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691.
692.
693.
Poonam Vashistha Shiv Shankar Gaur K. N. Tripathi 《Optical and Quantum Electronics》2007,39(9):717-721
We report here the study of refractive index and Propagation loss of ammonium dichromate doped poly (vinyl alcohol) thin films
by using a prism coupling technique. Transmissions of the doped films have been measured. It has been observed that doping
of ammonium dichromate increase the refractive index. Propagation losses are found to decrease up to dye concentration 0.02%
and thereafter increase rapidly. 相似文献
694.
Consider motion initiated in a viscous liquid in a smooth walled container. The liquid is initially at rest under uniform
pressure from an inert gas of negligible inertia. We show that if the contact line is pinned and the interface is single valued,
the contact angle has to remain constant throughout the motion. This is true even for motions of finite amplitude. Some implications
of the result are discussed. 相似文献
695.
Rajashri R. Naik Ashok K. Shakya Ghaleb A. Oriquat Shankar Katekhaye Anant Paradkar Hugo Fearnley James Fearnley 《Molecules (Basel, Switzerland)》2021,26(16)
Propolis is a resinous natural product collected by honeybees (Apis mellifera and others) from tree exudates that has been widely used in folk medicine. The present study was carried out to investigate the fatty acid composition, chemical constituents, antioxidant, and xanthine oxidase (XO) inhibitory activity of Jordanian propolis, collected from Al-Ghour, Jordan. The hexane extract of Jordanian propolis contained different fatty acids, which are reported for the first time by using GC-FID. The HPLC was carried out to identify important chemical constituents such as fatty acids, polyphenols and α-tocopherol. The antioxidant and xanthine oxidase inhibitory activities were also monitored. The major fatty acid identified were palmitic acid (44.6%), oleic acid (18:1∆9cis, 24.6%), arachidic acid (7.4%), stearic acid (5.4%), linoleic acid (18:2∆9–12cis, 3.1%), caprylic acid (2.9%), lignoceric acid (2.6%), cis-11,14-eicosaldienoic acid (20:2∆11–14cis, 2.4%), palmitoleic acid (1.5%), cis-11-eicosenoic acid (1.2%), α–linolenic acid (18:3∆9–12–15cis, 1.1%), cis-13,16-docosadienoic acid (22:2∆13–16cis, 1.0%), along with other fatty acids. The major chemical constituents identified using gradient HPLC-PDA analysis were pinocembrin (2.82%), chrysin (1.83%), luteolin-7-O-glucoside (1.23%), caffeic acid (1.12%), caffeic acid phenethyl ester (CAPE, 0.79%), apigenin (0.54%), galangin (0.46%), and luteolin (0.30%); while the minor constituents were hesperidin, quercetin, rutin, and vanillic acid. The percentage of α-tocopherol was 2.01 µg/g of the lipid fraction of propolis. Antioxidant properties of the extracts were determined via DPPH radical scavenging. The DPPH radical scavenging activities (IC50) of different extracts ranged from 6.13 to 60.5 µg/mL compared to ascorbic acid (1.21 µg/mL). The xanthine oxidase inhibition (IC50) ranged from 75.11 to 250.74 µg/mL compared to allopurinol (0.38 µg/mL). The results indicate that the various flavonoids, phenolic compounds, α-tocopherol, and other constituents which are present in propolis are responsible for the antioxidant and xanthine oxidation inhibition activity. To evaluate the safety studies of propolis, the pesticide residues were also monitored by LC-MS-MS 4500 Q-Trap. Trace amounts of pesticide residue (ng/mL) were detected in the samples, which are far below the permissible limit as per international guidelines. 相似文献
696.
V. Shankar V. Kumaran 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):607-622
The stability of wall modes in fluid flow through a flexible tube of radius R surrounded by a viscoelastic material in the region R < r < HR is analysed using a combination of asymptotic and numerical methods. The fluid is Newtonian, while the flexible wall is modelled
as an incompressible viscoelastic solid. In the limit of high Reynolds number (Re), the vorticity of the wall modes is confined to a region of thickness O(Re
-1/3) in the fluid near the wall of the tube. Previous numerical studies on the stability of Hagen-Poiseuille flow in a flexible
tube to axisymmetric disturbances have shown that the flow could be unstable in the limit of high Re, while previous high Reynolds number asymptotic analyses have revealed only stable modes. To resolve this discrepancy, the
present work re-examines the asymptotic analysis of wall modes in a flexible tube using a new set of scaling assumptions.
It is shown that wall modes in Hagen-Poiseuille flow in a flexible tube are indeed unstable in the limit of high Re in the scaling regime Re∼Σ3/4. Here Σ is a nondimensional parameter characterising the elasticity of the wall, and Σ≡ρGR
2/η2, where ρ and η are the density and viscosity of the fluid, and G is the shear modulus of the wall medium. The results from the present asymptotic analysis are in excellent agreement with
the previous numerical results. Importantly, the present work shows that the different types of unstable modes at high Reynolds
number reported in previous numerical studies are qualitatively the same: they all belong to the class of unstable wall modes
predicted in this paper.
