全文获取类型
收费全文 | 101385篇 |
免费 | 7710篇 |
国内免费 | 6073篇 |
专业分类
电工技术 | 3211篇 |
技术理论 | 2篇 |
综合类 | 5758篇 |
化学工业 | 25195篇 |
金属工艺 | 10397篇 |
机械仪表 | 4548篇 |
建筑科学 | 3213篇 |
矿业工程 | 2410篇 |
能源动力 | 2311篇 |
轻工业 | 7143篇 |
水利工程 | 1241篇 |
石油天然气 | 2912篇 |
武器工业 | 742篇 |
无线电 | 10549篇 |
一般工业技术 | 16906篇 |
冶金工业 | 3794篇 |
原子能技术 | 1169篇 |
自动化技术 | 13667篇 |
出版年
2024年 | 341篇 |
2023年 | 1667篇 |
2022年 | 3010篇 |
2021年 | 3619篇 |
2020年 | 2860篇 |
2019年 | 2570篇 |
2018年 | 2373篇 |
2017年 | 3000篇 |
2016年 | 3530篇 |
2015年 | 4232篇 |
2014年 | 5563篇 |
2013年 | 5740篇 |
2012年 | 6333篇 |
2011年 | 8685篇 |
2010年 | 6691篇 |
2009年 | 7204篇 |
2008年 | 6380篇 |
2007年 | 6927篇 |
2006年 | 5891篇 |
2005年 | 5129篇 |
2004年 | 4101篇 |
2003年 | 3727篇 |
2002年 | 3081篇 |
2001年 | 2049篇 |
2000年 | 1919篇 |
1999年 | 1582篇 |
1998年 | 1274篇 |
1997年 | 986篇 |
1996年 | 911篇 |
1995年 | 680篇 |
1994年 | 672篇 |
1993年 | 494篇 |
1992年 | 398篇 |
1991年 | 326篇 |
1990年 | 242篇 |
1989年 | 192篇 |
1988年 | 131篇 |
1987年 | 108篇 |
1986年 | 116篇 |
1985年 | 69篇 |
1984年 | 53篇 |
1983年 | 46篇 |
1982年 | 56篇 |
1981年 | 33篇 |
1980年 | 49篇 |
1979年 | 33篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 9篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A new microstructure, thornball, of zinc oxide (ZnO) was synthesized by a very simple solid vapor deposition process under lead oxide (PbO) atmosphere. The microthornballs consist of numerous needles, which extend outwards in all directions symmetrically. They have dimensions of 120 μm in diameter, while the average diameter of the needles is about 100-200 nm. The needles on the balls grow along the 〈0 0 0 1〉 orientation and have gradient compositions along radial. Control experiments proved that PbO played an important role in the growth. Additionally, photoluminescence property was observed and provided the evidence that PbO did not deteriorate the optical properties of ZnO thornballs. This kind of microstructures has potential applications in the field of photochemical catalysis. 相似文献
92.
喷射导管技术在深水钻井作业中的应用 总被引:9,自引:1,他引:8
深水油气日益成为海洋石油勘探开发的热点,但深水钻井作业面临着许多难题和挑战,喷射导管技术是解决深水浅层钻井难题的技术之一。该技术采用在喷射管柱内下动力钻具的方式,用钻入泥线以下的管串自身重力钻进,喷射到位后利用地层的粘附力和摩擦力稳固住导管,起出送入工具和管内钻具,完成导管的安装。喷射导管技术可避免因水泥浆密度过大而压破地层,也可避免深水由于低温等因素影响固井质量。我国第一口水深超千米的深水井——荔湾3-1-1井利用该技术成功完成了导管的安装,井口装置没有出现井口失稳的问题。随着我国深水勘探步伐的加快,越来越多的深水区块将投入勘探开发,喷射导管技术具有良好的应用前景。 相似文献
93.
