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1.
Solvent‐Dependent Structure of the I3− Ion Derived from Photoelectron Spectroscopy and Ab Initio Molecular Dynamics Simulations 下载免费PDF全文
Dr. Naresh K. Jena Ida Josefsson Dr. Susanna K. Eriksson Prof. Anders Hagfeldt Prof. Hans Siegbahn Prof. Olle Björneholm Prof. Håkan Rensmo Dr. Michael Odelius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):4049-4055
Ab initio molecular dynamics (MD) simulations of the solvation of LiI3 in four different solvents (water, methanol, ethanol, and acetonitrile) are employed to investigate the molecular and electronic structure of the I3? ion in relation to X‐ray photoelectron spectroscopy (XPS). Simulations show that hydrogen‐bond rearrangement in the solvation shell is coupled to intramolecular bond‐length asymmetry in the I3? ion. By a combination of charge analysis and I 4 d core‐level XPS measurements, the mechanism of the solvent‐induced distortions has been studied, and it has been concluded that charge localization mediates intermolecular interactions and intramolecular distortion. The approach involving a synergistic combination of theory and experiment probes the solvent‐dependent structure of the I3? ion, and the geometric structure has been correlated with the electronic structure. 相似文献
2.
Velusamy B. Subramanian Naresh Kumar Katari Thirupathi Dongala Sreekantha B. Jonnalagadda 《Biomedical chromatography : BMC》2020,34(1):e4719
A quality by design (QbD) based high-resolution HPLC method is described for determination of impurities in apixaban (APX) in the tablet dosage form. Employing a simple and stability-indicating HPLC method, nine known impurities were quantified with good peak resolution. Mobile phase A (MP-A) was prepared with buffer and acetonitrile 90:10 v/v, while mobile phase B (MP-B) contained water and acetonitrile 10:90 v/v. The gradient program was 0 min, MP-A 75%, B 25%; 20 min, MP-A 65%, B 35%; 30 min, MP-A 40%, B 60%; 40min, MP-A 40%, B 60%; 42 min, MP-A 75%, B 25%; and 50 min, MP-A 75%, B 25%. The chromatographic separation was achieved using a Zorbax RX C18 250 × 4.6 mm column, 5 μm (1.0 ml min−1, 280 nm, 50 μl) and a column temperature of 40°C. Several separation studies were carried out using design of experiments to optimize the method. Validation results confirm the applicability of the developed method for quality analysis and stability studies of the regular product on the manufacturing stream. 相似文献
3.
Thirupathi Dongala Naresh Kumar Katari Ashok Kumar Palakurthi Sreekantha B. Jonnalagadda 《Biomedical chromatography : BMC》2019,33(10)
We developed novel stability‐indicating HPLC method for simultaneous estimation of 14 impurities in excedrin tablet, a formulation with a combination of acetaminophen, aspirin, and caffeine. In addition, a new impurity that was generated through degradation of aspirin at high temperatures during the accelerated stability conditions was positively identified and confirmed, using liquid chromatography–mass spectrometry technique. The HPLC method was optimized using the Inertsustain C18, 250 × 4.6 mm, 5.0 μm column, employing simple gradient method. Forced degradation studies were performed under acidic, basic, oxidative and thermal conditions to prove the scope and stability‐indicating the nature of the method. The optimized method was validated as per the International Conference on Harmonization guidelines. The HPLC method showed linearity from LOQ concentration to 21 μg mL?1. Precision and intermediate precision values were <5% RSD. The validated HPLC method is currently applied for the routine testing of excedrin tablet formulations in quality control laboratories. 相似文献
4.
Parvateesam Yenda Naresh Kumar Katari Balasubramanian Satheesh Rambabu Gundla Siva Krishna Muchakayala Vijay Kumar Rekulapally 《Journal of separation science》2023,46(11):2200770
The design of an appropriate analytical method for assessing the quality of pharmaceuticals requires a deep understanding of science, and risk evaluation approaches are appreciated. The current study discusses how a related substance method was developed for Nintedanib esylate. The best possible separation between the critical peak pairs was achieved using an X-Select charged surface hybrid Phenyl Hexyl (150 × 4.6) mm, 3.5 μm column. A mixture of water, acetonitrile, and methanol in mobile phase-A (70:20:10) and mobile phase-B (20:70:10), with 0.1% trifluoroacetic acid and 0.05% formic acid in both eluents. The set flow rate, wavelength, and injection volumes were 1.0 ml/min, 285 nm, and 5 μl, respectively, with gradient elution. The method conditions were validated as per regulatory requirements and United States Pharmacopeia general chapter < 1225 >. The correlation coefficient for all impurities from the linearity experiment was found to be > 0.999. The % relative standard deviation from the precision experiments ranged from 0.4 to 3.6. The mean %recovery from the accuracy study ranged from 92.5 to 106.5. Demonstrated the power of the stability-indicating method through degradation studies; the active drug component is more vulnerable to oxidation than other conditions. Final method conditions were further evaluated using a full-factorial design. The robust method conditions were identified using the graphical optimization from the design space. 相似文献
5.