Received 12 June 2000 and Received in final form 8 November 2000 相似文献
697.
Si Hyun Kim Byoungsang Lee Jun Hyuk Heo Kyung Eun Lee Prabakaran Shankar Kwon‐Hoon Han Jung Heon Lee 《Particle & Particle Systems Characterization》2019,36(1)
The ζ‐potential and hydrodynamic size (dh) of nanoparticles (NPs) are systematically controlled by capping gold NPs (AuNPs) with polymers having different charges and treating them in NaCl solutions of diverse concentrations. Interactions between AuNPs in hydrogel are caused by chemical reactions induced by 1,4‐dithiothreitol. The effect of ζ‐potential is clear, as negatively charged AuNPs can be aggregated in neutral agarose gel, but the amount of aggregation is significantly affected by the magnitude of the negative surface charge on the AuNPs. However, all positively charged AuNPs show negligible aggregation in agarose gel with slightly negative polarity. The effect of dh on AuNP aggregation is different from that of ζ‐potential. Although AuNPs with small dh generally show more aggregation than those with large dh, the amount of AuNP capping layer is critical. Thus, the amount of polymer present on NP surface needs to be considered to investigate the effect of dh on AuNP aggregation. Through extended Derjaguin, Landau, Verwey, Overbeek (XDLVO) theory, it is shown that the charges of the AuNPs and the hydrogel, as well as the dh of the NPs, are related to electrostatic repulsion and steric hindrance, which affect AuNP aggregation in hydrogel. 相似文献
698.
TIAN Zong-Qiang PALMER James T. BUYSSE Ann VENKATRAMAN Shankar MENDONCA Rohan MCGRATH Mary E. 《高等学校化学学报》2000,21(Z1):148
Cysteine Proteases have been implicated in a broad spectrum of disease processes including cancer, arthritis, and viral and parasitie diseases[1]. Cathepsin K, a cysteine protease of the papain superfamily, is selectively expressed in osteoclasts and has been implicated in the process of bone resouption[2]. It is therefore considered a promising therapeutic target for treating diseases charccterized by excessive bone loss, such as osteoporosis[3]. Several chemotypes of cathepsin K inhibitors will be reviewed. The design and synthesis of potent inhibitors will also be discussed. 相似文献
699.
An axisymmetrical hemispherical asperity in contact with a rigid flat is modeled for an elastic–plastic material on the lines of the Kogut–Etsion Model (KE Model) and the Jackson–Green Model (JG Model). The present work extends the previous KE and JG works, accounting for the effect of realistic material behavior in terms of the varying yield strengths and the isotropic strain hardening behavior. The predicted results show that the transition behavior of the materials from the elastic–plastic to the fully plastic case is influenced by the yield strength and the tangent modulus (Et) and such transition do not take place at specific values of interference ratios as suggested by the KE model. New empirical relations are proposed to determine the contact load and the contact area based on the analysis. Numerical results from the finite element modeling are also validated with an experimental ball on flat configuration approach. 相似文献
700.
Ren X Li H Clarke RW Alves DA Ying L Klenerman D Balasubramanian S 《Journal of the American Chemical Society》2006,128(15):4992-5000
Telomerase is a nonclassical DNA polymerase that uses its integral RNA as a template to synthesize telomeric repeats onto chromosome ends. The molecular mechanism of telomerase is unique and involves a translocation step after the synthesis of each telomeric repeat. To directly measure the enzymatic turnover of substrate and the efficiency of the translocation step we have extended our two-color single molecule fluorescence coincidence method (Anal.Chem. 2003, 75, 1664-1670). The method employs Cy5-dATP incorporation into a DNA primer that has been prelabeled with a reference fluorophore. Measurements are performed in the single molecule regime and products, which necessarily have both fluorophores, are excited by two independent lasers, and give rise to coincident events. By counting the number of coincident events and using the coincidence detection efficiency, it is possible to determine the number of the extended products generated by attomole quantities of telomerase, without separation or the use of PCR or radioactivity. Histograms of the logarithms of the ratios of the Cy5 to the reference fluorophore fluorescence can be used to determine the length distribution of the products and hence the enzyme processivity. The mean processivity obtained from the single molecule fluorescence coincidence assay is 0.32 +/- 0.04, in good agreement with the value of 0.37 +/- 0.05 derived from the direct radioactive assay approach. The function of the alignment domain of human telomerase RNA in sustaining catalytic activity in vitro has been reevaluated using this method. Together with our previous results (Nucleic Acids Res. 2002, 30, 4470-4480) these experiments identify the essential residues in the alignment domain of human telomerase RNA that contribute to the activity and processivity of telomerase. 相似文献