全文获取类型
收费全文 | 511篇 |
免费 | 5篇 |
专业分类
化学 | 339篇 |
晶体学 | 9篇 |
力学 | 20篇 |
数学 | 61篇 |
物理学 | 87篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 42篇 |
2012年 | 28篇 |
2011年 | 38篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 24篇 |
2007年 | 36篇 |
2006年 | 36篇 |
2005年 | 33篇 |
2004年 | 32篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1985年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有516条查询结果,搜索用时 15 毫秒
171.
(R)‐2,3‐Cyclohexylideneglyceraldehyde,a Chiral Pool Synthon for the Synthesis of 2‐Azido‐1,3‐diols
下载免费PDF全文
![点击此处可从《Helvetica chimica acta》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Abdul Rouf Mushtaq A. Aga Brijesh Kumar Subhash C. Taneja 《Helvetica chimica acta》2015,98(6):823-833
A new approach was proposed for the synthesis of 2‐azido‐1,3‐diols from easily available and inexpensive chiral pool synthon (R)‐2,3‐O‐cyclohexylidene‐D ‐glyceraldehyde, through Mitsunobu azidation of 1,2‐diols. Both C(2) and C(1) azides in variable ratios were obtained in alkyl substituted diols with C(2) as the major one. 相似文献
172.
Gayathri V Ananthi S Chandronitha C Sangeetha MK Vasanthi HR 《Natural product research》2011,25(11):1110-1114
Nerium oleander Linn. (NO), an evergreen shrub, is used in folklore medicine as a cardiotonic and exhibits a wide spectrum of bioactivities. Herein, the hypolipidemic potential of the ethanolic extract of flowers of Nerium oleander (ENO) in a minimal dose was assessed. A high fat diet (HFD) resulted in a significant increase in cardiac lipids and lipoproteins and an increase in body weight gain. Simultaneous treatment with ENO significantly lowered the increase in body weight gain, lipid and lipoprotein levels, with a concomitant increase in HDL in the plasma and heart when compared to HFD-fed rats. Likewise, the activities of lipolytic enzymes were also upheld by the ENO treatment in the heart compared to HFD-fed rats. The above findings highlight the possible mechanism of N. oleander as a hypolipidemic agent in its use in folklore medicine as a cardiotonic. 相似文献
173.
We consider the combinatorial problem of embedding the metric defined by an unweighted graph into the real line, so as to minimize the distortion of the embedding. This problem is inspired by connections to Banach space theory and to computer science. After establishing a framework in which to study line embeddings, we focus on metrics defined by three specific families of trees: complete binary trees, fans, and combs. We construct asymptotically optimal (i.e., distortion‐minimizing) line embeddings for these metrics and prove their optimality via suitable lower bound arguments. It appears that even such specialized metrics require nontrivial constructions and proofs of optimality require sophisticated combinatorial arguments. The combinatorial techniques from our work might prove useful in further algorithmic research on low distortion metric embeddings. © 2011 Wiley Periodicals, Inc. J Graph Theory 67: 153–168, 2011 相似文献
174.
Subhash C. Bhatia Ruman Rani Rachna Bhatia Hardeep Anand 《The Journal of chemical thermodynamics》2011,43(3):479-486
Densities, ρ, and speeds of sound, u, of binary liquid mixtures of 1-nonanol with o-cresol, m-cresol, p-cresol and anisole have been measured over the entire range of composition at T = (293.15 and 313.15) K and at atmospheric pressure. Using these data, the excess molar volume, VE, molar free volume, Vf, parameters related to space-filling ability, Vf/V, non-linearity parameters, B/A, isentropic compressibility, κS, molar isentropic compressibility, KS,m, deviation of molar isentropic compressibility, , deviations of the speed of sound, uD, and limiting excess partial molar volume, , and isentropic compressibility, , have been calculated. The calculated excess and deviation functions have been fitted to the Redlich–Kister polynomial equations and the results analyzed in terms of molecular interactions and structural effects. 相似文献
175.
