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   52565篇
  免费   4209篇
  国内免费   2188篇
电工技术   1778篇
技术理论   1篇
综合类   2529篇
化学工业   12649篇
金属工艺   970篇
机械仪表   2392篇
建筑科学   929篇
矿业工程   1167篇
能源动力   2183篇
轻工业   10328篇
水利工程   291篇
石油天然气   20565篇
武器工业   65篇
无线电   315篇
一般工业技术   1260篇
冶金工业   850篇
原子能技术   53篇
自动化技术   637篇
  2024年   130篇
  2023年   672篇
  2022年   1375篇
  2021年   1742篇
  2020年   1811篇
  2019年   1717篇
  2018年   1443篇
  2017年   1825篇
  2016年   1940篇
  2015年   1792篇
  2014年   2934篇
  2013年   3303篇
  2012年   3671篇
  2011年   3732篇
  2010年   2587篇
  2009年   2407篇
  2008年   2118篇
  2007年   2788篇
  2006年   3040篇
  2005年   2685篇
  2004年   2374篇
  2003年   2213篇
  2002年   1917篇
  2001年   1600篇
  2000年   1399篇
  1999年   1187篇
  1998年   956篇
  1997年   804篇
  1996年   647篇
  1995年   512篇
  1994年   405篇
  1993年   255篇
  1992年   233篇
  1991年   176篇
  1990年   126篇
  1989年   85篇
  1988年   57篇
  1987年   46篇
  1986年   23篇
  1985年   62篇
  1984年   58篇
  1983年   40篇
  1982年   26篇
  1981年   9篇
  1980年   19篇
  1979年   5篇
  1978年   3篇
  1976年   4篇
  1951年   5篇
  1944年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Soybean oil hydrogenation alters the linolenic acid molecule to prevent the oil from becoming rancid, however, health reports have indicated trans-fat caused by hydrogenation, is not generally regarded as safe. Typical soybeans contain approximately 80 g kg−1 to 120 g kg−1 linolenic acid and 240 g kg−1 of oleic acid. In an effort to accommodate the need for high-quality oil, the United Soybean Board introduced an industry standard for a high oleic acid greater than 750 g kg−1 and linolenic acid less than 30 g kg−1 oil. By combing mutations in the soybean plant at four loci, FAD2-1A and FAD2-1B, oleate desaturase genes and FAD3A and FAD3C, linoleate desaturase genes, and seed oil will not require hydrogenation to prevent oxidation and produce high-quality oil. In 2017 and 2018, a study comparing four near-isogenic lines across multiple Tennessee locations was performed to identify agronomic traits associated with mutations in FAD3A and FAD3C loci, while holding FAD2-1A and FAD2-1B constant in the mutant (high oleic) state. Soybean lines were assessed for yield and oil quality based on mutations at FAD2-1 and FAD3 loci. Variations of wild-type and mutant genotypes were compared at FAD3A and FAD3C loci. Analysis using a generalized linear mixed model in SAS 9.4, indicated no yield drag or other negative agronomic traits associated with the high oleic and low linolenic acid genotype. All four mutations of fad2-1A, fad2-1B, fad3A, and fad3C were determined as necessary to produce a soybean with the new industry standard (>750 g kg−1 oleic and <30 g kg−1 linolenic acid) in a maturity group-IV-Late cultivar for Tennessee growers.  相似文献   
2.
3.
邹燕娣 《中国油脂》2021,46(7):143-147
为了建立一种准确性高、成本低的植物油中苯并(a)芘测定的样品前处理方法,基于GB 5009.7—2016以自制氧化铝柱为固相萃取柱,采用单因素试验对称样量、洗脱剂量、洗脱流速、吸附剂存放时间、吸附剂量这5个影响植物油中苯并(a)芘洗脱的因素进行研究,优化前处理条件,并对测定方法进行考察。结果表明:优化的前处理条件为称样量0.100 0 g、洗脱剂量120 mL、吸附剂(氧化铝)量22 g、洗脱流速1滴/2 s、吸附剂存放时间少于12周;方法检出限为0.2 μg/L,样品加标回收率为94.23%~100.00%,RSD为1.20%~7.36%;同一样品测定结果与SGS测定值接近,相对平均偏差为2.36%~3.50%。说明本试验方法测定结果准确,可应用于油脂企业植物油中痕量苯并(a)芘的测定。  相似文献   
4.
