全文获取类型
收费全文 | 4374篇 |
免费 | 59篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 16篇 |
综合类 | 3篇 |
化学工业 | 449篇 |
金属工艺 | 50篇 |
机械仪表 | 54篇 |
建筑科学 | 120篇 |
矿业工程 | 7篇 |
能源动力 | 48篇 |
轻工业 | 212篇 |
水利工程 | 35篇 |
石油天然气 | 5篇 |
无线电 | 265篇 |
一般工业技术 | 383篇 |
冶金工业 | 2477篇 |
原子能技术 | 17篇 |
自动化技术 | 300篇 |
出版年
2021年 | 25篇 |
2020年 | 19篇 |
2019年 | 27篇 |
2018年 | 31篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 26篇 |
2014年 | 51篇 |
2013年 | 116篇 |
2012年 | 78篇 |
2011年 | 141篇 |
2010年 | 82篇 |
2009年 | 83篇 |
2008年 | 107篇 |
2007年 | 112篇 |
2006年 | 105篇 |
2005年 | 111篇 |
2004年 | 79篇 |
2003年 | 71篇 |
2002年 | 70篇 |
2001年 | 58篇 |
2000年 | 53篇 |
1999年 | 111篇 |
1998年 | 698篇 |
1997年 | 410篇 |
1996年 | 281篇 |
1995年 | 167篇 |
1994年 | 139篇 |
1993年 | 133篇 |
1992年 | 60篇 |
1991年 | 48篇 |
1990年 | 58篇 |
1989年 | 52篇 |
1988年 | 55篇 |
1987年 | 50篇 |
1986年 | 57篇 |
1985年 | 60篇 |
1984年 | 34篇 |
1983年 | 39篇 |
1982年 | 36篇 |
1981年 | 36篇 |
1980年 | 32篇 |
1979年 | 19篇 |
1978年 | 28篇 |
1977年 | 71篇 |
1976年 | 128篇 |
1975年 | 23篇 |
1974年 | 20篇 |
1973年 | 15篇 |
1971年 | 11篇 |
排序方式: 共有4441条查询结果,搜索用时 15 毫秒
1.
Journal of Materials Science - 相似文献
2.
Predicting Forest Age Classes from High Spatial Resolution Remotely Sensed Imagery Using Voronoi Polygon Aggregation 总被引:1,自引:0,他引:1
Efficient identification of forest age is useful for forest management and ecological applications. Here we propose a user-assisted method for determining forest age using high spatial resolution remotely sensed imagery. This method requires individual trees to be extracted from imagery and represented as points. We use a local maximum filter to generate points that are converted to Voronoi polygons. Properties of the Voronoi polygons are correlated with forest age and used to aggregate points (trees) into areas (stands) based on three forest age classes. Accuracy of the aggregation ranges from approximately 68% to 78% and identification of the mature class is more consistent and accurate than the younger classes. 相似文献
3.
4.
5.
J Brake TJ Walsh CE Benton JN Petitte R Meijerhof G Pe?alva 《Canadian Metallurgical Quarterly》1997,76(1):144-151
The relative importance of fat and lean tissue mass in determining bone mineral mass among postmenopausal women was examined in this 1-year longitudinal study. Fifty postmenopausal Caucasian women entered the study; 45 of them completed a 1-year follow-up. Dual-energy X-ray absorptiometry was employed for measuring total and regional bone mineral density (BMD) and bone mineral content (BMC), fat tissue mass (FTM), lean tissue mass (LTM), and body weight. Results from linear regression analysis using the cross-sectional data (n = 50) of the study indicated that LTM explained a larger percentage of variation in bone mineral mass than did FTM. FTM and LTM were found to be moderately correlated (r = 0.55); when FTM was entered in the same predicting regression models, LTM was a significant predictor (p < 0.05) of the total and regional BMC, but not BMD. The percent FTM (and inversely %LTM) was correlated with BMD and BMC, but significant correlation was primarily found only for total body BMD (or BMC). Weight was the best predictor of total body BMD and BMC. Longitudinally (n = 45), annual changes in both FTM and weight were significantly associated with annual changes in regional BMD after adjustment for initial bone mineral values (p < 0.05). We conclude that bone mineral mass is more closely related to LTM than to FTM, while annual changes in regional BMD are more closely correlated with changes in FTM in healthy postmenopausal women. Meanwhile, increased body weight is significantly associated with increased bone mineral mass. 相似文献
6.
DC Reynolds CE Leak KK Bajaj CE Stutz RL Jones KR Evans PW Yu WM Theis 《Canadian Metallurgical Quarterly》1989,40(9):6210-6217
7.
8.
The mechanical fracture strength and toughness of short-fibre composites, injection moulded from compounds of poly(ethylene terephthalate) (PET) containing 10 and 30% (by weight) (w/o) glass, have been investigated and the dependence upon matrix hydrolytic stability determined. Mouldings have been characterised by several physical techniques to evaluate molecular weight, degradation rates, crystallinity and morphology, whilst time-dependent gravimetric data were derived to quantify sorption kinetics and allow comparisons with theoretical reaction rates to be made. During melt processing, PET is hydrolysed extremely rapidly by traces of moisture (<0.02w/o). yet the inherent strength of moulded composites declines significantly only below an apparently critical molecular weight. However, on long-term humid ageing in hot water, impact behaviour especially is rendered more complex by simultaneous crystallisation, molecular reorder and losses of interfacial bond strength. 相似文献
9.
10.
We present a new algorithm,
called MCS-M,
for computing minimal triangulations of graphs.
Lex-BFS, a seminal algorithm for recognizing chordal graphs,
was the genesis for two other classical algorithms:
LEX M and MCS.
LEX M extends the fundamental concept used in Lex-BFS,
resulting in an algorithm that not only recognizes chordality,
but also computes a minimal triangulation of an arbitrary graph.
MCS simplifies the fundamental concept used in Lex-BFS,
resulting in a simpler algorithm for recognizing chordal graphs.
The new algorithm MCS-M combines
the extension of LEX M with the simplification of MCS,
achieving all the results of LEX M in the same time complexity. 相似文献