全文获取类型
收费全文 | 503篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 306篇 |
晶体学 | 1篇 |
力学 | 29篇 |
数学 | 85篇 |
物理学 | 104篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 28篇 |
2019年 | 34篇 |
2018年 | 29篇 |
2017年 | 29篇 |
2016年 | 39篇 |
2015年 | 20篇 |
2014年 | 44篇 |
2013年 | 58篇 |
2012年 | 27篇 |
2011年 | 45篇 |
2010年 | 25篇 |
2009年 | 27篇 |
2008年 | 20篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1993年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有525条查询结果,搜索用时 203 毫秒
1.
Soltani Rad Mohammad Navid Behrouz Somayeh Mohammad-Javadi Mehdi Zarenezhad Elham 《Molecular diversity》2022,26(5):2503-2521
Molecular Diversity - The preparation, characterization and application of hydroxyapatite silica propyl bis aminoethoxy ethane cuprous complex (HASPBAEECC) as a novel hybrid nano-catalyst for... 相似文献
2.
Shayesteh S. Farjami B. Soltani M. A. Solimany 《International Journal of Infrared and Millimeter Waves》2002,23(12):1691-1697
We present and discuss infrared magnetoplasma reflectivity and surface polariton modes in Ga1–xNxAs. It assumed that the sample is characterized by a magnetoplasma dielectric tensor. Surface polariton dispersion for two component magnetoplasma was calculated from reflectivity spectra data. We detect transverse optic phonon of GaN sublattice in 470 cm-1. The origin of sharp feature in p-polarization reflectivity about 300 cm–1 as well as LO phonon frequency of GaAs sublattice is due to Brewster mode. An interesting feature of surface modes in Voigt geometry is nonreciprocalicity, which means that the frequency changes when the direction of propagation is reversed. Also, the infrared magnetoplasma reflectivity of GaNAs should be providing determination of the electrons and heavy holes effective mass and carrier's concentration. 相似文献
3.
Ti(IV) as TiCl3(O3SCF3) and TiO(O2CCF3)2 are used as efficient catalysts for oxidative coupling of aliphatic, aromatic and heteroaromatic thiols to their disulfides in the presence of NaI under air atmosphere. 相似文献
4.
Parasteh Pirasteh Ali Soltani Lazhar Haji Nicolas Errien 《Applied Surface Science》2006,253(4):1999-2002
In order to understand the optical loss mechanisms in porous silicon based waveguides, structural and optical studies have been performed. Scanning and transmission electron microscopic observations of porous silicon layers are obtained before and after an oxidation process at high temperature in wet O2. Pore size and shape of heavily p-type doped Si wafers are estimated and correlated to the optical properties of the material before and after oxidation. The refractive index was measured and compared to that determined by the Bruggeman model. 相似文献
5.
A kinetic spectrophotometric method for determination of trace nitrite in two dynamic ranges (2–100 and 100–500 ng/mL) based on its catalytic effect on the reaction between methylthymol blue and potassium bromate in acidic (sulfuric acid) media is described. The reaction was monitored spectrophotometrically by measuring the decreasing color of methylthymol blue at 437 nm by the fixed‐time method of 4.0 min at 30°C. The detection limit is 0.6 ng/mL, and the relative standard deviations for 50.0 and 250.0 ng/mL nitrite are 1.6% and 1.3%, respectively. The method was used for the determination of nitrite in water samples. 相似文献
6.
A simple one-pot procedure for the direct conversion of alcohols into azides using TsIm 总被引:1,自引:0,他引:1
A facile and efficient method for one-pot conversion of alcohols into azides using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, alcohols are refluxed with a mixture of NaN3, TsIm and triethylamine in the presence of catalytic amounts of tetra-n-butylammonium iodide (TBAI) in DMF affording the corresponding alkyl azides in good yields. This methodology is highly efficient for various structurally diverse alcohols with selectivity for ROH: 1° > 2° > 3°. 相似文献
7.
