全文获取类型
收费全文 | 24740篇 |
免费 | 3760篇 |
国内免费 | 2535篇 |
专业分类
电工技术 | 366篇 |
技术理论 | 1篇 |
综合类 | 1576篇 |
化学工业 | 5830篇 |
金属工艺 | 469篇 |
机械仪表 | 2706篇 |
建筑科学 | 2534篇 |
矿业工程 | 890篇 |
能源动力 | 954篇 |
轻工业 | 7451篇 |
水利工程 | 704篇 |
石油天然气 | 933篇 |
武器工业 | 150篇 |
无线电 | 663篇 |
一般工业技术 | 2054篇 |
冶金工业 | 2208篇 |
原子能技术 | 603篇 |
自动化技术 | 943篇 |
出版年
2024年 | 136篇 |
2023年 | 459篇 |
2022年 | 1105篇 |
2021年 | 1475篇 |
2020年 | 1259篇 |
2019年 | 1292篇 |
2018年 | 1182篇 |
2017年 | 1138篇 |
2016年 | 1282篇 |
2015年 | 1147篇 |
2014年 | 1619篇 |
2013年 | 2008篇 |
2012年 | 1763篇 |
2011年 | 1844篇 |
2010年 | 1268篇 |
2009年 | 1205篇 |
2008年 | 1080篇 |
2007年 | 1463篇 |
2006年 | 1234篇 |
2005年 | 1126篇 |
2004年 | 890篇 |
2003年 | 815篇 |
2002年 | 623篇 |
2001年 | 496篇 |
2000年 | 403篇 |
1999年 | 389篇 |
1998年 | 373篇 |
1997年 | 326篇 |
1996年 | 271篇 |
1995年 | 231篇 |
1994年 | 186篇 |
1993年 | 161篇 |
1992年 | 127篇 |
1991年 | 95篇 |
1990年 | 79篇 |
1989年 | 66篇 |
1988年 | 49篇 |
1987年 | 42篇 |
1986年 | 43篇 |
1985年 | 30篇 |
1984年 | 38篇 |
1983年 | 24篇 |
1982年 | 43篇 |
1981年 | 75篇 |
1980年 | 30篇 |
1979年 | 9篇 |
1973年 | 3篇 |
1959年 | 3篇 |
1955年 | 3篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
A series of macrocyclic(arylene multisulfide) oligomers were synthesized under high dilution conditions by reacting diphenyl ether/diphenyl/diphenyl disulfide/diphenyl methane with dichloro disulfide in the presence of a trace amount of iron powder by a one‐step reaction. From MALDI‐TOF mass spectra, it was established that the repeating units of the cyclization ranged from two to seven and the unit of macrocyclic(arylene multisulfide) oligomers had one to seven sulfur atoms. The macrocyclic oligomers readily underwent ring‐opening polymerization in the melt, resulting in linear, high molecular weight polymultisulfides. DSC thermograms demonstrated that the four polymultisulfides, derived from the macrocyclic(arylene multisulfide) oligomers, are amorphous in nature. The macrocyclic(arylene multisulfide) oligomers and polymers were analyzed by MALDI‐TOF‐MS, IR, HPLC, NMR, DSC, and TGA methods. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 735–741, 2004 相似文献
122.
M. Melzer J. Urban H. Sack-Kongehl K. Weiss H.-J. Freund R. Schlögl 《Catalysis Letters》2002,81(3-4):219-221
Vanadium clusters were prepared by the inert gas aggregation technique by evaporating V of high purity. Structural characterization was performed by high-resolution transmission electron microscopy. Apart from vanadium clusters of bcc structures in different orientations, crystalline VO clusters of NaCl structures were observed, which was attributed to the reaction with free oxygen present on the amorphous carbon substrates. The latter could be detected by electron energy-loss spectroscopy. The exposure of the samples to air caused a change to amorphous structures, which re-crystallized under the electron beam. This effect was interpreted as a reaction with water present in the air. 相似文献
123.
124.
本文以全氟羧酸离子交换膜为支撑体、乙二胺(EDA)为活性络合剂、制备促进传质膜。在常用的工业条件下,测定了纯CO_2以及CO_2/N_2二元混合物在该膜内的渗透通量。实测结果表明,此膜对CO_2的促进因子可达13.8,而对CO_2/N_2的分离因子高达316。本文假设促进传质过程的控制步骤为气体在膜相的扩散,据此导出了相应的机理模型,该模型与实测结果吻合良好。 相似文献
125.
