全文获取类型
收费全文 | 21887篇 |
免费 | 2501篇 |
国内免费 | 1458篇 |
专业分类
电工技术 | 1701篇 |
技术理论 | 6篇 |
综合类 | 1840篇 |
化学工业 | 2446篇 |
金属工艺 | 1264篇 |
机械仪表 | 1578篇 |
建筑科学 | 3636篇 |
矿业工程 | 1545篇 |
能源动力 | 729篇 |
轻工业 | 663篇 |
水利工程 | 1071篇 |
石油天然气 | 1479篇 |
武器工业 | 169篇 |
无线电 | 1590篇 |
一般工业技术 | 2220篇 |
冶金工业 | 1293篇 |
原子能技术 | 192篇 |
自动化技术 | 2424篇 |
出版年
2024年 | 29篇 |
2023年 | 260篇 |
2022年 | 514篇 |
2021年 | 637篇 |
2020年 | 729篇 |
2019年 | 613篇 |
2018年 | 525篇 |
2017年 | 752篇 |
2016年 | 880篇 |
2015年 | 939篇 |
2014年 | 1633篇 |
2013年 | 1287篇 |
2012年 | 1782篇 |
2011年 | 1764篇 |
2010年 | 1313篇 |
2009年 | 1385篇 |
2008年 | 1156篇 |
2007年 | 1473篇 |
2006年 | 1330篇 |
2005年 | 1057篇 |
2004年 | 908篇 |
2003年 | 819篇 |
2002年 | 727篇 |
2001年 | 669篇 |
2000年 | 518篇 |
1999年 | 417篇 |
1998年 | 313篇 |
1997年 | 255篇 |
1996年 | 208篇 |
1995年 | 210篇 |
1994年 | 150篇 |
1993年 | 91篇 |
1992年 | 75篇 |
1991年 | 59篇 |
1990年 | 63篇 |
1989年 | 40篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 8篇 |
1964年 | 12篇 |
1958年 | 7篇 |
1957年 | 11篇 |
1956年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
32.
Sushma A. Rawool Mrinal R. Pai A.M. Banerjee R.D. Bapat Chandrani Nayak A.K. Tripathi 《International Journal of Hydrogen Energy》2018,43(3):1271-1284
We have demonstrated earlier that maximum H2 generated @ 1.167 l/h/m2 over Cu0.02Ti0.98O2-δ photocatalyst with apparent quantum efficiency, AQE of 7.5% and solar fuel efficiency, SFE of 3.9% under sunlight. With an aim to scale-up the solar photocatalytic hydrogen process to pilot plant, optimization studies at lab scale as well as in upscaled photoreactors were performed over Cu0.02Ti0.98O2-δ, photocatalyst under UV/visible and sunlight. Cu0.02Ti0.98O2-δ was synthesized by facile sol-gel route and characterized by relevant techniques. Several operational parameters were investigated in order to finalize the conditions which are most favourable for photocatalytic hydrogen yield. Factors such as photocatalyst loadings, v/v concentration of sacrificial reagent, replacement of methanol by industrial waste glycerol, role of different configuration of light source with reactor, effect of stirring during the photocatalytic reaction, effect of fluctuations of solar flux at hourly basis, illumination area on hydrogen yield were studied. Contribution of each factor in determining the hydrogen yield was quantified. Relative standard deviation in hydrogen yield as a function of each factor was estimated. Our findings suggest that in addition to catalyst loadings and sacrificial reagent, improved dispersion of photocatalyst obtained by stirring the reaction mixture in horizontal geometry resulted in enhanced H2 yield. Hydrogen yield obtained at lab scale can be appropriately extrapolated with respect to illumination area instead of weight of photocatalyst. A relative standard deviation (RSD) of ± 3.82% and ± 4.53% in H2 yield was calculated for sunny and cloudy days in time zone of 10.30–16.30 h IST. Deviation of H2 yield was more on cloudy days and beyond 16:30 h. These studies have provided a daily window of 11:00–15:00 h to be utilized throughout the year for a commercial scaled up process, prohibiting the illumination during less productive hours of the day for shaping the improved economics of solar hydrogen generation. Our results obtained at lab scale would be useful to perform sunlight driven scaled –up photocatalytic process using low cost visible light efficient photocatalyst, Cu0.02Ti0.98O2-δ. 相似文献
33.
