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   221篇
  免费   14篇
  国内免费   15篇
林业   38篇
农学   8篇
  29篇
综合类   115篇
农作物   8篇
水产渔业   2篇
畜牧兽医   14篇
园艺   4篇
植物保护   32篇
  2023年   3篇
  2022年   9篇
  2021年   6篇
  2020年   5篇
  2019年   1篇
  2018年   5篇
  2017年   4篇
  2016年   7篇
  2015年   8篇
  2014年   13篇
  2013年   10篇
  2012年   20篇
  2011年   16篇
  2010年   11篇
  2009年   19篇
  2008年   11篇
  2007年   19篇
  2006年   17篇
  2005年   10篇
  2004年   7篇
  2003年   7篇
  2002年   7篇
  2001年   6篇
  2000年   7篇
  1999年   5篇
  1998年   3篇
  1997年   4篇
  1996年   1篇
  1995年   1篇
  1994年   3篇
  1993年   2篇
  1992年   1篇
  1988年   1篇
  1955年   1篇
排序方式: 共有250条查询结果,搜索用时 140 毫秒
1.
2.
以DMAc为溶剂,三乙胺为缚酸剂,十二酰氯为反应试剂,对羧甲基纤维素进行疏水改性,制备表面活性剂十二烷基酯化的羧甲基纤维素(CMC-R)。羧甲基纤维素与十二酰氯的质量比为1∶0.4,反应最佳温度为60℃,时间5 h。将合成的纤维素基表面活性剂CMC-R应用于旧新闻纸(ONP)脱墨,结果表明,单独使用CMC-R能提高废纸浆白度2.2%(ISO),纸浆的残余油墨量减少457.66 mm2/m2,减少了29.4%。而CMC-R与非离子表面活性剂脂肪醇聚氧乙烯醚(JFC)复配后,白度较CMC-R单独使用提高2.13%(ISO),残余油墨量减少3.18%。  相似文献   
3.
张浩  胡君 《农药学学报》2020,22(2):265-269
农药的有效利用与农药液滴在植物叶片上的蒸发过程息息相关。传统表面活性剂虽然可以改变液滴的蒸发模式或速率,但并不能根据外界环境变化对蒸发过程进行主动调节。为实现"自主调控"农药液滴蒸发的目的,本文设计合成了一种含丁二炔官能团的光响应性阳离子表面活性剂(PCDA-C6-NH3+),利用紫外光刺激改变其在液滴中的聚集状态,调控液滴的蒸发过程。该表面活性剂以10,12-二十五碳二炔酸(PCDA)作为骨架,通过酰胺化反应引入末端氨基并质子化后得到。采用紫外-可见光谱研究了PCDA-C6-NH3+的拓扑化学聚合反应,并利用静态表面张力和动态接触角分析了其紫外光照前后的表面活性和蒸发行为。该研究为实现液滴"自主调控"蒸发过程提供了一种新思路,对提高农药利用率具有重要意义。  相似文献   
4.
为表达和纯化SP-B蛋白,先对SP-B基因进行稀有密码子优化,PCR反应获得SP-B片段,构建重组质粒pGEX4T-1/SP-B,转化到E.coli BL21(DE3)中诱导表达;用SDS-PAGE与Western blot进行检测;用GSTPrep FF 16/10对融合蛋白进行纯化。经双酶切鉴定证实质粒中插入基因长250bp,测序结果与大鼠SP-B cDNA序列相符;质粒转化后用IPTG进行诱导,在分子质量约34ku处出现1个新条带,与pGEX4T-1/SP-B蛋白预期大小一致,且该融合蛋白能可溶性表达并被纯化。结果表明成功构建了pGEX4T-1/SP-B重组质粒,表达、纯化得到GST/SP-B蛋白,为研究肺表面活性物质替代药物奠定了基础。  相似文献   
5.
Two new amino acid-type amphoteric surfactants — disodiumN-(2-fatty acyl amino) ethyliminodiacetate and disodiumN-(2-fatty acyl amino) ethyl-N,N-bis[3-(2-hydroxy) propylsulfonate] amine — were synthesized using tall oil fatty acids as the raw material. Suitable processing conditions for synthesizing the intermediates and final products were probed. In addition, the chemical structures of the intermediates and the final products were identified by infrared spectroscopy, hydrogen nuclear magnetic resonance spectroscopy, and elemental analysis.  相似文献   
6.
1-Hydroxyethyl-2-alkyl-2-imidazoline (HEAI) and its derivative sulfonate amphoteric surfactant were synthesized using tall oil fatty acid as the raw material. Suitable experimental conditions for synthesizing the intermediate and final products were probed. Their chemical structures were also investigated by means of infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy. Based on the results of these analyses, it has been found that during the reaction process of HEAI with sodium 3-chloro-2-hydroxypropane sulfonate under alkaline condition the imidazoline ring was hydrolyzed to amides, and the obtained amphoteric surfactant was actually a complex mixture of amides. An etherification reaction in the hydroxyethyl group was also observed when the HEAI/sodium 3-chloro-2-hydroxypropane sulfonate molar ratio was more than 1:1.  相似文献   
7.
