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251.
The swinging Atwood machine, a prototype nonlinear dynamical system, is analyzed following an idea of Bogoliubov and Mitropolsky. A series solution is found for the radial and angular displacement as functions of time. The analysis is repeated in the resonance case, when the frequency of the driving force maintains a fixed ratio to that of the free motion. The condition of resonance requires the mass ratio to be equal to 2j
2–1, wherej is an integer not equal to one. 相似文献
252.
D. P. Chowdhury J. Arunachalam Rakesh Verma Sujit Pal S. Gangadharan 《Journal of Radioanalytical and Nuclear Chemistry》1992,158(2):463-470
40 MeV -particles have been used to determine oxygen impurity at ppm levels in silicon, copper, and stainless steel, through the radiochemical separation of18F from the matrix. The separation of18F has been carried out by two techniques, viz.(1) distillation of H2SiF6 and (2) precipitation of KBF4 and some modification has been applied in the separation, depending on the nature of interferences from the matrix. Instrumental approach was also carried out to determine the oxygen impurity at 100 ppm in Si matrix because this approach is not possible in Cu and stainless steel samples due to matrix activity. 相似文献
253.
Sudeshna Chakravorty A. Roy Chowdhury S. N. Paul 《International Journal of Theoretical Physics》1992,31(2):343-352
We analyze the effect of a nonzero streaming velocity of both positive and negative ions on the formation of solitary waves in a relativistic plasma. The thermodynamic situation is considered to be isothermal. For various values ofu
0/C andn
o/nowe obtain the variations of the amplitude and the width of the solitary wave. 相似文献
254.
Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals
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Nithin Pathoor Ansuman Halder Amitrajit Mukherjee Jaladhar Mahato Dr. Shaibal K. Sarkar Dr. Arindam Chowdhury 《Angewandte Chemie (International ed. in English)》2018,57(36):11603-11607
Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano‐emitters. Extended quantum‐confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi‐level blinking of entire individual organo–lead bromide perovskite microcrystals (volume=0.1–3 μm3) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 μm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long‐range (mesoscopic) electronic communication. 相似文献
255.
Krishnamoorthy G Webb SP Nguyen T Chowdhury PK Halder M Wills NJ Carpenter S Kraus GA Gordon MS Petrich JW 《Photochemistry and photobiology》2005,81(4):924-933
Hydroxy and methoxy perylene quinones are synthesized in an attempt to isolate the essential spectroscopic and biological features of light-induced antiviral agents such as hypericin and hypocrellin. Unlike their naturally occurring counterparts, these synthetic quinones bear the carbonyl, hydroxyl, and methoxy groups in the "bay region." The hydroxy and methoxy compounds have rich absorption spectra with broad features in the visible (approximately 450-800 nm) and relatively more intense and narrow features at wavelengths < or = 350 nm. High-level ab initio quantum mechanical calculations assign the features in the absorption spectra to electronic transitions from S0 to S2 and to higher-lying electronic states. The calculations indicate that in the ground state the trans dihydroxy isomer is 12.5 kcal/mol lower in energy than the cis dihydroxy isomer and is thus the only species present. The lowest-energy trans methoxy ground state isomer and the lowest-energy cis methoxy ground state isomer are found to be degenerate. An additional cis methoxy isomer 6.3 kcal/mol higher in energy than the global minimum is assumed to contribute to the spectrum and is also considered. Finally, the synthetic compounds exhibit similar light-induced antiviral activity to each other, but significantly less than that of hypericin. 相似文献
256.
Ananda Pramanik P. K. Chowdhury 《Journal of polymer science. Part A, Polymer chemistry》1969,7(4):1055-1073
Na amylose xanthate was prepared from potato starch by xanthation of amylose in dilute NaOH solution. Pure xanthate was then isolated and viscometric and turbidimetric studies on its ripening characteristics were carried out for a period of about 200 hrs. Prolonged ripening in air degraded the amylose chain without formation of gel. To study the nature of ripening more precisely, it was carried out in an identical way under N2 and followed both viscometrically and turbidimetrically. The refractive-index increment (dn/dc) of the xanthate solutions during ripening under both air and nitrogen was continuously measured so as to avoid any possible error in computing correct molecular weights during ripening. Light-scattering molecular weights (M?w) thus computed during the course of degradation of Na amylose xanthate extending for about 200 hr under both air and nitrogen were found to obey a first-order rate equation, In (M0/Mt) = Kt where Mo is the initial molecular weight, Mt the molecular weight at time t of ripening, and K the rate constant of the degradation process. 相似文献
257.
