全文获取类型
收费全文 | 21265篇 |
免费 | 2848篇 |
国内免费 | 997篇 |
专业分类
电工技术 | 409篇 |
综合类 | 1218篇 |
化学工业 | 7642篇 |
金属工艺 | 502篇 |
机械仪表 | 604篇 |
建筑科学 | 409篇 |
矿业工程 | 3044篇 |
能源动力 | 748篇 |
轻工业 | 1752篇 |
水利工程 | 196篇 |
石油天然气 | 1282篇 |
武器工业 | 151篇 |
无线电 | 1076篇 |
一般工业技术 | 2890篇 |
冶金工业 | 1543篇 |
原子能技术 | 568篇 |
自动化技术 | 1076篇 |
出版年
2024年 | 108篇 |
2023年 | 403篇 |
2022年 | 631篇 |
2021年 | 861篇 |
2020年 | 843篇 |
2019年 | 744篇 |
2018年 | 703篇 |
2017年 | 789篇 |
2016年 | 907篇 |
2015年 | 900篇 |
2014年 | 1338篇 |
2013年 | 1477篇 |
2012年 | 1751篇 |
2011年 | 1578篇 |
2010年 | 1155篇 |
2009年 | 1171篇 |
2008年 | 1020篇 |
2007年 | 1174篇 |
2006年 | 1123篇 |
2005年 | 1004篇 |
2004年 | 780篇 |
2003年 | 819篇 |
2002年 | 638篇 |
2001年 | 530篇 |
2000年 | 458篇 |
1999年 | 386篇 |
1998年 | 342篇 |
1997年 | 272篇 |
1996年 | 233篇 |
1995年 | 198篇 |
1994年 | 173篇 |
1993年 | 119篇 |
1992年 | 92篇 |
1991年 | 77篇 |
1990年 | 60篇 |
1989年 | 43篇 |
1988年 | 44篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1974年 | 3篇 |
1959年 | 3篇 |
1955年 | 1篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
介绍了气体膜分离原理;提出了理想膜过程的新概念;归纳了气体膜分离装置的运行特点;比较分析了气体膜分离过程中原料气流量控制的各种方法;提出通过在尾气侧安装调节阀来定量调节原料气流量的控制方法;该方法成功应用于金陵石化加氢裂化低分气中提取高浓氢的工艺中,验证了这种控制策略的正确性和有效性;整体的控制方案又进一步提高了膜分离装置的操作柔性及适应能力;该方法可同时保证渗透气快气浓度及回收率的性能指标,适用于所有气体膜分离过程中对处理气量的自动控制. 相似文献
223.
热溶过滤法脱除煤焦油沥青中喹啉不溶物的研究 总被引:3,自引:1,他引:3
以5种煤焦油沥青为原料,喹啉为溶剂,研究了热溶过滤法脱除喹啉不溶物(QI)等杂质的效应,目的是制备QI含量较低的净化沥青。结果表明:热溶过滤法可以有效地脱除喹啉不溶物,QI脱除率随滤网网目增加而提高,但阻力增加,脱除时间变长。综合考虑脱除率和实际可操作性,采用1000目的滤布,QI含量可以降到0.3%以下,基本能达到要求。采用凝胶色谱对QI脱除后沥青的组成和分子量分布的研究表明,热溶过滤脱除了沥青中的大分子组分,分子量减小,分子量分布变窄。 相似文献
224.
Cai Jun Wang Li Wu Ping Tong Lige Sun Shufeng 《Frontiers of Chemical Engineering in China》2007,1(3):271-276
This paper presents a novel method that uses the interception effect of gradient magnetic field on oxygen molecules to realize
enrichment. The use of two opposite magnetic poles of two magnets at a certain distance forms a magnetic space having a field
intensity gradient near its borders. When air injected into the magnetic space outflows from the magnetic space via its borders,
oxygen molecules in the air will experience the interception effect of the gradient magnetic field, but nitrogen molecules
will outflow from the magnetic space without hindrance. Thus, continuous oxygen enrichment is realized. The enrichment degree
of oxygen reaches 0.65% when the inlet and outlet air flows are 40 mL/min and 20 mL/min, respectively, and the gas temperature
is 298 K and the maximal product of magnetic flux density and its gradient is 563 T2/m (the distance between two magnetic poles is 1 mm). When the gas temperature rises to 343 K, the enrichment degree drops
to 0.32%; and when the maximal product of magnetic flux density and field intensity gradient drops to 101 T2/m (the distance between two magnetic poles is 4 mm), the enrichment degree drops to 0.23%. The experimental results show
that there is an optimal ratio between the inlet air flow and the outlet air flow. Under the experimental conditions in this
paper, the value is about 2.0. It is demonstrated that the method presented in this paper can continuously enrich oxygen and
has a higher enrichment degree than other oxygen-enrichment methods using magnetic separation.