A. Cardador-Martí nez E. Casta o-Tostado G. Loarca-Pi a 《Food Additives & Contaminants》2002,19(1):62-69
Polyphenols with antimutagenic and anticarcinogenic properties are present in fruits, vegetables and legumes. In this study, the Salmonella typhimurium tester strains TA98 and TA100 were used in the microsuspension assay to examine the antimutagenic effect of phenolic compounds extracted from the common bean (Phaseolus vulgaris) against mutagenicity induced by aflatoxin B 1 (AFB 1 ). A dose-response curve was constructed for AFB 1 ; from which a level of 40ng AFB 1 /tube was selected for all antimutagenicity assays. The AFB 1 and phenolic extract (PE) were not toxic to the bacteria at concentrations tested. In the case of PE, results were similar to the number of spontaneous revertants for TA98 and TA100. The inhibitory effect of PE against AFB 1 mutagenicity was dose-dependent at the lower concentrations tested (2.5, 5, 10, 12.5, 15 and 25 μg-equivalent ( + )-catechin/tube for TA98; 0.5, 1, 1.5, 2.5, 5, 10 and 25 μg-equivalent ( + )-catechin/ tube for TA100). Further, a two-stage incubation procedure was used to investigate the potential interaction between PE and AFB 1 . The greatest inhibitory effect of the PE on AFB 1 mutagenicity occurred when PE and AFB 1 were incubated together. When the bacteria were first incubated with PE followed by a second incubation with AFB 1 , lower inhibition was observed. Lower inhibition was also observed when the bacteria were first incubated with AFB 1 followed by a second incubation with PE. The results suggest that the mechanism of inhibition could involve the formation of a chemical complex between of PE and AFB 1 . 相似文献
94.
概述了鞍钢1780mm生产线技术改造工程中供电、传动及自动控制系统的构成、安装及调试技术要点,以及技术经济效果评述,可供同类工程施工参考. 相似文献
95.
J.-S. LiuJ.-H. Chuang 《Pattern recognition》2002,35(1):155-167
For choosing specific cross-ratios as 2D projective coordinates in various computer vision applications, a reasonable error analysis model is usually required. This investigation adopts the assumption of normal distribution for positioning errors of point features in an image to formulate the error variances of cross-ratios. Based on a geometry-based error analysis, a straightforward way of identifying the cross-ratios with minimum error variances is proposed. Simulation results show that the proposed approach, as well as a further simplified alternative, yield much better estimations of minimum error variances in terms of accuracy, cost, and stability compared with some other methods, e.g., the one based on the rule given by Georis et al. (IEEE Trans. Pattern Anal. Mach. Intell. 20 (4) (1998) 366). Some causes of the performance differences in the estimations are explained using a special configuration of point features. 相似文献
96.
乙炔在磁稳定床中的选择性加氢研究 总被引:1,自引:0,他引:1
制备了一种磁性Pd/Al2O3催化剂,采用磁稳定床考察了活性组分负载量、反应条件及CO浓度对乙炔加氢反应性能的影响。结果表明,当反应温度80℃、反应压力1.5MPa、空速9000h-1、磁场强度(H)25kA/m时,乙炔转化率为100%,乙烯选择性可达81%,具有优良的乙炔加氢活性和乙烯选择性,优于相同反应条件下的进口催化剂;250h稳定性实验结果表明,磁性Pd/Al2O3催化剂具有良好的初活性和乙烯选择性,催化剂性能稳定。 相似文献
97.
98.
The Y2O3: Yb3 , Er3 microstructures were fabricated by a hydrothermal method without surfactants.The microstructures structure was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM,KYKY 1000B).The up-conversion luminescence spectra were studied under 978 nm laser diode excitation.In Yb3 and Er3 codoped Y2 O3 microcrystals, the relative intensity of green emission became stronger as the morphology of sample changed from wires to films. 相似文献
99.
对耐火材料——棕刚玉粉的质量分析控制,提出了用实用性的检测方法测定其Al2O3含量。通过与国家标准分析方法的对比试验,证实快速实用分析方法测定棕刚玉粉中Al2O3含量是可行的。 相似文献
100.
Véronique Baroghel-Bouny Patrick Belin Matthias Maultzsch Dominique Henry 《Materials and Structures》2007,40(8):759-781
Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO3 spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch
procedure (spraying of 0.1-N AgNO3 solution + K2CrO4) as well as the procedure based on the use of a sole AgNO3 solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi
procedure (spraying of 0.1-N AgNO3 + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state
diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray
tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone)
and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods
have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus
time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The
possible sources of discrepancy on the results have been analysed. 相似文献