全文获取类型
收费全文 | 134506篇 |
免费 | 13782篇 |
国内免费 | 9035篇 |
专业分类
电工技术 | 10882篇 |
技术理论 | 13篇 |
综合类 | 11948篇 |
化学工业 | 17313篇 |
金属工艺 | 7774篇 |
机械仪表 | 8460篇 |
建筑科学 | 7166篇 |
矿业工程 | 4378篇 |
能源动力 | 3230篇 |
轻工业 | 7409篇 |
水利工程 | 2791篇 |
石油天然气 | 6184篇 |
武器工业 | 1378篇 |
无线电 | 12303篇 |
一般工业技术 | 9358篇 |
冶金工业 | 7177篇 |
原子能技术 | 1182篇 |
自动化技术 | 38377篇 |
出版年
2024年 | 434篇 |
2023年 | 1654篇 |
2022年 | 3349篇 |
2021年 | 4257篇 |
2020年 | 4546篇 |
2019年 | 3492篇 |
2018年 | 3101篇 |
2017年 | 3888篇 |
2016年 | 4532篇 |
2015年 | 5001篇 |
2014年 | 8650篇 |
2013年 | 8314篇 |
2012年 | 9847篇 |
2011年 | 10456篇 |
2010年 | 7871篇 |
2009年 | 7988篇 |
2008年 | 7923篇 |
2007年 | 9605篇 |
2006年 | 8602篇 |
2005年 | 7547篇 |
2004年 | 6547篇 |
2003年 | 5663篇 |
2002年 | 4626篇 |
2001年 | 3779篇 |
2000年 | 3176篇 |
1999年 | 2461篇 |
1998年 | 1872篇 |
1997年 | 1503篇 |
1996年 | 1345篇 |
1995年 | 1097篇 |
1994年 | 911篇 |
1993年 | 607篇 |
1992年 | 500篇 |
1991年 | 428篇 |
1990年 | 303篇 |
1989年 | 245篇 |
1988年 | 195篇 |
1987年 | 132篇 |
1986年 | 111篇 |
1985年 | 123篇 |
1984年 | 97篇 |
1983年 | 103篇 |
1982年 | 78篇 |
1981年 | 53篇 |
1980年 | 44篇 |
1979年 | 47篇 |
1978年 | 16篇 |
1977年 | 34篇 |
1976年 | 19篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
针对某厂铜电解种板工序存在的始极片质量波动较大的问题,从种板系统体积控制和添加剂匹配的角度出发,分析各种因素对始极片质量的影响,做出了相应的改进措施,使种板系统运行更加稳定,始极片质量得到进一步提升。 相似文献
52.
针对软件定义网络中,控制器无法保证下发的网络策略能够在转发设备上得到正确执行的安全问题,提出一种新的转发路径监控安全方案。首先以控制器的全局视图能力为基础,设计了基于OpenFlow协议的路径凭据交互处理机制;然后采用哈希链和消息验证码作为生成和处理转发路径凭据信息的关键技术;最后在此基础上,对Ryu控制器和Open vSwitch开源交换机进行深度优化,添加相应处理流程,建立轻量级的路径安全机制。测试结果表明,该机制能够有效保证数据转发路径安全,吞吐量消耗比SDN数据层可信转发方案(SDNsec)降低20%以上,更适用于路径复杂的网络环境,但时延和CPU使用率的浮动超过15%,有待进一步优化。 相似文献
53.
《Journal of the European Ceramic Society》2020,40(13):4655-4663
As a figure-of-merit, the rising ratio of crack propagation resistance to fracture initiation resistance indicates a reduction of the brittleness and enhances the thermal shock resistance of ordinary refractory ceramics. The significant nonlinear fracture behaviour is related to the development of a fracture process zone (FPZ). The universal dimensionless load–displacement diagram method is applied as a promising graphical method for the determination of R-curves for magnesia refractories showing different brittleness. By applying digital image correlation (DIC) together with the graphical method, the problems arisen with accurate determination of the fracture initiation resistance and the crack length are overcome. Meanwhile, the R-curve is subdivided with respect to the fracture processes, viz the fracture initiation, the development of FPZ and the onset of traction free macro-crack. With the simultaneous crack lengths evaluated from DIC, the contribution of each fracture process to the crack propagation resistance at certain loading stage is quantitatively presented. 相似文献
54.
为确保原CO压缩机在净化系统升级改造项目实施后能安全稳定运行,采取了流程优化、工艺条件论证、设备缺陷排查、联锁指标重新确定等一系列措施。改造措施实施后,CO压缩机出口压力稳定在3.23 MPa左右,有效缓解了前后工序压力波动对压缩机稳定运行的影响,各级水冷却器的换热效果也得到了较大的改善。 相似文献
56.
Paul Geoerg Florian Berchtold Steven Gwynne Karen Boyce Stefan Holl Anja Hofmann 《火与材料》2019,43(7):759-781
To quantify the evacuation process, evacuation practitioners use engineering egress data describing the occupant movement characteristics. These data are typically based to young and fit populations. However, the movement abilities of occupants who might be involved in evacuations are becoming more variable—with the building populations of today typically including increasing numbers of individuals: with impairments or who are otherwise elderly or generally less mobile. Thus, there will be an increasing proportion of building occupants with reduced ability to egress. For safe evacuation, there is therefore a need to provide valid engineering egress data considering pedestrians with disabilities. Gwynne and Boyce recently compiled a series of data sets related to the evacuation process to support practitioner activities in the chapter Engineering Data in the SFPE Handbook of Fire Protection Engineering. This paper supplements these data sets by providing information on and presenting data obtained from additional research related to the premovement and horizontal movement of participants with physical‐, cognitive‐, or age‐related disabilities. The aim is to provide an overview of currently available data sets related to, and key factors affecting the egress performance of, mixed ability populations which could be used to guide fire safety engineering decisions in the context of building design. 相似文献
57.
58.
59.
《Egyptian Journal of Petroleum》2015,24(1):19-25
Conventional water-softening processes usually involve the exchange of Na+ ions for Ca2+ and Mg2+ using commercial or synthesized ion exchangers. The differences in chemical compositions of the ooids can be attributed to the formation in different environments. In this paper, ooid grains form inside assembled semi-pilot softening unit through a continuous chemical process involving reaction between bicarbonate ions and added lime using natural seawater. Our sample of Mediterranean seawater has low Mg2+/Ca2+ ratio (1.98%) within the range chemically favorable for precipitation of low-Mg calcite ooids. Precipitation of calcite occurs around pure quartz sand grains which act as nucleation points (the bed required for sand vessel is 1.65 l). The shape of the sand grains controls the overall external morphology of the resulting ooids; they vary in size from 0.5 to 3.0 mm and have a high degree of polish due to surface abrasion caused by continuous agitation inside the softening system. Calcite ooid grains (1.53 kg) formed within the seawater-softening unit every 18 days have many of the ooid features formed in marine environments. Ooids grow to a significant size, at a rate of about 0.17 mm of one layer thickness per day inside the softening unit. The average weight percent of calcite precipitate is 35.48% after 18 days, at 10 °C, 60 l/min and pH 9.0. The pellets comprise mainly CaCO3 and SiO2 and some metal ions which may substitute for calcium ions in calcite are present only in trace amounts of the total composition. 相似文献
60.
概述了氢的主要工业生产方法和实际应用,详细介绍了氯碱氢三级脱水工艺过程,并运用在线分析手段,准确显示了干燥过程中的氯碱氢水分含量变化规律。 相似文献