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401.
Wojciech Zielenkiewicz Oleg V. Kulikov Iwona Kulis-Cwikla 《Journal of solution chemistry》1993,22(11):963-973
The enthalpies of dilution and densities of aqueous solutions of 12-crown-4, 15-crown-5, 18-crown-6, 1,10-diaza-18-crown-6 and cryptand (222) were measured at 25°C. The excess enthalpies and enthalpic coefficients of solute-solute interactions were calculated by the McMillan-Mayer theory formalism. Values for the apparent molar volumes at infinite dilution were determined by extrapolation. The contributions of the-CH2CH2O-group to values of h2 and to the limiting partial molar volume were calculated for the series of crown ethers studied. It is concluded that the hydrophobic hydration and the hydrophobic solute-solute interaction are predominant in the solutions investigated. 相似文献
402.
Iwona Tomaszkiewicz 《Thermochimica Acta》2004,420(1-2):33-36
Studies by fluorine bomb calorimetry that lead to the evaluation of thermodynamic properties of group-III nitrides are described. Results of the studies of the standard molar enthalpy of formation ΔfHm0 of two BN polymorphic forms and initial experiments on the combustion of GaN are presented. 相似文献
403.
Joyce Chau Iwona Garlicka Catherine Wolf J. Teh 《Journal of Thermal Analysis and Calorimetry》2007,90(3):713-719
The Modulated Differential Scanning Calorimeter (MDSC) technique, using TA Q1000 instrument, has been applied as a tool to
study the reversible and non-reversible heat flow characteristics of a wide range of polyethylenes. It was found that the
heat flow characteristic is dependent upon the heating rates and modulation period used in the test. By using a set of standard
test conditions, MDSC was found to be useful in studying the effect of previous thermal processing conditions, additive effects,
and also the density, MI, type of comonomer, and molecular architecture. 相似文献
404.
Badis M Tomaszkiewicz I Joly JP Rogalska E 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6259-6267
Four new chiral, amphiphilic crown ethers differing by the hydrophobic tailgroups were synthesized, and their capacity to recognize enantiomeric amino acids was examined using Langmuir films. Surface pressure and surface potential measurements performed on the subphases containing L or D enantiomers of alanine, valine, phenylglycine, and tryptophane indicate that the crown ethers forming the monolayer interact with the amino acids. The effects observed are ascribed to the formation of host-guest complexes. The differences in the magnitude of the effects measured show that the crown ethers are capable of discriminating between different amino acids as well as the enantiomers. Our results demonstrate that the structure of the monolayer plays a decisive role in the molecular recognition process including chiral recognition. 相似文献
405.
406.
Richard S. Herrick Iwona Wrona Glenn Jones Janet Shaw 《Journal of organometallic chemistry》2004,689(25):4848-4855
The title compounds were prepared in good yield by heating ester protected amino acids (H-l-Ala-OEt, H-β-Ala-OEt, H-L-Val-OMe, H-GABA-OMe, H-L-Asp(OMe)-OMe, H-L-Met-OMe) with Re(CO)5Cl in the presence of pyridine-2-carboxaldehyde. The resulting novel complexes contain a bound, conjugated diimine ligand with a pendant ester group. All compounds were characterized by 1H and 13C NMR, IR and UV-Vis spectroscopy. Compounds prepared from chiral amino esters give diastereomers because of the presence of a stereogenic metal center. Syntheses using Re(CO)5Br as starting material were discontinued because of metathesis involving the chloride in the amino ester · HCl salts and the metal bromide. Photophysical studies on Re(CO)3Cl(pyca-β-Ala-OEt), 2, show that it is luminescent in organic solvents in air at room temperature. The crystal structures of 2 and Re(CO)3Cl(pyca-l-Asp(OMe)-OMe), 5, were determined. 相似文献
407.
Comparison of antibody--antigen interactions on collagen measured by conventional immunological techniques and atomic force microscopy 总被引:2,自引:0,他引:2
Avci R Schweitzer M Boyd RD Wittmeyer J Steele A Toporski J Beech I Arce FT Spangler B Cole KM McKay DS 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):11053-11063
We have developed a means of using atomic force microscopy (AFM) to repeatedly localize a small area of interest (4 x 4 microm(2)) within a 0.5-cm(2) area on a heterogeneous sample, to obtain and localize high-resolution images and force measurements on nonideal samples (i.e., samples that better reflect actual biological systems, not prepared on atomically flat surfaces). We demonstrate the repeated localization and measurement of unbinding forces associated with antibody--antigen (ab--ag) interactions, by applying AFM in air and in liquid to visualize and measure polyclonal ab--ag interactions, using chicken collagen as a model system. We demonstrate that molecular interactions, in the form of ab--ag complexes, can be visualized by AFM when secondary antibodies are conjugated to 20-nm colloidal gold particles. We then compare those results with established immunological techniques, to demonstrate broader application of AFM technology to other systems. Data from AFM studies are compared with results obtained using immunological methods traditionally employed to investigate ab--ag interactions, including enzyme-linked immunosorbent assay, immunoblotting, and in situ immunofluorescence. Finally, using functionalized AFM tips with a flexible tether [poly(ethylene glycol) 800] to which a derivatized antibody was attached, we analyzed force curve data to measure the unbinding force of collagen antibody from its antigen, obtaining a value of approximately 90 +/- 40 pN with a MatLab code written to automate the analyses of force curves obtained in force--volume mode. The methodology we developed for embedded collagen sections can be readily applied to the investigation of other receptor--ligand interactions. 相似文献
408.
