全文获取类型
收费全文 | 286864篇 |
免费 | 5553篇 |
国内免费 | 2021篇 |
专业分类
电工技术 | 6385篇 |
综合类 | 2134篇 |
化学工业 | 42238篇 |
金属工艺 | 11092篇 |
机械仪表 | 9485篇 |
建筑科学 | 9153篇 |
矿业工程 | 1500篇 |
能源动力 | 8321篇 |
轻工业 | 23262篇 |
水利工程 | 2695篇 |
石油天然气 | 5073篇 |
武器工业 | 225篇 |
无线电 | 38482篇 |
一般工业技术 | 54458篇 |
冶金工业 | 50323篇 |
原子能技术 | 5545篇 |
自动化技术 | 24067篇 |
出版年
2022年 | 2299篇 |
2021年 | 3469篇 |
2020年 | 2639篇 |
2019年 | 2664篇 |
2018年 | 4099篇 |
2017年 | 4284篇 |
2016年 | 4291篇 |
2015年 | 3356篇 |
2014年 | 5424篇 |
2013年 | 13345篇 |
2012年 | 8185篇 |
2011年 | 10688篇 |
2010年 | 8684篇 |
2009年 | 9648篇 |
2008年 | 10116篇 |
2007年 | 10003篇 |
2006年 | 9118篇 |
2005年 | 8072篇 |
2004年 | 7365篇 |
2003年 | 7523篇 |
2002年 | 6993篇 |
2001年 | 7311篇 |
2000年 | 6870篇 |
1999年 | 7357篇 |
1998年 | 17416篇 |
1997年 | 12186篇 |
1996年 | 9563篇 |
1995年 | 7243篇 |
1994年 | 6397篇 |
1993年 | 6288篇 |
1992年 | 4441篇 |
1991年 | 4249篇 |
1990年 | 4093篇 |
1989年 | 3810篇 |
1988年 | 3699篇 |
1987年 | 3114篇 |
1986年 | 3018篇 |
1985年 | 3262篇 |
1984年 | 2972篇 |
1983年 | 2863篇 |
1982年 | 2668篇 |
1981年 | 2561篇 |
1980年 | 2487篇 |
1979年 | 2314篇 |
1978年 | 2114篇 |
1977年 | 2613篇 |
1976年 | 3573篇 |
1975年 | 1769篇 |
1974年 | 1735篇 |
1973年 | 1673篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
1.概况(见区域位置图)
鹿回头半岛位于海南省三亚市,半岛至三亚凤凰国际机场距离为20km左右,约20分钟车程,至市区距离则为3km左右,半岛西面为三亚湾,东面为小东海,面面为鹿回头公园,北面为南山岭,占据三亚市内独特的地理位置,具有得天独厚的风景资源,与市区交流联系便捷。 相似文献
102.
The bioaccumulation potentials by aquatic biota from aqueous solution were determined for seven polycyclic aromatic hydrocarbons (PAH). The PAH were tested usingDaphnia pulex and consisted of the following compounds: naphthalene, anthracene, phenanthrene, pyrene, 9-methylanthracene, benz(a)anthracene and perylene. Bioaccumulation kinetics were described as a first order approach to equilibrium in a two-compartment model (water and Daphnia), using a two-stage technique to estimate uptake and elimination rates, while accounting for decreasing aqueous concentrations. Estimates of equilibrium concentration factors were obtained by two methods: (1) evaluating the kinetic model as t tends to infinity and (2) direct measurement of concentration factor at t =24 h.Estimations of equilibrium concentration factors obtained by the two methods were in good agreement, and increased dramatically with increasing molecular weight within the series of compounds. The calculated n-octanol-water partition coefficient was shown to be a good predictor of bioaccumulation potential of PAH in Daphnia. PAH were concentrated from a high of about 10,000-fold for benz(a)anthracene to a low of about 100-fold for naphthalene. 相似文献
103.
K. Weber 《Water research》1976,10(3):237-241
The decomposition of parathion (O,O-diethyl-O-p-nitrophenylthiophosphate) in seawater has been followed in the laboratory. The influence of temperature, pH, salinity, and particulate matter on the degradation time and products is shown. Chemical hydrolysis as well as biodegradation occurred. The ratio of the two depends on the pretreatment of the water. During chemical hydrolysis dearylation and dealkylation occur. Biodegradation was observed through the disappearance of the organic nitro compounds. Among the degradation products dealkylated parathion was found to be stable against further hydrolysis and microbial degradation under environmental conditions. 相似文献
104.
Guseva T. V. Tikhonova I. O. Tsevelev V. N. Shchelchkov K. A. Averochkin E. M. 《Glass and Ceramics》2022,78(9):397-401
Glass and Ceramics - A system for technological regulation of adverse environmental impacts (AEI) that is based on the best available technologies (BAT) was analyzed. The expediency of updating the... 相似文献
105.
Pyatigor A. D. Myshelovka L. V. Vokhmyanina K. A. Sotnikova V. S. Kubankina A. A. Grigor’ev Yu. V. 《Glass and Ceramics》2022,79(1-2):62-64
Glass and Ceramics - The results of experimental studies of the transmission of 12 and 15 keV electron beams through tapered glass macro-capillaries are presented. Measurements showed that there is... 相似文献
106.
107.
Composites comprising Poly(Methyl Methacrylate) (PMMA) and CaCu3Ti4O12 (CCTO) via melt mixing followed by hot pressing were fabricated. These were characterized using X‐ray diffraction, thermo gravimetric, scanning electron microscopy, and Impedance analyzer for their structural, morphology, and dielectric properties. Composites were found to have better thermal stability than that of pure PMMA. The composite, with 38 Vol % of CCTO (in PMMA), exhibited remarkably low dielectric loss at high frequencies and the low frequency relaxation is attributed to the space charge polarization/MWS effect. Theoretical models were employed to rationalize the dielectric behavior of these composites. At higher temperatures, the relaxation peak shifts to higher frequencies, due to the merging of both β and α relaxations into a single dielectric dispersion peak. The AC conductivity in the high frequency region was attributed to the electronic polarization. POLYM. ENG. SCI., 54:551–558, 2014. © 2013 Society of Plastics Engineers 相似文献
108.
The three‐dimensional trajectories of polymer solution jets during the electrospinning of polymer nanofibers were experimentally investigated. Test conditions included water solutions of polyethylene oxide (PEO) with concentrations typical of those producing beaded nanofibers, driving voltages ranging from 5 kV to 15 kV to generate a single polymer jet and injection pressures ranging from 0 kPa to 55 kPa. The present holographic imaging setup resolved the spatial growth of the bending instabilities, which is beneficial for validating numerical models. The results also showed the bead formation on the polymer fiber in‐flight. POLYM. ENG. SCI., 54:1765–1773, 2014. © 2013 Society of Plastics Engineers 相似文献
109.
Lu Shen Jianming Xue Michel W. Barsoum Qing Huang 《Journal of the American Ceramic Society》2014,97(12):3721-3724
Inspired by pressure resistance welding of metallic materials, herein we describe how two MAX phases—Ti3SiC2 and Ti3AlC2—were successfully joined by a rapid electric current heating method in a pulsed electric current sintering furnace. No welding agent was employed and the total processing time was less than 6 min. When the bulk temperature of the joint couple exceeded 1070°C, good joints, with shear strength above 50 MPa, were achieved in both homo‐ and heterojunction joints. 相似文献
110.