全文获取类型
收费全文 | 245432篇 |
免费 | 2887篇 |
国内免费 | 434篇 |
专业分类
电工技术 | 4314篇 |
综合类 | 263篇 |
化学工业 | 40853篇 |
金属工艺 | 9407篇 |
机械仪表 | 7463篇 |
建筑科学 | 5621篇 |
矿业工程 | 1396篇 |
能源动力 | 5238篇 |
轻工业 | 25581篇 |
水利工程 | 2516篇 |
石油天然气 | 5108篇 |
武器工业 | 32篇 |
无线电 | 25244篇 |
一般工业技术 | 45263篇 |
冶金工业 | 45938篇 |
原子能技术 | 5976篇 |
自动化技术 | 18540篇 |
出版年
2021年 | 2434篇 |
2019年 | 2155篇 |
2018年 | 3631篇 |
2017年 | 3550篇 |
2016年 | 3827篇 |
2015年 | 2381篇 |
2014年 | 4071篇 |
2013年 | 10452篇 |
2012年 | 6380篇 |
2011年 | 8589篇 |
2010年 | 6767篇 |
2009年 | 7450篇 |
2008年 | 7794篇 |
2007年 | 7913篇 |
2006年 | 7027篇 |
2005年 | 6158篇 |
2004年 | 5933篇 |
2003年 | 5695篇 |
2002年 | 5766篇 |
2001年 | 5596篇 |
2000年 | 5429篇 |
1999年 | 5346篇 |
1998年 | 12613篇 |
1997年 | 8920篇 |
1996年 | 6890篇 |
1995年 | 5357篇 |
1994年 | 4765篇 |
1993年 | 4652篇 |
1992年 | 3685篇 |
1991年 | 3395篇 |
1990年 | 3611篇 |
1989年 | 3489篇 |
1988年 | 3326篇 |
1987年 | 2916篇 |
1986年 | 2949篇 |
1985年 | 3385篇 |
1984年 | 3224篇 |
1983年 | 2899篇 |
1982年 | 2748篇 |
1981年 | 2832篇 |
1980年 | 2721篇 |
1979年 | 2634篇 |
1978年 | 2689篇 |
1977年 | 2951篇 |
1976年 | 3805篇 |
1975年 | 2369篇 |
1974年 | 2242篇 |
1973年 | 2380篇 |
1972年 | 1972篇 |
1971年 | 1860篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper describes a database model based on the original rough sets theory. Its rough relations permit the representation of a rough set of tuples not definable in terms of the elementary classes, except through use of lower and upper approximations. The rough relational database model also incorporates indiscernibility in the representation and in all the operators of the rough relational algebra. This indiscernibility is based strictly on equivalence classes which must be defined for every attribute domain. There are several obvious applications for which the rough relational database model can more accurately model an enterprise than does the standard relational model. These include systems involving ambiguous, imprecise, or uncertain data. Retrieval over mismatched domains caused by the merging of one or more applications can be facilitated by the use of indiscernibility, and naive system users can achieve greater recall with the rough relational database. In addition, applications inherently “rough” could be more easily implemented and maintained in the rough relational database. 相似文献
992.
Mikhaylov I. E. 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2021,55(4):540-548
Power Technology and Engineering - This article describes a new method for calculating settlers for irrigation systems. The proposed method is based on the results of experimental research and... 相似文献
993.
A. N. Cherepanov V. V. Marchenkov V. E. Startsev N. V. Volkenshtein M. Glin'skii 《Journal of Low Temperature Physics》1990,80(3-4):135-151
The field and temperature dependence of the transverse magnetoresistivity and the Hall coefficient for single-crystal tungsten with a resistivity ratio 293K/4.2K varying from 780 to 80800 are measured at temperatures between 4.2 K and 50 K in magnetic fields up to 150 kOe. The role of the static skin effect and the temperature breakdown in the galvanomagnetic properties of the compensated metals is evaluated through experiments with tungsten. The experimental data shows that the galvanomagnetic properties of the compensated metals in the high magnetic fields are not dependent only on the Fermi surface geometry. A substantial role in their formation is played by the processes of the electron-surface and the intersheet electron-phonon scatterings. 相似文献
994.
