全文获取类型
收费全文 | 25588篇 |
免费 | 3356篇 |
国内免费 | 1202篇 |
专业分类
电工技术 | 821篇 |
综合类 | 1476篇 |
化学工业 | 5580篇 |
金属工艺 | 4609篇 |
机械仪表 | 1761篇 |
建筑科学 | 889篇 |
矿业工程 | 1020篇 |
能源动力 | 953篇 |
轻工业 | 1163篇 |
水利工程 | 281篇 |
石油天然气 | 744篇 |
武器工业 | 185篇 |
无线电 | 2344篇 |
一般工业技术 | 4861篇 |
冶金工业 | 2669篇 |
原子能技术 | 293篇 |
自动化技术 | 497篇 |
出版年
2024年 | 139篇 |
2023年 | 830篇 |
2022年 | 771篇 |
2021年 | 1056篇 |
2020年 | 1172篇 |
2019年 | 1131篇 |
2018年 | 897篇 |
2017年 | 1039篇 |
2016年 | 937篇 |
2015年 | 940篇 |
2014年 | 1355篇 |
2013年 | 1545篇 |
2012年 | 1597篇 |
2011年 | 1617篇 |
2010年 | 1168篇 |
2009年 | 1266篇 |
2008年 | 1130篇 |
2007年 | 1477篇 |
2006年 | 1449篇 |
2005年 | 1341篇 |
2004年 | 1054篇 |
2003年 | 1126篇 |
2002年 | 888篇 |
2001年 | 735篇 |
2000年 | 699篇 |
1999年 | 531篇 |
1998年 | 452篇 |
1997年 | 332篇 |
1996年 | 308篇 |
1995年 | 236篇 |
1994年 | 203篇 |
1993年 | 159篇 |
1992年 | 126篇 |
1991年 | 99篇 |
1990年 | 85篇 |
1989年 | 76篇 |
1988年 | 40篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 22篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
《分离科学与技术》2012,47(5):1164-1180
Abstract In this study water soluble complexible polymers, poly(vinyl pyrrolidone) (PVP) and dextran, were used for the ultrafiltration (UF) of aqueous Fe+3 solutions by using poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-MA) membranes. Effects of polymer concentration and pH on the volume collected in the filtration of Fe+3 solutions and percent retentions (R%) were examined. It was determined that increase in polymer concentration decreased the permeability of PMMA-co-MA membrane and pH increased the retention of Fe3+ solutions. R% for Fe3+ solutions were obtained as 62% and 48% with PVP and dextran respectively at pH 3.0, for a filtration period of 80 minutes and retention for Fe3+ solution without using any complex forming polymer was found as 14%. Membranes were characterized by AFM analysis and contact angle measurements. 相似文献
992.
《分离科学与技术》2012,47(11):2471-2490
Abstract Significant performance differences in the separation of desamido-insulin from insulin and of amitriptyline from imipramine have been found for five, macroscopically similar, preparative C18 silica materials. Structure-performance relations have been used to understand this difference. Physical measurements on the unpacked silica gels as well as chromatographic measurements have been carried out. The latter measurements comprise: hydrophobicity, metal impurity, steric selectivity and silanol activity. The performance difference could not be explained by the difference in hydrophobicity, steric selectivity or metal impurity between the materials. Instead a correlation between the silanol ion exchange activity and the selectivity could be found. The highest performance was found under conditions where the silanol groups have a moderate activity. For the separations considered in this work, the silanol groups have a beneficial effect. 相似文献
993.
《分离科学与技术》2012,47(16):2406-2412
A new sulfonamide containing polymeric sorbent for the removal of mercury ions from waste waters was prepared starting from poly(glycidyl methacrylate)-b-poly(ethylene glycol)-b-poly(glycidyl methacrylate) (PGMA- b -PEG- b -PGMA) triblock copolymer prepared by using the ATRP method. Epoxy groups on the block copolymer were functionalized with amino groups. Ammonia-functionalized PGMA- b -PEG- b -PGMA was treated with excess of benzenesulfonyl chloride to obtain a sulfonamide-based polymeric sorbent. The sulfonamide containing the polymeric sorbent with a 3.5 mmol · g?1 total nitrogen content is able to selectively sorb mercury from aqueous solutions. The mercury sorption capacity of the resin is around 3.12 mmol g?1 under non-buffered conditions. Experiments performed in identical conditions with several metal ions revealed that Cd(II), Pb(II), Zn(II), Fe(III), and Fe(II) also were extractable in quantities (0–0.45 mmol/g). The sorbed mercury can be eluted by repeated treatment with 4 M HNO3 without hydrolysis of the sulfonamide groups. 相似文献
994.
《分离科学与技术》2012,47(14):2963-2986
Abstract For the functional enhancement of chelating resins containing carboxylic acids, copolymer beads were prepared by suspension polymerization of styrene (St), methyl methacrylate (MMA), and divinylbenzene (DVB) in the presence of toluene as diluent. The phenyl rings of the beads were directly chloromethylated, and the carboxylic ester groups of the beads were converted into hydroxymethyl groups by reduction followed by chlorination to give chloromethyl groups, respectively. The chelating resins containing a pair of neighboring carboxylic acid groups (NCAGs) were obtained by the alkylation of chloromethyl groups in copolymer beads with diethyl malonate in the presence of sodium hydride followed by hydrolysis using aqueous alkali solution. Accordingly, the structural effects of the resins on the adsorption of heavy metal ions were investigated. Poly(St‐co‐DVB)‐based chelating resin containing NCAGs showed adsorption abilities toward heavy metal ions like Pb2+, Cd2+, and Cu2+, whereas poly(MMA‐co‐DVB)‐based chelating resin containing NCAGs showed adsorption abilities toward heavy metal ions like Cu2+, Cd2+, and Co2+. On the other hand, poly(St‐co‐MMA‐co‐DVB)‐based chelating resin containing NCAGs showed adsorption abilities toward heavy metal ions like Pb2+, Cd2+, Hg2+, Co2+, and Cu2+: a synergistic effect on the adsorption of heavy metal ions like Pb2+, Cd2+, Hg2+, and Co2+ was observed. The adsorption ability of poly(St‐co‐MMA‐co‐DVB)‐based chelating resin among three kinds of chelating resins was relatively good. 相似文献
995.
