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21.
Ramajayam Govindan Mohamed El-Sherbiny Khalid Mohamed Morsy Ibraheem Srinivasan Narasimhan Mohamed EL-Dosoky Mohamed Salama Fazil Ahmad Selvaraj Jayaraman Vishnu Priya Veeraraghavan Srinivasan Vengadassalapathy Surapaneni Krishna Mohan Vidhya Rekha Umapathy Gayathri Rengasamy Shazia Fathima Jaffer Hussain Maheshkumar Poomarimuthu Senthilkumar Kalimuthu 《Molecules (Basel, Switzerland)》2022,27(3)
22.
A preliminary assessment of microstructural and compositional characteristics of two variants of precarbonated and postcarbonated concrete mixes 下载免费PDF全文
The hydration, precarbonation, and postcarbonation microstructural and compositional attributes of 2 variants of concrete were studied using scanning electron microscope, energy dispersive spectroscopy, and X‐ray diffraction techniques. Results obtained showed presence of large number of diffraction peaks indicative of SiO2 as major phase. Higher pH, alkalinity, and absence of effects of carbonation were suggested from the presence of portlandite peaks. Evidence of effect of carbonation was studied through the analysis of the experimental diffraction peaks obtained postexposure to accelerated carbonation in a controlled environment. Presence of all the 3 polymorphs of calcium carbonate (CaCO3) such as aragonite, vaterite, and calcite depending upon the moisture content and the material constituting the concrete sample were envisaged signifying carbonation. Precipitation of these CaCO3 crystals was responsible for depletion of CH as well as calcium–silicate–hydrate, ettringite with the progress of carbonation as suggested by their absence in the X‐ray diffraction diffractograms of the carbonated samples. The crystal structure of the newly formed minerals in both the variants of concrete sample was highly controlled by the stages of carbonation, with development of amorphous CaCO3 (amalgamated with that of calcium hydrates) in early stages of carbonation as well as fully developed rhombohedral CaCO3 crystals in later stages. 相似文献
23.
Simultaneous velocity and temperature measurements in gaseous flow fields using the VENOM technique 总被引:1,自引:0,他引:1
We present an initial demonstration of simultaneous velocity and temperature mapping in gaseous flow fields using a new nitric oxide planar laser-induced fluorescence-based method. The vibrationally excited NO monitoring (VENOM) technique is an extension of two-component velocimetry using vibrationally excited NO generated from the photodissociation of seeded NO(2) [Appl. Opt. 48, 4414 (2009)], where the two sequential fluorescence images are obtained probing two different rotational states to provide both velocity and temperature maps. Comparisons to computational fluid dynamics simulations show that the initial VENOM measurements provide good velocity and temperature maps in the relatively high-density regions of the flow, where the rms uncertainties are approximately 5% for velocity and 9% for temperature. 相似文献
24.
The irreducible representations of the group SO(4) in which the SO(3) subgroup is reduced are studied by an explicit construction of the operators and the basis in the spinor representation. The basis function which is formally identical with that for the coupling of two angular momentaj
1 andj
2 is expressible in terms of a hypergeometric function and strongly resembles the one for the irreducible representations of the groups SO(3,1). For the Lorentz group, the bases for the unitary representations which require unphysical values ofj
1 andj
2 are found to be analytic continuation of those for SO(4). The realization of the unitary irreducible representations of the group SO(4) in the Hilbert space of these functions leads, for appropriate unphysical values ofj
1,j
2, to the Gelfand-Naimark formula for the principal and complementary series of the representations of SO(3;1). The matrix elements for finite transformations of SO(4) and SO(3,1) can be evaluated, in this approach, in a unified manner by using standard properties of the hypergeometric function. These turn out to be a finite sum of3
F
2-functions which, as expected, are polynomials for SO(4) and infinite series for SO(3,1). A number of special matrix elements are calculated from the general formula and these agree with the results obtained previously.The authors are deeply indebted to Professor S.Dutta Majumdar fo many important suggestions and clarifications. 相似文献
25.
R. Srinivasan 《Pramana》2006,66(1):3-30
Rotating dilute Bose-Einstein condensates (BEC) of alkali atoms offer a testing ground for theories of vortices in weakly
interacting superfluids. In a rotating super-fluid, quantised vortices, with a vorticity h/m, form above a critical velocity.