995.
Yu. Yu. Belous A. G. Kostornov Yu. M. Efimenko L. E. Lunin A. M. Volkhov 《Powder Metallurgy and Metal Ceramics》1990,29(1):71-73
Conclusions Permeable materials based on metallic fibers with porous layers sprayed on by the detonation gas method, in tangential filtering of media with ferromagnetic and abrasive impurities ensure fineness of cleaning 1–2 m with comparatively low hydraulic resistance. The application of a magnetic field to material with sprayed-on layer of magnetic alloy made it possible to increase permeability to ferromagnetic particles by a factor of more than 1.5.Translated from Poroshkovaya Metallurgiya, No. 1(325), pp. 77–80, January, 1990. 相似文献
996.
H. O. Menlove M. M. Fowler E. Garcia M. C. Miller M. A. Paciotti R. R. Ryan S. E. Jones 《Journal of Fusion Energy》1990,9(4):495-506
Experiments using high-efficiency neutron detectors have detected neutron emission from various forms of Pd and Ti metal in pressurized D2 gas cells and D2O electrolysis cells. Four independent neutron detectors based on3He gas tubes were used. Both random neutrons (0.05–0.2 n/s) and time-correlated neutron bursts (10–280 n) of 100-s duration were measured using time-correlation counting techniques. The majority of the neutron burst events occurred at –30°C as the samples were warming up from the liquid nitrogen temperature. 相似文献
997.
It has been demonstrated previously (see E.L. Ritman and A.A. Bove, in State of the Art in Quantitative Coronary Arteriography, p.67-78, 1986) that coronary artery anatomy can be visualized using high-speed, volume-scanning X-ray CT (computed tomography). In the current study it is demonstrated that local image reconstruction (i.e. the reconstruction kernel is ~2(+) mm long), as distinct from more conventional global image reconstruction (i.e. 200(+) mm kernel length), has the advantage of reducing the need for operator interactive image processing. In addition, the local reconstruction algorithm eliminates the need for recording the X-ray projection data over the full transaxial extent of the thorax because it requires only the X-ray attenuation data over the region of the heart. This latter aspect reduces the dynamic range requirements for the sensors and could reduce total X-ray exposure. 相似文献
998.
A. S. Zalesov S. E. Lisichkin 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1990,24(3):221-226
1. | The suggestions on calculating the strength of concrete joints with transverse reinforcements were made on the basis of using the method of secondary stress fields and permit more complete consideration of the effect of the characteristics of the stress state on the strength of massive members. |
2. | Unlike the preceding developments, the present suggestions make it possible to evaluate the reinforcement and concrete strength of the structural member being designed with pin resistance of the transverse bar reinforcement to the effect of the initial and secondary shear stresses in the longitudinal joint. |
3. | The installation of an additional amount of transverse reinforcement precludes the probability of separation of the massive member along the longitudinal block joint and provides reliable and safe operation of the structure. |
999.
Method of calculating the technological parameters when designing hydraulic-fill dams of silty soils
E. L. Vvedenskii 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1990,24(6):354-362
1. | Investigations showed that when constructing dams of fine-grained silty soils by hydraulic filling, it is expedient to use the technology of layerwise placement of soil with consolidation of each layer. |
2. | Dependences are given for calculating the thickness of the layers and period of consolidation of the soil on the basis of investigations of the dynamics of the hydrophysical properties of these soils in relation to technological factors. |
3. | Dependences are also proposed for predicting the density of the hydraulic-filled soil during construction, as well as the distribution of soil in the profile of the structure. |
4. | A method is proposed for calculating the technological parameters, in particular, the rate of construction of hydraulic-fill structures, calculating the size and number of the hydraulic-fill plots referred to one dredge, and prediction of the seepage discharge into the foundation of the dams during their hydraulic filling. |
5. | The proposed calculation methods make possible a more substantiated approach to the design of hydraulic-fill structures of fine-grained silty soils and technology of their construction. |
1000.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 31–32, February, 1990. 相似文献