全文获取类型
收费全文 | 37867篇 |
免费 | 3339篇 |
国内免费 | 1497篇 |
专业分类
电工技术 | 694篇 |
综合类 | 2003篇 |
化学工业 | 11504篇 |
金属工艺 | 6187篇 |
机械仪表 | 1195篇 |
建筑科学 | 1523篇 |
矿业工程 | 1151篇 |
能源动力 | 1165篇 |
轻工业 | 3790篇 |
水利工程 | 144篇 |
石油天然气 | 1321篇 |
武器工业 | 357篇 |
无线电 | 960篇 |
一般工业技术 | 5578篇 |
冶金工业 | 4553篇 |
原子能技术 | 361篇 |
自动化技术 | 217篇 |
出版年
2024年 | 139篇 |
2023年 | 601篇 |
2022年 | 1034篇 |
2021年 | 1209篇 |
2020年 | 1307篇 |
2019年 | 1053篇 |
2018年 | 1046篇 |
2017年 | 1248篇 |
2016年 | 1148篇 |
2015年 | 1259篇 |
2014年 | 1916篇 |
2013年 | 2133篇 |
2012年 | 2304篇 |
2011年 | 2692篇 |
2010年 | 2073篇 |
2009年 | 2050篇 |
2008年 | 1677篇 |
2007年 | 2478篇 |
2006年 | 2399篇 |
2005年 | 2120篇 |
2004年 | 1845篇 |
2003年 | 1586篇 |
2002年 | 1298篇 |
2001年 | 1087篇 |
2000年 | 911篇 |
1999年 | 741篇 |
1998年 | 698篇 |
1997年 | 513篇 |
1996年 | 452篇 |
1995年 | 340篇 |
1994年 | 340篇 |
1993年 | 221篇 |
1992年 | 188篇 |
1991年 | 112篇 |
1990年 | 106篇 |
1989年 | 89篇 |
1988年 | 41篇 |
1987年 | 37篇 |
1986年 | 31篇 |
1985年 | 27篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 28篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 2篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1959年 | 4篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
72.
Sea-air flux of CO2 in the Caribbean Sea estimated using in situ and remote sensing data 总被引:2,自引:0,他引:2
Empirical relationships between sea surface carbon dioxide fugacity (fCO2sw) and sea surface temperature (SST) were applied to datasets of remotely sensed SST to create fCO2sw fields in the Caribbean Sea. SST datasets from different sensors were used, as well as the SST fields created by optimum interpolation of bias corrected AVHRR data. Empirical relationships were derived using shipboard fCO2sw data, in situ SST data, and SST data from the remote sensing platforms. The results show that the application of a relationship based on shipboard SST data, on fields of remotely sensed SST yields biased fCO2sw values. This bias is reduced if the fCO2sw-SST relationships are derived using the same SST data that are used to create the SST fields. The fCO2sw fields found to best reproduce observed fCO2sw are used in combination with wind speed data from QuikSCAT to create weekly maps of the sea-air CO2 flux in the Caribbean Sea in 2002. The region to the SW of Cuba was a source of CO2 to the atmosphere throughout 2002, and the region to the NE was a sink during winter and spring and a source during summer and fall. The net uptake of CO2 in the region was doubled when potential skin layer effects on fCO2sw were taken into account. 相似文献
73.
籼米淀粉超微粉体的制备及其性质 总被引:3,自引:0,他引:3
研究了籼米淀粉超微粉体的一种新的制备方法 ,通过正交实验确定了酶处理淀粉的最佳条件 ,考察了淀粉的溶解度和膨润力。结果表明 ,酶处理淀粉的最佳工艺参数为 :水解温度45℃ ,时间为25h ,酶用量为水解淀粉的45%。随着粒径的减小 ,淀粉的溶解度增大 ,膨润力下降。 相似文献
74.
化学还原法制备纳米铜粉的研究 总被引:18,自引:1,他引:17
本文采用KBH4在液相中化学还原CuSO4,并加入KOH和络合剂EDTA ,制得了纳米级的纯净的铜粉 ,通过调整反应物的浓度 ,可以消除Cu2 O等杂质。制备的纳米铜粉还存在一定程度的团聚 ,需试验加入分散剂来改善。 相似文献
75.
76.
77.
Titanium Dioxide, TiO2, is a photocatalyst with a unique characteristic. A surface coated with TiO2 exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero. Inversely, the contact angle increases when the surface is shielded from UV. This superhydrophilic nature gives a self-cleaning effect to the coated surface and has already been applied to some construction materials, car coatings and so on. We applied this property to the enhancement of boiling heat transfer. An experiment involving the pool boiling of pure water has been performed to make clear the effect of high wettability on heat transfer characteristics. The heat transfer surface is a vertical copper cylinder of 17 mm in diameter and the measurement has been done at saturated temperature and in a steady state. Both TiO2-coated and non-coated surfaces were used for comparison. In the case of the TiO2-coated surface, it is exposed to UV light for a few hours before experiment and it is found that the maximum heat flux (CHF) is about two times larger than that of the uncoated surface. The temperature at minimum heat flux (MHF) for the superhydrophilic surface is higher by 100 K than that for the normal one. The superhydrophilic surface can be an ideal heat transfer surface. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
78.
超细粉碎技术现状及发展趋势 总被引:14,自引:2,他引:12
综述了国内外超细粉碎技术及设备的现状、进展,指出了其发展趋势,从工作原理、结构特点等方面详细介绍了超细粉碎典型设备,同时又指出了近年来国内外在此领域中的新进展,基于现存问题指出了今后超细粉碎研究的方向。 相似文献
79.
Fernando J Beltrn F Javier Rivas Olga Gimeno 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(9):973-984
Photocatalytic ozonation (1O3 + VUV + TiO2), ozonation (O3), catalytic ozonation (O3 + TiO2), ozone photolysis (O3 + VUV), photocatalysis (TiO2 + VUV) and photolysis (VUV) have been compared in terms of formation of intermediates, extent of, mineralization (TOC, COD, chloride, nitrate) and kinetics in the aqueous treatment of three phenols (phenol, p‐chlorophenol and p‐nitrophenol). In all cases, photocatalytic ozonation led to lower degradation times for chemical oxygen demand and total organic carbon removal. Intermediates formed were similar in the different oxidation systems with some exceptions. They can be classified into three different types: polyphenols (resorcinol, catechol, hydroquinone), unsaturated carboxylic acids (maleic and fumaric acids) and saturated carboxylic acids (glyoxylic, formic and oxalic acids). First order kinetic equations have been checked for the oxidation processes studied in the case of the parent compound. Rate constants of these systems have also been calculated. Copyright © 2005 Society of Chemical Industry 相似文献
80.
In this paper, we examine, both experimentally and theoretically, the kinetics of formation and microstructure of product
phases in thin film reactions, using the Nb/Al and Ti/Al systems as our prototypes. The results of calorimetry and microscopy
studies are interpreted using simple kinetic and morphology models. In particular, the kinetic models employed here focus
on the nucleation and growth components of the phase formation process and the morphology models provide a starting point
for the classification of product grain structures.
An erratum to this article is available at . 相似文献