首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   527746篇
  免费   7268篇
  国内免费   1492篇
电工技术   9607篇
综合类   538篇
化学工业   79216篇
金属工艺   20021篇
机械仪表   15291篇
建筑科学   12791篇
矿业工程   2273篇
能源动力   14678篇
轻工业   47214篇
水利工程   5262篇
石油天然气   9361篇
武器工业   37篇
无线电   60137篇
一般工业技术   102142篇
冶金工业   103640篇
原子能技术   10582篇
自动化技术   43716篇
  2022年   3254篇
  2021年   5050篇
  2020年   3622篇
  2019年   4723篇
  2018年   7966篇
  2017年   7752篇
  2016年   8071篇
  2015年   5654篇
  2014年   9413篇
  2013年   24320篇
  2012年   14801篇
  2011年   20344篇
  2010年   15926篇
  2009年   17824篇
  2008年   18164篇
  2007年   17815篇
  2006年   15553篇
  2005年   14247篇
  2004年   13622篇
  2003年   13417篇
  2002年   12652篇
  2001年   12845篇
  2000年   11877篇
  1999年   12605篇
  1998年   32826篇
  1997年   22904篇
  1996年   17457篇
  1995年   13042篇
  1994年   11288篇
  1993年   10980篇
  1992年   7913篇
  1991年   7421篇
  1990年   7266篇
  1989年   7013篇
  1988年   6468篇
  1987年   5770篇
  1986年   5658篇
  1985年   6269篇
  1984年   5905篇
  1983年   5174篇
  1982年   4903篇
  1981年   4968篇
  1980年   4707篇
  1979年   4611篇
  1978年   4412篇
  1977年   5339篇
  1976年   6972篇
  1975年   3801篇
  1974年   3551篇
  1973年   3665篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Serum total cholesterol, high density lipoprotein (HDL) cholesterol, and triglyceride levels were studied in healthy male and female subjects consuming for one-week periods a diet of conventional food (CF) providing 42% of energy as fat, principally butter fat, and then in random order nutritionally complete, defined formula diets of moderate (32%) to very low (1%) fat content. Compared to CF, the formula with 32% of energy as corn oil lowered serum cholesterol by 25% and the ratio of total to HDL-cholesterol by 13%. Low (9%) and very low (1–3%) fat formulas reduced HDL-cholesterol by as much as 40%, raised the total: HDL-cholesterol ratio by about 20% and raised serum triglyceride levels by as much as 100%. When low and very low fat formulas were ingested for three weeks, these effects persisted although maximal responses occurred during the first week. These results demonstrated that a moderate fat formula diet with a high P/S ratio had a more favorable effect on serum lipid levels than various low fat formulas. Low fat conventional food diets should be studied in long-term controlled metabolic experiments before such diets are recommended to the general population for coronary heart disease or cancer prevention.  相似文献   
112.
113.
Increased wetting of the coupling agent/epoxy resin interface was observed when γ-glycidoxypropyltrimethoxysilane, polyfunctional aminosilane and γ-aminopropyltriethoxysilane were applied respectively from methyllethylketone, dimethylformamide and water on woven glass cloths which had been cleaned at 300°C. However, when factory-applied coupling agents were burnt off the woven cloths and fresh coupling agents re-applied, it was found that the nature of the factory-applied coupling agent influenced subsequent wetting. Thinner glass fibres showed a greater improvement in wetting rate than thicker fibres in those solvents identified to be good for improved wettability, irrespective of the heat-cleaning temperature.  相似文献   
114.
Summary The equilibrium water contents of linear poly(acrylic acid) sodium salts with different degrees of neutralisation were found to be dependent on temperature and relative humidity. An octahedral model for the primary hydration of poly(acrylic acid) sodium salts (HIRAOKA and YOKOYAMA 1980) was critically evaluated in the light of these findings and an anomaly in the water uptake versus neutralisation curve at approximately 33% neutralisation was explained by the counterion condensation theory. (MANNING 1979).  相似文献   
115.
Site planning and economic forecasting for MRI require careful, individualized analysis of several possible sites. Particular attention should be accorded to the magnetic environment. Realistic estimates of financial feasibility will depend heavily on decisions of regulators and third-party payers.  相似文献   
116.
117.
Depending on the spectal width of the source illuminating an interferometer, measurement procedures can utilize either the whole interferogram, or only the fringe envelope, or only the fringe quick oscillations. With an ultraband spectrum source, a simplified adaptation of the methods of Fourier transform spectroscopy yields the variations of the test-fiber propagation constant over the whole wavelength-interval of the source. Chromatic dispersion can then be computed from a single interferogram. With narrower spectrum sources, only the fringe envelopes are utilized and yield measurements of mode delay, with application to chromatic and polarization mode dispersion. In this case, however, interferograms at several wavelengths are necessary. With even narrower spectrum sources, the fringe quick oscillations provide measurements of phase shifts, related to changes in the mode propagation constant, when outside perturbations are applied to the test fiber. A direct method for measuring the third-order nonlinear susceptibilities is discussed. In this case the outside perturbation is an intense pump laser field  相似文献   
118.
By using integral transform methods, an approach is developed to the solution of a problem on the temprature distribution in multilayer structures heated by cw scanning laser radiation, with phase transitions in the layers taken into account.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 6, pp. 1000–1010, December, 1987.  相似文献   
119.
The aim of this paper is the comparison of the axial flux (AF) structures versus the conventional radial flux (RF) structures for permanent-magnet synchronous motors. The comparison procedure is based on simple thermal considerations. Two motor typologies are chosen and compared in terms of delivered electromagnetic torque. The comparison is developed for different motor dimensions and the pole number influence is put into evidence. The paper reports the complete comparison procedure and the related results analysis. The obtained results show that, when the axial length is very short and the pole number is high, the AF motors can be an attractive alternative to the conventional RF solutions.  相似文献   
120.
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号