全文获取类型
收费全文 | 300833篇 |
免费 | 5154篇 |
国内免费 | 1801篇 |
专业分类
电工技术 | 5297篇 |
技术理论 | 4篇 |
综合类 | 3442篇 |
化学工业 | 43760篇 |
金属工艺 | 13554篇 |
机械仪表 | 10214篇 |
建筑科学 | 8294篇 |
矿业工程 | 2376篇 |
能源动力 | 6792篇 |
轻工业 | 21723篇 |
水利工程 | 3803篇 |
石油天然气 | 5494篇 |
武器工业 | 135篇 |
无线电 | 34708篇 |
一般工业技术 | 58288篇 |
冶金工业 | 40824篇 |
原子能技术 | 5498篇 |
自动化技术 | 43582篇 |
出版年
2022年 | 1508篇 |
2021年 | 2430篇 |
2020年 | 1776篇 |
2019年 | 2137篇 |
2018年 | 17229篇 |
2017年 | 16266篇 |
2016年 | 13064篇 |
2015年 | 3097篇 |
2014年 | 4247篇 |
2013年 | 10387篇 |
2012年 | 9253篇 |
2011年 | 17442篇 |
2010年 | 14599篇 |
2009年 | 12759篇 |
2008年 | 14045篇 |
2007年 | 15018篇 |
2006年 | 6724篇 |
2005年 | 7290篇 |
2004年 | 6686篇 |
2003年 | 6616篇 |
2002年 | 5571篇 |
2001年 | 5186篇 |
2000年 | 5259篇 |
1999年 | 5356篇 |
1998年 | 11968篇 |
1997年 | 8630篇 |
1996年 | 6887篇 |
1995年 | 4996篇 |
1994年 | 4593篇 |
1993年 | 4307篇 |
1992年 | 3408篇 |
1991年 | 3239篇 |
1990年 | 2997篇 |
1989年 | 3048篇 |
1988年 | 2914篇 |
1987年 | 2448篇 |
1986年 | 2353篇 |
1985年 | 2751篇 |
1984年 | 2528篇 |
1983年 | 2370篇 |
1982年 | 2119篇 |
1981年 | 2226篇 |
1980年 | 2045篇 |
1979年 | 2138篇 |
1978年 | 2134篇 |
1977年 | 2386篇 |
1976年 | 3206篇 |
1975年 | 1839篇 |
1974年 | 1767篇 |
1973年 | 1783篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Machine Learning - We propose a data-driven approach to quantify the uncertainty of models constructed by kernel methods. Our approach minimizes the needed distributional assumptions, hence,... 相似文献
52.
Manjin Kim Qinfen Gu Tanveer Hussain Yahia Ali Trevor B. Abbott Kazuhiro Nogita 《International Journal of Hydrogen Energy》2021,46(53):27096-27106
With superior properties of Mg such as high hydrogen storage capacity (7.6 wt% H/MgH2), low price, and low density, Mg has been widely studied as a promising candidate for solid-state hydrogen storage systems. However, a harsh activation procedure, slow hydrogenation/dehydrogenation process, and a high temperature for dehydrogenation prevent the use of Mg-based metal hydrides for practical applications. For these reasons, Mg-based alloys for hydrogen storage systems are generally alloyed with other elements to improve hydrogen sorption properties. In this article, we have added Na to cast Mg–La alloys and achieved a significant improvement in hydrogen absorption kinetics during the first activation cycle. The role of Na in Mg–La has been discussed based on the findings from microstructural observations, crystallography, and first principles calculations based on density functional theory. From our results in this study, we have found that the Na doped surface of Mg–La alloy systems have a lower adsorption energy for H2 compared to Na-free surfaces which facilitates adsorption and dissociation of hydrogen molecules leading to improvement of absorption kinetic. The effect of Na on the microstructure of these alloys, such as eutectic refinement and a density of twins is not highly correlated with absorption kinetics. 相似文献
53.
Weiguo Cao Wenjuan Li Liang Zhang Jianfa Chen Shuo Yu Zhuanghong Zhou Yun Zhang Xiaobo Shen Yingxin Tan 《International Journal of Hydrogen Energy》2021,46(52):26693-26707
The explosion venting duct can effectively reduce the hazard degree of a gas explosion and conduct the venting energy to the safe area. To investigate the flame quantitative propagation law of explosion venting with a duct, the effects of hydrogen fraction and explosion venting duct length on jet flame propagation characteristics of premixed H2-air mixtures were analyzed through experiment and simulation. The experiment results under initial conditions of room temperature and 1 atm show that when hydrogen fraction was high enough, part of the unburned hydrogen was mixed with air again to reach an ignitable concentration, resulting in the secondary combustion was easier produced and the duration of the secondary flame increased. With the increase of venting duct length, the flame front distance and propagation velocity increased. Meanwhile, the spatial distribution of pressure field and temperature field, and the propagation process and mechanism of the flame venting with a duct were analyzed using FLUENT software. The variation of the pressure wave and the pressure reflection oscillation law in the explosion venting duct was captured. Therefore, in the industrial explosion venting design with a duct, the hazard caused by the coupling of venting pressure and venting flame under different fractions should be considered comprehensively. 相似文献
54.
