangular microstrip antennas were investigated experimentally. Antennas were fabricated with different patch sizes and with electrical thicknesses ranging from 0.03 to 0.23 wavelengths in the dielectric substrate. The resonant frequencies were measured and compared to existing formulas. The bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured. 相似文献