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731.
732.
In this work, we examine the strength of various types of individual hydrogen bond (HB) in mixed methanol-water MnWm, (n+m=2 to 7) clusters, with an aim to understand the relative order of their strength, using our recently proposed molecular tailoring-based approach (MTA). Among all the types of HB, it is observed that the OM−H…OW HBs are the strongest (6.9 to 12.4 kcal mol−1). The next ones are OM−H…OM HBs (6.5 to 11.6 kcal mol−1). The OW−H…OW (0.2 to 10.9 kcal mol−1) and OW−H…OM HBs (0.3 to 10.3 kcal mol−1) are the weakest ones. This energetic ordering of HBs is seen to be different from the respective HB energies in the dimer i. e., OM−H…OM (5.0 to 6.0 kcal mol−1)>OW−H…OM (1.5 to 6.0 kcal mol−1)>OM−H…OW (3.8 to 5.6 kcal mol−1)>OW−H…OW (1.2 to 5.0 kcal mol−1). The plausible reason for the difference in the HB energy ordering may be attributed to the increase or decrease in HB strengths due to the formation of cooperative or anti-cooperative HB networks. For instance, the cooperativity contribution towards the different types of HB follows: OM−H…OW (2.4 to 8.6 kcal mol−1)>OM−H…OM (1.3 to 6.3 kcal mol−1)>OW−H…OW (−1.0 to 6.5 kcal mol−1)>OW−H…OM (−1.2 to 5.3 kcal mol−1). This ordering of cooperativity contribution is similar to the HB energy ordering obtained by the MTA-based method. It is emphasized here that, the interplay between the cooperative and anti-cooperative contributions are indispensable for the correct energetic ordering of these HBs. 相似文献
733.
Divya Chopra Marianna Kontopoulou Dimitris Vlassopoulos Savvas G. Hatzikiriakos 《Rheologica Acta》2002,41(1-2):10-24
We investigated the thermo- rheological behavior of high glass transition, high molecular weight and small dynamic asymmetry
blends of poly(styrene-co-maleic anhydride) (SMA) and poly (methyl methacrylate) (PMMA) with varying amounts of maleic anhydride (MA) content, namely
8 wt%, 14 wt% and 32 wt%, in the SMA component. The phase separation (binodal) temperature of each blend was determined rheologically
using a combination of dynamic frequency and temperature sweeps in parallel plate geometry; it was marked by a change in slope
of the elastic modulus and the occurrence of a peak in tan δ in temperature sweeps. Failure of the time-temperature superposition
principle and observation of two peaks in the Cole-Cole plots corroborated these findings. The blends displayed lower critical
solution temperature (LCST) behavior with the critical temperatures exhibiting a non-monotonic dependence on the MA content.
From rheological and thermal measurements it was concluded that SMA/PMMA blends containing 14% MA were more miscible than
those containing 8% or 32% MA, a finding attributed to the compositional dependence of the interplay between SMA-SMA and SMA-PMMA
interactions in the different samples. MA also influenced the dynamic asymmetry and pretransitional concentration fluctuations.
The phase diagrams corresponding to each blend were modeled using a two-parameter temperature dependent interaction parameter,
based on the concept of generalized Gibbs free energy of mixing. The fitted values of interaction parameter were in good agreement
with values calculated explicitly using the Flory-Huggins theory.
Received: 16 February 2001 Accepted: 11 July 2001 相似文献
734.
Alkene‐Directed N‐Attack Chemoselectivity in the Gold‐Catalyzed [2+2+1]‐Annulations of 1,6‐Enynes with N‐Hydroxyanilines
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Dr. Deepak B. Huple Bhanudas D. Mokar Prof. Dr. Rai‐Shung Liu 《Angewandte Chemie (International ed. in English)》2015,54(49):14924-14928
Kinetically unstable nitrones are generated from gold‐catalyzed reactions of 1,6‐enynes with N‐hydroxyanilines, and subsequently trapped by tethered alkenes to furnish [2+2+1]‐annulations. Our experimental data reveal that such nitrones arise from atypical N‐attack chemoselectivity that is triggered by tethered alkenes to facilitate the key protodeauration reaction. 相似文献
735.
