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1.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
2.
Flow visualization of chemical flocs in a simple extensional flow field reveals two distinct mechanisms for their breakage: splitting into a relatively small number of daughter fragments whose sizes are comparable to the parent flocs, along with continual disintegration by erosion to produce extremely fine particles from the extremities of the parent floc along the axis of extension. In turbulent flow, these two mechanisms still occur, although the kinematics of flow are more complex. This work presents a formulation of the population balance equation that governs the floc size distribution in turbulent flow, incorporating both the splitting and erosion mechanisms discussed above. Experiments were conducted in which floc size distributions of dilute suspensions are measured by a combination of techniques, including computerized optical scanning of photographs and pulse height analysis of signals from a light blockage transducer. The experimentally determined size distributions are then fit to those computed from the population balance equation, using constrained nonlinear least squares. This yields best values of certain coefficients that appear in the governing equation, providing a strategy to obtain a data base to promote deeper theoretical analysis. The method is demonstrated by analyzing data for kaolin-Fe(OH)3 flocs in aqueous suspensions. 相似文献
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Pandya SU Garçon C Chavant PY Py S Vallée Y 《Chemical communications (Cambridge, England)》2001,(18):1806-1807
The vinylzinc reagents derived from hydrozirconation of alkynes and transmetallation add readily to nitrones to yield pure (E)-N-allylhydroxylamines; some of these rearrange into O-allylhydroxylamines. 相似文献
5.
The 2,4-dichlorophenoxy acetic acid (2,4-D) is used as a systemic herbicide to control broadleaf weeds in wheat, corn, range land/pasture land, sorghum, and barley. In this study, a fast and efficient method is developed by selection of modified extraction apparatus and high-performance liquid chromatography (HPLC)-UV conditions for the determination of 2,4-D in soil samples. The method is applied to the study of soil samples collected from the agricultural field. The herbicide is extracted from soil samples by acetonitrile in a modified Soxhlet apparatus. The advantages of the apparatus are that it uses small volume of organic solvent, reduced time of extraction, and better recovery of the analyte. The extract is filtered using a very fine microfiber paper. The total extract is concentrated in a rotatory evaporator, dried under ultrahigh pure N2, and finally reconstituted in 1 mL of acetonitrile. HPLC-UV at 228 nm is used for analysis. The herbicide is identified and quantitated using the HPLC system. The method is validated by the analysis of spiked soil samples. Recoveries obtained varied from 85% to 100% for spiked soil samples. The limit of quantitation (LOQ) and the limit of detection (LOD) are 0.010 and 0.005 parts per million (ppm), respectively, for spiked soil samples. The LOQ and LOD are 0.006 and 0.003 ppm for unspiked soil samples. The measured concentrations of 2,4-D in spiked soil samples are between 0.010 and 0.020 ppm with an average of 0.016 +/- 0.003 ppm. For unspiked soil samples it is between 0.006 ppm and 0.012 ppm with an average of 0.009 +/- 0.002 ppm. The measured concentrations of 2,4-D in soil samples are generally low and do not exceed the regulatory agencies guidelines. 相似文献
6.
A solvent extraction separation of uranium, in the presence of thorium, cerium and lanthanides with a new calix[4]resorcinarene bearing eight hydroxamic acid groups (C4RAHA) is described. Quantitative extraction of uranium is possible in ethyl acetate solution of C4RAHA at pH 8.0. The lambda(max) and molar absorptivity (varepsilon) for uranium is 356nm and 8352Lmol(-1)cm(-1). The Binding ratio of uranium with C4RAHA as evaluated by Job's method is 4:1. The system obeys Beer's law over the range 0.075-6.0mugml(-1) of uranium with Sandell sensitivity 0.0284mugcm(-2). A preconcentration factor of 142 was achieved by directly aspirating the extract for GF-AAS measurements. The two-phase stability constant evaluated at 25 degrees C for uranium is 15.91. The complexation is characterized by favorable enthalpy and entropy changes. A liquid membrane transport study of uranium was carried out from source to the receiving phase under controlled conditions and a mechanism of transport is proposed. Uranium has been determined in standard and environmental samples. 相似文献
7.
V. K. Jain R. A. Pandya S. G. Pillai Y. K. Agrawal P. H. Kanaiya 《Journal of Analytical Chemistry》2007,62(2):104-112
In the present paper, solid-phase extractive preconcentration and separation of lanthanum(III) and cerium(III) using calix[4]arene-o-vanillinsemicarbazone
immobilized on a polymeric matrix, a Merrifield peptide resin, is proposed. The diamino derivative of calix[4]arene was first
diazotized and coupled with o-vanillinsemicarbazone to obtain a new “upper-rim” functionalized calix[4]arene-o-vanillinsemicarbazone.
It was then covalently linked to the Merrifield peptide resin and characterized by FT-IR and elemental analysis. Quantitative
studies were carried out by spectrophotometry and ICP-AES with a relative standard deviation of 1.7%. Various physicochemical
parameters like pH, concentration of eluting agents, flow rate, total sorption capacity, metal-ligand stoichiometry, exchange
kinetics, preconcentration factor, distribution coefficient, breakthrough capacity, resin stability, and effect of electrolytes
and associated metal ions have been studied. The uptake and stripping of these metal ions on the resin was fast, indicating
a better accessibility of La(III) and Ce(III) towards the chelating sites. Detection limits corresponded to three times the
standard deviation of the blank (3σB) and amounted to 3.05 and 6.86 μg/L, along with preconcentration factors of 153 and 133 for La(III) and Ce(III), respectively.
The robustness of the procedure is demonstrated by the recoveries obtained (>97.5%) for La(III) and Ce(III) in the presence
of several cations and anions. The proposed method was satisfactorily applied to the separation of La(III) and Ce(III) from
each other and also from U(VI) and Th(IV) by sequential acidic elution and varying pH. The validity of the method was tested
by analyzing these metal ions in monazite sand and standard geological materials.
The text was submitted by the authors in English. 相似文献
8.
Patel Chirag N. Kumar Sivakumar Prasanth Pandya Himanshu A. Rawal Rakesh M. 《Molecular diversity》2021,25(1):421-433
Molecular Diversity - The pandemic outbreak of the Corona viral infection has become a critical global health issue. Biophysical and structural evidence shows that spike protein possesses a high... 相似文献
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