Such vortices have been generated in BEC of alkali atoms by different techniques such as (a) wave function engineering of
a two-component BEC, (b) decay of solitons, (c) rotation of a thermal cloud before cooling it below the condensation temperature,
(d) stirring with an ‘optical’ spoon, (e) rotating a deformation in the anisotropic trap in which the condensate is trapped
and (f) by creating Berry phase by adiabatically reversing the axial magnetic field. Since the core of a vortex is a fraction
of a micrometer in diameter, it cannot be directly imaged optically. The condensate with vortices is allowed to ballistically
expand till the size increases by one order before the vortices are imaged. Surface wave spectroscopy and the change in aspect
ratio of a rotating cloud are the other techniques used. Studies have been made on the creation and dynamics of single vortex
and on systems with more than a hundred vortices. Results have been obtained on vortex nucleation, stability of vortex structures,
nature of the vortex lattice and defects in such a lattice. Important results are: (a) evidence exists that vortex nucleation
takes place by a surface mode instability; but this is not the only mechanism; (b) the vortex lattice is perfectly triangular
right up to the edge; (c) in the initial stages of rotation of the cloud a tangled web of vortices is seen; it takes a few
hundred milliseconds before the vortices arrange themselves in a lattice; this time appears to be independent of temperature;
(d) the decay of vortices appears to arise from the transfer of energy to the rotating thermal component and is dependent
on temperature; (e) defects in the lattices such as dislocations and grain boundaries are seen; (f) transverse oscillations
(Tkachenko modes) of the vortex lattice have been observed; and (g) giant vortices have been produced. These will be discussed. 相似文献
26.
The condensation reaction involving an aldehyde and diketone was efficiently promoted by the Ionic liquid, [Hbim]BF(4) (IL) as a reaction medium with methanol as co-solvent at ambient temperature under ultrasonic irradiation to afford the corresponding 1,8-dioxo-octahydro-xanthene (xanthene) derivatives in excellent yields. The advantages of this method include among others the use of a recyclable, non-volatile ionic liquid, which promotes this protocol under ambient temperature without the requirement of any added catalyst. The reaction times and yields are compared with p-TSA catalyzed synthesis of xanthenes under thermal conditions, which is also reported for the first time under our reaction conditions. 相似文献
27.
A comparative study of myo-inositol quantification using LCmodel at 1.5 T and 3.0 T with 3 D 1H proton spectroscopic imaging of the human brain 总被引:2,自引:0,他引:2
Myo-inositol is a strongly coupled system and resonates at four chemical shift positions. At 1.5 T, only the singlet component at 3.57 ppm is detected. However, at 3 T this resonance is resolved into its components at 3.55 ppm and 3.61 ppm. Due to the increased spectral resolution and signal-to-noise ratio, it is anticipated that the quantification of myo-inositol should improve at 3 T. Using data from normal controls and the LCmodel quantification procedure, we found that the quantification precision, reproducibility and detection sensitivity of myo-inositol is significantly better at 3 T relative to 1.5 T. 相似文献
28.
A.?NarayananEmail author R.?Srinivasan U.?K.?Khan A.?Vudayagiri H.?Ramachandran 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,31(1):107-112
The unusually narrow features in the fluorescence from 85Rb driven by two laser fields L1 and L2, reported in [1], are explained on the basis of a four-level density matrix calculation. The L2 laser enables atom transfer to the fluorescing levels connected by the strong L1 laser. In turn the L1 laser causes the Autler-Townes splitting of the upper levels connected by L2 laser. These two effects are shown to maximise fluorescence within a narrow spectral range of the scanned L2 laser due to velocity selection of atoms from co-propagating and counter propagating L1 and L2 lasers. The analysis reveals the existence of narrow spectral features from a collection of atoms at room temperature even in the absence of induced coherences between the levels.Received: 2 July 2004, Published online: 21 September 2004PACS:
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift - 32.80.Bx Level crossing and optical pumping 相似文献
29.
Sangya Chitranshi Dr. B. Adinarayana Mainak Das Dr. Won-Young Cha Prof. Dr. Dongho Kim Prof. Dr. A. Srinivasan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(56):12911-12915
Three distinct conformational structures of carbaoctaphyrins were prepared by incorporating bis-4,4'-biphenyl units in the macrocyclic core. The free-base form adopts a figure-eight conformation, whereas the protonation triggers a conformational change with a pyrrole ring inversion and acquires an open-framework structure. The insertion of bis-RhI metal ion in the macrocyclic core affords a singly twisted conformational structure. Furthermore, the local aromaticity in the bis-4,4'-biphenyl ring dominates the overall macrocyclic aromaticity in all three forms, and thus adopts nonaromatic characteristics. These results are supported by spectral as well as theoretical studies, and they are unambiguously confirmed by X-ray crystal analyses. 相似文献
30.
The first observation of the ESR spectra of Mn2+, entering substitutionally for Fe2+ in the Van Vleck paramagnet FeS2 (polycrystals), is reported. The data from 5 to 295 K fits the spin-Hamiltonian + , with g = 2.000 ± 0.001, A/β = ?95.0 ± 0.5 Oe and D/β varying from 50 Oe (5K) to 59 Oe (295 K). The temperature dependence of D can be described in terms of a single phonon-mode with frequency ? 145 cm?1. 相似文献