全文获取类型
收费全文 | 6499篇 |
免费 | 709篇 |
国内免费 | 242篇 |
专业分类
电工技术 | 112篇 |
综合类 | 472篇 |
化学工业 | 3666篇 |
金属工艺 | 268篇 |
机械仪表 | 36篇 |
建筑科学 | 322篇 |
矿业工程 | 287篇 |
能源动力 | 72篇 |
轻工业 | 576篇 |
水利工程 | 52篇 |
石油天然气 | 286篇 |
武器工业 | 12篇 |
无线电 | 186篇 |
一般工业技术 | 546篇 |
冶金工业 | 496篇 |
原子能技术 | 48篇 |
自动化技术 | 13篇 |
出版年
2024年 | 13篇 |
2023年 | 80篇 |
2022年 | 153篇 |
2021年 | 189篇 |
2020年 | 173篇 |
2019年 | 163篇 |
2018年 | 181篇 |
2017年 | 197篇 |
2016年 | 208篇 |
2015年 | 239篇 |
2014年 | 338篇 |
2013年 | 378篇 |
2012年 | 476篇 |
2011年 | 446篇 |
2010年 | 318篇 |
2009年 | 360篇 |
2008年 | 274篇 |
2007年 | 400篇 |
2006年 | 363篇 |
2005年 | 366篇 |
2004年 | 335篇 |
2003年 | 313篇 |
2002年 | 261篇 |
2001年 | 227篇 |
2000年 | 217篇 |
1999年 | 155篇 |
1998年 | 119篇 |
1997年 | 79篇 |
1996年 | 80篇 |
1995年 | 53篇 |
1994年 | 54篇 |
1993年 | 26篇 |
1992年 | 37篇 |
1991年 | 34篇 |
1990年 | 46篇 |
1989年 | 45篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1962年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有7450条查询结果,搜索用时 812 毫秒
41.
The impinging streams technology (abbreviated as IS) has good micromixing in the precipitation processes. The experiments were loaded with two reactants, BaCl2 and Na2SO4, to prepare BaSO4 in the impinging streams reactor, comparing with those in the direct precipitation (DP) reactor. XRD and TEM were used to analyze the crystal type, the morphology and size of particles through the photographs. The results indicate the size of the particles from IS is about 30 nm and of narrower distribution and finer dispersibility than that from DP. 相似文献
42.
60Si2Mn(A)弹簧钢的脱氧工艺 总被引:8,自引:3,他引:5
为了提高60Si2Mn(A)弹簧钢的质量,在LF精炼中进行了不同脱氧工艺的脱氧试验。结果表明:采用铝预脱氧、钡合金终脱氧及夹杂物变性脱氧工艺可使弹簧钢的氧含量降低到15×10-6以下,氧化物夹杂中Al2O3的比例小于40%。 相似文献
43.
Jantana Tangaromsuk Abhijeet P. Borole Maleeya Kruatrachue Prayad Pokethitiyook 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1375-1380
BACKGROUND: A single‐stage reactor, in which the growth of bacterial culture, induction of desulfurizing enzymes, and desulfurization reaction are carried out in a single step, was adopted to investigate desulfurization of dibenzothiophene (DBT) at high cell densities. Rhodococcus erythropolis, IGTS8 was used as the biocatalyst. Optimal conditions for bacterial growth and DBT desulfurization were investigated. RESULTS: Optimization of fermentation conditions was necessary to obtain high cell densities including controlling accumulation of acetate. Under optimal operating conditions, the maximum optical density at 600 nm (OD600) was measured to be 26.6 at 118 h of cultivation. When biodesulfurization of DBT in model oil with a high cell density culture of IGTS8 was investigated, accumulation of sulfate was found to limit the extent of desulfurization. A sulfate removal step was added to obtain a single‐stage integrated biodesulfurization process. Sulfate removal was achieved via an aqueous bleed stream and use of a separation unit to recycle the organic phase. CONCLUSION: A proof of principle of a complete system capable of biocatalyst growth, induction, desulfurization and by‐product separation was demonstrated. This system enables simplification of the biodesulfurization process and has potential to lower the operating cost of the bioprocess. Copyright © 2008 Society of Chemical Industry 相似文献
44.
用二氧化硫法处理贫软锰矿,得到含硫酸锰和连二硫酸锰的溶液,继而将该溶液进行净化,除杂,浓缩,结晶处理即得工业级硫酸锰,结晶母液用碳铵沉淀即得碳酸锰产品 相似文献
45.
The mechanisms governing the solubilizing interactions between zwitterionic/anionic mixed surfactant systems at different
molar fractions of the zwitterionic surfactant (Xzwitter) and neutral or electrically charged unilamellar liposomes were investigated. The mixed systems were formed by N-dodecyl-N,N-dimethylbetaine
and sodium dodecyl sulfate in the presence of piperazine-1,4-bis-(2-ethanesulfonic acid) buffer at pH 7.20. Unilamellar liposomes formed by egg phosphatidylcholine, in some cases together
with stearylamine or phosphatidic acid, were used. Solubilization was detected as a decrease in static light-scattering of
liposomes. Two parameters were regarded as corresponding to the effective surfactant/lipid molar ratios (Re) at which the
surfactant system (i) saturated the liposomes, Resat, and (ii) led to a total solubilization of liposomes, Resol. From these parameters the bilayer/aqueous medium surfactant partition coefficients for the saturation (Ksat) and complete bilayer solubilization (Ksol) were determined. When Xzwitter was 0.40, The Re and K parameters showed a maximum, whereas the critical micellar concentration (CMC) of these systems exhibited
a minimum, regardless of the electrical charge of bilayers. Given that the ability of the surfactant systems to saturate or
solubilize liposomes is inversely related to the Resat and Resol parameters, these capacities appear to be directly correlated with the CMC of the mixed systems. The similarity of both Ksat and Ksol (particularly for Xzwitter=0.2–0.8) suggests that a similar partition equilibrium governs both the saturation and the complete solubilization of bilayers,
the free surfactant concentration (Sa,Sb), remaining almost constant with similar values to the CMC for each mixed system studied. 相似文献
46.
