全文获取类型
收费全文 | 353篇 |
免费 | 8篇 |
专业分类
化学 | 269篇 |
晶体学 | 19篇 |
力学 | 11篇 |
数学 | 11篇 |
物理学 | 51篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 15篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 36篇 |
2012年 | 26篇 |
2011年 | 15篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 31篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1962年 | 1篇 |
1955年 | 1篇 |
1924年 | 1篇 |
1922年 | 1篇 |
1921年 | 1篇 |
排序方式: 共有361条查询结果,搜索用时 15 毫秒
21.
B. Bhushan A. Basumallick N.Y. Vasanthacharya S. Kumar D. Das 《Solid State Sciences》2010,12(7):1063-1069
Multiferroic nanoparticles of Bi1?xSrxFeO3 (x = 0, 0.01, 0.03, 0.05 and 0.07) were prepared by a facile sol–gel route and the variation of their structural, optical, dielectric and magnetic properties on strontium concentration has been studied. XRD and TEM results confirm the phase purity of the samples having high degree of crystallinity and monodispersity. The average particle size shows an exponential decline with increase in Sr concentration. A shape transformation from a multifaceted polygon to a spherical one has been observed as Sr concentration in the sample increases to 5%. In the second derivative FTIR spectra, the intensity of vibration peak at ~593 cm?1 that is characteristic of rhombohedral BiFeO3 is seen to decrease after Sr doping. All the samples showed typical M–H behavior of a ferromagnet with saturation magnetization achieved within an applied magnetic field of 10 kOe. The sample with 3% Sr substitution displayed saturation and remanent magnetization values 1.37 emu/g and 0.32 emu/g respectively that are highest among all the samples studied. Presence of exchange coupling produced due to interaction between the antiferromagnetic core and ferromagnetic shell is also observed in all Bi1?xSrxFeO3 nanoparticles. 相似文献
22.
Nirmal K. Shee Shanti G. Patra Michael G. B. Drew 《Journal of Coordination Chemistry》2016,69(24):3677-3691
Using the 1 : 2 condensate of benzil and 2-hydrazinopyridine as the ligand LH2 (H: dissociable NH proton), the red complex Cu(LH2)(ClO4)2 (1) was synthesized. The ligand also afforded the orange [Zn(LH2)(OH2)2](ClO4)2 (2). The X-ray crystal structures of the ligand, 1 and 2 have been determined. The metals in 1 and 2 have octahedral N4O2 environments. 1 is paramagnetic with μeff of one unpaired electron (1.63 μB and displays an axial EPR spectrum in the solid state with <g> = 2.07, characteristic of a (dx2?y2)1 ground state (g|| > g⊥; A|| = 16 mT). In cyclic voltammetry, 1 displays a two-electron oxidation around 0.9 V versus NHE. The two-electron oxidized (coulometrically) solution of 1 (golden yellow) gives an EPR spectrum with <g> = 2.17 and g|| < g⊥. The reaction of PPh3 with 1 yields the orange complex [Cu(LH2)(PPh3)](ClO4)2 (4). With the assumed chemical formula, the effective magnetization of 4 corresponds to one electron. Its EPR spectrum in the solid state is isotropic with g = 2.07. This g value yields a theoretical μeff of 1.80 μB at 298 K from Curie’s law, which matches very well with the experimental value of 1.89 μB at room temperature. Since single crystals of 4 could not be obtained, DFT calculations at the UBP86/6–311G(2d,p) level have been carried out and indicate that the cation in 4 is square pyramidal with the phosphine at the apex. The ease of the oxidation of the metal in 1 leads to the stabilization of the rare Cu(II)-P bond in 4. 相似文献
23.
