全文获取类型
收费全文 | 1083篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
综合类 | 1篇 |
化学工业 | 28篇 |
金属工艺 | 5篇 |
机械仪表 | 4篇 |
建筑科学 | 28篇 |
能源动力 | 7篇 |
轻工业 | 18篇 |
石油天然气 | 2篇 |
无线电 | 21篇 |
一般工业技术 | 41篇 |
冶金工业 | 892篇 |
原子能技术 | 25篇 |
自动化技术 | 12篇 |
出版年
2022年 | 2篇 |
2020年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 18篇 |
2012年 | 5篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 13篇 |
2007年 | 4篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 39篇 |
1998年 | 261篇 |
1997年 | 168篇 |
1996年 | 97篇 |
1995年 | 73篇 |
1994年 | 56篇 |
1993年 | 49篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 12篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1978年 | 3篇 |
1977年 | 23篇 |
1976年 | 53篇 |
1975年 | 4篇 |
1972年 | 3篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1086条查询结果,搜索用时 15 毫秒
21.
Reaching the goals moving with different speed (from 1 to 400 mm/sec), the chimpanzee revealed respective behavioural, emotional, instrumental, and cardiovascular responses. When obscuring the goal for a certain time, the chimpanzee nevertheless managed to reach it, the relations between the speed of approaching goal and behavioural or instrumental responses being preserved. Thereupon, the chimpanzee are able to reach the goal provided the latter's trace exceeds 5-10-fold the time of really acting stimulus. 相似文献
22.
23.
CG Campbell EC Titgemeyer RC Cochran TG Nagaraja RT Brandt 《Canadian Metallurgical Quarterly》1997,75(4):1167-1178
Three studies were conducted to evaluate amino acid utilization by cattle. In Exp. 1, five steers (580 kg) were fed 86% rolled corn diets with mixtures of amino acids containing up to 6 g/d DL-Met, 24 g/d L-Lys, 6 g/d L-Thr, and 3 g/d L-Trp. Treatments had little effect on ruminal fermentation, diet digestibility, N flow to the duodenum, or microbial efficiency. Ruminal concentrations of Met and Lys increased linearly (P < .05) with amino acid supplementation, whereas Thr responded quadratically, and Trp was not altered. In Exp. 2, four steers (414 kg) were used to measure effects of dietary monensin or laidlomycin propionate in high-grain diets supplemented with amino acids. Ionophores had no significant effect on ruminal fermentation or outflows of amino acids from the rumen. In Exp. 3, 100 steers (287 kg initial BW) were fed diets containing 1% of a nonprotein N source. Treatments were 1) no supplemental N (UREA), 2) UREA plus soybean meal (SBM), 3) UREA plus 2 g/d DL-Met, 8 g/d L-Lys, 2 g/d L-Thr, and 1 g/d L-Trp, or 4) UREA plus 4 g/d DL-Met, 16 g/d L-Lys, 4 g/d L-Thr, and 2 g/d L-Trp. During the growing period (diets based on whole-plant milo silage), gains were higher for SBM-supplemented steers than for UREA steers and intermediate for steers supplemented with amino acids. Few significant differences in performance were observed among treatments during the finishing phase (diets based on dry-rolled corn) or for the entire experiment, but cattle fed SBM or amino acids tended to be fatter and have better marbling scores and quality grades. Amino acids did not greatly alter ruminal fermentation or cattle performance. 相似文献
24.
