全文获取类型
收费全文 | 12130篇 |
免费 | 1239篇 |
国内免费 | 283篇 |
专业分类
电工技术 | 30篇 |
综合类 | 260篇 |
化学工业 | 5229篇 |
金属工艺 | 99篇 |
机械仪表 | 171篇 |
建筑科学 | 196篇 |
矿业工程 | 173篇 |
能源动力 | 183篇 |
轻工业 | 5654篇 |
水利工程 | 38篇 |
石油天然气 | 187篇 |
武器工业 | 4篇 |
无线电 | 153篇 |
一般工业技术 | 423篇 |
冶金工业 | 186篇 |
原子能技术 | 190篇 |
自动化技术 | 476篇 |
出版年
2024年 | 60篇 |
2023年 | 183篇 |
2022年 | 334篇 |
2021年 | 457篇 |
2020年 | 402篇 |
2019年 | 399篇 |
2018年 | 373篇 |
2017年 | 443篇 |
2016年 | 475篇 |
2015年 | 479篇 |
2014年 | 606篇 |
2013年 | 857篇 |
2012年 | 768篇 |
2011年 | 773篇 |
2010年 | 614篇 |
2009年 | 602篇 |
2008年 | 577篇 |
2007年 | 661篇 |
2006年 | 586篇 |
2005年 | 417篇 |
2004年 | 384篇 |
2003年 | 368篇 |
2002年 | 353篇 |
2001年 | 269篇 |
2000年 | 287篇 |
1999年 | 227篇 |
1998年 | 247篇 |
1997年 | 160篇 |
1996年 | 203篇 |
1995年 | 158篇 |
1994年 | 128篇 |
1993年 | 132篇 |
1992年 | 156篇 |
1991年 | 118篇 |
1990年 | 72篇 |
1989年 | 57篇 |
1988年 | 37篇 |
1987年 | 49篇 |
1986年 | 50篇 |
1985年 | 30篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 383 毫秒
51.
本文对氨基酸营养条件下植物体内硝酸盐含量变化及其机理,土施植物激素前体色氨酸和蛋氨酸对高等植物生长和化学组成的影响。氨基酸和氨基酸肥料对植物产量和品质的影响作了综述。 相似文献
52.
53.
Higher heating values (HHVs) of fatty acids (C4–C18) were measured and correlated using linear least square regression analysis. Equations were developed for the estimation of the HHVs of saturated fatty acids from their molecular weight (Mw), density (DN) and carbon number (CN). These equations are HHV = 0.0518 Mw + 29.76, HHV = −93.4 DN + 122.67 and HHV = 0.7271 CN + 31.419 with R2 values of 0.9895, 0.9798, and 0.9895, respectively. The correlations may be used for HHV estimation of mixtures of fatty acids developed from vegetable oils. 相似文献
54.
Habibeh Haddad Dabaghi Abdolmajid Bayandori Moghaddam Mahmood Kazemzad Rassoul Dinarvand Fezze Aryanasab Mohammad Reza Nabid 《Journal of Applied Electrochemistry》2008,38(3):409-413
Electrochemical treatment processes can significantly contribute to the protection of the environment through the minimization
of waste and toxic materials in effluents. From a pharmaceutical point of view and due to the existing resemblance between
the electrochemical and biological reactions, it can be assumed that the oxidation mechanisms on the electrode and in the
body share similar principles. In this paper, the application of electrochemical studies in the design of an environmentally
friendly method was delineated for the new hydrocaffeic acid (HCA, 3,4-dihydroxy hydrocinnamic acid) derivatives synthesis
at carbon electrodes in an undivided cell. In this cell, the EC mechanism reaction was involved, comprising two steps alternatively;
(1) electrochemical oxidation and (2) chemical reaction. In particular, the electro-organic reactions of HCA, an important
biological molecule, were studied in a water–acetonitrile (90:10 v/v) mixture in the presence of benzenesulfinic acid (3) and p-toluenesulfinic acid (4). The research included the use of a variety of experimental techniques, such as cyclic voltammetry, controlled-potential
electrolysis and product spectroscopic identification. 相似文献
55.
