全文获取类型
收费全文 | 1503篇 |
免费 | 56篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 24篇 |
综合类 | 6篇 |
化学工业 | 322篇 |
金属工艺 | 70篇 |
机械仪表 | 16篇 |
建筑科学 | 58篇 |
矿业工程 | 9篇 |
能源动力 | 53篇 |
轻工业 | 100篇 |
水利工程 | 14篇 |
石油天然气 | 5篇 |
无线电 | 202篇 |
一般工业技术 | 273篇 |
冶金工业 | 201篇 |
原子能技术 | 7篇 |
自动化技术 | 200篇 |
出版年
2022年 | 30篇 |
2021年 | 22篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 25篇 |
2017年 | 28篇 |
2016年 | 29篇 |
2015年 | 18篇 |
2014年 | 53篇 |
2013年 | 107篇 |
2012年 | 72篇 |
2011年 | 81篇 |
2010年 | 44篇 |
2009年 | 42篇 |
2008年 | 77篇 |
2007年 | 66篇 |
2006年 | 59篇 |
2005年 | 62篇 |
2004年 | 38篇 |
2003年 | 47篇 |
2002年 | 37篇 |
2001年 | 25篇 |
2000年 | 27篇 |
1999年 | 18篇 |
1998年 | 31篇 |
1997年 | 19篇 |
1996年 | 32篇 |
1995年 | 13篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 13篇 |
1991年 | 20篇 |
1990年 | 25篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1982年 | 12篇 |
1980年 | 18篇 |
1979年 | 9篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1973年 | 19篇 |
1972年 | 17篇 |
1971年 | 11篇 |
1969年 | 9篇 |
1961年 | 10篇 |
1959年 | 9篇 |
排序方式: 共有1560条查询结果,搜索用时 0 毫秒
31.
Leo MacDonald Ann Sherman 《Canadian Journal of Science, Mathematics, & Technology Education》2013,13(2-3):133-147
Abstract The focus of this paper is an examination of mentorship relationships developed as a result of six students’ participation in a local community science centre sponsored through an NSERC/CRYSTAL project. Each year, a number of students participate in after‐school activities sponsored by the community science centre. Much of this work involves a one‐to‐one approach, with a middle years or high school student working with a professor partner. The professor acts as a mentor to the student, facilitating learning in a manner not always feasible within a school setting with large class sizes. For some students this research may be the basis of a science fair project; for others if is simply a study based on individual interest. Mentored students were interviewed about the nature of that mentorship, with the goal of describing the experience from the students’ perspective. Questions focused on the student's experience of working with a mentor, including how the mentorship relationship was formed, what the importance of the voluntary nature of mentoring was, what the benefits and challenges of working with a mentor were, how the mentorship relationship affected the level of content knowledge the student gained, and what effect the mentoring relationship had on the student's continuing interest in science. The mentorship program offers students the opportunity to work within a developing community of practice. 相似文献
32.
A sharp interface model has been developed to model intermediate-phase growth under the influence of electromigration in a binary system. Simulation results show that the phase growth rate depends on both the magnitude and the direction of the applied current. With the current density fixed, at early times, there is a parabolic growth behavior for the intermediate phase, while at longer times, there is a linear phase growth behavior when the electron flow aids diffusion of atoms; however, a limiting thickness is found when the electron flow hinders diffusion. Qualitative analysis shows that the longer time behavior also holds in a binary system with multiple intermediate phases present. 相似文献
33.
Koen Decroos Marc Seefeldt Carsten Ohms Roumen Petrov Frederik Verhaeghe Leo Kestens 《国际钢铁研究》2011,82(8):911-917
The relation between texture and microstructure and the macroscopic solidification direction has been investigated for an austenitic 316L stainless steel weld. The fusion zone has been characterised by EBSD. Texture development has been simulated by thermal Finite Element Analysis coupled with a simple model of preferential <100>‐oriented solidification following the solidification direction. The thermal part is validated by means of thermocouple measurements at several locations on the specimen. The predicted texture is in very good agreement with the measured one. 相似文献
34.
35.
R. Timmreck K. Leo M. Riede 《Progress in Photovoltaics: Research and Applications》2015,23(10):1353-1356
Recently organic tandem solar cells with record efficiency had been shown comprising identical absorber materials in both subcells. Such structures pose new challenges for characterization. The standard test methods for measuring spectral response of tandem solar cells can not be applied. The standard procedures demand for different bias illumination during measuring spectral response allowing to select the subcell being current limiting. With subcells comprising identical absorber materials, thus having identical absorption spectra, such a selection is not trivial. In this paper, we show that with the help of detailed optical simulations of such tandem organic solar cells, their characterization is possible, and we apply the proposed method to a sample structure. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
36.
