全文获取类型
收费全文 | 362篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 174篇 |
晶体学 | 2篇 |
力学 | 26篇 |
数学 | 62篇 |
物理学 | 108篇 |
出版年
2022年 | 25篇 |
2021年 | 21篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 30篇 |
2012年 | 28篇 |
2011年 | 15篇 |
2010年 | 20篇 |
2009年 | 6篇 |
2008年 | 7篇 |
2007年 | 10篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 3篇 |
2003年 | 7篇 |
2002年 | 18篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有372条查询结果,搜索用时 15 毫秒
251.
Forced convection heat transfer and pressure drop characteristics of air flow inside a horizontal semi-circular duct are investigated
experimentally. The experiments are carried out on a semi-circular duct of 23 mm inner radius, 2 mm thickness, and 2,000 mm
length within a range of Reynolds number (8,242 ≤ Re ≤ 57,794)., under uniform wall heat flux conditions. The friction factor
is determined by measuring the axial static pressure at different selected axial stations along the semi-circular duct. The
variations of surface and mean air temperatures, local heat transfer coefficient, local Nusselt number, and the friction factor
with the axial dimensionless distance are presented. It is observed that, for a given value of Reynolds number, each of the
local heat transfer coefficient and the friction factor has a relatively high value near the entrance of the semi-circular
duct then it decreases with increasing the dimensionless axial distance until it approaches a nearly constant value at the
fully developed region. Also, it is found that, with increasing the Reynolds number the average heat transfer coefficient
is increased and the friction factor is decreased. Moreover, empirical correlations for the heat transfer coefficient and
friction factor as a function of the Reynolds number are obtained. 相似文献
252.
Ammar Haouat Habiba Rechek Diana C. G. A. Pinto Susana M. Cardoso Mnica S. G. A. Vlega Abdelhamid Boudjerda Artur M. S. Silva Ratiba Mekkiou 《Molecules (Basel, Switzerland)》2022,27(24)
In the present study, two extracts from the aerial parts of the endemic species Satureja hispidula were analyzed for the first time by ultra-high-performance liquid chromatography coupled with a diode array detector and an electrospray mass spectrometer (UHPLC-DAD-ESI/MS) method in order to identify and quantify their phenolic compounds. These extracts’ antioxidant, α-glucosidase and α-amylase inhibitory activities were also evaluated. UHPLC-DAD-ESI/MS allowed the identification of 28 and 20 compounds in the ethanolic and aqueous extracts, respectively; among them, 5-O-caffeoylquinic acid was the most abundant in both extracts. The biological assay results indicate that the species S. hispidula, besides its high antioxidant power, is also potentially useful for inhibiting the α-glucosidase enzyme. In both antioxidant and α-glucosidase inhibitory assays, the aqueous extract exhibited the most promising results, significantly better than the standards used as positive controls. 相似文献
253.
Tarek Gamal Abedelmaksoud Sobhy Mohamed Mohsen Lene Duedahl-Olesen Ammar B. Altemimi Mohamed Mohamed Elnikeety Francesco Cacciola Aberham Hailu Feyissa 《Molecules (Basel, Switzerland)》2022,27(6)
Processing technique and storage conditions are the main factors that affect the phytochemical profile of Not-from-Concentrate (NFC) juice, which could decrease the nutritional and bioactive properties of the corresponding juice. The aim of this study was to evaluate the quality changes that occurred in NFC mango juice after Ohmicsonication (OS) and during storage in comparison to other processing methods such as sonication (S), thermosonication (TS), ohmic heating (OH), and conventional heating (CH). Quality attributes such as polyphenoloxidase (PPO) and pectinmethylesterase (PME) activities, ascorbic acid and hydroxymethyl furfural (HMF) contents, total phenolics, total flavonoids, total carotenoids, electric conductivity, color values and microbial load (total plate count, mold, yeast, and psychrophilic bacteria) were examined. OS and OH treatments demonstrated the highest inactivation of PPO (100%), while CH and TS displaying inhibitions 89% and 90%, respectively and only S treatment exhibited insufficient inactivation of both PPO and microbial load. However, the inhibition of PME followed the order OS (96.5%) > OH (94.9%) > TS (92.5%) > CH (88.5%). The best treatment, with the highest retention of phytochemical contents (ascorbic acid, total carotenoids, antioxidant activity, total flavonoids, and total phenolic content) for NFC mango juice and during storage was obtained with OS treated samples compared to other treatments (in the order from the lowest to highest percentage, OS < OH < TS < CH). Consequently, the results indicated that OS could be applied as a new mild thermal treatment in the production of mango juice with improved quality properties of stored NFC mango juice. 相似文献
254.
