全文获取类型
收费全文 | 719篇 |
免费 | 44篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 14篇 |
综合类 | 42篇 |
化学工业 | 87篇 |
金属工艺 | 27篇 |
机械仪表 | 77篇 |
建筑科学 | 22篇 |
矿业工程 | 32篇 |
能源动力 | 206篇 |
轻工业 | 18篇 |
水利工程 | 8篇 |
石油天然气 | 60篇 |
武器工业 | 21篇 |
无线电 | 17篇 |
一般工业技术 | 51篇 |
冶金工业 | 34篇 |
原子能技术 | 43篇 |
自动化技术 | 19篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 21篇 |
2016年 | 19篇 |
2015年 | 18篇 |
2014年 | 44篇 |
2013年 | 33篇 |
2012年 | 61篇 |
2011年 | 63篇 |
2010年 | 42篇 |
2009年 | 35篇 |
2008年 | 34篇 |
2007年 | 33篇 |
2006年 | 36篇 |
2005年 | 34篇 |
2004年 | 45篇 |
2003年 | 23篇 |
2002年 | 29篇 |
2001年 | 24篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有778条查询结果,搜索用时 250 毫秒
1.
The goal of the study was to evaluate and compare the physical properties of control, pretreated and densified corn stover, switchgrass, and prairie cord grass samples. Ammonia Fiber Expansion (AFEX) pretreated switchgrass, corn stover, and prairie cord grass samples were densified by using the comPAKco device developed by Federal Machine Company of Fargo, ND. The densified biomass were referred as “PAKs” in this study. All feedstocks were ground into three different grind size of 2, 4 and 8 mm prior to AFEX pretreatment and the impact of grinding on pellet properties was studied. The results showed that the physical properties of AFEX-PAKed material were not influenced by the initial grind size of the feedstocks. The bulk density of the AFEX-PAKed biomass increased by 1.2–6 fold as compared to untreated and AFEX-pretreated materials. The durability of the AFEX-PAKed materials were between 78.25 and 95.2%, indicating that the AFEX-PAKed biomass can be transported easily. To understand the effect of storage on the physical properties of these materials, samples were stored in the ambient condition (20 ± 2 °C and 70 ± 5% relative humidity) for six months. After storage, thermal properties of the biomass did not change but glass transition temperature decreased. The water absorption index and water solubility index of AFEX-treated and AFEX-PAKed biomass showed mixed trends after storage. Moisture content decreased and durability increased upon storage. 相似文献
2.
In different computer models, shape is represented using different methodologies, to varying degrees of precision. This paper examines two approaches to shape representation, and their effects on accuracy in the context of cylindrical particle packing. Two discrete element method (DEM) based software packages are used. A X-ray CT scan of a packed bed provides the experimental measurements for comparison. Eight sphere-composite representations of the same cylindrical pellet were tested. Two of these gave results that quantitatively follow experimental measurements. A range of factors that in theory could affect accuracy of the simulation results are examined, including edge roundedness, surface roughness and restitutional behaviour as a function of sphere-composite representations. The conclusion is that, for packing at least, matching the object's overall shape and dimensions is not enough. Only when a high enough resolution is applied to corners and edges, could the sphere-composite approach possibly match the experimental data quantitatively. 相似文献
3.
气体引射器流体动力特性实验研究 总被引:5,自引:3,他引:2
在实验装置上对气体引射器计算基本公式进行了实测验证,分析了理论特性曲线的可信度。通过实验,获得一些参数对引射器工况的影响规律。 相似文献
4.
柴油机针阀体的乙炔低压渗碳 总被引:2,自引:0,他引:2
乙炔低压渗碳可以有效地避免在真空渗碳过程中产生炭黑和焦油,同时由于乙炔具有较高的供碳能力,使这一技术尤其适用于针阀体这样的小直径深盲孔零件。 相似文献
5.
介绍了用于HT-7托卡马克的的八管弹丸注入器的物理、工程设计原理和结构特点及配置的各种诊断手段。注入器采用气动发射技术,弹丸为1mm×1mm,1.2mm×1.2mm,1.5mm×l.5mm圆柱体氢丸,丸速0.8~1.5km/s工作频率1~8Hz。 相似文献
6.
针对双组分等温平行反应体系,分析讨论了以提高催化剂活性和选择性为目标时催化剂活性组分的最优分布形式(为δ-函数分布),并给出了确定这种反应体系的催化剂的最佳活性层位置的计算方法。结果表明:以提高选择性为目标的最佳活性层位置比以提高活性为目标的要更靠近催化剂核心,实用的最优位置应介于二者之间。最后,本文还研究了反应动力学级数、本性选择性以及内扩散模数(Thiele 模数)等因素对最佳活性层位置的影响。 相似文献
7.
8.
Fuel injection rate shaping is a strategy to improve fuel efficiency and reduce harmful emissions in diesel engines. Due to their fast response, piezoelectric fuel injectors are capable of rate shaping operation. This paper describes a model-based closed-loop controller of injection flow rate for a piezoelectric fuel injector. This within-an-engine-cycle control strategy utilizes a dynamic surface control scheme and shows an injection flow rate tracking capability. Practical issues with LabVIEW FPGA control implementation are also addressed. The performance of the controller is verified with simulation and experimental results at different rail pressures and desired injection rates. The experiments show a maximum error of total fuel per one injection event of 2.5%. A stability analysis is also included. 相似文献
9.
This study is an experimental investigation of heat and moisture transfer within a packed bed of polycrystalline, porous potash pellets. Experiments were first performed to determine the moisture uptake characteristics on individual pellets subject to a step-change in relative humidity. Then a bed of pellets was subjected to flows of humid air on the upper boundary and a cold impermeable surface on the lower boundary resulting in a temperature gradient across the bed. Temperature and moisture content were measured within the bed. It was found that moisture uptake is less for potash pellets and they are less likely to cake than granular and standard potash when subjected to the same ambient air conditions. This is due to the porous nature of the pellet and its nearly uniform size and spherical shape. 相似文献
10.