全文获取类型
收费全文 | 1514篇 |
免费 | 45篇 |
国内免费 | 3篇 |
专业分类
化学 | 1115篇 |
晶体学 | 25篇 |
力学 | 62篇 |
数学 | 92篇 |
物理学 | 268篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 30篇 |
2020年 | 42篇 |
2019年 | 49篇 |
2018年 | 40篇 |
2017年 | 36篇 |
2016年 | 44篇 |
2015年 | 47篇 |
2014年 | 55篇 |
2013年 | 109篇 |
2012年 | 119篇 |
2011年 | 122篇 |
2010年 | 65篇 |
2009年 | 60篇 |
2008年 | 110篇 |
2007年 | 68篇 |
2006年 | 89篇 |
2005年 | 65篇 |
2004年 | 46篇 |
2003年 | 36篇 |
2002年 | 33篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1964年 | 3篇 |
排序方式: 共有1562条查询结果,搜索用时 31 毫秒
71.
Ramesh C. Kamboj Dinesh Kumar Rita Arora Surinder Berar Geeta Sharma 《Journal of heterocyclic chemistry》2013,50(Z1):E200-E203
The photo‐irradiation of thienylchromenone resulted in the regioselective cyclization which is exclusively controlled by the nature of solvent used as reaction medium. Compared to nonpolar medium, polar solvent furnished a diverse array of novel angular tetracyclic photoproducts with gem‐dihydro functionality and exocyclic double bonds on the fused pyran ring, which is unprecedented to best of our knowledge. 相似文献
72.
One-pot synthesis of benzimidazole compounds from ortho-phenylenediamine and a variety of aldehydes was developed under mild reaction conditions. All the reactions were carried out in the presence of samarium triflate (10 mol%) in acetonitrile at room temperature. 相似文献
73.
A new series of urea, thiourea, and selenourea derivatives with thiazole moieties were synthesized by the nucleophilic addition reaction of (2-amino-4-(3-chlorophenyl)thiazol-5-yl)(2-chlorophenyl)methanone with various substituted isocyanates/ isothiocyanates/isoselenocynates in acetone having a catalytic amount of sodium hydroxide at room temperature with good yields. All the synthesized compounds were fully characterized by spectroscopic data and screened for their in vitro antioxidant activity using 1,1-diphenylpicrylhydrazyl (DPPH), nitric oxide (NO), and hydrogen peroxide (H2O2) radical scavenging methods. A preliminary study of the structure–activity relationship revealed that the compounds containing selenourea functionality along with halogen group have exhibited potent activity (IC50 ≤ 0.0309 µmol/mL) compared to the standards (IC50 ≤ 0.0814 µmol/mL). Thus the title compounds are a new class of potent antioxidant agents and worthy of further investigation. 相似文献
74.
Nguyen Huy Thuan Ramesh Prasad Pandey Ta Thi Thu Thuy Je Won Park Jae Kyung Sohng 《Applied biochemistry and biotechnology》2013,171(8):1956-1967
Myricetin is an important flavonol whose medically important properties include activities as an antioxidant, anticarcinogen, and antimutagen. The solubility, stability, and other biological properties of the compounds can be enhanced by conjugating aglycon with sugar moieties. The type of sugar moiety also plays a significant role in the biological and physical properties of the natural product glycosides. Reconstructed Escherichia coli containing thymidine diphosphate-α-l-rhamnose sugar gene cassette and Arabidopsis-derived glycosyltransferase were used for rhamnosylation of myricetin. Myricetin (100 μM) was exogenously supplemented to induced cultures of engineered E. coli. The formation of target product—myricetin-3-O-α-l-rhamnoside—was confirmed by chromatographic and NMR analyses. The yield of product was improved by using various mutants and methylated cyclodextrin as a molecular carrier for myricetin in combination with E. coli M3G3. The maximal yield of product is 55.6 μM (3.31-fold higher than the control E. coli MG3) and shows 55.6 % bioconversion of substrate under optimized conditions. 相似文献
75.
