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   469篇
  免费   26篇
  国内免费   27篇
化学   387篇
晶体学   2篇
力学   1篇
综合类   67篇
数学   5篇
物理学   60篇
  2023年   14篇
  2022年   15篇
  2021年   38篇
  2020年   16篇
  2019年   16篇
  2018年   20篇
  2017年   21篇
  2016年   31篇
  2015年   21篇
  2014年   21篇
  2013年   22篇
  2012年   18篇
  2011年   20篇
  2010年   18篇
  2009年   22篇
  2008年   12篇
  2007年   21篇
  2006年   19篇
  2005年   16篇
  2004年   12篇
  2003年   19篇
  2002年   15篇
  2001年   15篇
  2000年   10篇
  1999年   8篇
  1998年   16篇
  1997年   9篇
  1996年   11篇
  1995年   7篇
  1994年   4篇
  1993年   3篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   4篇
  1986年   1篇
排序方式: 共有522条查询结果,搜索用时 31 毫秒
1.
In this paper, we studied commercially available precipitated rice husk silica (RHS) with conventional precipitated silica, which has nearly the same surface area, and replaced part of the carbon black with RHS and conventional silica in a basic tread formulation. All formulations were mixed with the same amount of filler during the study. Silica was used at 15, 30 and 50 phr loading, and part of the carbon black was replaced by silica. Compound curing characteristics, physical properties, rebound resilience, heat generation, abrasion loss, dynamic properties and morphology were analyzed. The results indicated that RHS demonstrated compound properties comparable to those of conventional silica. As part of the carbon black was replaced with conventional silica, a slower cure rate, higher rebound resilience, lower heat generation, lower abrasion loss, and lower tan delta were observed with no significant change in physical properties, but some changes in physical properties were observed using one way ANOVA analysis. We found the same trend when replacing part of the carbon black with RHS, such as a slower cure rate, higher rebound resilience, lower heat generation, lower abrasion loss, and lower tan delta with no significant change in physical properties, but some changes in physical properties were observed using one way ANOVA. This sustainable material could be used to replace conventional silica in tire compounding, as well as to replace a portion of carbon black with RHS for improved heat build-up, rolling resistance, and abrasion loss.  相似文献   
2.
A simple and rapid analytical method for the detection of trifloxystrobin, trifloxystrobin acid and tebuconazole in soil, brown rice, paddy plants and rice hulls was established and validated by liquid chromatography with tandem mass spectrometry. Acceptable linearity (R2 > 0.99), accuracy (average recoveries of 74.3–108.5%) and precision (intra- and inter-day relative standard deviations of 0.9–8.8%) were obtained using the developed determination approach. In the field trial, the half-lives of trifloxystrobin and tebuconazole in paddy plants were 5.7–8.3 days in three locations throughout China, and the terminal residue concentrations of trifloxystrobin and tebuconazole were <100 and 500 μg/kg (maximum residue limits set by China), respectively, at harvest, which indicated that, based on the recommended application procedure, trifloxystrobin and tebuconazole are safe for use on rice. The risk assessment results demonstrated that, owing to risk quotient values of both fungicides being <100%, the potential risk of trifloxystrobin and tebuconazole on rice was acceptable for Chinese consumers. These data could provide supporting information for the proper use and safety evaluation of trifloxystrobin and tebuconazole in rice.  相似文献   
3.
Cytologic and embryologic studies on the reproductive pattern of male sterility line C1001 in rice (Oryza saliva L.) indicated that several types of apomixis were discovered in partial strains of male sterility line C1001 in rice. Under a fully separate condition, two possible apomixis embryogenesis ways in the ovules were observed: One way was that the embryo was initiated from the somatic cells of the ovules, and then pushed against the embryo sac to develop into a mature embryo. The other way was that the embryo was from the unfertilized egg cell or one of synergids, and then developed into a mature embryo in the form of haploid parthenogenesis without forming endosperm. Besides, the antipodal cells migrated in the embryo sac, and their cytoplasm became thin and vacuolated while mitosis was taking place, giving rise to a multicellular structure or a group of large cells each containing several nuclei. This paper also discusses the significance and patterns of apomixis in rice C1001.  相似文献   
4.
通过筛选水稻开花后48~50h的原胚和120~122h的分化胚的cDNA文库,得到一个在胚胎发育过程中表达有差异的克隆,命名为OsEES,测序结果显示OsEES含有一个预测的亚精氨合成酶结构域,编码一个大小约38×103(pI6.5)的蛋白.同时RNA原位杂交的结果显示开花48~50h的原胚中的信号强度明显大于开花120~122h的分化胚,表明OsEES可能在水稻胚胎发生过程中起到一定的调控作用.  相似文献   
5.