P. Carrasqueira H. Rocha J. M. Dias T. Ventura B. C. Ferreira M. C. Lopes 《International Transactions in Operational Research》2023,30(1):206-223
Radiation therapy is a technology-driven cancer treatment modality that has experienced significant advances over the last decades, due to multidisciplinary contributions that include engineering and computing. Recent technological developments allow the use of noncoplanar volumetric modulated arc therapy (VMAT), one of the most recent photon treatment techniques, in clinical practice. In this work, an automated noncoplanar arc trajectory optimization framework designed in two modular phases is presented. First, a noncoplanar beam angle optimization algorithm is used to obtain a set of noncoplanar irradiation directions. Then, anchored in these directions, an optimization strategy is proposed to compute an optimal arc trajectory. The computational experiments considered a pool of twelve difficult head-and-neck tumor cases. It was possible to observe that, for some of these cases, the optimized noncoplanar arc trajectories led to significant treatment planning quality improvements, when compared with coplanar VMAT treatment plans. Although these experiments were done in a research environment treatment planning software (matRad), the conclusions can be of interest for a clinical setting: automated procedures can simplify the current treatment workflow, produce high-quality treatment plans, making better use of human resources and allowing for unbiased comparisons between different treatment techniques. 相似文献
55.
El-Denglawey A. Issa Shams A. M. Saddeek Yasser B. Tekin H. O. Zakaly Hesham M. H. 《Journal of Inorganic and Organometallic Polymers and Materials》2021,31(10):3934-3942
Journal of Inorganic and Organometallic Polymers and Materials - This work aimed to investigate the impact of Lead-fluoride based glasses via theoretical and simulation techniques on mechanical and... 相似文献
56.
Kozhitov L. V. Kiselev B. G. Raykova T. B. Popkova A. V. Kostishin V. G. Muratov D. G. Yakushko E. V. Kosushkin V. G. Bebenin V. G. 《Russian Microelectronics》2019,48(8):599-612
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical... 相似文献
57.
58.
Mining high utility itemsets (HUIs) from transaction databases considers such factors as the unit profit and quantity of purchased items. Two-phase tree-based algorithms transform a database into compressed tree structures and generate candidate patterns through a recursive pattern-growth procedure. This procedure requires a lot of memory and time to construct conditional pattern trees. To address this issue, this study employs two compressed tree structures, namely, Utility Count Tree and String Utility Tree, to enumerate valid patterns and thus promote fast utility computation. Furthermore, the study presents an algorithm called single-phase utility computation (SPUC) that leverages these two tree structures to mine HUIs in a single phase by incorporating novel pruning strategies. Experiments conducted on both real and synthetic datasets demonstrate the superior performance of SPUC compared with IHUP, UP-Growth, and UP-Growth+ algorithms. 相似文献
59.
Chertkov Yu. B. Anikin M. N. Lebedev I. I. Naimushin A. G. Smol’nikov N. V. 《Atomic Energy》2021,131(1):42-45
Atomic Energy - The results of calculations and experimental determination of the neutronics characteristics of the IRT-T research reactor are presented. The IRT-T reactor is a pool reactor with... 相似文献
60.
Xiao-Ya Shangguan Bao-Lun Fang Chen-Xiao Xu Yuan Tan Yan-Gang Chen Zhi-Jun Xia Wei Chen 《Ceramics International》2021,47(5):6318-6328
A series of direct Z-scheme FeIn2S4/Bi2WO6 hierarchical heterostructures with intimate interface contacts were synthesized by in-situ growth route and characterized by systematical analyses. All as-prepared FeIn2S4/Bi2WO6 nanocomposites showed significantly enhanced photocatalytic activity towards photodegradation for the removal of tetracycline hydrochloride (TCH) in comparison with individual FeIn2S4 and Bi2WO6. Meanwhile, the highest photocatalytic degradation activity can be achieved by modulating adding amount of FeIn2S4 in FeIn2S4/Bi2WO6 nanocomposites and the optimized component ratio of FeIn2S4 to Bi2WO6 is determined to be 10 wt%. The enhanced photocatalytic activity could be ascribed to efficient separation between photogenerated holes and electrons based on the construction of direct Z-scheme system. The high photocatalytic stability of resultant 10 wt% FeIn2S4/Bi2WO6 nanocomposites was revealed through six successive recycling reactions. The main intermediate generated during TCH photodegradation was explored by HPLC-MS. Besides, the direct Z-scheme photocatalytic mechanism was confirmed by band position analysis, electron spin resonance (ESR) and active species capture experiment. 相似文献