全文获取类型
收费全文 | 21166篇 |
免费 | 1611篇 |
国内免费 | 664篇 |
专业分类
电工技术 | 904篇 |
技术理论 | 2篇 |
综合类 | 2060篇 |
化学工业 | 1527篇 |
金属工艺 | 697篇 |
机械仪表 | 661篇 |
建筑科学 | 9477篇 |
矿业工程 | 1234篇 |
能源动力 | 820篇 |
轻工业 | 747篇 |
水利工程 | 1488篇 |
石油天然气 | 542篇 |
武器工业 | 91篇 |
无线电 | 643篇 |
一般工业技术 | 1044篇 |
冶金工业 | 607篇 |
原子能技术 | 264篇 |
自动化技术 | 633篇 |
出版年
2024年 | 67篇 |
2023年 | 192篇 |
2022年 | 457篇 |
2021年 | 553篇 |
2020年 | 537篇 |
2019年 | 375篇 |
2018年 | 418篇 |
2017年 | 494篇 |
2016年 | 587篇 |
2015年 | 660篇 |
2014年 | 1454篇 |
2013年 | 1035篇 |
2012年 | 1596篇 |
2011年 | 1794篇 |
2010年 | 1440篇 |
2009年 | 1431篇 |
2008年 | 1275篇 |
2007年 | 1593篇 |
2006年 | 1374篇 |
2005年 | 1163篇 |
2004年 | 846篇 |
2003年 | 766篇 |
2002年 | 645篇 |
2001年 | 531篇 |
2000年 | 480篇 |
1999年 | 384篇 |
1998年 | 263篇 |
1997年 | 228篇 |
1996年 | 175篇 |
1995年 | 132篇 |
1994年 | 111篇 |
1993年 | 79篇 |
1992年 | 70篇 |
1991年 | 49篇 |
1990年 | 20篇 |
1989年 | 36篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 18篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
91.
文章通过对夏热冬冷地区建筑节能应考虑的因素及相关技术指标,及高舒适的低能耗技术构成等方面的论述,从理论和实践中加以分析了目前建筑节能面临的问题和误区,从技术角度分析入手,提出了相应的解决措施和方法,以达到舒适和节能的要求为目的.同时还从另一个方面提醒购房者在购房时要增强节能意识,警惕假节能. 相似文献
92.
高速公路水毁成因及防治措施 总被引:1,自引:0,他引:1
从高速公路水泥混凝土路面裂缝,挖方地段护面墙开裂、拦水带与路面衔接部位裂缝,急流槽水泥砂浆勾缝脱落等方面分析了高速公路水毁的成因,并提出了切实可行的防治措施,保证了高速公路的正常运营。 相似文献
93.
94.
介绍了电子商务,以及目前电子商务的发展趋势及对社会的影响,特别阐述了蓬勃发展的电子商务对企业集团的经营环境与手段的影响。 相似文献
95.
In this study, experimental and three-dimensional numerical studies were performed to investigate the effects of plate spacing and temperature difference on natural convection between isothermally heated upward-facing lower horizontal plate and externally insulated horizontal upper plate. Air is used as the heat transfer medium. Rayleigh number varied in the 1108–2.339 × 105 range. Several numerical simulations for three-dimensional steady laminar and turbulent flows heat transfer were carried out using a commercial CFD code Fluent 6.2. Results have shown that there is a good agreement between the numerical and present experimental results as well as with available data in literature. 相似文献
96.
David C. Whitehead Katherine M. Goulden Roy D. Hartley 《Journal of the science of food and agriculture》1985,36(5):311-318
The distribution of 10 nutrient elements was assessed in three fractions of herbage samples of perennial ryegrass, tall fescue, white clover and lucerne. The cell wall fraction, prepared by mechanical disintegration of undried material, contained the following proportions of the total herbage content of the major elements: N, 2.9–16.4%; P, 3.0–6.9%; S, 3.6–17.2%; Ca, 11.3–51.8%; Mg. 6.4–27.6% and K, 0.1–1.7%. Substantial though more variable proportions of the trace element cations, Fe, Mn, Zn and Cu were also present in the cell wall fraction. The extent to which the elements were soluble in water was assessed by analysis of the water-insoluble fraction prepared from freeze-dried samples of each herbage. The proportions of the total herbage content of the major elements soluble in water were: N, 30–57%; P, 80–92%; S, 35–71%; Ca, 48–69%; Mg. 65–83% and K, 90–96%. With the trace element cations the proportions soluble in water were more variable, though they were generally less than 70% of the total. The extent to which the various elements were soluble in 80% aqueous ethanol was assessed by analysis of the insoluble fraction prepared from freeze-dried materials. With each of the major elements, smaller proportions of the total herbage content were soluble in 80% ethanol than in water, which may reflect in part the lower solubility of proteins and pectin. With the trace element cations, the differences in solubility between 80% ethanol and water were generally small and inconsistent. 相似文献
97.
介绍探地雷达探测方法,探讨使用高频探地雷达探测粘土心墙堆石坝坝顶混凝土路面裂缝,达到快速、无损查明坝顶混凝土裂缝的性质与成因的目的. 相似文献
98.
应用有限元分析方法,对相同周长、相同壁厚的扁管在直边段和圆弧半径的不同比值条件下与所能承受最大外压力的关系进行了分析.并对计算分析取得的数据进行拟和得到了扁管在直边段和圆弧半径的不同比值条件下能承受最大外压力的关系及经验公式. 相似文献
99.
100.
This paper presents a 3D noncontacting sensor system designed to measure the position and orientation of a robot end effector. This measurement system includes two parts: a tridimensional object including four spheres placed along the axes of a tetrahedron and a set of three orthogonally pointed cameras. The purpose is to design a measurement system characterized by easy relationships in order to satisfy real-time constraints. The system has been used in two experiments: first, to calibrate a parallel robot and validate the geometrical control performance, then as an exteroceptive sensor in an assembly task. The system computes position and orientation of the tetrahedron in 100 ms time. The position and orientation accuracy are, respectively, 0.6 mm and 0.2 deg in a workspace, being a cube with 0.3 m sides. 相似文献