全文获取类型
收费全文 | 18452篇 |
免费 | 2275篇 |
国内免费 | 2252篇 |
专业分类
电工技术 | 307篇 |
技术理论 | 1篇 |
综合类 | 1334篇 |
化学工业 | 4649篇 |
金属工艺 | 360篇 |
机械仪表 | 2170篇 |
建筑科学 | 2453篇 |
矿业工程 | 794篇 |
能源动力 | 885篇 |
轻工业 | 4229篇 |
水利工程 | 683篇 |
石油天然气 | 635篇 |
武器工业 | 127篇 |
无线电 | 487篇 |
一般工业技术 | 1654篇 |
冶金工业 | 800篇 |
原子能技术 | 431篇 |
自动化技术 | 980篇 |
出版年
2024年 | 94篇 |
2023年 | 312篇 |
2022年 | 778篇 |
2021年 | 1074篇 |
2020年 | 936篇 |
2019年 | 958篇 |
2018年 | 881篇 |
2017年 | 784篇 |
2016年 | 864篇 |
2015年 | 765篇 |
2014年 | 1102篇 |
2013年 | 1448篇 |
2012年 | 1161篇 |
2011年 | 1292篇 |
2010年 | 947篇 |
2009年 | 885篇 |
2008年 | 851篇 |
2007年 | 1103篇 |
2006年 | 955篇 |
2005年 | 911篇 |
2004年 | 737篇 |
2003年 | 677篇 |
2002年 | 518篇 |
2001年 | 422篇 |
2000年 | 332篇 |
1999年 | 313篇 |
1998年 | 300篇 |
1997年 | 279篇 |
1996年 | 209篇 |
1995年 | 186篇 |
1994年 | 158篇 |
1993年 | 138篇 |
1992年 | 105篇 |
1991年 | 78篇 |
1990年 | 60篇 |
1989年 | 50篇 |
1988年 | 42篇 |
1987年 | 36篇 |
1986年 | 35篇 |
1985年 | 24篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 51篇 |
1980年 | 21篇 |
1979年 | 7篇 |
1959年 | 2篇 |
1957年 | 2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
61.
62.
Axisymmetrical, two dimensional mass transfer in a tube and a through-hole was studied. The elliptic convective-diffusion equation was solved numerically by taking into account both the axial and radial diffusion in the entrance region of an infinite tube. The whole mass-transfer region in a tube of finite length was also studied by dividing the domain into several regions according to different mass-transfer mechanisms. A similar analysis is then conducted for a through-hole geometry by assuming a modified Hagen-Poiseuille fluid pattern. Results show that mass-transfer rate in a through-hole is larger than that in a tube by approximately 10%. This is due primarily to faster fluid flow within the concentration boundary layer in a through-hole. 相似文献
63.
根据拟稳态一维扩散原理,建立了气相扩散系数的测定装置。在该装置上,测定了8个体系的气相扩散系数,其中CH_2Cl_2-空气,CH_2Cl_2-H_2,CH_3CH_2Br-空气,CH_3Cl_2Br-H_2,CHCl_3-H_2等5个体系的气相扩散系数实验值,迄今尚未见文献报道。实验结果表明,本测试装置稳定性好,实验误差小,实验装置体积小,测试过程较为简便。 相似文献
64.
65.
K. Remananda Rao 《加拿大化工杂志》1993,71(5):685-688
A unique characteristic linear dimension (d), defined as the cube root of the specific liquid holdup (hsp) in the packed column, was used to correlate successfully the liquid film mass transfer coefficient kLa for gas absorption-desorption for sparingly soluble gases in liquids below loading. To produce this simple, dimensionless correlation, kLa data reported in literature were used, covering a wide range of physical properties of liquids, packings and operating conditions. This new approach showed operating holdup as an important factor in gas liquid mass transfer. 相似文献
66.
The combustion of single bituminous char particles (4-12 mm diameter) was studied in a turbulent fluidized bed operated at 1098 K using air as the fluidising medium. Results indicated that particles burn with constant density following a shrinking sphere model. Burning rates are much higher than those observed in a bubbling fluidized bed. The rate of transfer of oxygen to the particle surface is also higher than that observed in bubbling beds. A model is proposed to calculate the Sherwood numbers of the burning carbon particles. Experimental values of the Sherwood numbers agree well with those predicted from the model. 相似文献
67.
Particle-liquid mass transfer in a co-current three-phase fluidized bed of glass beads, water and air was studied with two measurement techniques. Both techniques measured the weight loss of a few particles coated with benzoic acid in a bed of inert glass beads. The effects of liquid and gas velocities, gas distribution and surface active agents on particle-liquid mass transfer in a three-phase fluidized bed were thus determined. In the absence of surface active agents in the liquid, particle-liquid mass transfer rates in a three-phase fluidized bed were up to 30% higher than in the corresponding liquid fluidized bed. When surface active agents were added to the liquid, the particle-liquid mass transfer rate was increased by up to about 100% in the three-phase fluidized bed, relative to the liquid fluidized bed. The particle-liquid mass transfer coefficient was found to be inversely proportional to the liquid hold-up in the three-phase fluidized bed. 相似文献
68.
The zonal disintegration phenomenon (ZDP) is a typical phenomenon in deep block rock masses. In order to investigate the mechanism of ZDP, an improved non-linear Hock-Brown strength criterion and a bi-linear constitutive model of rock mass were used to analyze the elasto-plastic stress field of the enclosing rock mass around a deep round tunnel. The radius of the plastic region and stress of the enclosing rock mass were obtained by introducing dimensionless parameters of radial distance. The results show that tunneling in deep rock mass causes a maximum stress zone to appear in the vicinity of the boundary of the elastic and the plas-tic zone in the surrounding rock mass. Under the compression of a large tangential force and a small radial force, the rock mass in the maximum stress zone was in an approximate uniaxial loading state, which could lead to a split failure in the rock mass. 相似文献
69.
针对大体积混凝土结构构件实体强度与普通标准养护试块强度发展规律间的差别等问题,通过研究实际工程尺寸试件温度场的分布和实验室混凝土变温养护试验,以不同养护制度下的试块强度得出了大体积混凝土结构实体强度的发展规律,为工程施工提供了依据,成功地解决了工期与质量的矛盾,取得了较好的技术经济效果. 相似文献
70.
针对商品化聚乳酸微球粒径分布较宽难于适用气溶胶给药要求的不足,采用水力空化混合强化超临界流体辅助雾化技术(SAA-HCM)制备聚乳酸(PLA)超细微粒.该技术主要特点是通过在超临界流体和液相进料处引入水力空化混合器,强化两相间的混合.考察SAA-HCM过程混合器压力、温度、沉淀器温度、进料中CO2与液体溶液质量流量比和溶液质量浓度等操作参数对微粒形态和粒径分布的影响,成功制备出球形度较好,粒径分布较窄(1~3μm)的PLA微球.经X射线衍射(XRD)分析和差示扫描量热(DSC)分析显示,与原料PLA相比,微球晶型及热曲线变化不大,但结晶度下降.同时把操作参数与相行为进行关联,探讨了影响颗粒形貌的机理.对比超临界流体辅助雾化法(SAA)的实验结果表明:水力空化的引入能有效强化混合器内的两相传质,混合更好,能制备出适用于气溶胶给药要求的超细微粒. 相似文献