Translated from Journal of Beijing University of Chemical Technology, 2006, 33(5): 62–66 [译自: 北京化工大学学报] 相似文献
225.
Microcapsules with phenolic resin (PFR) shell and n‐hexadecane (HD) core were prepared by controlled precipitation of the polymer from droplets of oil‐in‐water emulsion, followed by a heat‐curing process. The droplets of the oil phase are composed of a polymer (PFR), a good solvent (ethyl acetate), and a poor solvent (HD) for the polymer. Removal of the good solvent from the droplets leads to the formation of microcapsules with the poor solvent encapsulated by the polymer. The microstructure, morphology, and phase‐change property as well as thermal stability of the microcapsules were systematically characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimety (DSC), and thermogravimetric analysis (TGA). The phase‐change microcapsules exhibit smooth and perfect structure, and the shell thickness is a constant fraction of the capsule radius. The initial weight loss temperature of the microcapsules was determined to be 330°C in N2 and 255°C in air, respectively, while that of the bulk HD is only about 120°C both in air and N2 atmospheres. The weight loss mechanism of the microcapsules in different atmosphere is not the same, changing from the pyrolysis temperature of the core material in N2 to the evaporation of core material caused by the fracture of shell material in air. The melting point of HD in microcapsules is slightly lower than that of bulk HD, and a supercooling was observed upon crystallization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
226.
Chlorinated poly(vinyl chloride) (CPVC)/poly(vinyl pyrrolidone) (PVP) membranes were prepared by using the solvent system tetrahydrofuran (THF)/n‐butyl alcohol (n‐BA) to investigate the possibility of pore size and pore‐size distribution control. The coagulation of CPVC/PVP solution was induced by the exposure to water vapor at 25 (±0.5)°C. The average pore diameter, dp, and the size distribution of pores on the surface of the membrane were quantified through the image analyzer from the images visualized by field emission scanning electron microscope (FE‐SEM). Surface pore size and distribution of the prepared CPVC/PVP membrane were strongly affected by the relative humidity (RH) in the environment and the content of PVP used as an additive. Particularly, in the case of CPVC membrane without PVP, the mean pore size was 0.15–0.2 μm, depending on the RH. The pore distribution became broad with the increase of the RH. The membranes had open pores as confirmed by the hydraulic permeation experiment. In addition, the water flux and membrane resistance (Rm) were greatly affected by the composition of polymer solution and the RH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1195–1202, 2002 相似文献
227.
228.
应用XRD、TEM、SAD及EDS等测试技术,系统地研究了TiO2及烧成温度对K2O-Na2O-CaO-MgO-ZnO-Al2O3-SiO2系瓷釉显微结构的作用。结果表明,在1140-1220℃烧 ,瓷釉中都存在分相与析晶现象,液滴相富含Ti^4+、Ca^2+、Zn^2+而基体玻璃相富含Si^4+,析出的晶体主要为钛榍石。随烧成温度的提高,析出晶体的数量不断减少。另外,当TiO2加入量增加时瓷釉的 相似文献
229.
膜分离技术在丙烯尾气回收中的应用 总被引:2,自引:0,他引:2
分析了聚丙烯生产过程中压缩 /冷凝法丙烯尾气回收的不足 ,介绍了压缩 /冷凝 /有机蒸汽膜法在丙烯尾气回收中的应用 相似文献
230.
本文通过不混溶温度的确定,分相玻璃沥滤速率的测定以及NMR定量分析,研究了P_2O_6对Na_2O-B_2O_3-SiO_2系统玻璃结构和沥滤性质的影响。结果表明,P_2O_5在很大程度上促进钠硼硅分相玻璃的沥滤并非压抑“硼反常”所致,而是由以下三种因素综合作用的结果:(1)P_2O_5促进了钠硼硅玻璃的分相,使连通富硅相骨架尺寸增大;(2)P_2O_5的加入使富硅相骨架间隙中沉积的SiO_2量减少,减小了可溶相扩散阻力;(3)P_2O_5也使可溶相的溶解速率加快。 相似文献