为探讨硫酸盐含量对全固废材料固化盐渍土抗压强度及微观结构的影响,采用击实试验和无侧限抗压强度试验,并结合扫描电镜、EDS、X射线衍射和热重分析等微观测试结果,从固化盐渍土的火山灰反应产物及其数量等角度分析含盐量对固化盐渍土抗压强度变化的影响。结果表明:硫酸盐含量低于2.7%时,固化盐渍土抗压强度随含盐量的增加呈先增大后减小,抗压强度峰值对应的含盐量为1.8%;固化盐渍土的火山灰反应产物主要为C-S-H和AFt,硫酸盐含量从0.3%增至1.8%时,反应产物明显增多,致使固化土抗压强度增大;但当硫酸盐含量从1.8%增至2.7%时,膨胀性AFt将试件内部孔隙完全填充并产生胀裂破坏,造成抗压强度降低。研究成果为全固废材料固化硫酸盐渍土的工程应用奠定了基础,对环境保护也有积极贡献。 相似文献
47.
Kallwass Helmut K.W.; Surewicz Witold K.; Parris Wendy; Macfarlane Emma L.A.; Luyten Marcel A.; Kay Cyril M.; Gold Marvin; Jones J.Bryan 《Protein engineering, design & selection : PEDS》1992,5(8):769-774
Lactate dehydrogenases are of considerable interest as stereospecificcatalysts in the chemical preparation of enantiomerically pure-hydroxyacid synthons. For such applications in synthetic organicchemistry it would be desirable to have enzymes which tolerateelevated temperatures for prolonged reaction times, to increaseproductivity and to extend then applicability to poor substrates.Here, two examples are reported of significant thermostabilizations,induced by sitedirected mutagenesis, of an already thermostableprotein, the L-lactate dehydrogenase (EC 1.1.1.27
[EC]
, 35 kDa permonomer subunit) from Bacillus stearothermophilus. Thermal inactivationof this enzyme is accompanied by irreversible unfolding of thenative protein structure. The replacement of Argl71 by Tyr stabilizesthe enzyme against thermal inactivation and unfolding. Thisstabilizing effect appears to be based on improved interactionsbetween the subunits in the core of the active dimeric or tetramericforms of the enzyme. The thermal stability of L-lactate dehydrogenasevariants with an active site Arg residue, either in the 171(wild-type) or in the 102 position, is further increased bysulfate ions. The two stabilizing effects are additive, as foundfor the Argl71Tyr/ Gln1O2Arg double mutant, for which the stabilityof the protein in 100 mM sulfate solution reaches that of L-lactatedehydrogenases from extreme thermophiles. All mutant proteinsretain significant catalytic activity, both in the presenceand absence of stnhilfoing salts, and are viable catalysts inpreparative scale reactions. 相似文献
48.
The effects of SO2 and SO3 in the environment on the hot corrosion behavior of Ni in the temperature range 750–950°C has been studied. Below the melting point of Na2SO4 (884°C), rapid corrosion takes place by formation of a Na2SO4-NiSO4 melt, which can penetrate the porous oxide scale and give rise to sulfide information by coming in contact with the metal. The distribution of the sulfides depends on the SO2 level in the ambient gas. Continued corrosion occurs by a sulfidation-oxidation mechanism. At temperatures above the melting point of Na2SO4, accelerated degradation occurs via dissolution of the surface scale, followed by reprecipitation of the oxide in a nonprotective form.Deceased 相似文献
49.
武城县瑞源水厂以南水北调东段末端调蓄水库大屯水库为水源,原水中氟化物和硫酸盐超标,采用常规处理+臭氧-活性炭工艺并不能去除氟化物和硫酸盐,此次水厂升级改造采用超滤-反渗透双膜法对活性炭滤池出水进行深度处理。膜车间出水与活性炭池出水以1∶2勾兑后,氟化物浓度≤1 mg/L,硫酸盐浓度≤250 mg/L,水质达标,运行稳定。通过对工艺设计参数及运行效果现状分析,总结了双膜法在工艺设计及水厂运行方面的经验,建议工程设计处理氟化物和硫酸盐时采用双膜法,运行时加强数据监控,及时进行清洗护理工作,以延长膜组件使用寿命,降低水厂运行成本。 相似文献
50.
液相化学还原法制备不同形貌的多晶纳米镍 总被引:1,自引:0,他引:1
采用液相化学还原法,在1,2-丙二醇体系中,分别使用吐温-80(Tween-80)、聚乙二醇-6000(PEG-6000)和十二烷基硫酸钠(SDS)与聚乙二醇-6000(PEG-6000)的混合物作为修饰剂,利用1,2-丙二醇还原相同母体醋酸镍,制备形貌分别为海绵体、纤维状、雪花状的多晶纳米镍;在水体系中,使用SDS为修饰剂,利用水合肼还原相同母体醋酸镍,制备球形多晶纳米镍。通过X射线衍射(XRD)、透射电子显微镜(TEM)、选区电子衍射(SAED)对纳米镍进行表征。利用傅立叶红外(FTIR)分析初步解释不同形貌纳米镍的形成机理。 相似文献