全文获取类型
收费全文 | 352214篇 |
免费 | 28990篇 |
国内免费 | 16475篇 |
专业分类
电工技术 | 22024篇 |
技术理论 | 59篇 |
综合类 | 46595篇 |
化学工业 | 40684篇 |
金属工艺 | 17783篇 |
机械仪表 | 19305篇 |
建筑科学 | 50247篇 |
矿业工程 | 17754篇 |
能源动力 | 17212篇 |
轻工业 | 18709篇 |
水利工程 | 16884篇 |
石油天然气 | 15332篇 |
武器工业 | 3140篇 |
无线电 | 21352篇 |
一般工业技术 | 26780篇 |
冶金工业 | 20801篇 |
原子能技术 | 4087篇 |
自动化技术 | 38931篇 |
出版年
2024年 | 1095篇 |
2023年 | 3388篇 |
2022年 | 6763篇 |
2021年 | 7928篇 |
2020年 | 8504篇 |
2019年 | 6928篇 |
2018年 | 6553篇 |
2017年 | 8032篇 |
2016年 | 9694篇 |
2015年 | 10871篇 |
2014年 | 20879篇 |
2013年 | 18379篇 |
2012年 | 23616篇 |
2011年 | 25310篇 |
2010年 | 19814篇 |
2009年 | 20927篇 |
2008年 | 19031篇 |
2007年 | 25156篇 |
2006年 | 23698篇 |
2005年 | 20606篇 |
2004年 | 17370篇 |
2003年 | 15715篇 |
2002年 | 13157篇 |
2001年 | 11035篇 |
2000年 | 9320篇 |
1999年 | 7595篇 |
1998年 | 5770篇 |
1997年 | 5012篇 |
1996年 | 4532篇 |
1995年 | 3803篇 |
1994年 | 3308篇 |
1993年 | 2535篇 |
1992年 | 2224篇 |
1991年 | 1610篇 |
1990年 | 1405篇 |
1989年 | 1258篇 |
1988年 | 973篇 |
1987年 | 667篇 |
1986年 | 505篇 |
1985年 | 409篇 |
1984年 | 409篇 |
1983年 | 305篇 |
1982年 | 270篇 |
1981年 | 193篇 |
1980年 | 163篇 |
1979年 | 126篇 |
1978年 | 74篇 |
1977年 | 79篇 |
1975年 | 67篇 |
1959年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b. 相似文献
13.
14.
The supervision of a hybrid power plant, including solar panels, a gas microturbine and a storage unit operating under varying solar power profiles is considered. The Economic Supervisory Predictive controller assigns the power references to the controlled subsystems of the hybrid cell using a financial criterion. A prediction of the renewable sources power is embedded into the supervisor. Results deteriorate when the solar power is unsteady, owing to the inaccuracy of the predictions for a long-range horizon of 10 s. The receding horizon is switched between an upper and a lower value according to the amplitude of the solar power trend. Theoretical results show the relevance of horizon switching, according to a tradeoff between performance and prediction accuracy. Experimental results, obtained in a Hardware In the Loop (HIL) framework, show the relevance of the variable horizon approach. Power amplifiers allow us to simulate virtual components, such as a gas microturbine, and to blend their powers with that of real devices (storage unit, real solar panels). In this case, fuel savings, reaching 15%, obtained under unsteady operating conditions lead to a better overall performance of the hybrid cell. The overall savings obtained in the experiments amount to 12%. 相似文献
15.
A small handful of recent studies have addressed a phenomenon known as “phantom vibration syndrome”. This refers to when phone users perceive their device to vibrate, indicating that a call or text is incoming, when in fact the phone did not vibrate at all. Though these studies show that most users do not find phantom vibration hallucinations to be very bothersome, they also find that a large majority of users experience this phenomenon. This paper explores what the striking prevalence of phantom vibration syndrome means for our contemporary relationships with technology. I begin with a review of the theories purporting to explain these data, which largely rely on particular understandings of the brain. Next I develop an alternative theory of phantom vibration syndrome based on insights from the philosophical tradition of phenomenology. This account considers the ways users develop bodily and perceptual habits regarding how the phone is understood and used. By critically contrasting these different theories, we can refine our questions about what the high prevalence of phantom vibration syndrome implies about our contemporary technological situation. 相似文献
16.
对鞍钢股份无缝钢管厂连轧机前毛管坯横移装置存在的设计缺陷进行了分析,并提出改进方案,将原横移装置由高架轨道横移机构及上下升降链传动装置,改进为地面轨道横移系统及同步旋转臂实现取管、放管过程。实施后消除了生产故障,缩短了轧制周期,降低生产成本。 相似文献
17.
《低温学》2015
He-3 is generally recognized for its ability to provide more excellent thermophysical performance than He-4, especially in the 4 K temperature range. However, this was not always the case in our preliminary experiments on a three-stage Stirling-type pulse tube cryocooler (SPTC). Our ongoing studies, as reported in this paper, demonstrate that the different working fluids also affect the performance through their phase shifting capability. This feature has been passed over in large part by researchers considering refrigerant substitution. Unlike previous theoretical analyses that focus primarily on regenerator losses, this report investigates the effects of the working fluid on the phase angle at the cold end in order to quantitatively reveal the relationship between the lowest attainable temperature and the cooling capacity. The analysis agrees well with our experimental results on a three-stage SPTC. While running with the operating parameters optimized for He-3, the lowest temperature of the SPTC decreased from 5.4 K down to 4.03 K. This is the lowest refrigeration temperature ever achieved with a three-stage SPTC. 相似文献
19.
Salman M.A. Salman 《国际水资源开发杂志》2015,31(1):4-16
The United Nations Watercourses Convention entered into force on 17 August 2014, following a long and complex journey that dates back to 1970 when the UN referred the matter to its legal arm, the International Law Commission. This article follows the Convention through that long and turbulent road, examines its main provisions and analyses the reasons for the delay of its entry into force. It concludes by answering the question of why entry into force of the Convention should indeed matter. 相似文献
20.
电网的安全水平主要取决于其使用产品的质量是否过关。如果产品的质量较好,则能建造出优质的电网,电网的安全水平便会随之提高。因此,应加强对产品质量的监督管理,从而提高电网的安全水平。我们可建立质量监督管理系统,及时抽检出质量不过关的产品,从而消除电网运行过程中潜在的安全隐患。 相似文献