Joos TO Schrenk M Höpfl P Kröger K Chowdhury U Stoll D Schörner D Dürr M Herick K Rupp S Sohn K Hämmerle H 《Electrophoresis》2000,21(13):2641-2650
In order to quantify autoantibodies in the sera of patients with autoimmune disease, we have created a microarray-based immunoassay that allows the simultaneous analysis of 18 known autoantigens. The microarrays contain serial dilutions of the various antigens, thereby allowing accurate determination of autoantibody titer using minimal amounts of serum. The assay is very sensitive and highly specific: as little as 40 fg of a known protein standard can be detected with little or no cross-reactivity to nonspecific proteins. The signal intensities observed from serial dilutions of immobilized antigen correlate well with serial dilutions of autoimmune sera. Miniaturized and highly parallelized immunoassays like these will reduce costs by decreasing reagent consumption and improve efficiency by greatly increasing the number of assays that can be performed with a single serum sample. This system will significantly facilitate and accelerate the diagnostics of autoimmune diseases and can be adapted easily to any other kind of immunoassay. 相似文献
258.
The unimolecular and collision-induced fragmentation reactions of the enolate ion of 2,3-butanedione, [CH3COCOCH2]?, have been studied, Unimolecular fragmentation on the metastable ion time-scale forms [HCCO]?, [C2H3O]?, [C3H5O]? and [CH3CO2]?. Charge inversion mass spectrometry shows that the [C2H3O]? ion is the acetyl anion while the [C3H5O]? product is the acetone enolate ion; formation of the latter product involves a large release of kinetic energy (T 1/2 = 0.99 eV). The fragmentation reactions occurring following collisional activation have been determined for 8 keV collisions and over the range 1.5–30 eV center-of-mass collision energy. Formation of [HCCO]? and [CH3CO]? are of the most important reactions following collisional activation and it is concluded that the two reactions have similar critical reaction energies even though formation of [HCCO]? is favored thermochemically. 相似文献
259.
Comparison of analytical techniques for purity evaluation of single-walled carbon nanotubes 总被引:1,自引:0,他引:1
Itkis ME Perea DE Jung R Niyogi S Haddon RC 《Journal of the American Chemical Society》2005,127(10):3439-3448
We compare popular analytical techniques, including scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and Raman and near-infrared (NIR) spectroscopy, for the evaluation of the purity of bulk quantities of single-walled carbon nanotubes (SWNTs). Despite their importance as imaging techniques, SEM and TEM are not capable of quantitatively evaluating the purity of typical inhomogeneous bulk SWNT samples because the image frame visualizes less than 1 pg of SWNT material; furthermore, there is no published algorithm to convert such images into numerical data. The TGA technique is capable of measuring the amount of metal catalyst in an SWNT sample, but does not provide an unambiguous separation between the content of SWNTs and carbonaceous impurities. We discuss the utilization of solution-phase near-infrared spectroscopy and solution-phase Raman spectroscopy to quantitatively compare arbitrary samples of bulk SWNT materials of different purities. The primary goal of this paper is to provide the chemical community with a realistic evaluation of current analytical tools for the purity evaluation of a bulk sample of SWNTs. The secondary goal is to draw attention to the growing crisis in the SWNT industry as a result of the lack of quality control and the misleading advertising by suppliers of this material. 相似文献
260.
Bhattacharya S Chattopadhyay S Nayak SK Banerjee M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(1-3):729-735
Supramolecular complexation of [60]- and [70]fullerenes with 37-allyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert butyl)calix[6]arene (I) has been studied in CCl(4) medium by NMR spectrometric method. All of the complexes are found to be stable with 1:1 stoichiometry. Formation constants (K) of the above supramolecular complexes have been determined from systematic variation of NMR chemical shifts of specific protons of I in the presence of [60]- and [70]fullerenes. Trends in the K value suggest that [70]fullerene binds more strongly with I relative to [60]fullerene. Both PM3 and ab initio calculations reveal that the intermolecular interaction in the [70]fullerene/I complex proceeds through quite deep energy minima. 相似文献