全文获取类型
收费全文 | 387172篇 |
免费 | 31396篇 |
国内免费 | 18197篇 |
专业分类
电工技术 | 23264篇 |
技术理论 | 45篇 |
综合类 | 29013篇 |
化学工业 | 63656篇 |
金属工艺 | 23147篇 |
机械仪表 | 24460篇 |
建筑科学 | 29811篇 |
矿业工程 | 13085篇 |
能源动力 | 10500篇 |
轻工业 | 27487篇 |
水利工程 | 7839篇 |
石油天然气 | 24354篇 |
武器工业 | 3347篇 |
无线电 | 41701篇 |
一般工业技术 | 41958篇 |
冶金工业 | 19751篇 |
原子能技术 | 4083篇 |
自动化技术 | 49264篇 |
出版年
2024年 | 1671篇 |
2023年 | 6134篇 |
2022年 | 11152篇 |
2021年 | 15450篇 |
2020年 | 11603篇 |
2019年 | 9337篇 |
2018年 | 10748篇 |
2017年 | 12019篇 |
2016年 | 11039篇 |
2015年 | 15260篇 |
2014年 | 19166篇 |
2013年 | 22994篇 |
2012年 | 25094篇 |
2011年 | 27830篇 |
2010年 | 24684篇 |
2009年 | 23479篇 |
2008年 | 23087篇 |
2007年 | 21991篇 |
2006年 | 22083篇 |
2005年 | 19235篇 |
2004年 | 13118篇 |
2003年 | 11368篇 |
2002年 | 10550篇 |
2001年 | 9433篇 |
2000年 | 9229篇 |
1999年 | 9558篇 |
1998年 | 7214篇 |
1997年 | 6166篇 |
1996年 | 5845篇 |
1995年 | 4813篇 |
1994年 | 3916篇 |
1993年 | 2643篇 |
1992年 | 2093篇 |
1991年 | 1580篇 |
1990年 | 1251篇 |
1989年 | 1005篇 |
1988年 | 838篇 |
1987年 | 528篇 |
1986年 | 413篇 |
1985年 | 258篇 |
1984年 | 208篇 |
1983年 | 166篇 |
1982年 | 130篇 |
1981年 | 80篇 |
1980年 | 101篇 |
1979年 | 51篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 28篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
讨论了直流法在线测量钯氢化物电极电阻时的电化学效应,计算了电解液的共导、测量电流与电解电流引起的浓差电池效应以及电极作为集流体引起的电阻贡献。结果表明:当电极具有高的长度与半径比值、粗糙的表面、高的溶液电导以及大的电解电流时容易引起显著的附加电阻。 相似文献
75.
Grain refinement of Al-7Si alloys and the efficiency assessment by recognition of cooling curves 总被引:5,自引:0,他引:5
Under sand cup solidification condition, the influence of Ti, B concentration, and holding time on the grain size of a high-purity
Al-7Si alloy has been systematically studied. It is found that the grain size decreases rapidly at lower Ti or B additions,
and is almost constant at the higher concentrations. For Al-3B refined Al-7Si alloys, the grain size increases at the initial
period of holding time, and then rapidly becomes independent of holding time; while for Al-7Si alloys refined with Al-5Ti-1B,
the grain size increases with holding time throughout. To evaluate the refinement efficiency, a new method named “intelligent
evaluating of melt quality by pattern recognition of thermal analysis cooling curves” has also been introduced in this article.
The results show that comparing the cooling curve of the evaluated melt with those in a database to find the most similar
one to it can precisely assess the grain refinement efficiency of the measured Al-7Si alloy. In addition, the influence of
Ti, B addition levels, and pouring temperatures on some characteristic parameters of cooling curve has also been discussed. 相似文献
76.
Yung Ting Liang-Chiang Chen Chun-Chung Li Jeng-Lin Huang 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(4):847-853
A new type of piezoelectric linear motor incorporating a traveling wave has been developed. The linear motor is comprised of a stator and a carriage. The stator design, which consists of a meander-line structure and gear teeth mounted on the meander-line structure, is the focus of this article. The meander-line structure is constructed with bimorph actuators arranged in a line. These actuators are driven by two phased sets of alternating current (ac) in order to generate a traveling wave. The traveling wave is transferred to the gear teeth, by which the carriage is driven. Modeling of the stator is derived by use of a strain energy method. The performance of various materials is evaluated by analytical and experimental methods. The analytical and the experimental results are quite approximate. Modal analysis is investigated using ANSYS. Appropriate modes associated with ultrasonic levels of resonant frequency are selected to obtain desired motion and to enhance the output performance. Surface speed for various applied input voltage are studied and indicate a nearly linear relationship. The stator in combination with the carriage makes up the linear motor. 相似文献
77.
The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride. 相似文献
78.
79.
Qing Li 《Computer Standards & Interfaces》1991,13(1-3):99-103
The term ‘object-oriented database’ has been used to refer to different characteristics and mechanisms supported by semantic databases and (behaviorally) object-oriented ones. While this indicates the current confusion due to the lack of a common model, it also suggests the potential desirability of combining these two kinds of modeling facilities into the same nutshell. This paper summarizes from these two paradigms the features common to both, the features influenced/adopted by each other, and the features which are presented in one paradigm but missing from the other. After a brief analysis and discussion of these features, we conclude this paper by proposing our major theme: a complete object data model should take the union of the facilities offered by these two kinds of models. 相似文献
80.
A 78-year-old Chinese woman presented with recurrent postprandial abdominal pain. Computerised tomography revealed a small bowel tumour causing volvulus of a segment of the small bowel. Laparotomy confirmed an extraluminal ileal tumour with partial volvulus of the involved small bowel segment. Small bowel resection was done. Histological and ultrastructural studies confirmed a gastrointestinal autonomic nerve tumour. We review the medical literature on this rare tumour. 相似文献