全文获取类型
收费全文 | 1324篇 |
免费 | 33篇 |
国内免费 | 4篇 |
专业分类
化学 | 760篇 |
晶体学 | 14篇 |
力学 | 64篇 |
数学 | 82篇 |
物理学 | 441篇 |
出版年
2023年 | 8篇 |
2022年 | 28篇 |
2021年 | 26篇 |
2020年 | 48篇 |
2019年 | 24篇 |
2018年 | 30篇 |
2017年 | 36篇 |
2016年 | 46篇 |
2015年 | 24篇 |
2014年 | 34篇 |
2013年 | 95篇 |
2012年 | 60篇 |
2011年 | 75篇 |
2010年 | 51篇 |
2009年 | 46篇 |
2008年 | 64篇 |
2007年 | 63篇 |
2006年 | 71篇 |
2005年 | 54篇 |
2004年 | 48篇 |
2003年 | 32篇 |
2002年 | 34篇 |
2001年 | 14篇 |
2000年 | 22篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1973年 | 16篇 |
1956年 | 7篇 |
排序方式: 共有1361条查询结果,搜索用时 15 毫秒
191.
Gaurav Bhargava 《Tetrahedron》2008,64(13):3017-3024
The chemo- as well as regioselective imino Diels-Alder reactions of 5-dienyl pyrimidinones with N-aryl as well as N-naphthyl imines in the presence of a different Lewis acid catalysts resulting in novel quinoline and benzoquinoline derivatives are reported. 相似文献
192.
α,β-Unsaturated anilides bearing allylic leaving groups undergo photochemical electrocyclic ring closure to produce zwitterionic intermediates which eliminate carboxylate and phenolate leaving groups. 相似文献
193.
Gaurav Sharma 《Tetrahedron letters》2008,49(27):4269-4271
An efficient synthesis of 1,3-diaryl-2,3-dihydro-1,5-benzothiazepines has been developed by the reaction of various 1,3-diaryl-2-propenones with 2-aminothiophenol in water under neutral conditions catalysed by SDS. Excellent chemoselectivity was observed for substrates possessing halogen atoms or nitro/alkoxy/thioalkyl groups which did not undergo competitive aromatic nucleophilic substitution of the halogen atoms or the nitro group, reduction of the nitro or the α,β-unsaturated carbonyl group, or dealkylation of the alkoxy/thioalkoxy groups. 相似文献
194.
Maity J Shakya G Singh SK Ravikumar VT Parmar VS Prasad AK 《The Journal of organic chemistry》2008,73(14):5629-5632
Candida antarctica lipase-B (CAL-B) immobilized on lewatite selectively acylated the primary hydroxyl group of the furanosyl nucleoside in a mixture of 1-(alpha-D-arabinofuranosyl)thymine and 1-(alpha-D-arabinopyranosyl)thymine. This selective biocatalytic acylation of furanosyl nucleoside has enabled us an easy separation of arabinofuranosyl thymine from an inseparable mixture with arabinopyranosyl thymine. The primary hydroxyl selective acylation methodology of arabinonucleoside has also been successfully used for the separation of 1-(beta-D-xylofuranosyl)thymine and 1-(beta-D-xylopyranosyl)thymine from a mixture of the two, which demonstrate the generality of the enzymatic methodology for separation of furanosyl and pyranosyl nucleosides. 相似文献
195.
Theoretical study was performed to investigate how the degree of hydration affects the structures and properties of the canonical form (keto-N9H) of guanine in the ground and lowest singlet pipi* excited state. This work is the continuation of our earlier work where we have studied the hydration of guanine in the first solvation shell with one, three, five, and six water molecules. In the present investigation, we have considered 7-13 water molecules in hydrating guanine. Ground-state geometries were optimized at the Hartree-Fock level, whereas the configuration interaction-singles (CIS) method was used for the excited-state geometry optimization. The 6-311G(d,p) basis set was used in all calculations. The harmonic vibrational frequency analysis was used to determine the nature of the optimized ground- and excited-state potential energy surfaces; all geometries were found to be minima at the respective potential surfaces. It was found that the degree of hydration has a significant influence on the excited-state structural nonplanarity of guanine. It is expected that excited-state dynamics of guanine will depend on the degree of hydration. Ground- and excited-state geometries of selected hydrated species were also optimized in the bulk water solution using the polarizable continuum model (PCM). It was found that bulk water solution generally does not have significant influence on the structure of the hydrated species. Effects of hydration on different stretching vibrations in the ground and excited states are also discussed. 相似文献
196.
