全文获取类型
收费全文 | 1548篇 |
免费 | 66篇 |
国内免费 | 32篇 |
专业分类
化学 | 1252篇 |
晶体学 | 7篇 |
力学 | 61篇 |
数学 | 128篇 |
物理学 | 198篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 47篇 |
2021年 | 53篇 |
2020年 | 93篇 |
2019年 | 84篇 |
2018年 | 122篇 |
2017年 | 64篇 |
2016年 | 126篇 |
2015年 | 81篇 |
2014年 | 116篇 |
2013年 | 211篇 |
2012年 | 117篇 |
2011年 | 117篇 |
2010年 | 83篇 |
2009年 | 77篇 |
2008年 | 67篇 |
2007年 | 46篇 |
2006年 | 24篇 |
2005年 | 24篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 15篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1646条查询结果,搜索用时 0 毫秒
51.
Bagheri Maedeh Gholamzadeh Parisa Mohammadi Ziarani Ghodsi Badiei Alireza 《Research on Chemical Intermediates》2019,45(6):3301-3310
Research on Chemical Intermediates - A dual-functional silica-based catalyst was prepared by treating fumed silica with amino-containing silane then 1,4-butane sultone. The presence of functional... 相似文献
52.
A straightforward and modular preparative approach to 1,3,5-triaroylbenzene-based functionalized cyclophane ring systems has been developed. The key cyclophane-forming macrocyclization reaction was accomplished during the course of a regioselective cross-benzannulation between bis(aryl ethynyl) ketone and enaminone reactants. Macrocyclic products with ring sizes ranging from 18- to 22-membered were successfully constructed. The composition of the tether connecting the two aryl ethynyl ketone fragments can be easily varied; consequently, this method is suitable for construction of a diverse range of structurally distinct cyclophane products. To illustrate this feature, cyclophanes possessing xylyl, alkyl, di(ethylene triamine), and di(ethylene oxy) bridging units were synthesized in isolated yields of 11-46%. Three new cyclophanes (calixarene-like macrocyles 8 and 9, as well as crownophane 18) were structurally characterized by X-ray diffractometry. 相似文献
53.
In this paper, molecular dynamics simulation was performed to investigate the liquid∕vapor interfacial structure of neat polar liquids. Large-scale ensembles of liquid pyridine and its alkyl derivatives, 4-methylpyridine and 4-ethylpyridine, were simulated by classical molecular dynamics at 298 K. For the liquid system of low polarity, the surface density profile of the atoms meet exactly at the middle of interfacial region, and atoms of hydrophobic nature can be hardly discriminated from hydrophilic ones in either vapor or liquid sides. For a liquid system of high polarity, the density profile of atoms with different nature is highly discriminated all over the interfacial region, and as the polarity increases, a dense region of atomic density is clearly developed in the subsurface region. The recognized bivariate method was also used to study the molecular orientational distribution quantitatively. Orientational analysis of the three liquid systems indicates that the pyridine ring plane in the outmost surface tends to be vertical. Its tendency in the innermost interfacial region is parallel. The orientational states available to 4-ethylpyridine and pyridine are discriminated by predicting the possibility of a bisector-wise tumbling for the ring plane in pyridine and a side-wise tumbling in 4-ethylpyridine. The orientational distribution maps explain the trend of experimental surface tension and surface entropy. As the dipole moment of these liquids increases with the alkyl chain length, the surface structural profile changes from a regular definite one to a surface of complex atomic structure involving a dense phase near the interface. The development of dense region in alkyl derivatives is the result of segregation of molecules due to the alkyl group, which is captured and discriminated by molecular dynamics simulation even when the length of a short alkyl chain is increased by one carbon atom. 相似文献
54.
55.
Mohamad Javad Tahmasebi Birgani Fatemeh Seif Nahid Chegeni Mohamad Reza Bayatiani 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(3):1367-1370
In consideration the radiological properties of materials and studying the scattering processes in atomic and nuclear physics, the effective atomic and mass numbers is widely employed. These numbers have been calculated for any mixed or composite materials in interaction with high energy photons (Linac in radiation therapy). A pair equation in terms of these numbers is obtained. The first equation has been derived from the conservation of mass energy law and the second by minimizing the binding energy from the semiempirical mass formula (Myers and Swiatecki formula) that gives a relation between atomic and mass numbers for stable nuclei approximately. By these equations one can obtain the effective atomic and mass numbers for any compound or mixed materials uniquely. These numbers are calculated for some materials and compared with the other studies. 相似文献
56.