为缓解高产高效矿井采掘接续紧张局面,鄂尔多斯地区综采工作面多采用“两进一回”的巷道布置形式,辅运巷在回采结束后用作下一工作面的回风巷,两进风巷之间采用大煤柱护巷。但随着该地区采深600 m以上的深部矿井增多,冲击地压灾害问题逐渐显现,双巷大煤柱留设的弊端也暴露出来。针对此问题,以鄂尔多斯红庆河煤矿3-1101大采高综采工作面为例,对不同宽度煤柱留设的应力分布规律进行建模研究,提出了合理的煤柱留设宽度,为鄂尔多斯地区类似条件矿井的安全高效开采提供参考依据。 相似文献
34.
针对大口径管道施工过程中存在施工周期长,施工难度大,工程成本高等问题,提出一种新型优化管段分段技术和管段组对方案。结果表明:该制作技术能保证大口管道安装施工顺利进行;有效地解决现有大口径套管安装过程中的技术难题。该方法具有创新性、实用性、可靠性等优点,在工程建设的许多领域,具有推广应用价值。 相似文献
35.
36.
The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers. This paper focuses on designing a class of 2R1T (R: Rotation; T: Translation) parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension (2D) large rotational angles. In order to construct 2D rotational degrees of freedom (DOFs), a platform with 2D revolute joints is proposed first. Based on the constraint screw theory, the feasible limbs that can be connected in the platform are synthesized. In order to provide constant rotational axis for the platform, a class of redundant limbs are designed. A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion. The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform. The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed. The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers. 相似文献
37.
Large confined space has high incidence of fires, which seriously threatens the safety of people working there. Understanding the distribution of smoke in such large space is critical to fire development prediction and smoke control. Three improved methods for the stratification interface prediction of fire smoke are developed, including of improved intra-variance, integral ratio and N-percentage methods. In these methods, the interface height is determined by the vertical temperature distribution based on a three-layer smoke zone model, which is an improvement of a two-layer zone model. Thereafter, the three improved methods are applied to several typical fire cases simulated CFD to predict the smoke interface, and their applicability and reliability are verified by comparison of the smoke stratification results with the filed simulation results. Results show that the three improved methods can effectively determine the location of the three-layer zone model's interface, and they have the ability to predict smoke interface for fires with different fire source types and ventilation conditions. 相似文献
38.
通过对大直径平底负压容器平底板的设计计算,平底板计算厚度很厚。通过分析,提出了对平底板采取加强措施,从而减薄平底板计算厚度的方法。该容器在实际生产过程中性能可靠、稳定,对类似设备设计具有借鉴意义。 相似文献
39.
40.
A dynamic creep mechanism has been proposed and verified through a case study. A secondary superheater tube burst occurred in a 43 MW coal-fired boiler. Microstructural examination indicates that the overheating temperatures reached 900 °C (above Ac3). The overheating duration was estimated to be 3 h by calculating with LMP formula. The 710 μm steam-side scale and 960 μm fireside scale built-up in the short time of overheating. The burst scenario was a short-term severe overheating on the basis of the long-term creep. The multilayer oxide scales on both sides have been studied with ESEM/EDS, indicating FeO. At 900 °C, full decarburization had gone throughout the tube. As the strength reduced due to the decarburization, the creep mechanism transformed from long-term intergranular creep to short-term transgranular rupture. The two types of dimples on the fractograph and two types of cracks in the microstructures confirmed the mechanism transformation. The overheating, the scale buildup and the decarburization constituted the full picture of the dynamic creep rupture. 相似文献