全文获取类型
收费全文 | 77251篇 |
免费 | 7610篇 |
国内免费 | 1919篇 |
专业分类
电工技术 | 2861篇 |
技术理论 | 7篇 |
综合类 | 3073篇 |
化学工业 | 16623篇 |
金属工艺 | 3160篇 |
机械仪表 | 4645篇 |
建筑科学 | 13594篇 |
矿业工程 | 2107篇 |
能源动力 | 1797篇 |
轻工业 | 7595篇 |
水利工程 | 1520篇 |
石油天然气 | 2029篇 |
武器工业 | 348篇 |
无线电 | 5671篇 |
一般工业技术 | 7528篇 |
冶金工业 | 3465篇 |
原子能技术 | 750篇 |
自动化技术 | 10007篇 |
出版年
2024年 | 243篇 |
2023年 | 1242篇 |
2022年 | 3816篇 |
2021年 | 4165篇 |
2020年 | 2174篇 |
2019年 | 2040篇 |
2018年 | 2253篇 |
2017年 | 2805篇 |
2016年 | 4141篇 |
2015年 | 4659篇 |
2014年 | 5549篇 |
2013年 | 5479篇 |
2012年 | 4548篇 |
2011年 | 4162篇 |
2010年 | 3358篇 |
2009年 | 3367篇 |
2008年 | 3001篇 |
2007年 | 4457篇 |
2006年 | 4697篇 |
2005年 | 4075篇 |
2004年 | 2899篇 |
2003年 | 2801篇 |
2002年 | 2151篇 |
2001年 | 1504篇 |
2000年 | 1424篇 |
1999年 | 1068篇 |
1998年 | 778篇 |
1997年 | 605篇 |
1996年 | 523篇 |
1995年 | 415篇 |
1994年 | 361篇 |
1993年 | 266篇 |
1992年 | 221篇 |
1991年 | 188篇 |
1990年 | 171篇 |
1989年 | 125篇 |
1988年 | 86篇 |
1987年 | 78篇 |
1986年 | 77篇 |
1985年 | 99篇 |
1984年 | 105篇 |
1983年 | 77篇 |
1982年 | 42篇 |
1981年 | 55篇 |
1980年 | 62篇 |
1966年 | 25篇 |
1964年 | 34篇 |
1962年 | 65篇 |
1959年 | 21篇 |
1955年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
商业创新模式下的建筑设计服务 总被引:1,自引:0,他引:1
购物中心作为一种现代的零售商业模式,从上世纪90年代进入中国后,已为一般民众厂为接受。文章首先简要地介绍了美国购物中心的开发历史和类型,尤其是近年来出现的生活方式中心的特点和发展趋势。对于购物中心在中国的开发、规划设计中经常遇到的一些内容,如融资方式,主力商店和专卖店等进行了讨论。最后对于建筑师在这新的商业模式下如何与设计团队一起提供专业服务方面根据自身的经验提出了自己的看法。 相似文献
132.
Titipong Issariyakul Mangesh G. KulkarniAjay K. Dalai Narendra N. Bakhshi 《Fuel Processing Technology》2007
Transesterification of waste fryer grease (WFG) containing 5–6 wt.% free fatty acid (FFA) was carried out with methanol, ethanol, and mixtures of methanol/ethanol maintaining the oil to alcohol molar ratio of 1:6, and initially with KOH as a catalyst. Mixtures of methanol and ethanol were used for transesterification in order to use the better solvent property of ethanol and rapid equilibrium using methanol. Formation of soap by reaction of FFA present in WFG with KOH instigated difficulty in the separation of glycerol from biodiesel ester. To untangle this problem, two-stage (acid and alkali catalyzed) method was used for biodiesel synthesis. More than 90% ester was obtained when two-stage method was used compared to ∼ 50% ester in single stage alkaline catalyst. In the case of mixed alcohol, a relatively smaller amount of ethyl esters was formed along with methyl esters. Acid value, viscosity, and cetane number of all the esters prepared from WFG were within the range of the ASTM standard. Esters obtained from WFG showed good performance as a lubricity additive. 相似文献
133.
134.
N. F. Kuschevskaya A. E. Kushchevskii A. I. Oleshko 《Powder Metallurgy and Metal Ceramics》2006,45(3-4):202-206
The possibility of utilizing nanopowders of iron and Fe-Co-Ni produced bu a thermochemical method in the fabrication of sealing
composition materials is investigated. It is established that such hermetic sealing composition materials function reliably
under extremal conditions and guarantee elevated strength of adhesion to the surface of the metal and high corrosion and temperature
stability.
