全文获取类型
收费全文 | 589篇 |
免费 | 37篇 |
国内免费 | 11篇 |
专业分类
化学 | 495篇 |
晶体学 | 4篇 |
力学 | 2篇 |
数学 | 58篇 |
物理学 | 78篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 22篇 |
2020年 | 18篇 |
2019年 | 41篇 |
2018年 | 43篇 |
2017年 | 24篇 |
2016年 | 37篇 |
2015年 | 38篇 |
2014年 | 34篇 |
2013年 | 84篇 |
2012年 | 37篇 |
2011年 | 53篇 |
2010年 | 26篇 |
2009年 | 28篇 |
2008年 | 25篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 16篇 |
2004年 | 21篇 |
2003年 | 4篇 |
2002年 | 15篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有637条查询结果,搜索用时 93 毫秒
111.
Dwyer JT Holden J Andrews K Roseland J Zhao C Schweitzer A Perry CR Harnly J Wolf WR Picciano MF Fisher KD Saldanha LG Yetley EA Betz JM Coates PM Milner JA Whitted J Burt V Radimer K Wilger J Sharpless KE Hardy CJ 《Analytical and bioanalytical chemistry》2007,389(1):37-46
This article illustrates the importance of having analytical data on the vitamin and mineral contents of dietary supplements
in nutrition studies, and describes efforts to develop an analytically validated dietary supplement ingredient database (DSID)
by a consortium of federal agencies in the USA. Preliminary studies of multivitamin mineral supplements marketed in the USA
that were analyzed as candidates for the DSID are summarized. Challenges are summarized, possible future directions are outlined,
and some related programs at the Office of Dietary Supplements, National Institutes of Health are described. The DSID should
be helpful to researchers in assessing relationships between intakes of vitamins and minerals and health outcomes. 相似文献
112.
Ammar S Mahjoub MA Charfi N Skandarani I Chekir-Ghedira L Mighri Z 《Chemical & pharmaceutical bulletin》2007,55(3):385-388
A new skeleton of an O-heteroside natural substance named zinolol, the first representative of a new class of aminated hydroxyhydroquinone, has been isolated from the whole plant Anagallis monelli. Its structure has been established by one and two dimensional NMR spectroscopic procedures. Antioxidant, mutagenic, antimutagenic activities were realised and positive results were recorded. 相似文献
113.
Shahbaz Ali Muneeba Kousar Qin Xin Dragan Pamu
ar Muhammad Shazib Hameed Rabia Fayyaz 《Entropy (Basel, Switzerland)》2021,23(11)
In this research article, we motivate and introduce the concept of possibility belief interval-valued N-soft sets. It has a great significance for enhancing the performance of decision-making procedures in many theories of uncertainty. The N-soft set theory is arising as an effective mathematical tool for dealing with precision and uncertainties more than the soft set theory. In this regard, we extend the concept of belief interval-valued soft set to possibility belief interval-valued N-soft set (by accumulating possibility and belief interval with N-soft set), and we also explain its practical calculations. To this objective, we defined related theoretical notions, for example, belief interval-valued N-soft set, possibility belief interval-valued N-soft set, their algebraic operations, and examined some of their fundamental properties. Furthermore, we developed two algorithms by using max-AND and min-OR operations of possibility belief interval-valued N-soft set for decision-making problems and also justify its applicability with numerical examples. 相似文献
114.
Meryem Saidi Phuoc Hoang Ho Pankaj Yadav Fabrice Salles Clarence Charnay Luc Girard Leila Boukli-Hacene Philippe Trens 《Molecules (Basel, Switzerland)》2021,26(24)
This paper reports on the comparison of three zirconium-based metal organic frameworks (MOFs) for the capture of carbon dioxide and ethanol vapour at ambient conditions. In terms of efficiency, two parameters were evaluated by experimental and modeling means, namely the nature of the ligands and the size of the cavities. We demonstrated that amongst three Zr-based MOFs, MIP-202 has the highest affinity for CO2 (−50 kJ·mol−1 at low coverage against around −20 kJ·mol−1 for MOF-801 and Muc Zr MOF), which could be related to the presence of amino functions borne by its aspartic acid ligands as well as the presence of extra-framework anions. On the other side, regardless of the ligand size, these three materials were able to adsorb similar amounts of carbon dioxide at 1 atm (between 2 and 2.5 µmol·m−2 at 298 K). These experimental findings were consistent with modeling studies, despite chemisorption effects, which could not be taken into consideration by classical Monte Carlo simulations. Ethanol adsorption confirmed these results, higher enthalpies being found at low coverage for the three materials because of stronger van der Waals interactions. Two distinct sorption processes were proposed in the case of MIP-202 to explain the shape of the enthalpic profiles. 相似文献
115.
116.
