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   205篇
  免费   3篇
林业   18篇
农学   7篇
基础科学   3篇
  47篇
综合类   24篇
农作物   20篇
水产渔业   11篇
畜牧兽医   34篇
园艺   2篇
植物保护   42篇
  2022年   8篇
  2021年   5篇
  2020年   3篇
  2019年   7篇
  2018年   12篇
  2017年   11篇
  2016年   11篇
  2015年   14篇
  2014年   7篇
  2013年   18篇
  2012年   19篇
  2011年   16篇
  2010年   6篇
  2009年   9篇
  2008年   10篇
  2007年   6篇
  2006年   3篇
  2005年   5篇
  2004年   3篇
  2003年   4篇
  2002年   6篇
  2001年   1篇
  2000年   4篇
  1999年   2篇
  1998年   3篇
  1996年   2篇
  1995年   1篇
  1988年   2篇
  1987年   1篇
  1982年   1篇
  1976年   1篇
  1974年   2篇
  1973年   2篇
  1972年   1篇
  1967年   2篇
排序方式: 共有208条查询结果,搜索用时 0 毫秒
41.
Contamination of metal ions in soil and water represents more pressing threats to resources as well as human health. The present research was carried out to screen the phytosequester plants growing in industrial waste- and wastewater-affected industrial areas of Okhla, New Delhi, India. Accumulation trend of metal Fe, Zn, Cu, Cr, Pb, Cd, Hg, and As from soil and wastewater by plants were collected for study. Among aquatic plants Hydrilla verticillata, Marsilea quadrifolia, and Ipomea aquatica were found to be highest metals accumulator, Eclipta alba and Sesbania cannabina among terrestrial plant were highest accumulator of metals. Among the algal spp. Spirulina platensis and Phormidium papyraceum were the most efficient in accumulating Cd and Hg. The maximum bioconcentration factor (BCF) was recorded in Hygroryza aristata for the metals (Hg, Cd) in M. quadrifolia (Cd, Cr), in E. alba (Cr, Cu), and in S. platensis (Hg, Pb). However, the translocation factor (TF) of metals was found more in M. quadrifolia followed by I. aquatica than other plants. Among all the plants, H. verticillata showed high TF and low BCF values for toxic metals (Pb, Cr) and was suitable for phytostabilization of these metals. Our study showed that native plant species growing on contaminated sites may have a potential of phytosequestration of these metals.  相似文献   
42.
2006年8月和12月,在新疆车尔臣河下游阿克塔孜牧场,对塔里木马鹿夏季和冬季生境的选择进行了研究。选择5类生态因子,并设置290个10 m×10 m样方。选择结果表明,塔里木马鹿喜欢胡杨和芦苇、植被覆盖度较大、水源距离较近和认为干扰距离>1 000 m的环境。其中,夏季多选择芦苇草甸,冬季选择胡杨林和柽柳灌丛。对生境特征的主成分分析显示,前3个主成分的累计贡献率夏季达到71.277%,冬季达到67.925%,可以反映塔里木马鹿的生境特征。同时表明,影响塔里木马鹿生境选择的主要因素依次为人为干扰、植被类型和距水源距离。  相似文献   
43.
Biodiesel is a biodegradable, renewable, non-toxic and environmentally friendly alternative fuel. The cost of raw materials comprises 60-88% of the production cost in commercial biodiesel (fatty acid methyl esters, FAMEs) production. Therefore, the use of low-cost raw material as a substrate and an in situ process for biodiesel production are being preferred. In this case, rice bran, which contains 13.5% oil, was an interesting substrate. In situ esterification of high-acidity rice bran with methanol and sulfuric acid catalyst was investigated. The individual and interaction effects of methanol to rice bran ratio, sulfuric acid catalyst concentration and reaction time on purity and recovery of biodiesel were discussed. Our results suggest that under the following operation conditions: methanol to rice bran ratio of 5 mL/g, sulfuric acid concentration in methanol of 1.5 vol.%, and reaction time of 60 min, an in situ esterification operated on rice bran could yield FAMEs with a high purity and recovery. By applying an in situ esterification with n-hexane/water extractions, Indonesia will be succesfull in obtaining biodiesel from rice bran up to 96,000 ton per year.  相似文献   
44.
Journal of Plant Diseases and Protection - The efficacy of four bi- and tri-cyclic sesquiterpenes, namely inuloxins A, B and C and α-costic acid, extracted from aerial parts of Dittrichia...  相似文献   
45.
新疆山地针叶林乔木胸径-树高关系分析   总被引:3,自引:0,他引:3  
树木的生长包括了径向生长和垂直生长两个方面,这两方面具有密切的关系,这一关系既受到树木本身的控制,同时也受森林立地条件的影响.通过分析新疆阿尔泰山、天山南北坡以及昆仑山区11个地点120个样方的胸径-树高关系.结果表明:昆仑山的尖削度(taper)显著大于其余3地,其潜在最大树高(potential height,H*...  相似文献   
46.
达坂城地区荒漠及农业区鼠类群落的聚类分析   总被引:2,自引:1,他引:2  
本文根据1993.8-1995.5的调查资料并采用了聚类分析对达坂城地区荒漠及农业区鼠类群落进行了分析研究,结果表明,该地区的鼠类可划分为3种群落,小林姬鼠+褐家鼠+小家鼠群落;小林姬鼠+灰仓鼠群落;红尾沙鼠+五趾跳鼠群落;群落的多样性指数以群落A最高,次为群落;群落C的多样性最低。  相似文献   
47.