Dr. Pradeep Chopra Dr. Tejabhiram Yadavalli Francesco Palmieri Dr. Seino A. K. Jongkees Dr. Luca Unione Prof. Dr. Deepak Shukla Prof. Dr. Geert-Jan Boons 《Angewandte Chemie (International ed. in English)》2023,62(41):e202309838
Herpes simplex virus (HSV-1) employs heparan sulfate (HS) as receptor for cell attachment and entry. During late-stage infection, the virus induces the upregulation of human heparanase (Hpse) to remove cell surface HS allowing viral spread. We hypothesized that inhibition of Hpse will prevent viral release thereby representing a new therapeutic strategy for HSV-1. A range of HS-oligosaccharides was prepared to examine the importance of chain length and 2-O-sulfation of iduronic moieties for Hpse inhibition. It was found that hexa- and octasaccharides potently inhibited the enzyme and that 2-O-sulfation of iduronic acid is tolerated. Computational studies provided a rationale for the observed structure–activity relationship. Treatment of human corneal epithelial cells (HCEs) infected with HSV-1 with the hexa- and octasaccharide blocked viral induced shedding of HS which significantly reduced spread of virions. The compounds also inhibited migration and proliferation of immortalized HCEs thereby providing additional therapeutic properties. 相似文献
197.
The objective of this paper is to present some sufficient conditions for approximate controllability of semilinear fractional control system of order \({\alpha \in (1, 2]}\) with infinite delay. The results are obtained by the theory of strongly continuous \({\alpha}\)-order cosine family and sequence method. At the end, an example is given to illustrate the theory. 相似文献
198.
199.
William Wilson Anku Samuel Osei-Bonsu Oppong Sudheesh Kumar Shukla Eric Selorm Agorku Penny Poomani Govender 《Research on Chemical Intermediates》2016,42(10):7231-7245
Photocatalytic decolorization properties of cobalt doped-ZrO2-multiwalled carbon nanotubes (Co–ZrO2–MWCNTs) and chitosan–sodium alginate encapsulated Co–ZrO2–MWCNTs (CS/Alg–Co–ZrO2–MWCNTs) with varying weight percentage of Co–ZrO2–MWCNTs are presented in this research paper. The Co–ZrO2–MWCNTs was first synthesized through homogenous co-precipitation method and introduced into the chitosan–sodium sodium alginate (CS/Alg) biopolymer matrix. The bio-nanocomposites were characterized using X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, (UV–Vis)-spectroscopy and energy dispersive spectroscopy to obtain information on their structure, formation, morphology, size and elemental analysis. The photodecolorization efficiency of the samples was determined through their decolorization of trypan blue dye aqueous solution in 180 min. Recyclability of the catalysts was also assessed. The bio-nanocomposites experienced reduced band gap values with subsequent improvement in visible light activity compared to the uncapped Co–ZrO2–MWCNTs. All the CS/Alg–Co–ZrO2–MWCNTs exhibited higher photodecolorization activities than the uncapped Co–ZrO2–MWCNTs. The most efficient catalyst (CS/Alg–40 % Co–ZrO2–MWCNTs) with a band gap of 2.56 eV displayed 94 % decolorization efficiency of the dye. Though reusability of the catalyst is significant, its efficiency diminished consistently after each cycle. 相似文献
200.
Srivastava Anshu Garg Gaurav Sharma Poojadevi Shah Nancy Sharma Sonal Shrivastava Neeta 《平面色谱法杂志一现代薄层色谱法》2016,29(3):203-208
JPC – Journal of Planar Chromatography – Modern TLC - Bacopa monnieri (L.) Pennell, commonly known as Brahmi, is an important medicinal plant of the Ayurvedic System of Medicine and is... 相似文献