Moser DP Fredrickson JK Geist DR Arntzen EV Peacock AD Li SM Spadoni T McKinley JP 《Environmental science & technology》2003,37(22):5127-5134
Biogeochemical processes within riverbed hyporheic zones (HZ) can potentially impact the fate and transport of contaminants. We evaluated a modified freeze core technique for the collection of intact cobble-bed samples from the Columbia River HZ along a stretch of the Hanford Reach in Washington State and investigated microbiological and geochemical parameters of corresponding frozen and unfrozen samples. During three sampling periods (March, May, and November 2000), relatively high numbers of viable aerobic heterotrophic bacteria were recovered from both unfrozen (10(6)-10(7) cfu/g) and frozen samples (10(5)-10(6) cfu/g). Relatively large populations of sulfate-, nitrate-, and iron-reducing bacteria were present, and significant concentrations of acid-volatile sulfide were measured in some samples, indicating that anoxic regions exist within this zone. Cr(VI), a priority groundwater pollutant on adjacent U.S. Department of Energy lands, was probably removed from solution in HZ samples by a combination of microbial activity and chemical reduction, presumably via products of anaerobic microbial metabolism. These results suggest that biogeochemical processes in the Columbia River HZ may contribute to the natural attenuation of Cr(VI). Although freezing modestly diminished recovery of viable bacteria, freeze core techniques proved reliable for the collection of intact hyporheic sediments. 相似文献
25.
Summary Raman LAM and internal mode studies have been made on crystals of linear polyethylene formed in dilute solution. The molecular weight range, 5×104–1.5×106, was much greater than has been studied heretofore. The crystallite core thickness and degree of crystallinity was found to be independent of molecular weight for a given crystallization mode. The internal mode analysis indicates a substantial disordered overlayer, which is primarily isotropic in character. 相似文献
26.
The X-ray photographs of fresh never-dried cotton fibers are compared with those of dried fibers. The crystallite size of never-dried cotton fibers shows no significant correlation with maturity and orientation and is about the same as those of dried cotton fibers. 相似文献
27.
The cermet fuel (U3 O8 dispersed in Al) being considered for use in the Savannah River Site Reactors is thermodynamically unstable because of the potential for an exothermic metallothermic reduction reaction. This paper describes work performed to quantify the extent of reaction during powder metallurgy (P/M) processing of the U3 O8 —Al cermet fuel, and to determine the effect of partial reduction to U4 O9 on the metallothermic reduction reaction. During the fabrication of the U3 O8 —Al cermet fuel by the P/M technique, a significant portion of the U3 O8 is reduced to U4 O9 . The reaction between U4 O9 and Al is also exothermic; however, the maximum heat released by the reaction is substantially less than that released for the U3 O8 —Al reaction, approximately 335 J (80 cal) per gram of oxide reacted compared to 940 J (225 cal). Metallothermic reduction reactions for U3 O8 /U4 O9 /Al mixtures do not occur at the normal reactor operating temperature, ∼ 370 K (∼ 100°C) or at temperatures below the melting point of aluminum, 930 K (660°C). 相似文献
28.
Speciation of arsenic, chromium, and vanadium in red mud samples from the Ajka spill site, Hungary 总被引:1,自引:0,他引:1
Burke IT Mayes WM Peacock CL Brown AP Jarvis AP Gruiz K 《Environmental science & technology》2012,46(6):3085-3092
Results are presented from X-ray absorption spectroscopy based analysis of As, Cr, and V speciation within samples of bauxite ore processing residue (red mud) collected from the spill site at Ajka, Western Hungary. Cr K-edge XANES analysis found that Cr is present as Cr(3+) substituted into hematite, consistent with TEM analysis. V K-edge XANES spectra have E(1/2) position and pre-edge features consistent with the presence of V(5+) species, possibly associated with Ca-aluminosilicate phases. As K-edge XANES spectra identified As present as As(5+). EXAFS analysis reveals arsenate phases in red mud samples. When alkaline leachate from the spill site is neutralized with HCl, 94% As and 71% V are removed from solution during the formation of amorphous Al-oxyhydroxide. EXAFS analysis of As in this precipitate reveals the presence of arsenate Al-oxyhydroxide surface complexes. These results suggest that in the circumneutral pH, oxic conditions found in the Torna and Upper Marcal catchments, incorporation and sorption, respectively, will restrict the environmental mobility of Cr and As. V is inefficiently removed from solution by neutralization, therefore, the red mud may act as a source of mobile V(5+) where the red mud deposits are not removed from affected land. 相似文献
29.