全文获取类型
收费全文 | 35042篇 |
免费 | 3447篇 |
国内免费 | 3211篇 |
专业分类
电工技术 | 1553篇 |
技术理论 | 1篇 |
综合类 | 3639篇 |
化学工业 | 4280篇 |
金属工艺 | 923篇 |
机械仪表 | 968篇 |
建筑科学 | 10901篇 |
矿业工程 | 2480篇 |
能源动力 | 1072篇 |
轻工业 | 2063篇 |
水利工程 | 3805篇 |
石油天然气 | 4257篇 |
武器工业 | 71篇 |
无线电 | 541篇 |
一般工业技术 | 1812篇 |
冶金工业 | 1826篇 |
原子能技术 | 235篇 |
自动化技术 | 1273篇 |
出版年
2024年 | 144篇 |
2023年 | 383篇 |
2022年 | 840篇 |
2021年 | 1134篇 |
2020年 | 1133篇 |
2019年 | 923篇 |
2018年 | 901篇 |
2017年 | 1100篇 |
2016年 | 1205篇 |
2015年 | 1253篇 |
2014年 | 2394篇 |
2013年 | 2085篇 |
2012年 | 2759篇 |
2011年 | 2913篇 |
2010年 | 2172篇 |
2009年 | 2119篇 |
2008年 | 1884篇 |
2007年 | 2455篇 |
2006年 | 2246篇 |
2005年 | 2188篇 |
2004年 | 1796篇 |
2003年 | 1496篇 |
2002年 | 1155篇 |
2001年 | 969篇 |
2000年 | 848篇 |
1999年 | 647篇 |
1998年 | 548篇 |
1997年 | 433篇 |
1996年 | 345篇 |
1995年 | 262篇 |
1994年 | 223篇 |
1993年 | 123篇 |
1992年 | 124篇 |
1991年 | 97篇 |
1990年 | 78篇 |
1989年 | 59篇 |
1988年 | 44篇 |
1987年 | 37篇 |
1986年 | 35篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 41篇 |
1977年 | 3篇 |
1964年 | 2篇 |
1959年 | 2篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
劈裂真空法加固软土地基试验研究 总被引:3,自引:0,他引:3
在分析常规真空预压法加固软土地基局限性的基础上,提出了劈裂真空法加固深厚软土地基新技术。介绍了劈裂真空法的基本原理和施工工艺。依托江苏省江海高速公路软基处理项目进行了劈裂真空法与常规真空法加固软土地基的对比试验段工程,对软基加固过程中的真空度、孔隙水压力、地表沉降、深层水平位移和地下水位等进行监测,并通过加固前后现场 CPTU 原位测试、取样和室内土工试验等方法对加固效果对比分析。试验结果表明:劈裂真空法可以提高真空荷载向深层土体的传递效率,提高深部软土的加固效果,进而提高真空预压法的有效处理深度;同时劈裂真空法还可以加速地基固结,缩短地基处理工期,有利于工后沉降的控制。试验工程表明,劈裂真空法是加固深厚软土地基的有效方法,具有很好的工程应用前景。 相似文献
992.
993.
A surface soil moisture model with improved spatial resolution was developed using remotely sensed apparent thermal inertia (ATI). The model integrates the surface temperature derived from TM/ETM+ image and the mean surface temperature from MODIS images to improve the spatial resolution of soil temperature difference based on the heat conduction equation, which is necessary to calculate the ATI. Consequently, the spatial resolution of ATI and SMC can be enhanced from 1 km to 120 m (TM) or 60 m (ETM+). Moreover, the enhanced ATI has a much stronger correlation coefficient (R2) with SMC (0.789) than the surface reflectance (0.108) or the ATI derived only from MODIS images (0.264). Based on the regression statistics of the field SMC measurement and enhanced ATI, a linear regression model with an RMS error of 1.90% was found. 相似文献
994.
寇莹 《合成材料老化与应用》2014,(3):13-15
本文考察聚丁二酸丁二醇酯(PBS)在不同土壤中的降解情况,从当地取堆肥土、污泥土、垃圾土和花园土对PBS进行土埋法降解试验,通过测定降解过程中的失重率变化和对PBS降解前后表面形态观察,得出PBS在不同土壤中的降解顺序,为塑料的可降解性能的进一步研究奠定基础。 相似文献
995.
996.
997.
从煤层水力压裂技术原理开始分析,根据水力压裂施工技术和系统布置分析其局限性,提出了面对不同地质时的增透技术创新。 相似文献
998.
It is recognized that most damage to reinforced concrete structures is caused by insufficient durability rather than by low strength. In most cases, the quality and thickness of the cover concrete (“covercrete”) determine the service life of the structure. Since the quality of the covercrete is influenced, not only by the mix composition, but also by the placing and curing conditions, it is appropriate to measure the achieved properties on the structure rather than just on separately cast specimens. Swiss Standard SIA 262 on “Concrete Construction” recommends checking the “impermeability” of the cover concrete on site. With that aim, a non‐destructive method to measure the air‐permeability on site has been standardized (SIA 262/1 Annex E). A team of Swiss experts was appointed by the Swiss Federal Highway Administration (ASTRA) to prepare recommendations for specifying, measuring, and assessing the conformity of the air‐permeability kT. This paper describes these recommendations covering: (a) specification of limiting values of kT as function of the exposure class; (b) sampling of the measurement points; (c) testing (including suitable temperature and moisture conditions); (d) evaluation of conformity with specified values; (e) expected impact on service life. 相似文献
999.
One of the most useful geosynthetics in soil reinforcement is geogrid due to its high tensile strength, having a great influence on soil skeleton reinforcement and eventually, increasing bearing capacity of the foundation. In this research, a series of 36 repeated plate load tests have been carried out to investigate the scale effect on geogrid-reinforced soil, tending to further understanding of the behaviour of geogrid-reinforced soil system. Four different soil grains sizes, two different geogrid's aperture sizes (with roughly the same tensile strength) and three different loading plate sizes are the variables considered. During the tests, the applied loading and soil surface settlements were recorded to evaluate the systems' response. As it was expected, the reinforced soil exhibited higher bearing capacity than the unreinforced status, up to 635%. The results show that increasing loading plate size and soils' particle size fortify the response of foundation, especially in reinforced status, against the loading plate penetration. The results further focused on the important role of scale effect on the response of reinforced foundation. It was understood that the optimum nominal aperture size of geogrids should be about 4 times of medium grain size of soil. Also, it was found out that in order to acquisition of highest reinforcement benefits, the footing's width should be in the range 13–25 (20 in average) times of medium grain size of the backfill. Finally, to achieve the best results, it is recommended that the aperture size of geogrids should be selected roughly 0.2 times of footing width. 相似文献
1000.
为研究盾构施工引起的地面沉降,选取宁波地区有代表性的典型土层,运用经验公式与数值模拟相结合的方法,定性分析了盾构施工扰动引起的各土层沉降曲线形态。提出了初始敏感因子和深度敏感因子的概念,推导得出了各典型土层的敏感因子的初步建议值,详细阐述了地面沉降与盾构埋深的线形相关性。为盾构近距离穿越重大管线或建、构筑物等风险点时穿越土层的选择提供了理论参考,对地铁线路平、纵断面确定具有指导意义。 相似文献