全文获取类型
收费全文 | 1918篇 |
免费 | 82篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 37篇 |
综合类 | 3篇 |
化学工业 | 480篇 |
金属工艺 | 43篇 |
机械仪表 | 96篇 |
建筑科学 | 24篇 |
矿业工程 | 5篇 |
能源动力 | 96篇 |
轻工业 | 93篇 |
水利工程 | 5篇 |
石油天然气 | 3篇 |
无线电 | 251篇 |
一般工业技术 | 420篇 |
冶金工业 | 159篇 |
原子能技术 | 8篇 |
自动化技术 | 280篇 |
出版年
2023年 | 27篇 |
2022年 | 51篇 |
2021年 | 55篇 |
2020年 | 45篇 |
2019年 | 50篇 |
2018年 | 59篇 |
2017年 | 70篇 |
2016年 | 75篇 |
2015年 | 57篇 |
2014年 | 66篇 |
2013年 | 134篇 |
2012年 | 82篇 |
2011年 | 113篇 |
2010年 | 70篇 |
2009年 | 84篇 |
2008年 | 74篇 |
2007年 | 67篇 |
2006年 | 55篇 |
2005年 | 34篇 |
2004年 | 30篇 |
2003年 | 44篇 |
2002年 | 32篇 |
2001年 | 33篇 |
2000年 | 32篇 |
1999年 | 32篇 |
1998年 | 45篇 |
1997年 | 47篇 |
1996年 | 29篇 |
1995年 | 24篇 |
1994年 | 30篇 |
1993年 | 26篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 29篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 19篇 |
1975年 | 11篇 |
1970年 | 10篇 |
排序方式: 共有2003条查询结果,搜索用时 17 毫秒
141.
Selecting a threshold from the gradient histogram, a histogram of gradient magnitudes, of an image plays a crucial role in a gradient based edge detection system. This paper presents a methodology to determine the threshold from a gradient histogram generated using any kind of linear gradient operator on an image. We consider the image as a random process with dependent samples, model the gradient histogram using theories of random process and random input to a system, and determine a region of interest in the gradient histogram using certain properties of a probability density function. Standard histogram thresholding techniques are then used within the region of interest to get the threshold value. To obtain the edges, this threshold value is then used as the upper threshold of the hysteresis thresholding technique that follows the non-maximum suppression operation applied on the gradient magnitude image. The proposed methodology of determining a threshold in a gradient histogram is deduced through rigorous analysis and hence it helps in achieving consistently appreciable edge detection performance. Experimental results using different real-life and benchmark images are shown to demonstrate the effectiveness of the proposed technique. 相似文献
142.
143.
Dutta M. Rakshit A. Bhattacharyya S.N. 《IEEE transactions on instrumentation and measurement》2001,50(5):1048-1052
An automatic ac bridge method employing the principle of balancing by means of a stochastic gradient search algorithm is presented. Among the various gradient search techniques, the Widrow-Hoff least mean square (LMS) technique has been chosen as it involves a low computational burden. The LMS algorithm has been used by the authors for the operation of an ac bridge operating with continuous variables. The relevant operation has been verified by simulation; it can also measure negative impedance. A relation has been established between parameters to be used in the LMS algorithm for discrete and continuous versions of the bridge. The balance convergence time for a relatively simple form of the LMS bridge, namely, the R-R type bridge, has been theoretically established and experimentally verified both by simulation and real-time implementation. The frequency response of the LMS algorithm has also been determined 相似文献
144.
This study concerns the preparation and evaluation of nonionic surfactants prepared from polyethylene glycol (PEG) esters
of castor oil fatty acid, a source of hydroxy fatty acid. A lipase-catalyzed esterification reaction has been employed to
prepare PEG esters of hydroxy acid to overcome problems associated with chemical processes. Castor oil fatty acid (85% ricinoleic
acid) was mixed with PEG of different molecular weight. Rhizomucor miehei lipase was added as catalyst (10% level) and the reaction was continued at 60°C under 2 mm Hg pressure for 360 min. Conversion
of PEG to esters was in the range of 86–94%, depending on the molecular size of PEG. The products were isolated and examined
for surface activity by surface tension measurement. Surface tension values measured at 25°C were about 36–37 dynes/cm. 相似文献
145.
The problem of electromagnetic scattering from a plate with a rim loading for transverse electric (TE) and transverse magnetic (TM) polarizations is investigated. The analysis is based on the work of R. Tiberio et al. (ibid., vol.AP-33, no.8, p.867-73, 1985) on the uniform geometrical theory of diffraction analysis of a wedge with two face impedances. The two-dimensional field is converted into three-dimensional field using Siegel's 2-D to 3-D conversion formula. The corner effects are neglected. The width of the coating around the edges which gives the same result as a uniformly coated plate of the same size is estimated. Hence, the percentage of saving of radar-absorbing material (RAM) can also be estimated for practical application in radar cross-section (RCS) reduction problems 相似文献
146.
Anil G. Khadakkar K. Ravi Sankar P. Rathinam R. Narayanan S. P. Rao J. K. Popli 《Strain》1997,33(2):57-60
This paper describes an experimental investigation carried out involving instrumentation, measurement and monitoring of stresses in a large diameter gas pipeline during its lowering operations. It also highlights the ingenious techniques developed and adopted to overcome the difficulties pertaining to long leadwires, measurement of existing strains on the curved surface of a pipeline and protection of strain gauge installations. These novel methods were used to ensure smooth and proper functioning of strain gauge instrumentation even under the severe field conditions at site for more than two weeks, till the lowering operations and pipeline monitoring was successfully completed. 相似文献
147.
K.H. Sabeena Farvin S. Hari Senthil KumarR. Anandan Suseela MathewT.V. Sankar P.G. Viswanathan Nair 《Food chemistry》2007,105(4):1390-1395
We have investigated the preventive effects of squalene against isoprenaline-induced myocardial infarction in male albino rats. Supplementation with squalene significantly prevented the isoprenaline-induced adverse changes in the levels of protein and glycoprotein components in plasma and heart tissue of experimental groups of rats. It exerted an antioxidant effect by inhibiting the isoprenaline-induced lipid peroxidation and by maintaining the level of non-enzymatic free radical-scavenger, reduced glutathione at near normalcy. Histopathological observations also confirmed the possible cardioprotective action of squalene by maintaining the normal architecture of the heart tissue. The results of the present investigation demonstrate that supplementation with squalene offers cardioprotection in experimental rats by its antioxidant and membrane- stabilizing properties. 相似文献
148.
149.
A discrete reliability-growth model (appropriate for success-failure data) whose derivation parallels that of a popular nonhomogeneous Poisson process model (appropriate for continuous failure time data) is considered.,Following J. M. Finkelstein (ibid. vol.R-32, p.508-11, Dec. 1983) continuous analog estimators are defined for use with the discrete model when there is a constant prespecified number of test trials between system configuration changes. The large-sample properties of these estimators, including consistency and normality, are established. Large-sample standard-error formulas and confidence interval procedures are developed 相似文献
150.
The adhesion and film failure studies on nano-composite SiCN thin films on silicon, glass and steel have been carried out. It was observed that both coating as well as the substrate has an influence on the adhesion of film. The films on hard substrate Si failed adhesively whereas on softer substrate, steel, cohesive failure was observed. The measured critical load was around 18 N and 24 N for SiCN film on silicon and steel substrate respectively. A decrease in critical load and interface toughness with the increase of substrate temperature during deposition for glass and steel substrate was observed. 相似文献