全文获取类型
收费全文 | 1400篇 |
免费 | 47篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 25篇 |
综合类 | 12篇 |
化学工业 | 273篇 |
金属工艺 | 22篇 |
机械仪表 | 43篇 |
建筑科学 | 55篇 |
矿业工程 | 25篇 |
能源动力 | 45篇 |
轻工业 | 72篇 |
水利工程 | 26篇 |
石油天然气 | 17篇 |
无线电 | 107篇 |
一般工业技术 | 228篇 |
冶金工业 | 220篇 |
原子能技术 | 27篇 |
自动化技术 | 263篇 |
出版年
2022年 | 10篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 21篇 |
2018年 | 25篇 |
2017年 | 28篇 |
2016年 | 25篇 |
2015年 | 22篇 |
2014年 | 27篇 |
2013年 | 113篇 |
2012年 | 58篇 |
2011年 | 84篇 |
2010年 | 52篇 |
2009年 | 55篇 |
2008年 | 73篇 |
2007年 | 64篇 |
2006年 | 39篇 |
2005年 | 50篇 |
2004年 | 51篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 28篇 |
2000年 | 24篇 |
1999年 | 25篇 |
1998年 | 28篇 |
1997年 | 34篇 |
1996年 | 36篇 |
1995年 | 37篇 |
1994年 | 31篇 |
1993年 | 17篇 |
1992年 | 23篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 16篇 |
1986年 | 21篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 12篇 |
1972年 | 9篇 |
排序方式: 共有1460条查询结果,搜索用时 15 毫秒
71.
72.
Robert J. Osborn Nathan F. Taylor Chance W. Spencer Don R. Collins 《Aerosol science and technology》2013,47(9):759-772
A field-deployable instrument has been developed that isolates from an ambient aerosol those particles that have critical supersaturations, Sc, within a narrow, user-specified, range. This Differential Activation Separator (DAS) consists of two continuous flow diffusion chambers housed within a single enclosure. Particles are introduced into the upstream chamber referred to as the CCN remover (CCNR) near the centerline between a warm, water-soaked, plate and a cool, continuously circulated, water bath. Those particles that activate at the resulting peak supersaturation, Sp, grow quickly and fall into the water bath. The remaining aerosol enters the second chamber referred to as the CCN separator (CCNS), which differs from the CCNR primarily in the use of a salt solution in the lower bath. The imposed temperature differential establishes an Sp slightly higher than that maintained in the upstream chamber, while the presence of a salt solution at the lower boundary results in a subsaturated region in roughly the lower half of the chamber. Those particles having (Sp)CCNR < S c < (Sp)CCNS activate in this chamber and begin to fall due to gravitational settling. Before reaching the lower bath, the droplets evaporate in the subsaturated environment and continue to travel towards the chamber exit. The previously activated particles in the lower half of the chamber and the unactivated particles in the upper half are extracted in separate flows that are subsequently dried. Calibration of the DAS was achieved by measuring the size distribution of separated particles when a polydisperse ammonium sulfate aerosol was introduced. 相似文献
73.
介绍了一种新型的车辆清洗装置─—汽车风挡玻璃刮水器。主要技术特征是一双输出轴电动机,通过两根软轴连接减速器,带动雨刷摆动,从而保证了两个雨刷的同步。 相似文献
74.
随着社会的发展,高工专人才培养遇到前所未有的挑战.高工专必须立足培养技术应用型,而摆脱学科型模式,同时,在教育观念上要重新构架教育类型和结构,在课程设置上强调应用性、适应性,在教学方法上提倡多样性和参与性等,从而走出一条适合自己发展的改革创新之路. 相似文献
75.
Efficient schemes for broadcasting popular videos 总被引:4,自引:0,他引:4
We provide a formal framework for studying broadcasting schemes and design a family of schemes for broadcasting popular videos,
the greedy disk-conserving broadcasting (GDB) family. We analyze the resource requirements for GDB, i.e., the number of server
broadcast channels, the client storage space, and the client I/O bandwidth required by GDB. Our analysis shows that all of
our proposed broadcasting schemes are within a small factor of the optimal scheme in terms of the server bandwidth requirement.