Behzad Haghighi Mohammad Reza Hussaindokht Mohammad Reza Bozorgmehr Naser Seyed Matin 《中国化学快报》2007,18(9):1154-1158
In this paper five equations of state are tested for checking their ability to predict the Joule-Thomson inversion curve.These five equations of state are:Mohsennia-Modarres-Mansoori(MMM),Ji-Lemp(JL),modified Soave-Redlich-Kwang(SRK)equation of state by Graboski(MSRK1),modified SRK equation of state by Peneloux and Rauzy(MSRK2),and modified Peng-Robinson (PR)equation of state by Rauzy(PRmr).The investigated equations of state give good prediction of the low-temperature branch of the inversion curve,except for MMM equation of state.The high-temperature branch and the peak of the inversion curve have been observed,in general,to be sensitive to the applied equation of state.The values of the maximum inversion temperature and maximum inversion pressure are calculated for each component used in this work. 相似文献
8.
Behzad Zeynizadeh 《中国化学会会志》2005,52(3):525-530
α,β‐Unsaturated aldehydes and ketones were reduced readily and exclusively to their corresponding allylic alcohols with NaBH4 and catalytic amounts of titanyl acetylacetonate at room temperature. Reduction reactions were carried out in CH3CN or THF. This reducing system was also efficient for the reduction of α‐diketones and acyloins to their corresponding vicinal diols in CH3CN. 相似文献
9.
A simple modification to a commercially available gas chromatograph isotope ratio mass spectrometer (GC/IRMS) allows rapid and precise determination of the stable isotopes ((13)C and (18)O) of CO(2) at ambient CO(2) concentrations. A sample loop was inserted downstream of the GC injection port and used to introduce small volumes of air samples into the GC/IRMS. This procedure does not require a cryofocusing step and significantly reduces the analysis time. The precisions for delta(13)C and delta(18)O of CO(2) at ambient concentration were +/-0.164 and +/-0.247 per thousand, respectively. This modified GC/IRMS was used to test the effects of storage on the (18)O and (13)C isotopic ratios of CO(2) at ambient concentrations in four container types. On average, the change in the (13)C-CO(2) and (18)O-CO(2) ratios of samples after one week of storage in glass vials equipped with butyl rubber stoppers (Bellco Glass Inc.) were depleted by 0.12 and by 0.20 per thousand, respectively. The (13)C ratios in aluminum canisters (Scotty II and IV, Scott Specialty Gasses) after one month of storage were depleted, on average, by 0.73 and 2.04 per thousand, respectively, while the (18)O ratios were depleted by 0.38 and 1.20 per thousand for the Scotty II and IV, respectively. After a month of storage in electropolished containers (Summa canisters, Biospheric Research Corporation), the (13)C-CO(2) and (18)O-CO(2) ratios were depleted, on average, by 0.26 and enriched by 0.30 per thousand, respectively, close to the precision of measurements. Samples were collected at a mature hardwood forest for CO(2) concentration determination and isotopic analysis. A comparison of CO(2) concentrations determined with an infrared gas analyzer and from sample voltages, determined on the GC/IRMS concurrent with the isotopic analysis, indicated that CO(2) concentrations can be determined reliably with the GC/IRMS technique. The (13)C and (18)O ratios of nighttime ecosystem-respired CO(2), determined from the intercept of Keeling plots, were -26.11 per thousand (V-PDB) and -8.81 per thousand (V-PDB-CO(2)), respectively. 相似文献
10.
Behpour M Attaran AM Ghoreishi SM Soltani N 《Analytical and bioanalytical chemistry》2005,382(2):444-447
A sensitive, selective and simple preconcentration method for ultra-trace gold determination has been developed that uses naphthalene–methyltrioctyl ammonium chloride (Aliquat 336s) as an adsorbent. Gold, in the form of AuCl4–, was retained by the adsorbent in the column at a flow rate of 1 ml min–1. After filtration, the solid mass consisting of the gold complex and naphthalene was dissolved out of the column with 5 ml of N,N-dimethylformamide (DMF), and the metal was then determined by atomic absorption spectrometry. In the initial solution, the calibration graph of absorbance versus gold concentration was found to be linear in the range 0.5–150 ng ml–1 Au(III) with r=0.997 (n =9), and the 3 s detection limit was 0.428 ng ml–1. The relative standard deviation for eight replicate measurements of 20 g of gold was 2.14%. Preconcentration factors of 390 and 650 were achieved using 5 ml and 3 ml of DMF, respectively. The proposed method was successfully applied to the determination of gold in wastewater, processed pool water, slurry pool water, and raw well-water from the Moteh gold mine, and synthetic samples. 相似文献