全文获取类型
收费全文 | 8440篇 |
免费 | 1088篇 |
国内免费 | 626篇 |
专业分类
电工技术 | 380篇 |
技术理论 | 2篇 |
综合类 | 1114篇 |
化学工业 | 125篇 |
金属工艺 | 43篇 |
机械仪表 | 86篇 |
建筑科学 | 1113篇 |
矿业工程 | 718篇 |
能源动力 | 504篇 |
轻工业 | 75篇 |
水利工程 | 4471篇 |
石油天然气 | 273篇 |
武器工业 | 56篇 |
无线电 | 495篇 |
一般工业技术 | 159篇 |
冶金工业 | 104篇 |
原子能技术 | 51篇 |
自动化技术 | 385篇 |
出版年
2024年 | 31篇 |
2023年 | 101篇 |
2022年 | 227篇 |
2021年 | 268篇 |
2020年 | 263篇 |
2019年 | 268篇 |
2018年 | 300篇 |
2017年 | 341篇 |
2016年 | 359篇 |
2015年 | 345篇 |
2014年 | 550篇 |
2013年 | 470篇 |
2012年 | 636篇 |
2011年 | 654篇 |
2010年 | 470篇 |
2009年 | 522篇 |
2008年 | 454篇 |
2007年 | 563篇 |
2006年 | 493篇 |
2005年 | 458篇 |
2004年 | 429篇 |
2003年 | 315篇 |
2002年 | 315篇 |
2001年 | 272篇 |
2000年 | 228篇 |
1999年 | 187篇 |
1998年 | 124篇 |
1997年 | 113篇 |
1996年 | 76篇 |
1995年 | 74篇 |
1994年 | 66篇 |
1993年 | 61篇 |
1992年 | 32篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
Can Ercan S. Esra Safran Artuğ Türkmenoğlu Uğur Karabakal 《Journal of surfactants and detergents》2021,24(1):139-147
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated. 相似文献
2.
道教洞天福地作为中国名山风景的经典类型之一,在宗教山岳景观中占据独特地位。浙东天台山水神秀,历代高道以入山隐修为主要目的,形成了道教在区域山林的景观文化基础。从天台山“神仙之乡”的文化背景出发,从“想象与实践”的视角切入,梳理了天台山洞天福地的景观流变:分析其“不死之福庭”地域性景观的形成经历了“赤城→桐柏”的信仰转移过程;以天台山为坐标,洞天福地格局打破了区域“层级”分布特征,而呈现大范围“州郡”空间格局。作为“联结点”的天台山,洞天世界沟通了宇宙、山、人3个基本场域,由此衍生出“洞宫”式和“周回”式山岳空间营建典范。旨在挖掘洞天福地中典型案例的价值,为中国洞天福地体系的构建提供理论依据。 相似文献
3.
为解决21000工作面采空区及顶板涌水问题,根据工作面出水点的不同情况,采取了集水器导水、老塘设挡水堰截水、挖排水沟疏水等多项治水措施,经统计排水量达33~42m3/h,有效控制了水情,确保了工作面正常生产。 相似文献
4.
5.
6.
Recently, preemption techniques have attracted considerable attention as a means to provide differentiated quality of service
in optical burst switching (OBS) networks. This paper is focused on the analysis of preemption probabilities for bursts within
the same priority class. As proposed by Vokkarane and Jue ((2003)* IEEE J Select Areas Commun 21(7): 1198–1209) an incoming
burst will preempt the burst in service, within the same priority class, if the residual length of the burst in service is
smaller than the incoming burst length. For a general case with wavelength conversion, the preemption probability of contending
bursts with a generic service distribution, not necessarily exponential, is analyzed. First, we show that the size distribution
for the preempting bursts is shifted to larger values, in comparison to the original burst size distribution. Second, we obtain
an upper and lower bound for the preemption probability. Finally, the asymptotic behavior of the OBS switch is analyzed showing
that preemption will always occur for a very large number of wavelengths. 相似文献
7.
8.
9.
10.
三峡水库减淤增容调度方式研究——多汛限水位调度方案 总被引:8,自引:0,他引:8
本文建议在汛期中小流量时(Q<35000m3/s),将坝前水位维持在148~151m;出现汛情且流量更较大后,将坝前水位降低到143m;入库流量大于35000m3/s且短期预报将出现大于十年一遇洪水时,预泄洪水到135m.按这一调度,汛期约80%时间可以维持在较高水位,一般洪水期。汛限水位143m不影响坝区通航,135m水位迎洪可大量增加防洪库客。到100年后可减淤30亿m3,增加防洪库容约40亿m3.变动回水区减淤40%,优化了坝区水沙搭配,可改善通航条件。降低库区洪水位,缓解防洪与移民的矛盾。可对发电带来较大好处:提高发电效益,减少粗沙过机。初期水库排沙比大于原方案,可减轻下游冲刷。同时,可减小三峡汛初泄水与鄱阳湖防洪的矛盾。 相似文献