全文获取类型
收费全文 | 296830篇 |
免费 | 3927篇 |
国内免费 | 1028篇 |
专业分类
电工技术 | 5420篇 |
综合类 | 409篇 |
化学工业 | 47438篇 |
金属工艺 | 12213篇 |
机械仪表 | 9035篇 |
建筑科学 | 7347篇 |
矿业工程 | 1950篇 |
能源动力 | 7114篇 |
轻工业 | 27138篇 |
水利工程 | 3318篇 |
石油天然气 | 7252篇 |
武器工业 | 29篇 |
无线电 | 32257篇 |
一般工业技术 | 58573篇 |
冶金工业 | 51541篇 |
原子能技术 | 7611篇 |
自动化技术 | 23140篇 |
出版年
2021年 | 2567篇 |
2019年 | 2284篇 |
2018年 | 4134篇 |
2017年 | 4103篇 |
2016年 | 4416篇 |
2015年 | 2863篇 |
2014年 | 4762篇 |
2013年 | 12909篇 |
2012年 | 7480篇 |
2011年 | 9861篇 |
2010年 | 8148篇 |
2009年 | 9205篇 |
2008年 | 9403篇 |
2007年 | 9235篇 |
2006年 | 8162篇 |
2005年 | 7550篇 |
2004年 | 7009篇 |
2003年 | 6721篇 |
2002年 | 6804篇 |
2001年 | 6596篇 |
2000年 | 6271篇 |
1999年 | 6297篇 |
1998年 | 14806篇 |
1997年 | 11083篇 |
1996年 | 8623篇 |
1995年 | 6562篇 |
1994年 | 5955篇 |
1993年 | 5817篇 |
1992年 | 4504篇 |
1991年 | 4460篇 |
1990年 | 4296篇 |
1989年 | 4317篇 |
1988年 | 4266篇 |
1987年 | 3604篇 |
1986年 | 3604篇 |
1985年 | 4186篇 |
1984年 | 3979篇 |
1983年 | 3634篇 |
1982年 | 3439篇 |
1981年 | 3574篇 |
1980年 | 3430篇 |
1979年 | 3379篇 |
1978年 | 3457篇 |
1977年 | 3931篇 |
1976年 | 5045篇 |
1975年 | 3162篇 |
1974年 | 3020篇 |
1973年 | 3030篇 |
1972年 | 2655篇 |
1971年 | 2475篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
More than one hundred samples of European beers have been investigated by the new SNIF-NMR method which is based on 2H NMR at the natural abundance level and enables site-specific natural isotope fractionation factors in ethanol to be determined. The relative (R) and absolute (D/H)i, parameters are shown to be characteristic of the country where the beers are brewed and the observed variations are explained in terms of cereal composition, water resource, and manufacturing processing (fermentation, yeast, temperature cycle). These new parameters find analytical and mechanistic applications in the identification of a beer and in the investigation of a fermentation process. 相似文献
993.
994.
To monitor the use of synthetic growth promoting hormones in red meat animals requires a sensitive and rapid method of analysis. This paper describes the development of such a method for these agents in bile, based on a high pressure liquid chromatographic purification procedure with detection and estimation by radioimmunoassay. 相似文献
995.
Two pairs of expanded granular sludge bed (EGSB) bioreactors, R1/R2 and R3/R4, were designed. R1/R2 were used for mesophilic (37 degrees C) treatment of synthetic wastewater over a 100-day trial. A successful start-up was achieved by R1 and R2, with COD removal over 90%. Both reactors were operated under identical parameters; however, increased organic loading induced a reduction in COD removal by R1, while R2 maintained satisfactory performance throughout the experiment. R3/R4 were operated at 15 degrees C throughout a 422-day trial and were used for the stabilisation of volatile fatty acid-based wastewater. Phenol was introduced to R4 at an applied loading rate of 1 kg phenol m(-3)d(-1), which was increased to 2 kg phenol m(-3)d(-1). No phenol was supplied to R3. Efficient COD conversion was recorded in both R3 and R4, thus demonstrating the feasibility of high-rate phenol degradation under psychrophilic conditions. Terminal restriction fragment length polymorphism analysis was applied to the characterisation of microbial community dynamics within each of the reactors. The results indicated a microbiological basis for the deviation, in terms of operational performance, of R1 and R2. TRFLP analyses indicated stable microbial communities in R3 and R4, but detected changes in the abundance of specific ribotypes in response to phenol mineralisation. 相似文献
996.
997.
James M. Watkins Ronald Dermott Stephen J. Lozano Edward L. Mills Lars G. Rudstam Jill V. Scharold 《Journal of Great Lakes research》2007,33(3):642-657
The status of invasive dreissenid mussels (Dreissena polymorpha and D. bugensis) and native amphipods (Diporeia spp.) in Lake Ontario was assessed in 2003 and compared with historical data. D. polymorpha (zebra mussels) were rarely observed in 2003, having been displaced by D. bugensis (quagga mussels). D. bugensis expanded its depth range from 38 m depth in 1995 to 174 m in 2003 and this dreissenid reached densities averaging 8,000/m2 at all sites < 90 m. During the same time period, Diporeia populations almost completely disappeared from 0–90 m depth, continuing a declining trend from 1994–1997 reported in previous studies. The average density of Diporeia in the 30–90 m depth interval decreased from 1,380/m2 to 63/m2 between 1997 and 2003. Prior to 2003, areas deeper than 90 m represented a refuge for Diporeia, but even these deep populations decreased, with densities declining from 2,181/m2 in 1999 to 545/m2 in 2003. Two common hypotheses for the decline of Diporeia in the Great Lakes are food limitation and a toxin/pathogen associated with dreissenid pseudofeces. The Diporeia decline in deep waters preceded the expansion of D. bugensis to these depths, and suggests that shallow dreissenid populations remotely influence profundal habitats. This pattern of decline is consistent with mechanisms that act from some distance including nearshore dreissenid grazing and downslope transport of pseudofeces. 相似文献
998.
I. V. Brusilovskii V. D. Vermel' V. V. Mitrofovich Yu. G. Moskovko 《Chemical and Petroleum Engineering》1992,28(3):159-161
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 3, pp. 8–9, March, 1992. 相似文献
999.
A probabilistic seismic hazard analysis, in conjunction with subsurface geologic investigations, was used to evaluate the liquefaction potential of sand layers at Western Area Power Adminstration's Tracy, California, substation site. The seismic hazard analysis evaluates the peak ground acceleration corresponding to a lower level earthquake with a 50-percent probability of occurrence in 150 years, and two upper level earthquakes with a 10-percent probability of occurrence in 50 and 100 years. Based on the results of the geologic investigations and seismologic studies, it was concluded that the potential of liquefaction at the site for the design earthquakes was low 相似文献
1000.