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941.
At the single-molecule level, this laboratory has been making direct measurements of polymer diffusion at and near surfaces. Parameters of special interest have been to understand (a) the role of molecular weight, N; (b) the role of surface coverage, which may range from dilute to saturated, and (c) the role of the surface, which may range from hard (a silicon wafer) to soft (a supported lipid bilayer), and (d) the use of external fields to direct the transport of small molecules through narrow surface channels that are one macromolecule thick. 相似文献
942.
The present study examines the feasibility of combining the correlation‐consistent basis sets developed by Dunning and coworkers with the hybrid Hartree–Fock/density functional method B3LYP. Furthermore, extrapolation to the complete basis set (CBS) limit minimizes errors due to the presence of an incomplete basis set and can act as a rigorous test of the limitations of the B3LYP method. Equilibrium geometries, energies, and harmonic vibrational frequencies were determined for a series of well‐studied, yet computationally challenging, small inorganics and their respective ions. The results were then extrapolated to the CBS limit, where applicable, and compared to experiment. It was found that a union between the hybrid Hartree–Fock/density functional B3LYP method and Dunning's augmented correlation‐consistent basis sets gave results that were comparable to molecular orbital methods that explicitly account for electron correlation. Furthermore, the minimum basis set necessary to attain reasonable results for the systems studied was aug‐cc‐pVTZ. Upgrading to the aug‐cc‐pVQZ level and subsequent extrapolation to the CBS limit further improved the overall agreement with the experiment. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 207–216, 1999 相似文献
943.
A new set of effective atomic charges of different conformers of alanine dipeptide is presented. These charges are obtained by fitting the electrostatic potential resulting from the ab initio SCF wave function of the system obtained in a 6-31G basis set. A specific fit procedure is used providing charges weakly dependent on the fit points as well as on the geometry of the molecule. It is shown that these charges retain a reasonable chemical meaning. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 473–482, 1999 相似文献
944.
D. Genest 《Journal of computational chemistry》1999,20(14):1571-1576
A numerical study of the accuracy on the determination of a unique global canonical correlation coefficient C between two groups of random variables is presented as a function of the number of variables of both groups (n and m, respectively), of the sampling size N and of the actual level of correlation C between the groups. The method used to estimate C has been already described (Briki, F.; Genest, D. Biophys Chem 1994, 52, 35–43; and J Biomol Struct Dynam 1995, 12, 1063–1082), and is implemented in the home made program TECOR. To check the accuracy on the estimation of C for given values of n, m, N, and C, samples of the random variables are synthesized (with known C), then TECOR is used to get an estimated value M of the global canonical coefficient, which is compared to the actual value C. Special attention is paid to the application of the method to the analysis from molecular dynamics simulation trajectories of concerted motions of two groups of atoms (not larger than about 20 atoms) in the course of internal deformation of biopolymers. It is found that there is a good agreement between M and C for moderate and high correlation (C≥0.35), provided that at least about 2000 configurations are stored during the molecular dynamics simulation. If C is smaller than 0.35, the method can overestimate its value if the number of configurations is not increased, especially for larger groups. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1571–1576, 1999 相似文献
945.
Navzer D. Sachinvala Othman A. Hamed David L. Winsor Walter P. Niemczura Karol Maskos Dharnidhar V. Parikh Wolfgang Glasser Ulli Becker Eugene J. Blanchard Noelie R. Bertoniere 《Journal of polymer science. Part A, Polymer chemistry》1999,37(21):4019-4032
Tri-O-methylcellulose was prepared from partially O-methylated cellulose and its chemical shifts (1H and 13C), and proton coupling constants were assigned using the following NMR methods: (1) One-dimensional 1H and 13C spectra of the title compound were used to assign functional groups and to compare with literature data; (2) double quantum filtered proton–proton correlation spectroscopy (1H, 1H DQF-COSY) was used to assign the chemical shifts of the network of 7 protons in the anhydroglucose portion of the repeat unit; (3) the heteronuclear single-quantum coherence (HSQC) spectrum was used to establish connectivities between the bonded protons and carbons; (4) the heteronuclear multiple-bond correlation (HMBC) spectrum was used to connect the hydrogens of the methyl ethers to their respective sugar carbons; (5) the combination of HSQC and HMBC spectra was used to assign the 13C shifts of the methyl ethers; (6) all spectra were used in combination to verify the assigned chemical shifts; (7) first-order proton coupling constants data (JH,H in Hz) were obtained from the resolution-enhanced proton spectra. The NMR spectra of tri-O-methylcellulose and other cellulose ethers do not resemble the spectra of similarly substituted cellobioses. Although the 1H and 13C shifts and coupling constants of 2,3,6-tri-O-methylcellulose closely resemble those of methyl tetra-O-methyl-β-D -glucoside, there are differences with regard to the chemical shifts and the order of appearances of the resonating nuclei of the methyl ether appendages and the proton at position 4 in the pyranose ring. H4 in tri-O-methylcellulose is deshielded by the acetal system comprising the β-1→4 linkage, and it resonates downfield. H4 in the permethylated glucoside is not as deshielded by the equitorial O-methyl group at C4, and it resonates upfield. The order of appearance of the 1H and 13C resonances in the spectra of the tri-O-methylcellulose repeat unit (from upfield to downfield) are H2 < H3 < H5 < H6a < H3a < H2a < pro R H6B < H4 < pro S H6A ≪ H1 and C6a < C3a < C2a < C6 < C5 < C4 < C2 < C3 ≪ C1, respectively. Close examination of the pyranose ring coupling constants of the repeat unit in tri-O-methylcellulose supports the 4C1 arrangement of the glucopyranose ring. Examination of the proton coupling constants about the C5-C6 bond (J5,6A and J5,6B) in the nuclear Overhauser effect difference spectra revealed that the C6 O-methyl group is predominantly in the gauche gauche conformation about the C5-C6 bond for the polymer in solution. © 1999 John Wiley & Sons, Inc.* J Polym Sci A: Polym Chem 37: 4019–4032, 1999 相似文献
946.