基于冠层多光谱数据预测水稻氮素营养状况   总被引:5,自引:0,他引:5  
A soil batch experiment was conducted to investigate both separate and compound effects of three types of surfactants: anionic dodecylbenzene sulfonic acid sodiumsalt (DBSS), cationic cetyltrimethylammonium bromide (CTAB), and nonionic nonyl phenol polyethyleneoxy ether (TX-100), as well as ethylenediaminetetraacetic acid (EDTA) on cadmium solubility, sorption kinetics, and sorption-desorption behavior in purple soil. The results indicated that both individual application of the three types of surfactants and surfactants combined with EDTA could stimulate Cd extraction from the soil with a general effectiveness ranking of EDTA/TX-100 〉 EDTA/DBSS 〉 EDTA/CTAB 〉 EDTA 〉 TX-100 〉 DBSS 〉 CTAB. Further study showed that the compound application of surfactants and EDTA had stronger (P 〈 0.05) effects on Cd solubility than those added individually. The application of surfactants and EDTA to purple soil (P 〈 0.05) decreased the proportion of Cd sorbed, while their effectiveness ranking was similar to that of enhanced solubilization. The sorption kinetics of Cd in purple soil was best described by the double-constant equation, while the Freundlich equation gave an excellent fit to the sorption isotherm curves. Therefore, surfactant-enhanced remediation of Cd contaminated soil is feasible and further research should be conducted.  相似文献   
8.
Abstract

Although crude oil contamination is a constraint for crop production, some plants can develop under crude oil contaminated conditions by utilizing crude oil as nutrients after decomposition. A greenhouse trial was conducted to investigate growth, nutritional composition and enzymatic response of vetiver grass in confronting with crude-oil contamination as affected by gibberellic acid (GA) and Tween 80. Application of GA or co-application of GA with Tween 80 significantly increased mean shoot dry weight. Application of Twee 80 alone or in combination with GA significantly increased mean root dry weight as compared to control which was attributed to the effectiveness of Tween 80 alone or in combination with GA on the removal of total petroleum hydrocarbons from polluted soil. Application of crude oil diminished shoot phosphorus, iron, zinc and manganese uptakes. Application of GA and Tween 80, however, compensated the decrease in nutrient uptakes in vetiver grass resulted from crude-oil contamination. Application of crude oil at both 2 and 4% (W/W) levels increased catalase (CAT) activity and proline (PRO) content. Superoxide dismutase (SOD) activity increased only following the application of 2% crude oil level, while addition of all amendments decreased CAT activity. Addition of GA decreased activity of SOD. None of the studied amendments had a significant effect on PRO content. Application of a combination of GA and Tween 80 under crude oil contamination are recommendable since such treatments not only inhibited adverse effect of crude oil on nutrients uptake but also caused that vetiver grass tolerated high level of crude oil contamination.  相似文献   
9.
Salinity is considered as a major abiotic stress affecting crop production in arid and semi-arid regions in the world. Surfactants can improve water-use efficiency in saline soils and improve crop yield. This study was conducted to evaluate the effect of salinity stress and surfactant treatments on photosynthetic pigments and nutrition elements of fenugreek in the Crop and Soil Science greenhouse at the Pennsylvania State University (University Park, PA, USA) in 2013. The experiment was conducted using a 5 × 3 factorial randomized complete block design with three replications. Factor A consisted of five salinity levels [0, 4, 6, 8, and 10 ds m–1 sodium chloride (NaCl)] while factor B consisted of three nonionic surfactant levels (0, 1, and 3 ppm). The results indicated a stepwise reduction in photosynthetic pigments of fenugreek as salt stress increased, however, Peroxidase and polyphenol oxidase activity increased in fenugreek leaves as salinity stress increased. Levels of surfactant application had different effects on nutrient uptake. Some nutrient elements such as sodium, phosphorus, copper, manganese, and zinc content increased while others decreased at high salinity conditions. Surfactant application rate of 3 ppm at moderate and high salinity levels and 1 ppm at lower salinity levels had a good performance in enhancing the total photosynthetic and carotenoid activities in fenugreek.  相似文献   
10.
研究了Triton X-100对漆酶氧化去除水溶液中苯酚的作用.苯酚和漆酶浓度分别是50 mg/L和 0.05 mg/mL时,提高苯酚去除率的Triton X-100最佳浓度是155 μM.Triton X-100的浓度从31~930 μM时漆酶活性随之增长,在930 μM Triton X-100存在时有最大增值17%.苯酚的初始浓度分别为50, 100, 200, 400和600 mg/L 时,155 μM Triton X-100作用下6 h后,苯酚去除率分别是对照组的1.2, 1.6, 3.4, 4.5和5.7倍.结果表明Triton X-100可以作为水处理或修复过程的添加剂来提高由漆酶催化的苯酚去除率.  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