全文获取类型
收费全文 | 69739篇 |
免费 | 4690篇 |
国内免费 | 2044篇 |
专业分类
电工技术 | 2806篇 |
技术理论 | 8篇 |
综合类 | 3045篇 |
化学工业 | 13043篇 |
金属工艺 | 3192篇 |
机械仪表 | 3592篇 |
建筑科学 | 4618篇 |
矿业工程 | 1796篇 |
能源动力 | 1963篇 |
轻工业 | 4142篇 |
水利工程 | 1041篇 |
石油天然气 | 4061篇 |
武器工业 | 444篇 |
无线电 | 6732篇 |
一般工业技术 | 9246篇 |
冶金工业 | 6996篇 |
原子能技术 | 656篇 |
自动化技术 | 9092篇 |
出版年
2024年 | 260篇 |
2023年 | 997篇 |
2022年 | 1630篇 |
2021年 | 2241篇 |
2020年 | 1761篇 |
2019年 | 1584篇 |
2018年 | 1779篇 |
2017年 | 1946篇 |
2016年 | 1821篇 |
2015年 | 2222篇 |
2014年 | 2817篇 |
2013年 | 4125篇 |
2012年 | 3678篇 |
2011年 | 4247篇 |
2010年 | 3519篇 |
2009年 | 3437篇 |
2008年 | 3636篇 |
2007年 | 3465篇 |
2006年 | 3375篇 |
2005年 | 3017篇 |
2004年 | 2081篇 |
2003年 | 1953篇 |
2002年 | 1804篇 |
2001年 | 1459篇 |
2000年 | 1575篇 |
1999年 | 1785篇 |
1998年 | 1564篇 |
1997年 | 1331篇 |
1996年 | 1221篇 |
1995年 | 1122篇 |
1994年 | 939篇 |
1993年 | 828篇 |
1992年 | 673篇 |
1991年 | 489篇 |
1990年 | 493篇 |
1989年 | 431篇 |
1988年 | 400篇 |
1987年 | 337篇 |
1986年 | 345篇 |
1985年 | 333篇 |
1984年 | 326篇 |
1983年 | 322篇 |
1982年 | 255篇 |
1981年 | 273篇 |
1980年 | 264篇 |
1979年 | 255篇 |
1978年 | 228篇 |
1977年 | 229篇 |
1976年 | 205篇 |
1975年 | 195篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Sustainable Development and Management of Water Resources in the Hei River Basin of North-west China
The quantitative and qualitative evaluation of water, land and biotic resources in the inland river basins is important in the arid zone. Analysis of the exploitation potential of water resources and the environmental changes through water development can help people in the sustainable development and management of water resources within the basin. Water resources development has affected the scale of oasis establishment in the middle reaches and the existence of lower-reach oases in the Hei River basin. Exploitation and utilization of water resources at the present stage should bring about a harmonic relation between economic development and the ecological environment in the whole basin. The whole area should be considered as an entirety to adopt feasible engineering and administrative measures such as strengthening the protection of water resources in upper streams, macro-control of water consumption and implementing water-saving measures in middle and lower reaches, quantitatively managing and allotting water resources in accordance with regional conditions and adherence to comprehensive rehabilitation. Thus, economic, environmental and social benefits of water resources can be enhanced. 相似文献
102.
Liang Y.C. Wenjiang Zeng Pick Hong Ong Zhaoxia Gao Jun Cai Balasubramanian N. 《Electron Device Letters, IEEE》2002,23(12):700-703
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology. 相似文献
103.
两种波长激光血管内照射生物效应比较 总被引:2,自引:0,他引:2
目的:研究同等照射条件的低强度532nm与633nm激光血管内照射生物效应的特点。方法:用532nm和633nm激光对健康大耳白家兔血管内照射,平均照射功率均设定在5mW左右,照射总能量约12J。两组家兔均于照前及照后1d、4d、7d、11d采集外周血,检测血浆ET、NO、MDA含量和SOD活性。结果:两组家兔上述各指标随照后时间的变化规律相似,经方差分析组间各指标都没有显著性差异。结论:同等照射条件下,低强度532nm与633nm激光照射血液的生物效应相似。 相似文献
104.
105.
106.
107.
James A. Chiddix 《International Journal of Communication Systems》1989,2(2):87-93
This paper updates a scenario for the evolutionary integration of optical fibre transmission technology into existing cable television networks first presented in 1988. The resulting ‘fibre backbone’ yields a hybrid fibre/coaxial network with significantly better reliability and transmission quality than present systems. System and electro-optical component advances in the last year are reviewed, and the merits of various modulation techniques are examined. The fibre backbone approach emphasizes continuing the broadband delivery of a large number of video signals to the consumer. 相似文献
108.
Action calculi, which generalise process calculi such as Petri nets, π-calculusand ambient calculus, have been presented
in terms of action graphs. We here offer linear action graphs as a primitive basis for action calculi. This paper presents the category of embeddings of undirected linear
action graphs without nesting, using a novel form of graphical reasoning which simplifies some otherwise complex manipulations
in regular algebra. The results are adapted in a few lines to directed graphs. This work is part of a long-term search for
a uniform behavioural theory for process calculi.
Received October 2000 / Accepted in revised form April 2001 相似文献
109.
Serum total cholesterol, high density lipoprotein (HDL) cholesterol, and triglyceride levels were studied in healthy male
and female subjects consuming for one-week periods a diet of conventional food (CF) providing 42% of energy as fat, principally
butter fat, and then in random order nutritionally complete, defined formula diets of moderate (32%) to very low (1%) fat
content. Compared to CF, the formula with 32% of energy as corn oil lowered serum cholesterol by 25% and the ratio of total
to HDL-cholesterol by 13%. Low (9%) and very low (1–3%) fat formulas reduced HDL-cholesterol by as much as 40%, raised the
total: HDL-cholesterol ratio by about 20% and raised serum triglyceride levels by as much as 100%. When low and very low fat
formulas were ingested for three weeks, these effects persisted although maximal responses occurred during the first week.
These results demonstrated that a moderate fat formula diet with a high P/S ratio had a more favorable effect on serum lipid
levels than various low fat formulas. Low fat conventional food diets should be studied in long-term controlled metabolic
experiments before such diets are recommended to the general population for coronary heart disease or cancer prevention. 相似文献
110.
The global market for liquid mixed‐metal stabilizers is migrating toward heavy‐metal‐free products, Historically, these systems have not been performance and cost competitive. High efficiency calcium‐zinc stabilizers have the potential to replace heavy‐metal‐based products. The intrinsic value of non‐phenolic lubricating calcium intermediates and calcium‐zinc stabilizers is discussed. 相似文献