Chorng‐Shyan Chern Cheng‐Kang Lee Chia‐Che Ho 《Journal of polymer science. Part A, Polymer chemistry》1999,37(10):1489-1499
Stable chitosan‐modified polymethyl methacrylate (PMMA) latex particles were prepared by using 2,2′‐azobis(2‐amidinopropane) dihydrochloride (V‐50) as the cationic initiator. The polymerization rate (Rp) is controlled by the V‐50 concentration ([V‐50]) and Rp is less sensitive to the chitosan concentration ([C]) used in the synthesis work. The reaction system follows Smith–Ewart Case III kinetics due to the relatively large particles produced. The zeta potential data show that the isoelectric point (pI) of the latex particles is 10.7. The amounts of V‐50 (CV‐50) and chitosan (Cc) ultimately incorporated into the particles correlate reasonably well with [V‐50] and [C], respectively. At pH 7, the quantity of the negatively charged bovine serum albumin (BSA, pI = 4.8) adsorbed on the positively charged chitosan‐free particles (Q) via the electrostatic interaction increases with increasing CV‐50. However, Q is relatively insensitive to changes in Cc. This result implies that only the outermost region of the hairy chitosan‐modified particles is available for adsorption of the relatively large protein species. Colloidal stability shows a significant influence on the BSA adsorption process. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1489–1499, 1999 相似文献
947.
Seung‐Yeop Kwak Soo Gyung Jung Young Seo Yoon Dae Woo Ihm 《Journal of Polymer Science.Polymer Physics》1999,37(13):1429-1440
In the present article, some new events on the surface morphology of the aromatic polyamide thin‐film‐composite (TFC) membranes were demonstrated in conjunction with their inherent chemical nature. In addition, the detailed, quantitative understanding of the microscopic surface features was shown to be essential in controlling the water permeability and eventually developing the high performance membranes. The surface roughness and the surface area were mainly affected by the existence or nonexistence of the crosslinking and/or the free amide groups not pertinent to the formation of the hydrogen bonding, which in turn contributed to the water permeability. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1429–1440, 1999 相似文献
948.
949.
Dr. Mauricio Rodríguez-Mayorga Dr. Eloy Ramos-Cordoba Prof. Xabier Lopez Prof. Miquel Solà Prof. Jesus M. Ugalde Dr. Eduard Matito 《ChemistryOpen》2019,8(4):411-417
We analyze the Coulomb hole of Ne from highly-accurate CISD wave functions obtained from optimized even-tempered basis sets. Using a two-fold extrapolation procedure we obtain highly accurate results that recover 97 % of the correlation energy. We confirm the existence of a shoulder in the short-range region of the Coulomb hole of the Ne atom, which is due to an internal reorganization of the K-shell caused by electron correlation of the core electrons. The feature is very sensitive to the quality of the basis set in the core region and it is not exclusive to Ne, being also present in most of second-row atoms, thus confirming that it is due to K-shell correlation effects. 相似文献
950.
Chen-Huan Wu 《Physics letters. A》2019,383(6):550-557
We theoretically investigate the current–current correlation of the two-dimensional (2D) parabolic Dirac system in hexogonal lattice. The analytical expressions of the random phase approximation (RPA) susceptibility, Ruderman–Kittel–Kasuya–Yosida (RKKY) Hamiltonian, and the diamagnetic orbital susceptibility in noninteracting case base on the density–density or current–current correlation function are derived and quantitatively analyzed. In noninteracting case, the dynamical polarization within RPA, and spin transverse susceptibility as well as the RKKY interaction (when close to the half-filling) are related to the current–current response in the 2D parabolic Dirac systems. Both the cases of anisotropic dispersion and isotropic dispersion are discussed. 相似文献