N. Ilayaraja A. Manivel D. Velayutham M. Noel 《Journal of Applied Electrochemistry》2008,38(2):175-186
Electrochemical perfluorination (ECPF) of n-hexanoyl, n-heptanoyl, n-octanoyl, n-nonanoyl and n-decanoyl chlorides was carried out under identical experimental conditions in liquid HF. The product distribution among perfluorinated
carboxylic acids, perfluoro ethers, perfluoroalkanes, isomerised and fragmented products containing less number of carbon
atoms was identified using 19F NMR. The selectivity of C6–C10 perfluoro carboxylic acid varied between 29 and 36%. The alkali insoluble perfluoro cyclic ether and perfluoro alkane fractions
increased with increasing chain length. The increase of perfluoroalkane fractions is mainly due to decarboxylation. Cyclic
ether fractions also decreased slightly with increase in chain length. Among the cyclic ethers α substituted oxolanes were
the predominant products. Six membered cyclic ethers were always found to contain β substitution. The possible pathways for
these products are also indicated.
An erratum to this article can be found at 相似文献
56.
Bile acids as constituents for dental composites: in vitro cytotoxicity of (meth)acrylate and other ester derivatives of bile acids.
下载免费PDF全文
![点击此处可从《Journal of the Royal Society Interface》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Marc A Gauthier Pierre Simard Zhao Zhang X X Zhu 《Journal of the Royal Society Interface》2007,4(17):1145-1150
Methacrylic derivatives of bile acids have been synthesized for use as monomers in dental composites. Polymeric dental materials are known to leach cytotoxic unreacted monomers and degradation products. In this study, the in vitro cytotoxicity of bile acids and their derivatives towards 3T3 fibroblasts has been evaluated by colorimetric MTT assay and compared with that of the common dental monomers BisGMA, UDMA and TEGDMA. In general, the bile acids and their derivatives induced mitochondrial dysfunction at similar or higher concentrations than the commercial dental monomers. Certain monomers did not influence MTT response over their entire range of solubility. 相似文献
57.
58.
A novel and efficient way of producing of aldonic acids is reported. The selective catalytic oxidation of monosaccharides (arabinose, ribose, xylose, lyxose, mannose, rhamnose, glucose, galactose, N-acetyl-glucosamine) and disaccharides (lactose, maltose, cellobiose, melibiose) on Au, Pd and Pt catalysts was investigated. By using the gold catalyst, a total selectivity with respect to aldonic acids and a high catalytic activity for all investigated sugars was found. The reaction conditions for the production of maltobionic and lactobionic acids via oxidation on gold catalysts were optimised. A high long-term stability of two different gold catalysts for the oxidation of maltose and lactose, respectively, was found. 相似文献
59.
Separations through reactions can provide reliable and economically viable alternatives to established methods of separation,
particularly for close boiling substances. New strategies in ‘Dissociation Extraction’ and ‘Dissociation Extractive Crystallization’
for separation of close boiling acidic/basic mixtures have been highlighted. Separations with aqueous solutions of hydrotrope
and aqueous micellar solutions have been brought out. Separations by membranes with facilitated transport is potentially attractive.
This paper is dedicated to Dr L K Doraiswamy on his sixtieth birthday. 相似文献
60.
The authors of this paper investigated the influence of esters of rapeseed oil fatty acids on the lubricating properties of
mineral lubricants containing chosen AW/EP additives. Methyl esters, ethylene glycol esters, and glycerol esters as well as
some commercial AW/EP packages based on zinc dialkyldithiophosphate, S–P organic compounds, and sulphurized esters of fatty
acids were tested. The tribological tests were carried out with the use of a four-ball machine. Antiwear (AW) properties of
tested compositions were determined using their limiting load of wear (Goz(40)). It appears that the AW action of esters of rapeseed oil fatty acids depends on their structure. The best AW action is shown
by compositions of mineral oil lubricants containing AW/EP additives and methyl esters of rapeseed oil fatty acids. The SEM/EDS
analysis of the scar surface layer indicated that the presence of these esters in lubricants causes a change in the interaction
between AW/EP additives and the metal surface. These observations were confirmed by the XPS surface analysis. 相似文献