全文获取类型
收费全文 | 3220篇 |
免费 | 202篇 |
国内免费 | 114篇 |
专业分类
化学 | 2297篇 |
晶体学 | 5篇 |
力学 | 198篇 |
综合类 | 36篇 |
数学 | 152篇 |
物理学 | 848篇 |
出版年
2024年 | 7篇 |
2023年 | 49篇 |
2022年 | 115篇 |
2021年 | 90篇 |
2020年 | 96篇 |
2019年 | 70篇 |
2018年 | 58篇 |
2017年 | 148篇 |
2016年 | 180篇 |
2015年 | 166篇 |
2014年 | 164篇 |
2013年 | 223篇 |
2012年 | 179篇 |
2011年 | 210篇 |
2010年 | 156篇 |
2009年 | 172篇 |
2008年 | 158篇 |
2007年 | 179篇 |
2006年 | 200篇 |
2005年 | 123篇 |
2004年 | 149篇 |
2003年 | 105篇 |
2002年 | 79篇 |
2001年 | 41篇 |
2000年 | 50篇 |
1999年 | 41篇 |
1998年 | 32篇 |
1997年 | 49篇 |
1996年 | 54篇 |
1995年 | 25篇 |
1994年 | 20篇 |
1993年 | 24篇 |
1992年 | 9篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有3536条查询结果,搜索用时 453 毫秒
991.
Development and validation of passive samplers for atmospheric monitoring of SO2, NO2, O3 and H2S in tropical areas 总被引:1,自引:0,他引:1
Traditionally the monitoring of atmospheric pollutants is aimed at managing accidents and short-term actions for the protection of human health on local and regional scales. These monitoring networks required continuous measurements with high time resolution, involving costly equipment, operation and maintenance. More recent simulations with mathematical models and scenario-building on regional, continental and global scales, as well as studies of environmental personal exposure are demanding three main types of monitoring design, where need for special resolution surpasses the one of temporal resolution: remote places, where no electric power nor trained human resources are available; validation of dispersion simulation by mathematical modeling on regional to larger scales; indoor measurements where people are acting under noise restriction such as residences, school and hospitals. To meet these demands environmental passive samplers for atmospheric gaseous pollutants have been developed and applied for different situations and environments of Brazil. Passive samplers were developed based on molecular diffusion of gas through a static layer of air with fixed filters impregnated with a specific solution for SO2, NO2, O3 and H2S and used in the following situations: in remote forest area, urban areas with different characteristics - near the sea, with clean ocean air masses coming in and in areas under direct industrial influence. The passive samplers showed good performance when exposed to different types of areas and during different periods: accuracy of measurements, based on standard deviation, were within the recommended limit by the European Union of ± 25% for this type of device and precision below the maximum of 20% cited in the literature, with variation of 2.0 to 16% in the case of these work. The passive devices were able of measuring concentrations very low as those found in the Amazon region (0.58 ± 0.05 µg m− 3 SO2 and 1.10 ± 0.07 µg m− 3 NO2) and higher concentrations in industrial areas (20.0 ± 1.3 µg m− 3 SO2 e 21.0 ± 1.3 µg m− 3 NO2). 相似文献
992.
Application of selected ion monitoring to the analysis of triacylglycerols in olive oil by high temperature-gas chromatography/mass spectrometry 总被引:1,自引:0,他引:1
The analysis of the triacylglycerol (TAG) composition of oils is a very challenging task, since the TAGs have very similar physico-chemical properties. In this work, a high temperature-gas chromatographic method coupled to electron ionization-mass spectrometry (HT-GC/EI-MS), in the Selected Ion Monitoring (SIM) mode, method was developed for the analysis of TAGs in the olive oil; this is a method suitable for routine analysis. This method was developed using commercially available standard TAGs. The TAGs studied were separated according to their equivalent carbon number and degree of unsaturation. The peak assignment was carried out by locating the characteristic fragment ions having the same retention time on the SIM profile such as [RCO+74]+ and [RCO+128]+ ions, due to the fatty acyl residues on sn-1, sn-2 and sn-3 positions of the TAG molecule and the [M−OCOR]+ ions corresponding to the acyl ions. The developed method was very useful to eliminate the interferences that appeared in the mass spectrum since electron ionization can prevent satisfactory interpretation of spectra. 相似文献
993.
