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101.
Chen Q Saltiel C Manickavasagam S Schadler LS Siegel RW Yang H 《Journal of colloid and interface science》2004,280(1):91-97
The aggregation behavior of colloidal single-walled carbon nanotubes (SWNT) in dilute aqueous suspensions was investigated using a novel light scattering measurement technique. The aggregation of SWNT in three suspensions was examined: (1) nanotubes after acid treatment; (2) as-received nanotubes stabilized by a nonionic surfactant; and (3) acid-treated nanotubes with nonionic surfactant. Continuous light scattering measurements of the SWNT suspensions (probing the 38-436 nm length scale) made over two weeks showed that the nanotubes in each sample formed networks with fractal-like structures. The as-received nanotubes were stable over the measurement period, while the acid-treated nanotube suspension showed greater dispersion variability over time, yielding looser structures at large length scales and more compact structures at smaller length scales. The addition of surfactant to the acid-treated suspension significantly enhanced nanotube dispersion. 相似文献
102.
J.B. Goodenough A. Hamnett B.J. Kennedy R. Manoharan S.A. Weeks 《Journal of Electroanalytical Chemistry》1988,240(1-2)
A novel Pt + Ru electrode material is shown to be highly active for the direct electro-oxidation of methanol in H2SO4 solutions and to show very little tendency to poison. X-ray photoelectron spectroscopy of this material before use as an anode showed that the ruthenium is oxidised and that there is an important surface concentration of oxidised platinum. After prolonged use as a methanol-oxidation anode, the concentration of oxidised platinum is somewhat increased and there is no evidence for any Pt-CO or Pt2 = CO species; rather adsorbed formate is present. These data are consistent with Ru acting as a promoter of active surface oxygen. Dispersion of the Pt and Ru on a pure carbon support gives a much greater performance per gram of precious metal; however, the initial increase in overpotential is greater by over 100 mV. The differences in the catalytic behaviour of these two materials is discussed, and the importance of competing reactions is considered. 相似文献
103.
Pattanayek R Sethaphong L Pan C Prhavc M Prakash TP Manoharan M Egli M 《Journal of the American Chemical Society》2004,126(46):15006-15007
Chemical modification of nucleic acids at the 2'-position of ribose has generated antisense oligonucleotides (AONs) with a range of desirable properties. Electron-withdrawing substituents such as 2'-O-[2-(methoxy)ethyl] (MOE) confer enhanced RNA affinity relative to that of DNA by conformationally preorganizing an AON for pairing with the RNA target and by improving backbone hydration. 2'-Substitution of the ribose has also been shown to increase nuclease resistance and cellular uptake via changes in lipophilicity. Interestingly, incorporation of either 2'-O-[2-(methylamino)-2-oxoethyl]- (NMA) or 2'-O-(N-methylcarbamate)-modified (NMC) residues into AONs has divergent effects on RNA affinity. Incorporation of 2'-O-NMA-T considerably improves RNA affinity while incorporation of 2'-O-NMC-T drastically reduces RNA affinity. Crystal structures at high resolution of A-form DNA duplexes containing either 2'-O-NMA-T or 2'-O-NMC-T shed light on the structural origins of the surprisingly large difference in stability given the relatively minor difference in chemistry between NMA and NMC. NMA substituents adopt an extended conformation and use either their carbonyl oxygen or amino nitrogen to trap water molecules between phosphate group and sugar. The conformational properties of NMA and the observed hydration patterns are reminiscent of those found in the structures of 2'-O-MOE-modified RNA. Conversely, the carbonyl oxygen of NMC and O2 of T are in close contact, providing evidence that an unfavorable electrostatic interaction and the absence of a stable water structure are the main reasons for the loss in thermodynamic stability as a result of incorporation of 2'-O-NMC-modified residues. 相似文献
104.
Sugandha Singhal Pankaj Khanna Siva S. Panda Leena Khanna 《Journal of heterocyclic chemistry》2019,56(10):2702-2729
Benzimidazole is a heterocyclic moiety of immense importance as it acts as a primary “biolinker” in diverse synthetic routes to obtain bioactive compounds. Substituted benzimidazoles are known to possess a varied range of pharmacological applications, namely, anti‐cancer, anti‐diabetic, anti‐inflammatory, and antiviral like anti‐HIV and anti‐fungal. A number of reviews covering the important aspects of benzimidazoles such as pharmacological activities, SAR studies, and well‐known methods of synthesis have appeared in the literature. However, green synthetic methods particularly using transition metal (TM) catalysts and their nanoparticles, although being more viable and extensively applied by researchers in the present scenario, have not been exclusively and expansively reviewed. Besides this, the vital precursors required for knitting the skeleton of benzimidazole are mainly o‐aryldiamines. The conventional synthesis generally involved the condensation of these diamines with carbonyl/carboxylic acid derivatives either via high temperature heating or via adding strong acids, mostly resulting in poor yields or mixtures. However, recent trends are replacing these conditions by mild and green conditions through TM catalysts. Therefore, the current review emphasizes on the recent trends adopted in the synthesis of benzimidazoles using condensation reaction of o‐phenylenediamines and various aldehydes/ester/amide/alcohols with TM in a catalytic role in nanoform and under environmentally benign green conditions. 相似文献
105.
