全文获取类型
收费全文 | 234526篇 |
免费 | 20564篇 |
国内免费 | 10236篇 |
专业分类
电工技术 | 14287篇 |
技术理论 | 30篇 |
综合类 | 23182篇 |
化学工业 | 34384篇 |
金属工艺 | 10435篇 |
机械仪表 | 11835篇 |
建筑科学 | 31695篇 |
矿业工程 | 13048篇 |
能源动力 | 8548篇 |
轻工业 | 17437篇 |
水利工程 | 10716篇 |
石油天然气 | 12652篇 |
武器工业 | 3320篇 |
无线电 | 14544篇 |
一般工业技术 | 18563篇 |
冶金工业 | 11851篇 |
原子能技术 | 1711篇 |
自动化技术 | 27088篇 |
出版年
2024年 | 1133篇 |
2023年 | 3147篇 |
2022年 | 5901篇 |
2021年 | 7831篇 |
2020年 | 7608篇 |
2019年 | 5817篇 |
2018年 | 5464篇 |
2017年 | 6857篇 |
2016年 | 8179篇 |
2015年 | 8815篇 |
2014年 | 15815篇 |
2013年 | 14056篇 |
2012年 | 16866篇 |
2011年 | 18541篇 |
2010年 | 13669篇 |
2009年 | 13878篇 |
2008年 | 12667篇 |
2007年 | 15463篇 |
2006年 | 14064篇 |
2005年 | 12318篇 |
2004年 | 10250篇 |
2003年 | 8899篇 |
2002年 | 7294篇 |
2001年 | 6014篇 |
2000年 | 5109篇 |
1999年 | 4047篇 |
1998年 | 2895篇 |
1997年 | 2517篇 |
1996年 | 2047篇 |
1995年 | 1679篇 |
1994年 | 1446篇 |
1993年 | 1041篇 |
1992年 | 838篇 |
1991年 | 586篇 |
1990年 | 499篇 |
1989年 | 475篇 |
1988年 | 264篇 |
1987年 | 202篇 |
1986年 | 171篇 |
1985年 | 201篇 |
1984年 | 145篇 |
1983年 | 126篇 |
1982年 | 65篇 |
1981年 | 77篇 |
1980年 | 83篇 |
1979年 | 38篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1975年 | 20篇 |
1959年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
本文提出采用高分子有机材料配合,生产石膏制品防水防潮剂的生产方法和工艺。该剂还可以应用到氧化镁系列板材,同时提出开发珠光或彩色防水防潮剂,能达到满足的装饰效果,值提开发推广。 相似文献
72.
Whey is an undurable product. treated very often as a waste which pollutes the natural environment. Whey which is a valuable source of protein, lactose, vitamins and mineral salts should be utilized completely. The present paper is a proposal of whey drying on porous carriers. It is proved experimentally that the proposed drying method guarantees good product quality. 相似文献
73.
74.
朱珉 《电气电子教学学报》2002,24(6):55-56
本文介绍由东南大学组织编写,东南大学出版社出版的《电工电子实践课程丛书》的编写背景,每本教材内容的简要内容,特色与使用情况。 相似文献
75.
本文介绍以PC-1500(A)型袖珍计算机为主体的地面放射性总量数据采集及处理系统的方案、硬件、软件及应用。 相似文献
76.