Saeed Shahrokhian Fatemeh Ghorbani-Bidkorbeh Ali Mohammadi Rasoul Dinarvand 《Journal of Solid State Electrochemistry》2012,16(4):1643-1650
A mixture of multi-walled carbon nanotube/graphite paste electrode modified with a salophen complex of cobalt was prepared
and was applied for the study of the electrochemical behavior of 6-mercaptopurine (MP) using cyclic and differential pulse
voltammetry (DPV). An excellent electrocatalytic activity toward the oxidation of MP was achieved, which led to a considerable
lowering in the anodic overpotential and remarkable increase in the response sensitivity in comparison with unmodified electrode.
Utilizing DPV method, a linear dynamic range of 1–100 μM with detection limit of 0.1 μM was obtained in phosphate buffer of
pH 3.0. The electrochemical detection system was very stable, and the reproducibility of the electrode response, based on
the six measurements during 1 month, was less than 3.0% for the slope of the calibration curves of MP. The electrochemical
method as a simple, sensitive, and selective method was developed for the determination of MP in pharmaceutical dosage form
and human plasma without any treatments. 相似文献
57.
Ali A. Mohammadi Armin Hadadzahmatkesh Mohammad R. Asghariganjeh 《Monatshefte für Chemie / Chemical Monthly》2012,124(5):931-933
Abstract
FeNH4(SO4)2·12H2O (alum) efficiently catalyzes the one-pot three-component reaction of dimedone, aldehydes, and 3-aminocrotonate to afford 1,4-dihydropyridines. The work-up is easy, and the products are obtained in good to excellent yields and high purity. 相似文献58.
Farsi R. Mohammadi M. K. Saghanezhad S. J. 《Russian Journal of Organic Chemistry》2021,57(12):2002-2009
Russian Journal of Organic Chemistry - Herein, we report the sulfonamide-functionalized covalent organic framework (COF-SO3H), prepared by condensation of melamine and terephthalaldehyde and... 相似文献
59.
Masoud Salavati-Niasari Bahareh Shoshtari-Yeganeh Fatemeh Mohandes 《Journal of Cluster Science》2013,24(3):657-667
In this work, Pb(II)N,N-bis(salicylidene)-ethylenediamine; [Pb(salen)]; was applied as lead precursor to synthesis PbSe nanostructures. Besides [Pb(salen)], SeCl4 and reducing agents like N2H4·H2O have been employed for the production of PbSe nanostructures via a solvothermal route at 180 °C for 3 h in propylene glycol. The effect of preparation factors such as temperature, reaction time, and surfactant on the morphology of PbSe nanostructures was investigated. The experimental results indicated that PbSe synthesized at 150 and 210 °C was composed of agglomerated particles. On the other hand, the use of KBH4 as reducing agent led to produce PbSe with higher particle size and agglomeration. The as-prepared PbSe nanostructures were characterized by XRD, SEM, TEM, EDS, and FT-IR. 相似文献
60.
F. Ahmadi M. Saberkari R. Abiri H. Mohammadi Motlagh H. Saberkari 《Applied biochemistry and biotechnology》2013,170(4):988-1009
A tetrahedral Zn(II) complex with the second generation fluoroquinolone, norfloxacin, was prepared and characterized (NOR–Zn complex, NZC). The antibacterial efficiency of the NZC was tested on two Gram-positive and four Gram-negative bacteria by minimum inhibitory concentration method. The cytotoxic potential of NZC on MDA (human breast adenocarcinoma), Caco-2 (human colon adenocarcinoma), and Hela (human cervix carcinoma) cell lines was studied. The DNA interaction property of the NZC has been investigated using UV–vis, fluorescence, Fourier transform infrared, as well as cyclic voltammetry methods. Intrinsic binding constant (K b ), thermodynamic, and other spectroscopic and voltammetric data indicate that the NZC has more affinity for DNA than for norfloxacin and interacted with DNA via two modes: electrostatic and outside hydrogen binding. The proposed DNA binding mode supports the large enhancement in the cytotoxicity and antibacterial activity of NZC. 相似文献