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排序方式: 共有568条查询结果,搜索用时 31 毫秒
81.
Pankaj Jain Satish D. Joglekar Subhadip Mitra 《The European Physical Journal C - Particles and Fields》2008,57(4):671-680
We compute the two photon exchange contributions to elastic scattering of polarized electrons from target protons. We use
a non-local field theory formalism for this calculation. The formalism maintains gauge invariance and provides a systematic
procedure for making this calculation. The results depend on one unknown parameter,
. We compute the two photon exchange correction to the ratio of electric to magnetic form factors extracted using polarization
transfer experiments. The correction is found to be small if
. However, for larger values of
, the correction can be quite significant. The correction to the polarization transfer results goes in the right direction
to explain their difference with the ratio measured by the Rosenbluth separation method. We find that the difference between
the two experimental results can be explained for a wide range of values of the parameter
. We also find that the corrections due to two photon exchange depend on the photon longitudinal polarization ε. Hence, we predict an ε dependence of the form factor ratio extracted using the polarization transfer technique. Finally, we obtain a limit on
by requiring that the non-linearity in ε dependence of the unpolarized reduced cross section is within experimental errors. 相似文献
82.
Senlian Hong Pankaj Sahai‐Hernandez Digantkumar Gopaldas Chapla Kelley W. Moremen David Traver Peng Wu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(40):14465-14471
Dynamic turnover of cell‐surface glycans is involved in a myriad of biological events, making this process an attractive target for in vivo molecular imaging. Metabolic glycan labeling coupled with bioorthogonal chemistry has paved the way for visualizing glycans in living organisms. However, a two‐step labeling sequence is required, which suffers from the tissue‐penetration difficulties of the imaging probes. Here, by exploring the substrate promiscuity of endogenous glycosyltransferases, we developed a single‐step fluorescent glycan labeling strategy by using fluorophore‐tagged analogues of the nucleotide sugars. Injecting fluorophore‐tagged sialic acid and fucose into the yolk of zebrafish embryos at the one‐cell stage enables systematic imaging of sialylation and fucosylation in live zebrafish embryos at distinct developmental stages. From these studies, we obtained insights into the role of sialylated and fucosylated glycans in zebrafish hematopoiesis. 相似文献
83.
Eti Mehrotra Jyotsna Vishwakarma Avinash C. Tripathi Pankaj K. Sonar 《Natural product research》2019,33(4):568-572
The present study explored the schizonticidal potential of traditionally used Magnolia champaca (L.) Baill. ex. Pierre flowers, identifying constituents of interest. The extraction of phytoconstituents was carried out by microwave-assisted technique, isolated via column chromatography, and characterised by various physicochemical, spectral (IR, 1H-NMR and Mass) and chromatographic (HPTLC) techniques. Both the isolated compounds (parthenolide and costunolide diepoxide) exhibited potent schizonticidal antimalarial activity during primary screening in rodent models, with maximum parasitaemia suppression (85.18% and 83.65%, respectively) at a dose of 20 mg/kg body weight when compared to the standard drugs chloroquine and artesunate. In silico techniques were employed to identify the probable biological target and mechanism of action of these isolated compounds. Molecular docking studies also predicted the binding orientations and multi-targeted action of these compounds, in particular costunolide diepoxide with maximum affinity towards SERCA and DHFR proteins. Additionally, favourable in silico ADMET parameters were envisaged through various computational programmes. 相似文献
84.
Pangkita Deka Biraj Jyoti Borah Himadri Saikia Pankaj Bharali 《Chemical record (New York, N.Y.)》2019,19(2-3):462-473
This account provides an overview of current research activities on nanoparticles containing the earth‐abundant and inexpensive element copper (Cu) and Cu‐based nanoparticles, especially in the field of environmental catalysis. The different synthetic strategies with possible modification of the chemical/ physical properties of these nanoparticles using such strategies and/or conditions to improve catalytic activity are presented. The design and development of support and/or bimetallic systems (e. g., alloys, intermetallic, etc.) are also included. Herein, we report synthetic approaches of Cu and Cu‐based nanoparticles (monometallic copper, bimetallic copper and copper (II) oxide nanoparticles/nanostructures) and impregnation of such nanoparticles onto support material (e. g., Co3O4 nanostructure), along with their applications as environmental catalyst for various oxidation and reduction reactions. Finally, this account provides necessary advances and perspectives of Cu‐based nanoparticles in the environmental catalysis. 相似文献
85.
