全文获取类型
收费全文 | 36334篇 |
免费 | 3338篇 |
国内免费 | 1713篇 |
专业分类
电工技术 | 1195篇 |
综合类 | 2487篇 |
化学工业 | 9515篇 |
金属工艺 | 2346篇 |
机械仪表 | 1140篇 |
建筑科学 | 2265篇 |
矿业工程 | 1360篇 |
能源动力 | 1536篇 |
轻工业 | 5696篇 |
水利工程 | 654篇 |
石油天然气 | 2138篇 |
武器工业 | 607篇 |
无线电 | 1695篇 |
一般工业技术 | 3449篇 |
冶金工业 | 2407篇 |
原子能技术 | 323篇 |
自动化技术 | 2572篇 |
出版年
2024年 | 138篇 |
2023年 | 585篇 |
2022年 | 982篇 |
2021年 | 1212篇 |
2020年 | 1197篇 |
2019年 | 1170篇 |
2018年 | 1066篇 |
2017年 | 1291篇 |
2016年 | 1355篇 |
2015年 | 1311篇 |
2014年 | 2135篇 |
2013年 | 2260篇 |
2012年 | 2567篇 |
2011年 | 2629篇 |
2010年 | 1974篇 |
2009年 | 1891篇 |
2008年 | 1653篇 |
2007年 | 2163篇 |
2006年 | 2079篇 |
2005年 | 1808篇 |
2004年 | 1714篇 |
2003年 | 1435篇 |
2002年 | 1222篇 |
2001年 | 997篇 |
2000年 | 880篇 |
1999年 | 670篇 |
1998年 | 511篇 |
1997年 | 442篇 |
1996年 | 355篇 |
1995年 | 327篇 |
1994年 | 285篇 |
1993年 | 201篇 |
1992年 | 192篇 |
1991年 | 145篇 |
1990年 | 104篇 |
1989年 | 79篇 |
1988年 | 67篇 |
1987年 | 46篇 |
1986年 | 34篇 |
1985年 | 43篇 |
1984年 | 32篇 |
1983年 | 14篇 |
1982年 | 30篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1964年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Johann Vollmann Heinrich Grausgruber Helmut Wagentristl Heinrich Wohleser Pavel Michele 《Journal of the science of food and agriculture》2003,83(15):1581-1586
The presence of protease inhibitors in soybean prohibits the utilisation of the raw beans for food and feed. However, little information is available about environmental influences and the effects of nitrogen and sulphur supply on the antinutritional constituents of soybean. As these factors may influence protease inhibitors, soybean genotypes segregated according to the presence or absence of the Kunitz trypsin inhibitor have been evaluated for trypsin inhibitor activity (TIA) in field trials. TIA was affected significantly by environment (geographical location), fertilisation treatment and genotype. Environmental means of TIA were between 69.5 and 104.8 mg g?1. Nitrogen application, which caused an increase in seed protein content, resulted in a reduction in TIA by about 15% as compared with the control. Remarkably, simultaneous application of nitrogen and sulphur in the form of ammonium sulphate had a similar reductive effect on TIA to that of nitrogen application alone, although soybean protease inhibitors are rich in sulphur amino acids. Significant genetic variation in TIA was found both within the genotype class with the Kunitz inhibitor present as well as within the class lacking this inhibitor. The results suggest that TIA of soybean may be modified considerably by genetic improvement and appropriate agronomic management. Copyright © 2003 Society of Chemical Industry 相似文献
83.
磷铝杂原子固体酸催化剂催化合成乙酸异丙酯 总被引:5,自引:0,他引:5
高文艺 《精细石油化工进展》2003,4(12):30-31
以丙烯和乙酸为原料 ,自制的磷铝杂原子固体酸作催化剂催化合成了乙酸异丙酯 ,考察了反应温度、反应压力、反应空速 (LHSV)及催化剂用量对酯化反应的影响 ,同时考察了固体酸催化剂的重复使用性。确定了最佳合成条件 :反应压力 1 5MPa,反应温度 1 60℃ ,反应空速2 0h-1,催化剂用量 2 0g。在此条件下 ,酯化率可达 91 5 % ,乙酸异丙酯选择性达 99 0 % ,且催化剂的重复使用性良好。 相似文献
84.
