全文获取类型
收费全文 | 47867篇 |
免费 | 3527篇 |
国内免费 | 1990篇 |
专业分类
电工技术 | 1924篇 |
技术理论 | 2篇 |
综合类 | 3300篇 |
化学工业 | 22380篇 |
金属工艺 | 1603篇 |
机械仪表 | 1107篇 |
建筑科学 | 695篇 |
矿业工程 | 1389篇 |
能源动力 | 4794篇 |
轻工业 | 1431篇 |
水利工程 | 76篇 |
石油天然气 | 2335篇 |
武器工业 | 842篇 |
无线电 | 1876篇 |
一般工业技术 | 5483篇 |
冶金工业 | 1735篇 |
原子能技术 | 205篇 |
自动化技术 | 2207篇 |
出版年
2024年 | 107篇 |
2023年 | 535篇 |
2022年 | 915篇 |
2021年 | 1186篇 |
2020年 | 1173篇 |
2019年 | 970篇 |
2018年 | 1017篇 |
2017年 | 1161篇 |
2016年 | 1377篇 |
2015年 | 1394篇 |
2014年 | 2369篇 |
2013年 | 2280篇 |
2012年 | 2978篇 |
2011年 | 3673篇 |
2010年 | 2750篇 |
2009年 | 3054篇 |
2008年 | 2614篇 |
2007年 | 3414篇 |
2006年 | 3041篇 |
2005年 | 2797篇 |
2004年 | 2344篇 |
2003年 | 2134篇 |
2002年 | 1891篇 |
2001年 | 1566篇 |
2000年 | 1361篇 |
1999年 | 1081篇 |
1998年 | 871篇 |
1997年 | 658篇 |
1996年 | 566篇 |
1995年 | 464篇 |
1994年 | 400篇 |
1993年 | 297篇 |
1992年 | 236篇 |
1991年 | 151篇 |
1990年 | 139篇 |
1989年 | 83篇 |
1988年 | 63篇 |
1987年 | 52篇 |
1986年 | 28篇 |
1985年 | 42篇 |
1984年 | 40篇 |
1983年 | 18篇 |
1982年 | 25篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
A new phenolformaldehyde polymer resin containing potential soft‐type donor atoms (sulfur atoms) was synthesized by the reaction of sodium salt of 2,4‐dihydroxyacetophenone formaldehyde resin with carbon disulfide. The resin was characterized by elemental analysis, IR, and 1H‐NMR spectral studies. Because of its insolubility in aqueous media, the resin was successfully used in the removal of Pb(II) and Cd(II). Parameters such as the effect of pH, the effect of time, competitive studies, the effect of initial metal‐ion concentration, and the recyclability of the polymer resin were studied. The amount of metal removed by the resin was determined with atomic absorption spectrophotometry. The retention properties were strongly dependent on pH. The elution of metal ions was investigated in acid media. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1932–1936, 2004 相似文献
73.
Combustion tests were carried out with Minto coal in combination with three different limestones in the University of British Columbia (UBC) pilot scale (152 mm square x 7.3 m tall) circulating fluidized bed combustion (CFBC) unit. Operating conditions were chosen to be typical of those employed in large-scale CFBC power boilers. Recycling of fine particles captured by the secondary cyclone was found to be of considerable importance in increasing sulphur capture, enhancing combustion efficiency and reducing the amount of calcium sulphide in the solids residues. NOx emissions increased as the Ca:S ratio increased. Local gas concentrations inside the reactor were strongly influenced by the core-annulus solids distribution patterns which characterize circulating fluidized beds. 相似文献
74.
在双筐并流氨合成塔中使用了A110-1-H/A110-1型氨合成催化剂,使用寿命达1740天,累计产氨438378t.该催化剂组合具有低温活性好、易还原、高催化活性、高抗毒能力、良好的热稳定性与破碎强度等优点. 相似文献
75.
Isidoro Izquierdo Cubero Maria T. Plaza Lopez-Espinosa Anthony C. Richardson 《Journal of chemical ecology》1993,19(6):1265-1283
The synthesis of (2S,5R)-(1) and (2R,5R)-2-methyl-1,6-dioxaspiro [4.5]decane (2) from (2RS,5R,8R,9R,10S)-8,9,10-trihydroxy-2-methyl-1, 6-dioxaspiro[4.5]decane (8), obtained in five steps fromd-fructose using Wittig's methodology, reduction, and spiroketalation, has been accomplished by a Corey dideoxygenation at C-8,9, followed by a Barton deoxygenation at C-10, of the appropriately protected derivatives.Enantiospecific synthesis of spirocetals. Part V. For Part IV, see Izquierdo et al. (1992). 相似文献
76.
