全文获取类型
收费全文 | 8604篇 |
免费 | 1189篇 |
国内免费 | 764篇 |
专业分类
化学 | 5337篇 |
晶体学 | 164篇 |
力学 | 143篇 |
综合类 | 51篇 |
数学 | 105篇 |
物理学 | 4757篇 |
出版年
2024年 | 15篇 |
2023年 | 63篇 |
2022年 | 185篇 |
2021年 | 224篇 |
2020年 | 233篇 |
2019年 | 198篇 |
2018年 | 214篇 |
2017年 | 287篇 |
2016年 | 307篇 |
2015年 | 300篇 |
2014年 | 401篇 |
2013年 | 698篇 |
2012年 | 641篇 |
2011年 | 488篇 |
2010年 | 392篇 |
2009年 | 524篇 |
2008年 | 510篇 |
2007年 | 641篇 |
2006年 | 486篇 |
2005年 | 474篇 |
2004年 | 432篇 |
2003年 | 381篇 |
2002年 | 333篇 |
2001年 | 253篇 |
2000年 | 227篇 |
1999年 | 252篇 |
1998年 | 199篇 |
1997年 | 207篇 |
1996年 | 165篇 |
1995年 | 137篇 |
1994年 | 126篇 |
1993年 | 115篇 |
1992年 | 92篇 |
1991年 | 90篇 |
1990年 | 51篇 |
1989年 | 51篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 10篇 |
1984年 | 22篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
241.
The microwave acid digestion method was applied to the decomposition of rock samples and optimum conditions were investigated. Samples of 10–100 mg were decomposed by changing the amount and composition of acid, heating time and number of reheating steps and then the concentrations of Si, Fe, Mn, Na, K and Mg in these samples were measured. The concentrations agreed with reported values when 10 mg of sample were decomposed by heating for 60 s with 0.3 ml of concentrated HNO3 and 0.1 ml of concentrated HF. Similarly, 100 mg of sample were also decomposed successfully by heating for 45–110 s with 0.3–1.0 ml of concentrated HNO3 and 0.4–0.7 ml of concentrated HF. It is concluded that the microwave acid digestion method decomposes rock samples with a very short heating time and with small amount of reagents compared with methods using conventional sealed PTFE vessels, which require several hours for the heating step and several millilitres of reagents. 相似文献
242.
A method for the determination of sulfide based on its interference with the determination of Hg by cold vapor atomic absorption spectrometry is described. The decrease in mercury absorbance at 253.7nm is proportional to the concentration of sulfide over the range of 10–320ngmL–1. The limit of detection was found to be 7ngmL–1 and the relative standard deviation (R.S.D.) for the determination of different concentrations of sulfide was in the range of 1.8–2.2%. This method was applied to the determination of sulfide in whole human blood after gas-phase separation. 相似文献
243.
混合溶剂火焰原子吸收法直接测定原油中的镍刘广东袁存光张丙华刘文钦(石油大学(华东),山东东营257062)彭力(中国石油天然气总公司环保处,北京100724)关键词原油,混合溶剂,无机盐标准,原子吸收法,镍测定原油中,微量元素镍、钒、铁、铜的存在对... 相似文献
244.
Matrix element of the Gallilean invariant nonrelativistic reduction of the pseudoscalar-pseudovector interaction has been
calculated for free pion absorption by a single nucleon inside the nucleus of16O. The Hartree-Fock wavefunctions obtained with the unitary-model-operator approach starting with the hard-core nucleon-nucleon
interaction have been used for the π-capturing nucleon in the initial state. The initial pion distortion in the presence of
nuclear field of the absorbing nucleus prior to its absorption together with the Coulomb interaction with the finite nuclear
size has been taken into account. The distortion of the emitted proton in the field of the residual nucleus has also been
considered. The differential cross-sections have been obtained and calculated results are compared with the previous experimental
and theoretical work. 相似文献
245.
Joseph P. Sattler George J. Simonis 《International Journal of Infrared and Millimeter Waves》1984,5(4):465-473
We report the refractive indices and absorption coefficients for four beryllia (BeO) ceramic samples. These dielectric properties have been measured over the range from 4 to 18 cm–1 by use of a Michelson interferometer. The index n, follows the linear relationship n=0.6517 cm3/g×+0.7130 with density, , over the range 2.8<<3.0 g/cm3. 相似文献
246.