Manohar Radhakrishnan Malathy Palayam Ammar B. Altemimi Lakshminarayanan Karthik Gunasekaran Krishnasamy Francesco Cacciola Lakshmanan Govindan 《Molecules (Basel, Switzerland)》2022,27(4)
A 24 kDa leucine-rich protein from ion exchange fractions of Solanum trilobatum, which has anti-bacterial activity against both the Gram-negative Vibrio cholerae and Gram-positive Staphylococcus aureus bacteria has been purified. In this study, mass spectrometry analysis identified the leucine richness and found a luminal binding protein (LBP). Circular dichroism suggests that the protein was predominantly composed of α- helical contents of its secondary structure. Scanning electron microscopy visualized the characteristics and morphological and structural changes in LBP-treated bacterium. Further in vitro studies confirmed that mannose-, trehalose- and raffinose-treated LBP completely inhibited the hemagglutination ability towards rat red blood cells. Altogether, these studies suggest that LBP could bind to sugar moieties which are abundantly distributed on bacterial surface which are essential for maintaining the structural integrity of bacteria. Considering that Solanum triolbatum is a well-known medicinal and edible plant, in order to shed light on its ancient usage in this work, an efficient anti-microbial protein was isolated, characterized and its in vitro functional study against human pathogenic bacteria was evaluated. 相似文献
255.
Mohammad F. R. Fouda Mokhles M. Abd‐Elzaher Rafeek A. Abdelsamaia Ammar A. Labib 《应用有机金属化学》2007,21(8):613-625
Organometallic chemistry and biochemistry have been merged in the last two decades into a new field: bioorganometallic chemistry. This new research area was devoted to the synthesis of new organometallic compounds and their biological and medical effects against some types of diseases, such as cancer and malaria. For several years, the use of ferrocene in bioorganometallic chemistry has been growing rapidly, and several promising applications have been developed since ferrocene is a stable, nontoxic compound and has good redox properties. This review will focus on ferrocenyl compounds which have been biologically evaluated against certain diseases. This area has attracted many researchers due to the promising results of some ferrocene compounds in the medicinal applications. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
256.
We compute the first cohomology spaces
of the Lie superalgebra with coefficients in the superspace of linear differential operators acting on weighted densities on the supercircle S
1|1. The structure of these spaces was conjectured in (Gargoubi et al. in Lett Math Phys 79:5165, 2007). In fact, we prove here
that the situation is a little bit more complicated.
相似文献
257.
Mokhles M. Abd-Elzaher Ammar A. Labib Hanan A. Mousa Samia A. Moustafa Mohamed M. Abdallah 《Research on Chemical Intermediates》2014,40(5):1923-1936
A ferrocenyl ligand 1 was prepared from condensation of 5-methyl-2-furaldehyde with l,l′-diacetylferrocene dihydrazone. This ligand forms 1:1 complexes with cobalt(II), nickel(II), copper(II) and zinc(II) 2–5 in good yield. Characterization of the ligand and complexes was carried out using infrared, nuclear magnetic resonance, mass spectra, electronic absorption, magnetic susceptibility, molar conductivity, and elemental analysis. Cytotoxic activity of the prepared ligand and its complexes were tested against different human cancer cell lines. The results suggested that the synthesized compounds were more potent than the comparative standards drugs used in most cases, whereas they had less activity in the others. 相似文献
258.
We investigate two scheduling problems. The first is scheduling with agreements (SWA) that consists in scheduling a set of jobs non-preemptively on identical machines in a minimum time, subject to constraints that only some specific jobs can be scheduled concurrently. These constraints are represented by an agreement graph. We extend the NP-hardness of SWA with three distinct values of processing times to only two values and this definitely closes the complexity status of SWA on two machines with two fixed processing times. The second problem is the so-called resource-constrained scheduling. We prove that SWA is polynomially equivalent to a special case of the resource-constrained scheduling and deduce new complexity results of the latter. 相似文献
259.
Mourad Cherif Arbi Mgaidi Naceur Ammar Géraldine Vallée Walter Fürst 《Journal of solution chemistry》2000,29(3):255-269
The Raman spectrum of aqueous phosphoric acid has been investigated at apparentconcentrations of 0.3 to 9.7 mol-dm–3 at 25°C. A quantitative analysis hasbeen made over this concentration range after the determination of the responsecoefficients of the H2PO–
4 and H3PO4 species. In the first step, the spectra wereinterpreted assuming that only two species (H2PO–
4 and H3PO4) were present inthe system. The dissociation of phosphoric acid obtained in this case is consistentwith the values Preston and Adams(1) obtained, and which was also found fromRaman spectroscopy. However, a discrepancy exists between the representationsfrom spectra and experimental ones. This discrepancy can be removed if anotherspecies, the anionic dimer H5P2O–
8 is taken into account. Therefore, in the secondstep, a modified interpretation of the spectra, was used to determine theconcentrations of the H2PO–
4, H5P2O–
8, and H3PO4 species and to deduce the correspondingdegree of dissociation of the acid, as well as the speciation of the solutions as afunction of the apparent concentration of phosphoric acid. As in the results Elmoreand co-workers,2 which were deduced from pH measurements, the degree ofdissociation reaches a minimum and then increases significantly for apparentphosphoric acid concentrations greater than 1 mol-dm–3. 相似文献
260.