Hoseini L Roozbeh J Sagheb M Karbalay-Doust S Noorafshan A 《Micron (Oxford, England : 1993)》2009,40(2):226-230
Anabolic androgenic steroids are widely used by athletes for increasing their muscle mass. These drugs are also used by some patients with chronic renal disease. But the effect of these drugs on the renal structure has received less attention. To investigate which parts of the kidney are affected by these drugs, mice kidneys were studied stereologically after injection of nandrolone decanoate (ND), an anabolic androgenic steroid. The treated group received nandrolone decanoate intraperitoneally (solved in olive oil) in doses of 3mg/kg of body weight and administered in one, two and three doses, respectively, in the first, second and third week of treatment. The mice in the control group received an olive oil solution. One week after the last injection, the mice were anaesthetized and their kidney removed. The analysis of data revealed that the weight of kidney was increased approximately 30% (p < or = 0.006) and its volume increased approximately 25% (p < or = 0.02) in ND treated mice in comparison with the control group. The volume of the cortex increased in ND treated animals approximately 44% (p < or = 0.006). Proximal convoluted tubules (PCT) and distal convoluted tubules (DCT) volume increased approximately 25% (p < or = 0.02) and approximately 68% (p < or = 0.02) in ND treated mice. The volume of glomeruli, other ducts, connective tissues, vessels and the length of PCT, DCT, collecting and Henle's ducts and vessels did not show significant differences. CONCLUSION: ND can increase the volume of the renal cortex and its two main parts, i.e. PCT and DCT in mice. 相似文献
117.
Samia Mahouche Nejib Mekni Leila Abbassi Philippe Lang Christian Perruchot Mohamed Jouini Fayna Mammeri Mireille Turmine Hatem Ben Romdhane Mohamed M. Chehimi 《Surface science》2009,603(21):3205-3211
Bis-alkynylated oligoethyleneglycol (OEG) and a monopropargyl-functionalized perfluorinated ethylene glycol (FEG) were clicked to azide-functionalized gold surface (Au–N3) at room temperature via the well known 1,3 cycloaddition click chemical reaction. The Au–N3 substrate was obtained by nucleophilic attack of NaN3 on gold substrates modified by the electrochemical reduction of the , +N2–C6H4–CH2Br diazonium salt. This electrochemical process yields aryl layer-modified gold of the type Au–C6H4–CH2Br (hereafter Au–Br). The untreated and modified gold plates were examined by XPS, PMIRRAS and contact angle measurements. XPS brought evidence for electrografting aryl layers by the detection of Br3d; azide functionalization by the increase of the N/Br atomic ratio; and click reaction of OEG with Au–N3 by the increase of O/N ratio. In addition, the perfluorinated plate (Au-FEG) exhibited F1s and characteristic C1s peaks from -(CF2)7- chain and terminal CF3. Infra red spectroscopy (PMIRRAS) evidenced (i) grafting N3 to Au–Br; (ii) characteristic stretching bands, from ethylene glycol units, C–O–C (1100–1300 cm−1); CF2 (1000–1100 cm−1) and CF3 (1100–1350 cm−1) from FEG grafts; and (iii) suppression of alkynyl bands from OEG and FEG after surface click chemistry. More importantly, PMIRRAS results support an important bridging of the bispropargyl oligoethylene glycol at the gold surface. Water drop contact angles were found to be 48.7° and 83.0° for Au-OEG and Au-FEG, respectively, therefore highlighting the control over the hydrophilic/hydrophobic character of the clicked substrate.This work shows that clicking macromolecules to grafted, diazonium salt-derived aryl layers is a novel, simple and valuable approach for designing robust, functional surface organic coatings. 相似文献
118.
A novel Brönsted acidic room temperature ionic liquid (1‐H‐3‐methyl‐imidazolium bisulfate) is found to catalyze efficiently the acetylation of a wide rang of alcohols as well as phenols with acetic anhydride in good to excellent yields at 50°C under solvent‐free conditions. Products are easily isolated by extraction with ether and the protocol is mild and green, compared to the existing method based on toxic solvents. 相似文献
119.
Gabriella Leo Laura Cartechini Piero Pucci Antonio Sgamellotti Gennaro Marino Leila Birolo 《Analytical and bioanalytical chemistry》2009,395(7):2269-2280
The identification of proteinaceous components in paintings remains a challenging task for several reasons. In addition to
the minute amount of sample available, complex and variable chemical composition of the paints themselves, possible simultaneous
presence of several binders and contaminants, and degradation of the original materials due to aging and pollution are complicating
factors. We proposed proteomic strategies for the identification of proteins in binders of paintings that can be adapted to
overcome the requirements and difficulties presented by specific samples. In particular, we worked on (1) the development
of a minimally invasive method based on the direct tryptic cleavage of the sample without protein extraction; (2) the use
of microwave to enhance the enzymatic digestion yield, followed by the analysis of the peptide mixtures by nanoLC-MS/MS with
electrospray ionization (ESI). Moreover, as an additional tool to tackle the problem of contaminating proteins, we exploited
the possibility of generating an exclusion list of the mass signals that in a first run had been fragmented and that the mass
spectrometer had to ignore for fragmentation in a subsequent run. The methods, tested on model samples, allowed the identification
of milk proteins in a sample from paintings attributed to Cimabue and Giotto, thirteenth-century Italian masters, decorating
the vaults of the upper church in the Basilica of St. Francis in Assisi, Italy. 相似文献
120.
Davarani SS Najafi NM Ramyar S Masoumi L Shamsipur M 《Chemical & pharmaceutical bulletin》2006,54(7):959-962
Electrochemical oxidation of catechol and some 3-substituted catechols (1a--c) has been studied in the presence of 2-chloro-5,5-dimethyl-1,3-cyclohexanedione (3) in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the quinones derived from catechols (1a--c) participate in a Michael addition reaction with 2-chloro-5,5-dimethyl-1,3-cyclohexanedione (3) with consumption of only two electrons per molecule of (1a--c) to from the corresponding benzoforans (10a--c). The electrochemical synthesis of benzofurans has been successfully performed at a carbon rod electrode and in an undivided cell with high yields and purity. 相似文献