全文获取类型
收费全文 | 662篇 |
免费 | 64篇 |
国内免费 | 37篇 |
专业分类
化学 | 284篇 |
晶体学 | 23篇 |
力学 | 88篇 |
综合类 | 2篇 |
数学 | 31篇 |
物理学 | 335篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 21篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 18篇 |
2017年 | 26篇 |
2016年 | 27篇 |
2015年 | 35篇 |
2014年 | 49篇 |
2013年 | 66篇 |
2012年 | 39篇 |
2011年 | 53篇 |
2010年 | 28篇 |
2009年 | 49篇 |
2008年 | 32篇 |
2007年 | 43篇 |
2006年 | 34篇 |
2005年 | 29篇 |
2004年 | 17篇 |
2003年 | 23篇 |
2002年 | 19篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有763条查询结果,搜索用时 31 毫秒
41.
An X-ray fluorescence (XRF) method for the rapid and non-destructive analysis of 30 non-organic elements in plant leaves over five orders of magnitude concentration from several percentage of dry weight to sub-milligram per kilogram, is described. There is a growing need for a simple method of monitoring non-organic trace elements in plant material, especially those which accumulate in soils with application of fertilisers, both inorganic and biosolids. Earlier attempts to use XRF for the analysis of plant material suffered from sensitivity loss due to the high background of organic matrices caused by scattering of the X-ray source. We overcome this by using polarised X-ray sources in a Cartesian geometrical arrangement with sample and energy dispersive detector (EDPXRF), a configuration which can achieve an order of magnitude reduction in background compared with unpolarised sources. Further sensitivity gains are made using a high power tube as a source of primary X-rays and for some analytes employing secondary targets for near-monochromatic excitation. Sample preparation is simple involving only pulverising and briquetting of dried samples. Accuracy is evaluated by comparing data obtained for the suite of NIST plant leaf samples (NIST 1515 apple leaves, NIST 1547 peach leaves, NIST 1570a spinach leaves, NIST 1573a tomato leaves and NIST 1575a pine needles) and tobacco leaf standards CTA-OTL-1 and CTA-VTL-2. The data compare well over the whole concentration range and the method provides a rapid analytical tool for monitoring potentially toxic trace elements in all types of foliage with adequate sensitivity for many purposes. 相似文献
42.
43.
外源性加硒法增加枣中硒含量的研究 总被引:3,自引:0,他引:3
以不同深度硒溶液对枣树进行不同次数的叶面喷施,得到了不同硒含量的枣样品,用荧光光度法测定了样品中硒的含量。结果表明,与对照组相比,用外源性加硒法可明显提高枣中硒的含量;并且可通过调节喷施液浓度和喷施次数,得到硒含量适宜的成熟小枣。 相似文献
44.
植物激素吲哚乙酸电化学生物传感器的研究 总被引:2,自引:0,他引:2
本文提出了以绿豆芽叶片组织-二茂铁修饰的碳糊电板(LFMCE)作为植物激素吲哚乙酸传感器的研制,探讨了影响电极性能的因素,初步研究了吲哚乙酸氧化酶处于最优活性的基本条件。实验表明,此电极在NaH2PO4-Na2HPO4(pH5.8)缓冲溶液中对植物生长素有良好的电催化作用,氧化峰电位约在0.42V左右。用循环伏安法测得的氧化峰电流变化值与吲哚乙酸浓度在8-l60μg/mL范围内呈良好的线性关系,检测下限为4.2μg/mL,相关系数为0.9984,在样品回收率的测定中取得满意结果。 相似文献
45.
Dr. Vincent Maurice Dr. Guylhaine Clavel Prof. Markus Antonietti Dr. Cristina Giordano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11624-11630
Porous TiNxOy‐based particles were synthesized by an aerosol spray process. At first, the starting sol solution containing the metal precursor and the nitrogen source is sprayed to form an aerosol that is subsequently pyrolysed at different temperatures. The obtained dried particles are an amorphous coordination “polymer” rich in carbon and nitrogen. These “glassy” particles are finally thermally treated at 800 °C, promoting the crystallization of the particles and the release of a major part of the carbon. As the particles keep their original shape, carbon loss and density increase during the crystallization step and lead to the development of an accessible pore structure. The process was analyzed and extended to the synthesis of other metal nitrides, such as VN and W2N, thereby showing its general validity for the production of functional nanocrystalline nitride ceramics with high porosity still occupying a relatively small volume, and otherwise not easily accessible. 相似文献
46.
Atsushi Takamizawa Kayoko Mishina Kenzo Hiraoka 《Journal of mass spectrometry : JMS》2012,47(2):221-225
Covalent bonds are often created by a reaction between chemicals and protein before causing various adverse effects in a cell. Dimethylaminoethyl methacrylate (DMAEMA), which has moderate toxicity, causes skin inflammation and throat irritation. For this study, we investigated a reaction mechanism between myoglobin and (DMAEMA) using a new analytical tool developed at our laboratory: laser spray mass spectrometry technique. It was found that initially DMAEMA was added to the amino group of protein by the Michael addition mechanism; the added DMAEMA was hydrolyzed to methacrylic acid using an autocatalytic system. The results of this study indicate the feasibility of the laser spray technique in analyses of reaction dynamics. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
47.
Silver-doped calcium phosphate nanopowders were successfully prepared by the cost-effective electrostatic spray-pyrolysis
process. The properties of the silver-doped nanopowder annealed at 500°C for 30 min were investigated through X-ray diffraction
analysis, field emission scanning electron microscope, and Fourier transform infrared spectroscopy. The silver-doped nanopowders
with 70–90 nm particle size showed an antibacterial performance against Escherichia coli. 相似文献
48.
Homogeneous ZnO Nanoparticles by Flame Spray Pyrolysis 总被引:2,自引:0,他引:2
Zinc oxide (ZnO) nanoparticles were made by flame spray pyrolysis (FSP) of zinc acrylate–methanol–acetic acid solution. The effect of solution feed rate on particle specific surface area (SSA) and crystalline size was examined. The average primary particle diameter can be controlled from 10 to 20nm by the solution feed rate. All powders were crystalline zincite. The primary particle diameter observed by transmission electron microscopy (TEM) was in agreement with the equivalent average primary particle diameter calculated from the SSA as well as with the crystalline size calculated from the X-ray diffraction (XRD) patterns for all powders, indicating that the primary particles were rather uniform in diameter and single crystals. Increasing the solution feed rate increases the flame height, and therefore coalescence and/or surface growth was enhanced, resulting in larger primary particles. Compared with ZnO nanoparticles made by other processes, the FSP-made powder exhibits some of the smallest and most homogeneous primary particles. Furthermore, the FSP-made powder has comparable BET equivalent primary particle diameter with but higher crystallinity than sol–gel derived ZnO powders. 相似文献
49.
50.
Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO2 and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO2 sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO2 sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO2 occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO2 sol and ZA, creating a ZnO and SiO2 mixture. The reaction of ZnO with SiO2 was likely to be enhanced by ECM of the SiO2 sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn1.7SiO4 mixed phase. 相似文献