With the increase of industrialization and urbanization, humankind faces massive oil-based pollution due to tanker accidents, human error, and natural disasters. For this, hydrophobic sorbents are fabricated and their applications for the removal of oil from polluted water sources are investigated. These hydrophobic sorbents are prepared by the condensation reaction of poly(dimethylsiloxane) and tris[3-(trimethoxysilyl)propyl]isocyanurate cross-linker via bulk polymerization. The obtained sorbents exhibit high oil sorption capacity, fast absorption–desorption kinetics, and great reusability. Moreover, they can selectively absorb oil from the water surface, thus making them practical for water clean-up applications.  相似文献   
5.
Nowadays, oil pollution has become more serious, which causes great threats both to the ecological environment and human life. In this study, a novel type of multifunctional deacetylated cellulose acetate/polyurethane (d-MCA:MTPU) composite nanofiber membranes for oil/water separation are successfully fabricated by electrospinning, which show super-amphiphilicity in air, super-hydrophilicity in oil, and oleophobicity in water. All the d-MCA:MTPU composite nanofiber membranes with different mass ratios can be used as water-removing, oil-removing, and emulsion separation substance only by gravity driving force. The highest separation flux for water and oil reaches up to 37 000 and 74 000 L m−2 h−1, respectively, and all the separation efficiencies are more than 99%. They have outstanding comprehensive mechanics performance, which can be controlled by simply adjusting the mass ratios. They show excellent antifouling and self-cleaning ability, endowing powerful cyclic stability and reusability. Those results show that d-MCA:MTPU composite nanofiber membranes have great application prospects in oil/water separation.  相似文献   
6.
7.
为探究某加氢装置高压换热器管束腐蚀泄漏原因,利用Aspen Plus工艺模拟软件计算了冷低压分离器油相(简称冷低分油)中水质量分数分别为1%,2%,3%时,冷低分油系统的露点温度、氯化铵结晶温度、氯化铵潮解点温度和相对湿度。结果表明:相较于经验的露点温度预测方法,通过引入潮解点、划分系统“湿环境”温度范围判断氯化铵垢下腐蚀风险区域的方法与实际腐蚀案例更为切合;在3种油相含水条件下,换热器管束存在氯化铵垢下腐蚀的“湿环境”温度范围分别为:50~103 ℃,50~161 ℃,50~176 ℃;随着油相中含水量的提高,“湿环境”腐蚀区域逐渐向高温部位迁移,预计铵盐导致的垢下腐蚀将会愈加严重。  相似文献   
8.
采用裂解色谱(PY-GC-MS)、电子顺磁共振波谱(EPR)和红外光谱(FTIR)等技术手段,分析了Estonia油页岩中干酪根及其热解产物的结构特性,研究了不同温度下中间产物与最终产物的关联性。结果显示:油页岩热解符合干酪根热解为中间产物热沥青,热沥青再热解为页岩油、干馏气和半焦等产物反应路径,中间产物热沥青的生成趋势反映了终产物的生成速率变化;H2、CH4和C2~C5组分主要来自热沥青中脂肪烃的芳构化、芳香族化合物烷基侧链的断裂及含氧化合物的缩聚等,干酪根热解产生的烷烃和烯烃类化合物是产油气的主要组分。干酪根和页岩油的自由基自旋浓度明显低于热沥青和半焦;半焦g值最大,干酪根次之,热沥青和页岩油的g值偏低。  相似文献   
9.
10.
The heterogeneous catalysis of transesterification of gmelina seed oil to biodiesel is evaluated. The oil was extracted from the seeds with n‐hexane by solvent extraction and characterized to determine its physiochemical properties. Response surface methodology was applied to optimize the effect of process variables on the biodiesel yield. The base‐activated clay catalyst performed as montmorillonite clay with the characteristic property of a Brønsted acid. It has an improved surface area after activation that enhanced its catalytic activity on transesterification reaction. Under optimal conditions, the biodiesel yield was 70.1 %, thus demonstrating that the model predicted well the biodiesel production.  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