全文获取类型
收费全文 | 21123篇 |
免费 | 980篇 |
国内免费 | 674篇 |
专业分类
电工技术 | 847篇 |
技术理论 | 1篇 |
综合类 | 981篇 |
化学工业 | 2746篇 |
金属工艺 | 1190篇 |
机械仪表 | 3096篇 |
建筑科学 | 1775篇 |
矿业工程 | 496篇 |
能源动力 | 1178篇 |
轻工业 | 1038篇 |
水利工程 | 332篇 |
石油天然气 | 904篇 |
武器工业 | 109篇 |
无线电 | 1089篇 |
一般工业技术 | 1625篇 |
冶金工业 | 886篇 |
原子能技术 | 401篇 |
自动化技术 | 4083篇 |
出版年
2024年 | 26篇 |
2023年 | 190篇 |
2022年 | 298篇 |
2021年 | 404篇 |
2020年 | 394篇 |
2019年 | 327篇 |
2018年 | 342篇 |
2017年 | 363篇 |
2016年 | 536篇 |
2015年 | 657篇 |
2014年 | 1132篇 |
2013年 | 1363篇 |
2012年 | 1254篇 |
2011年 | 1704篇 |
2010年 | 1126篇 |
2009年 | 1198篇 |
2008年 | 1038篇 |
2007年 | 1189篇 |
2006年 | 1117篇 |
2005年 | 1113篇 |
2004年 | 951篇 |
2003年 | 899篇 |
2002年 | 806篇 |
2001年 | 590篇 |
2000年 | 527篇 |
1999年 | 577篇 |
1998年 | 498篇 |
1997年 | 404篇 |
1996年 | 351篇 |
1995年 | 342篇 |
1994年 | 202篇 |
1993年 | 159篇 |
1992年 | 133篇 |
1991年 | 110篇 |
1990年 | 77篇 |
1989年 | 74篇 |
1988年 | 73篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 34篇 |
1984年 | 32篇 |
1983年 | 21篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 10篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
41.
根据已经发表的实验数据,针对镓铝铟磷发光材料的提出了一组经验公式及相应的曲线,作为GaAlInP可见光材料设计的依据或参考。 相似文献
42.
43.
R. E. Uhrig 《Progress in Nuclear Energy》1995,29(3-4):357-370
The integrated use of neural network and noise analysis technologies offers advantages not available by the use of either technology alone. The application of neural network technology to noise analysis offers an opportunity to expand the scope of problems where noise analysis is useful and unique ways in which the integration of these technologies can be used productively. The two-sensor technique, in which the responses of two sensors to an unknown driving source are related, is used to demonstration such integration. The relationship between power spectral densities (PSDs) of accelerometer signals is derived theoretically using noise analysis to demonstrate its uniqueness. This relationship is modeled from experimental data using a neural network when the system is working properly, and the actual PSD of one sensor is compared with the PSD of that sensor predicted by the neural network using the PSD of the other sensor as an input. A significant deviation between the actual and predicted PSDs indicate that system is changing (i.e., failing). Experiments carried out on check valves and bearings illustrate the usefulness of the methodology developed. 相似文献
44.
Jeong-Woo Choi Jun Hyo Park Shin Chul Lee Dong-Il Kim Won Hong Lee 《Korean Journal of Chemical Engineering》1995,12(5):528-534
The on-line sensing of viable cell weight in plant cell culture process is applied to analysis and control of process. The
fiber-optic fluorescence sensor was constructed to measure the NADH-dependent fluorescence inNicotiana tabacum plant cell culture and the analysis of fluorescence signal was done to be correlated with the viable cell weight. The structured
kinetic model for cell growth was proposed to estimate the theoretical viable cell weight. The dimensional analysis was proposed
for the interpretation of fluorescence signal, in which the path length, the inner filter effect and the hydrodynamic conditions
were considered as the key factors on fluorescence signal. The dimensional analysis and empirical correlation of fluorescence
signal to viable cell weight was applied to the interpretation of the detected fluorescence signal during cultivation. The
proposed interpretation of fluorescence signal using dimensional analysis was well correlated with the viable cell weight
estimated by the structured kinetic model as well as by empirical correlation. 相似文献
45.
《Drying Technology》2007,25(7):1175-1183
Although considerable progress has been made in the development of experimental techniques for investigating velocity distribution inside a fixed bed, these techniques were limited to special cases. Consequently, the velocity distribution is normally measured at downstream of the fixed bed and then this measurement is considered to be representative for the flow inside the bed. To evaluate the representativeness of this technique, this work presents a study of the change in the flow characteristics, starting from the boundary of the fixed bed within the pipe to a downstream position where the experimental measurement is taken, by using simulations based on computational fluid dynamics methods. 相似文献
46.
Tree-shaped flow structures designed by minimizing path lengths 总被引:1,自引:0,他引:1
S. LorenteW. Wechsatol A. Bejan 《International Journal of Heat and Mass Transfer》2002,45(16):3299-3312
This paper outlines a direct route to the construction of effective tree-shaped flow structures. Dendritic flow structures dominate the design of natural and engineered flow systems, especially in thermal and fluid systems. The starting point is the optimization of the shape of each elemental area or volume, such that the length of the flow path housed by the element is minimized. Proceeding toward larger and more complex structures - from elements, to first constructs, second constructs, etc. - the paper develops tree-shaped flow structures between one point and a straight line, one point and a plane, a circle and its center, and a point and many points distributed uniformly over an area. In the latter, the construction method is applied to a fluid flow configuration with laminar fully developed flow. The constructions reveal several features that are supported by empirical observations of natural tree-shaped flows: asymmetry, flow rate imbalance, pairing or bifurcation, angles between branches, and Y-shaped constructs that lie in a plane. It is shown that these basic features are necessary because of “packing”, i.e., assembling optimized elements into a fixed space, and filling the space completely. For the flow between an area and one point, the best elemental shape is the regular hexagon. It is shown that the emergence of string-shaped links that connect two or more elements are necessary features, which are also required by packing. Strings cover some of the inner zones of the tree network, particularly the inner zones of large and complex trees. Dichotomous Y-shaped constructs dominate the tree structure, especially the peripheral zones of the tree canopy. The practical importance of the simplified design method is discussed. 相似文献
47.
48.
介绍了食用盐新国标制定的指导思想,新标准的特点及所修订的内容,指出为做好食用盐的质量检测要掌握和控制的技术要点,以保证和提高盐质分析结果的准确度,确保食用盐产品质量符合标准要求。 相似文献
49.
起重搬运作业的安全风险分析 总被引:2,自引:1,他引:1
用安全系统的理论和方法 ,以起重作业为研究对象 ,通过危险识别 ,对造成人员损伤的危险事件发生的可能性和导致伤害后果的严重程度 ,进行了定性的风险分析 ,介绍了我国采取的针对性综合管理对策 相似文献
50.
The objective of this work is to simulate the gas flow across a concrete wall of a nuclear power plant internal enclosure. In the laboratory, permeability measurements are generally made on cylindrical samples (15 cm diameter×5 cm height: ∅ 15×5 cm) with a steady-state experiment. To be able to predict structural behaviour, we studied size effect and steady-state time with a modified CEMBUREAU permeability test. A statistical approach showed that there is no size effect on concrete permeability. Laboratory results found on cylindrical samples can be applied to tests in situ, where concrete specimens are thicker. A model based on the mass balance relation provided times to reach steady state and reproduced experimental flow kinetics for uniform water content across specimens. 相似文献