全文获取类型
收费全文 | 233589篇 |
免费 | 26423篇 |
国内免费 | 14387篇 |
专业分类
电工技术 | 15990篇 |
技术理论 | 5篇 |
综合类 | 22932篇 |
化学工业 | 32208篇 |
金属工艺 | 14143篇 |
机械仪表 | 17859篇 |
建筑科学 | 18459篇 |
矿业工程 | 10998篇 |
能源动力 | 8921篇 |
轻工业 | 12690篇 |
水利工程 | 7223篇 |
石油天然气 | 12570篇 |
武器工业 | 4426篇 |
无线电 | 21594篇 |
一般工业技术 | 23817篇 |
冶金工业 | 9428篇 |
原子能技术 | 3309篇 |
自动化技术 | 37827篇 |
出版年
2024年 | 1049篇 |
2023年 | 3598篇 |
2022年 | 8416篇 |
2021年 | 9258篇 |
2020年 | 7664篇 |
2019年 | 6421篇 |
2018年 | 6394篇 |
2017年 | 8267篇 |
2016年 | 10200篇 |
2015年 | 11265篇 |
2014年 | 15467篇 |
2013年 | 15005篇 |
2012年 | 16201篇 |
2011年 | 16831篇 |
2010年 | 13016篇 |
2009年 | 13171篇 |
2008年 | 12484篇 |
2007年 | 15818篇 |
2006年 | 14539篇 |
2005年 | 12361篇 |
2004年 | 9884篇 |
2003年 | 8564篇 |
2002年 | 6976篇 |
2001年 | 5668篇 |
2000年 | 4898篇 |
1999年 | 3740篇 |
1998年 | 2893篇 |
1997年 | 2502篇 |
1996年 | 2156篇 |
1995年 | 1786篇 |
1994年 | 1555篇 |
1993年 | 1100篇 |
1992年 | 906篇 |
1991年 | 753篇 |
1990年 | 629篇 |
1989年 | 558篇 |
1988年 | 375篇 |
1987年 | 275篇 |
1986年 | 224篇 |
1985年 | 194篇 |
1984年 | 218篇 |
1983年 | 152篇 |
1982年 | 140篇 |
1981年 | 100篇 |
1980年 | 105篇 |
1979年 | 79篇 |
1966年 | 34篇 |
1964年 | 44篇 |
1962年 | 67篇 |
1959年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
以重庆市甄子岩29号危岩体为研究对象,基于现场调查和分析解剖,建立UDEC离散元数值计算模型,对其演化变形过程进行模拟分析。研究表明,在巨大的自重作用下,由于基座岩体岩质软,岩体较破碎,且基座外侧为直立的陡崖,具有完整的临空面,从而使基座岩体易发生压缩流变及剪切流变,进而使危岩体存在滑移垮塌的危险。 相似文献
2.
本文以云杉八齿小蠹Ips typographus Linnaeus为例,经标本选取,观察虫体整体形态,绘制整体结构草图,电子显微镜观察局部、得到局部数字图像,分别建立虫体每一部分的高精度细节。把模型每部分拼装在一起组成整体模型,构建出了云杉八齿小蠹三维虚拟昆虫数字化模型。 相似文献
3.
AbstractIndustry 4.0 aims at providing a digital representation of a production landscape, but the challenges in building, maintaining, optimizing, and evolving digital models in inter-organizational production chains have not been identified yet in a systematic manner. In this paper, various Industry 4.0 research and technical challenges are addressed, and their present scenario is discussed. Moreover, in this article, the novel concept of developing experience-based virtual models of engineering entities, process, and the factory is presented. These models of production units, processes, and procedures are accomplished by virtual engineering object (VEO), virtual engineering process (VEP), and virtual engineering factory (VEF), using the knowledge representation technique of Decisional DNA. This blend of the virtual and physical domains permits monitoring of systems and analysis of data to foresee problems before they occur, develop new opportunities, prevent downtime, and even plan for the future by using simulations. Furthermore, the proposed virtual model concept not only has the capability of Query Processing and Data Integration for Industrial Data but also real-time visualization of data stream processing. 相似文献
4.