LeAnn Southward Hogan Elizabeth Marschall Carol Folt Roy A. Stein 《Journal of Great Lakes research》2007,33(1):46-61
Lake Erie's food web has been dramatically modified by exotic species. Both exotic dreissenid mussels and the round goby Neogobius melanastomus have shifted the food web from a pelagicbased to a benthic-based one, potentially creating a new pathway for contaminant transfer to top predators. Before the invasion of round gobies, few predators of dreissenids occurred in Lake Erie, allowing contaminants to be confined to these benthic organisms. The invasion of the round goby has produced a new pathway through which these contaminants can enter the food web. To characterize heavy-metal transfer through this new food web and to assess risk to humans, water, surficial sediment, dreissenid, round goby, and smallmouth bass Micropterus dolomieui samples were collected at three sites during summers, 2002 and 2003, and analyzed for total lead (Pb), total mercury (Hg), and methyl mercury (MeHg). In addition, we compared smallmouth bass Pb and Hg concentrations to those measured in 1993/1994, before round gobies were prevalent. Pb biodiminished and MeHg biomagnified through the food web to smallmouth bass; patterns were similar among our three sites. Total Pb concentrations in smallmouth bass were higher before the incorporation of round gobies into their diet. We attributed this decline to changes in food web structure, changes in contaminant burdens in prey, or declines in sediment Pb concentrations in Lake Erie. By comparison, Hg concentrations in smallmouth bass changed little, before and after the round goby invasion, possibly due to a shift in diet that increased growth. Despite a decline in sediment Hg concentrations in Lake Erie, smallmouth bass continued to accumulate Hg at historical rates possibly because of their high consumption rates of benthivorous round gobies. As smallmouth bass continue to consume round gobies during their lives, their Hg concentrations may well continue to increase, potentially increasing the risk of Hg contamination to humans. 相似文献
77.
John W. Reeder 《国际能源研究杂志》1985,9(3):229-239
This paper examines in a very broad fashion the formation of geothermal resources at lithospheric subduction zones. Regions of highly silicic calc-alkaline Quaternary volcanoes and/or plutons have been identified as prime candidates for having high-temperature hydrothermal systems. Regions of large tholeiitic Quaternary volcanoes have been identified as prime candidates for having large moderate-temperature hydrothermal systems. In addition, active magmatic, phreatomagnetic, and/or tectonic fracturing must be occurring in order to keep any moderate to high temperature hydrothermal system from chemically sealing. Connate, meteoric and/or oceanic water sources must also be present. Owing to tectonic and magmatic processes, volcanic arcs of subduction zones represent regions of the crust that have anomalously high mechanical and heat energy. Such arc regions are expected to contain significantly more moderate to high temperature hydrothermal systems than what is presently known. Many of these arcs are briefly discussed with respect to their potential for containing such resources. 相似文献
78.
Steady laminar binary mixed convection flow along a vertical circular cone under the combined buoyancy effects of thermal and species diffusion is studied analytically. The analysis is confined to mass diffusion processes with low concentration levels. In the analysis the surface of the cone is assumed to be at a uniform temperature and uniform concentration. Numerical results for the local Sherwood number, local Nusselt number and local friction factor are presented. Representative temperature, concentration and velocity profiles are also shown. The analysis covers the diffusion of common gases and vapours into air. Considerations are given to the situations where the buoyancy forces assist and oppose the forced convection flow for various possible combinations of the thermal and species diffusion processes. 相似文献
79.
M. J. Gonzlez-Tejera M. A. La De Plaza E. De Snchez La Blanca I. Hernndez-Fuentes 《Polymer International》1993,31(1):45-50
The electrochemical behaviour, FTIR spectrum and the morphology of polypyrrole-polystyrenesulphonate (PPy-PSS) films obtained potentiostatically at 0.6 V in a 0.05m Py + 1.7 × 10?2m NaPSS medium have been analysed. Different electrochemical parameters have been modified in order to establish the first polaron formation, the reversibility of the redox process and the doping mechanism. The FTIR spectrum confirms the existence of C?O groups in the film structure and two possible explanations are suggested. SEM reveals a higher homogeneity in these films than in PPy films doped with smaller counterions. 相似文献
80.
Peng Dangcong Jin Qiting 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1993,58(1):89-93
The anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up-flow anaerobic sludge blanket reactor—UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5–10 kg COD m?3 day?1, the UASB reactor achieved 50–60% COD removal efficiencies. Gas production was 2–3 dm3 per dm3 of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster-like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability. 相似文献