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61.
Sulfation of multiple hydroxylated small organic molecules is fraught with problems of poor yield, multitude of products, and long reaction times. We have developed a rapid microwave-based method for synthesis of highly sulfated small organic molecules, which affords the per-sulfated product in moderate to excellent yields and high purity. The method is expected to be of value in the discovery of per-sulfated organic molecules as mimics of glycosaminoglycans, which are being increasingly recognized as modulators of key physiological functions. 相似文献
62.
Recently, single-crystals of tin selenide (SnSe) have drawn immense attention in the field of thermoelectrics due to their anisotropic layered crystal structure and ultra-low lattice thermal conductivity. Layered SnSe has an orthorhombic crystal structure (Pnma) at ambient conditions. However, the cubic rock-salt phase (Fmm) of SnSe can only be stabilized at very high pressure and thus, the experimental realization of the cubic phase remains elusive. Herein, we have successfully stabilized the high-pressure cubic rock-salt phase of SnSe by alloying with AgBiSe2 (0.30 ≤ x ≤ 0.80) at ambient temperature and pressure. The orthorhombic polycrystalline phase is stable in (SnSe)1−x(AgBiSe2)x in the composition range of 0.00 ≤ x < 0.28, which corresponds to narrow band gap semiconductors, whereas the band gap closes upon increasing the concentration of AgBiSe2 (0.30 ≤ x < 0.70) leading to the cubic rock-salt structure. We confirmed the stabilization of the cubic structure at x = 0.30 and associated changes in the electronic structure using first-principles theoretical calculations. The pristine cubic SnSe exhibited the topological crystalline insulator (TCI) quantum phase, but the cubic (SnSe)1−x(AgBiSe2)x (x = 0.33) showed a semi-metallic electronic structure with overlapping conduction and valence bands. The cubic polycrystalline (SnSe)1−x(AgBiSe2)x (x = 0.30) sample showed n-type conduction at room temperature, while the orthorhombic (SnSe)1−x(AgBiSe2)x (0.00 ≤ x < 0.28) samples retained p-type character. Thus, by optimizing the electronic structure and the thermoelectric properties of polycrystalline SnSe, a high zT of 1.3 at 823 K has been achieved in (SnSe)0.78(AgBiSe2)0.22.AgBiSe2 alloying in SnSe tailors its crystal and electronic structures, which boost its thermoelectric figure of merit to 1.3. 相似文献
63.
Anélia N. Gurova Ana P.C. Ribeiro Carlos A. Nieto de Castro Umesh V. Mardolcar 《Fluid Phase Equilibria》2009
The relative permittivity (?r) data of 1,1,1-trifluoroethane (HFC-143a), (CAS N# 420-46-2), a hydrofluorocarbon (HFC) developed as a refrigerant that has zero ozone depletion potential, is reported. The relative permittivity of HFC-143a in the liquid phase was measured using a direct capacitance method at temperatures from T = 218 to 294 K and at pressures up to P = 15 MPa, for a frequency of 10 kHz. The uncertainty of the ?r measurements is estimated to be better than ±1.2 × 10−2. A complete set of tables of experimental data as a function of temperature, pressure and density, is presented that covers the dielectric property needs for most engineering applications. To study the dependence of ?r on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyse the data. The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase (μ*). The apparent dipole moment obtained was μ* = 3.293 D. The effective dipole in the liquid state predicted by the Kirkwood–Frölich theory is 2.530 D. The measured values are compared with density functional and density functional self-consistent calculations (SCIPCM) of the electronic distribution and of the dipole moment of HFC-143a. Finally, the values of the isobaric thermal expansion and isothermal compressibility were estimated from the reported measurements. 相似文献
64.
Umesh A. Fegade Suban K. Sahoo Amanpreet Singh Narinder Singh Sanjay B. Attarde Anil S. Kuwar 《Analytica chimica acta》2015
A fluorescent based receptor (4Z)-4-(4-diethylamino)-2-hydroxybenzylidene amino)-1,2dihydro-1,5-dimethyl-2-phenylpyrazol-3-one (receptor 3) was developed for the highly selective and sensitive detection of Cu2+ and Zn2+ in semi-aqueous system. The fluorescence of receptor 3 was enhanced and quenched, respectively, with the addition of Zn2+ and Cu2+ ions over other surveyed cations. The receptor formed host-guest complexes in 1:1 stoichiometry with the detection limit of 5 nM and 15 nM for Cu2+ and Zn2+ ions, respectively. Further, we have effectively utilized the two metal ions (Cu2+ and Zn2+) as chemical inputs for the manufacture of INHIBIT type logic gate at molecular level using the fluorescence responses of receptor 3 at 450 nm. 相似文献
65.
Bhavesh Babulal Gabani Suresh P. Sulochana Vinay Kiran Umesh Todmal Ramesh Mullangi 《Biomedical chromatography : BMC》2019,33(11)
A liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) method has been developed and validated for the quantification of tunicamycin in rat plasma as per regulatory guideline. Chromatography of tunicamycin and the IS in the processed plasma samples was achieved on an X‐Terra phenyl column using a binary gradient (mobile phase A, acetonitrile and mobile phase B, 5 mm ammonium formate) elution at a flow rate of 0.6 ml/min. LC–MS/MS was operated under the multiple reaction monitoring mode using the electrospray ionization technique in positive ion mode and the transitions of m/z 817.18 → 596.10, 831.43 → 610.10, 845.29 → 624.10, 859.23 → 638.10 and 309.24 → 163.20 were used to quantitate homologs A–D and the IS, respectively. The total chromatographic run time was 4.5 min. The correlation coefficient (r2) was >0.99 for all homologs with accuracy 90.7–107.4% and precision 0.74–15.1%. The recovery of homologs was 78.6–90.2%. No carryover was observed and the matrix effect was minimal. Tunicamycin four homologs were found to be stable on the bench‐top for 6 h, for up to three freeze–thaw cycles, in the injector for 24 h and for 1 month at ?80 ° C. The applicability of the validated method has been demonstrated in a rat pharmacokinetic study. 相似文献
66.
