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21.
An anisotropic elastic-damage model for initially-isotropic materials is presented. The model is based on a pseudo-logarithmic
second-order damage tensor rate. To derive the complete expression of the tangent stiffness entering the rate constitutive
law, various tensor operations and derivatives of tensor functions must be developed. Such derivations have been performed
in compact form. Some useful tensor derivatives and a table of tensor algebra operations are given in Appendix. This note
should interest engineering researchers involved in the development of constitutive models through tensor formalism.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
22.
Fiona Brady John F. Gallagher Carol Murphy 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):365-368
The title compounds, C12H13NO4, are derived from l ‐threonine and dl ‐threonine, respectively. Hydrogen bonding in the chiral derivative, (2S/3R)‐3‐hydroxy‐2‐(1‐oxoisoindolin‐2‐yl)butanoic acid, consists of O—Hacid?Oalkyl—H?O=Cindole chains [O?O 2.659 (3) and 2.718 (3) Å], Csp3—H?O and three C—H?πarene interactions. In the (2R,3S/2S,3R) racemate, conventional carboxylic acid hydrogen bonding as cyclical (O—H?O=C)2 [graph set R22(8)] is present, with Oalkyl—H?O=Cindole, Csp3—H?O and C—H?πarene interactions. The COOH group geometry differs between the two forms, with C—O, C=O, C—C—O and C—C=O bond lengths and angles of 1.322 (3) and 1.193 (3) Å, and 109.7 (2) and 125.4 (3)°, respectively, in the chiral structure, and 1.2961 (17) and 1.2210 (18) Å, and 113.29 (12) and 122.63 (13)°, respectively, in the racemate structure. The O—C=O angles of 124.9 (3) and 124.05 (14)° are similar. The differences arise from the contrasting COOH hydrogen‐bonding environments in the two structures. 相似文献
23.
Knight-Scott J Farace E Simnad VI Siragy HM Manning CA 《Magnetic resonance imaging》2002,20(9):681-689
The (1)H NMR water signal from spectroscopic voxels localized in gray matter contains contributions from tissue and cerebral spinal fluid (CSF). A typically weak CSF signal at short echo times makes separating the tissue and CSF spin-lattice relaxation times (T(1)) difficult, often yielding poor precision in a bi-exponential relaxation model. Simulations show that reducing the variables in the T(1) model by using known signal intensity values significantly improves the precision of the T(1) measurement. The method was validated on studies on eight healthy subjects (four males and four females, mean age 21 +/- 2 years) through a total of twenty-four spectroscopic relaxation studies. Each study included both T(1) and spin-spin relaxation (T(2)) experiments. All volumes were localized along the Sylvian fissure using a stimulated echo localization technique with a mixing time of 10 ms. The T(2) experiment consisted of 16 stimulated echo acquisitions ranging from a minimum echo time (TE) of 20 ms to a maximum of 1000 ms, with a repetition time of 12 s. All T(1) experiments consisted of 16 stimulated echo acquisition, using a homospoil saturation recovery technique with a minimum recovery time of 50 ms and a maximum 12 s. The results of the T(2) measurements provided the signal intensity values used in the bi-exponential T(1) model. The mean T(1) values when the signal intensities were constrained by the T(2) results were 1055.4 ms +/- 7.4% for tissue and 5393.5 ms +/- 59% for CSF. When the signal intensities remained free variables in the model, the mean T(1) values were 1085 ms +/- 19.4% and 5038.8 ms +/- 113.0% for tissue and CSF, respectively. The resulting improvement in precision allows the water tissue T(1) value to be included in the spectroscopic characterization of brain tissue. 相似文献
24.
The 17O NMR spectra for a series of saturated diols were investigated. From these studies both hydroxyl induced substituent chemical shift (SCS) effects of hydroxyl oxygen 17O NMR chemical shifts were determined. In addition, linear correlations between the 17O chemical shift of the hydroxyl oxygen (ROH) and the 13C chemical shift for the methyl group in the corresponding hydrocarbon (RCH3) were obtained. 相似文献
25.
