全文获取类型
收费全文 | 11626篇 |
免费 | 1250篇 |
国内免费 | 760篇 |
专业分类
电工技术 | 422篇 |
综合类 | 958篇 |
化学工业 | 2751篇 |
金属工艺 | 692篇 |
机械仪表 | 515篇 |
建筑科学 | 824篇 |
矿业工程 | 1090篇 |
能源动力 | 666篇 |
轻工业 | 1202篇 |
水利工程 | 584篇 |
石油天然气 | 605篇 |
武器工业 | 63篇 |
无线电 | 594篇 |
一般工业技术 | 1163篇 |
冶金工业 | 703篇 |
原子能技术 | 339篇 |
自动化技术 | 465篇 |
出版年
2024年 | 29篇 |
2023年 | 156篇 |
2022年 | 293篇 |
2021年 | 371篇 |
2020年 | 398篇 |
2019年 | 355篇 |
2018年 | 337篇 |
2017年 | 433篇 |
2016年 | 458篇 |
2015年 | 478篇 |
2014年 | 685篇 |
2013年 | 848篇 |
2012年 | 848篇 |
2011年 | 956篇 |
2010年 | 643篇 |
2009年 | 626篇 |
2008年 | 595篇 |
2007年 | 705篇 |
2006年 | 656篇 |
2005年 | 509篇 |
2004年 | 472篇 |
2003年 | 431篇 |
2002年 | 360篇 |
2001年 | 289篇 |
2000年 | 260篇 |
1999年 | 249篇 |
1998年 | 179篇 |
1997年 | 158篇 |
1996年 | 145篇 |
1995年 | 134篇 |
1994年 | 121篇 |
1993年 | 79篇 |
1992年 | 87篇 |
1991年 | 45篇 |
1990年 | 55篇 |
1989年 | 37篇 |
1988年 | 34篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1959年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
以分子热力学为基础 ,对气体吸收过程进行了理论分析 ,导出了传质通量的数学表达式。根据该文分析 ,气液界面传质的源动力来自界面处气液两相的不平衡 ,即只要有传质发生 ,液相界面处的浓度就不会达到与气相呈平衡的浓度。对于气相阻力可以忽略的吸收过程 ,两相传质速率的大小主要取决于液相的溶质界面浓度和液膜厚度 ,影响溶质界面浓度和液膜厚度的主要因素是近界面液相侧的流场分布。利用近界面浓度与液膜厚度的激光测定结果 ,计算了甲醇、乙醇及正丙醇吸收CO2 气泡的传质通量 ,计算结果与实验值吻合良好 相似文献
105.
K. N. Mehrotra M. Chauhan R. K. Shukla 《Journal of the American Oil Chemists' Society》1996,73(7):897-902
The ultrasonic velocity and density measurements of europium soaps in a mixture of benzene and methanol (3:2, vol/vol) were
used to evaluate various acoustic parameters and molar volume and to determine the critical micelle concentration. The results
showed that the ultrasonic velocity, specific acoustic impedance, molar sound velocity, and molar compressibility increase,
and intermolecular free length, adiabatic Compressibility, and relative association decrease with increasing concentration
and chainlength of the soap. The results were interpreted in terms of soap-solvent interaction. 相似文献
106.
Riitta Kettunen Sanna Saarnio Pertti J. Martikainen Jouko Silvola 《Nutrient Cycling in Agroecosystems》2006,74(2):175-189
The effects of elevated atmospheric CO2 concentration on soil moisture, N2O fluxes, and biomass production of Phleum pratense were studied in the laboratory. Farmed peat and sandy soil mesocosms sown with P. pratense were fertilized with a commercial fertilizer. In peat soil 10 g N m−2 of commercial fertilizer were added and in sandy soil 15 g N m−2. In both experiments, soil moisture was regulated with deionized water; 18 mesocosms were tended to keep equally moist, and
the other 18 were watered with equal amounts of water. Nine mesocosms from both watering treatments were grown under ambient
(360 μmol mol−1) CO2 concentration and the remaining nine under doubled (720 μmol mol−1) CO2. N2O efflux was monitored using a closed chamber technique and a gas chromatograph. The elevated supply of CO2 increased production of above- and belowground biomass, soil moisture and N2O fluxes, but decreased the total N content in the aboveground biomass, especially for the sandy soil. In similar water levels,
N2O efflux from the sandy soil was the same magnitude as that from the peat soil. In addition to moisture, N availability was
the main limiting factor for N2O production, but C availability also seemed to regulate the denitrification activity. In addition to an increase in C availability
the increase in the N2O efflux under the raised CO2 concentration also required a simultaneous increase in soil moisture. 相似文献
107.
Hydraulic resistance of rigid polyurethane foams to penetration by water at high pressures is studied in this work in the context of buoyancy applications. Micron sized silica particles are used as nucleating agents. The effect of the variation of the concentrations of the surfactant, water, and nucleating agent on cell structure, closed cell content, and compressive modulus, is examined. Foams have densities in the range of 145 to 165 kg/m3. At a particular water concentration, with increase in the concentration of the surfactant, the window area of the cells becomes smaller and the hydraulic resistance of the foam increases. A cell window is the lamella of the foam material that separates two adjacent cells. With increase in the concentration of water keeping surfactant concentration constant, the average window area remains almost the same but the cell window area distribution becomes wider and the hydraulic resistance of the foams decreases. Foams made with silica have smaller cell windows but lower hydraulic resistance than that of the foams made without silica. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2830–2837, 2004 相似文献
108.
The preparation of dibasic acid-containing soy phospholipid was made by transesterification reaction with alkyl ester of diabasic acid with both lipase and alkoxide as a catalyst. The extent of incorporation of a dibasic acid varied with the molecular size of the dibasic acid. The extent of incorporation in soy phospholipids was 4–13% in the case of adipic acid and 9–20% in the case of sebacic acid. The surface-active properties of these modified soy phospholipids were examined and were found to be different from those of the original (unmodified) soy phospholipid. The interfacial properties such as critical micelle concentration (CMC), γCMC, surface excess concentration Γmax, and minimum area per molecule (Å), and thermodynamic parameters such as standard free energy of micellization, were found to depend on the hydrophobic part of the dibasic acids. 相似文献
109.
110.
断续流对旋流器油水分离效率影响的实验研究 总被引:2,自引:0,他引:2
目前,大部分井下油水分离的旋流器由地面游梁式抽油机通过抽油杆柱提供能量,这样进入旋流器流量产生断续现象。通过实验证明断续流流量的不连续性使旋流器油水分离效率下降5%以内,存在一定负影响;溢流含油浓度越高,断续流对旋流分离效率的负影响也越大,所以井下油水分离过程中,不能偏面追求过高的溢流口含油浓度,提高分流比F与入口含油浓度C_i比值,减小断续流对分离效率的影响。 相似文献