Thomas Thelin 《Empirical Software Engineering》2003,8(3):309-313
This thesis describes six empirical investigations of two techniques applied to software inspections, namely reading techniques and fault content estimation techniques. The first part of the thesis presents a series of experiments of a novel reading technique called usage-based reading. The second part investigates fault content estimation applied to the software inspection process. The estimation methods used are capture-recapture and curve fitting. 相似文献
85.
曾喜银 《湖南冶金职业技术学院学报》2003,(4)
电视教材的节奏包含两个方面的内容:其一是内容情节节奏,其类型选择要根据教学内容、教学目标、教学对象、教学组织形式、电视教材类型而定;其二是表现形式节奏,主要包括画面的视觉节奏、摄像机镜头的运动节奏、景别变化节奏、镜头长度节奏、镜头组接节奏、应用电子特技产生的节奏、声音节奏等。 相似文献
86.
合成直链烷基苯环境友好固体酸催化剂的研究 Ⅲ .催化剂失活原因分析 总被引:1,自引:0,他引:1
采用固定床反应器,对催化剂的稳定性进行了初步评价。在120℃、空速相同、液固反应条件下,高苯烯比时催化剂的稳定性明显高于低苯烯比时;在苯烯比和空速相同、液固反应条件下,相对低温反应时,催化剂的稳定性明显高于高温反应。IR分析结果表明,同新鲜和反应后未失活的催化剂相比,失活后催化剂的活性组分特征衍射峰消失,出现的新的特征衍射峰可能同—CH基的振动有关。TG分析结果表明,失活后催化剂在空气流中焙烧,失重幅度比新鲜催化剂大。 相似文献
87.
介绍ICP—AES法测定硅铝钡中的钡的分析方法,用氢氟酸一硝酸一高氯酸混合酸溶解试样,用钡的233.527nm谱线测定钡.该方法简便快速,精密度好,准确度高,加标试验回收率为99%~100%,相对标准偏差为0.25%~0.56%. 相似文献
88.
固体中光声拉曼效应的理论分析 总被引:2,自引:1,他引:1
从非线性波动方程出发,运用准平衡模型以及热弹理论,对固体样品中光声拉曼效应进行理论分析,导出了脉冲激光泵浦下光声拉曼信号的解析表达式,并总结分析了固体中光声拉曼效应的一些原理特性、实验问题和应用价值。 相似文献
89.
The equilibrium moisture content (EMC) characteristics of high oleic sunflower seeds and kernels between 10 and 55°C were determined by equilibrating the samples to known relative humidities (RH) above saturated salt solutions. EMC of the kernels was lower than that of seeds in the range of 11 to 96% ERH and at 25 and 40°C. Hysteresis effect was found for the EMC properties of seeds and kernels at 25°C. Four EMC-ERH models (modified Henderson, Chung-Pfost, Halsey, and Guggenheim-Anderson-de Boer) and their estimated parameters were evaluated for goodness of fit. GAB and Halsey equations showed the best fitting of experimental data although GAB equation adjusted for temperature described the EMC data the best. Components of the seed as oil content or hull/kernel ratio did not explain the slight differences in EMC found between the varieties. 相似文献
90.
P. S. Lawson 《Biomass & bioenergy》1992,2(1-6):319-330
In recent years it has been recognised by an increasing number of nations that there is considerable energy potential within MSW. As a result many countries have established R,D& D programmes to examine methods of exploiting this potential. The IEA's MSW Conversion Activity was set up in 1986 to provide an infrastructure for sharing information and co-ordinating work in this area internationally. This Activity was extended in 1989 and currently a total of 9 nations participate in it.
To cope with the wide scope of the area (encompassing both biological and thermal processing of MSW) the Activity was divided into three subgroups or Expert Working Groups (EWGs). Each of these dealt with a distinct area of expertise:
- 1. •Downstream effects of source separation and screening of MSW
- 2. •Sampling and analytical protocols
- 3. •Landfill gas
In addition to these groups a central secretariat based at Harwell (UK) has provided guidance, established and administered databases of contacts and produced a series of national reports.
This paper describes the achievements of the Activity and discusses work proposed for the future. 相似文献