Naresh Kumar Rajendran Blassan P. George Nicolette N. Houreld Heidi Abrahamse 《Molecules (Basel, Switzerland)》2021,26(10)
Recently, the biosynthesis of zinc oxide nanoparticles (ZnO NPs) from crude extracts and phytochemicals has attracted much attention. Green synthesis of NPs is cost-effective, eco-friendly, and is a promising alternative for chemical synthesis. This study involves ZnO NPs synthesis using Rubus fairholmianus root extract (RE) as an efficient reducing agent. The UV spectrum of RE-ZnO NPs exhibited a peak at 357 nm due to intrinsic bandgap absorption and an XRD pattern that matches the ZnO crystal structure (JCPDS card no: 36-1451). The average particle size calculated from the Debye–Scherrer equation is 11.34 nm. SEM analysis showed that the RE-ZnO NPs spherical in shape with clusters (1–100 nm). The antibacterial activity of the NPs was tested against Staphylococcus aureus using agar well diffusion, minimum inhibitory concentration, and bacterial growth assay. The R. fairholmianus phytochemicals facilitate the synthesis of stable ZnO NPs and showed antibacterial activity. 相似文献
6.
Naresh Vasudevan 《Journal of Elasticity》1990,23(2-3):181-199
In Part I of this two part paper, we developed analytical expressions for the crack face displacements due to an applied point traction as well as a moving point source of dilatation. In this sequel to Part I, we present numerical results for the crack face displacements in the form of displacement-time records at fixed locations on the crack face. For the stationary point traction problem, the results are more or less in keeping with the predictions made in Part I, with the Rayleigh pulse giving a large contribution for an applied step load.In the case of the moving point microfracture with a step time dependence, in addition to the diffracted compressional, shear and Rayleigh arrivals there is observed the evolution of a new pulse whose amplitude and position on the time record shifts changes if the calculations are done for a different crack speed. Results are also presented for a microfracture with an oscillatory time dependence. Once again, the first arrival of the surface pulse appears to be the most prominent arrival on the record. Further explorations of the parameters and source functions would be required before comparisons with experimental data can be made. 相似文献
7.
A range of activated indole-2-carboxylate derivatives was prepared via the Hemetsberger indole synthesis. Vilsmeier formylation was explored to establish regioselectivity and to prepare a range of new indole carbaldehydes. The indole aldehydes were reduced to the corresponding hydroxymethylindoles in good yields by the use of sodium borohydride in THF. Symmetrical 4,4′-, 6,6′- and 7,7′-diindolylmethanes were prepared via the acid-catalysed reaction of the corresponding hydroxymethylindoles. Furthermore, the treatment of methyl 4-hydroxymethyl-5,6-dimethoxyindole-2-carboxylate and a range of methyl indole esters with acetic acid led to the formation of unsymmetrical 4,6′- and 4,7′-dindolylmethanes. 相似文献
8.
Sharma Deepak Sharma Naresh Brahmbhatt D. I. Gupta Vivek K. 《Crystallography Reports》2019,64(7):1047-1050
Crystallography Reports - The crystal structure of the title compound is determined by single crystal X-ray structure analysis. The structure was solved by direct method and refined to a final... 相似文献
9.
David Tong Jackie Wu Nathan Bazinski Donghyun Koo Naresh Vemula Prof. Dr. Brian L. Pagenkopf 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(67):15244-15247
Cycloadditions of strained carbocycles promoted by Lewis acids are powerful methods to construct heterocyclic frameworks. In fact, the formal [3+2] cycloadditions of donor–acceptor (DA) cyclopropanes with nitriles has seen particular success in synthesis. In this work, we report on the first [4+2] cycloaddition of nitriles with DA cyclobutanes by Lewis acid activation. Tetrahydropyridine derivatives were obtained in up to 91 % yield from various aryl-activated cyclobutane diesters and aliphatic or aromatic nitriles. 相似文献
10.