全文获取类型
收费全文 | 1910篇 |
免费 | 88篇 |
国内免费 | 42篇 |
专业分类
化学 | 1454篇 |
晶体学 | 11篇 |
力学 | 88篇 |
数学 | 195篇 |
物理学 | 292篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 32篇 |
2021年 | 74篇 |
2020年 | 103篇 |
2019年 | 92篇 |
2018年 | 120篇 |
2017年 | 93篇 |
2016年 | 148篇 |
2015年 | 97篇 |
2014年 | 142篇 |
2013年 | 237篇 |
2012年 | 149篇 |
2011年 | 146篇 |
2010年 | 126篇 |
2009年 | 110篇 |
2008年 | 111篇 |
2007年 | 69篇 |
2006年 | 39篇 |
2005年 | 26篇 |
2004年 | 25篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有2040条查询结果,搜索用时 15 毫秒
931.
Mohammad Hossein Mosslemin Mohammad Reza Nateghi Razieh Mohebat 《Monatshefte für Chemie / Chemical Monthly》2008,139(10):1247-1250
A clean, simple, one-pot, and efficient synthesis of 1,2-dihydro-1-aryl[1,3]oxazino[5,6-f]quinolin-3-one and 1,2-dihydro-1-arylnaphtho[1,2-e]-[1,3]oxazine-3-one derivatives was accomplished in good yields via reaction between 6-quinolinol or 2-naphthol, aromatic aldehydes, and methyl carbamate in aqueous medium catalyzed by TEBA (triethylbenzylammonium chloride).
Correspondence: Mohammad Hossein Mosslemin, Department of Chemistry, Islamic Azad University, Yazd 8916871967, Iran. 相似文献
932.
Hossein Tavana Dietmar Appelhans Rong-Chuan Zhuang Stefan Zschoche Karina Grundke Michael L. Hair A. Wilhelm Neumann 《Colloid and polymer science》2006,284(5):497-505
Surface energetics of two fluorinated maleimide copolymers containing fluorinated side chain, i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF), are studied by contact angle measurements with 10 liquids consisting
of fairly bulky molecules. Because of the inertness of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane
(DMCPS) molecules, their contact angles are used to determine the surface tension of the two polymers. It is found that other
liquids show specific interactions with the ETMF films, and their contact angles deviate from a smooth curve that represents
the surface tension of ETMF, i.e., 11.00 mJ/m2. On ODMF surfaces, only OMCTS and DMCPS yield useful contact angles. Other liquids either dissolve the polymer film or show
a slip-stick pattern. This finding is discussed in terms of interactions between segments of the polymer chains and the test
liquids. OMCTS and DMCPS are suggested as the appropriate probe liquids, meeting specific criteria necessary for the determination
of accurate surface tension of fluoropolymers. 相似文献
933.
Hossein A. Dabbagh Alireza Najafi-Chermahini Soodabeh Banibairami 《Tetrahedron letters》2006,47(23):3929-3932
The synthesis and characterization of 5-(1-(2-(1H-tetrazole-5-yloxy)naphthalen-1-yl)naphthalen-2-yloxy)-1H-tetrazole (BIZOL) as the first bis-tetrazole BINOL-type ligands is described. 相似文献
934.
935.
Shoja Sajede Mahmoodi Nosrat Ollah Ghafouri Hossein Rassa Mehdi Sharafshah Alireza Panahi Kokhdan Esmaeel 《Research on Chemical Intermediates》2020,46(7):3327-3339
Research on Chemical Intermediates - The structure of urea has received special attention due to its biological activity. A new and efficient one-pot three-component reaction for the synthesis of... 相似文献
936.
Tavakol Hossein Shahabi Dana Keshavarzipour Fariba Hashemi Fatemeh 《Structural chemistry》2020,31(1):399-409
Structural Chemistry - In this work, the interactions between simple carbon nanotubes (CNTs) and doped carbon nanotubes (DCNTs; with sulfur, boron, aluminum, silicon, phosphorus, or nitrogen) as... 相似文献
937.
Boag NM Haghgooie H Hassanzadeh A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,69(1):156-159
The formation of Pt(eta(5)-C(5)Me(5))(CO){C(O)NR(2)} (R=Me, Et) complexes was established by spectroscopic analysis. The infrared spectra of these complexes showed a sharp absorption due to the presence of coordinated carbonyl group in the region 2017-2013cm(-1). The N,N-dialkylcarbamoyl ligands showed a characteristic CO stretching absorption in the range 1609-1616cm(-1). The proton NMR spectra of these complexes revealed the expected singlet arising from five equivalent methyl groups on the cyclopentadienyl ring with satellites due to coupling to (195)Pt. The N-methyl and N-ethyl protons exhibited very broad resonances due to restricted rotation about the N-C bond at room temperature. On cooling to -30 degrees C, the N,N-dimethyl protons for complex Pt(eta(5)-C(5)Me(5))(CO){C(O)NMe(2)} showed two sharp singlets at delta 2.86 and 3.09ppm as expected for the static structure. For the N,N-diethyl derivative, Pt(eta(5)-C(5)Me(5))(CO){C(O)NEt(2)}, the methyl protons exhibited only a single triplet at delta 1.06ppm at -10 degrees C due to coupling with the methylene protons. This single resonance arises through accidental overlap as the methylene protons of the ethyl groups are inequivalent at this temperature and each exhibited a quartet at delta 3.33 and 3.70ppm due to coupling with the methyl protons. The singlet resonances for the methyl and ring carbons of the eta(5)-C(5)Me(5) group found in (13)C{(1)H} NMR spectra are illustrative of the chemical equivalence of all the carbon atoms caused by free rotation of the ring in these complexes. The signals attributable to the carbonyl and carbamoyl carbon atom resonances are found downfield as two singlets each with a large coupling constant to platinum. The platinum coupling constants of the downfield resonances could not be identified for Pt(eta(5)-C(5)Me(5))(CO){C(O)NMe(2)} due to presence of impurities. 相似文献
938.
Fe(HSO4)3 has been used as an efficient and reeyclable catalyst for the one-pot synthesis of 14-aryl- or alkyl-14H-dibenzo[a,j]xanthene derivatives by the reaction of 2-naphtol and aldehydes. Different types of aromatic and aliphatic aldehydes are used in the reaction and in all cases the products were obtained in good to excellent yields. 相似文献
939.
The reaction of 2-imino-3-(2-propynyl)-1,3-benzothiazole with various iodobenzenes in the presence of a palladium catalyst leads to the production of 2-benzylimidazo[2,1-b][1,3]benzothiazoles. 相似文献
940.
Production and properties of a biosurfactant obtained from a member of the Bacillus subtilis group (PTCC 1696) 总被引:1,自引:0,他引:1
Ghojavand H Vahabzadeh F Roayaei E Shahraki AK 《Journal of colloid and interface science》2008,324(1-2):172-176
The production and properties of a biosurfactant, synthesized by a member of the Bacillus subtilis group (PTCC 1696) which was isolated from an Iranian oil field, have been investigated. The biosurfactant, which was produced as a primary metabolite associated with the growth of PTCC 1696, was able to reduce the surface and interfacial tension of media to 26.7 and 0.1 mN/m, respectively. Crude biosurfactant and acid precipitated biosurfactant have critical micelle concentrations of 10 and 100 mug/ml, respectively. The stability of the biosurfactant at different salinities, pH and temperature and also its emulsifying activity have been investigated. It is an effective surfactant at very low concentrations over a wide range of temperatures, pHs and salt concentrations and also has the ability to emulsify oil, which is essential for enhanced oil recovery. 相似文献