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201.
Sets of electrooptical parameters (eop's), suitable for longer n-paraffins and less constrained than those already used to fit the IR intensities of CH4 and C2H6 and their deuterated derivatives, are presented and discussed. The technique adopted in the least-squares refinement of eop's from experimental data is discussed in detail. 相似文献
202.
Sergio A. Guerrero Carlos M. Sanabría Alirio Palma Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(4):408-415
(2R*,4S*)‐Methyl 2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐benz[b]azepine‐2‐carboxylate, C12H13NO3, (I), and its reduction product (2R*,4S*)‐methyl 4‐hydroxy‐2,3,4,5‐tetrahydro‐1H‐benz[b]azepine‐2‐carboxylate, C12H15NO3, (II), both crystallize as single enantiomers in the space group P212121, while the hydrolysis product (2RS,4SR)‐4‐hydroxy‐2,3,4,5‐tetrahydro‐1H‐benz[b]azepine‐2‐carboxylic acid, C11H13NO3, (III), and the lactone (2RS,5SR)‐8‐(trifluoromethoxy)‐5,6‐dihydro‐1H‐2,5‐methanobenz[e][1,4]oxazocin‐3(2H)‐one, C12H10F3NO3, (IV), both crystallize as racemic mixtures in the space group P21/c. The molecules of compound (IV) are linked into centrosymmetric R22(10) dimers by N—H...O hydrogen bonds, and those of compound (I) are linked into chains by C—H...π(arene) hydrogen bonds. A combination of O—H...O and O—H...N hydrogen bonds links the molecules of compound (III) into sheets containing equal numbers of R44(14) and R44(26) rings, and a combination of C—H...π(arene) hydrogen bonds and three‐centre O—H...(N,O) hydrogen bonds links the molecules of compound (II) into a three‐dimensional framework structure. Comparisons are made with some related compounds. 相似文献
203.
Sergio Rosselli 《Tetrahedron》2004,60(40):8791-8800
Examination of 1H and 13C NMR spectra allows the establishment of rules for assigning the correct configuration at C-15 of 15-hydroxy-, 15-methoxy-, 15-ethoxy-hexahydrofurofuran neoclerodane diterpenoids. The structure of several diterpenoids has been assigned or ammended. 相似文献
204.
Rory?H.?Uibel Emily?C.?Heider Jennifer?L.?Gasser Joel?M.?HarrisEmail author Edward?M.?Eyring Sergio?Petrucci 《Journal of solution chemistry》2005,34(5):499-514
Advances have been made recently in broadening the accessible ultrasonic absorption frequency range and improving the detectability of minor species present in solution using Raman spectroscopy. Development of chemometric techniques in these areas needs to keep pace with the improvement of these experimental methods. Refinements in the analysis of ultrasonic and Raman data based on multivariable least squares and factor analysis, respectively, are examined to investigate the kinetics of zinc thiocyanate complex formation in water. Analysis of ultrasonic absorption relaxation spectra verified that the observed process in aqueous Zn(SCN)2 involves substitution of water from the first coordination shell of Zn2+. Use of a multivariable least-squares error surface is described that enhances the reliability of assigned frequencies of ultrasonic absorption maxima. Factor analysis of Raman scattering data provided direct evidence that at least four complex species, such as Zn(SCN)+ and Zn(SCN)2, are simultaneously present in the aqueous zinc thiocyanate solutions. 相似文献
205.
Sergio R. Calvo 《Surface science》2007,601(1):165-171
We investigate the reactivity of various PtxPdy combinations (with x + y = 10 and various x:y ratios) towards the adsorption of specific intermediates of the oxygen reduction, using the B3PW91 hybrid density functional theory. The reactivity is shown to be not only sensitive to the composition of the cluster, but also to the atomic distribution. The calculations indicate that two different ensembles: one ordered and one randomly mixed, with overall composition Pt3Pd7 are thermodynamically more favorable than pure Pt10 for the oxygen reduction reaction. The reasons for this behavior are clearly explained in terms of the atomic and electronic distribution, which makes the Pd atoms to act as electron donors both to Pt atoms and to the adsorbates, thus the reactivity of the Pd atoms in such environment becomes intermediate between Pt and Pd. Moreover, it is found that in a mixed Pt3Pd7 state the electronic distribution makes the average atom more similar to Pt than to Pd, whereas in an ordered Pt3Pd7 cluster, the average atom is more similar to Pd than to Pt. 相似文献
206.
