全文获取类型
收费全文 | 430篇 |
免费 | 9篇 |
专业分类
化学 | 271篇 |
晶体学 | 10篇 |
力学 | 12篇 |
数学 | 35篇 |
物理学 | 111篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 27篇 |
2012年 | 25篇 |
2011年 | 36篇 |
2010年 | 25篇 |
2009年 | 23篇 |
2008年 | 30篇 |
2007年 | 25篇 |
2006年 | 23篇 |
2005年 | 21篇 |
2004年 | 13篇 |
2003年 | 16篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有439条查询结果,搜索用时 15 毫秒
21.
22.
We report the first preparation of furo- and thieno-fused 1,3-diazepine-4,6-dione derivatives starting from ethyl 2-(2-methoxy-2-oxoethyl)-3-furancarboxylate and -thiophencarboxylate. The ester functionalities connected to the hetero-ring were converted regiospecifically into the desired amides. The ester groups attached to the methylene unit were converted into isocyanates via Curtius rearrangement. The ring-closure reaction was performed in the presence of lithium bis(trimethylsilyl)amide at room temperature to give furo- and thieno-fused diazepinone derivatives. 相似文献
23.
24.
Nurcan Balci Levent Toppare Ural Akbulut Dietmar Stanke Manfred L. Hallensleben 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1727-1739
Abstract Electrically conducting polypyrrole grafts with poly[(methyl meth-acrylate)-co-(2-(N-pyrrolyl) ethyl methacrylate)] (PMMA-co-PEMA) were synthesized by constant potential electrolysis. Cyclic Voltammetry, DSC, TGA, SEM and elemental analysis were used in order to characterize the free standing films. Conductivities of the polymers were measured by a four-probe technique. 相似文献
25.
Murat Güney Selçuk Eşsiz Arif Daştan Metin Balci Ottorino De Lucchi Ertan Şahin Fabrizio Fabris 《Helvetica chimica acta》2013,96(5):941-950
Stereoisomerically pure endo‐ and exo‐7‐halo‐7‐(trimethylstannyl)benzonorcar‐3‐enes (=endo‐ and exo‐(1‐halo‐1a,2,7,7a‐tetrahydro‐1H‐cyclopropa[b]naphthalen‐1‐yl)trimethylstannane) 4 and 6 were selectively obtained by lithium? tin or magnesium? tin transmetalation in good yields (Scheme 2 and 3). The reaction of these compounds with copper(I) thiophene‐2‐carboxylate (CuTC) produced in both cases the corresponding CS‐symmetric bicyclopropylidene (=cyclopropylidenecyclopropane) syn‐ 1 , a single diastereoisomer (Schemes 5 and 6). The structure of syn‐ 1 was undoubtedly elucidated by X‐ray single crystal diffraction. The coupling mechanism of the carbenoid cyclopropane is discussed (Scheme 7). 相似文献
26.
A novel synthesis of 1,2,4-oxadiazoles and isoxazoles is described by utilizing the reactions between amidoximes and α,β-alkynic aldehydes and/or ketones. Conjugate addition products, obtained from amidoximes and α,β-alkynic aldehydes and/or ketones, afford 1,2,4-oxadiazoles and isoxazoles when treated with bases and acids, respectively. 1,2,4-Oxadiazoles can also be synthesized directly from amidoximes and α,β-alkynic aldehydes in a one-pot manner under basic conditions. The reactions are general for a variety of starting compounds and tolerate the presence of aryl, heteroaryl and alkyl groups. 相似文献
27.
Transformation of cyclohexa-1,3- and 1,4-dienes to carbasugars is described. Photooxygenation of dienes gave bicyclic endoperoxides, which were reduced with thiourea to the corresponding 1,4-diols with cis-configuration. Lactonization of the remaining double bond by oxidative addition of acetic acid to the double bond in the presence of Mn(OAc)3 followed by lactone ring-opening reaction gave the target branched carbasugars. 相似文献
28.
We report herein the synthesis of a novel class of compounds, ethyl 4-oxo-4H-furo[3,2-c]pyran-6-yl carbonate, (7E)-7-[(dimethylamino)methylene]-4H-furo[3,2-c]pyran-4,6(7H)-dione, 5-oxo-N-phenyl-2,5-dihydro-4H-furo[3,2-b]pyrrole-4-carboxamide, and 5-oxo-N-phenyl-5,6-dihydro-4H-thieno[3,2-b]pyrrole-4-carboxamide starting from the corresponding acid derivatives. Intramolecular cyclization in the presence of thionyl chloride formed the target fused ring systems. Additional transformation was seen in the cyclization of furan-fused heterocycle. A mechanism was proposed based on experimental and computational findings. 相似文献
29.
Mohammed Safar Saeed Balci Esra Qadir Hussein Ahmed Qader Ibrahim Nazem Saydam Sinan Dagdelen Fethi 《Journal of Thermal Analysis and Calorimetry》2022,147(21):11705-11713
Journal of Thermal Analysis and Calorimetry - The influence of four different quantities of niobium (Nb) on some physical and chemical properties of Ni-Ti alloy was examined in this study.... 相似文献
30.
Nilgün KABAY Yasemin BAYGU Metin AK zzet KARA EsraNur KAYA Mahmut DURMU Yaar G
K 《Turkish Journal of Chemistry》2021,45(1):143
The current study describes the synthesis, electrochemical, computational, and photochemical properties of octa (3-hydroxypropylthio) substituted cobalt (II) ( 4 ), copper (II) ( 5 ), nickel (II) ( 6 ) and zinc(II) ( 7 ) phthalocyanine derivatives. These novel compounds were characterized by elemental analysis,1H,13C NMR, FT-IR, UV-Vis, and MS. The redox behaviors of these metallo-phthalocyanines were investigated by the cyclic voltammetric method. The optimized molecular structure and gauge-including atomic orbital (GIAO)1H and13C NMR chemical shift values of these phthalocyanines in the ground state had been calculated by using B3LYP/6–31G(d,p) basis set. The outcomes of the optimized molecular structure were given and compared with the experimental NMR values. The photochemical properties including photodegradation and singlet oxygen generation of zinc(II) phthalocyanine were studied in DMSO solution for the determination of its photosensitizer behaviors. 相似文献