全文获取类型
收费全文 | 2013篇 |
免费 | 58篇 |
国内免费 | 5篇 |
专业分类
化学 | 1262篇 |
晶体学 | 30篇 |
力学 | 61篇 |
数学 | 181篇 |
物理学 | 542篇 |
出版年
2023年 | 17篇 |
2022年 | 44篇 |
2021年 | 48篇 |
2020年 | 66篇 |
2019年 | 63篇 |
2018年 | 51篇 |
2017年 | 44篇 |
2016年 | 65篇 |
2015年 | 50篇 |
2014年 | 66篇 |
2013年 | 155篇 |
2012年 | 123篇 |
2011年 | 123篇 |
2010年 | 91篇 |
2009年 | 67篇 |
2008年 | 109篇 |
2007年 | 83篇 |
2006年 | 76篇 |
2005年 | 65篇 |
2004年 | 36篇 |
2003年 | 38篇 |
2002年 | 38篇 |
2001年 | 17篇 |
2000年 | 24篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 22篇 |
1976年 | 31篇 |
1975年 | 14篇 |
1974年 | 12篇 |
1973年 | 14篇 |
排序方式: 共有2076条查询结果,搜索用时 0 毫秒
81.
In this paper we study properties of numerical solutions of Burger’s equation. Burgers’ equation is reduced to the heat equation on which we apply the Douglas finite difference scheme. The method is shown to be unconditionally stable, fourth order accurate in space and second order accurate in time. Two test problems are used to validate the algorithm. Numerical solutions for various values of viscosity are calculated and it is concluded that the proposed method performs well. 相似文献
82.
In this paper, we introduced a summation‐integral type modification of Szász–Mirakjan operators. Calculation of moments, density in some space, a direct result and a Voronvskaja‐type result, are obtained. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
83.
Harsh Kumar Kanchan Bhardwaj Natlia Cruz-Martins Eugenie Nepovimova Patrik Oleksak Daljeet Singh Dhanjal Sonali Bhardwaj Reena Singh Chirag Chopra Rachna Verma Prem Parkash Chauhan Dinesh Kumar Kamil Ku
a 《Molecules (Basel, Switzerland)》2021,26(11)
The ingestion of contaminated water and food is known to cause food illness. Moreover, on assessing the patients suffering from foodborne disease has revealed the role of microbes in such diseases. Concerning which different methods have been developed for protecting food from microbes, the treatment of food with chemicals has been reported to exhibit an unwanted organoleptic effect while also affecting the nutritional value of food. Owing to these challenges, the demand for natural food preservatives has substantially increased. Therefore, the interest of researchers and food industries has shifted towards fruit polyphenols as potent inhibitors of foodborne bacteria. Recently, numerous fruit polyphenols have been acclaimed for their ability to avert toxin production and biofilm formation. Furthermore, various studies have recommended using fruit polyphenols solely or in combination with chemical disinfectants and food preservatives. Currently, different nanoparticles have been synthesized using fruit polyphenols to curb the growth of pathogenic microbes. Hence, this review intends to summarize the current knowledge about fruit polyphenols as antibacterial agents against foodborne pathogens. Additionally, the application of different fruit extracts in synthesizing functionalized nanoparticles has also been discussed. 相似文献
84.
[formula: see text] The reactions of glycals with ceric(IV) ammonium nitrate and sodium iodide in the presence of acetic acid provides 2-deoxy-2-iodo-alpha-mannopyranosyl acetates with good stereoselectivity. In the majority of the cases examined, the selectivity was considerably better than that from reactions using N-iodosuccinimide and HOAc. 相似文献
85.
Somnath Narayan Karad Prof. Dr. Rai‐Shung Liu 《Angewandte Chemie (International ed. in English)》2014,53(21):5444-5448
We report the first success in the gold‐catalyzed oxoarylations of nitriles with pyridine‐derived N‐oxides using gold carbenes as initiators. These oxoarylations were also achieved satisfactorily in intermolecular three‐component oxidations, including diverse alkenyldiazo esters, nitriles, and pyridine‐based oxides. 相似文献
86.