Radisic D Bowen KH Dabkowska I Storoniak P Rak J Gutowski M 《Journal of the American Chemical Society》2005,127(17):6443-6450
The anionic base pairs of adenine and thymine, (AT)(-), and 9-methyladenine and 1-methylthymine, (MAMT)(-), have been investigated both theoretically and experimentally in a complementary, synergistic study. Calculations on (AT)(-) found that it had undergone a barrier-free proton transfer (BFPT) similar to that seen in other dimer anion systems and that its structural configuration was neither Watson-Crick (WC) nor Hoogsteen (HS). The vertical detachment energy (VDE) of (AT)(-) was determined by anion photoelectron spectroscopy and found to be in agreement with the VDE value predicted by theory for the BFPT mechanism. An AT pair in DNA is structurally immobilized into the WC configuration, in part, by being bonded to the sugars of the double helix. This circumstance was mimicked by methylating the sites on both A and T where these sugars would have been tied, viz., 9-methyladenine and 1-methylthymine. Calculations found no BFPT in (MAMT)(-) and a resulting (MAMT)(-) configuration that was either HS or WC, with the configurations differing in stability by ca. 2 kcal/mol. The photoelectron spectrum of (MAMT)(-) occurred at a completely different electron binding energy than had (AT)(-). Moreover, the VDE value of (MAMT)(-) was in agreement with that predicted by theory. The configuration of (MAMT)(-) and its lack of electron-induced proton transfer are inter-related. While there may be other pathways for electron-induced DNA alterations, BFPT in the WC/HS configurations of (AT)(-) is not feasible. 相似文献
409.
13C cross-polarization magic angle spinning (CP/MAS) NMR data for 2,2,5,7,8-pentamethylchroman-6-ol (2), 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox c) (3) and its acetate (4), 2-methoxy-2,2,5,7,8-pentamethylchroman-6-ol (5), 2-hydroxy-2,2,5,7,8-pentamethylchroman-6-ol (6) and 2,2,5,7,8-pentamethylchroman (7) are reported. A deshielding of 7.7 ppm for the carboxylic carbon was observed in solid Trolox due to formation of intermolecular hydrogen bonds within cyclic dimers. Such crystal packing permits effective cross-polarization and fast relaxation (short T1rho(H)). The impact of the proton concentration on the CP dynamics is reflected by the longer T(CP) and T1rhoH for Trolox-d2 (deuterated at mobile proton sites). The calculated GIAO RHF shielding constants are sensitive to intramolecular effects: rotation around the C-6-O bond (changes of sigma up to 8 ppm) and conformation at C-2. 相似文献
410.
Anusiewicz I Berdys-Kochanska J Czaplewski C Sobczyk M Daranowski EM Skurski P Simons J 《The journal of physical chemistry. A》2005,109(1):240-249
In an attempt to shed light on the mechanism by which gaseous samples of negatively charged oligonucleotides undergo extremely slow (i.e., over 1-1000 s) charge loss, we have carried out molecular dynamics simulations on an oligonucleotide anion, T(5)(3-), containing five thymine, deoxyribose, and phosphate units in which the first, third, and fifth phosphates are negatively charged. The study is aimed at determining the rate at which an electron is detached from such a trianion by way of an internal Coulomb repulsion induced event. In this process, the intrinsic 5.0-5.1 eV electron binding strength of each phosphate site is reduced by the repulsive Coulomb potentials of the other two negative sites. As geometrical fluctuations cause the distances among the three negative phosphate sites to change, this causes the Coulomb repulsion energies at these sites to fluctuate. Once the Coulomb potential at any phosphate site exceeds ca. 5 eV, the electron on that site is able to undergo autodetachment. Although such an electron must tunnel through a barrier to escape, it is shown that the tunneling rate is not the rate-limiting step in electron loss; instead, it is the rate at which geometrical fluctuations cause the Coulomb potentials to exceed 5 eV that determines the rate of electron loss. Because these rates are extremely slow, special techniques had to be introduced to allow results of dynamics simulations on more flexible models of T(5)(3-) to be extrapolated to predict the behavior of the actual T(5)(3-). 相似文献