全文获取类型
收费全文 | 403342篇 |
免费 | 5137篇 |
国内免费 | 1361篇 |
专业分类
电工技术 | 7566篇 |
综合类 | 316篇 |
化学工业 | 59856篇 |
金属工艺 | 16429篇 |
机械仪表 | 13491篇 |
建筑科学 | 8347篇 |
矿业工程 | 2154篇 |
能源动力 | 11539篇 |
轻工业 | 28456篇 |
水利工程 | 4266篇 |
石油天然气 | 7913篇 |
武器工业 | 17篇 |
无线电 | 49238篇 |
一般工业技术 | 82984篇 |
冶金工业 | 74985篇 |
原子能技术 | 9183篇 |
自动化技术 | 33100篇 |
出版年
2022年 | 2550篇 |
2021年 | 3884篇 |
2020年 | 2942篇 |
2019年 | 3801篇 |
2018年 | 6480篇 |
2017年 | 6476篇 |
2016年 | 6920篇 |
2015年 | 4319篇 |
2014年 | 7134篇 |
2013年 | 20027篇 |
2012年 | 11410篇 |
2011年 | 15260篇 |
2010年 | 12139篇 |
2009年 | 13710篇 |
2008年 | 14051篇 |
2007年 | 13820篇 |
2006年 | 12418篇 |
2005年 | 11113篇 |
2004年 | 10510篇 |
2003年 | 10418篇 |
2002年 | 9832篇 |
2001年 | 9735篇 |
2000年 | 9134篇 |
1999年 | 9522篇 |
1998年 | 24338篇 |
1997年 | 16718篇 |
1996年 | 12799篇 |
1995年 | 9518篇 |
1994年 | 8363篇 |
1993年 | 8381篇 |
1992年 | 6057篇 |
1991年 | 5696篇 |
1990年 | 5684篇 |
1989年 | 5318篇 |
1988年 | 5045篇 |
1987年 | 4419篇 |
1986年 | 4299篇 |
1985年 | 4812篇 |
1984年 | 4423篇 |
1983年 | 3994篇 |
1982年 | 3654篇 |
1981年 | 3731篇 |
1980年 | 3429篇 |
1979年 | 3326篇 |
1978年 | 3334篇 |
1977年 | 3750篇 |
1976年 | 4849篇 |
1975年 | 2851篇 |
1974年 | 2663篇 |
1973年 | 2733篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A method for assessing the differential risk of failure among a system's modules is proposed. The procedure has three components: external-risk assessment, module exposure, and module-failure likelihood. External-risk assessment is a consideration of the system's environment, almost independent of the software's details. To estimate module exposure, the model relates individual modules and their potential faults to the external-failure modes and their economic consequences by reverse-engineering the specifications and analyzing each module's expected use. To estimate failure likelihood, the method uses a reliability model. The method constitutes theoretical foundation for the cost-effective development of software that attempts to reduce the risk of failure. Managers can use the failure-risk estimates to better determine how much testing effort can be economically justified 相似文献
992.
993.
994.
P. S. Theocaris 《Acta Mechanica》1991,89(1-4):93-121
Summary Cellular solids and brittle foams are increasingly finding application in constructions mainly as core materials for loaded sandwich structures where the loading of the structure generates multiaxial stress states on them. It has been established that the principal mechanism of deformation is based on the cell-wall bending and closed-cell as well as open-cell foams present similar stiffnesses. Therefore simple relations are found for their tensile, compressive and shear strengths and their elastic properties.It has been established in this paper that the modes of failure of such materials can be satisfactorily described by the elliptic paraboloid failure criterion for the general orthotropic body. Then, as soon as the yield or failure stresses in simple tension and compression are measured along the three principal stress directions of the material the failure locus is unequivocally defined and all the properties of the material under any complicated load can be accurately established. However, since these materials fail in the compression-compression-compression octant of the principal stress space by elastic buckling, the EPFS-criterion is cut-off by an ellipsoid surface, with intercepts along the principal axes the respective compressive failure stresses.The criterion thus established yields satisfactory results. It has been tested among others in a reticulated vitreous carbon foam as well as in an aluminium foam. The experimental results for these foams existing in the literature are fitting better with this universal criterion than any other considered, thus indicating the validity of the elliptic paraboloid failure criterion also for this type of materials. 相似文献
995.
The study suggests improvements in the design of new houses to conserve energy and enhance indoor thermal comfort. Summer temperature records show that a new house has an average indoor temperature of 35°C with the ambient average 31°C. The traditional house in the old city recorded 28°C for the same period. Winter temperatures in both types of houses were similar (12°C) when not occupied. Architectural features of the two houses were compared to identify those responsible for difference in the thermal performance. Larger exposed surface and window areas, higher overall heat transfer coefficient and weaker thermal coupling with the ground for the new houses seems to contribute to their inferior thermal performance. 相似文献
996.
997.
Pull-out experiments have been carried out on single production fibres under carefully controlled conditions. Four parameters were determined. The interfacial yield stresses, of about 9–14 MPa, were very much smaller than the shear strengths of the bulk polymers in the case of an epoxy, whether post-cured or not, and a non-post-cured polyester. Values for the work of fracture of the interface varied from 140 to 300 Jm?2, and again were less than those of the polymer. Interface failure sometimes took place in the epoxy rather than at the fibre surface, whereas with the polyester it always took place at the fibre surface. After interface failure, pull-out was governed by friction, with maximum shear stresses of 7–10 MPa for polyester, and 21–34 MPa for epoxy, the higher values being obtained for the post-cured resins. Average frictional shear stresses were sometimes less than a half of the maximum shear stress, indicating that the fibre Poisson's shrinkage was playing an important role in the pull-out process. A silicone release agent reduced the frictional shear stresses to 2·5 MPa, with both resins. 相似文献
998.
Canham R.O. Smith S.L. Tyrrell A.M. 《Vision, Image and Signal Processing, IEE Proceedings -》2005,152(6):741-749
Complex and highly distorted line drawings are produced by subjects attempting the Rey Complex Figure test, a clinical test of neuropsychological assessment. However, the marking scheme conventionally employed can be subjective and unreliable. In this paper, the first stages in automating this scoring system are investigated using a robust technique to locate a reduced set of scoring sections and a knowledge-based system that employs spatial metrics and fuzzy approximation techniques. Testing the technique using clinical data produced encouraging results that support the argument that this is a feasible approach for implementing a fully automated system, and that in its current state, can be immediately applied in a semi-automated system. 相似文献
999.
I. S. Panidi V. A. Trofimov N. S. Lepikhina 《Chemistry and Technology of Fuels and Oils》2006,42(6):440-445
Equations are proposed for calculating the molar volume of liquid hydrocarbons used in production of surfactants. With such
data, it will be possible to calculate most of the physicochemical properties of these hydrocarbons to solve many process
problems.
__________
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 6, pp. 39–41, Novemmber–December, 2006. 相似文献
1000.
Measurements of gel time of the epoxy system DGEBA(n=0)/m-XDA were carried out using rheometry and dielectric analysis with the objective of checking the validity of Mangion-Johari equation (DEA) and Harran-Laudouard criterium (rheometry) for gel time determination. In this work, gel times obtained by rheometry and dielectric analysis are compared and conversions at gel time calculated. From the experimental results obtained for gel times it was found a reasonable agreement between the two techniques that lead to gel conversion values very close to those obtained using Flory equation. 相似文献