全文获取类型
收费全文 | 73448篇 |
免费 | 8496篇 |
国内免费 | 4213篇 |
专业分类
电工技术 | 12212篇 |
技术理论 | 13篇 |
综合类 | 5316篇 |
化学工业 | 8787篇 |
金属工艺 | 2585篇 |
机械仪表 | 3085篇 |
建筑科学 | 9981篇 |
矿业工程 | 2050篇 |
能源动力 | 12889篇 |
轻工业 | 2091篇 |
水利工程 | 1486篇 |
石油天然气 | 2130篇 |
武器工业 | 614篇 |
无线电 | 5412篇 |
一般工业技术 | 7671篇 |
冶金工业 | 3653篇 |
原子能技术 | 1258篇 |
自动化技术 | 4924篇 |
出版年
2024年 | 508篇 |
2023年 | 1715篇 |
2022年 | 2732篇 |
2021年 | 3002篇 |
2020年 | 3199篇 |
2019年 | 2821篇 |
2018年 | 2363篇 |
2017年 | 2819篇 |
2016年 | 3145篇 |
2015年 | 3078篇 |
2014年 | 5137篇 |
2013年 | 4894篇 |
2012年 | 5346篇 |
2011年 | 6028篇 |
2010年 | 4619篇 |
2009年 | 4687篇 |
2008年 | 4223篇 |
2007年 | 4608篇 |
2006年 | 3648篇 |
2005年 | 2819篇 |
2004年 | 2338篇 |
2003年 | 2011篇 |
2002年 | 1779篇 |
2001年 | 1517篇 |
2000年 | 1310篇 |
1999年 | 1039篇 |
1998年 | 842篇 |
1997年 | 648篇 |
1996年 | 598篇 |
1995年 | 441篇 |
1994年 | 396篇 |
1993年 | 314篇 |
1992年 | 240篇 |
1991年 | 218篇 |
1990年 | 184篇 |
1989年 | 151篇 |
1988年 | 123篇 |
1987年 | 98篇 |
1986年 | 65篇 |
1985年 | 94篇 |
1984年 | 82篇 |
1983年 | 50篇 |
1982年 | 71篇 |
1981年 | 32篇 |
1980年 | 43篇 |
1979年 | 25篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1959年 | 5篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
介绍了基于西门子楼宇自控系统的空调计费系统的软硬件设计和具体实现.该系统的特点是借助西门子S600系统强大的数据处理和控制能力,采用时间记录和能量测量相结合的方法进行计费,具有实时监测和定时输出报表功能.该系统计量准确、计费合理、安全可靠、性价比高,满足了现代物业管理的需要. 相似文献
104.
The results are given of numerical solution of the Boltzmann equation in a binomial approximation in view of elastic and inelastic electron collisions in Xe+CH4 mixtures and in pure methane. The electron energy distribution functions obtained are used to calculate the electron transport coefficients for E/N values of up to several Townsends, i.e., the drift velocity, mobility, average and characteristic energies, diffusion coefficient. The results of calculation for pure methane fit the available experimental data. A similarity rule is found for the electron transport coefficients in a Xe+CH4 mixture with different concentrations of methane molecules, which enables one to determine the values of transport coefficients in a mixture with a minor (less than 30 percents) methane content. 相似文献
105.
The Simulation of Impact Loads on Beam-type Structures using a Pseudo-dynamic Procedure 总被引:5,自引:0,他引:5
F. J. Q. Melo J. A. O. Carneiro P. P. Camanho C. L. Tavares A. A. Fernandes 《Strain》2004,40(1):13-23
Abstract: This study proposes an alternate method for the analysis of beams with solid cross-section or built as a framed structure and subjected to transverse impact loads from an external striker. The procedure used in the analysis is a combination of two essential tools using pseudo-dynamic techniques. The method reported here involves only one degree of freedom for the structure modelling and assumes an elastic contact between an external striker and the beam structure, which in reality does not happen. As only one degree of freedom is considered in the analysis, some important limitations are inherent to the method proposed here. Essentially, there is the difficulty of modelling the displacement field associated with the transient structure behaviour accurately, as a consequence of fast-rate impact loads. Another difficulty faced by the method refers to a local structure behaviour associated with contact loads. The present method can deal with large displacements in transversely loaded beams associated to a collapse mechanism having a simple geometry and defined with precision from a single parameter. This ensures reasonable accuracy in the evaluation of the strain energy absorbing capacity of transversely impacted beam structures using a single degree of freedom model in a pseudo-dynamic procedure. 相似文献
106.
