全文获取类型
收费全文 | 56575篇 |
免费 | 5434篇 |
国内免费 | 3396篇 |
专业分类
电工技术 | 5698篇 |
技术理论 | 4篇 |
综合类 | 5362篇 |
化学工业 | 7079篇 |
金属工艺 | 1749篇 |
机械仪表 | 2742篇 |
建筑科学 | 6223篇 |
矿业工程 | 2351篇 |
能源动力 | 4905篇 |
轻工业 | 3105篇 |
水利工程 | 1806篇 |
石油天然气 | 4265篇 |
武器工业 | 523篇 |
无线电 | 6039篇 |
一般工业技术 | 5099篇 |
冶金工业 | 2554篇 |
原子能技术 | 1159篇 |
自动化技术 | 4742篇 |
出版年
2024年 | 227篇 |
2023年 | 814篇 |
2022年 | 1717篇 |
2021年 | 2059篇 |
2020年 | 1972篇 |
2019年 | 1621篇 |
2018年 | 1571篇 |
2017年 | 1918篇 |
2016年 | 2215篇 |
2015年 | 2347篇 |
2014年 | 3586篇 |
2013年 | 3733篇 |
2012年 | 4058篇 |
2011年 | 4500篇 |
2010年 | 3405篇 |
2009年 | 3473篇 |
2008年 | 3217篇 |
2007年 | 3622篇 |
2006年 | 3263篇 |
2005年 | 2685篇 |
2004年 | 2189篇 |
2003年 | 1905篇 |
2002年 | 1632篇 |
2001年 | 1376篇 |
2000年 | 1139篇 |
1999年 | 961篇 |
1998年 | 717篇 |
1997年 | 610篇 |
1996年 | 579篇 |
1995年 | 458篇 |
1994年 | 381篇 |
1993年 | 247篇 |
1992年 | 201篇 |
1991年 | 181篇 |
1990年 | 156篇 |
1989年 | 135篇 |
1988年 | 119篇 |
1987年 | 71篇 |
1986年 | 53篇 |
1985年 | 38篇 |
1984年 | 47篇 |
1983年 | 20篇 |
1982年 | 30篇 |
1981年 | 26篇 |
1980年 | 11篇 |
1964年 | 11篇 |
1961年 | 9篇 |
1960年 | 11篇 |
1959年 | 11篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
环境因子的定义及研究现状 总被引:12,自引:0,他引:12
胡斌 《太赫兹科学与电子信息学报》2003,1(1):88-92
从普遍接受的三个基本假设出发,讨论环境因子的定义和失效机理不变的约束条件,重点综述环境因子的研究现状和常用方法,并探讨引入反应论模型解决环境因子预测问题的可能途径。 相似文献
103.
介绍了AUTOCONER-338型自动络筒机空气捻接器的接头要求与影响接头质量的因素,并且就不同品种的纱线选用不同接头工艺进行了简单分析;介绍了如何评价络筒切疵有效性与影响切疵率的因素.通过以上2方面的分析介绍,及时调整设计与工艺,提高了生产效率,改善了布面质量. 相似文献
104.
E. Gomez 《Chemical engineering science》2006,61(14):4595-4604
The influence of oxygen transport rate on Rhodococcus erythropolis cultures has been studied in a stirred tank bioreactor under different transport and uptake conditions. Oxygen uptake rate has been measured by applying a modified dynamic method and a kinetic model is proposed, obtaining the kinetic parameter values: specific maintenance and yield coefficients. The volumetric mass transfer coefficients under inert conditions, kLa, and during the bioprocess, KLa, have been determined. The values obtained are different and a biological enhancement factor E, has been considered. These parameters have been predicted by the theoretical model and good agreement with experimental data under the conditions studied has been found. The oxygen limitation has been expressed by a modified dimensionless Damköhler number, Da, the relationship between transport and biological reaction rates. This number decreases with increasing stirrer speed; that is, when mass transport resistance decreases. The efficiency of oxygen utilization can be determined by a film effectiveness factor, η. The effectiveness factor was found to be a strong function of Damköhler number and decrease with increasing Da. Furthermore, oxygen concentration into culture depends on the mass transfer and consumption rates. The theoretical model proposed is able to reasonably predict the evolution of dissolved oxygen concentration with time of cultivation. 相似文献
105.
This study deals with evaluating the energy and exergy utilization efficiencies in the Turkish agricultural sector over a 12‐year period from 1990 to 2001. In the energy and exergy analyses, two main energy sources, namely fuels and electricity, are taken into consideration, while the sectoral energy and exergy efficiencies are compared for this period. These main energy sources include diesel for tractors and other vehicles, and electricity for pumps. Overall energy utilization efficiencies are obtained to vary between 29.1 and 41.1%, while overall exergy utilization efficiencies are found to range from 27.9 to 37.4% in the analysed years, respectively. It may be concluded that the present technique proposed here may be used as a useful tool in analysing and evaluating the energy and exergy utilization efficiencies, identifying energy efficiency and/or energy conservation opportunities and dictating the energy strategies of countries. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
106.
107.
N. K. Savant P. S. Ongkingco I. V. Zarate F. M. Torrizo P. J. Stangel 《Nutrient Cycling in Agroecosystems》1991,28(3):323-331
A plunger-type, completely hand-operated applicator prototype, made of polyvinyl chloride (PVC), for deep placement of urea briquettes (UB), i.e., pillow-shaped urea supergranules with edges, in line transplanted rice has been developed for use by small-scale rice farmers. The field evaluation of the applicator was conducted in the Philippines during the 1989 dry season. The applicator consistently placed UB at proper depth (7 to 8 cm), which resulted in low concentrations of urea N (<7 ppm) in about 4 cm of floodwater 1 day after placement. These findings indicated that the prototype worked properly. Average work output of the applicator was 0.20 ha workday–1 and may increase with practice. The yields of irrigated transplanted rice in the field trials show that agronomic efficiencies of hand-placed UB and applicator-placed UB were equal and were superior to those of split-applied prilled urea. 相似文献
108.
The solubilities of ethyl palmitate, ethyl oleate, ethyl eicosapentaenoate (EPA) and ethyl docosahexaenoate (DHA) in supercritical
carbon dioxide were determined by a continuous flow method. The solubilities of fatty acid ethyl esters increased with pressure
and decreased as the temperature was increased. An empirical equation, similar to Chrastil's equation, was used to describe
the relationship between solute solubility and the density of carbon dioxide. The empirical equation was further used to qualitatively
estimate the separation efficiency of isolating EPA and DHA ethyl esters from fatty acid esters. The operating conditions
yielding high solubility gave fast extraction rate but resulted in low separation efficiency. Experiments were conducted to
separate ethyl EPA and ethyl DHA from a model mixture containing four fatty acid ethyl esters and from esterified squid visceral
oil. The experimental data compared closely with the calculated values. 相似文献
109.
介绍了Delta4型压力筛生产全漂白硫酸盐法马尾松浆的运行情况,对存在的问题进行分析探讨,并对比了技改重新选型后的生产情况。 相似文献
110.