全文获取类型
收费全文 | 45826篇 |
免费 | 5108篇 |
国内免费 | 4100篇 |
专业分类
电工技术 | 2135篇 |
技术理论 | 1篇 |
综合类 | 4852篇 |
化学工业 | 8269篇 |
金属工艺 | 4507篇 |
机械仪表 | 5484篇 |
建筑科学 | 3929篇 |
矿业工程 | 2366篇 |
能源动力 | 1156篇 |
轻工业 | 3285篇 |
水利工程 | 1042篇 |
石油天然气 | 2956篇 |
武器工业 | 632篇 |
无线电 | 2255篇 |
一般工业技术 | 4800篇 |
冶金工业 | 1720篇 |
原子能技术 | 275篇 |
自动化技术 | 5370篇 |
出版年
2024年 | 533篇 |
2023年 | 1506篇 |
2022年 | 2524篇 |
2021年 | 2494篇 |
2020年 | 2030篇 |
2019年 | 1589篇 |
2018年 | 1413篇 |
2017年 | 1587篇 |
2016年 | 1673篇 |
2015年 | 1696篇 |
2014年 | 2427篇 |
2013年 | 2190篇 |
2012年 | 2943篇 |
2011年 | 3176篇 |
2010年 | 2473篇 |
2009年 | 2701篇 |
2008年 | 2250篇 |
2007年 | 3034篇 |
2006年 | 2831篇 |
2005年 | 2366篇 |
2004年 | 1866篇 |
2003年 | 1748篇 |
2002年 | 1429篇 |
2001年 | 1161篇 |
2000年 | 1028篇 |
1999年 | 843篇 |
1998年 | 708篇 |
1997年 | 522篇 |
1996年 | 465篇 |
1995年 | 385篇 |
1994年 | 358篇 |
1993年 | 232篇 |
1992年 | 180篇 |
1991年 | 170篇 |
1990年 | 118篇 |
1989年 | 91篇 |
1988年 | 79篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 22篇 |
1979年 | 7篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1959年 | 4篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Hari B. Goyal M. O. Garg K. R. Rao R. D. Srivastava 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):49-56
The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid. 相似文献
102.
对无缝钢管生产所用的内壁除鳞材料———除氧化物剂中各个组分的性质和作用进行了阐述,提出了除氧化物剂的除氧机理。 相似文献
103.
贾方 《电子工业专用设备》2002,31(4):238-240
介绍了新近研制的APTD - 0 0三极放电管全自动打印机的结构特点及整机设计的关键技术 ,阐述了自动上料机构、打印机构和控制电路的设计 相似文献
104.
As part of a study of the possible application of polymerisable Langmuir-Blodgett (LB) films as ultra-fine-line e-beam resists, an investigation of the variation of film structure of 22-tricosenoic acid with differing deposition conditions has been made. Unexpected effects with significant implications for deposition speed and resist sensitivity have been observed, and the new techniques for film characterisation developed during the investigation have resulted in a revised model of deposition explaining the observed independence of the disorder causing optical scattering and the macroscopic features observed by polarised microscopy. 相似文献
105.
一步法合成松香改性酚醛树脂 总被引:2,自引:0,他引:2
探讨了一步法合成松香改性酚醛树脂的反应机理,确定了最佳原料组成及合成工艺,由此制备出高溶解粘度和矿油容纳度的松香改性酚醛树脂,是一种性能优异的高级胶印油墨连接料 相似文献
106.
Studies on Catalytic Side-Chain Oxidation of Nitroaromatics to Aldehydes with Oxygen 总被引:2,自引:0,他引:2
The side-chain oxidation of 2-nitrotoluene in liquid phase in the presence of catalytic amount of manganese sulfate and stoichiometric amount of potassium hydroxide with oxygen was studied. In the most favorable conditions, over 80% of conversion of 2-nitrotoluene and 50% of selectivity to 2-nitrobenzaldehyde was achieved. Effects of the reaction parameters on the conversion of the reactant and the selectivity of the product were examined. These results, together with EPR spectroscopic study, show that a benzyl anion was formed in the early stage of the reaction, which was then converted to the final product via a free radical mechanism. 相似文献
107.