叙述了VSR(The Variable Spin Regulator)调节技术在南钢气体供应公司成功应用的实例。实际运行证明,VSR调节技术具有调节灵敏、抗喘、节能、软启动等方面的技术优势。文中还简明地阐述了VSR调节技术的原理并分析比较了液偶及变频调节。 相似文献
107.
本对影响氧化铝熟料单筒冷却机冷却效率的因素进行了分析,并提出了相应的节能技术改造措施,取得了明显的节能效益。 相似文献
108.
D. SHERMAN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(1):32-40
Fracture experiments with silicon specimens in recent years have shown the need for a new approach to the analysis of rapidly propagating cracks in single crystals. Behaviour and phenomena have been revealed that fracture in these materials is rather different from the fracture of both amorphous and polycrystalline materials. We show that continuum mechanics is insufficient for analyzing crack propagation in single crystals since it is unable to consider atomistic‐scale phenomena. Accordingly, we describe basic phenomena associated with rapid crack propagation in silicon : (i) anisotropic velocity‐dependent R‐curve behaviour, as a key phenomenon dictating atomistic scale behaviour, (ii) crack deflection from one cleavage plane to another as a mesoscopic scale phenomenon in single‐crystal fracture, (iii) the Rayleigh surface wave speed as the limiting crack tip velocity is re‐examined, (vi) the lowest crack velocity in brittle crystals is examined, and finally (v) the interaction between crack path and preferred cleavage planes in single crystals is depicted. 相似文献
109.
The Environmental Effects Committee of the ASCE Energy Engineering Division has been developing a report on “Energy Production and Reservoir Water Quality” for publication. The report covers the regulatory framework that dictates much of the procedures for studies related to this topic, the fundamental reservoir hydrodynamics and water quality modeling used in preparing studies, the kinds of studies that can be prepared at different levels of analysis, and a series of applications that illustrate the problems encountered and applications of the various techniques. This study of hydrothermal modeling as applied to examining cooling tower alternatives for an existing steam electric station on a moderately large reservoir is included in this report and is presented here as an illustration of the types of studies included. This particular study subtended the usual steam electric plant cooling water discharge studies that relate to specific regulatory thermal plume size standards, and had to be designed around developing plant and cooling tower operations that would meet specific fisheries requirements for a zone of passage and refuge for fishes throughout the receiving embayment. After being used in developing cooling tower and plant operating details for the designers to work with, it was required that the hydrothermal modeling results be verified under actual tower operating conditions. In addition, it was required that the impact of the combined operations on dissolved oxygen be examined in detail. This paper covers the background to setting up the study, the kinds of statistical comparisons used to verify the hydrothermal studies, and similar studies for the analysis of dissolved oxygen distributions. 相似文献
110.
Development of new burner technology is common practice nowadays. Standardized test codes are available to conduct tests to determine operating characteristics and thermal performance of different parts of steam generating units. This paper describes the results of testing performed to evaluate thermal efficiency of a 74.5?kW fire-tube steam generator fired with a new premixed flame burner in comparison to a typical standard-retrofit diffusion flame burner system. Two premixed flame burners sized at 7.6 and 10.1?cm were tested. Testing was performed in accordance with the ASME PTC 4.1 Power Test Code. The evaluation was conducted in the range of small- to mid-sized, natural gas-fired applications, from 1.06?to?2.64×106?kJ/h. The environmental nitrogen oxide (NOx) emissions performance was also compared for both burner technologies. The results of this evaluation indicate that firing the test boiler with the 7.6?cm new burner slightly improves unit thermal efficiency by 4.0–3.3% for a unit load ranging from approximately 1.06?to?1.79×106?kJ/h, respectively. Operation with the 10.1?cm new burner improves the thermal efficiency by approximately 1.6% at 2.32×106?kJ/h. The uncertainty in the measurements used in the efficiency calculations should account for approximately ±1.5% uncertainty in the reported gross efficiency. Reductions in NOx emissions of the order of 10% resulted from operation with the new premixed flame burners. 相似文献