大型综合室内亲子乐园属于高大空间,设有游乐设施和游戏的特殊性使得对空间的舒适性要求一致,但是送风气流遇阻严重,室内存在较多气流死角,影响室内空气质量和儿童健康。因此其空调设计不仅需要考虑温度、风速的空间均匀度,还要考虑各点的空气龄和PMV-PPD指标。以天津某亲子乐园为研究对象,利用scSTREAM软件对适用于该房间的辐射供冷加新风、置换通风、混合通风三种空调方式的送风效果进行数值模拟分析,从流场的均匀性、人员的热舒适性等方面对模拟结果进行探讨,研究结果表明辐射供冷加新风方式的空间均匀性和PMV指标最佳,混合通风方式的空气龄最小。 相似文献
5.
6.
Effects of different carbon sources and C/N values on nonvolatile taste components of Pleurotus eryngii 下载免费PDF全文
Wen Li Xiaobei Li Yan Yang Feng Zhou Yanfang Liu Shuai Zhou Hailong Yu 《International Journal of Food Science & Technology》2015,50(11):2360-2366
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels. 相似文献
7.
N-K2Ti4O9/MIL-101 composites were successfully synthesized by a facile hydrothermal method, and were characterized by powder X-ray diffraction, UV–vis diffuse reflectance spectroscopy, the valence band X-ray photoelectron spectroscopy, field emission transmission electron microscopy, photoluminescence emission spectra, N2 adsorption–desorption and thermogravimetric analysis. Photocatalytic activities of N-K2Ti4O9, MIL-101 and the composites were investigated by the degradation of Rhodamine B (RhB) under visible light irradiation. The results show that the composites exhibit higher photocatalytic activity as compared with the pure materials. The synergistically enhanced photocatalytic activity of the composites is due to big adsorption capacity of MIL-101 and high separation efficiency of photogenerated electron-hole pairs through interfaces between N-K2Ti4O9 and MIL-101. 相似文献
8.
Akira Yamamoto Kentaro Teramura Saburo Hosokawa Tsunehiro Tanaka 《Science and Technology of Advanced Materials》2015,16(2)
The effect of SO2 gas was investigated on the activity of the photo-assisted selective catalytic reduction of nitrogen monoxide (NO) with ammonia (NH3) over a TiO2 photocatalyst in the presence of excess oxygen (photo-SCR). The introduction of SO2 (300 ppm) greatly decreased the activity of the photo-SCR at 373 K. The increment of the reaction temperature enhanced the resistance to SO2 gas, and at 553 K the conversion of NO was stable for at least 300 min of the reaction. X-ray diffraction, FTIR spectroscopy, thermogravimetry and differential thermal analysis, x-ray photoelectron spectroscopy (XPS), elemental analysis and N2 adsorption measurement revealed that the ammonium sulfate species were generated after the reaction. There was a strong negative correlation between the deposition amount of the ammonium sulfate species and the specific surface area. Based on the above relationship, we concluded that the deposition of the ammonium sulfate species decreased the specific surface area by plugging the pore structure of the catalyst, and the decrease of the specific surface area resulted in the deactivation of the catalyst. 相似文献
9.
10.
The Interplay of Modulus,Strength, and Ductility in Adhesive Design Using Biomimetic Polymer Chemistry 下载免费PDF全文
High‐performance adhesives require mechanical properties tuned to demands of the surroundings. A mismatch in stiffness between substrate and adhesive leads to stress concentrations and fracture when the bonding is subjected to mechanical load. Balancing material strength versus ductility, as well as considering the relationship between adhesive modulus and substrate modulus, creates stronger joints. However, a detailed understanding of how these properties interplay is lacking. Here, a biomimetic terpolymer is altered systematically to identify regions of optimal bonding. Mechanical properties of these terpolymers are tailored by controlling the amount of a methyl methacrylate stiff monomer versus a similar monomer containing flexible poly(ethylene glycol) chains. Dopamine methacrylamide, the cross‐linking monomer, is a catechol moiety analogous to 3,4‐dihydroxyphenylalanine, a key component in the adhesive proteins of marine mussels. Bulk adhesion of this family of terpolymers is tested on metal and plastic substrates. Incorporating higher amounts of poly(ethylene glycol) into the terpolymer introduces flexibility and ductility. By taking a systematic approach to polymer design, the region in which material strength and ductility are balanced in relation to the substrate modulus is found, thereby yielding the most robust joints. 相似文献