108.
K. Yasuda Y. Tomita Y. Masuda T. Ishiguro Y. Kawauchi H. Morishita Y. Agata 《Journal of Electronic Materials》2002,31(7):785-790
Iodine doping of CdTe layers grown on (100) GaAs by metal-organic vapor phase epitaxy (MOVPE) was studied using diethyltelluride
(DETe) and diisopropyltelluride (DiPTe) as tellurium precursors and ethyliodine (EI) as a dopant. Electron densities of doped
layers increased gradually with decreasing the growth temperature from 425°C to 325°C. Doped layers grown with DETe had higher
electron densities than those grown with DiPTe. When the hot-wall temperature was increased from 200°C to 250°C at the growth
temperature of 325°C, doped layers grown with DETe showed an increase of the electron density from 3.7×1016 cm−3 to 2.6×1018 cm−3. On the other hand, such an increase of the electron density was not observed for layers grown with DiPTe. The mechanisms
for different doping properties for DETe and DiPTe were studied on the basis of the growth characteristics for these precursors.
Higher thermal stability of DETe than that of DiPTe was considered to cause the difference of doping properties. With increasing
the hot-wall temperature from 200°C to 250°C, the effective ratio of Cd to Te species on the growth surface became larger
for layers grown with DETe than those grown with DiPTe. This was considered to decrease the compensation of doped iodine and
to increase the electron density of layers grown with DETe. The effective ratio of Cd to Te species on the growth surface
also increased with decreasing growth temperature. This was considered to increase the electron density with decreasing growth
temperature. 相似文献
109.
The methodology of response reactions (RERs) introduced earlier from thermodynamic and kinetic considerations is used in this work to develop a new algorithm for the classification and enumeration of unique/direct reaction routes (RRs) and overall reactions (ORs). According to the RERs approach, a unique set of both RRs and ORs may be generated starting from any conceivable set of linearly independent RRs and ORs. In particular, the direct ORs may be most conveniently enumerated starting from the formula matrix of the terminal species (reactants and products), i.e., without any relation to the elementary reactions comprising the detailed mechanism. Depending on the type of ORs produced by the RRs one can distinguish between two distinct types of direct RRs. Namely, one option is to define a direct RR by specifying the intermediate species that need to be eliminated. This type of RR is referred to as Milner RRs. The other option is to require the direct RRs to produce RERs, thus resulting in RRs referred to as Happel-Sellers RRs. 相似文献
110.
川东北三叠系飞仙关组鲕滩气藏有利储集层的形成与分布 总被引:19,自引:5,他引:14
川东北地区三叠系飞仙关组鲕滩气藏是近年四川盆地碳酸盐岩天然气勘探取得重大突破的领域,目前在中国石油探区内已发现罗家寨、渡口河、铁山坡等大中型气藏。对鲕滩气藏白云岩储集层进行岩心观察、显微薄片分析,并进行微量元素、流体包裹体、X衍射、阴极发光及电子探针等分析,结果表明,白云岩化和多期溶蚀是形成优质白云岩储集层的关键因素,混合云化与埋藏云化的叠加作用是形成孔隙性白云岩储集层的基本条件。飞仙关组鲕滩气藏储集层经历了4期溶蚀作用,即同生期溶蚀作用、浅埋期溶蚀作用、深埋期溶蚀作用和抬升期溶蚀作用,形成优质白云岩储集层的主要溶蚀作用是浅埋期和深埋期的溶蚀作用。优质白云岩储集层主要分布在台缘鲕粒滩相带,纵向与亮晶鲕粒灰岩呈韵律性互层,横向主要分布在鲕粒滩坝靠近漏湖-潮坪一侧。 相似文献