全文获取类型
收费全文 | 18764篇 |
免费 | 528篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 251篇 |
综合类 | 9篇 |
化学工业 | 3639篇 |
金属工艺 | 303篇 |
机械仪表 | 363篇 |
建筑科学 | 1160篇 |
矿业工程 | 111篇 |
能源动力 | 527篇 |
轻工业 | 1438篇 |
水利工程 | 159篇 |
石油天然气 | 195篇 |
武器工业 | 1篇 |
无线电 | 1125篇 |
一般工业技术 | 2951篇 |
冶金工业 | 4398篇 |
原子能技术 | 170篇 |
自动化技术 | 2513篇 |
出版年
2022年 | 143篇 |
2021年 | 222篇 |
2020年 | 171篇 |
2019年 | 232篇 |
2018年 | 273篇 |
2017年 | 268篇 |
2016年 | 326篇 |
2015年 | 243篇 |
2014年 | 398篇 |
2013年 | 1124篇 |
2012年 | 681篇 |
2011年 | 892篇 |
2010年 | 698篇 |
2009年 | 689篇 |
2008年 | 879篇 |
2007年 | 893篇 |
2006年 | 711篇 |
2005年 | 734篇 |
2004年 | 576篇 |
2003年 | 586篇 |
2002年 | 528篇 |
2001年 | 340篇 |
2000年 | 312篇 |
1999年 | 326篇 |
1998年 | 354篇 |
1997年 | 327篇 |
1996年 | 325篇 |
1995年 | 348篇 |
1994年 | 288篇 |
1993年 | 327篇 |
1992年 | 274篇 |
1991年 | 171篇 |
1990年 | 245篇 |
1989年 | 293篇 |
1988年 | 213篇 |
1987年 | 227篇 |
1986年 | 219篇 |
1985年 | 273篇 |
1984年 | 273篇 |
1983年 | 236篇 |
1982年 | 232篇 |
1981年 | 223篇 |
1980年 | 182篇 |
1979年 | 200篇 |
1978年 | 183篇 |
1977年 | 197篇 |
1976年 | 165篇 |
1975年 | 184篇 |
1974年 | 175篇 |
1973年 | 138篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
A method for measuring the unperturbed radius of gyration and the degree of long-chain branching in Gaussian-distribution polymers is proposed. Polyvinyl chloride (PVC) and polyvinyl acetate (PVAc) were selected to illustrate the method. It was observed that PVC samples prepared by homogeneous and heterogeneous polymerizations exhibit the same degree of long-chain branching. This conclusion is supported by viscometric data. The polydispersity ratios (Mw/Mn) indicate that both types of polymerizations would yield a very small amount of total branching (long chain and short chain.) The calculated unperturbed radius of gyration of linear PVC samples was found to be 0.185 \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {\frac{{{\rm \dot A}^{\rm 2} {\rm mole}}}{{{\rm gm}}}} \right) $\end{document}, and that of PVAc was determined to be 0.107 \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {\frac{{{\rm \dot A}^{\rm 2} {\rm mole}}}{{{\rm gm}}}} \right) $\end{document}. The value obtained for PVC is shown to be in agreement with the value determined from the viscometric method as described in our previous work. 相似文献
982.
983.
984.
985.
Watson Charles G.; Thomas Richard W.; Anderson Dennis; Felling James 《Canadian Metallurgical Quarterly》1968,32(6):679
Attempted to determine whether the Reitan-Halstead Organic Test Battery separates neuropsychiatric hospital organics from schizophrenics. It was administered to 25 schizophrenics and 25 cerebral-lesion organics at each of 2 chronicity levels. Only 1 of the 24 diagnosis/diagnosis * chronicity effects used to evaluate the data was significant at the .05 level, indicating that actuarial application of Reitan-Halstead scores is of no practical value in the separation of the 2 groups. To determine whether expert clinicians might improve upon the actuarial results, protocols of 24 schizophrenics and 24 organics were sent to 8 Reitan-Halstead experts who were instructed to separate them into brain-damaged and schizophrenic diagnostic groups. The mean number of correct classifications, 25.5 out of 48 suggested that clinical judgment added nothing to actuarial prediction in this case. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
986.