Ramesh H. Shah 《Journal of carbohydrate chemistry》2013,32(1):139-146
D-Erythrose was synthesized in four steps from D-ribono-1,4-lactone via the 3,5-O-benzylidene derivative of the latter compound. Reduction of the benzylidene D-ribonolactone, and periodate cleavage of the resulting 3,5-O-benzylidene-D- ribitol were performed in a one-flask reaction. The ensuing 2,4-O-benzylidene-D-erythrose was hydrolyzed with 10% acetic acid to obtain syrupy D-erythrose. 相似文献
76.
The application of graphene and related nanomaterials like boron nitride (BN) nanosheets, BN-graphene hybrid nanomaterials, and graphene oxide (GO) for adsorption of anticancer chemotherapeutic camptothecin (CPT) along with the effect on electronic properties prior to functionalization and after functionalization has been reported using density functional theory (DFT) calculations. The inclusion of dispersion correction to DFT is instrumental in accounting for van der Waals π–π stacking between CPT and the nanomaterial. The adsorption of CPT exhibits significant strain within the nanosheets and noncovalent adsorption of CPT is thermodynamically favoured onto the nanosheets. In case of GO, surface incorporation of functional groups result in significant crumpling along the basal plane and the interaction is basically mediated by H-bonding rather than π–π stacking. Docking studies predict the plausible binding of CPT, CPT functionalized graphene and GO with topoisomerase I (top 1) signifying that CPT interacts through π stacking with AT and GC base pairs of DNA and in presence of nano support, DNA bases preferentially gets bound to the basal plane of graphene and GO rather than the edges. At a theoretical level of understanding, our studies point out the noncovalent interaction of CPT with graphene based nanomaterials and GO for loading and delivery of anticancer chemotherapeutic along with active binding to Top1 protein. 相似文献
77.
G. Satish K. Harsha Vardhan ReddyK. Ramesh B.S.P. Anil KumarY.V.D. Nageswar 《Tetrahedron letters》2014
A simple and efficient, ligand-free C–N cross-coupling of aryl halides/benzyl bromides with trans-4-hydroxy-l-proline has been developed to produce aromatized N-substituted pyrroles, using a catalytic amount of magnetically separable and recyclable CuFe2O4 nanoparticles, in the presence of Cs2CO3 in DMSO at 100 °C. 相似文献
78.
Gurjaspreet Singh Satinderpal Singh Mangat Jandeep Singh Aanchal Arora Ramesh K. Sharma 《Tetrahedron letters》2014
The copper-catalyzed ‘click silylation’ has been exploited for the chemical modification of γ-azidopropyltriethoxysilane (AzPTES) with a wide range of terminal alkynes (1a–1v) in a one-pot operation. The novel 1,2,3-triazole-triethoxysilane derivatives (2a–2v) were synthesized by this procedure and comprehensively characterized by IR spectra, 1H and 13C NMR, and HRMS studies. 相似文献
79.
80.
Omar Sarheed Manar Dibi Kanteti V. R. N. S. Ramesh Markus Drechsler 《Molecules (Basel, Switzerland)》2021,26(9)
Transdermal drug delivery of lidocaine is a good choice for local anesthetic delivery. Microemulsions have shown great effectiveness for the transdermal transport of lidocaine. Oil-in-water nanoemulsions are particularly suitable for encapsulation of lipophilic molecules because of their ability to form stable and transparent delivery systems with good skin permeation. However, fabrication of nanoemulsions containing lidocaine to provide an extended local anesthetic effect is challenging. Hence, the aim of this study was to address this issue by employing alginate-based o/w nanocarriers using nanoemulsion template that is prepared by combined approaches of ultrasound and phase inversion temperature (PIT). In this study, the influence of system composition such as oil type, oil and surfactant concentration on the particle size, in vitro release and skin permeation of lidocaine nanoemulsions was investigated. Structural characterization of lidocaine nanoemulsions as a function of water dilution was done using DSC. Nanoemulsions with small droplet diameters (d < 150 nm) were obtained as demonstrated by dynamic light scattering (DLS) and cryo-TEM. These nanoemulsions were also able to release 90% of their content within 24-h through PDMS and pig skin and able to the drug release over a 48-h. This extended-release profile is highly favorable in transdermal drug delivery and shows the great potential of this nanoemulsion as delivery system. 相似文献