全文获取类型
收费全文 | 40838篇 |
免费 | 4517篇 |
国内免费 | 2685篇 |
专业分类
电工技术 | 2851篇 |
技术理论 | 7篇 |
综合类 | 3177篇 |
化学工业 | 7028篇 |
金属工艺 | 1554篇 |
机械仪表 | 1541篇 |
建筑科学 | 2968篇 |
矿业工程 | 1911篇 |
能源动力 | 3061篇 |
轻工业 | 1790篇 |
水利工程 | 2022篇 |
石油天然气 | 1510篇 |
武器工业 | 252篇 |
无线电 | 3154篇 |
一般工业技术 | 3763篇 |
冶金工业 | 3540篇 |
原子能技术 | 675篇 |
自动化技术 | 7236篇 |
出版年
2024年 | 180篇 |
2023年 | 791篇 |
2022年 | 1248篇 |
2021年 | 1406篇 |
2020年 | 1584篇 |
2019年 | 1389篇 |
2018年 | 1239篇 |
2017年 | 1531篇 |
2016年 | 1675篇 |
2015年 | 1586篇 |
2014年 | 2692篇 |
2013年 | 2743篇 |
2012年 | 3165篇 |
2011年 | 3541篇 |
2010年 | 2614篇 |
2009年 | 2628篇 |
2008年 | 2434篇 |
2007年 | 2579篇 |
2006年 | 2228篇 |
2005年 | 1746篇 |
2004年 | 1385篇 |
2003年 | 1275篇 |
2002年 | 1067篇 |
2001年 | 862篇 |
2000年 | 778篇 |
1999年 | 668篇 |
1998年 | 507篇 |
1997年 | 385篇 |
1996年 | 390篇 |
1995年 | 291篇 |
1994年 | 291篇 |
1993年 | 207篇 |
1992年 | 194篇 |
1991年 | 131篇 |
1990年 | 76篇 |
1989年 | 74篇 |
1988年 | 60篇 |
1987年 | 37篇 |
1986年 | 43篇 |
1985年 | 46篇 |
1984年 | 37篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1966年 | 10篇 |
1964年 | 21篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
系统介绍了舞钢开发的针状铁素体型X70宽厚板的设计思路、工艺特点和实物水平;采用电炉 炉外精炼 连铸 TMCP工艺生产的X70宽厚板满足西气东输专用技术条件的要求,并批量应用在西气东输主干线工程中。 相似文献
32.
Ahmad Nozad Golikand Elaheh Lohrasbi Mohammad Ghannadi Maragheh Mehdi Asgari 《Journal of Applied Electrochemistry》2008,38(6):869-874
The effect of carbon surface oxidation on platinum supported carbon particles (Pt/C) with nitric acid was investigated by
cyclic voltammetry, electrochemical impedance spectroscopy, polarization experiments and chronoamperometry. Cyclic voltammograms,
polarization curves and electrochemical impedance spectra showed that the treated catalyst had much larger active surface
area and higher ionic conductivity than the untreated catalyst, and provided enhanced performance for oxygen reduction. The
formation of acidic groups was examined by IR spectra. The Pt/C surface oxidation had a large effect on the performance of
a gas diffusion electrode for oxygen reduction reaction. 相似文献
33.
Iron(III) oxide tablets were electrolytically reduced to iron in molten sodium hydroxide at 530 °C and recovered to produce
iron with 2 wt.% oxygen suitable for re-melting. The cell was operated at 1.7 V and an inert nickel anode was used. The thermodynamics
and mechanism of the process was also investigated. By controlling the activity of sodium oxide in the melt, the cell could
be operated below the decomposition voltage of the electrolyte with the net sequence of events being the ionization of oxygen,
its subsequent transport to the anode and discharge leaving behind iron at the cathode. A reduction time of 1 h was achieved
for a 1 g oxide tablet (close to the theoretical reduction time predicted by Faraday’s laws) at a current density of 520 mA cm−2 with iron phase yields of ∼90 wt.%. The energy consumption was 2.8 kWh kg−1. 相似文献
34.