Consuelo Montes de Correa H. Ai´da Luz Villa 《Applied catalysis. B, Environmental》1996,10(4):313-323
The effect of Pd-loading on Pd-NaZSM-5 and Pd-NaMordenite catalysts prepared by ion exchange was studied for methane combustion with excess oxygen (1% CH4, 18% O2, balance N2) in the temperature range 40–500°C. Fresh and calcined samples (3 h, 450°C) showed methane conversions proportional to Pd-loading on Pd-NaZSM-5 catalysts, while conversions decreased with Pd-loading on calcined Pd-NaMordenite catalysts. TOF (number of methane molecules converted per second per Pd2+ ion) for over exchanged Pd-NaZSM5-116 was low as compared to under exchanged Pd-NaZSM5-80 and Pd-NaZSM5-58 samples. Close TOF's were found for the last two samples at 330°C. TOF differences in Pd-NaMordenite catalysts demonstrate the heterogeneity of Pd+2 sites due to structurally nonidentical locations of cations. TOF's appear to be related to Na/Pd ratios in both catalyst types. Apparent activation energies for Pd-NaZSM-5 materials are higher than those for Pd-NaMordenite catalysts. 相似文献
77.
Isidoro Izquierdo Cubero Maria T. Plaza López-Espinosa Rafael Acuña Castillo 《Journal of chemical ecology》1991,17(8):1529-1541
The synthesis of the title compound13 has been carried out through the preparation of its precursor, (3R,4R,5S,6R)-3,4,5-trihydroxy-1,7-dioxaspiro[5.5]undecane (6), obtained fromd-fructose using Wittig's methodology, reduction, and spiroketalation. Compound6 was transformed into13 by a Barton deoxygenation at C-5 followed by a Corey dideoxygenation at C-3,4 of the appropriately protected derivatives.Enantiospecific synthesis of spiroacetals. Part II. For Part I, see Izquierdo and Plaza (1990). 相似文献
78.
Noboru Hashimoto Yasushi Sawada Takashi Bando Hiroyoshi Yoden Shigehito Deki 《Journal of the American Ceramic Society》1991,74(6):1282-1286
AIN powder was synthesized from aluminum polynuclear complexes. Basic aluminum chloride and basic aluminum lactate were used as the aluminum polynuclear complexes. These starting materials and glucose were dissolved in water and mixed homogeneously. AIN powder was obtained by calcining after drying and precalcining at 800°C under nitrogen gas flow. Then excess carbon was removed by firing in air. Nitridation in the system was investigated and compared with that in the alumina–carbon black system. It was found that in our reaction system nitridation began and proceeded at lower calcination temperatures above 1200°C than in the alumina–carbon black system. Using aluminum polynuclear complexes, AIN was synthesized through the nitridation of γ-alumina and produced in a very fine and sharp particle size distribution. 相似文献
79.
合成气中氨含量测定方法的改进 总被引:1,自引:0,他引:1
用快速测定仪测定气体中的氨含量,采气量为50ml,可准确测出高含量氨体积百分比含量为80%-100%和低含量氨体积百分比含量为1%-20%的样气,该仪器结构简单,易于制造,测定过程简单,结果准确,一目了然。 相似文献
80.
Matthias Berger Manfred P. Schnelder 《Journal of the American Oil Chemists' Society》1992,69(10):961-965
Regioisomerically pure 1(3)-rac-monoacylglycerols are conveniently prepared in high yields (>75%) and in multigram quantities by enzymatic esterification
of glycerol in the presence of various lipases(Chromobacterium viscosum, Rhizopus delemar, Rhizomucor miehei) with a variety of different acyl donors, such as free fatty acids, fatty acid alkyl esters, vinyl esters and triacylglycerols,
as well as natural fats and oils. All reactions are carried out in aprotic organic solvents with low water content, namelyn-hexane, diethyl ether, tBuOMe or mixtures of these solvents. Essential for the success of these transformations were the
following two factors. First, the creation of an artificial interphase between the solvent-immiscible hydrophilic glycerol
and the hydrophobic reaction medium by its adsorption onto a solid support. Second, a facile system for the separation of
the desired monoacylglycerol from the reaction mixture, coupled with the continuous recycling of acyl donor and undesirable
by-products. 相似文献