全文获取类型
收费全文 | 2556篇 |
免费 | 59篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 22篇 |
综合类 | 1篇 |
化学工业 | 465篇 |
金属工艺 | 49篇 |
机械仪表 | 51篇 |
建筑科学 | 121篇 |
矿业工程 | 7篇 |
能源动力 | 48篇 |
轻工业 | 208篇 |
水利工程 | 35篇 |
石油天然气 | 1篇 |
无线电 | 268篇 |
一般工业技术 | 391篇 |
冶金工业 | 626篇 |
原子能技术 | 18篇 |
自动化技术 | 310篇 |
出版年
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 29篇 |
2018年 | 32篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 26篇 |
2014年 | 51篇 |
2013年 | 124篇 |
2012年 | 78篇 |
2011年 | 139篇 |
2010年 | 81篇 |
2009年 | 82篇 |
2008年 | 105篇 |
2007年 | 109篇 |
2006年 | 105篇 |
2005年 | 112篇 |
2004年 | 82篇 |
2003年 | 67篇 |
2002年 | 71篇 |
2001年 | 60篇 |
2000年 | 50篇 |
1999年 | 59篇 |
1998年 | 114篇 |
1997年 | 76篇 |
1996年 | 82篇 |
1995年 | 49篇 |
1994年 | 48篇 |
1993年 | 35篇 |
1992年 | 35篇 |
1991年 | 23篇 |
1990年 | 34篇 |
1989年 | 38篇 |
1988年 | 35篇 |
1987年 | 27篇 |
1986年 | 34篇 |
1985年 | 44篇 |
1984年 | 34篇 |
1983年 | 38篇 |
1982年 | 31篇 |
1981年 | 24篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 20篇 |
1973年 | 16篇 |
1971年 | 11篇 |
排序方式: 共有2621条查询结果,搜索用时 31 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.
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
5.
6.
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
7.
Formaldehyde is used in ruminant feeding for different purposes including the protection of dietary proteins from ruminal degradation. The formaldehyde content of milk of goats fed various levels of formaldehyde-treated soybean oil-meal has been determined by using a sensitive HPLC method. Results showed a significant linear correlation between ingested formaldehyde and formaldehyde concentration in milk. About 0.02% of ingested formaldehyde was excreted in milk, as free formaldehyde. 相似文献
8.
D Barry J Bea D Bernd T DeFauw C Marr T McCormick JK Mitchell M O'Neil M Pittman D Strum 《Canadian Metallurgical Quarterly》1994,68(11):42, 44-46, 48
In cooperation with McManis Associates, Hospitals & Health Networks recently convened a CEO summit on physician/hospital integration activities. In the third report of a three-part series on the summit, leading health care executives discuss investor capital needs, strategic information management needs, and the management competencies required for capitated managed care success. 相似文献
9.
Quantitative analyses of flow and stage data, remote sensing and geographic information systems analysis, and field studies were used to assess the impact of dams and diversions on the point bar habitat of the Sacramento Valley Tiger Beetle (Cicindela hirticollis abrupta). The reaches of interest include sites of known historic populations of C. h. abrupta along the Sacramento River from approximately 8 km north of Colusa southward to the confluence with the Feather River and along the Feather River between Yuba City and its confluence with the Sacramento River. The results from this study show that construction of two major dams has altered flows such that prolonged and increased flows during summer, fall, and early winter have most likely disrupted life cycles, flooded larvae, drowned overwintering adults and led to high mortality. Additionally, habitat availability has decreased over time because point bars have decreased in number and area causing increased distances between populations and isolation of populations. Moreover, point bar armouring, channel scouring, altered flows, redirected flows through weirs, and lithologic controls have produced a bimodal distribution of mean grain sizes in the Sacramento River in which the more northern bars contain gravel deposits and more southern bars possess fine sands. These conditions negatively alter moisture retention and sediment compaction and, consequently, burrowing conditions needed by this tiger beetle. Additionally, more stabilized flows (reduced variability) and increased fine‐grained deposition have enabled development and encroachment of vegetation onto the sand bars. Finally, human stresses, such as foot traffic and vehicular traffic may have interfered with burrowing, ovipositing, and foraging. The combination of these stress factors has most likely led to a reduction in source populations and, ultimately, the apparent extirpation of the entire metapopulation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
10.
Reviews the research on psychosocial aspects of classroom environment by outlining economical, hand-scorable classroom environment instruments (i.e., Classroom Environment Scale, Individualized Classroom Environment Questionnaire, a class inventory developed by the present author and colleagues [1982]) and describing their past uses. Studies on the effects of classroom environment on student outcomes, use of environment variables as process criteria in evaluating educational innovations, and teachers' practical attempts to use learning environment assessments to guide improvements in classrooms are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献