本文研究了用低分子酚醛树脂(LMWPF)浸渍竹篾(巨草竹属)。竹子样品是竹秆的基部和中部。采用真空法.用低分子酚醛树脂处理竹篾后,评估处理后的竹篾增重率加湿含率。竹篾浸渍在树脂增加的时间越长,其增重率就越高。浸渍120min后,基部和中部的增重率分别提高了4.51%和7.52%。  相似文献   
48.
This study investigated the effects of impregnation modification via vacuum resin impregnation on physical and mechanical properties of sugar palm (Arenga pinnata) fibres. The fibre was evacuated at a constant impregnation pressure of 1000 mmHg impregnation times (0, 5, 10, 15, 20 and 25 min) with two different impregnation agents: phenol formaldehyde (PF) and unsaturated polyester (UP). A notable improvement in the physical properties of sugar palm fibres was observed after they were impregnated with PF and UP for 5 min, shown by the reduction of their moisture content (91 % and 89 %, respectively) and water absorption (43 % and 41 %, respectively) compared to the control sample. However, no significant improvement (p≤0.05) in the physical properties of fibre was observed when the impregnation time was extended (from 10 to 25 min) using both impregnation agents. As for the mechanical properties of the fibre, significant improvement was observed after they were impregnated for 5 min. The fibres impregnated with UP resulted in better fibre toughness and improved mechanical properties as shown in their higher tensile strength and elongation at break compared to the fibres impregnated with PF. Both the physical and mechanical properties showed no significant improvement (p≤0.05) after time for impregnation was extended (from 10 to 25 min) using both impregnation agents. Therefore, it can be concluded that the physical and mechanical properties of sugar palm fibre could be enhanced by impregnating the fibre with thermosetting polymer (PF and UP) for 5 min. It was shown that impregnation with unsaturated polyester (UP) showed better improvement than phenol formaldehyde (PF). In addition, this study also concluded that the unsatisfactory enhancement of the properties of sugar palm fibre even after the impregnation time was extended from 10 to 25 min was due to the use of low impregnation pressure of 1000 mmHg.  相似文献   
49.
This study was carried out to determine the level of certain biochemical variables reflecting the energy metabolic statuses during the first week of lactation in goats. A total of 120 Anglo-Nubian, Angora, Baladi, and Damascus does (30 does per breed) were used throughout 5 consecutive parities (30 does per parity) to investigate the effect of breed, parity, day of lactation, and their interaction on serum metabolites including total protein, albumin, globulin, glucose, total lipids, cholesterol, and transaminases. Blood samples were collected every other day during the first week of lactation. Baladi does had the greatest (P < 0.001) values in all measured biochemical variables followed by Anglo-Nubian [in total protein, globulin, and aminotransferase (AST)] and Damascus (in globulin and AST) and then Angora, which had the lowest (P < 0.001) values for all variables. Fifth parity exhibited the greatest (P < 0.001) values in all serum metabolites compared with other parities except for alanine transaminase (ALT) enzyme activity in which the greatest (P = 0.046) values were observed in the first and fourth parties. Serum concentrations of the measured variables increased gradually throughout the first day after kidding until the seventh day for total protein (P < 0.001), albumin (P = 0.013), globulin (P = 0.017), and cholesterol (P = 0.028) whereas serum glucose concentration exhibited an opposite trend. Serum concentrations of total lipids and enzyme activities of AST and ALT were not affected by day (P > 0.05) after kidding. Baladi goats had the least (P < 0.001) serum insulin concentration, which was associated (P < 0.001) with greatest serum glucose concentration. Serum triiodothyronine (T(3)) was inversely correlated (P = 0.032) with milk yield whereas greatest (P = 0.003) T(3) concentrations were associated with least (P < 0.001) milk yield recorded in Angora goats. Animal physiological responses and their indices were not affected (P > 0.05) by breed whereas both rectal temperature and coefficient of heat tolerance were affected (P < 0.001) by parity in an opposite direction. Baladi goats expressed an aspect of adaptability where their rectal temperature decreased and coefficient of heat tolerance increased with increasing parity number.  相似文献   
50.
Reproductive stage frost poses a major constraint for wheat production in countries such as Australia.However,little progress has been made in identifying key genes to overcome the constraint.In the present study,a severe frost event hit two large-scale field trials consisting of six doubled haploid(DH)wheat populations at reproductive stage(young microspore stage)in Western Australia,leading to the identification of 30 robust frost QTL on 17 chromosomes.The major 18 QTL with the phenotype variation over 9.5%were located on 13 chromosomes including 2 A,2 B,2 D,3 A,4 A,4 B,4 D,5 A,5 D,6 D,7 A,7 B and7 D.Most frost QTL were closely linked to the QTL of anthesis,maturity,Zadok stages as well as linked to anthesis related genes.Out of those,six QTL were repetitively detected on the homologous regions on 2 B,4 B,4 D,5 A,5 D,7 A in more than two populations.Results showed that the frost damage is associated with alleles of Vrn-A1 a,Vrn-D1 a,Rht-B1 b,Rht-D1 b,and the high copy number of Ppd-B1.However,anthesis QTL and anthesis related genes of Vrn-B1 a and Ta FT3-1 B on chromosomes 5 B and 1 B did not lead to frost damage,indicating that these early-flowering phenotype related genes are compatible with frost tolerance and thus can be utilised in breeding.Our results also indicate that wild-type alleles Rht-B1 a and Rht-D1 a can be used when breeding for frost-tolerant varieties without delaying flowering time.  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