全文获取类型
收费全文 | 1101篇 |
免费 | 90篇 |
国内免费 | 35篇 |
专业分类
电工技术 | 18篇 |
综合类 | 39篇 |
化学工业 | 272篇 |
金属工艺 | 169篇 |
机械仪表 | 41篇 |
建筑科学 | 50篇 |
矿业工程 | 7篇 |
能源动力 | 49篇 |
轻工业 | 8篇 |
水利工程 | 16篇 |
石油天然气 | 8篇 |
武器工业 | 2篇 |
无线电 | 80篇 |
一般工业技术 | 306篇 |
冶金工业 | 65篇 |
原子能技术 | 16篇 |
自动化技术 | 80篇 |
出版年
2023年 | 36篇 |
2022年 | 22篇 |
2021年 | 36篇 |
2020年 | 44篇 |
2019年 | 41篇 |
2018年 | 55篇 |
2017年 | 38篇 |
2016年 | 30篇 |
2015年 | 24篇 |
2014年 | 47篇 |
2013年 | 85篇 |
2012年 | 52篇 |
2011年 | 105篇 |
2010年 | 30篇 |
2009年 | 45篇 |
2008年 | 51篇 |
2007年 | 44篇 |
2006年 | 34篇 |
2005年 | 32篇 |
2004年 | 38篇 |
2003年 | 45篇 |
2002年 | 39篇 |
2001年 | 32篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 19篇 |
1997年 | 28篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 18篇 |
1990年 | 33篇 |
1989年 | 12篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有1226条查询结果,搜索用时 15 毫秒
51.
Nishant SHARMA Kaustubh DASGUPTA Arindam DEY 《Frontiers of Structural and Civil Engineering》2020,14(1):62
This article describes a novel approach for deciding optimal horizontal extent of soil domain to be used for finite element based numerical dynamic soil structure interaction (SSI) studies. SSI model for a 12 storied building frame, supported on pile foundation-soil system, is developed in the finite element based software framework, OpenSEES. Three different structure-foundation configurations are analyzed under different ground motion characteristics. Lateral extent of soil domain, along with the soil properties, were varied exhaustively for a particular structural configuration. Based on the reduction in the variation of acceleration response at different locations in the SSI system (quantified by normalized root mean square error, NRMSE), the optimum lateral extent of the soil domain is prescribed for various structural widths, soil types and peak ground acceleration levels of ground motion. Compared to the past studies, error estimation analysis shows that the relationships prescribed in the present study are credible and more inclusive of the various factors that influence SSI. These relationships can be readily applied for deciding upon the lateral extent of the soil domain for conducting precise SSI analysis with reduced computational time. 相似文献
52.
53.
《Materials Science & Technology》2013,29(9):1144-1147
AbstractPaired twins in an extruded Mg–3Al–1Zn alloy are investigated by using electron backscattered diffraction in the current paper. The results show that these paired twins are discovered at low misorientation grain boundaries. The twin variant (1–102)[?1101] is operated in the paired twins. Additionally, a macroscopic angle exists in the paired twins and is determined by the c axis misorientation of the grains. 相似文献
54.
The effect of Zn and Y on hot-tearing susceptibility (HTS) of Mg–xZn–2xY (x?=?1, 1.67, 2.67) alloys is investigated. It is found that the microstructure of the alloys is mainly composed of α-Mg, long-period stacking-ordered (LPSO) phase and W-phase. Both theoretical and experimental results illustrated that HTS of the investigated alloys is in the following order: Mg–1Zn–2Y > Mg–1.67Zn–3.34Y > Mg–2.67Zn–5.34Y. For Mg–2.67Zn–5.34Y alloy, LPSO phase content reaches at the maximum and its grain size reaches at minimum of 16.4 µm, and the pinning effect of the LPSO phase on grain boundaries is considered to be an important reason for reducing HTS of the alloy. 相似文献
55.
