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911.
H. Wetzel und S. Peter 《Fresenius' Journal of Analytical Chemistry》1962,190(1):208-212
Zusammenfassung Die Methode der Ringpapierchromatographie unter Anwendung von UV-Licht als einfachem Hilfsmittel zur Unterscheidung organischen Materials wurde hinsichtlich der Möglichkeit überprüft, zahlenmäßig greifbare Ergebnisse zu erhalten, die eine sichere Klassifizierung und Unterscheidung bituminöser Stoffe ermöglichen. Es wurde gefunden, daß für eine gute Reproduzierbarkeit der Ergebnisse die gleichmäßige Aufgabe der Lösung auf das Papier wesentlich ist. Ein äußerst gleichmäßiger Zufluß, der mit der Sauggeschwindigkeit des Papieres korrespondiert, konnte mit Hilfe eines Mikrodosiergerätes, das von einem Motor gleichmäßig angetrieben wurde, erzielt werden. Die erhaltenen Flächen für die verschiedenen Substanzgruppen stellen ein relatives, gut reproduzierbares Maß für die Zusammensetzung der untersuchten Proben dar.Herrn Prof. Dr. W. Fischer zum 60. Geburtstag gewidmet. 相似文献
912.
Some aspects of the transition probability P(, ) between states , on unital *-algebras are discussed. It is shown that P increases under the action of any stochastic linear map T, i.e., P(T, T)P(, ). Some properties of P are derived in starting from a recently-proved characterization of the quantity in question. 相似文献
913.
Milan Melník Peter Mikuš 《Phosphorus, sulfur, and silicon and the related elements》2020,195(5):367-370
AbstractIn this review, the structural data of monomeric platinum(II) complexes with inner coordination spheres of Pt(η2-P2L)(SiL)2, Pt(η2-P2L)(η2-Si2L) and Pt(η2-P,SiL)2 are classified and analyzed. These complexes crystallize in three crystal systems: monoclinic (8 examples), triclinic (4 examples) and orthorhombic (4 examples). Distorted square-planar environments about the Pt(II) atoms are built up by combination of homobi-P,P with two monodentate Si donor ligands; homobi-PP with homo-Si,Si donor ligands, or heterobi-P,Si donor ligands. The chelating ligands create metallacycles with the following angles: 65.0° (SiOSi) < 83.1° (SiC2Si) < 85.2° (PC2P) < 88.8° (SiSi2Si)). The mean Pt-P and Pt-Si bond distances in Pt(η2-P2L)·(SiL)2 complexes are 2.319 and 2.365?Å; in Pt(η2-P2L)(η2-Si2L) the values are 2.316 and 2.360?Å. The complex [Pt{η2-Me2P(C2B10H10)SiMe2}2] exists in two isomeric forms, a monoclinic cis- and a triclinic trans-isomer. The structural data are compared and discussed with the complexes of inner coordination spheres: Pt(η2-P2L)(XL)2 (X?=?O, N, CN, BL, Cl, SL, SeL, Br, or I) and Pt(η2-P2L)(η2-X2L) (X?=?OL, NL, SL or SeL). 相似文献
914.
In the Claus process hydrogen sulfide reacts to elemental sulfur. Because the Claus reaction is thermodynamically limited, sulfur compounds are still present in Claus tailgas. To avoid air pollution, the tailgas has to be treated.Alfa- and gamma-alumina are being used either as a catalyst or as a support for an active component in the Claus process and some tailgas treatment processes. In order to elucidate the mechanism of the Claus reaction, the adsorption of sulfur dioxide on both of the above aluminas was investigated using Fourier transform infrared spectroscopy.Different adsorbed species displaying a different heat of adsorption were detected. A broad band near 3500 cm–1 is associated with the basic hydroxyl groups. This band is assigned to a hydrogen bond between the surface of alumina and a bisulfite species. As bisulfite species are reactive towards hydrogen sulfide, we assume that bisulfite species are active intermediates on alumina in the Claus reaction. 相似文献
915.
Reed M. Izatt Gypzy C. Lindh Ronald L. Bruening Peter Huszthy John D. Lamb Jerald S. Bradshaw James J. Christensen 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(6):739-745
The macrocycle-mediated fluxes of several alkali metal cations have been determined in a H2O-CH2Cl2-H2O liquid membrane system. Water-insoluble proton-ionizable macrocycles of the pyridono type were used. The proton-ionizable feature allows the coupling of cation transport to reverse H+ transport. This feature offers promise for the effective separation and/or concentration of alkali metal ions with the metal transport being driven by a pH gradient. A counter anion in the source phase is not co-transported. The desired separation of a particular metal ion involves its selective complexation with the macrocycle, subsequent extraction from the aqueous phase to the organic phase, and exchange for H+ at the organic phase-receiving phase interface. Factors affecting transport which were studied include ring size, source phase pH, and receiving phase pH. Lithium was transported at a rate higher than that of the other alkali metals in both single and competitive systems using a 15-crown-5 pyridono carrier. 相似文献
916.
