全文获取类型
收费全文 | 294134篇 |
免费 | 33235篇 |
国内免费 | 21655篇 |
专业分类
电工技术 | 26868篇 |
技术理论 | 4篇 |
综合类 | 27849篇 |
化学工业 | 38115篇 |
金属工艺 | 19436篇 |
机械仪表 | 20092篇 |
建筑科学 | 24411篇 |
矿业工程 | 10564篇 |
能源动力 | 8446篇 |
轻工业 | 27219篇 |
水利工程 | 9040篇 |
石油天然气 | 11904篇 |
武器工业 | 3904篇 |
无线电 | 33886篇 |
一般工业技术 | 27455篇 |
冶金工业 | 11598篇 |
原子能技术 | 4115篇 |
自动化技术 | 44118篇 |
出版年
2024年 | 1670篇 |
2023年 | 4815篇 |
2022年 | 10277篇 |
2021年 | 13685篇 |
2020年 | 10131篇 |
2019年 | 7539篇 |
2018年 | 8164篇 |
2017年 | 9720篇 |
2016年 | 8364篇 |
2015年 | 13021篇 |
2014年 | 16430篇 |
2013年 | 19358篇 |
2012年 | 23506篇 |
2011年 | 24760篇 |
2010年 | 23156篇 |
2009年 | 22397篇 |
2008年 | 22493篇 |
2007年 | 21785篇 |
2006年 | 19361篇 |
2005年 | 15421篇 |
2004年 | 11095篇 |
2003年 | 8227篇 |
2002年 | 7753篇 |
2001年 | 7052篇 |
2000年 | 5582篇 |
1999年 | 3349篇 |
1998年 | 1853篇 |
1997年 | 1473篇 |
1996年 | 1352篇 |
1995年 | 1159篇 |
1994年 | 940篇 |
1993年 | 641篇 |
1992年 | 519篇 |
1991年 | 389篇 |
1990年 | 304篇 |
1989年 | 292篇 |
1988年 | 199篇 |
1987年 | 134篇 |
1986年 | 120篇 |
1985年 | 54篇 |
1984年 | 50篇 |
1983年 | 34篇 |
1982年 | 41篇 |
1981年 | 51篇 |
1980年 | 73篇 |
1979年 | 57篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1959年 | 33篇 |
1951年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The reaction between MgO and graphite powders under flowing argon atmosphere was studied using a dynamic thermogravimetric
method. In the temperature range 293 to 1973 K, the effects of compacting pressure, magnesia/carbon ratio, heating rate, Ar
carrier-gas flow rate, and CO-partial pressure were investigated. An experimentally determined reaction mechanism was proposed
and discussed. The reduction process could be divided into two stages. The first stage includes the direct reaction between
MgO and graphite particles and partial gas-solid reaction at relatively low temperature (below 1750 K). The overall reaction
rate depends on the solid phase-boundary reaction between magnesia and carbon particles. The second stage is the gas-solid
reaction between CO and MgO, which determines the overall reaction rate. The apparent activation energies of the two stages
were estimated to be 208.29 and 374.13 kJ/mol, respectively. 相似文献
962.
王卫军 《煤炭学报(英文版)》2003,9(1):17-21
The movement principle of sidewalls and floor of extraction opening is analyzed, it is found that floor heave not only has something to do with the floor strata, but sidewalls. The effect of sidewall anchor and corner anchor is studied, the mechanical principle of reinforcing sidewalls and corners is put forward and applied in engineering practice. 相似文献
963.
介绍了圆形超细金属/合金丝制备技术基本原理、技术特点及基本性能,主要包括拉拔技术、电解腐蚀技术及熔融快速凝固技术。回顾了超细W、Mo、Al丝等在Z箍缩丝阵负载材料中的应用。 相似文献
964.
965.
966.
结合青藏铁路建设物资储备基地的实际情况,探讨了铁路线统购统发材料的管理模式及业务流程,总结出在实际工作中应借鉴的经验和注意的问题。 相似文献
967.
968.
通过分析影响磁体高温性能的因素,设计了新磁体的成分为:Cu含量高,Fe含量低,Zr适量,Sm含量高;采用粉末冶金工艺制备了高温Sm_2(CoFeCuZr)_(17)永磁体。制得的磁体室温磁性能为:B_r1.075 T,H_(ei)2 098.2 kA/m,H_(eb) 776.1 kA/m,H_k843.8 kA/m,(BH)_(max)210.0 kj/m~3;在200℃时的磁性能为:B_r0.991 T,H_(ci)1 175.7 kA/m,H_(cb)531.7 kA/m,H_k577.9 kA/m,(BH)_(max)172.5 kJ/m~3;矫顽力温度系数β(20~200℃)为-0.24%/℃。经理论分析和实验验证,磁体的使用温度均超过400℃,为高温环境(高于400℃)提供了一种实用性永磁材料。 相似文献
969.
Tingfang Hu Jinpeng Chen Haiyan Wang Jun Min Wei 《Petroleum Science and Technology》2006,24(12):1477-1484
Etherification reaction of FCC light gasoline over Hβ zeolite was investigated to decrease the light olefins in motor gasoline while enhancing octane. Etherification activity of several molecular sieve catalysts for FCC light gasoline was studied in a fixed-bed reactor. The influence of pore-enlarging agent (PEG) with different molecular weight, binder (γ-Al2O3), and peptizing agent (HNO3) in the shaping process on etherification activity of Hβ zeolite was studied. The impregnating ways of precursor of oxides and the order of extruding and impregnating were also investigated. The results show that the activity of extruded Hβ zeolite before impregnating precursor of oxides is higher than the reverse order. The best shaping condition obtained was PEG-4000 10%, γ-Al2O3 20%, and HNO3 10%. At the optimal reaction condition, the conversion of tert-olefins reached the peak. 62.93%, the yield of TAME, is also high and the technology can be applied to industry as well. 相似文献
970.
Wei Fen Zhang Xi Guang Chen Pi Wu Li Cheng Sheng Liu Qiang Zhi He 《Drying Technology》2008,26(1):108-115
Three kinds of carboxymethyl chitosan/β-cyclodextrin microspheres loaded with theophylline were prepared by spray drying intended for pulmonary delivery. Mucociliotoxicity, permeation rate, and drug release characteristics of the product were investigated. The microspheres obtained by spray drying were found to be spherical with smooth or wrinkled surfaces. The mean particle size was between 3.39 and 6.06 µm. The microspheres demonstrated high product yield (43.7-50.2%), high drug loading (13.7-38.1%), and high encapsulation efficiency (86.9-92.8%). FT-IR indicated that there were interactions of theophylline with carboxymethyl chitosan matrix. Further studies on mucociliotoxicity and permeation confirmed that microspheres had better adaptability and high permeation rate. In vitro drug release from the microspheres was not related to the drug/polymer ratios. 相似文献