研究了原子化器温度、载气流速、KBH4 浓度等条件对流动注射 氢化物发生 原子吸收光谱法 (FI-HG -AAS)测定硒时的影响。建立了FI-HG -AAS测定大米中硒的分析方法。在优化的工作条件下 ,测定硒的最低检测浓度为 0 3 3 μg·L- 1,线性范围为 0~ 5 0 μg·L- 1,相对标准偏差小于 4% ,加标回收率为 94%~ 1 0 2 %。本法克服了传统的间断氢化物发生 原子吸收光谱法分析速度慢、样品耗量大、操作繁琐且因手工进样在进样速度和进样体积上容易带来误差等缺点。方法操作简便、快速 ,灵敏度及自动化程度高 ,已广泛应用于大米及富硒大米中微量硒的测定  相似文献   
6.
微量三十烷醇(TRIA)与GA3配合使用,比GA3单独使用能明显地促进幼苗生长和增加幼苗干物质积累.同时还增强了GA3对幼叶中叶绿素含量、可溶性蛋白质含量、呼吸速率、细胞膜透性和过氧化物酶活性的影响.GA3+TRIA与GA3处理相比,促进幼叶内源GA3水平提高,稳定保持内源ZT于一定水平,TRIA在GA3低浓度时降低IAA水平,在高浓度时则提高IAA水平.作者认为TRIA可作为GA3处理时的增效剂.  相似文献   
7.
钙黄绿素蓝荧光法测定食品中的微量锌(Ⅱ)   总被引:5,自引:0,他引:5  
本文研究了在CTMAB存在下,用钙黄绿素蓝荧光法测定食品中的微量锌(Ⅱ)的实验条件。在本实验条件下,Zn(Ⅱ)与钙黄绿素蓝生成1:1的配合物使钙黄绿素蓝的荧光增强,最大激发波长和最大发射波长分别为353nm和440nm。  相似文献   
8.
磷肥和硒施用对稻米硒、钙、锌等营养累积的影响   总被引:6,自引:0,他引:6  
研究了施用不同水平磷肥和硒对稻米中硒、钙、锌、镁、硫等人体必需营养吸收累积的影响。结果表明,适量施磷,降低米中硒含量;大量施磷,又促进硒在米中累积。施磷肥一般不利于钙和锌在稻米中累积,适量施磷增加稻米中镁、硫含量,而过量施用磷肥显著降低钙、锌、镁、硫等矿质营养的含量,影响稻米营养品质。适量施硒,一般提高稻米的矿质营养含量;过量施硒,特别在高磷水平下则降低矿质营养含量。  相似文献   
9.
Utilization of one waste material to control pollution caused by another is of high significance in the remediation of environmental problems. Rice husk, an abundantly available agricultural waste, can be used as a low cost adsorbent for dyes and heavy metals in effluent streams. The possible utilization of rice husk ash as an adsorbent for methylene blue dye from aqueous solutions has been investigated. Ash samples from husks of two origins were prepared at different temperatures and their physical, chemical spectroscopic and morphological properties were determined. XRD, FTIR and SEM were some of the techniques adopted for the characterization. The samples were also analyzed for bulk density, pH, nitrogen adsorption properties and lime reactivity. Experiments of methylene blue adsorption on the ash samples were conducted using batch technique and a comparative study was made. Results were analyzed using linear, Langmuir and Freundlich isotherms. The values of separation factor indicate that most of the ash samples do adsorb the dye molecules, but in varying quantities. Calcination at 900C reduces the adsorption capacity of the ash to a great extent. Regression analysis shows that the experimental data fits both Langmuir and Freundlich isotherms for certain concentration limits. The adsorbate species are most probably transported from the bulk of the solution into the solid phase through intra-particle diffusion process. Kinetics of adsorption was found to follow pseudo second order rate equation with R 2∼ 0.99. The highest adsorption capacity (Q 0) achieved is found to be ∼690 mg/g, which is even higher than the values reported for activated carbon from rice husk. The adsorption capacity of the ash samples are in good agreement with their surface area and pore volume.  相似文献   
10.
高效液相色谱法测定糙米粉中的维生素   总被引:7,自引:1,他引:7  
吴红京  王勇 《色谱》1996,14(2):140-142
高效液相色谱法测定糙米粉中的维生素吴红京,唐根源,王勇(中国科学院福建物质结构研究所福州350002)(福建药品检验所福州350001)1前言众所周知,糙米粉有很高的营养价值,含有人体必需的多种维生素。用高效液相色谱法(HPLC)和薄层色谱法(TLC...  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