全文获取类型
收费全文 | 247103篇 |
免费 | 23407篇 |
国内免费 | 13943篇 |
专业分类
电工技术 | 16734篇 |
技术理论 | 10篇 |
综合类 | 27948篇 |
化学工业 | 34495篇 |
金属工艺 | 9042篇 |
机械仪表 | 14046篇 |
建筑科学 | 34213篇 |
矿业工程 | 12000篇 |
能源动力 | 10977篇 |
轻工业 | 13133篇 |
水利工程 | 25193篇 |
石油天然气 | 14515篇 |
武器工业 | 2453篇 |
无线电 | 12738篇 |
一般工业技术 | 24005篇 |
冶金工业 | 9317篇 |
原子能技术 | 3889篇 |
自动化技术 | 19745篇 |
出版年
2024年 | 790篇 |
2023年 | 2727篇 |
2022年 | 5496篇 |
2021年 | 6559篇 |
2020年 | 7228篇 |
2019年 | 6234篇 |
2018年 | 5988篇 |
2017年 | 7577篇 |
2016年 | 8455篇 |
2015年 | 8734篇 |
2014年 | 14761篇 |
2013年 | 14602篇 |
2012年 | 18825篇 |
2011年 | 19040篇 |
2010年 | 14564篇 |
2009年 | 15113篇 |
2008年 | 13778篇 |
2007年 | 17378篇 |
2006年 | 15583篇 |
2005年 | 13553篇 |
2004年 | 10918篇 |
2003年 | 9602篇 |
2002年 | 8197篇 |
2001年 | 6792篇 |
2000年 | 5900篇 |
1999年 | 4861篇 |
1998年 | 3754篇 |
1997年 | 3241篇 |
1996年 | 2664篇 |
1995年 | 2400篇 |
1994年 | 1961篇 |
1993年 | 1437篇 |
1992年 | 1247篇 |
1991年 | 919篇 |
1990年 | 760篇 |
1989年 | 742篇 |
1988年 | 510篇 |
1987年 | 358篇 |
1986年 | 279篇 |
1985年 | 188篇 |
1984年 | 175篇 |
1983年 | 94篇 |
1982年 | 84篇 |
1981年 | 72篇 |
1980年 | 57篇 |
1979年 | 54篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1975年 | 19篇 |
1959年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
辽宁省是水资源严重短缺的省份之一,水资源不足已成为制约全省经济社会可持续发展的瓶颈。通过对全省大型取用水户的调查分析,找出了辽宁省节水工作中存在的问题,提出了节约用水工作的对策和建议。 相似文献
992.
底水油藏射孔优化设计 总被引:2,自引:1,他引:1
为了优化底水油藏的生产参数,研究了不同产量时射孔长度的优化方法。采用球面流和径向流相结合的模型推导了临界产量和无水采油量的计算公式,分别以临界产量和无水采油量为标准,对胜利油田桩西区块底水油藏上6口油井的射孔长度进行了优化设计,优化结果表明,对于底水油藏应首先按照临界产量对射孔长度进行优化设计,如果得到的最大临界产量不符合实际生产的要求,就应按照无水采油量进行射孔优化设计。研究表明,当油井产量超过临界产量后,以临界产量为标准得到的优化射孔长度会减小油井的无水采油量。 相似文献
993.
Economic ideas and processes are becoming increasingly integrated with more traditional engineering and hydrologic models
of water management problems. Combining economic management concepts and performance indicators with an engineering-level
of understanding of a hydrologic system can provide results and insights more directly relevant for water management decisions
and policies. When such models are developed and used with involvement of stakeholders, they can become a basis for shared
understanding of water problems as a foundation for negotiated management and policy solutions. When implemented with optimization
software, integrated hydro-economic models also can suggest promising innovative solutions for policy-makers to consider.
Their applications to river basin management problems are reviewed. Economic and integrated economic-engineering-hydrologic
modeling is then discussed in the context of the evolving European Water Framework Directive. Relevant items are cost recovery
and water pricing, cost-effectiveness of water management measures, and public participation in decision processes. 相似文献
994.
995.
