全文获取类型
收费全文 | 1324篇 |
免费 | 70篇 |
国内免费 | 27篇 |
专业分类
化学 | 1095篇 |
晶体学 | 9篇 |
力学 | 31篇 |
数学 | 99篇 |
物理学 | 187篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 56篇 |
2021年 | 61篇 |
2020年 | 91篇 |
2019年 | 83篇 |
2018年 | 115篇 |
2017年 | 84篇 |
2016年 | 90篇 |
2015年 | 65篇 |
2014年 | 104篇 |
2013年 | 130篇 |
2012年 | 106篇 |
2011年 | 93篇 |
2010年 | 63篇 |
2009年 | 52篇 |
2008年 | 62篇 |
2007年 | 49篇 |
2006年 | 22篇 |
2005年 | 22篇 |
2004年 | 13篇 |
2003年 | 13篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1981年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1421条查询结果,搜索用时 0 毫秒
81.
Issa Yavari Maryam Sabbaghan Zinatossadat Hossaini Majid Ghazanfarpour‐Darjani 《Helvetica chimica acta》2008,91(6):1144-1147
Triphenyl phosphite reacts smoothly with dialkyl acetylenedicarboxylates and hexachloroacetone to produce alkyl 2‐(dichloromethylene)‐2,5‐dihydro‐5‐oxo‐4‐(trichloromethyl)furan‐3‐carboxylates in good yields. 相似文献
82.
An efficient experimentally simple and inexpensive catalyst system for the selective amidation of aryl iodides using 15 mol% of CuI as catalyst, 15 mol% of L-proline as ligand and KF/Al2O3 as a base in toluene is described. 相似文献
83.
A dynamic kinetic model for the oxidation of phenol in water by an UV/H2O2 process is developed. The model is based on the elementary chemical and photochemical reactions, initiated by the photolysis of hydrogen peroxide into hydroxyl radicals. The model is validated by using experimental data obtained from the open literature for an actual UV/H2O2 process. Using those data and the developed kinetic model, kinetic rate constants for phenol intermediates, catechol and hydroquinone, are estimated. Moreover, the optimum initial hydrogen peroxide concentration is estimated by means of the validated model. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 34–43, 2008 相似文献
84.
85.
Mirabegron is a novel β3-adrenoceptor agonist containing an amide group. It was subjected to stress conditions of acidic and alkaline hydrolyses. The hydrolytic degradation product was isolated and its structure was confirmed using mass and IR spectrometry. Two stability-indicating chromatographic methods have been proposed for the determination of mirabegron. TLC method was applied using silica gel as stationary phase and chloroform–methanol–ammonia (9.0:1.0:0.1 by volume) as the mobile phase, and chromatograms were scanned at 250 nm. Accurate determination of the drug was achieved over the concentration range of 2–12 μg per band. In addition, an isocratic HPLC method was developed on Agilent C18 column (150 mm × 4.5 mm I.D., particle size 5 µm) using ethanol-phosphate buffer pH 2.5 (30:70, by volume) as a mobile phase with flow rate of 1 mL min?1.The intact drug was detected at 250 nm with running time less than 5 min. Mirabegron was determined accurately in a concentration range of 1–25 µg mL?1. The proposed chromatographic methods were applied successfully for the assay of mirabegron in pharmaceutical dosage form and both methods were validated as per the International Conference on Harmonization guidelines and statistically compared with a reported gradient HPLC method. 相似文献
86.
Microstructure of nickel nanoparticles embedded in carbon films: case study on annealing effect by micromorphology analysis 下载免费PDF全文
Ştefan Ţălu Miroslaw Bramowicz Slawomir Kulesza Azizollah Shafiekhani Maryam Rahmati Atefeh Ghaderi Mohammad Ahmadirad Shahram Solaymani 《Surface and interface analysis : SIA》2017,49(3):153-160
The presented study is aimed at analyzing the surface texture of amorphous hydrogenated carbon layers containing nickel nanoparticles (Ni‐NPs@a‐C:H) within their structure, which were deposited by Radio Frequency (RF) sputtering and RF‐Plasma Enhanced Chemical Vapor Deposition (RF‐PECVD) methods on glass substrates. Prepared films were then used as research material following their annealing at two different temperatures of 250 °C and 350 °C in an inert argon atmosphere. Series of height samples were taken with the help of atomic force microscopy (AFM) operating in a non‐contact mode and examined in order to determine their fractal characteristics. Raw AFM data were first plane‐fitted to remove the surface bow exhibiting the so‐called residual surface, and then numerically processed to calculate the Areal Autocorrelation Function (AACF), which was later used to compute the Structure Function (SF). The log–log plots of the latter served for calculation of fractal properties of surfaces under investigation, including fractal dimension D, and pseudo‐topothesy K. The analysis of 3‐D surface texture helps to understand their essential characteristics and their implications as well as graphical models and their implementation in computer simulation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
87.
