全文获取类型
收费全文 | 241398篇 |
免费 | 2631篇 |
国内免费 | 428篇 |
专业分类
电工技术 | 4296篇 |
综合类 | 257篇 |
化学工业 | 39405篇 |
金属工艺 | 9386篇 |
机械仪表 | 7399篇 |
建筑科学 | 5448篇 |
矿业工程 | 1391篇 |
能源动力 | 5157篇 |
轻工业 | 24817篇 |
水利工程 | 2476篇 |
石油天然气 | 5092篇 |
武器工业 | 32篇 |
无线电 | 25050篇 |
一般工业技术 | 44806篇 |
冶金工业 | 45368篇 |
原子能技术 | 5950篇 |
自动化技术 | 18127篇 |
出版年
2021年 | 2118篇 |
2019年 | 2018篇 |
2018年 | 3494篇 |
2017年 | 3425篇 |
2016年 | 3694篇 |
2015年 | 2237篇 |
2014年 | 3904篇 |
2013年 | 10190篇 |
2012年 | 6156篇 |
2011年 | 8310篇 |
2010年 | 6555篇 |
2009年 | 7245篇 |
2008年 | 7591篇 |
2007年 | 7721篇 |
2006年 | 6891篇 |
2005年 | 6051篇 |
2004年 | 5818篇 |
2003年 | 5600篇 |
2002年 | 5677篇 |
2001年 | 5561篇 |
2000年 | 5387篇 |
1999年 | 5303篇 |
1998年 | 12575篇 |
1997年 | 8896篇 |
1996年 | 6856篇 |
1995年 | 5331篇 |
1994年 | 4738篇 |
1993年 | 4625篇 |
1992年 | 3668篇 |
1991年 | 3387篇 |
1990年 | 3593篇 |
1989年 | 3473篇 |
1988年 | 3303篇 |
1987年 | 2895篇 |
1986年 | 2932篇 |
1985年 | 3373篇 |
1984年 | 3219篇 |
1983年 | 2892篇 |
1982年 | 2738篇 |
1981年 | 2821篇 |
1980年 | 2719篇 |
1979年 | 2625篇 |
1978年 | 2685篇 |
1977年 | 2948篇 |
1976年 | 3805篇 |
1975年 | 2368篇 |
1974年 | 2242篇 |
1973年 | 2376篇 |
1972年 | 1970篇 |
1971年 | 1858篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
981.
We have performed tribotechnical tests of carbonaceous filled polytetrafluoroethylene in a wide range of loads with the recording of acoustic emission signals. Based on a spectral analysis of the sequence of rms deviations of acoustic emission signals using a discrete Fourier transform, we have constructed a normalized energy spectrum. We show that the mass wear of the material can be determined from the power of the high-frequency component of the spectrum obtained. 相似文献
982.
983.
The solution of several electrostatic potential problems involving open spherical perfectly conducting shells is presented in the context of the dual series equations method. These equations are a consequence of mixed boundary conditions imposed on the electric potential and field. A solution is given for the dual series equations corresponding to two concentric spherical shells, one of which has a circular aperture. The aperture dipole moment, the capacity, and field penetration of some electrostatic devices are also calculated. 相似文献
984.
985.
The 226Ra and 228Ra content of the lichens Umbilicaria cylindrica, U. deusta, U. murina and U. hirsuta has been determined as a function of the growth altitude above sea level, based on data derived from material collected from localities in southwest Poland. These data are interpreted as graphs and formulae to show the influence of environmental factors, particularly altitude, on the concentration of 226Ra and 228Ra, and the coefficients of accumulation calculated. 相似文献
986.
987.
988.
An ion implanter of cylindrical geometry is described suitable for uniform implantation at a few keV of inert gas ions of narrow energy distribution into conducting targets of axial symmetry. For helium implantation the ion current in the present device can easily be maintained at over 1 mA, allowing high dose implantation of large areas (several tens of cm2) in minutes. For temperature control of the target, a thermal shunt is incorporated. The sizes and the implantation energy of the device are scalable. Reactive gases can also be implanted with the device when operated at lower pressures and ion currents. 相似文献
989.
We administered bovine growth hormone to six Holstein cows in a Latin square design to study the relationship between dose of growth hormone and response of milk yield. Treatments were 0, 5, 10, 25, 50, and 100 IU/day of pituitary-derived bovine growth hormone administered in once-daily subcutaneous injections. Feed intake and yield of milk and milk components were measured for the last 5 days of each 10-day injection period. Yields of milk, protein, and fat increased in a dose-responsive fashion up to 32, 27, and 46% (for the 100 IU treatment) above control (26.7, .90, and .98 kg/day). Concentration of lactose in milk was not influenced by treatment, but at larger doses of growth hormone, milk fat percent was elevated and protein percent declined. As a result, milk energy secretion in response to 100 IU/day was increased 37% from control (19.2 Mcal/day). Both energy and nitrogen balance decreased with increasing growth hormone. Limited blood samples (timed to coincide with peak concentration of growth hormone postinjection) indicated treatment did not affect concentrations of glucose or insulin in blood plasma but increased concentration of growth hormone. Concentration of nonesterified fatty acids in blood plasma was increased slightly only at the 100 IU/day dose for which energy balance was negative. 相似文献
990.
A. M. Hashem D. Goldschmidt E. El-Magd 《Materialwissenschaft und Werkstofftechnik》1994,25(3):133-138
Various heat treatments of the single-crystal nickel-base superalloy SRR99 have been carried out to produce a wide range of initial γ′ phase morphology. The cavitation damage has been studied after creep fracture at 850°C and stresses between 400MPa and 650 Mpa. The crep fracture surfaces and longitudinal sections of crept specimens have been examined by image analysing system in order to determine the size distribution and the area fraction of (001)-planes cracks on fracture surface characterise the creep crack damage level. The cracking morphology in fractured material as a function of stress and γ′-phase size has also been investigated. The results show, that crack propagation occurred anisotropically on (001) crystallographic planes perpendicular to the aplied stress along the γ/γ′ interfaces. It was found, that creep cracks dependent on the shape and size of γ′-phases developing at the temperature and stress level. 相似文献