全文获取类型
收费全文 | 211643篇 |
免费 | 15871篇 |
国内免费 | 7774篇 |
专业分类
电工技术 | 11229篇 |
技术理论 | 14篇 |
综合类 | 11213篇 |
化学工业 | 35706篇 |
金属工艺 | 10524篇 |
机械仪表 | 11997篇 |
建筑科学 | 16415篇 |
矿业工程 | 4942篇 |
能源动力 | 5849篇 |
轻工业 | 12685篇 |
水利工程 | 3212篇 |
石油天然气 | 11073篇 |
武器工业 | 1345篇 |
无线电 | 25483篇 |
一般工业技术 | 26701篇 |
冶金工业 | 17330篇 |
原子能技术 | 2114篇 |
自动化技术 | 27456篇 |
出版年
2024年 | 881篇 |
2023年 | 3261篇 |
2022年 | 5826篇 |
2021年 | 7877篇 |
2020年 | 5795篇 |
2019年 | 5009篇 |
2018年 | 5414篇 |
2017年 | 6199篇 |
2016年 | 5692篇 |
2015年 | 7291篇 |
2014年 | 9520篇 |
2013年 | 12269篇 |
2012年 | 12227篇 |
2011年 | 13873篇 |
2010年 | 11611篇 |
2009年 | 11460篇 |
2008年 | 10872篇 |
2007年 | 10469篇 |
2006年 | 10858篇 |
2005年 | 9631篇 |
2004年 | 6563篇 |
2003年 | 5784篇 |
2002年 | 5251篇 |
2001年 | 4726篇 |
2000年 | 4871篇 |
1999年 | 5795篇 |
1998年 | 7188篇 |
1997年 | 5470篇 |
1996年 | 4701篇 |
1995年 | 3693篇 |
1994年 | 3109篇 |
1993年 | 2569篇 |
1992年 | 1749篇 |
1991年 | 1377篇 |
1990年 | 1120篇 |
1989年 | 966篇 |
1988年 | 780篇 |
1987年 | 579篇 |
1986年 | 470篇 |
1985年 | 393篇 |
1984年 | 212篇 |
1983年 | 210篇 |
1982年 | 195篇 |
1981年 | 191篇 |
1980年 | 188篇 |
1979年 | 97篇 |
1978年 | 89篇 |
1977年 | 243篇 |
1976年 | 427篇 |
1975年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
Discretization of boundary integral equations leads, in general, to fully populated non-symmetric linear systems of equations. An inherent drawback of boundary element method (BEM) is that, the non-symmetric dense linear systems must be solved. For large-scale problems, the direct methods require expensive computational cost and therefore the iterative methods are perhaps more preferable. This paper studies the comparative performances of preconditioned Krylov subspace solvers as bi-conjugate gradient (Bi-CG), generalized minimal residual (GMRES), conjugate gradient squared (CGS), quasi-minimal residual (QMR) and bi-conjugate gradient stabilized (Bi-CGStab) for the solution of dense non-symmetric systems. Several general preconditioners are also considered and assessed. The results of numerical experiments suggest that the preconditioned Krylov subspace methods are effective approaches solving the large-scale dense non-symmetric linear systems arising from BEM. 相似文献
994.
995.
陈伯夫 《石油化工设备技术》2003,24(3):10-13
熔体过滤器为聚酯装置关键设备,其国产化问题一直未能解决。该文通过对天津分公司200kt/a聚酯装置熔体过滤器改造方案的介绍,探讨了其国产化条件,分析了国产熔体过滤器的结构特点,并与进口过滤器进行了对比,提出了一些看法。 相似文献
996.
针对当前矿井提升机低速运行稳定性差、控制准确性低的主要问题,提出了应用交流电机直接转矩控制技术,采用优化U-N磁链模型和优化PI控制算法,并提出了相应的办法进行优化设计,经实际运行表明:提高了提升机的低速运行平稳性和控制精度。 相似文献
997.