Nahid Shahabadi Soheila Kashanian Marzieh Khosravi Maryam Mahdavi 《Transition Metal Chemistry》2010,35(6):699-705
The water-soluble Ni(II) complex, [Ni(bipy)2(phen-dione)](OAc)2·2H2O (bipy = 2,2′-bipyridine and phen-dione = 1,10-phenanthroline-5,6-dione) has been synthesized and characterized by physico-chemical
and spectroscopic methods. The binding interactions of this complex with calf thymus DNA (CT-DNA) were investigated using
fluorimetry, spectrophotometry, circular dichroism and viscosimetry. In fluorimetric studies, the enthalpy and entropy of
the reaction between the complex and CT-DNA showed that the reaction is exothermic (ΔH = −123.9 kJ mol−1; ΔS = −323.5 J mol−1 K−1). The competitive binding studies showed that the complex could not release methylene blue completely. The complex showed
absorption hyperchromism in its UV–Vis spectrum with DNA. The calculated binding constant, K
b obtained from UV–Vis absorption studies was 2 × 105 M−1. Moreover, the complex induced detectable changes in the CD spectrum of CT-DNA, as well as changes in its viscosity. The
results suggest that this nickel(II) complex interact with CT-DNA via a groove-binding mode. 相似文献
88.
Anglin EJ Salisbury C Bailey S Hor M Macardle P Fenech M Thissen H Voelcker NH 《Lab on a chip》2010,10(24):3413-3421
We report on surface-engineered microarrays that provide in situ cell sorting, localization, and immobilization of various subsets of human primary lymphocytes, followed by an on-chip bioassay for ionizing-radiation-induced cytogenetic damage. The microarray format eliminates the necessity of separating cell sub-populations by alternative means (such as fluorescence- or magnetic-activated cell sorting) prior to performing informational bioassays. To exemplify the potential of this on-chip cytometry approach, we have integrated the cytokinesis-block micronucleus cytome (CBMNcyt) assay with the microarray platform for analysis of the chromosome damage profile of specific subsets of human peripheral lymphocytes. Microarray results were compared with data obtained from the traditional CBMNcyt assay on heterogeneous lymphocyte populations, and with flow cytometry data. Our results suggest that cytogenetic damage caused by ionizing radiation is not uniformly distributed across all lymphocytes subsets, but rather concentrated in specific subsets. The salient features of our approach are that it requires very small volumes of reagents, allows sorting of lymphocyte subsets in situ, increases parallelism of cell assays and is amenable to high content microscopy analysis. The on-chip cytometry format opens new vistas for advanced cell-based assays, potentially bringing to light important information which remains hidden with conventional assays and hence engendering new discoveries in cell biology. 相似文献
89.
Maryam Ezoddin Farzaneh Shemirani Mohammad Reza Jamali 《Journal of Analytical Chemistry》2010,65(2):153-158
In this research, simple, rapid and efficient method, dispersive liquid-liquid microextraction (DLLME) combined fiber optic
-linear array detection spectrophotometry (FO-LADS) was developed using a cylindrical micro-cell for preconcentration and
determination of Cu(II) in samples. DLLME and FO-LADS methods have good matching conditions for being combined since FO-LADS
is a suitable method for the determination of analytes in low volume of the remained phase obtained after DLLME. Molar absorptivity
of complex Cu with (4-benzylp iperidineditiocarbamate potassium salt) (BPDC) was determined as 2.75 × 104 L mol-1 cm-1 at 7nmax = 436 nm. Under the optimum conditions the calibration graph was linear in the rage of 2–70 fug L-1 with detection limit of 0.34 fug L-1. The proposed procedure was successfully applied to the determination of Cu(II) in real water samples and human urine sample. 相似文献
90.
A selective and sensitive method for simultaneous determination of lead, zinc and copper by adsorptive differential pulse
cathodic stripping voltammetry is presented. The method is based on adsorptive accumulation of the complexes of Pb(II), Zn(II),
and Cu(II) ions with dopamine onto hanging mercury drop electrode (HMDE), followed by reduction of adsorbed species by differential
pulse cathodic stripping voltammetry. The effect of experimental parameters such as pH, dopamine concentration, accumulation
time and potential and scan rate were examined. Under the optimized conditions, linear calibration curves were established
for the concentration of Pb, Zn, and Cu in the ranges of 5–150, 5–250, and 1–150 ng/mL, respectively. Detection limits of
0.06, 0.25, and 0.04 ng/mL for Pb, Zn, and Cu were obtained. An application of the proposed method is reported for the determination
of these elements in some real samples such as natural waters and alloys. 相似文献