全文获取类型
收费全文 | 52601篇 |
免费 | 7449篇 |
国内免费 | 3971篇 |
专业分类
电工技术 | 10458篇 |
技术理论 | 2篇 |
综合类 | 5621篇 |
化学工业 | 5740篇 |
金属工艺 | 1401篇 |
机械仪表 | 2422篇 |
建筑科学 | 6387篇 |
矿业工程 | 1763篇 |
能源动力 | 2038篇 |
轻工业 | 1679篇 |
水利工程 | 2204篇 |
石油天然气 | 2886篇 |
武器工业 | 525篇 |
无线电 | 5250篇 |
一般工业技术 | 4413篇 |
冶金工业 | 2512篇 |
原子能技术 | 1009篇 |
自动化技术 | 7711篇 |
出版年
2024年 | 306篇 |
2023年 | 881篇 |
2022年 | 1742篇 |
2021年 | 1988篇 |
2020年 | 2281篇 |
2019年 | 1931篇 |
2018年 | 1813篇 |
2017年 | 2201篇 |
2016年 | 2202篇 |
2015年 | 2370篇 |
2014年 | 3403篇 |
2013年 | 3665篇 |
2012年 | 3830篇 |
2011年 | 4079篇 |
2010年 | 3025篇 |
2009年 | 3144篇 |
2008年 | 3058篇 |
2007年 | 3441篇 |
2006年 | 3089篇 |
2005年 | 2496篇 |
2004年 | 2244篇 |
2003年 | 1906篇 |
2002年 | 1521篇 |
2001年 | 1259篇 |
2000年 | 1069篇 |
1999年 | 900篇 |
1998年 | 732篇 |
1997年 | 563篇 |
1996年 | 483篇 |
1995年 | 430篇 |
1994年 | 436篇 |
1993年 | 287篇 |
1992年 | 229篇 |
1991年 | 200篇 |
1990年 | 172篇 |
1989年 | 149篇 |
1988年 | 107篇 |
1987年 | 81篇 |
1986年 | 55篇 |
1985年 | 57篇 |
1984年 | 43篇 |
1983年 | 29篇 |
1982年 | 30篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1959年 | 10篇 |
1957年 | 5篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The activation of safety valves causes the development of flow reaction forces that have to be transferred in an adequate way via the piping to the steel structure or via the connected vessel into the foundation. If the safety valve outlet piping is connected to a blowdown system or, in case of blowing off into the atmosphere, are equipped with a T‐piece at the outlet, the stationary reaction forces are compensated completely. The transient opening process, however, develops flow reaction forces which culminate in peaks of short duration. In this article, a simple method will be proposed for the estimation of the resulting reaction forces as a function of the length of the pipe at the safety valve outlet. CFD calculations and blowdown tests executed with a full‐lift safety valve have confirmed this method on principle. Special importance is attributed to the short duration of the effect of the reaction forces which seems to have only a negligible impact on the supporting steel structure. 相似文献
2.
针对不同地质目标的叠前时间偏移成像解释评价 总被引:3,自引:0,他引:3
随着计算机硬件和地震勘探成像技术的发展,叠前时间偏移正逐步替代常规的NMO加DMO加叠后时间偏移成为地震数据成像处理方法的主流。但对于不同的地质目标,叠前时间偏移的成像效果是否优于常规NMO加DMO加叠后时间偏移的成像效果呢?为此,从地震数据成像处理方法、处理流程和处理参数等方面进行了讨论,并基于某地区三维数据常规处理结果和叠前时间偏移处理结果,针对不同地质目标进行了剖析与评价。认为:叠前时间偏移成像的垂向分辨率较常规处理明显降低,但对于空间波阻抗变化明显的河流和断层,叠前时间偏移成像的空间分辨率要高于常规处理;对于小于1/4波长的叠置薄储层,叠前时间偏移成像的垂向和空间分辨率低于常规处理结果。 相似文献
3.
4.
5.
6.
Analysis of non-stationary electrochemical oscillations emerges utilization of the techniques allowing an observation of time evolution of their parameters such as instantaneous frequency, amplitude or frequency band. An algorithm of extraction of these parameters can be based on one of linear or quadratic time-frequency representations of oscillations record. In this paper, the authors present representatives of such transformations (Choi-Williams and Cone-shaped) originating from one of the most popular joint time-frequency energy distribution—Wigner-Ville distribution. Short introduction to the mathematics of the topic discussed is provided, then the authors present an example of application in the analysis of current oscillations of copper dissolution process. 相似文献
7.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
8.
Thirty patients who had undergone either a right or left unilateral temporal lobectomy (14 RTL; 16 LTL) and 16 control participants were tested on a computerized human analogue of the Morris Water Maze. The procedure was designed to compare allocentric and egocentric spatial memory. In the allocentric condition, participants searched for a target location on the screen, guided by object cues. Between trials, participants had to walk around the screen, which disrupted egocentric memory representation. In the egocentric condition, participants remained in the same position, but the object cues were shifted between searches to prevent them from using allocentric memory. Only the RTL group was impaired on the allocentric condition, and neither the LTL nor RTL group was impaired on additional tests of spatial working memory or spatial manipulation. The results support the notion that the right anterior temporal lobe stores long-term allocentric spatial memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
This article deals with the kinetics of two-step anionic polymerization by way of a non-steady state method. Several molecular parameters can be evaluated using the formulae developed. A bimodal molecular weight distribution function for the resulting polymer is derived from the set of kinetic differential equations, which is in agreement with the experimental data reported. 相似文献
10.
本文运用一典型的人工神经网络模型─“反向传播”模型,对高氧化态(Ⅱ─Ⅳ)三核金属簇合物的构型分布进行了分析,得到了较好的分类、预报结果为化合物结构分析提供了新的工具。 相似文献