C. Tsonos A. KanapitsasD. Triantis C. AnastasiadisI. Stavrakas P. PissisE. Neagu 《Ceramics International》2011,37(1):207-214
The main purpose of this work is to study the dielectric response of commercial low voltage ZnO varistors by means of dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC) in a wide temperature range. Four relaxation processes have been studied here and all of them demonstrate Cole-Davidson behaviour. The first two faster relaxation mechanisms are known processes in ZnO varistors and those are related to the ZnO bulk traps. The next one faster relaxation mechanism attributed to the MWS polarization which should be related to the intergranular Bi-rich microregions. The remaining slower relaxation mechanism is associated to the grain boundaries interfaces. Based on the block model for the ZnO varistor a gradual reduction in the total depletion width is observed at a temperature about 330 K, which can be considered that is due to the gradual decrease of the interface states density at this temperature region. 相似文献
56.
Pramod Chaitanya Ritu Mishra Pradeep Kumar Ahirwal O. P. Thakur Lakshman Pandey 《Integrated ferroelectrics》2015,159(1):121-126
The electrical behavior of strontium titanate borosilicate glass ceramics (SrO.TiO2- 2SiO2.B2O3) with additives K2O, La2O3, CoO and Nb2O5 was studied by using Impedance Spectroscopy as a function of temperature and composition. An equivalent circuit model having three parallel RC's connected in series with a capacitor C4 could represent the data well. By comparing the complex modulus plots with simulated ones and looking at the values of the time constants these RC's were attributed to represent crystalline, glassy and glass-crystal interface regions of the glass- ceramic whereas C4 represented the glass-ceramic sample and contact electrode interface. When the glass ceramic sample contained only SrTiO3 crystalline phase and the remaining glassy matrix, the interface capacitance showed an Arrhenius type of nature with an activation energy (0.11 ± 0.04) eV and when the glass- ceramic sample contained number of crystalline phases no clear cut trend appeared. These findings are useful in selecting suitable electrodes for applications as well as in deciding upon experimental techniques for measurement of dielectric constants of materials. 相似文献
57.
Beatrix Haselsberger 《Planning Theory & Practice》2013,14(4):505-526
In our globalised, interconnected world the impact of borders on space and people is increasingly debated. This article aims to unpack the complex concept of “thick” and “thin” borders. It builds on the assumption that borders are boundary sets comprised of overlapping geopolitical, sociocultural, economic and biophysical layers and are the outcome of a bordering process. A two-step approach towards the decoding of borders is introduced. Using a planning perspective, the article seeks to explain the various functions of borders, to examine power practices within the bordering process and to ascertain the relational geographies demarcated by different types of boundaries. It illustrates why those cross-border activities which address only the geopolitical dimension of the border tend to fail. 相似文献
58.
Extraordinary toughening enhancement and flexural strength in Si3N4 composites using graphene sheets
《Journal of the European Ceramic Society》2014,34(2):161-169
Two types of Si3N4 composites containing graphene nanostructures using two different graphene sources, pristine graphene nanoplatelets and graphene oxide layers were produced by Spark Plasma Sintering. The maximum toughness of 10.4 MPa m1/2, measured by flexure testing of pre-cracked bars, was achieved for a composite (∼60β/40α-Si3N4, ∼300 nm grain size) with 4 vol.% of reduced graphene oxide, indicating a toughening enhancement of 135% when compared to a similar Si3N4. This was also accompanied by a 10% increase in flexure strength (1040 MPa). For the composites with thicker graphene nanoplateletes only a 40% of toughness increase (6.6 MPa m1/2) without strength improvement was observed for the same filler content. The large difference in the maximum toughness values accomplished for both types of composites was attributed to variations in the graphene/Si3N4 interface characteristics and the extent of monolayer graphene exfoliation. 相似文献
59.
60.
LI Qintao NI Zhichun GONG Jinlong ZHU Dezhang ZHU Zhiyuan 《核技术(英文版)》2007,18(5):276-281
An effective method by low energy carbonhydrogen ion treatment to enhance field emission of the carbon nanotubes (CNTs) is demonstrated. Comparing with control, field emission (FE) currents of the CNTs by carbonhydrogen ion irradiation increased, and the turn-on field and the threshold field decreased significantly. The structure characteristic revealed by transmission electron microscopy demonstrates that CNTs are coated by nano-graphite particles after being treated with low energy carbonhydrogen ion and that there are large quantities of defects and grain boundaries in the coated layer. It is considered that the coating layer can decrease the effective surface work function of CNTs and correspondingly increase field emission. In addition, the defects, the grain boundaries and the C-H dipoles forming in the process of the low energy ions irradiation can effectively enhance the field emission. 相似文献