Namsin Park Takeyuki Shiraishi Kazuyoshi Kamisugi Yoshitaka Hara Keita Iizuka Takashi Kado Shuzi Hayase 《Journal of Applied Electrochemistry》2008,38(3):371-375
A direct ethanol fuel cell (DEFC), which is less prone to ethanol crossover, is reported. The cell consists of PtRu/C catalyst as the anode, Nafion® 117 membrane, and Ni–Co–Fe (NCF) composite catalyst as the cathode. The NCF catalyst was synthesized by mixing Ni, Co, and Fe complexes into a polymer matrix (melamine-formaldehyde resins), followed by heating the mixture at 800 °C under inert atmosphere. TEM and EDX experiments suggest that the NCF catalyst has alloy structures of Ni, Co and Fe. The catalytic activity of the NCF catalyst for the oxygen reduction reaction (ORR) was compared with that of commercially available Pt/C (CAP) catalyst at different ethanol concentrations. The decrease in open circuit voltage (Voc) of the DEFC equipped with the NCF catalysts was less than that of CAP catalyst at higher ethanol concentrations. The NCF catalyst was less prone to ethanol oxidation at cathode even when ethanol crossover occurred through the Nafion®117 film, which prevents voltage drop at the cathode. However, the CAP catalyst did oxidize ethanol at the cathode and caused a decrease in voltage at higher ethanol concentrations. 相似文献
35.
Maw-Ling Wang Venugopal Rajendran 《Journal of the Chinese Institute of Chemical Engineers》2008,39(5):533-537
Propenylbenzenes and cinnamic acid derivatives yield correspondingly substituted benzaldehydes when oxidized by lead-ruthenium pyrochlore oxide in the presence of sodium hydrochlorite as a co-oxidant at pH 11 under heterogeneous conditions. The reaction of terminal and internal aliphatic alkenes under similar conditions affords no aldehydes. 相似文献
36.
以三聚磷酸钠生产过程为例,论述了在以纯碱为原料的非强酸性水溶液体系中,由于反应不完全导致反应物中存在少量的碳酸盐,这部分碳酸盐干扰了用酸碱滴定法测量的中和度,并据此提出中和度分析改进方法.由此可以推广到其它以纯碱为原料的非强酸性水溶液体系中. 相似文献
37.
Theorists have predicted that repetition blindness (RB) should be absent for nonwords because they do not activate preexisting mental types. The authors hypothesized that RB would be observed for nonwords because RB can occur at a sublexical level. Four experiments showed that RB is observed for word-nonword pairs (noon noof), orthographically similar nonwords (glome glame), and identical repetitions (plass plass). More RB was found for words than for nonwords. Prior researchers may have failed to find RB for nonwords because display conditions that allow 2 words to be reliably encoded are insufficient for nonwords, or because observers coped with low ability to encode nonwords by using guessing strategies that do not require creating a mental type or tokenizing it. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
38.
39.
Legendre orthogonal moments have been widely used in the field of image analysis. Because their computation by a direct method is very time expensive, recent efforts have been devoted to the reduction of computational complexity. Nevertheless, the existing algorithms are mainly focused on binary images. We propose here a new fast method for computing the Legendre moments, which is not only suitable for binary images but also for grey level images. We first establish a recurrence formula of one-dimensional (1D) Legendre moments by using the recursive property of Legendre polynomials. As a result, the 1D Legendre moments of order p, Lp=Lp(0), can be expressed as a linear combination of Lp-1(1) and Lp-2(0). Based on this relationship, the 1D Legendre moments Lp(0) can thus be obtained from the arrays of L1(a) and L0(a), where a is an integer number less than p. To further decrease the computation complexity, an algorithm, in which no multiplication is required, is used to compute these quantities. The method is then extended to the calculation of the two-dimensional Legendre moments Lpq. We show that the proposed method is more efficient than the direct method. 相似文献
40.
本文主要完成了液态金属钠高温沸腾实验回路的应力分析与计算,确定了回路高温区连接管系的布置型式和支吊架系统,是该回路总体设计的重要组成部分。 相似文献