全文获取类型
收费全文 | 48603篇 |
免费 | 5197篇 |
国内免费 | 3200篇 |
专业分类
电工技术 | 3120篇 |
综合类 | 4310篇 |
化学工业 | 7176篇 |
金属工艺 | 2334篇 |
机械仪表 | 2006篇 |
建筑科学 | 5260篇 |
矿业工程 | 2829篇 |
能源动力 | 1920篇 |
轻工业 | 3349篇 |
水利工程 | 1420篇 |
石油天然气 | 2415篇 |
武器工业 | 540篇 |
无线电 | 6532篇 |
一般工业技术 | 6796篇 |
冶金工业 | 3380篇 |
原子能技术 | 1048篇 |
自动化技术 | 2565篇 |
出版年
2024年 | 245篇 |
2023年 | 844篇 |
2022年 | 1519篇 |
2021年 | 1795篇 |
2020年 | 1833篇 |
2019年 | 1653篇 |
2018年 | 1414篇 |
2017年 | 1825篇 |
2016年 | 1803篇 |
2015年 | 1939篇 |
2014年 | 2867篇 |
2013年 | 2936篇 |
2012年 | 3299篇 |
2011年 | 3596篇 |
2010年 | 2717篇 |
2009年 | 2842篇 |
2008年 | 2567篇 |
2007年 | 3093篇 |
2006年 | 2813篇 |
2005年 | 2352篇 |
2004年 | 1989篇 |
2003年 | 1793篇 |
2002年 | 1571篇 |
2001年 | 1254篇 |
2000年 | 1161篇 |
1999年 | 897篇 |
1998年 | 682篇 |
1997年 | 666篇 |
1996年 | 544篇 |
1995年 | 461篇 |
1994年 | 425篇 |
1993年 | 334篇 |
1992年 | 248篇 |
1991年 | 212篇 |
1990年 | 183篇 |
1989年 | 151篇 |
1988年 | 110篇 |
1987年 | 71篇 |
1986年 | 50篇 |
1985年 | 37篇 |
1984年 | 37篇 |
1983年 | 23篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1965年 | 6篇 |
1963年 | 6篇 |
1959年 | 11篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
YANG WeiFeng ZHANG QingZhao WANG MingGang & XIA Yang Key Laboratory of Microelectronics Devices & Integrated Technology 《中国科学:信息科学(英文版)》2011,(8)
In this paper, the cone-shaped patterned sapphire substrates (PSS) were etched by an inductively couple plasma with BCl 3 as the reacting gas. The influence of the operating pressure and the RF bias power on subtrenches of the cone-shaped PSS and the formation mechanism of subtrenches were investigated. The profiles of patterns were characterized by FESEM (field emission scanning electron microscope). It showed that the subtrench size varied with the operating pressure and the RF bias power. As the operatin... 相似文献
62.
当液膜表面同时存在热非平衡效应和切应力作用时,引发液膜流动不稳定的扰动及其影响将更为复杂。基于边界层理论,通过建立气液界面受热非平衡效应和切应力耦合作用的液膜流动的理论模型,采用包含弱非线性项的积分法,推导出热非平衡效应下剪切液膜流的表面波积分演化模型,模型中包括了相变强度、切应力、雷诺数和倾斜角度等不同参数的影响,为分析复杂边界条件下的液膜流的演化特征和稳定性提供了一种可借鉴的理论模型。 相似文献
63.
Atsuyoshi Nishina Kohji Kubota Hiromu Kameoka Toshihiko Osawa 《Journal of the American Oil Chemists' Society》1991,68(10):735-739
A substance with antioxidant properties was obtained from the hexane extract of roots ofRumex japonicus Houtt. The active component of the hexane extract was isolated and characterized as 2-acetyl-1,8-dihydroxy-3-methyl naphthalene,
trivially named musizin (MUS). The antioxidant activities of MUS in six types of fats and oils were higher than that of butyl
hydroxyanisole (BHA) and δ-tocopherol (δ-TOC). Together, TOC and MUS have a synergistic effect, because comparable amounts
of either had lower antioxidant activity than various combinations of the two antioxidants. When we studied the antioxidant
properties of a mixture of MUS and δ-TOC with methyl linoleate (MeLH), we found that the rates of destruction of the two antioxidants
were comparable, but that their destruction occurred sequentially, with MUS first followed by δ-TOC, after which the oxidation
of MeLH quickly occurred. Comparison of the antioxidant activity of MUS and its analogs suggests that only one of the two
hydroxyl groups in MUS is involved in its antioxidant activit. Intermolecular hydrogen bonding may be involved. 相似文献
64.