Indrajeet J. Barve Chan‐Yu Chen Deepak B. Salunke Prof. Wen‐Sheng Chung Prof. Chung‐Ming Sun 《化学:亚洲杂志》2012,7(7):1684-1690
The present article describes the design and synthesis of new biprivileged molecular scaffolds with diverse structural features. Commercially available, simple heterocyclic building blocks such as 4‐fluoro‐3‐nitrobenzoic acid, 2‐chloro‐3‐nitrobenzoic acid, and indoline were utilized for the synthesis of the novel heterocycles. Pictet–Spengler‐type condensation was used as a key step to construct tetracyclic indolo‐benzodiazepines and indolo‐quinoxalines linked with substituted benzimidazoles. Analysis of single crystals of representative compounds showed that these molecular skeletons have the potential to present various substituents with distinct three‐dimensional orientations. 相似文献
736.
This study is the first to focus on the potential use of carbon nanotube (CNT) scaffolds as enzyme immobilization substrates for analytical purposes. Besides all the well-known advantages of CNT, three-dimensional scaffolds can significantly increase the amount of enzymes adsorbed per unit area, preserve the catalytic activity of the adsorbed molecules, and allow effective exposure to substrates present in the adjacent medium. Additionally, our results indicate that the sensitivity of analytical probes based on enzyme-loaded CNT scaffolds is proportional to the thickness of the scaffold providing 3-fold sensitivity improvements with respect to the control surfaces. 相似文献
737.
Dheer Singh Anju Chopra Mitra Bhanu Patel Amarjit Singh Sarpal 《Chromatographia》2011,74(1-2):121-126
Although the concentration of nitrogen compounds in crude oil is relatively low, they can become more concentrated in petroleum distillates and poison the catalysts used in refining processes. They cause undesirable deposits, color formation and odor in products; they also contribute to air pollution and some are highly carcinogenic. The poisoned catalyst becomes deactivated for hydrodesulfurization and unable to remove sulfur from middle distillates. In order to understand the effect on catalytic processes, it is desirable to identify the nitrogen compounds in various petroleum distillates. This paper compares the nitrogen species profiles in different petroleum distillates using a nitrogen chemiluminescence detector. In addition, four different petroleum distillate samples from different refineries were analyzed to find the variation in their nitrogen profiles. The nitrogen compounds in petroleum distillate samples were identified as anilines, quinolines, indoles, and carbazoles and their alkyl derivatives. Quantitation was carried out against known reference standards. The quantitative data were compared to the total nitrogen content determined by elemental analysis. 相似文献
738.
B. C. Joshi Bhawna Khulbey Deepak Upreti Charu Chandra Dhaundiyal 《Indian Journal of Physics》2010,84(4):405-412
A study of energy transfer from samarium to erbium ions in zinc phosphate glass has been performed for a range of donor (1.0
wt% fixed) and acceptor concentrations ranging from 0.2 wt% to 1.2 wt%. The intensity of emission spectra of Sm3+ ions in the presence of Er3+ ions shows an overall decrease, thereby suggesting a non radiative energy transfer from Sm3+ ions to Er3+ ions. The interaction mechanism between the donor and acceptor ions is found to be mainly electric dipole-dipole in nature.
The parameters required for the quantitative study of energy transfer e.g. energy transfer efficiencies, transfer probabilities,
critical transfer distances have been computed. 相似文献
739.
Bapurao B. Shingate Braja G. Hazra Deepak B. SalunkeVandana S. Pore 《Tetrahedron letters》2011,52(45):6007-6010
A variety of Δ8(9)-lanosterol derivatives were converted into 7,11-dienones using t-butyl hydroperoxide in the presence of ruthenium chloride (RuCl3) in good yields. 相似文献
740.