《分离科学与技术》2012,47(15):3167-3185
Abstract Molecular recognition based separation systems have received much attention because of their high selectivity for target molecules. Molecular imprinting has been recognized as a promising technique for the development of affinity adsorbents. Molecularly imprinted polymers (MIP) are easy to prepare, stable, inexpensive, and capable of molecular recognition. Cadmium is a carcinogenic and mutagenic element. The limit value of cadmium in blood should be no higher than 50 pg/L when exposure to cadmium is unavoidable in industry. There is no specific treatment available for acute or chronic metal poisoning. Besides supportive therapy and hemodialysis, metal poisoning is often treated with commercially available chelating agents including EDTA and dimercaprol. However, there is histopathological evidence for increased toxicity in animals when these agents are utilized. The aim of this study is to prepare superporous ion‐imprinted polymer monolith which can be used for the selective removal of Cd2+ ions from Cd2+‐overdosed human plasma. N‐methacryloly‐(L)‐cysteinemethylester (MAC) was chosen as the complexing monomer. In the first step, MAC synthesized by using methacryloyl chloride and cysteine. Cd2+ was complexed with MAC monomer and the Cd2+‐imprinted poly(HEMA‐MAC) monoliths were synthesized by bulk polymerization. After that, Cd2+ ions were removed by 0.1 M thiourea and 0.1 M HNO3 solutions, respectively. Cd2+‐imprinted poly(HEMA‐MAC) monoliths had a specific surface area of 226.8 m2/g and the swelling ratio was determined to be 76%. According to the elemental analysis results, monoliths contain approximately 58.3 µmol/g of MAC. The maximum adsorption capacity for Cd2+ ions was 26.6 µmol/g of the dry weight of monolith. The adsorption capacity decreased significantly from 23.25 µmol/g to 3.08 µmol/g polymer with the increase of the flow‐rate from 1 mL/min to 4 mL/min. The Cd2+‐imprinted poly(HEMA‐MAC) monolith could be used many times without decreasing their adsorption capacities significantly. 相似文献
996.
《分离科学与技术》2012,47(5):819-828
Abstract Nuclear fuel can be purged, that is metal impurities can be extracted from the uranium hexafluoride, by feeding an additional component, a kind of Freon, C6F12, which is chemically stable with respect to uranium hexafluoride, into the centrifuge purge cascade. The metal impurities are then continuously withdrawn from the purge cascade as a result of the additional feed. Centrifuges can not be easily used for the purge process without the Freon because the amount of metal impurities in the nuclear fuel is usually very small, thus the flow of impurities withdrawn from the product end of the purge cascade needs to be periodically closed down to minimize the loss of uranium hexafluoride. This results in the accumulation of light impurities such as air and HF in stages near the product end of the purge cascade. These light impurities inside the centrifuges may reduce the working effectiveness of the centrifuges or even put them out of service. The additional Freon eliminates this problem, because the light gas can be extracted from the cascade as soon as it reaches the product end of the cascade. Numerical calculations using a typical metal impurity CrO2F2 illustrate the effect of the additional Freon feed in the purge process. 相似文献
997.
《分离科学与技术》2012,47(14):3243-3257
Abstract Synthetic procedures for new mixed‐donor macrocycle compounds were reported. The macrocyclic compounds were used in solvent extraction metal picrates such as Ag+, Hg2+, Cd2+, Zn2+, Cu2+, Ni2+, Mn2+, Pb2+, and Co2+. The metal picrate extractions were investigated at 25±0.1°C with the aid of UV‐visible spectrometry. It was found that 6,7,9,10,12,13,23,24‐octahydro‐19H,26Hdibenzo[h,t](1,4,7,13,16,22,10,19) dioxatetrathiadiazasiclotetracosine‐20,27(21H,28H)‐dione showed selectivity towards Ag+, Hg2+, and Cd2+ among the other metals. The extraction constants (Log Kex) and complex compositions were determined for the Ag+ and Hg2+ complexes for this compound and 9,10,12,13,23,24,26,27,29,30‐decahydro‐5H,15H‐dibenzo‐[h,w][1,4,7,13,16,19,25‐,10,22] dioxapentathiadiazacycloheptacosine‐6,16(7H,17H)‐dione. 相似文献
998.
999.
1000.
粉煤灰处理含重金属废水试验研究 总被引:14,自引:0,他引:14
本文比较了粉煤灰及酸活化粉煤灰处理重金属离子的性能 ,着重探讨了酸活化粉煤灰去除工业电镀废水中重金属离子铬、铅、铜、镉的适宜条件 ,经处理后的废水可达到排放标准。同时提出了一套成功的粉煤灰活化工艺 ,具有较好的社会效益和经济效益。 相似文献