An Iron‐Catalyzed Cascade Approach to Benzo[b]carbazole Synthesis Followed by 1,4‐Sulfonyl Migration
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Siva Senthil Kumar Boominathan Gopal Chandru Senadi Dr. Jaya Kishore Vandavasi Dr. Jeff Yi‐Fu Chen Prof. Dr. Jeh‐Jeng Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3193-3197
A simple and straightforward approach was developed to construct 5H‐benzo[b]carbazole derivatives by iron catalysis in a cascade sequence. The notable features of this work include an atom‐economical cascade sequence, unprecedented 1,4‐sulfonyl migration, tolerance of a variety of functional groups, good yields, and an economical catalytic system. 相似文献
106.
107.
Mingqing Xiao Yuan Lin James H. Myatt R. Chris Camphouse Siva S. Banda 《Journal of Applied Mathematics and Computing》2006,22(1-2):67-82
In this paper, we present a finite difference method for the implementation of the rotation of a circular cylinder in the incompressible flow field by solving the two-dimensional unsteady Navier-Stokes equations. The approach is to use staggered grid method so that the accuracy and order of convergence of the associated algorithms can be maintained. The proposed method is easy to be implemented and is effective. A set of simulations for the flow dynamics is provided to show the computational results. 相似文献
108.
Siva Kumar Talluri 《Tetrahedron》2007,63(39):9758-9763
An efficient enantioselective synthesis of (R)-selegiline has been achieved by two routes, via proline-catalyzed α-aminooxylation as well as α-amination of phenylpropanaldehyde as the key step. 相似文献
109.
A well‐defined triazole functionalized porous triazine based polymers act as solid heterogeneous catalyst after incorporating palladium oxide nanoparticles (PdO@TTAS) have been synthesized and thoroughly characterized by various techniques such as, FT‐IR, UV‐DRS, solid state 13C CP‐MAS, XPS, powder X‐ray diffraction, TGA, SEM and TEM analysis has been detailed illustrated. It is important to note that synthesized catalytic performance for carbonylation of aryl halides (X = I, Br) with EDC.HCl (N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride), and formic acid was found to be an effective CO source in the presence of triethylamine as a base and DMF as a solvent medium at 80 °C for about 3 hr. The PdO@TTAS catalyst exhibits superior catalytic performance and along with good yield (up to 90%). Moreover, studying the heterogeneity and reusability of the environmentally friendly solid catalyst can be easily separated by simple filtration and then recycled for several times. In this reaction method, we avoided ligand, additive, promoters and CO gas, due to additional problem arise by using gaseous CO, highly toxic greenhouse gases and high pressurized reaction setup. 相似文献
110.
Prabu Manoharan R. S. K. Vijayan Nanda Ghoshal 《Journal of computer-aided molecular design》2010,24(10):843-864
The ability to identify fragments that interact with a biological target is a key step in FBDD. To date, the concept of fragment
based drug design (FBDD) is increasingly driven by bio-physical methods. To expand the boundaries of QSAR paradigm, and to
rationalize FBDD using In silico approach, we propose a fragment based QSAR methodology referred here in as FB-QSAR. The FB-QSAR methodology was validated
on a dataset consisting of 52 Hydroxy ethylamine (HEA) inhibitors, disclosed by GlaxoSmithKline Pharmaceuticals as potential anti-Alzheimer agents. To address the issue of target selectivity, a major confounding factor
in the development of selective BACE1 inhibitors, FB-QSSR models were developed using the reported off target activity values.
A heat map constructed, based on the activity and selectivity profile of the individual R-group fragments, and was in turn
used to identify superior R-group fragments. Further, simultaneous optimization of multiple properties, an issue encountered
in real-world drug discovery scenario, and often overlooked in QSAR approaches, was addressed using a Multi Objective (MO-QSPR)
method that balances properties, based on the defined objectives. MO-QSPR was implemented using Derringer and Suich desirability
algorithm to identify the optimal level of independent variables (X) that could confer a trade-off between selectivity and activity. The results obtained from FB-QSAR were further substantiated
using MIF (Molecular Interaction Fields) studies. To exemplify the potentials of FB-QSAR and MO-QSPR in a pragmatic fashion,
the insights gleaned from the MO-QSPR study was reverse engineered using Inverse-QSAR in a combinatorial fashion to enumerate
some prospective novel, potent and selective BACE1 inhibitors. 相似文献