Nonequilibrium steady-state currents, unlike their equilibrium counterparts, continuously dissipate energy into their physical surroundings leading to entropy production and time-reversal symmetry breaking. This Letter discusses these issues in the context of quantum impurity models. We use simple thermodynamic arguments to define the rate of entropy production sigma and show that sigma has a simple information-theoretic interpretation in terms of nonequilibrium distribution functions. This allows us to show that the entropy production is strictly positive for any nonequilibrium steady state. We conclude by applying these ideas to the resonance level model and the Kondo model. 相似文献
86.
We solve the general problem of mixing of electromagnetic and scalar or pseudoscalar fields coupled by axion-type interactions
L
int = g
ϕ
ϕε
μναβ
F
μν
F
αβ
. The problem depends on several dimensionful scales, including the magnitude and direction of background magnetic field,
the pseudoscalar mass, plasma frequency, propagation frequency, wave number, and finally the pseudoscalar coupling. We apply
the results to the first consistent calculations of the mixing of light propagating in a background magnetic field of varying
directions, which show a great variety of fascinating resonant and polarization effects.
相似文献
87.
Metal embedded in metal oxide nanoparticles are active as catalyst in plethora of industrially important reactions. Herein, embedded Cu@Fe2O3 nanoparticles was synthesized via a one step hydrothermal strategy which selectively catalyzes the hydrogenation of diverse nitroaromatics in H2O at room temperature. The remarkable catalytic performance is due to the successful hybridization of metallic Cu and Fe2O3 which in turn allows easy electroflipping between various oxidation states of Cu and Fe. Azo- and azoxy-compounds are not formed during the catalyzed process. This evidently establish that the hydrogenation of nitroaromatics proceeds via direct route with >99% selectivity to the corresponding anilines. 相似文献
88.
89.
Pankaj Kumar Chaurasia Sudha Yadava Shashi Lata Bharati Sunil Kumar Singh 《Green Chemistry Letters and Reviews》2014,7(1):100-104
This communication reports the selective bioconversions of substituted toluenes to substituted benzaldehydes without the help of any mediators by purified laccase of indigenous fungal strain Fomes durissimus microbial type culture collection (MTCC)-1173. Molecular mass of laccase purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was found to be 74.86 kDa (~75 kDa). By using this purified laccase, selective bioconversions of 3-nitrotoluene to 3-nitrobenzaldehyde, 2-fluorotoluene to 2-fluorobenzaldehyde, 4-fluorotoluene to 4-fluorobenzaldehyde, 2-chlorotoluene to 2-chlorobenzaldehyde and 4-chlorotoluene to 4-chlorobenzaldehyde have been done without the help of mediator molecules within 1–2 hrs at room temperature and pressure with high yields (>90%). All the above bioconversions are good examples of green chemistry. 相似文献
90.
N‐Heterocyclic Carbene Catalysis via Azolium Dienolates: An Efficient Strategy for Remote Enantioselective Functionalizations 下载免费PDF全文
Dr. Xiang‐Yu Chen Qiang Liu Dr. Pankaj Chauhan Prof. Dr. Dieter Enders 《Angewandte Chemie (International ed. in English)》2018,57(15):3862-3873
N‐heterocyclic carbene (NHC) catalysis has emerged as a powerful strategy in organic synthesis. In recent years a number of reviews have been published on NHC‐catalyzed transformations involving Breslow intermediates, acyl azoliums, α,β‐unsaturated acyl azoliums, homoenolate equivalents, and azolium enolates. However, the azolium dienolate intermediates generated by NHCs have been employed in asymmetric synthesis only very recently, especially in cycloadditions dealing with remote functionalization. This Minireview highlights all the developments and the new advances in NHC‐catalyzed asymmetric cycloaddition reactions involving azolium dienolate intermediates. 相似文献