全文获取类型
收费全文 | 56339篇 |
免费 | 5804篇 |
国内免费 | 3707篇 |
专业分类
电工技术 | 3293篇 |
技术理论 | 1篇 |
综合类 | 5366篇 |
化学工业 | 8341篇 |
金属工艺 | 3851篇 |
机械仪表 | 2558篇 |
建筑科学 | 5575篇 |
矿业工程 | 2781篇 |
能源动力 | 2562篇 |
轻工业 | 3652篇 |
水利工程 | 2077篇 |
石油天然气 | 3471篇 |
武器工业 | 757篇 |
无线电 | 5413篇 |
一般工业技术 | 6352篇 |
冶金工业 | 3534篇 |
原子能技术 | 1174篇 |
自动化技术 | 5092篇 |
出版年
2024年 | 222篇 |
2023年 | 781篇 |
2022年 | 1470篇 |
2021年 | 1804篇 |
2020年 | 2024篇 |
2019年 | 1694篇 |
2018年 | 1644篇 |
2017年 | 2101篇 |
2016年 | 2288篇 |
2015年 | 2375篇 |
2014年 | 3605篇 |
2013年 | 3785篇 |
2012年 | 4391篇 |
2011年 | 4434篇 |
2010年 | 3368篇 |
2009年 | 3255篇 |
2008年 | 2913篇 |
2007年 | 3596篇 |
2006年 | 3075篇 |
2005年 | 2616篇 |
2004年 | 2288篇 |
2003年 | 1986篇 |
2002年 | 1655篇 |
2001年 | 1441篇 |
2000年 | 1202篇 |
1999年 | 977篇 |
1998年 | 822篇 |
1997年 | 724篇 |
1996年 | 662篇 |
1995年 | 534篇 |
1994年 | 419篇 |
1993年 | 309篇 |
1992年 | 276篇 |
1991年 | 255篇 |
1990年 | 210篇 |
1989年 | 151篇 |
1988年 | 105篇 |
1987年 | 68篇 |
1986年 | 57篇 |
1985年 | 58篇 |
1984年 | 49篇 |
1983年 | 28篇 |
1982年 | 26篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1975年 | 9篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
川中地区上三叠统天然气地球化学特征及成藏过程探讨 总被引:3,自引:0,他引:3
川中地区上三叠统是一套自生自储的天然气成藏系统,天然气中甲烷含量为88%~96%,重烃(C2+)含量一般在6%~9%之间,二氧化碳和硫化氢等非烃气体含量普遍较低;天然气干燥系数(C1/C2+)为5~15,并且随深度增加而呈现升高的趋势;天然气和凝析油轻烃中的甲基环己烷、庚烷和异庚烷值变化表明天然气主要来源于腐殖型母质;天然气甲烷和乙烷碳同位素分别为-39.00‰~-41.00‰和-25.00‰~-27.00‰,具有典型煤成气特征。川中地区上三叠统烃源岩在燕山期持续沉降埋藏过程中,达到高成熟早期阶段;在喜山期,该地区大约2500m地层的剥蚀,使地层温度和压力大幅度降低,故储层中早期低成熟残余天然气的卸压膨胀作用和水溶气的脱溶作用为晚期天然气聚集成藏提供了重要的气源,同时也使气藏中甲烷碳同位素变轻。 相似文献
142.
Larry Wos 《Journal of Automated Reasoning》1987,3(4):433-435
This article is the fourth of a series of articles discussing various open research problems in automated reasoning. The problem proposed for research focuses on finding criteria that would enable an automated reasoning program to expand or contract definitions wisely. For evaluating a proposed solution to this research problem, we include suggestions concerning possible test problems.This work was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under contract W-31-109-Eng-38. 相似文献
143.
Xueyuan ZhangWenle He Inger Odnevall Wallinder Jinshan PanChristofer Leygraf 《Corrosion Science》2002,44(9):2131-2151
Instantaneous corrosion rates of naturally patinated copper of varying age (16 months, 138 and 145 years) have been determined during continuous rain events in the laboratory with electrochemical impedance spectroscopy using a two-electrode cell. The two-electrode cell was found to yield the same information in bulk rainwater as a conventional three-electrode cell.Relatively constant corrosion rates, between 0.2 and 0.6 μm/y, were determined for samples having a two-layer structure with an inner brownish layer of cuprous oxide and an outer greenish layer of basic copper salts (138, 145 years). Samples with cuprous oxide as the dominating phase of the patina (16 months) showed higher and somewhat increasing corrosion rates during a rain event (from 0.6 to 1.2 μm/y). During a continuous rain event, corrosion rates were found to be approximately 10 (brownish patina) and 25 times (greenish patina) lower than corresponding instantaneous runoff rates. The first flush phenomena of the runoff process, with an increased concentration during first flush and a relatively constant concentration during steady state, was indirectly seen as an increase in solution conductivity during the first rain volume followed by relative constant value. The contribution of the concentration in the first flush to the total annual runoff rate was significant for panels having a greenish layer (138, 145 years) whereas it was negligible for panels having a brownish layer (16 months). 相似文献
144.
145.
修井作业中的自动起下管柱系统探讨 总被引:2,自引:0,他引:2
目前在油田修井作业中起下管柱的人工作业量大、工作效率低、危险性大、工作条件差。提出了一种自动起下管柱作业系统,主要包括通井机、井架、液压钳、筒式吊卡、卡瓦支座、立式排管架和控制系统等,支座卡瓦为弹性体微条嵌入式结构,筒式吊卡能自动卡入和松开管柱接箍,排管架可实现管柱的立式排放,控制系统协调各部分的工作。该系统构思新颖,结构简单,技术可行,并能够与现有修井设备配合使用,实现油田修井作业的自动化。 相似文献
146.
147.
通过有限元数值模拟方法得出滚珠旋压中薄壁管在不同凹模旋转速度条件下轴向进给比的变化规律及工件的成形规律,并对模拟结果的等效应变分布做了分析,并与实验结果进行比较,给出薄壁管滚珠旋压时进给比的选取范围.结果表明,进给比对滚珠旋压中薄壁管直径的胀缩和工件的质量有着显著的影响.另外,从计算的模具所受的三向载荷变化情况分析了模具的使用寿命. 相似文献
148.
姚新荣 《河南纺织高等专科学校学报》2007,19(3):24-27
2006年2月15日财政部颁布的《企业会计准则》中有多处要求采用实际利率法计算摊余成本和利息,而会计职称考试用书等资料则采用列表形式。本文在分析实际利率法内涵的基础上,通过若干实例解析了利用账簿记录计算各期摊余成本。 相似文献
149.
Yu. V. Balaban-Irmenin N. G. Fokina 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2007,41(5):306-312
The effect of internal-corrosion inhibitors on heating-system pipelines is investigated. Tests were conducted on a testing
device for polarization measurements under conditions corresponding to the Rostov Heat-Supply System. The concentration of
OEDP-zinc, which provides a high degree of protection from general corrosion, is determined. The reagent has been successfully
incorporated into the Rostov No. 2 TPP.
__________
Translated from élektricheskie Stantsii, No. 7, July 2007, pp. 37–43. 相似文献
150.
In various medium‐to‐large‐scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat‐release rate and smoke‐production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi‐directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献