The present work demonstrates the synthesis and characterization of adducts with bis(O,O′-diisopropylmonothiophosphato)nickel(II) complex, Ni{S(O)P(OiPr)2}2(L)
n
(n = 2, L = pyridine, 2-picoline, 3-picoline; n = 1, L = 2,2′-bipyridyl and 1,10-phenanthroline). The crystallographic investigation of Ni{S(O)P(OiPr)2}2(C5H5N)2 reveals distorted octahedral geometry around the central nickel(II) atom. The monothiophosphate moieties show anisobidentate
coordination to the central metal, while the pyridine ligands are in cis positions. These nickel(II) adducts were characterized by elemental analysis, a range of spectroscopic techniques, and magnetic
susceptibility measurement. 相似文献
176.
Dang TT Zhu Y Ghosh SC Chen A Chai CL Seayad AM 《Chemical communications (Cambridge, England)》2012,48(12):1805-1807
An efficient amide synthesis by atmospheric pressure aminocarbonylation using palladium nanoparticles supported on MOF-5 is reported. Interestingly, only 0.5 wt% palladium loading was required to achieve high yields. The catalyst is recyclable and offers negligible palladium leaching. 相似文献
177.
NADH is a coenzyme which plays a central role in cellular growth and metabolism. It is an intracellular fluorophore which
fluoresces at 460 nm when cells are irradiated by 340 nm wavelength of light. The application of NADH+H+ fluorescence measurement for characterization of biomass and its metabolic activity during batch fermentation of 1,3-propanediol
(1,3-PD) using Clostridium diolis was investigated in this study. A linear correlation between net fluorescence and biomass concentration was observed during
both the initial and final phases of 1,3-PD fermentation. This could be used as an on-line indicator of biomass concentration inside the bioreactor thereby eliminating the need for sampling and off-line analysis for establishing biomass concentration during these phases. Also a sharp decline in the NADH+H+ fluorescence value was obtained towards the end of fermentation which could be a significant on-line, in situ signal of substrate
depletion in the bioreactor and therefore possible fresh nutrient feed for enhanced production of 1,3-PD by repetitive and/or
various fed-batch cultivation(s). This is the first report on the use of NADH + H+ fluorescence measurement technique for 1,3-PD fermentation. 相似文献
178.
Subhash P. Chavan Kishor R. Harale Vedavati G. Puranik Rupesh L. Gawade 《Tetrahedron letters》2012,53(21):2647-2650
The formal synthesis of (?)-stemoamide was achieved starting from l-pyroglutamic acid. The key steps used are the allylation using BF3·OEt2, ring closing metathesis, allylic oxidation and a novel epimerization at C8. 相似文献
179.
Jamadar A Duhme-Klair AK Vemuri K Sritharan M Dandawate P Padhye S 《Dalton transactions (Cambridge, England : 2003)》2012,41(30):9192-9201
A series of eight pyruvate-based aroylhydrazones was synthesised and characterised. The reaction of the sodium salts of the aroylhydrazones with one equivalent of copper(II) chloride allowed the isolation of neutral 1:1 complexes in which the hydrazones occupy three basal coordination sites of a square pyramidal Cu(II)-centre, with two solvent molecules completing the coordination sphere. Structural details were obtained through the determination of the crystal structures of two representative pyruvate-based aroylhydrazones and three Cu(II) complexes. The evaluation of the antimycobacterial activity of the sodium salts of the eight pryruvate hydrazones showed that the compounds are essentially inactive in their anionic form. The corresponding neutral Cu(II) complexes, however, exhibit promising antimycobacterial activities if tested under high iron (8 μg Fe per mL) conditions. As observed for the related antimycobacterial agent isoniazid, the activity of the complexes decreases if the M. tuberculosis cells are grown under low iron (0.02 μg Fe per mL) conditions. The Cu(II) complexes may thus have a similar mode of action and may require an iron-containing heme-dependent peroxidase for activation. 相似文献
180.
Rosa E. Diaz Renu Sharma Karalee Jarvis Qinglei Zhang Subhash Mahajan 《Journal of Crystal Growth》2012,341(1):1-6
We report direct observations of the nucleation and early stages of growth of GaN nanowires. The nanowires were formed by exposing Au+Ga droplets to ammonia. The formation process was observed in situ, and controlled in real time using an environmental transmission electron microscope. Observations show that nuclei forms only at thin region of the Au+Ga, following only the VLS mechanism. The droplet–nanowire interface in the initial stages is multi-faceted, and become planar during the growth. Chemical and structural analysis shows that the resulting nuclei are GaN with the wurtzite structure. 相似文献