__________
Translated from Poroshkaya Metallurgiya, Nos. 3–4(448), pp. 112–117, March–April, 2006. 相似文献
135.
136.
Owing to the rough warehouse handling of storage sacks in tropical areas in Africa, a suitable storage sack should not support de novo growth of fungal spores because this would reduce the tensile strength of the packaging material and act as a springboard for infecting grain contents. This paper reports the effect of activity of saprophytic fungi on the tensile strength of jute and woven polypropylene sacks. New woven polypropylene sacks carried lower levels of fungal spores (1.3×101 cfu/72 cm2) than jute sacks (3.0×103 cfu/72 cm2). The natural mould penetration and growth was examined on sections (4×5 cm) of both jute and woven polypropylene after previous incubation at relative humidities of 55, 60, 65, 70, 75, 80, 90 and 95% for 10 weeks by placing them on Sabouraud's Agar. There was a significant difference (P = 0.05 level of significance) between the higher penetration of mould growth on jute sacks and that obtained on woven polypropylene sacks. Saprophytic fungi (Aspergillus candidus, A. flavus, A. fumigatus, A. niger, A. japonicus, A. parasiticus, A. ustus, Fusarium oxysporium, F. moniliforme, Penicillium verucosum var. cyclopium, Rhizopus oryzae and Trichoderma viride) isolated from jute sacks reduced tensile strength, measured by an Instron Model 1026, by 50–75% after 10 weeks at 90% R.H. Same fungal species on woven polypropylene sacks did not alter the tensile strength. Woven polypropylene sacks did not absorb moisture whilst the moisture content of jute sacks increased by 5.3–6.0% in 10 weeks at 90% R.H. with concomitant increase in mould and yeast counts by 1–2 log cycles. Evidence is presented to show that there was a positive correlation between the final mycoflora on jute sacks and loss in tensile strength. No correlation, however, was found between the total aerobic bacteria on jute sacks and the concomitant reduction in tensile strength. Fungi therefore play a major role in the reduction of tensile strength of jute sacks. Sterilization by gamma irradiation (8.0 kGy) of jute and woven polypropylene sacks did not affect their intrinsic tensile strength. Woven polypropylene sacks therefore have many microbiological and physical advantages over the traditional jute sacks to merit their use for grain storage in tropical areas like Ghana. 相似文献
137.
辽河油田东部凹陷火山岩油藏较为集中分布.然而常规酸化效果较差.经采用三元酸(粉末硝酸、盐酸和氢氟酸)前置液压裂酸化后.获得显著的增产效果,进一步表明该项酸化工艺技术成熟,宜于推广应用。同时也面临技术集成再创新机遇.适应更广泛的地质需求。 相似文献
138.
浅谈京津冀都市圈区域水资源战略 总被引:1,自引:0,他引:1
京津冀都市圈区域发展已纳入国家整体发展战略,在全国占有十分重要的地位。但京津冀都市圈面临着水资源缺乏、生态恶化、水污染等一系列水问题,严重影响了区域经济社会发展。针对存在的问题,要构建区域新型水资源配置格局,提高城乡供水保证率;积极建设节水型社会;加快农村水利基础设施建设,解决农村居民饮水安全:加强水生态系统保护与修复;做好饮用水水源地保护和水功能区管理;做好跨省河流的水量分配。 相似文献
139.
Design for a high power-density Astron reactor 总被引:1,自引:0,他引:1
N. C. Christofilos 《Journal of Fusion Energy》1989,8(1-2):97-105
A liquid lithium blanket surrounding the plasma volume is described. The liquid lithium flows along magnetic flux tubes at a high speed. There is no vacuum wall between the blanket and the plasma. The E-layer of relativistic particles within which the plasma is confined serves as a vacuum wall protecting the plasma from the lithium vapor, which is continuously produced at the surface of the blanket, by ionizing the lithium atoms and ejecting the same along open magnetic lines. The heat load at the surface of the blanket generated by 14 MeV neutrons can be several hundred MW per square meter.Work performed under the auspices of the U.S. Atomic Energy Commission.Deceased September 24, 1972. 相似文献
140.
机电排灌工程是丘陵、滨湖地区的主要灌溉设施,必须建立适应市场经济的管理新机制,确保工程良性运行和巩固发展,满足不断发展的工农业生产需要。 相似文献