全文获取类型
收费全文 | 390017篇 |
免费 | 5865篇 |
国内免费 | 2306篇 |
专业分类
电工技术 | 8070篇 |
技术理论 | 5篇 |
综合类 | 1343篇 |
化学工业 | 62648篇 |
金属工艺 | 15799篇 |
机械仪表 | 11856篇 |
建筑科学 | 10410篇 |
矿业工程 | 2002篇 |
能源动力 | 8950篇 |
轻工业 | 40050篇 |
水利工程 | 3851篇 |
石油天然气 | 6514篇 |
武器工业 | 248篇 |
无线电 | 44681篇 |
一般工业技术 | 73174篇 |
冶金工业 | 68613篇 |
原子能技术 | 7489篇 |
自动化技术 | 32485篇 |
出版年
2021年 | 3097篇 |
2019年 | 2818篇 |
2018年 | 4272篇 |
2017年 | 4296篇 |
2016年 | 4705篇 |
2015年 | 3673篇 |
2014年 | 6042篇 |
2013年 | 16945篇 |
2012年 | 10257篇 |
2011年 | 13928篇 |
2010年 | 11019篇 |
2009年 | 12092篇 |
2008年 | 13241篇 |
2007年 | 13633篇 |
2006年 | 11979篇 |
2005年 | 10809篇 |
2004年 | 9974篇 |
2003年 | 9481篇 |
2002年 | 9472篇 |
2001年 | 9574篇 |
2000年 | 9014篇 |
1999年 | 8963篇 |
1998年 | 18714篇 |
1997年 | 14099篇 |
1996年 | 11143篇 |
1995年 | 8739篇 |
1994年 | 7969篇 |
1993年 | 7699篇 |
1992年 | 6309篇 |
1991年 | 6033篇 |
1990年 | 6063篇 |
1989年 | 6015篇 |
1988年 | 5639篇 |
1987年 | 4918篇 |
1986年 | 4897篇 |
1985年 | 5644篇 |
1984年 | 5329篇 |
1983年 | 4975篇 |
1982年 | 4510篇 |
1981年 | 4665篇 |
1980年 | 4295篇 |
1979年 | 4484篇 |
1978年 | 4279篇 |
1977年 | 4702篇 |
1976年 | 5999篇 |
1975年 | 3840篇 |
1974年 | 3560篇 |
1973年 | 3608篇 |
1972年 | 3022篇 |
1971年 | 2786篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
M. Polák M. Majoro F. Hanic J. Pitel M. Kedrová P. Kottman J. Talapa L. Vencel 《Journal of Superconductivity》1989,2(2):219-233
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ
cs
and the intergranular transport current densityJ
cr
are identical if the measurement conditions are similar. A degradation ofJ
cs
measured in the external field with AC ripple has been observed. 相似文献
74.
Containment structures have several regions in which the continuity of the cylindrical pressure boundary is interrupted, e.g., shell penetrations, discontinuous stiffeners, and changes in the shell thickness. Significant strain concentrations can occur in these areas of discontinuity. The Sandia National Laboratories 1:8-scale steel containment equipment hatch was analyzed as an example of an eccentricity at a stiffener intersection.A portion of the as-built 1:8-scale model was modeled with the ANSYS general purpose finite element program using triangular, thin shell finite elements. The overall size of the model was determined from Saint-Venant type considerations of the stress field around the hatch. Shell elements were used to model the ring and formed stiffeners. Geometric and material nonlinear behavior were included. The model was loaded using discrete load steps up to a pressure of 165 psig. At this pressure, the maximum strain was 19.7 percent in the formed stiffener near its intersection with the ring stiffener. The finite element solution demonstrated the very localized nature of the strain field near the ring/formed stiffener intersection.In an attempt to reduce analysis costs, a small portion of the 1:8-scale model immediately surrounding the ring/formed stiffener intersection was selected for further analysis. Two smaller models, a ring/formed stiffener intersection and a ring/circular stiffener intersection, were studied. The models were significantly smaller than the regions used previously. A comparison of the two intersection models showed that the circular stiffener is a more efficient configuration. 相似文献
75.
Arthur W. Westerberg 《Computers & Chemical Engineering》1985,9(5):421-429
The last dozen years have produced almost 50 English language articles on the synthesis of separation systems [1]. Most work has considered separating a single relatively ideal mixture into sharply split, usually pure-component products using systems of single-feed, two-product distillation columns. Of late, the work has considered heat-integrating these columns to reduce energy consumption. Present research will very likely produce valuable results for nonsharp separations.Earlier approaches developed both algorithmic- and heuristic-based tree search algorithms for discovering the better systems of non-heat-integrated columns. New results permit the design of heat-integrated systems.The paper highlights the above developments. 相似文献
76.
P.W. Hawkes 《Ultramicroscopy》1985,17(2):151-156
Modifications of solid water and their transitions are described as they relate to cryo electron microscopy. In particular, the various amorphous states (amorphous polymorphs) as they exist below 100 K are extensively investigated. The “high-density” midification exhibits a lower viscosity than the “low-density” form. Differences are also observed in the mechanism of void formation due to electron irradiation: in the high-density form, voids are formed — not, however, in the low-density form. Together with the reaction to radiation damage, the physical properties of amorphous solid water are discussed with respect to embedding of organic specimens. Finally, the conditions and pitfalls associated with preparation of thin and entirely vitrified ice layers by shock-freezing are described. 相似文献
77.
V. L. Ozol' L. F. Kandyba N. T. Bychenkov L. A. Zbarskii B. E. Koropov 《Metallurgist》1989,33(8):156-156
Lenin Dnepropetrovsk Pipe Plant. Translated from Metallurg, No. 8, p. 39, August, 1989. 相似文献
78.
79.
Occupational airway diseases are now receiving attention in industry, although study is hampered by a lack of readily-available data. The interpretation of the data that is available, and also of the root problems themselves, is itself a difficult problem. This paper has been written as a literature review which it is hoped that other researchers can take either as a starting point or as a refresher. 相似文献
80.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed. 相似文献