Tingfang Hu Jinpeng Chen Haiyan Wang Jun Min Wei 《Petroleum Science and Technology》2006,24(12):1477-1484
Etherification reaction of FCC light gasoline over Hβ zeolite was investigated to decrease the light olefins in motor gasoline while enhancing octane. Etherification activity of several molecular sieve catalysts for FCC light gasoline was studied in a fixed-bed reactor. The influence of pore-enlarging agent (PEG) with different molecular weight, binder (γ-Al2O3), and peptizing agent (HNO3) in the shaping process on etherification activity of Hβ zeolite was studied. The impregnating ways of precursor of oxides and the order of extruding and impregnating were also investigated. The results show that the activity of extruded Hβ zeolite before impregnating precursor of oxides is higher than the reverse order. The best shaping condition obtained was PEG-4000 10%, γ-Al2O3 20%, and HNO3 10%. At the optimal reaction condition, the conversion of tert-olefins reached the peak. 62.93%, the yield of TAME, is also high and the technology can be applied to industry as well. 相似文献
998.
Shui-Jinn Wang Shiue-Lung Chen Kai-Ming Uang Wei-Chi Lee Tron-Min Chen Chao-Hsuing Chen Bor-wen Liou 《Photonics Technology Letters, IEEE》2006,18(10):1146-1148
In this study, the performance of vertical-structured high-power GaN-based light-emitting diodes (VM-LEDs) with a transparent and low-resistant indium-zinc oxide (IZO) film as a current spreading layer (CSL) was investigated. Nickel electroplating and patterned laser liftoff techniques were employed for the transfer of sapphire substrate to nickel substrate. The novel IZO CSL atop n-side-up VM-LEDs offering benefits of superior current spreading ability, larger extraction efficiency, and lower forward voltage drop was demonstrated. As compared to the regular LED without IZO CSL, the use of an IZO CSL with an optimum thickness of around 300 nm leads to an increase in light output power by 97.1 (67.8)% and a decrease in forward voltage drop by 4.9 (15.5)% under an injection current of 350 (800) mA. 相似文献
999.
Wei Fen Zhang Xi Guang Chen Pi Wu Li Cheng Sheng Liu Qiang Zhi He 《Drying Technology》2008,26(1):108-115
Three kinds of carboxymethyl chitosan/β-cyclodextrin microspheres loaded with theophylline were prepared by spray drying intended for pulmonary delivery. Mucociliotoxicity, permeation rate, and drug release characteristics of the product were investigated. The microspheres obtained by spray drying were found to be spherical with smooth or wrinkled surfaces. The mean particle size was between 3.39 and 6.06 µm. The microspheres demonstrated high product yield (43.7-50.2%), high drug loading (13.7-38.1%), and high encapsulation efficiency (86.9-92.8%). FT-IR indicated that there were interactions of theophylline with carboxymethyl chitosan matrix. Further studies on mucociliotoxicity and permeation confirmed that microspheres had better adaptability and high permeation rate. In vitro drug release from the microspheres was not related to the drug/polymer ratios. 相似文献
1000.
You-Im Chang Yu-Sheng Chen Wei-You Cheng 《Journal of the Chinese Institute of Chemical Engineers》2008,39(1):85-100
The deposition morphology of Brownian/non-Brownian particles within a constricted tube is investigated by applying the Brownian dynamics simulation method in the present paper. Two different geometric structures, the parabolic constricted tube (PCT) and the sinusoidal constricted tube (SCT), are adopted. The effect of various types of the total interaction energy curves of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and of the shadow area cast by those deposited particles, on the particles’ collection efficiencies are also examined. For the PCT structure, under the same interaction energy curve, it is found that the non-Brownian particles always own a higher collection efficiency than that of the Brownian particles. Since the deposition location moves closer to the constriction part of the tube, the collection efficiencies of the Brownian/non-Brownian particles increase with the decrease of flow velocity. The SCT behaves differently, it is found that the collection efficiencies of non-Brownian particles are only slightly higher than those of Brownian particles when SCT is adopted. The steep slope of the tube wall near the constriction part of SCT dominates the whole deposition process of Brownian/non-Brownian particles. In comparison with the available experimental data, it is found that the present method can give a good simulation result. 相似文献