全文获取类型
收费全文 | 91793篇 |
免费 | 6189篇 |
国内免费 | 8152篇 |
专业分类
电工技术 | 5973篇 |
技术理论 | 4篇 |
综合类 | 9340篇 |
化学工业 | 12449篇 |
金属工艺 | 8523篇 |
机械仪表 | 5941篇 |
建筑科学 | 5946篇 |
矿业工程 | 2168篇 |
能源动力 | 2288篇 |
轻工业 | 6348篇 |
水利工程 | 2117篇 |
石油天然气 | 5970篇 |
武器工业 | 796篇 |
无线电 | 10820篇 |
一般工业技术 | 9903篇 |
冶金工业 | 3337篇 |
原子能技术 | 2231篇 |
自动化技术 | 11980篇 |
出版年
2024年 | 245篇 |
2023年 | 889篇 |
2022年 | 1704篇 |
2021年 | 2403篇 |
2020年 | 1754篇 |
2019年 | 1543篇 |
2018年 | 1640篇 |
2017年 | 1914篇 |
2016年 | 1873篇 |
2015年 | 2538篇 |
2014年 | 3361篇 |
2013年 | 3939篇 |
2012年 | 4390篇 |
2011年 | 8210篇 |
2010年 | 5867篇 |
2009年 | 4654篇 |
2008年 | 4748篇 |
2007年 | 4153篇 |
2006年 | 4329篇 |
2005年 | 4027篇 |
2004年 | 6073篇 |
2003年 | 4422篇 |
2002年 | 4674篇 |
2001年 | 3417篇 |
2000年 | 2523篇 |
1999年 | 3026篇 |
1998年 | 2280篇 |
1997年 | 2123篇 |
1996年 | 1448篇 |
1995年 | 1233篇 |
1994年 | 1025篇 |
1993年 | 2342篇 |
1992年 | 1804篇 |
1991年 | 1296篇 |
1990年 | 1179篇 |
1989年 | 909篇 |
1988年 | 625篇 |
1987年 | 363篇 |
1986年 | 266篇 |
1985年 | 160篇 |
1984年 | 114篇 |
1983年 | 65篇 |
1982年 | 63篇 |
1981年 | 52篇 |
1980年 | 87篇 |
1979年 | 68篇 |
1965年 | 59篇 |
1959年 | 30篇 |
1958年 | 26篇 |
1957年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献
23.
磷矿中七种金属元素的光谱法测定 总被引:2,自引:0,他引:2
研究了磷矿样品中7种金属元素锰、钴、镍,锌、铬、钼及铋的分析方法,选择了灵敏度高干扰少的谱线,绘制出工作曲线,对样品进行了科学处理,不必进行化学分离即可对七种元素同时测定,经合成样分析、回收实验及样品测定,证明此方法精确可靠,其回收率在98%-102%之间。 相似文献
24.
In this paper we design an experiment which can be depicted as a simple scenario, a very limited 'world'. In this world, there are an actor that can pursue a project and an observer that is keeping its eyes on the actor. We try to show in the experiment that the observer can to some degree understand the actor based on its knowledge and some metaphors, i.e. understand what the actor is doing and why. As the conclusion of this experiment, we try to show some features of 'understanding'. These are (1) that 'understanding' has to be based on some preliminary knowledge; (2) that 'understanding' is a process of incremental learning; (3) that, as for symbolic systems, some metaphors are necessary for mapping real entities into concepts in mind. 相似文献
25.
Huai Wen-xin Wuhan University of Hydraulic & Electric Engineering Wuhan Hubei P.R.China Prof.Li Wei 《水动力学研究与进展(B辑)》1993,(3)
Turbulence represents an essential aspect in atmospheric and oceanic circulations.In particu-lar,it is a preponderant factor in the dispersion of pollutants of artificial or natural origin.Thevertical turbulent jets,plumes and buoyant jets discharging into static environment is one of themost important and basic flow patterns related with the environment pollution.These flows havenumerous important applications,for example,thrust augmentors,waste disposal plumes fromstacks and combustion systems,and significant problems of turbulent diffusion. 相似文献
26.
Yu Jin Joshi S.G. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(3):491-494
It is found that an acoustic wave which is nearly polarized in the shear horizontal (SH) direction can propagate along the X axis of a Z-cut lithium niobate plate if the ratio h/λ, where h=plate thickness and λ=acoustic wavelength, is less than about 0.5. Attractive properties of this quasi-SH wave include: (1) phase velocity nearly constant for all values of h/λ; (2) ability to propagate in contact with a liquid medium; and (3) electromechanical coupling coefficient as high as 0.15. These properties make the wave attractive for use in a variety of sensor and signal processing applications. An example of sensor applications is illustrated by using the wave to measure conductivity of liquids (aqueous KCl solution). The frequency of a 12-MHz quasi-SH mode oscillator fabricated on a 0.48 wavelength thick Z-X lithium niobate plate is found to vary by more than 80 kHz for variation in KCI concentration from 0 to 0.15% 相似文献
27.
分别测量了LaNi4.25Al0.75和LaNi4.75Al0.25两种合金样品在未吸氘及不同含氘量的氘化物样品的中子衍射谱,用Rietveld程序拟合出它们的晶体结构,并观察到了一些过去未曾注意的现象.LaNi4.25-Al0.75在吸氘过程中,氘原子优先占据的原子坐标为(0.17,0.32,0.45). 相似文献
28.
29.
30.
Yi Jin Chieko Toeda Takeo Kawaguchi Toshinobu Seki Kazuhiko Juni 《Drug development and industrial pharmacy》1996,22(7):653-658
Permeation of zidovudine (3'-azido-3'-deoxythymidine, AZT) and probenecid from oily bases containing an alcohol through rat skin was examined. Isopropyl myristate (IPM), as an oily vehicle, showed a penetration enhancing effect for AZT and probenecid. Ethanol, n-propanol, and n-butanol were used as additives in IPM and were examined for their own permeation and the enhancing effect on the permeation of AZT and probenecid. The skin permeation of AZT and probenecid from IPM was enhanced by addition of the alcohol in IPM. The degree of the enhancement was decreased with increasing lipophilicity of the alcohol used. me permeation rate of the drug from those systems was shown to be governed by penetration-enhancing effects of the oily base and alcohol, and the penetration of the alcohol itself through the skin. 相似文献