全文获取类型
收费全文 | 133598篇 |
免费 | 11207篇 |
国内免费 | 6609篇 |
专业分类
电工技术 | 8510篇 |
综合类 | 9933篇 |
化学工业 | 15231篇 |
金属工艺 | 6479篇 |
机械仪表 | 6603篇 |
建筑科学 | 6813篇 |
矿业工程 | 4123篇 |
能源动力 | 2860篇 |
轻工业 | 12272篇 |
水利工程 | 3578篇 |
石油天然气 | 3011篇 |
武器工业 | 1569篇 |
无线电 | 9702篇 |
一般工业技术 | 10078篇 |
冶金工业 | 31906篇 |
原子能技术 | 1616篇 |
自动化技术 | 17130篇 |
出版年
2024年 | 548篇 |
2023年 | 1642篇 |
2022年 | 3681篇 |
2021年 | 4602篇 |
2020年 | 3215篇 |
2019年 | 2210篇 |
2018年 | 2811篇 |
2017年 | 3210篇 |
2016年 | 3394篇 |
2015年 | 4633篇 |
2014年 | 5211篇 |
2013年 | 6113篇 |
2012年 | 9374篇 |
2011年 | 9902篇 |
2010年 | 7848篇 |
2009年 | 7315篇 |
2008年 | 7270篇 |
2007年 | 7109篇 |
2006年 | 6104篇 |
2005年 | 7625篇 |
2004年 | 5735篇 |
2003年 | 4200篇 |
2002年 | 2747篇 |
2001年 | 2488篇 |
2000年 | 1711篇 |
1999年 | 1346篇 |
1998年 | 8736篇 |
1997年 | 5281篇 |
1996年 | 3461篇 |
1995年 | 1995篇 |
1994年 | 1529篇 |
1993年 | 1619篇 |
1992年 | 360篇 |
1991年 | 419篇 |
1990年 | 421篇 |
1989年 | 386篇 |
1988年 | 382篇 |
1987年 | 299篇 |
1986年 | 267篇 |
1985年 | 219篇 |
1984年 | 78篇 |
1983年 | 96篇 |
1982年 | 167篇 |
1981年 | 215篇 |
1980年 | 263篇 |
1979年 | 76篇 |
1978年 | 109篇 |
1977年 | 761篇 |
1976年 | 1592篇 |
1975年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
801.
本文对白云鄂博主矿采场铁公路联合运输向公路运输转换位置是否确定为1638m水平以及运输工艺转换过程中相关问题进行分析论证,提出主矿采场铁路至少可向下延深一个水平,技术上可行,节约运费千万元以上。 相似文献
802.
803.
Horizontal subsurface flow constructed wetlands have proven their efficiency in treating wastewater and removing the pollutants of concern. Treatment efficiency depends on the wastewater residence time, which is a function of the hydraulic loading and the physical conditions of the constructed filter system, which can be described with effective parameters such as: hydraulic conductivity, porosity, dispersivity etc. Because spatial variability is often scale dependent, these effective parameters may be affected by the scale of the system being studied. In this paper the results of tracer experiments in constructed filters using saturated horizontal flow at three scales (small and medium lab scales and full-scale system) using the same filter media is reported. Light-weight aggregate (filter media termed Filtralite-P) was used at all scales. Increasing the scale was associated with increasing dispersivity, meanwhile hydraulic conductivity experienced dramatic reduction and variation by increasing the examined scale. Observed changes in the hydraulic parameters indicate that heterogeneity at different scales should be taken into account when the performance of LWA filters are evaluated from small-scale experiments. 相似文献
804.
805.
Which signals are important in gaining attention in science? For a group of 1,371 scientific articles published in 17 demography
journals in the years 1990-1992 we track their influence and discern which signals are important in receiving citations. Three
types of signals are examined: the author's reputation (as producer of the idea), the journal (as the broker of the idea),
and the state of uncitedness (as an indication of the assessment by the scientific community of an idea). The empirical analysis
points out that, first, the reputation of journals plays an overriding role in gaining attention in science. Second, in contrast
to common wisdom, the state of uncitedness does not affect the future probability of being cited. And third, the reputation
of a journal may help to get late recognition (so-called sleeping beauties) as well as generate 'flash-in-the-pans': immediately
noted articles but apparently not very influential in the long run. 相似文献
806.
略谈政府垄断土地一级市场的问题和对策 总被引:1,自引:0,他引:1
政府垄断土地一级市场要强化对土地市场的监管、规范和垄断 ;完善土地市场机制 ,发挥市场配置土地资源的基础性作用 相似文献
807.
The appraisal process consists of the subjective evaluation that occurs during an individual's encounter with significant events in the environment, determining the nature of the emotional reaction and experience. Placed in the context of appraisal theories of emotion-elicitation and differentiation, the aim of the present research was to test empirically the hypothesis that the intrinsic pleasantness evaluation occurs before the goal conduciveness evaluation. In two studies, intrinsically pleasant and unpleasant images were used to manipulate pleasantness, and a specific event in a Pacman-type videogame was used to manipulate goal conduciveness. Facial EMG was used to measure facial reactions to each evaluation. As predicted, facial reactions to the intrinsic pleasantness manipulation were faster than facial reactions to the goal conduciveness manipulation. These results provide good empirical support for the sequential nature of the appraisal process. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
808.
针对有限元仿真分析中结构自振周期减小的问题,讨论了几种主要的影响因素,并借用商品化设计软件TBSA,ETABS 和有限元分析软件ANSYS,通过对一个简单结构的多次计算,比较了这些因素的影响大小。 相似文献
809.
810.
Matrix metalloproteinases are thought to be key players in the remodelling activity of cells associated with both physiological and pathological processes. They share a relatively conserved structure with a number of identifiable modules linked to their specific functions. The structure of the individual domains of a number of matrix metalloproteinases have now been elucidated. Here we review these data in the light of complementary studies on the behaviour of these enzymes in biological systems. In particular we focus on the C-terminal hemopexin-like domain which has intriguingly specific roles in individual matrix metalloproteinases. 相似文献