Frederick Wieland Lawrence Hawley Abe Feinberg Mike Di Loreto Leo Blume Joseph Ruffles Peter Reiher Brian Beckman Philip Hontalas Steven Bellenot David Jefferson 《Concurrency and Computation》1989,1(1):35-50
This paper analyzes the performance of a discrete-event combat simulation executed on a parallel processor under control of the Time Warp Operating System. Time Warp is in a class of distributed simulation methods called Optimistic methods which have proven to be useful over a wide range of simulations. The combat simulation used for this performance study, called STB88, is a division-corps model incorporating a number of different types of computations. The speed-up for three versions of this model on the Caltech/JPL Mark III Hypercube and the BBN Butterfly parallel processors was measured relative to an efficient sequential execution of the same model on the same hardware. The results indicate that STB88 version 1 achieves a speed-up of 28.6 on 60 Mark III processors, while STB88 version 2 achieves a speed-up of 36.8 on 100 Butterfly processors. Version 3 of STB88 achieved a speed-up of 38.5 on 128 Mark III processors. The versions differed only in their interface to Time Warp. On the Butterfly, the sequential execution completed in 2 hours, while the 100 processor execution completed in 3.2 minutes. 相似文献
37.
38.
Abdul Latif Ahmad Choe Peng Leo Syamsul Rizal Abd. Shukor 《Journal of Porous Materials》2009,16(1):33-40
Porous γ-alumina with well arranged secondary mesopores has been contrived using nanosized templating units. The pore size
of templated mesopores is precisely controlled as the pore shrinkage is insignificant. The primary pore diameter is ca. 4 nm
and the secondary pore diameter is ca. 50 nm. The porous material was characterized using N2 adsorption/desorption, TEM, XRD and FT-IR. γ-alumina with bimodal pore size distribution shows improved intra-particle diffusion
compared to γ-alumina with unimodal pore size distribution in a simple dye adsorption test. γ-alumina with different porous
structures were then impregnated with vanadium oxide for catalytic effect comparison. It was perceived that secondary pores
improve the styrene oxidation rate after the conversion of styrene reaches 30%. 相似文献
39.
Camden Debruler Wenda Wu Kevin Cox Brice Vanness T. Leo Liu 《Advanced functional materials》2020,30(24)
Here, a pH neutral aqueous organic redox flow battery (AORFB) consisting of three electrolytes channels (i.e., an anolyte channel, a catholyte channel, and a central salt water channel) to achieve integrated energy storage and desalination is reported. Employing a low cost, chemically stable methyl viologen (MV) anolyte, and sodium ferrocyanide catholyte, this desalination AORFB is capable of desalinating simulated seawater (0.56 m NaCl) down to 0.023 m salt concentration at an energy cost of 2.4 W h L?1 of fresh water—competitive with current reverse osmosis technologies. Simultaneously, the cell delivers stored energy at 79.7% efficiency with a cell voltage of 0.85 V. Furthermore, the cell is also capable of higher current operation up to 15 mA cm?2, providing 4.55 mL of fresh water per hour. Combining energy storage and water desalination into such a bifunctional device offers the opportunity to address two growing global issues from one hardware installation. 相似文献
40.
Accumulating evidence suggests that hypothalamic luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) are two hypophysiotropic factors which modulate the immune response. The aim of the present study was to determine the in vivo effects of an intravenous bolus of LHRH and TRH on plasma interferon (IFN)-gamma production in five normoprolactinemic women with irregular menstrual cycles. We also determined prolactin (PRL), thyrotropin (TSH), follicle stimulating hormone (FSH), and luteinizing hormone (LH) levels before and after intravenous administration of LHRH and TRH. The results demonstrate that intravenous bolus of LHRH/TRH increases plasma IFN-gamma levels, with the maximum response 45 min after in vivo administration of hypothalamic peptides and after peak levels of adenohypophyseal hormones (PRL: 15 min; TSH: 30 min; FSH: 30 min; LH: 30 min). In order to investigate a possible direct action of hypothalamic hormones on immune cells, we also evaluated, in the same subjects, the influence of LHRH and TRH on IFN-gamma production by human peripheral blood mononuclear cells (PBMCs), collected before the intravenous administration of the peptides and stimulated in vitro with bacterial superantigen staphylococcal enterotoxin A (SEA) and concanavalin A (Con A). LHRH and TRH, separately and together, significantly enhanced in vitro IFN-gamma production by SEA- and ConA-activated PBMCs. The present results suggest that hypothalamic peptides (LHRH and TRH) directly, and/or indirectly pituitary hormones (PRL, TSH, FSH, and LH) or IL-2, have stimulatory effect on IFN-gamma producing cells and are further evidence of interactions between the neuroendocrine and immune systems. 相似文献