Diana DiBerardino Robert J. Rafac Steven Boone Vladislav P. Gerginov Carol E. Tanner 《Optics Communications》2002,210(3-6):233-243
This paper describes the position-sensitive light-collection system that we use in our fast-beam laser experiments. The collection system consists of fiber-optic bundles whose facets are arranged to accept light emitted from a beam of fluorescent atoms. The flexibility of the fiber bundles allows their use in scanning collection systems with precise position sensitivity. We describe calculations of geometrical collection efficiency using a numerical integration scheme and compare the results with measurements. We also compare the collection efficiencies of the different fiber bundle arrangements that we used as our apparatus evolved with the implementation of various improvements. 相似文献
26.
A straightforward, high-yielding procedure has been developed for the manufacture of substituted vinylphenols from 2- and 4-hydroxybenzaldehydes utilising classical Knoevenagel condensation reaction conditions. 相似文献
27.
Carol Korzeniewski Rukma Basnayake Ganesh Vijayaraghavan Zhengrong Li Shanhong Xu Dominick J. Casadonte Jr. 《Surface science》2004,573(1):100-108
The electrochemical oxidation of CH3OH at nanometer-scale PtRu catalyst materials is reported. Comparisons are made between the properties of a Johnson Matthey (JM) PtRu black sample (50 at.% Ru (XRu ≈ 0.5)) and PtRu particles (2-6 nm, nominally XRu ≈ 0.5) prepared by sonication under anhydrous conditions. Cyclic voltammetry and in situ infrared spectroscopy measurements show the catalysts are active for the oxidation of 0.5 M CH3OH in 0.1 M HClO4 at temperatures between ambient and 70 °C. The sonochemically prepared PtRu sample displayed properties characteristic of bulk PtRu alloys with XRu ≈ 0.5. Evidence for phase separation of Pt and Ru was observed in CO stripping voltammetry from the JM catalyst adsorbed at low metal loadings (20 μg/cm2) on bulk Au electrodes. Per gram of catalyst, the JM material was more active toward CO2 formation and displayed greater resistance to poisoning by adsorbed CO than the sonochemically prepared material during ambient temperature oxidation of 0.5 M CH3OH in 0.1 M HClO4. 相似文献
28.
Liliana Cseh Carol Csunderlik Ingo Pantenburg Gerd Meyer Otilia Costisor 《无机化学与普通化学杂志》2003,629(6):985-988
The complex Co(C14H13NO)2Cl2 with the protonated N‐salicylidene‐p‐toluidine ligand was synthesized from an ethanolic solution of CoCl2·6H2O and N‐salicylidene‐p‐toluidine. The crystal structure was determined from X‐ray single crystal data (monoclinic, space group Cc, a = 1496.2(3) pm, b = 1257.4(4) pm, c = 1544.6(3) pm, β = 115.01(1)°, Z = 4). Co2+ adopts a distorted tetrahedral geometry. The UV‐Vis and IR spectra of the complex are discussed. 相似文献
29.
Takehiko Yamato Carol Pérez-Casas Shofiur Rahman Zeng Xi Mark R. J. Elsegood Carl Redshaw 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):193-197
A novel receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. The tetrathiacalix[4]arene
diamide shows strong intramolecular hydrogen bonding. The binding behavior towards K+ and halides has been examined by 1H NMR titration experiments. 相似文献
30.
Dietmar Seyferth Don P. Duncan Carol K. Haas 《Journal of organometallic chemistry》1979,164(3):305-316
The reaction of 1,1-dimethyl-trans-2,3,-bis(2′,2′-dimethylcyclopropylidene)-1-silirane with S8 gives a mixture of four isomeric products derived from incorporation of one sulfur atom and a cyclopropylcarbinyl-to-butenyl type rearrangement. This silirane reacts with t-butyl mercaptan to give a product of mercaptan addition in which a cyclopropylcarbinyl-to-butenyl rearrangement also has occurred. Hexamethylsilirane reacts with S8 to give 1,1,4,4,5,5-hexamethyl-2,3-dithia-1-silacyclopentane in high yield. These reactions are discussed in terms of free radical mechanisms. 相似文献