全文获取类型
收费全文 | 1850篇 |
免费 | 89篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 23篇 |
综合类 | 1篇 |
化学工业 | 402篇 |
金属工艺 | 15篇 |
机械仪表 | 49篇 |
建筑科学 | 38篇 |
矿业工程 | 4篇 |
能源动力 | 39篇 |
轻工业 | 302篇 |
水利工程 | 12篇 |
石油天然气 | 3篇 |
无线电 | 256篇 |
一般工业技术 | 333篇 |
冶金工业 | 275篇 |
原子能技术 | 27篇 |
自动化技术 | 170篇 |
出版年
2023年 | 12篇 |
2022年 | 37篇 |
2021年 | 36篇 |
2020年 | 22篇 |
2019年 | 36篇 |
2018年 | 45篇 |
2017年 | 36篇 |
2016年 | 42篇 |
2015年 | 31篇 |
2014年 | 47篇 |
2013年 | 90篇 |
2012年 | 75篇 |
2011年 | 129篇 |
2010年 | 68篇 |
2009年 | 68篇 |
2008年 | 90篇 |
2007年 | 74篇 |
2006年 | 61篇 |
2005年 | 40篇 |
2004年 | 38篇 |
2003年 | 47篇 |
2002年 | 53篇 |
2001年 | 32篇 |
2000年 | 41篇 |
1999年 | 42篇 |
1998年 | 77篇 |
1997年 | 74篇 |
1996年 | 55篇 |
1995年 | 33篇 |
1994年 | 35篇 |
1993年 | 26篇 |
1992年 | 12篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1980年 | 10篇 |
1978年 | 8篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1974年 | 8篇 |
1912年 | 13篇 |
1911年 | 63篇 |
1910年 | 27篇 |
1909年 | 34篇 |
排序方式: 共有1949条查询结果,搜索用时 15 毫秒
1.
2.
3.
Takuma Suzuki Hang-Ju Ko Agus Setiawan Jung-Jin Kim Koh Saitoh Masami Terauchi Takafumi Yao 《Materials Science in Semiconductor Processing》2003,6(5-6):519-521
We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH3 is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH3 pre-exposure helps form a Zn3N2 layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar. 相似文献
4.
JP Clement 《Canadian Metallurgical Quarterly》1997,34(4):340-350
The purpose of this paper is to determine whether dynamic cost shifting occurred among acute care hospitals during the period from the early 1980s to the early 1990s and, if so, whether market factors affected the ability to shift costs. Evidence from this study of California acute care hospitals during three time intervals shows that the hospital did practice dynamic cost shifting, but that their ability to shift costs decreased over time. Surprisingly, hospital competition and HMO penetration did not influence cost shifting. However, increasing HMO penetration (measured as the HMO percentage of hospital discharges) did decrease both net prices and costs for the early part of the study, but later was associated with increases in both. 相似文献
5.
A mica-based machinable glass-ceramic has been converted to a glass-ceramic containing cordiertie and body-centered cubic chondrodite through heat treatment at temperatures higher than that used for the crystallization of mica. The machinability is lost, microhardness increases, and the thermal expansion coefficient decreases with the change of the crystalline phase from mica to cordierite and chondrodite. 相似文献
6.
The effect of duty cycle of pulsed dc currents on the critical length-current density product, (jlc), was measured using the Blech-Kinsbron edge-displacement technique [Thin Solid Films 25, 327 (1975)]. Unencapsulated Al edge-displacement segments mere stressed at various duty cycles and the critical lengths, the so-called “Blech lengths”, were measured. It was found that jlc increased with decreasing duty cycle. We measured a factor of 2.6 increase in jlc for the 25% duty cycle as compared to dc. This duty cycle dependence of Blech length implies that electromigration resistance for an integrated circuit would be increased for small duty cycle operation by increasing the fraction of interconnects which are sub-Blech-length and are not susceptible to EM damage 相似文献
7.
To evaluate an association between Helicobacter pylori (H. pylori) infection and chronic atrophic gastritis (CAG), an established precursor of gastric cancer, we performed a cross-sectional study using IgG antibody against H. pylori and pepsinogens of blood donors in four prefectures in Japan. Although a geographic correlation between the age-adjusted prevalence rates for H. pylori infection and those for CAG was not seen, the age-adjusted odds ratios (OR) of H. pylori infection for CAG were high in each area (around five for men and from four to 12.6 for women). The association between them weakened with advancing age; the ORs in the youngest age group (16-29 yrs) and in the oldest age group (50-64 yrs) were 12.5 and 2.8 for men, and 11.5 and 5.2 for women, respectively. These findings suggest that H. pylori infection is strongly associated with CAG, while there are some other factors interacting in the development of CAG. A prospective cohort study in which CAG and H. pylori infection are taken into account will be necessary to assess the risks of gastric cancer. 相似文献
8.
Clement M. Gosselin 《野外机器人技术杂志》1995,12(12):857-869
Parallel robotic manipulators are complex mechanical systems that lead to involved kinematic and dynamic equations. Hence, the design of such systems is in general not intuitive, and advanced simulation and design tools specialized for this type of architecture are highly desirable. This article discusses the kinematic simulation and computer-aided design of three-degree-of-freedom spherical parallel manipulators with either prismatic or revolute actuators. The kinematic analysis of spherical parallel manipulators is first reviewed. Solutions for the direct and inverse kinematic problems are given, and the expressions for the singularity loci are then introduced. The determination of the workspace of this type of manipulator is also addressed. Finally, a computer package developed specifically for the CAD of spherical parallel manipulators is presented. This package allows the interactive analysis of manipulators of arbitrary architecture including the representation of the workspace, the representation of singularities, and the graphic animation of trajectories specified either by the direct or the inverse kinematic module. It can be used for the design of any spherical parallel three-degree-of-freedom actuated mechanism, which can find many applications in high-performance robotic systems. © 3995 John Wiley & Sons, Inc. 相似文献
9.
H Koh Y Hashimoto H Takagi K Hirota H Ishihara A Matsuki 《Canadian Metallurgical Quarterly》1993,42(2):217-224
The purpose of the study was to explore the relationship between the exposure of adolescents in the seventh and eighth grades to cigarette advertising and their being smokers. A survey questionnaire given to 602 adolescents assessed their exposure to cigarette advertising and provided measures of their smoking behavior, demographic characteristics, and some psychosocial variables. The results indicated that exposure to cigarette advertising and having friends who smoked were predictive of current smoking status. Adolescents with high exposure to cigarette advertising were significantly more likely to be smokers, according to several measures of smoking behavior, than were those with low exposure to cigarette advertising. The findings extend previous research identifying factors that may play a role in the initiation and maintenance of smoking among adolescents. 相似文献
10.
This paper presents stability results for discrete-time model-based predictive control system subject to an input amplitude constraint. It is shown that the input amplitude constrained control system may provide a stable control system in the sense of BIBO when the system to be controlled is of a class of the system poles which consist of multiple integrators and a stable polynomial. The solution of Diophantine equations and their properties are addressed. Simulation study is also carried out and it is shown that the output of the system may converge to the reference signal for certain degree of constraints. 相似文献