The display parameters and the stability of the various mesophases of a newly synthesised racemic mixture of anti-ferroelectric liquid crystals (AFLCs) have been boosted with the help of the electron beam irradiation. The mixture has phase sequence of isotropic–smectic C–smectic CA crystal. The effective macroscopic polarisation and transition temperatures of the various mesophases of the irradiated mixture have increased as compared with the pure mixture. The macroscopic polarisation of the mixture has increased from 21 to 27 nC/cm2 due to the irradiation. From various studies, we have observed that the temperature range of the smectic CA phase has increased by 20.6°C with marginal decrease in the temperature range of the smectic C phase. 相似文献
87.
Addition of ethenyllithium reagents to the carbonyl group of dialkyl squarate-derived 1-alkynylbicyclo[3.2.0]hept-2-ene-7-ones (15), followed by a TBAF workup, results in a low-temperature anion-accelerated alkoxy-Cope rearrangement which proceeds by way of a strained cyclic allene intermediates (e.g.,17). This leads to the formation of angularly fused triquinanes (e.g., 20) in which each of the rings is functionally differentiated. Bicyclo[6.3. 0]undecadienones (e.g., 36) are the major products when the reactions are quenched with aqueous bicarbonate rather than TBAF. Under analogous conditions 2-alkylidene-1-alkynylbicyclo[3.2. 0]heptan-7-ones also give bicyclo[6.3.0]undecadienones by a mechanism that was established to involve a 1,5-hydrgen shift in a strained allene intermediate. The synthetic scope and mechanism of these and related transformations are discussed. 相似文献
88.
Narayan Mukherjee 《Tetrahedron letters》2008,49(6):1037-1040
An efficient polycondensation reaction between α,ω-diformyl functional aromatics, namely 2,5-diheptyloxy-1,4-diformylbenzene and side-chain substituted α,ω-diformyl oligo(p-phenylene vinylene) (OPV) with hydrazine afforded novel soluble and processable conjugated polymers, P1 and P2, respectively. The reaction conditions were investigated and structural analysis of the polymers was carried out by means of 1H, 13C, 15N NMR, indicating all-trans configured CN-NC linkages. The molecular weights Mn were observed at ∼1100-1400 g/mol for P1 and ∼8700-10,500 g/mol for P2. The optical properties showed absorption maxima at ∼455 nm and ∼487 nm for P1 and P2 (CHCl3 solutions), respectively, red shifted by 31-60 nm relative to the monomer aromatics due to conjugation through the azine linkage. The emission maxima are observed at ∼515 nm and ∼560 nm for P1 and P2 (CHCl3 solutions), respectively. Thin films of P2 readily undergo n-doping. 相似文献
89.
P. S. Verma T. Venkateshwar Rao A. Jayaraman P. S. N. Murthy G. C. Joshi 《Fresenius' Journal of Analytical Chemistry》1994,348(11):742-744
The Fe(III)-EDTA complex reacts with sulfide ion in a fast electron transfer reaction, oxidising the latter to elemental sulfur and getting itself reduced to Fe(II). The reaction has been developed for the quantitative estimation of sulfide ion by titration against the Fe(III)-EDTA complex, measuring the redox potential of the system. Repeated use of a given quantity of the complex solution by the process of regeneration has been demonstrated. The possibility of its practical application in liquid phase oxidation processes of recovering sulfur from H2S is emphasized. 相似文献
90.
Gupta Madan Mohan Srivastava Alpana Tripathi Arvind Kumar Misra Himanshu Verma Ram Kishore 《平面色谱法杂志一现代薄层色谱法》2006,19(4):282-287
JPC – Journal of Planar Chromatography – Modern TLC - High-performance thin-layer chromatography (HPTLC) has been used for normal-phase separation of the components of hexane,... 相似文献