薄膜扩散梯度技术在环境监测中的应用进展 总被引:1,自引:0,他引:1
介绍了薄膜扩散梯度(DGT)技术的基本原理,着重评述了其在环境监测中测定重金属有效态和预测重金属生物有效性的应用研究,并展望了DGT技术的发展趋势(引用文献43篇)。 相似文献
994.
以金属凝胶纤维为模板制备环境响应型共聚物一维纳米结构 总被引:1,自引:0,他引:1
分别以4-乙烯基吡啶(4VP)、丙烯酸(AAc)和N-异丙基丙烯酰胺(NIPAM)为共聚单体,以金属凝胶纤维为模板,通过自由基共聚合得到了具有环境响应性的共聚物一维纳米结构.采用红外光谱(FTIR)、流变仪和透射电子显微镜(TEM)等表征了共聚物一维纳米结构的组成、强度及微观形貌.结果表明,共聚单体与模板的配位能力强弱对所得到的共聚物一维纳米结构的产率、强度和形貌有很重要的影响.3种共聚物都具有相应的p H响应性和温度响应性,并且共聚单体含量越高,响应性越明显. 相似文献
995.
996.
997.
998.
A sensor with potential for the development of a “chemical barcode” for real-time monitoring of fish freshness is described. This on-package sensor contains a pH sensitive dye, bromocresol green, that responds through visible colour change to basic volatile spoilage compounds, such as trimethylamine (TMA), ammonia (NH3) and dimethylamine (DMA) collectively known as Total Volatile Basic Nitrogen (TVB-N). The sensor characteristics were studied as well as its response with standard ammonia gas. Trials on cod and under-utilised species have verified that the sensor response correlates with bacterial growth patterns in fish samples thus enabling the “real-time” monitoring of spoilage in various fish species. The sensor response can be interrogated with a simple, inexpensive reflectance colorimeter that we have developed based on two light emitting diodes (LEDs) and a photodetector. 相似文献
999.
设计了一种含有8-oxoG碱基的新型分子信标, 结合酶促反应发展了一种非同位素标记的人8-oxoG-鸟嘌呤糖苷酶1(hOGG1)的活性分析新方法, 检出限可达0.0125 U/mL. 此外, 该方法还可用于快速考察金属离子对酶促反应的影响和肿瘤细胞中hOGG1活性水平的定量检测. 实验结果表明, 该方法简单、 灵敏, 有望用于肿瘤样品中hOGG1活性的高通量分析和hOGG1抑制剂的筛选. 相似文献
1000.
钢在中国大陆的大气腐蚀研究 总被引:12,自引:0,他引:12
本文分析了我国七个试验点十七种钢的八年大气腐蚀试验结果 .表明 ,对碳钢和低合金钢 ,危害最大的污染是二氧化硫及氯离子 ,与公认一致 .但是 ,二氧化硫仅在开始头 1- 2年内危害突出 ,其后作用明显下降 .对非耐候钢 ,湿热条件在短期里对腐蚀的影响并不大 ,但长期暴露危害作用非常大 ,如果同时存在污染 ,更会造成很严重的腐蚀 ,值得特别注意 .由于腐蚀情况与时间因素有关 ,碳钢、低合金钢在不同腐蚀环境中 ,暴露第一年所显示的大气腐蚀性规律与长期暴露所显示的不同 ,如果用短期暴露数据判断钢的耐蚀性或环境的腐蚀性 ,都会导致错误的结论 相似文献