Gómez-Graña S Hubert F Testard F Guerrero-Martínez A Grillo I Liz-Marzán LM Spalla O 《Langmuir : the ACS journal of surfaces and colloids》2012,28(2):1453-1459
Gold nanorods in aqueous solution are generally surrounded by surfactants or capping agents. This is crucial for anisotropic growth during synthesis and for their final stability in solution. When CTAB is used, a bilayer has been evidenced from analytical methods even though no direct morphological characterization of the precise thickness and compactness has been reported. The type of surfactant layer is also relevant to understand the marked difference in further self-assembling properties of gold nanorods as experienced using 16-EO(1)-16 gemini surfactant instead of CTAB. To obtain a direct measure of the thickness of the surfactant layer on gold nanorods synthesized by the seeded growth method, we coupled TEM, SAXS, and SANS experiments for the two different cases, CTAB and gemini 16-EO(1)-16. Despite the strong residual signal from micelles in excess, it can be concluded that the thickness is imposed by the chain length of the surfactant and corresponds to a bilayer with partial interdigitation. 相似文献
207.
208.
Eleonora Freire Sergio Baggio Juan Carlos Muoz Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):m299-m301
The structure of the title compound, [Ni(ths)(bbip)(dmf)]·H2O [ths is thiosulfate, S2O3; bbip is 2,6‐bis(1H‐benzimidazol‐2‐yl)pyridine, C21H13N5; and dmf is dimethylformamide, C3H7NO], is monomeric, with the nickel ion octahedrally surrounded by an N,N′,N′′‐tridentate bbip molecule, an S,O‐bidentate ths molecule and an O‐monodentate dmf molecule. The H atoms of the hydration water molecule and the amino groups of bbip are involved in hydrogen bonding and determine a spatial organization of broad layers parallel to (001), which are connected by weak interactions. 相似文献
209.
Markus Dbbelin Garciela Arias Iraida Loinaz Irantzu Llarena David Mecerreyes Sergio Moya 《Macromolecular rapid communications》2008,29(11):871-875
In this communication, polyanionic poly(potassium 3‐sulfopropyl methacrylate) (PSPM) brushes were switched from hydrophilic to hydrophobic by exchange of the counter cations. First, poly(potassium 3‐sulfopropyl methacrylate) brushes were grown by means of atom transfer radical polymerization (ATRP) from thiol monolayers of initiating ω‐mercaptoundecyl bromoisobutyrate and mixed monolayers of thiol initiator and 1‐undecanothiol (blank thiol) attached to gold surfaces. The kinetics of the polymerization reaction were followed by means of the quartz microbalance technique with dissipation (QCM‐D). The collapse of PSPM brushes in the presence of cationic surfactants like quaternary ammonium salts (tetraethylammonium bromide, hexadecyltrimethylammonium bromide) and imidazolium salts (1‐dodecyl‐3‐methylimidazolium bromide, 1H,1H,2H,2H‐perfluoro‐1‐decyl‐3‐methylimidazolium bromide) was shown by QCM‐D. Water contact angle measurements proved that the wettability of the surface could be tuned reversibly from hydrophilic values (<30 °) to hydrophobic ones (>85 °).
210.
Sergio Caucao Gabriel N. Gatica Ricardo Oyarzúa 《Numerical Methods for Partial Differential Equations》2019,35(1):295-324
In this article, we consider an augmented fully mixed variational formulation that has been recently proposed for the nonisothermal Oldroyd–Stokes problem, and develop an a posteriori error analysis for the 2‐D and 3‐D versions of the associated mixed finite element scheme. More precisely, we derive two reliable and efficient residual‐based a posteriori error estimators for this problem on arbitrary (convex or nonconvex) polygonal and polyhedral regions. The reliability of the proposed estimators draws mainly upon the uniform ellipticity of the bilinear forms of the continuous formulation, suitable assumptions on the domain and the data, stable Helmholtz decompositions, and the local approximation properties of the Clément and Raviart–Thomas operators. On the other hand, inverse inequalities, the localization technique based on bubble functions, and known results from previous works are the main tools yielding the efficiency estimate. Finally, several numerical results confirming the properties of the a posteriori error estimators and illustrating the performance of the associated adaptive algorithms are reported. 相似文献