Furthermore, GDB exhibits a tradeoff between any two of the three resources. We compare our scheme with a recently proposed
broadcasting scheme, skyscraper broadcasting (SB). With GDB, we can reduce the client storage space by as much as 50% or the
number of server channels by as much as 30% at the cost of a small additional increase in the amount of client I/O bandwidth.
If we require the client I/O bandwidth of GDB to be identical to that of SB, GDB needs only 70% of the client storage space
required by SB or one less server channel than SB does. In addition, we show that with small client I/O bandwidth, the resource
requirements of GDB are close to the minimum achievable by any disk-conserving broadcasting scheme. 相似文献
76.
Using Real-Time Stereo Vision for Mobile Robot Navigation 总被引:10,自引:1,他引:9
This paper describes a working vision-based mobile robot that navigates and autonomously explores its environment while building occupancy grid maps of the environment. We present a method for reducing stereo vision disparity images to two-dimensional map information. Stereo vision has several attributes that set it apart from other sensors more commonly used for occupancy grid mapping. We discuss these attributes, the errors that some of them create, and how to overcome them. We reduce errors by segmenting disparity images based on continuous disparity surfaces to reject spikes caused by stereo mismatches. Stereo vision processing and map updates are done at 5 Hz and the robot moves at speeds of 300 cm/s. 相似文献
77.
本文假定多裂隙岩体的裂隙为直径γ、张开度t的圆盘状,利用裂隙面几何参数提供的统计分布,考虑压剪应力作用下的法向变形及剪胀一扩容变形,推导出裂隙岩体中的水力模型. 相似文献
78.
T. Don Stacy 《Utilities Policy》1991,1(5)
Oil companies such as Amoco Canada are now rushing to overturn corporate structures and cultures that took generations to create and nurture. They are doing so in order to survive in the difficult times the Canadian oil industry is facing: rising costs, increasing government rent sharing, and expectations of modest price increases. The overhaul needed is in three parts: the first involves rationalization of properties and staff reductions; the second, increasing productivity of the human resources of the firm through a thorough-going change in the corporate philosophy. The third calls for royalty and tax regimes that create a favourable economic environment. 相似文献
79.
Bioassay-directed fractionation of an EtOH extract of Curcuma zedoaria led to isolation of an active curcuminoid, which was identified as demethoxycurcumin (2) by comparison of its 1H and 13C NMR spectra with literature data and by direct comparison with synthetic material. Curcumin (1) and bisdemethoxycurcumin (3) were also obtained. Curcuminoids (1-3) were synthesized and demonstrated to be cytotoxic against human ovarian cancer OVCAR-3 cells. The observed CD50 values of 1, 2, and 3 were 4.4, 3.8, and 3.1 microg/mL, respectively. Three additional novel compounds, 3, 7-dimethylindan-5-carboxylic acid (4), curcolonol (5), and guaidiol (6), were also isolated from the EtOH extract. The structures and relative stereochemistry of 4-6 were determined by spectroscopic methods and X-ray crystallographic analysis. 相似文献
80.
Two studies were conducted to assess the dimensionality of supervision. The purpose of Study 1 was to identify the salient dimensions of supervision from the counselor trainee's perspective and to determine if dimensions for trainees corresponded to the dimensions found previously for supervisors. In doing so the dimensionality and construct validity of Bernard's (1979) model was examined by using 15 doctoral trainees. For Study 2 Bernard's model was expanded to incorporate the self-supervisor role and was tested in combination with Littrell, Lee-Borden, and Lorenz's (1979) model. Counselor trainees from a master's (n?=?25) and a doctoral (n?=?23) program participated. The three dimensions that emerged in Study 1 and in Study 2 were remarkably consistent in content and label across the two studies. In terms of dimensionality, Bernard's model and the extended model were modestly supported, whereas Littrell et al.'s model received minimal support. Little evidence was found to suggest that trainees from master's and doctoral programs differed at all in terms of their cognitive maps of supervision. Implications and limitations of the studies were discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献