首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4437篇
  免费   647篇
  国内免费   119篇
电工技术   31篇
综合类   159篇
化学工业   1115篇
金属工艺   64篇
机械仪表   65篇
建筑科学   52篇
矿业工程   33篇
能源动力   65篇
轻工业   3021篇
水利工程   20篇
石油天然气   50篇
武器工业   4篇
无线电   95篇
一般工业技术   162篇
冶金工业   70篇
原子能技术   42篇
自动化技术   155篇
  2024年   46篇
  2023年   119篇
  2022年   221篇
  2021年   262篇
  2020年   210篇
  2019年   240篇
  2018年   223篇
  2017年   235篇
  2016年   175篇
  2015年   199篇
  2014年   227篇
  2013年   278篇
  2012年   348篇
  2011年   364篇
  2010年   208篇
  2009年   206篇
  2008年   167篇
  2007年   210篇
  2006年   187篇
  2005年   154篇
  2004年   120篇
  2003年   147篇
  2002年   92篇
  2001年   74篇
  2000年   66篇
  1999年   50篇
  1998年   57篇
  1997年   41篇
  1996年   43篇
  1995年   41篇
  1994年   34篇
  1993年   20篇
  1992年   28篇
  1991年   24篇
  1990年   32篇
  1989年   14篇
  1988年   8篇
  1987年   6篇
  1986年   6篇
  1985年   6篇
  1984年   4篇
  1983年   1篇
  1982年   4篇
  1981年   2篇
  1980年   3篇
  1973年   1篇
排序方式: 共有5203条查询结果,搜索用时 15 毫秒
31.
氢氧化铝微粉生产过程中晶种分解的研究   总被引:1,自引:0,他引:1  
晶种分解是种分法生产氢氧化铝微粉的工序,介绍了控制铝酸钠精制液的分解温度、分解时间、搅拌强度等条件并添加特制的高活性晶种做晶种生产优质氢氧化铝微粉的生产过程,并通过对几个月的生产跟踪分析研究,得出氢氧化铝微粉的晶种分解主要与晶种的质量和数量、分解温度、分解时间及搅拌强度等因素有关,这对于进一步完善氢氧化铝微粉的生产工艺起到很大的作用。  相似文献   
32.
In pot and field experiments conducted in 1990 and 1991 on an acid sandy, phosphorus (P) deficient soil in Niger, West Africa, the effect of seed coating on seedling emergence, early growth and grain yield of pearl millet (Pennisetum glaucum (L.) R. Br.) was studied. Seeds of pearl millet were coated with different rates (0; 0.5; 1.0; 2.0; 5.0; 10.0 mg P seed–1) and types of P fertilizers (single superphosphate, ammonium dihydrogen phosphate; monocalcium phosphate, sodium dihydrogen phosphate and sodium triphosphate). Seedling emergence was generally reduced at coating rates higher than 0.5 mg P seed–1 and prevented with single superphosphate and sodium triphosphate at rates higher than 5 mg P seed–1. No correlation was found between the pH and osmomolity of the coatings and final emergence of millet seedlings. The most favourable effect on plant growth and P content was achieved with ammonium dihydrogen phosphate (AHP) as seed coating. This was attributed to the enhancement effect of ammonium on P uptake. Compared to the untreated control dry matter production at 20 days after planting (DAP) was increased by 280%, P content per plant by 330%, total biomass at maturity by 30% and grain yield by 45%. Although seed coating with AHP may be harmful to seedlings emergence, it represents a suitable method to enhance early growth and increase yield of pearl millet.  相似文献   
33.
陈申宽  王佐魁 《农药》1997,36(1):33-35
1994-1995年通过室内盆栽和田间试验示范结果表明,应用甲基异柳磷与多菌灵和硼钼微肥混配拦种,对大豆安全无害,对大事产根潜蝇,根腐病和大豆胞囊线虫病防效分别为93.1%,64.9%和67.6,比不处理对照增产12.0-30.3%。  相似文献   
34.
This study demonstrates the usefulness of capillary supercritical fluid chromatography (SFC) for the characterization of triacylglycerols of edible oils and fats. Triacylglycerols were separated according to the acyl carbon number and the degree of unsaturation on a 25% cyanopropyl/25% phenyl/50% methylpolysiloxane stationary phase. Valuable information concerning the triacylglycerol composition of berry oils was obtained, despite the overlapping of certain triacylglycerol peaks. Simultaneous analysis of fat-soluble vitamins and triacylglycerols is not practical by capillary SFC with flame-ionization detection because of the low concentration of naturally-occurring fat-soluble vitamins in edible oils. Therefore, higher loading of the sample, which led to overloading of triacylglycerols, was required to get reasonable peaks for fat-soluble vitamins. The method was applied to the characterization of triacylglycerols and tocopherols in sea buckthorn pulp and seed oil, and cloudberry seed oil without any sample purification prior to SFC. In addition, the stationary phase proved useful for separating the more complex mixtures of triacylglycerols found in milk fat and in fish oil.  相似文献   
35.
