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1.
The object of the present paper is to study quasi-conformally flat weakly Ricci symmetric manifolds.
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2.
Nanocrystalline thin films of copper selenide have been grown on glass and tin doped-indium oxide substrates using chemical method. At ambient temperature, golden films have been synthesized and annealed at 200 °C for 1 h and were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy and UV-vis spectrophotometry techniques, respectively. Cu2−xSe phase was confirmed by XRD pattern and spherical grains of 30 ± 4 - 40 ± 4 nm in size aggregated over about 130 ± 10 nm islands were seen by SEM images. Effect of annealing on crystallinity improvement, band edge shift and photoelectrochemical performance (under 80 mW/cm2 light intensity and in lithium iodide electrolyte) has been studied and reported. Observed p-type electrical conductivity in copper selenide thin films make it a suitable candidate for heterojunction solar cells. 相似文献
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4.
Judit E. Puskas Sam W. P. Chan Kimberley B. McAuley Sohel Shaikh Gabor Kaszas 《Journal of polymer science. Part A, Polymer chemistry》2005,43(22):5394-5413
This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (kp) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, kp = 1.35 × 104 L mol?1 s?1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded kp = 1.01 × 107 L mol?1 s?1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl4 from various laboratories yielded of ΔH ~?25 and ?34.5 kJ/mol for high and low TMPCl/TiCl4 ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ~ ?40 kJ/mol, whereas H2O/TiCl4 in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = ?12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005 相似文献
5.
[reaction: see text] A variety of key precursors to the intramolecular Diels-Alder reaction of furan diene (IMDAF) have been prepared via a very facile 1,4-addition of O-, S-, N-, and C-centered nucleophiles possessing unsaturated tether to beta-furyl nitroethylene. Subsequent IMDAF reaction of the 1,4-adducts, carried out under thermal conditions, provided five- and six-membered carbocycles and heterocycles fused to an easily cleavable oxabicycloheptene moiety. The structure and stereochemistry of the cycloadducts were determined by 2D-NMR experiments and further confirmed by X-ray crystallography. The salient features of the strategy include high degree of stereoselectivity (>80:20) in the cycloaddition, atom and step economy, and generation of multiple chiral centers and functionalities. The feasibility of the cleavage of the oxa bridge in the cycloadducts to afford novel multifunctional molecules has also been demonstrated. 相似文献
6.
This paper discusses the kinetic simulation of TiCl4--coinitiated living carbocationic isobutylene (IB) polymerizations governed by dormant-active equilibria, using a mechanistic model. Two kinetic models were constructed from the same underlying mechanism: one using a commercial simulation software package (Predici®), and the other using the method of moments. Parameter estimation from experimental batch reactor data with Predici yielded a rate constant of propagation kp = 4.64 × 108 ± 2.75 × 108 L/mol s, with no constraints imposed. This agrees with kp data measured with diffusion clock and competition methods, but disagrees with kinetically obtained kp values. Estimation of rate constants with Predici® and the GREG parameter estimation software packages revealed that it was difficult to estimate the complete set of kinetic parameters, due to correlated effects of the parameters on model predictions. Estimability analysis confirmed that some of the strongly correlating parameters could not be estimated simultaneously using the available experimental data. Using kp = 6 × 108 ± 2.75 × 108 L/mol s measured by Mayr, and using starting estimates of other rate constants defined by experimentally observed correlations, yielded the set of rate constants required for the simulations. Both kinetic models yielded good agreement with experimental data, with the exception of Mw values that slightly diverged from the theoretically predicted ‘Mw−Mn = constant’ relationship. This may indicate the occurrence of a minor side reaction. However, the kp/k−1 = 17.5 L/mol average run length calculated from measured and simulated MWD data agrees well with earlier literature values. 相似文献
7.
Yahya S. Alqahtani Sunil S. More Keerthana R. Ibrahim Ahmed Shaikh Anusha K. J. Veena S. More Francois N. Niyonzima Uday M. Muddapur Aejaz A. Khan 《Molecules (Basel, Switzerland)》2022,27(13)
Enzymes that degrade pectin are called pectinases. Pectinases of microbial origin are used in juice clarification as the process is cost-effective. This study screened a pectinase-producing bacterium isolated from soil and identified as Bacillus subtilis 15A B-92 based on the 16S rRNA molecular technique. The purified pectinase from the isolate showed 99.6 U/mg specific activity and 11.6-fold purity. The molecular weight of the purified bacterial pectinase was 14.41 ± 1 kD. Optimum pectinase activity was found at pH 4.5 and 50 °C, and the enzyme was 100% stable for 3.5 h in these conditions. No enzymatic inhibition or activation effect was seen with Fe2+, Ca2+, or Mg2+. However, a slight inhibition was seen with Cu2+, Mn2+, and Zn2+. Tween 20 and 80 slightly inhibited the pectinase, whereas iodoacetic acid (IAA), ethylenediaminetetraacetate (EDTA), urea, and sodium dodecyl sulfate (SDS) showed potent inhibition. The bacterial pectinase degraded citrus pectin (100%); however, it was inactive in the presence of galactose. With citrus pectin as the substrate, the Km and Vmax were calculated as 1.72 mg/mL and 1609 U/g, respectively. The high affinity of pectinase for its substrate makes the process cost-effective when utilized in food industries. The obtained pectinase was able to clarify orange and apple juices, justifying its application in the food industry. 相似文献
8.
S. U. Tekale S. S. Kauthale R. U. Shaikh R. P. Marathe R. B. Nawale R. P. Pawar 《Journal of the Iranian Chemical Society》2014,11(3):717-724
A green and atom-efficient one-pot protocol for the synthesis of some novel α-aminophosphonates using micron-particulate AlN/Al as a new reusable heterogeneous catalyst by the Kabachnik–Fields reaction under solvent-free conditions has been developed. The synthesized α-aminophosphonates were screened for several biological activities. They all were investigated to exhibit moderate to promising antioxidant, anti-inflammatory and cytotoxic properties. 相似文献
9.
An efficient and convenient conversion of oximes to corresponding carbonyl compounds with sodium perborate in glacial acetic acid is reported. 相似文献
10.
A series of donor–acceptor compounds 2–6 have been synthesized, via Knoevenagel condensation reaction (using conventional method, as well as microwave method). The ferrocene unit acts as a donor, conjugated phenyl–acetylene linker act as a π-electron relay unit, and malononitrile, cyanoacetic acid, and indanone groups act as acceptor. The electronic absorption spectra displayed a broad intramolecular charge transfer (CT) band in the visible region (450–650 nm). The electrochemical studies suggest considerable donor–acceptor interaction. The single crystal X-ray structure of 2, and 3 are reported, the structure reveals that 2 is nearly planar compared to 3. The supramolecular structure of 2 exhibits intramolecular C–H–π, and C–H–N interaction, which leads to formation of 2D network, whereas compound 3 shows head to tail dimer formation through C–H–π, and π–π interaction. 相似文献