Recently, it has been reported by our group and others1.2 that loss of curing agent is encountered during the curing of small droplets or thin films of amine cured epoxies. In our earlier study3 results were reported on loss of curing agent in small droplets used in conducting the rnicrobond, single fiber test for determination of interfacial shear strength (ISS). It was reported that use of a volatile curing agent (meta-phenylene diamine (m-PDA) with DGEBA resin) resulted in increasing amounts of curing agent being lost (as measured by T8 of the cured droplets) with decreasing droplet size during the processing procedure. Droplets smaller than 150 micrometers were seen to lose up to 40% of the curing agent leading to alteration of the mechanical properties of the droplet and, therefore, causing measured values of ISS to be exceedingly low. Use of a less volatile curing agent (Jeffamine 700, a polyether diamine, Texaco Specialty Chemicals) in combination with DGEBA resin produced results which indicated that loss of curing agent was not occuring. This study was undertaken to show the relationships between film (or droplet) size and the amount of curing agent lost (during the processing) for three different aminecured epoxy systems. 相似文献
65.
The object of the present study was to investigate the effect of superimposed dynamic and static stresses on mechanical and thermal properties of some epoxy adhesives. It was found that combinations of shear creep and torsional oscillations, applied simultaneously to adhesive joints at temperatures within the glassy range of the adhesive, led to strengthening of the joints in shear and to an increase in the glass transition temperature of the adhesive. Similar loading stresses applied at temperatures close to the Tg of the adhesive, led to opposite effects on the above mentioned properties of the joints. The width of the glassy-rubbery transition of the adhesives increased, in the whole range of temperatures used in this study and for all epoxy compositions, as a result of subjecting the joints to superimposed dynamic and static stresses. The broadening of the glass transition was interpreted as a result of the stiffening of polymer network during the combined stressing experiments. A linear relationship was found between the area of endothermal peaks in the first DSC scan of specimens subjected prior to test to superimposed dynamic and static stresses at temperatures below Tg, and the shear strength of the joints. In agreement with this observation and with literature data, a linear relationship was revealed also between the glass transition temperature of the resins (measured in the first DSC scan) and the shear strength of the joints. Based on experimental observations and on some literature information, it was suggested that the strengthening of the joint, as well as the changes in thermal properties of the adhesives, are mainly due to physical processes, such as short-range orientation of network chains and an increase in intermolecular interaction between highly polar sites of the network. The possibility that superimposed stressing led to changes in chemical crosslinking was discussed but it seems that no such reactions occurred. 相似文献
66.
前文报道了外加磁场对吸附在硅胶表面上的芳砜光解反应的影响,本文报道外加磁场影响光化学反应的另一个例子——电子转移光敏化1,2-二苯乙烯的异构化。 近年来电子转移光敏化反应引起了有机光化学家们的极大注意。一些异构化、重排、裂解、氧化反应都可以通过电子转移机理敏化。电子转移光敏化的机理可以用(1)描述。图中A和D分别代表电子的受体和给体。 相似文献
67.
张帆 《吉林化工学院学报》2015,(7):76-79
采用目标追求的入世、出世量表筛选出入世水平高组(70名)和低组(72)大学生,出世水平高组(68名)和低组(71名)大学生,探讨不同入世、出世水平大学生在奖学金申请、选修课和求职应聘三种决策任务领域上的框架效应及其在性别上的特点。结果发现:(1)不同出入世水平大学生在决策任务上的框架效应特点不同,入世水平高分组和低分组、出世水平高分组和低分组在奖学金申请问题上均出现了经典的框架效应;(2)在奖学金申请问题上,男性被试和女性被试的选择出现了明显的经典的框架效应。 相似文献
68.
文兴吾 《成都电子机械高等专科学校学报》2015,(3):1-4
从爱因斯坦建立狭义相对论的科学方法与狭义相对论理论的逻辑构成入手,综合运用A· P·弗伦奇在国际著名的改革教材“美国麻州理工学院物理学导论丛书”第二卷《狭义相对论》中的研究观点和闵可夫斯基的四维时空理论,阐明狭义相对论与钟慢效应之间的正确关系。 相似文献
69.
Based on the parametric analysis of the expanding zone of the vacuum dust suction mouth, the flow in the vacuum dust suction mouth was simulated by computational fluid dynamics (CFD) software, Fluent. The effects of the expanding zone parameters on flow simulation were analyzed. The results show that simulation effects depend on threshold values of the expanding zone parameters of the dust suction mouth, and the threshold values of the expanding zone can be obtained according to the different structures of the vacuum dust suction mouth and be selected as the geometric parameters in calculating, and also corners of the expanding zone make unobvious difference in calculation accuracy and in computational efficiency compared with no corner. The simulation results provide practical guidance to the flow simulation on the dust suction mouth. 相似文献
70.
This paper reports an experimental study of laser spot welding on stainless steel sheets. A pulsed Nd:YAG laser was used to weld the stainless steel specimen in the range of laser energy 0.6–1.2 J and incident angle 30–75° (the angle of the laser beam incident direction to the sheet surface). Metallography was applied to measure the cross-sectional size and shape of the welded spot. From the experimental results, it is found that as the laser energy increases, the penetration depth, bead length, and bead width of the welded spot increase. As the laser incident angle increases, the penetration depth and the bead width increase while the bead length decreases. The results illustrate that the shape and size of the welded spot depend not only on the laser energy, but also on the incident angle of laser beam. 相似文献