全文获取类型
收费全文 | 600677篇 |
免费 | 53839篇 |
国内免费 | 36388篇 |
专业分类
电工技术 | 68388篇 |
技术理论 | 30篇 |
综合类 | 53868篇 |
化学工业 | 81884篇 |
金属工艺 | 29310篇 |
机械仪表 | 42339篇 |
建筑科学 | 43110篇 |
矿业工程 | 19165篇 |
能源动力 | 20336篇 |
轻工业 | 28969篇 |
水利工程 | 13669篇 |
石油天然气 | 21058篇 |
武器工业 | 7328篇 |
无线电 | 59576篇 |
一般工业技术 | 49979篇 |
冶金工业 | 23000篇 |
原子能技术 | 6042篇 |
自动化技术 | 122853篇 |
出版年
2024年 | 2168篇 |
2023年 | 7632篇 |
2022年 | 14994篇 |
2021年 | 17649篇 |
2020年 | 16153篇 |
2019年 | 13732篇 |
2018年 | 12792篇 |
2017年 | 17301篇 |
2016年 | 20097篇 |
2015年 | 22090篇 |
2014年 | 35958篇 |
2013年 | 34529篇 |
2012年 | 40763篇 |
2011年 | 44998篇 |
2010年 | 35002篇 |
2009年 | 36945篇 |
2008年 | 35781篇 |
2007年 | 43853篇 |
2006年 | 40461篇 |
2005年 | 34489篇 |
2004年 | 28260篇 |
2003年 | 25686篇 |
2002年 | 20287篇 |
2001年 | 16463篇 |
2000年 | 14214篇 |
1999年 | 11172篇 |
1998年 | 8388篇 |
1997年 | 7060篇 |
1996年 | 6141篇 |
1995年 | 5263篇 |
1994年 | 4558篇 |
1993年 | 3357篇 |
1992年 | 2732篇 |
1991年 | 2005篇 |
1990年 | 1572篇 |
1989年 | 1336篇 |
1988年 | 921篇 |
1987年 | 605篇 |
1986年 | 483篇 |
1985年 | 428篇 |
1984年 | 430篇 |
1983年 | 320篇 |
1982年 | 308篇 |
1981年 | 260篇 |
1980年 | 206篇 |
1979年 | 159篇 |
1978年 | 112篇 |
1977年 | 112篇 |
1976年 | 70篇 |
1962年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The reaction of lignite in a slagging gasifier produces reactants which in turn form 5,5-dimethylhydantoin (DMH) as a major constituent in the condensate water. Variations in plant operating conditions made it impossible to accurately study the kinetics of formation of DMH in the actual gasifier water, and thus a model system was chosen. The reaction of acetone cyanohydrin in the presence of excess ammonium carbonate at concentrations approaching those obtained in the condensate water were studied at 50,70, and 90 °C. Secondorder kinetics were obeyed, and the pseudo second-order rate constants at the respective temperatures were 1.86, 3.6, and 4.62 dm3 mol? 1 h? 1. Independent variation of the concentration of either acetone, cyanide, ammonia or carbonate gave results consistent with the interpretation that the formation of DMH is first order in all reactants: rate of formation of DMH = k[acetone][HCN][NH3][CO2]. The pseudo second-order rate constant is a complex rate constant including several rapid equilibria. A mechanism consistent with the kinetic data is presented. 相似文献
992.
B. Bereqvist 《Strain》1987,23(1):7-13
The design and performance of precision bending equipment for testing straight beams with constant rectangular section under a pure bending moment is described. Part 1 deals with the loading arrangements and Part 2 with the rig for measuring beam deflection. The methods for recording deflection of strain gauges applied on the beam have been described elsewhere.1–4
The reactions to the deadweight gravity loads are taken via ball bearings. The total bending moment inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2Ga confidence interval about the mean (2Gcim ), is about ± 25 x. 10-4% , for 23 tests with a steel beam with 15 mm × 75 mm cross sectional dimensions, loaded to 1-1.5 mm/m strain.
The measuring rig stands on the beam via hardened and polished spherical segment feet and uses a capacitive transducer system with less than 5nm resolution. Various application tasks are described. The total inaccuracy of the measured deflection, i.e. apart from bending moment inaccuracy, is about ± 35 times 104% for about 10 reproduced, not repeated, tests with the same steel beam. The deflection for such a beam is of the order of 2 to 4 mm. 相似文献
The reactions to the deadweight gravity loads are taken via ball bearings. The total bending moment inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2Ga confidence interval about the mean (2G
The measuring rig stands on the beam via hardened and polished spherical segment feet and uses a capacitive transducer system with less than 5nm resolution. Various application tasks are described. The total inaccuracy of the measured deflection, i.e. apart from bending moment inaccuracy, is about ± 35 times 10
993.
994.
Colour Centres and Energy Transfer in BaF2-xClx:Eu2+ Phosphors 总被引:1,自引:1,他引:0
The optical absorption spectra of BaF2-xClx:Eu2 after ultraviolet (UV) light excitation were investigated.The differences between the absorption spectra after and before excitation (DAS) were observed.The DAS increase at both the high and the low energy side of F band in BaF2-xClx:Eu2 after 245 nm UV light excitation.The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres (association of F(Cl-) centres), whose absorption band matches the HeNe laser better, may explain the latter.In the write-in process, the transfer of electrons is via tunneling.In the readout process, the transfer of electrons captured in F(F-) and Fa centres is more likely via tunneling, and that of F(Cl-) centres is more likely via conduction band. 相似文献
995.
996.
本文介绍了一个用户接口管理系统NUUIMS的设计和实现.重点叙述了该系统基于规范化目标用户接口模型的设计思想,系统组成及描述方法.文章也讨论了使用NUUIMS设计而成的用户接口的特点. 相似文献
997.
Yan Jianhui Zhang Houan Tang Siwen Li Yimin 《中国稀土学报(英文版)》2006,24(5):548-548
The oxidation behavior of 0. 8% La2O3- Mo5Si3/MoSi2 composites at 1200℃ in air was investigated. The results reveal that the oxidation resistance of the material with 0. 8% La2O3 and Mo5Si3 is impaired. The oxidation resistance is decreased with increasing Mo5Si3 content. The mass loss follows a linear law in the initial oxidation. With oxidation time prolonging, a continuous and dense oxidation scale prevents oxygen from diffusing increasing when and leads to mass change a Mo5Si3 content is less than 30%. However, the composite shows "PEST" with the addition of 40% Mo5Si3. With increasing Mo5Si3 content, the oxidation resistance of 0.8% La2O3- Mo5Si3/MoSi2 decreases. This attributes to the poor oxidation resistance of M05Si3 and the relative density decreasing of 0. 8% La2O3-Mo5Si3/MoSi2 composite. 相似文献
998.
本文对吊车在吊装货物时如何消除货物的摆动进行了研究,提出了利用最优状态调节器进行消摆的方案,并进行了计算机仿真和在吊车模型上的实时控制实验,结果表明,该方法具有很好的消摆效果和较强的鲁棒性。 相似文献
999.
1000.
文章在通过对混凝土裂缝产生的原因进行分析的基础上,阐述了对在界河倒虹吸施工中预应力混凝土裂缝所采取的预控措施。 相似文献