全文获取类型
收费全文 | 1168篇 |
免费 | 59篇 |
国内免费 | 25篇 |
专业分类
化学 | 984篇 |
晶体学 | 8篇 |
力学 | 14篇 |
数学 | 90篇 |
物理学 | 156篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 46篇 |
2021年 | 50篇 |
2020年 | 79篇 |
2019年 | 75篇 |
2018年 | 107篇 |
2017年 | 76篇 |
2016年 | 80篇 |
2015年 | 57篇 |
2014年 | 90篇 |
2013年 | 119篇 |
2012年 | 98篇 |
2011年 | 77篇 |
2010年 | 55篇 |
2009年 | 45篇 |
2008年 | 57篇 |
2007年 | 43篇 |
2006年 | 19篇 |
2005年 | 20篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1252条查询结果,搜索用时 15 毫秒
51.
In this work, the ionic liquid (IL)[C6mim][PF6] was used as IL-based extractant for dispersive liquid–liquid microextraction, followed by back-extraction and HPLC/UV–Vis determination of 3-indole acetic acid (IAA) in pea plant. The effects of some crucial factors such as chemical structure and volume of IL, pH adjustment, dissolution temperature, extraction time, centrifugation time, and ionic strength of aqueous sample were studied. The linear range of the HPLC method for IAA quantification was 17.5 × 10?2–36.8 mg L?1. LOD, LOQ, method recovery, and preconcentration factor values were 0.170 mg L?1, 0.175 mg L?1, 98.3, and 40 %, respectively. The RSD for the suggested method was calculated as 0.93 % at 35.04 mg L?1 of IAA and each IL phase was able to be reused for at least four DLLME/back-extraction cycles. To evaluate the applicability of the suggested method, IAA was determined in pea plant samples. 相似文献
52.
Isoquinoline reacts with ethyl bromopyruvate in the presence of dialkyl acetylenedicarboxylates or diaryloylacetylenes to produce dialkyl 1-(2-ethoxy-2-oxoacetyl)pyrrolo[2,1-a]isoquinoline-2,3-dicarboxylates or ethyl 2-[2,3-diaryloylpyrrolo[2,1-a]isoquinoline-1-yl]-2-oxoacetates in good yields. 相似文献
53.
Maryam Ataeefard Siamak Moradian Mojtaba Mirabedini Morteza Ebrahimi Saeed Asiaban 《Plasma Chemistry and Plasma Processing》2008,28(3):377-390
The surface of a LDPE was modified by Ar, O2, N2, CO2 gaseous plasma. The changes in surface morphology and surface wettability were investigated using AFM and SEM. The surface
chemical changes of LDPE were also characterized by FTIR-ATR. The SEM and AFM results demonstrated variable changes in surface
roughness for different types of plasma gas used, the changes being more for the Ar and N2 plasma treatments. Considering the nature of the LDPE film, XRD studies were carried out to determine changes in the percentage
crystalinity. The results showed that all low pressure O2, Ar, N2, CO2 gas plasmas improved the wettability of LDPE films. Contact angles decreased significantly depending on the discharge powers
and exposure times. Surface morphology was also found to vary with plasma discharge powers, exposure times, and the type of
gas being used. Ar and N2 gas plasmas in general produced more superior results. 相似文献
54.
Mohammad Ali Zolfigol Kamal Amani Maryam Hajjami Arash Ghorbani-Choghamarani 《Monatshefte für Chemie / Chemical Monthly》2008,121(4):895-899
A wide range of aliphatic or aromatic sulfides are selectively oxidized to the corresponding sulfoxides using ammonium cerium
(IV) nitrate (CAN) and a catalytic amount of KBr or NaBr in the presence of wet SiO2 in CH2Cl2 under heterogeneous conditions in moderate to high yields. 相似文献
55.
Maryam Mohammadikish Fatemeh Davar Mohammad Reza Loghman-Estarki 《Journal of Cluster Science》2013,24(1):217-231
In this work, we report a facile hydrothermal method for the preparation of three dimensional hollow ZnS nanostructures, using Zinc bis(salicyle aldehitato), Zn(Sal)2, thioacetamide (TAA) and thioglycolic acid (TGA) as Zn2+, sulfur source and capping agent, respectively. The ZnS solid and hollow sphere was produced from the self-assembly of nanoparticles with diameters of 11 ± 2 nm with TGA and TGA, TAA, respectively. Furthermore, with changing zinc precursor from Zn(Sal)2 to zinc acetate [Zn(OAC)2], ZnS nanorods were obtained. The products were characterized by XRD, SEM, TEM, selected area electron diffraction, and FT-IR spectra. The influence of surfactant (Polyethylene glycol) on the morphology of the products was also investigated. Possible formation mechanism and optical properties of these architectures were also reported. 相似文献
56.
57.
Haleh Kangarlou Arash Abdollahi Maryam Motallebi Aghgonbad 《Optics and Spectroscopy》2012,113(3):321-326
Zinc sulfide nano layers were deposited on glass substrates at 300 K by physical vapor deposition method, under high vacuum conditions and different deposition angles. Thickness of the layers were measured 73 nm, by quartz crystal method. Optical reflectance and transmittance of the layers were measured in the wave length of 300?C1100 nm. Optical constants were calculated by Kramers-Kronig relations. The influence of deposition angle in optical properties of ZnS nano layers are investigated. By using Generalized Gradient Approximations in context of plane wave pseudo-potentials (norm conserving and Ultrasoft) and full-potential linearized augmented plane wave methods, Band structure calculated and compared with experimental results. Possible energy transitions are also reported. 相似文献
58.
59.
Akbar Mobinikhaledi Hassan Moghanian Maryam Deinavizadeh 《Comptes Rendus Chimie》2013,16(11):1035-1041
A simple and efficient procedure for the synthesis of 9H-xanthene or bisphenol derivatives has been developed by one-pot condensation of xylenols with aromatic aldehydes in the presence of p-toluenesulfonic acid (pTSA) as a catalyst under solvent-free conditions at 100 °C. It is noteworthy that the condensation reaction of 3,5-xylenol with aldehydes produces 9H-xanthene derivatives, while the reaction with other xylenols leads to the corresponding bisphenol derivatives. Different types of aromatic aldehydes are used in the reaction and in every case the products were obtained in good to excellent yields. The structures of these compounds were established on the basis of IR, 1H NMR, 13C NMR and CHN data. 相似文献
60.
Mohammad Ali Taher Maryam Fayazi Behjat Pooramiri Masoud Ghanei-Motlagh Ali Dorehgiraee 《Journal of the Iranian Chemical Society》2013,10(1):151-159
A new solvent polymeric membrane (PME) and coated graphite (CGE) electrodes based on 3-amino-2-mercapto-3H-quinazolin-4-one as a suitable carrier for La(III) ion are described. The sensors exhibited a Nernstian response for La(III) ion over a wide concentration range (3.0 × 10?7 to 1.0 × 10?1 M for PME and 1.0 × 10?7 to 1.0 × 10?1 M for CGE) with a slope of 20.1 ± 0.3 (PME) and 23.4 ± 0.4 (CGE) mV decade?1. The lower detection limits by PME and CGE were 2.0 × 10?7 and 7.1 × 10?8 M, respectively. The potentiometric response of the proposed electrodes was independent of the pH of the test solution in the pH range 3.0–9.0 with a fast response time (<10 s). The applications of prepared sensors were demonstrated in the determination of lanthanum ions in spiked water sample and also utilized for indirect determination of fluoride content of two mouth wash preparation samples. 相似文献