The composition of the territorial marking pheromones from mandibular glands of males of the beewolvesPhilanthus crabroniformis, P. barbatus, andP. pulcher have been determined. The structures of the components were elucidated by gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared spectroscopy. The major compound ofP. crabroniformis is isopropyl tetradecanoate, with somewhat lesser amounts of 2-tridecanone, 3-methyl-3-butenyl tetradecanoate, and 928 (Z)(E)-11-eicosen-1-ol. The major compounds ofP. barbatus are ethyl tetradecanoate and hexadecanal, which are present in approximately a 6040 ratio. These two compounds comprise over 95% of the neutral lipids. Also present in lesser amounts are ethyl dodecanoate, tetradecanal, hexadecan-1-ol, a
x
-octadecen-1-ol, and octadecan-1-ol. The major compounds ofP. pulcher are ethyl (Z)-7-hexadecenoate and geranylgeraniol acetate, which comprise nearly 90% of the neutral lipid fraction, with smaller amounts of tetradecanal, pentadecanal, and ethyl hexadecanoate; trace amounts of
x
hexadecenal, hexadecanal, and octadecanal are also present. 相似文献
126.
原子吸收光谱法测定土壤中的微量金属元素 总被引:1,自引:1,他引:1
采用火焰原子吸收光谱法测定了不同地区土壤样品中的铅、铜、镍、锌元素的含量,相对标准偏差为0.1-3.3,回收率为99.6%-101.6%。该方法简单、快速,并具有良好的精密度和准确度。重点讨论了前处理方法、共存离子对测定结果的影响。 相似文献
127.
Baishen Liang Alessandro Gomez Jose L. Castillo Daniel E. Rosner 《Chemical Engineering Communications》1989,85(1):113-133
In carrying out partial vapor condensations using actively cooled surfaces it is known that 'mist' formation can occur within thermal boundary layers (Rosner and Epstein, 1968), dramatically modifying total deposition fluxes. Using a combination of flash-evaporation (Rosner and Liang, 1986) and laser probing techniques, we report new experimental results on binary alkali salt (K2SO4 + Na2SO4) deposition from combustion gases showing that the deposition rate of potassium sulfate first increases with the addition of sodium sulfate until the concentration of Na2SO4 reaches a (target surface temperature dependent) 'threshold' value. Further increases in the concentration of Na2SO4 dramatically decrease the total deposition rate of K2SO4, implying that potassium sulfate-containing microdroplets are formed within the thermal boundary layer, which, despite their thermophoretic drift toward the target, are not collected as effectively as the 'parent' K2SO4-vapor species. Laser light scattering measurements clearly reveal that suspended particles exist near the deposition surface under these conditions. Our experimental results on mass transfer rate and light scattering are consistent with those predicted using laminar boundary layer theory (Castillo and Rosner, 1989b) coupling both binary salt vapor deposition with particle vapor scavenging and deposition. Comparisons of our observed mist onset conditions (implying critical supersaturations near unity) with those expected using homogeneous nucleation theory suggest that the binary alkali sulfate mist nucleation mechanism is, instead, heterogeneous, even in our relatively 'clean' combustion products. Because of the; well-known vapor pressure reduction phenomenon associated here with the formation of non-ideal solutions, binary systems are shown to provide convenient 'vehicles' to investigate BL mist formation onset conditions and CVD-rate consequences without requiring the more extreme surface coolings characteristic of unary condensible vapor systems. An understanding of this dramatic phenomenon, obtained via such laboratory experiments and calculations, will allow its inclusion in future deposition rate calculations of engineering importance. 相似文献
128.
129.
多孔介质内部热质传递的等效耦合扩散模型的推导及其应用 总被引:1,自引:2,他引:1
基于Whitaker的体积平均方程,在不附加任何新的假设的基础上,对多孔介质内部热质传递的等效耦合扩散模型进行推导,得出了多孔介质内部热质传递的等效耦合扩散模型。并应用该模型对瓷质砖体干燥过程进行了数值模拟,模拟结果与实验结果十分吻合。 相似文献
130.