A new method for characterization of stratified thermal energy stores (TES) that integrates both the first law and the second law concerns is presented here. The first law concern is incorporated into a quantity called energy response factor and the second law concern into an entropy generation ratio. A product of these two quantities is at the heart of the TES efficiency definitions. This approach removes the overemphasis of the existing methods either on the first or the second law of thermodynamics which often biases the characterization results. The information about the evolution of the temperature field of the system in time is the prerequisite of the new method. It may be obtained from experiments or from suitable numerical simulations. The current method can be easily integrated into computational fluid dynamic (CFD) simulations and thus facilitate CFD-based design analysis. As an example of such CFD-integrated analysis, a large-scale hot water seasonal heat store is numerically studied to identify the effects of aspect ratio, containment shape, internal structures, and containment size on their efficiency. The results suggest the effectiveness of the new method in deriving useful design insights. 相似文献
996.
对天津及其滨海新区生态城市水利建设进行了分析。研究了在淡水资源极度匮乏的条件下,有效开发利用非常规水资源的必要性、重要性和现实性。认为天津市对水资源应遵循节水、治污、高效配置,妥善处理生活、生产、生态之间的关系,力求平衡调配。供水水源应是多元的,增加非常规水资源(污水、海/咸水、雨/洪水)的利用,同时增加可用地下水,外调来水等,逐步进入可持续发展配置。 相似文献
997.
An assessment of hydrocarbon and metal/metalloids (arsenic, cadmium, copper, lead, mercury, selenium, zinc) contamination in sediments from Lake Mulwala, Australia, was undertaken. The objectives of the study were: (i) to determine the extent of contamination in the lake sediments, compared to Australian and international sediment quality guidelines, and (ii) to attempt to identify the contaminant sources to the lake. With the exception of a few samples containing elevated levels of arsenic and/or mercury, the levels of all contaminants in the sediment samples taken from the lake were below the ‘lower trigger’ of the Australian Sediment Quality Guidelines that would warrant further investigation. High molecular weight hydrocarbons (up to 700 mg kg−1) were found in most sediment samples. Non‐metric statistical analysis indicated that the contaminant distribution was different in different parts of the lake, with the lowest concentrations generally found at the influent to the lake. No definitive source(s) of contamination could be identified for either metalloids or hydrocarbons. 相似文献
998.
A.J. MILLER F.J. SCHULTZ A. OSER J.L. HALLMAN S.A. PALUMBO 《Journal of food science》1994,59(4):739-741
Swine carcass microflora were evaluated for selected foodborne pathogens after exposure to reconditioned water during scalding, dehairing, and polishing operations. Reused water had been reconditioned and chlorinated. Rodac plates applied to hams were used to assess carcass microflora. Water samples were enumerated using membrane filtration or spiral plating. Sampling was at mid-week throughout the year. Total aerobic plate counts on hams were unaffected by treating with potable or reconditioned waters. No differences were observed for staphylococci, enterics, fecal streptococci, Listeria monocytogenes, coliforms, and Aeromonas levels. A preevisceration potable water carcass wash reduced the bacterial load, regardless of initial treatment. Bacterial counts on carcasses paralleled those in water. Reuse is an alternative to potable water for initial slaughter operations without diminishing bacteriologic safety. 相似文献
999.
Properties of Edible Films from Total Milk Protein 总被引:5,自引:0,他引:5
The mechanical properties and water vapor permeability of edible films made from various total milk proteins (TMPs) were investigated. Two TMPs obtained from nonfat dry milk (NDM) by removing lactose and three TMPs obtained from a commercial source were studied. Lactose was extracted from NDM by ultrafiltration or suspension in ethanol followed by filtration. TMP concentrate obtained by ultrafiltration (UF) produced films with the lowest water vapor permeability (WVP) and the highest tensile strength at break. Commercial TMP concentrates produced films more ductile than those from the UF-TMP or retentate from ethanol extraction. Further research is needed to improve mechanical properties of UF-TMP films without increasing the WVP. 相似文献
1000.
本文从理论和实践上综述了磁化水的特性、磁化机理、国内外的发展近况及其使用安装等。该法用于锅炉和各类冷却水处理有广泛的前景。 相似文献