Sesame seed (Sesamum indicum L.) is a rich source of furofuran lignans with a wide range of potential biological activities. The major lignans in sesame seeds are the oil‐soluble sesamin and sesamolin, as well as glucosides of sesaminol and sesamolinol that reside in the defatted sesame flour. Upon refining of sesame oil, acid‐catalyzed transformation of sesamin to episesamin and of sesamolin to epimeric sesaminols takes place, making the profile of refined sesame oils different from that of virgin oils. In this study, the total lignan content of 14 sesame seeds ranged between 405 and 1178 mg/100 g and the total lignan content in 14 different products, including tahini, ranged between 11 and 763 mg/100 g. The content of sesamin and sesamolin in ten commercial virgin and roasted sesame oils was in the range of 444–1601 mg/100 g oil. In five refined sesame oils, sesamin ranged between 118 and 401 mg/100 g seed, episesamin between 12 and 206 mg/100 g seed, and the total contents of sesaminol epimers between 5 and 35 mg/100 g seed, and no sesamolin was found. Thus, there is a great variation in the types and amounts of lignans in sesame seeds, seed products and oils. This knowledge is important for nutritionists working on resolving the connection between diet and health. Since the consumption of sesame seed products is increasing steadily in Europe and USA, it is important to include sesame seed lignans in databases and studies pertinent to the nutritional significance of antioxidants and phytoestrogens. It is also important to differentiate between virgin, roasted and refined sesame oils.  相似文献   
36.
The aim of the present study was to highlight the main differences between seed oils produced from conventionally cultivated crops and organically cultivated ones and processed using mild extraction procedures. The composition and the nutritional and health aspects of both types of sunflower seed oils were compared and were analytically tested to determine the macroscopic differences in proximate composition, the main differences in the minor components, the main quality parameters, the in vitro antioxidant activity, and the presence of trans-ethylene steroisomers in FA. No significant trends were found in the oil samples for TAG and FA composition, but remarkable differences were found in the composition of minor components and in the main chemical and analytical quality properties. The organically grown samples had a higher total antioxidant activity compared with the conventional samples. Trans FA were found only in the conventional oils.  相似文献   
37.
目的选育Vero细胞森林脑炎疫苗适应毒种。方法将森林脑炎疫苗鼠脑病毒“森张”株在Vero细胞上连续传代适应,并对不同代次收获的病毒液的病毒滴度、免疫原性、稳定性等进行检测。结果“森张”株病毒在Vero细胞上传代适应后,病毒滴度达8·5LgLD50/ml;免疫血清中和抗体效价高于1∶20,其它检测项目均符合疫苗生产用毒种的要求。结论Vero细胞适应的“森张”株毒种的初步特性显示可作为制备Vero细胞森林脑炎疫苗用毒种。  相似文献   
38.
黄荆提取物对几种害虫的杀虫活性   总被引:17,自引:0,他引:17  
袁林  薛明  邢健  李昌浩 《农药》2004,43(2):70-72
研究了黄荆种子二氯甲烷提取物对5种害虫的杀虫活性以及对天敌异色瓢虫的安全性。结果表明:黄荆提取物对菜青虫、小菜蛾、麦长管蚜和桃蚜都有较高的杀虫活性,尤其是对菜青虫的活性最高,稀释100倍,处理4龄幼虫死亡率可达93.3%。但对大猿叶甲的杀虫活性则很低。黄荆提取物对异色瓢虫幼虫有一定的杀虫活性,但对其成虫无任何影响。本研究结果为开发利用这一新的杀虫植物资源提供了依据。  相似文献   
39.
以过硫酸铵为引发剂,十二烷基硫酸钠为乳化剂,采用种子聚合工艺,合成了偏氯乙烯质量分数为23%~43%的羧基偏氯乙烯丁苯胶乳。通过电镜观察到所合成的胶乳粒子具有核-壳结构。通过测定胶闰子表面层的羧基数量,研究了羧基的分布,结果表明,羧酸种类对羧基在胶乳粒子中及在聚合体系中的分布有重要影响,该胶乳作为地毯背衬粘合剂,具有粘合力高,极限氧指数高的特点,是一种较好的阻燃性粘合剂。  相似文献   
40.
杨城  赵奇  康立 《计算机工程》2014,(12):114-120,125
互联网的迅速发展与网络服务的高度分散,促使广大网民不断注册更多的账户,并导致口令重用行为普遍化,使得用户信息面临泄露的风险。为此,基于2011年底互联网泄密门数据和大学生在线调查数据,分析了网民口令的结构特征和重用行为,并由此设计融入信息维度和分级管理思想的多维口令体系。该体系以根口令-重用码结构为基础,内容维包含多个独立的信息因子,构成口令的可记忆性主体;形式维负责形式变换,以提升口令的复杂性和安全性;时空维用于保障口令的时效性和重用性。对比量化分析结果表明,该口令体系具备良好的记忆性和便捷性,能有效抵御暴力攻击和熟人攻击。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号