This paper reports the design and modelling of a wide-band, low insertion loss finline SPST switch using beam lead PIN diodes at the Ka-band. A unilateral asymmetric finline with an offset slot has been used to realize a transmission line with lower impedance to best match the impedance of the diode. Finline tapered transitions have been designed with exponential profiles for minimum reflection coefficient over the band. Wide-band operation, covering the full Ka-band, has been achieved with reactive tuning by varying the diode spacing. Four PIN diodes have been shunt mounted across the unilateral asymmetric finline slot. An insertion loss of 0.9 dB minimum and 1.65 dB maximum over the entire Ka-band and isolation of >25 dB from 26.5 to 35GHz and >20 dB over the complete Kaband has been achieved. 相似文献
67.
68.
Umesh Balakrishnan Nallamuthu Ananthi Sakthivel Tamil Selvan Ravindra Pal Dr. Katsuhiko Ariga Dr. Sivan Velmathi Dr. Ajayan Vinu Dr. 《化学:亚洲杂志》2010,5(4):897-903
The immobilization of chiral oxazaborolidine complex in the well‐ordered mesochannels of SBA‐15 is demonstrated by a postsynthetic approach using 3‐aminopropyltriethoxysilane as a reactive surface modifier. The immobilized catalysts are characterized by various techniques, such as XRD, nitrogen adsorption, HRSEM, UV/Vis diffuse reflectance spectroscopy, and FTIR spectroscopy. The catalysts are used for the enantioselective reduction of aromatic prochiral ketones. The activity of the chiral oxazaborolidine complex immobilized SBA‐15 catalysts is also compared with that of the pure chiral oxazaborolidine complex, which is a homogeneous catalyst. It is found that the activity of the chiral complex immobilized SBA‐15 heterogeneous catalyst is comparable with that of the homogeneous catalyst. 相似文献
69.
Two new methods based on FT–Raman spectroscopy, one simple, based on band intensity ratio, and the other using a partial least squares (PLS) regression model, are proposed to determine cellulose I crystallinity. In the simple method, crystallinity in cellulose I samples was determined based on univariate regression that was first developed using the Raman band intensity ratio of the 380 and 1,096 cm?1 bands. For calibration purposes, 80.5% crystalline and 120-min milled (0% crystalline) Whatman CC31 and six cellulose mixtures produced with crystallinities in the range 10.9–64% were used. When intensity ratios were plotted against crystallinities of the calibration set samples, the plot showed a linear correlation (coefficient of determination R 2 = 0.992). Average standard error calculated from replicate Raman acquisitions indicated that the cellulose Raman crystallinity model was reliable. Crystallinities of the cellulose mixtures samples were also calculated from X-ray diffractograms using the amorphous contribution subtraction (Segal) method and it was found that the Raman model was better. Additionally, using both Raman and X-ray techniques, sample crystallinities were determined from partially crystalline cellulose samples that were generated by grinding Whatman CC31 in a vibratory mill. The two techniques showed significant differences. In the second approach, successful Raman PLS regression models for crystallinity, covering the 0–80.5% range, were generated from the ten calibration set Raman spectra. Both univariate-Raman and WAXS determined crystallinities were used as references. The calibration models had strong relationships between determined and predicted crystallinity values (R 2 = 0.998 and 0.984, for univariate-Raman and WAXS referenced models, respectively). Compared to WAXS, univariate-Raman referenced model was found to be better (root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) values of 6.1 and 7.9% vs. 1.8 and 3.3%, respectively). It was concluded that either of the two Raman methods could be used for cellulose I crystallinity determination in cellulose samples. 相似文献
70.
Umesh N. Tripathi Ghanshyam Srivastava Ram C. Mehrotra 《Transition Metal Chemistry》1994,19(6):564-566
Summary Solids of the stoichiometric formulae [Fe{S2P(OPr-n)2}3] and [Fe{S2PO2G}3] (G = —CH2CMe2CH2—, CMe2–CMe2— or —CH2CH2CHMe—) are precipitated from the reactions of FeCl3 with ammonium dithiophosphates in water. Soluble complexes of the type [Fe{S2PO2G}2], formed by the reactions of FeCl2 with NH4[{S2PO2G}] in MeOH, can be extracted with benzene. Adducts of the types [Fe{S2PO2G}2L] and [Fe{S2PO2G}2(PPh3)2] are formed by the reaction of [Fe{S2PO2G}2] with L (L = 2,2-bipyridyl or 1,10-phenanthroline) and PPh3, respectively. All the compounds have been characterized by i.r. and u.v.-vis. spectroscopy and magnetic studies.This paper is dedicated to the late Dr. G. Srivastava, Associate Professor, Department of Chemistry, Rajasthan University, Jaipur. 相似文献