全文获取类型
收费全文 | 5206篇 |
免费 | 370篇 |
国内免费 | 161篇 |
专业分类
电工技术 | 96篇 |
综合类 | 305篇 |
化学工业 | 1645篇 |
金属工艺 | 196篇 |
机械仪表 | 91篇 |
建筑科学 | 258篇 |
矿业工程 | 121篇 |
能源动力 | 192篇 |
轻工业 | 1545篇 |
水利工程 | 72篇 |
石油天然气 | 162篇 |
武器工业 | 7篇 |
无线电 | 164篇 |
一般工业技术 | 457篇 |
冶金工业 | 149篇 |
原子能技术 | 86篇 |
自动化技术 | 191篇 |
出版年
2024年 | 18篇 |
2023年 | 63篇 |
2022年 | 117篇 |
2021年 | 127篇 |
2020年 | 149篇 |
2019年 | 165篇 |
2018年 | 146篇 |
2017年 | 195篇 |
2016年 | 149篇 |
2015年 | 195篇 |
2014年 | 251篇 |
2013年 | 383篇 |
2012年 | 349篇 |
2011年 | 414篇 |
2010年 | 325篇 |
2009年 | 324篇 |
2008年 | 272篇 |
2007年 | 342篇 |
2006年 | 263篇 |
2005年 | 224篇 |
2004年 | 197篇 |
2003年 | 190篇 |
2002年 | 161篇 |
2001年 | 83篇 |
2000年 | 94篇 |
1999年 | 82篇 |
1998年 | 68篇 |
1997年 | 50篇 |
1996年 | 47篇 |
1995年 | 47篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 36篇 |
1991年 | 26篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有5737条查询结果,搜索用时 10 毫秒
31.
为了探究影响GH5家族β-甘露聚糖酶最适pH的各种因素,利用该酶的序列信息,构建了基于氨基酸组成的β-甘露聚糖酶理化性质与其最适pH的相关性模型。结果表明:该酶N端氨基酸序列是影响其最适pH的重要因素,在243个理化性质中有17个呈极显著相关,其中7个呈正相关。优化的转移能量参数相关性最高,为0.78:7个正相关的理化性质中,与螺旋相关的理化性质占3个。优化的转移能量参数和螺旋是影响pH稳定性的最重要的因素。所建立的模型为研究该酶酸碱适应性机理提供了一种简单有效的方法。 相似文献
32.
Jing Zhang 《Electrochimica acta》2006,51(20):4262-4270
A copolymer, poly(aniline-co-m-aminophenol), has been synthesized using repeated potential cycling. The monomer concentration ratio, acid concentration and applied potential strongly affect the copolymerization rate and the properties of the copolymer. The optimum conditions for the copolymerization are that the scan potential range is controlled between −0.10 and 0.95 V (vs.SCE), and a solution consists of 0.34 M aniline, 0.012 M m-aminophenol and 2 M H2SO4. The IR spectra of the copolymers demonstrate that the m-aminophenol units are included in the copolymer chains. The cyclic voltammograms of the copolymers in 0.3 M Na2SO4 solution with various pH values were performed at the potential ranges from −0.20 to 0.80 V and at a scan rate of 60 mV s−1. The results indicate that the copolymer still hold 41.7% of the electrochemical activity when the copolymer electrode was transferred from a solution of pH 5.0 to a solution of pH 11.0 in the potential range of −0.20 to 0.80 V. An impedance plot of the copolymer in a solution with pH 12.0 and at 0.40 V is constructed of a semicircle and a Warburg line with a slope of 1. This means that the electrode reaction of the copolymer at pH 12.0 is also under mass transfer control. The conductivity of the copolymer prepared under the optimum conditions is 1.42 S cm−1, and slightly depends on the pH value. Thus, the pH dependence of the electrical properties of the copolymer is improved compared with poly(aniline-co-o-aminophenol), and is much better than that of the parent polyaniline. 相似文献
33.
Xylose fermentation by Pichia stipitis was examined using a two-stage batch process. The cells were first grown aerobically on D-xylose (5 g/L), whereafter additional xylose (10 g/L) was added and fermented during anaerobic conditions (T=30°C). The optimum pH value for a fermentation with constant pH was found to be 4.5 (maximum specific ethanol production rate 0.21 g/(g h). Forced square wave cycling of the pH between 4 and 5, and 3.5 and 5.5 (cycle time 30 min) during the fermentation stage resulted in a fermentation rate lower than the maximum rate, but with unchanged ethanol yields. 相似文献
34.
35.
The rate and mechanism of the electroreduction of chlorine on electrooxidised ruthenium has been investigated with focus on the effect of solution pH. Current/potential curves for the reduction process in solutions with constant chloride concentration of 1.0 mol dm−3 and varying H+ concentration have been obtained with the use of the rotating disk electrode technique (RDE). It was found that the chlorine reduction rate is highly inhibited in solutions with high H+ concentrations and that it can be satisfactorily described by the Erenburg mechanism, previously suggested for the chlorine evolution on RuO2 and RTO. The expression of the kinetic current as a function of chlorine and H+ concentration was obtained by solving the elementary rate equations of the kinetic mechanism. The kinetic constants obtained from the correlation of the kinetic current expression to the experimental data were used to simulate the dependence of the surface coverages and elementary reaction rates on overpotential. 相似文献
36.