Mariana Antunes Vieira Bernhard Welz Adilson Jos Curtius 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):251-2067
A simple and reliable method for the determination of arsenic in sediment and in coal without sample digestion, based on hydride generation from slurry samples is proposed. After grinding the samples to a particle size of 50 μm, the sample powder was mixed with aqua regia and hydrofluoric acid in an ultrasonic bath for 30 min. After diluting the mixture with hydrochloric acid, the slurry was allowed to stand for 48 h, and an aliquot was used for hydride generation with sodium borohydride. More than 80% of the arsenic was leached to the aqueous phase under these conditions, except for one sediment sample with very high silica content. The generated arsine was collected in a graphite tube, treated with 0.5 mg of iridium as a permanent modifier, and the arsenic determination was carried out by electrothermal atomic absorption spectrometry. The same tube could be used for at least 160 cycles without any re-treatment. The greatest advantage of the method was that only a minimum of reagents and sample handling were required, reducing the risks of contamination and/or analyte loss. However, the addition calibration technique had to be used in order to obtain results within the 95% confidence level for 11 certified reference materials, 5 sediments, 5 coals and one coal fly ash. One certified sediment slurry was spiked with the analyte and the resulting addition calibration curve was used for the analysis of the certified sediments. Similarly, one certified coal was used to obtain the addition calibration curve for the coal and coal fly ash samples. The recoveries of the certified values, except for one sediment, were between 91 and 115%. The limits of detection in the samples were 0.54 and 0.7 μg g−1 for the coal and sediment samples, respectively, obtained for 1 ml of slurry containing 1 mg of sample. 相似文献
247.
Pilar Bermejo-Barrera Maria José Lorenzo-Alonso Manuel Aboal-Somoza Adela Bermejo-Barrera 《Mikrochimica acta》1994,117(1-2):49-64
A method for the determination of arsenic in slurries of mussel tissue using palladium-magnesium nitrate as modifier was optimized. The slurry was stabilized by a 0.015% (v/v) of Triton X-100. To achieve complete mineralization the slurries were ashed at 480 °C for 10s in an air flow (50 ml/min) and at 1200 °C for 15s in an argon flow (300 ml/min) in the presence of Pd—Mg(NO3)2 as modifier. The optimum atomization temperature was 2200 °C. The precision and accuracy of the method were studied using the Reference Material BCR n ° 278 Mussel Tissue (Mytilus edulis). The detection limit (LOD) of the final slurry solution was 1 g/l of arsenic corresponding to an arsenic level in the mussel of 1.3 g/g, for a 0.5% (m/v) slurry. Results of calibration using aqueous standards and the standard additions method were compared. The method was applied to the determination of arsenic in mussels from the Galician coast. The levels found lie between 2 and 9.3 g/g of arsenic. 相似文献
248.
通过自由基共聚合合成了含有高二阶非线性光学活性偶氮单元的侧链液晶共聚物。共聚物的液晶转变温度为DSC测定,实验证明当偶氮单元含量超过40mol%时,共聚物的液晶性消失。通过高压电场对该聚合物膜进行针尖电晕极化取向,并由紫外测试给出了聚合物膜的取向参数及其稳定性,对液晶聚合物的非线性光学性质进行了初步的研究。 相似文献
249.
Trapping Copper Phthalocyanine in a Silica Sono-Xerogel 总被引:1,自引:0,他引:1
R. Litrán E. Blanco M. Ramírez-del-solar L. Esquivias 《Journal of Sol-Gel Science and Technology》1997,8(1-3):985-990
A copper phthalocyanine (CuPc) has been encapsulated in silica. The trapping effects were studied comparing the UV-Vis absorption
spectra of some CuPc solutions and composites prepared under different conditions. The trapped organic molecules’ stability
was monitored during the gelation and drying processes. Leachability test have been carried out with the aim of checking the
trapping efficiency. Hydrolysis water of pH=2 and a molar ratioR
w
=6 mol acid H2O/mol TMOS leads to a higher CuPc stacking angle homogeneity. The increase of Pc induces a narrower mesopore distribution
and helps the stabilization of the composite. 相似文献
250.
Using infrared reflection absorption spectroscopy (IRRAS), quartz crystal microbalance (QMB) measurements, and X-ray photoelectron spectroscopy (XPS) in combination with chemical derivatization techniques the VUV photolysis of polyethylene (PE), polypropylene (PP), and polystyrene (PS) was investigated. A mass balance obtained from the quantification of the data was used to suggest reaction path ways. Although PE and PP behave similar, the mass loss is about 8 times higher in the case of PP. These differences originate from the higher disproportionation to recombination ratio for the branched polymer. Both polymers form double bonds and at extended treatment times they tend to crosslink. PS is rather stable due to the possibility of the energy dissipation by fluorescence. 相似文献