A hybrid process, which simultaneously produces mechanical power and hydrogen and oxygen from water by the use of solar energy, is presented. The performance of the process is evaluated. Realistic constraints on the efficiencies of optical and mechanical components are used. A preliminary estimate of its economics is also presented. 相似文献
987.
Wang James R. Newton Richard W. Rouse John W. 《Geoscience and Remote Sensing, IEEE Transactions on》1980,(4):296-302
The tilled row structure is known to be one of the important factors affecting the observations of the microwave emission from a natural surface. Measurements of this effect were carried out with both L-and X-band radiometers mounted on a mobile truck on a bare 40 m × 45 m row tilled field. The soil moisture content during the measurements ranged from ~10 to ~30 percent by dry weight. The results of these measurements showed that the variations of the antenna temperatures with incident angle ? changed with the azimuthal angle ? measured from the row direction. In particular, at ? = 0° and ? ? 45°, the observed horizontally and vertically polarized antenna temperatures, TBH(?, ?) and TBV(?, ?), were not equal. In general, TBH(?°, ?) > TBV(?°, ?) when 0° ? ? < 45° and TBH(?°, ?) < TBV(0°, ?) when 45° < ? ? 90°. The difference between TBH(0°, ?) and TBV(0°, ?) was observed to decrease with ? approaching 45° and/or with soil moisture content. A numerical calculation based on a composite surface roughness-a small-scale RMS height variations superimposed on a large periodic row structure-was made and found to predict the observed features within the model's limit of accuracy. It was concluded that the difference between TBV(0°, ?) and TBH(0°, ?) was due to the change in the local angle of field emission within the antenna field of view caused by the large-scale row structure. 相似文献
988.
ADSORPTION OF ORGANICS FROM A TRUE IN-SITU OIL SHALE RETORT WATER ON ACTIVATED CARBON IN PACKED BEDS
Enayat Pedram Anthony L. Hines Richard E. Poulson David O. Cooney 《Chemical Engineering Communications》1982,15(5):291-304
The adsorption of a true in-situ oil shale retort water on activated carbon at 278 and 298 K was studied in batch experiments and in packed beds with continuous liquid flow. The isotherms were nonlinear over the liquid concentration 0 to 875 mg/1. Breakthrough curves were obtained in packed bed experiments as a function of bed length, particle size, and liquid velocity. A differential approach was used to calculate the mass transfer coefficients and the rates of adsorption. Also the breakthrough curves were analyzed to establish the relative importance of the various individual mechanisms that contributed to the overall adsorption process. 相似文献
989.
After being separated from their mothers, 48 Ss (20–30 mo old) were given either an unrecognizable or a sharply focused photograph of their mother to carry with them in an unfamiliar playroom. A female escort either correctly identified the photograph for the Ss, mislabeled it as a picture of a stranger, or gave it no verbal label. Ss with a clear photograph played, explored, and remained in the playroom longer than those presented with a blurred image. They also held, looked at, and spontaneously named the picture more. The verbal labels exerted no effects on separation behaviors or on responses directed toward the photographs. Results indicate that visual perception alone can suffice to provide Ss as young as 20 mo with some of the functional properties of their mother. (71 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
990.
Historically food has been produced by using solar energy, natural fertilizer and manual labor. However, as populations have increased food products had to be increased proportionately so it has become necessary to use industrial equipment instead of manual labor and artificial fertilizer in place of manure. Thus, in modern agriculture, fuel energy has largely replaced animate energy. This has made the food delivery system one of the most energy intensive industries. It is apparent that this demand for energy will increase because the world population is expected to double by the end of the century and hence will require rapid increases in food production.This paper sets forth the energy supply and demand situation as it concerns food production. Also, considered are externalities such as climate and population. Finally, an agenda for future research in the energy-food sector is presented. 相似文献