全文获取类型
收费全文 | 32879篇 |
免费 | 4659篇 |
国内免费 | 5879篇 |
专业分类
电工技术 | 429篇 |
技术理论 | 1篇 |
综合类 | 2834篇 |
化学工业 | 5479篇 |
金属工艺 | 463篇 |
机械仪表 | 2271篇 |
建筑科学 | 7968篇 |
矿业工程 | 5673篇 |
能源动力 | 1144篇 |
轻工业 | 4324篇 |
水利工程 | 2155篇 |
石油天然气 | 5042篇 |
武器工业 | 145篇 |
无线电 | 499篇 |
一般工业技术 | 2195篇 |
冶金工业 | 1455篇 |
原子能技术 | 478篇 |
自动化技术 | 862篇 |
出版年
2024年 | 142篇 |
2023年 | 456篇 |
2022年 | 1230篇 |
2021年 | 1695篇 |
2020年 | 1571篇 |
2019年 | 1474篇 |
2018年 | 1378篇 |
2017年 | 1419篇 |
2016年 | 1560篇 |
2015年 | 1437篇 |
2014年 | 2136篇 |
2013年 | 2396篇 |
2012年 | 2487篇 |
2011年 | 2628篇 |
2010年 | 1930篇 |
2009年 | 1899篇 |
2008年 | 1760篇 |
2007年 | 2136篇 |
2006年 | 1980篇 |
2005年 | 1960篇 |
2004年 | 1600篇 |
2003年 | 1379篇 |
2002年 | 1010篇 |
2001年 | 842篇 |
2000年 | 746篇 |
1999年 | 677篇 |
1998年 | 584篇 |
1997年 | 548篇 |
1996年 | 415篇 |
1995年 | 409篇 |
1994年 | 351篇 |
1993年 | 263篇 |
1992年 | 188篇 |
1991年 | 135篇 |
1990年 | 103篇 |
1989年 | 82篇 |
1988年 | 66篇 |
1987年 | 53篇 |
1986年 | 59篇 |
1985年 | 30篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1981年 | 57篇 |
1980年 | 28篇 |
1979年 | 13篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1955年 | 3篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
地应力对工程岩体的稳定性影响很大,工程实践中常需定量地确定工程范围内的地应力。本文简要地介绍了地应力的概念、应用及常用的测量方法。 相似文献
53.
利用短周期地脉动推断深层地基S波速度 总被引:3,自引:0,他引:3
从二维随机波场的相关理论出发,提出了如何从短周期地脉动(频率>0.5Hz)时域信号中计算Rayleigh波弥散曲线,进而反演深层地基剪切波(S波)速度的理论方法和分析技术,并结合实测信号的分析结果,探讨了该方法的可行性和实用性。 相似文献
54.
Thomas J. R. Hughes Arif Masud Isaac Harari 《International journal for numerical methods in engineering》1995,38(19):3193-3210
Finite element methods for dynamic analysis employing elements with drilling degrees of freedom are presented. The formulation is based on a variational principle in which displacements and rotations are interpolated independently. The issue of zero masses corresponding to rotational degrees of freedom is addressed and techniques for defining consistent and lumped rotational mass matrices are presented. 相似文献
55.
岩壁梁是一种新型结构,为通过一定深度的锚杆将钢筋混凝土梁固定在地下厂房两侧的岩壁上,而吊车荷载则通过锚杆和钢筋混凝土与岩石接触面的摩擦力传到岩体上,形成岩壁梁和岩体共同受力的结构。岩壁梁是地下厂房施工和运行的核心建筑物,岩壁梁锚杆和混凝土的施工质量是直接关系到岩壁梁成败的关键,所以施工技术和施工质量均要求极高,是地下厂房系统施工的重点和难点。本文介绍了瀑布沟水电站地下厂房岩壁梁锚杆和混凝土施工的关键技术及质量控制经验,可供同类工程借鉴参考。 相似文献
56.
Rates of ammonia (NH3) loss from a ryegrass sward measured using a system of small wind tunnels were compared with concurrent measurements made using a micrometeorological mass balance method. Measurements were made during two experiments within a circular plot (radius 10m) treated with urea at a rate of 200kgNha?1. In the first experiment, air speed through the tunnels was adjusted as necessary to maintain a value of approximately 1ms?1. This value differed on most occasions from the mean ambient wind speed which was measured at a height of 250mm and which ranged from 0.61 to 2.95ms?1. Rates of loss measured using the wind tunnels differed by a factor of between two and five from those measured using the mass balance method; there was no consistent pattern in the differences between the rates of loss. The total losses of NH3 measured during 15 days were equivalent to 49.1 and 30.2kg Nha?1 for the mass balance and wind tunnel methods, respectively. In the second experiment, air speed through the tunnels was adjusted as necessary to maintain a value as close as possible to the mean ambient wind speed measured at a height of 250mm. Rates of NH3 loss measured using the two methods did not differ significantly; total losses of NH3 during 17 days were equivalent to 96.9 and 101kg Nha?1 for the mass balance and wind tunnel methods, respectively. The difference between the findings of the two experiments could be attributed to the direct effect of air speed through the tunnels rather than to differences between ambient temperatures and those inside the tunnels. During and following periods of rain the rates of loss measured using the tunnels were up to six times greater than those observed with the mass balance method. Rates of loss measured by the two methods became similar again when the tunnels were moved following rain. The study demonstrates that enclosures can be designed and operated to provide reliable measurements of the rate of NH3 loss from grassland. Potential applications of the two methods are discussed. 相似文献
57.
辽河油田东部凹陷火山岩油藏较为集中分布.然而常规酸化效果较差.经采用三元酸(粉末硝酸、盐酸和氢氟酸)前置液压裂酸化后.获得显著的增产效果,进一步表明该项酸化工艺技术成熟,宜于推广应用。同时也面临技术集成再创新机遇.适应更广泛的地质需求。 相似文献
58.
A methodology for evaluating the reactivity of titanium with mould materials during casting has been developed. Microhardness
profiles and analysis of oxygen contamination have provided an index for evaluation of the reactivity of titanium. Microhardness
profile delineates two distinct regions, one of which is characterised by a low value of hardness which is invariant with
distance. The reaction products are uniformly distributed in the metal in this region. The second is characterised by a sharp
decrease in microhardness with distance from the metal-mould interface. It represents a diffusion zone for solutes that dissolve
into titanium from the mould. The qualitative profiles for contaminants determined by scanning electron probe microanalyser
and secondary ion mass spectroscopy in the as-cast titanium were found to be similar to that of microhardness, implying that
microhardness can be considered as an index of the contamination resulting from metal-mould reaction. 相似文献
59.
节理岩体的代表单元集合体模型及弹性参数预测 总被引:8,自引:0,他引:8
本文明确提出了节理岩体“代表单元集合体”的概念和模型,通过对节理岩体的“代表单元集合体”进行数值模拟,研究了节理岩体的“代表单元集合体”的变形特性,建立了节理岩体的弹性模型,提出了预测节理岩体宏观等效弹性参数的计算机模拟方法,并将其应用于岩体工程稳定性分析中。 相似文献
60.