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921.
922.
E. Rakovský D. Joniakov R. Gyepes P. Schwendt Z. Mi
ka 《Crystal Research and Technology》2005,40(7):719-722
The new compound, [CuCl(phen)2]3H3V10O28 · 7 H2O, was prepared by reaction of an aqueous KVO3 solution (pH 3) with an aqueous solution of CuSO4 · 5 H2O in which 1,10‐phenanthroline (phen) and KCl were added. The crystal structure of the compound was determined, and the proton position in H3V10O283– were calculated by the bond length/bond number method and also determined from difference electron density map. The protons are bound to colinearly arranged μ–OV2 and μ–OV3 groups which is the common protonation type in trihydrogen decavanadates. The structure crystallizes in P1 space group symmetry. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
923.
924.
925.
Two methods are proposed, one for the location of saddle points and one for the calculation of steepest-descent paths on multidimensional surfaces. Both methods are based on a constrained simplex optimization technique that avoids the evaluation of gradients or second derivative matrices. Three chemical reactions of increasing structural complexity are studied within the PRDDO SCF approximation. Predicted properties of reaction hypersurfaces are in good overall agreement with those determined by gradient minimization and gradient following algorithms in connection with various ab initio SCF methods. Computational efforts required by the new procedures are discussed. 相似文献
926.
Zusammenfassung In der vorliegenden Arbeit wird eine Methode zur Retentionsindex-Bestimmung beschrieben, die von einem kubischen Zusammenhang zwischen Bruttoretentionszeit-Differenzen der Referenzhomologen und der Kohlenstoffzahl ausgeht. Hieraus ergeben sich direkt die Nettoretentionszeiten. Der Fehler der Totzeitbestimmung entfällt bei dieser Methode. Mit den so gewonnenen Nettoretentionszeiten erhält man über einen kubischen Zusammenhang zwischen 1g ts=f(C) die Retentionsindices. Extrapolationen und Interpolationen sind über 300 Retentionsindexeinheiten mit einem mittleren Fehler von ±0,02 Retentionsindexeinheiten möglich. Das Verfahren bietet sich für eine automatische Berechnung der I-Werte mittels on-line-Datenverarbeitung an.
Cubic calculation of retention indices without determining the dead-time tm
Summary The method for the calculation of retention indices described here is based on a third order relationship between the logarithm of differences of unadjusted retention times of homologues and the carbon number. From this adjusted retention times are directly calculated. A determination of the dead-time is not necessary thus avoiding the errors connected with this factor. A cubic equation for the logarithm of the adjusted retention time lg ts as a function of carbon number Cn is used for the retention index calculation. Extrapolations and interpolations can be done over a range of 300 index units with an average deviation of ±0.02 i.u.. The method offers the possibility of an automated on-line calculation of retention indices by computer merely on the basis of unadjusted retention times.相似文献
927.
928.
Linjuan Zhang Jing Zhou Jianyong Zhang Jing Su Shuo Zhang Ning Chen Yunpeng Jia Jiong Li Yu Wang Jian-Qiang Wang 《Journal of synchrotron radiation》2016,23(3):758-768
Obtaining structural information of uranyl species at an atomic/molecular scale is a critical step to control and predict their physical and chemical properties. To obtain such information, experimental and theoretical L3‐edge X‐ray absorption near‐edge structure (XANES) spectra of uranium were studied systematically for uranyl complexes. It was demonstrated that the bond lengths (R) in the uranyl species and relative energy positions (ΔE) of the XANES were determined as follows: ΔE1 = 168.3/R(U—Oax)2 ? 38.5 (for the axial plane) and ΔE2 = 428.4/R(U—Oeq)2 ? 37.1 (for the equatorial plane). These formulae could be used to directly extract the distances between the uranium absorber and oxygen ligand atoms in the axial and equatorial planes of uranyl ions based on the U L3‐edge XANES experimental data. In addition, the relative weights were estimated for each configuration derived from the water molecule and nitrate ligand based on the obtained average equatorial coordination bond lengths in a series of uranyl nitrate complexes with progressively varied nitrate concentrations. Results obtained from XANES analysis were identical to that from extended X‐ray absorption fine‐structure (EXAFS) analysis. XANES analysis is applicable to ubiquitous uranyl–ligand complexes, such as the uranyl–carbonate complex. Most importantly, the XANES research method could be extended to low‐concentration uranyl systems, as indicated by the results of the uranyl–amidoximate complex (~40 p.p.m. uranium). Quantitative XANES analysis, a reliable and straightforward method, provides a simplified approach applied to the structural chemistry of actinides. 相似文献
929.
Most thin films have different thermal expansion coefficients from their substrates, thus thermal stresses will be introduced into the films when the temperature is changed during annealing and service. Calculations of these stresses for grains in various crystallographic orientations have been made for seven BCC transition metals Cr, Fe, Mo, Nb, Ta, V and W. Neglecting W, which is isotropic and the stresses are equiaxial and without grain orientation (hkl) dependence, the BCC metals may be grouped into two classes. In the first class (Cr, Mo, Nb and V), the (100)-oriented grains have the largest stresses, while the stresses σ1 and σ2 in other (hkl)-oriented grains decrease linearly with the increase of the angle between (hkl) and (100), and with σ1 〈 σ2 except in (100)- and (lll)-oriented grains. In the second class (Fe and Ta), on the contrary, the (100)-oriented grains have the lowest stresses, and the stresses σ1 and σ2 in other (hkl)-oriented grains increase linearly with the increase of the angle between (hkl) and (100), and with σ1 〉 σ2 except in (100)- and (111)-oriented grains. 相似文献
930.
Ab initio calculations of accurate dissociation energy and analytic potential energy function for the second excited state B1∏ of 7LiH 下载免费PDF全文
The reasonable dissociation limit of the second excited singlet state
B1∏ of 7LiH molecule is obtained. The accurate dissociation energy and
equilibrium geometry of the B1\Pi state are calculated using a
symmetry-adapted-cluster configuration--interaction method in full active space. The
whole potential energy curve for the B1∏ state is obtained over the
internuclear distance ranging from about 0.10nm to 0.54nm, and has a least-square
fit to the analytic Murrell--Sorbie function form. The vertical excitation energy is
calculated from the ground state to the
B1∏ state and compared with previous theoretical results. The
equilibrium internuclear distance obtained by geometry optimization is found to be
quite different from that obtained by single-point energy scanning under the same
calculation condition. Based on the analytic potential energy function, the harmonic
frequency value of the B1∏ state is estimated. A comparison of the
theoretical calculations of dissociation energies, equilibrium interatomic distances
and the analytic potential energy function with those obtained by previous
theoretical results clearly shows that the present work is more comprehensive and in
better agreement with experiments than previous theories, thus it is an improvement
on previous theories. 相似文献