The effects of hydrogen-charging on anodic dissolution of pipe steel under near-neutral pH condition were studied by electrochemical techniques. Hydrogen-charging enhances the anodic dissolution rate of the steel. The hydrogen-enhanced dissolution increases with increasing charging current density. The hydrogen effect is attributed to the alteration of chemical potential and exchange current density of steel. Hydrogen-charging affects the corrosion process of the steel. In particular, at a high charging current density, a layer of corrosion product forms on the electrode surface to change corrosion potential and interfacial double-charge layer capacitance as well as charge-transfer resistance. The hydrogen effect factor for enhanced anodic dissolution of steel at an anodic potential of −0.4 V (SCE) is 1.53 only. Hydrogen-enhanced anodic dissolution of steel by itself may not be the major factor contributing to the high rate of crack growth in pipe steel in near-neutral pH electrolyte. A further investigation of the synergistic effect of hydrogen and stress on dissolution at the crack-tip is essential to determine the mechanism of near-neutral pH stress corrosion cracking of pipelines. 相似文献
37.
PE, one of the major phospholipids in oilseed soapstock, may react with gossypol to form Schiff bases. PE amounts to 20–30%
of the phosphorus compounds in soap-stock. In this report, the dependence on pH of the Schiff base products between PE and
gossypol was investigated using a spectrophotometer, an HPLC equipped with an ELSD, and an LC-MS system. We observed that
at pH 7 the Schiff reaction product and reactants were clearly detected by ELSD, absorption, and LC-MS spectra. The absorption
spectra displayed the characteristic peak for the Schiff bases around 430–440 nm. The absorption spectra also indicated that
the reaction was pH dependent. The reaction temperatures were 60 and 90°C. The LC-MS spectra supported the formation of Schiff
bases as well as methyl ether derivatives of gossypol in alcohol at the elevated temperatures. The implications of these experimental
findings are presented in this paper. 相似文献
38.
龙泉金矿在全泥氰化提金过程中产生含氰化物174.76mg/L的洗涤废水,通过碱式氯化法处理后,再由渣浆泵送入尾矿库进行自然净化作用,污水得到进一步净化,尾矿库溢流废水氰化物浓度低于0.5mg/L,废水排入小梅溪后,下游第一个居民取水点氰化物浓度低于0.004mg/L,达到了国家规定的标准。 相似文献
39.
以9-蒽甲酸(9-ACA)为发光剂,八乙基卟啉钯(Pd OEP)为光敏剂,在二者最佳配比〔n(9-ACA)∶n(Pd OEP)=80∶1〕下,构建了对溶液中氢离子和氢氧根离子具备灵敏响应性的上转换发光体系9-ACA/PdOEP。当pH处于4~8以及8~11时,上转换发光强度均与pH呈现良好的线性关系。参比实验中,单一组分9-ACA本身的荧光强度与pH没有呈现线性关系,证明了9-ACA/Pd OEP体系对于pH的宽范围响应来源于光敏剂与发光剂之间的三线态-三线态能量转移(TTET)过程。 相似文献
40.
A field experiment was conducted on an acid sulfate soil in Thailand to determine the effect of N fertilization practices on the fate of fertilizer-N and yield of lowland rice (Oryza sativa L.). A delayed broadcast application of ammonium phosphate sulfate (16-20-0) or urea was compared with basal incorporation of urea, deep placement of urea as urea supergranules (USG), and amendment of urea with a urease inhibitor. Deep placement of urea as USG significantly reduced floodwater urea- and ammoniacal-N concentrations following N application but did not reduce N loss, as determined from an15N balance, in this experiment where runoff loss was prevented. The urease inhibitor, phenyl phosphorodiamidate (PPD), had little effect on floodwater urea- and ammoniacal-N, and it did not reduce N loss. The floodwater pH never exceeded 4.5 in the 7 days following the first N applications, and application of 16-20-0 reduced floodwater pH by 0.1 to 0.3 units below the no-N control. The low floodwater pH indicated that ammonia volatilization was unimportant for all the N fertilization practices. Floodwater ammoniacal-N concentrations following application of urea or 16-20-0 were greater on this Sulfic Tropaquept than on an Andaqueptic Haplaquoll with near neutral pH and alkaline floodwater. The prolonged, high floodwater N concentrations on this Sulfic Tropaquept suggested that runoff loss of applied N might be a potentially serious problem when heavy rainfall or poor water control follow N fertilization. The unaccounted-for15N in the15N balances, which presumably represented gaseous N losses, ranged from 20 to 26% of the applied N and was unaffected by urea fertilization practice. Grain yield and N uptake were significantly increased with applied N, but grain yield was not significantly affected by urea fertilization practice. Yield was significantly lower (P = 0.05) for 16-20-0 than for urea; however, this difference in yield might be due to later application of P and hence delayed availability of P in the 16-20-0 treatment. 相似文献