Leslie M. Connaughton J. Peter Hershey Frank J. Millero 《Journal of solution chemistry》1986,15(12):989-1002
The densities of the major sea salts (NaCl, Na2SO4, MgCl2, and MgSO4) have been measured from 25 to 95°C and to saturation. These results have been combined with literature data and fitted to equations of the form $$\Delta d = Am{\text{ }} + {\text{ }}Bm^{3/2} {\text{ }} + {\text{ }}Cm^2 {\text{ }} + {\text{ }}Dm^{5/2} $$ where Δd=d?do (do is the density of water) and A, B, and C, etc., are polynomial functions of temperature. The standard deviations of the fits were better than ±50×10?6 g-cm?3 for all the salts from 0 to 95°C and to saturation. The apparent molal volumes V? of the salts have been fitted to the equations of Pitzer. The infinite dilution values of V? were in good agreement with literature data, provided the results were not overfit. The large deviations of V? for MgSO4 from additivity as a function of concentration were attributed to the formation of MgSO4 ion pairs. 相似文献
917.
The thermal expansion of VN1?x was determined from measurements of the lattice parameters in the temperature range of 298–1000 K and in the composition range of VN0.707–VN0.996. Within the accuracy of the results the expansion of the lattice parameter with temperature is not dependent on the composition. The lattice parameter as a function of composition ([N]/[V]=0.707?0.996) and temperature (298–1000 K) is given by $$\begin{gathered} a([N]/[V],T) = 0.38872 + 0.02488([N]/[V]) - \hfill \\ - (1.083 \pm 0.021) \cdot 10^{ - 4} T^{1/2} + (6.2 \pm 0.1) \cdot 10^{ - 6} T. \hfill \\ \end{gathered} $$ . The coefficient of linear thermal expansion as a function of temperature (in the same range) is given by $$\alpha (T) = a([N]/[V],T)^{ - 1} [( - 5.04 \pm 0.01) \cdot 10^5 T^{ - 1/2} + (6.2 \pm 0.1) \cdot 10^{ - 6} ].$$ . The average linear thermal expansion coefficient is $$\alpha _{av} = 9.70 \pm 0.15 \cdot 10^{ - 6} K^{ - 1} (298 - 1 000K).$$ . The data are compared with those of several fcc transition metal nitrides collected and evaluated from the literature. 相似文献
918.
The phenomenon of enthalpy-entropy compensation in gas chromatography is examined. Using 53 probe solutes that span a wide range in size (dispersive interaction), dipolarity, hydrogen-bond-donor and hydrogen-bond-acceptor strength, enthalpy-entropy compensation is not observed, while for probe solutes within a homologous series enthalpy-entropy compensation is observed as predicted by the linear salvation energy relationship methodology. 相似文献
919.
Mitchell RH Ward TR Chen Y Wang Y Weerawarna SA Dibble PW Marsella MJ Almutairi A Wang ZQ 《Journal of the American Chemical Society》2003,125(10):2974-2988
The syntheses of several new simple negative, a simple positive, and multiple negative photochromes containing the dihydropyrene-cyclophanediene photochromic system are described. The photo-openings of the negative photochromes, the [e]-annelated benzo (7), naphtho (9), anthro (11), furano (19), and triphenyleno (15) derivatives of the parent 2,7-di-tert-butyl-trans-10b,10c-dimethyl-dihydropyrene (5), as well as its 4,5-dibromo derivative (13), are described to give the corresponding cyclophanedienes, as well as their photoclosures and thermal closures back to the dihydropyrenes. These are compared to the results obtained for the positive photochrome dibenzo[e,l]dihydropyrene (21) and to the bis(dihydropyreno)chrysene (44) and the (dihydropyrenobenzo)(benzo)metacyclophanediene (47) photochromes, which have more than one photochromic switch present and thus have more than a simple "on-off" state. Thermodynamic data are obtained for the thermal closing reactions. The anthrodihydropyrene (12) has the fastest thermal closing (tau(1/2) = 20 min), while the furanodihydropyrene (19') has the slowest (tau(1/2) = 63 h) at 46 degrees C. An electrochemical readout of the state of the switch is demonstrated for the benzodihydropyrene (7). 相似文献
920.
Ring strain energies (RSEs) are predicted using homodesmotic reactions at the B3LYP/6-31G* level of theory. Substituents are conserved in the acyclic reference and any difference in energy between the ring and the acyclic reference corresponds exclusively to RSE. Small rings are stabilized by alkyl substituents and this stabilization decreases as the size of the ring increases. There is a destabilization of medium sized rings. Greater stabilization is found upon alkyl substitution at a double bond in an unsaturated ring and this stabilization decreases as ring size increases. The effects of cis-1,2-disubstitution on RSEs have been evaluated and indicate stabilization for both small and medium sized rings. RSEs of saturated and unsaturated polycyclic systems agree well with the RSEs derived from experimental thermochemical data. RSEs are reported for substituted norbornanes, norbornenes, and norbornadienes to complement experimental studies. 相似文献