Surgical sutures are probably the most widely used medical devices in healthcare applications for wound closure. During their application, sutures may be exposed to microorganisms present in the environment leading to bacterial biofilm formation, and thereon to surgical site infections. The physicochemical characteristics of the polymeric substrate play a major role in directing the behavior of the suture in a biological milieu. In such a context, it is necessary to develop sutures which actively repel and inhibit bacterial adherence and colonization on their surfaces. Drug eluting sutures have been proposed as a solution to this dilemma. Currently, bioactive agents (natural or synthetic) are being incorporated in polymeric materials via various methods including blending and compounding, surface functionalization and conjugation, and coating to render antimicrobial surgical sutures. However, each of these methods has its own pros and cons. Depending upon the nature of the substrate, an appropriate processing technique has to be chosen. In this article, we review the recent state-of-the-art developments and strategies in antimicrobial surgical suture fabrication. The efficacy and mechanism of these sutures in controlling infection is critically analyzed. However, such bioactive agent incorporated sutures have to be tested in clinically randomized trials to accurately gauze their applicability in a surgical setting. Presently, very few antimicrobial surgical sutures are available commercially. Therefore, there is a great scope for market development in this area. 相似文献
24.
Propranolol, a β‐adrenergic receptor antagonist, is a chiral compound that is marketed as a racemate, but only the (S)‐(?)‐enantiomer is responsible for the β‐adrenoceptor blocking activity. Different chromatographic methods have been applied for separation and determination of enantiomers of (RS)‐propranolol. In this article a review is presented on different liquid chromatographic methods used for enantioseparation of (RS)‐propranolol, using both HPLC and TLC. In addition, some aspects of enantioseparation under achiral phases of liquid chromatography have been briefly mentioned. 相似文献
25.
The aromaticity of metal-metal quintuple bonded complexes of the type M2L2 (M=Cr, Mo, and W; L=amidinate) are studied employing gauge including magnetically induced ring current (GIMIC) analysis and electron density of delocalized bonds (EDDB). It is found that the complexes possess two types of aromaticity: i) Hückel aromaticity through delocalization of ligand π electrons with metal-metal δ-bond-forming 6 conjugated electrons (4π and 2δ) ring; ii) Craig-Möbius aromaticity through delocalization of π electrons of both the ligands with metal d-orbitals in Craig type orientation forming 10π electrons ring with a double twist. Extended transition state natural orbital chemical valence (ETS-NOCV) and canonical molecular orbital natural chemical shielding (CMO-NCS) analysis confirm the Craig-Möbius type arrangement of the orbitals. Furthermore, the unprecedented Hückel and Möbius type aromaticity is confirmed from the plot of the current pathways using 3D line integral convolution (3D-LIC) plots. The metal-metal bond order also increases down the group as justified from the complete active space self-consistent field (CASSCF) analysis. Due to an increase in the π and δ electron conjugation, both the Hückel and Möbius aromaticity increase down the group. 相似文献
26.
Andrey Shatskiy Anton Axelsson Elena V. Stepanova Jian-Quan Liu Azamat Z. Temerdashev Bhushan P. Kore Bjrn Blomkvist James M. Gardner Peter Dinr Markus D. Krks 《Chemical science》2021,12(15):5430
A protocol for stereoselective C-radical addition to a chiral glyoxylate-derived N-sulfinyl imine was developed through visible light-promoted photoredox catalysis, providing a convenient method for the synthesis of unnatural α-amino acids. The developed protocol allows the use of ubiquitous carboxylic acids as radical precursors without prior derivatization. The protocol utilizes near-stoichiometric amounts of the imine and the acid radical precursor in combination with a catalytic amount of an organic acridinium-based photocatalyst. Alternative mechanisms for the developed transformation are discussed and corroborated by experimental and computational studies.A protocol for stereoselective C-radical addition to a chiral glyoxylate-derived N-sulfinyl imine was developed through visible light-promoted photoredox catalysis, providing a convenient method for the synthesis of unnatural α-amino acids. 相似文献
27.
Deepanshi Jaiswal Avantika Pandey Madhoolika Agrawal Shashi Bhushan Agrawal 《Photochemistry and photobiology》2023,99(1):45-56
Plants are inevitably grown in presence of sunlight, therefore bound to be exposed to natural UV-B radiation. Several studies have already been conducted with UV-B and medicinal plants and only few studies showed dose dependent variation. The present study aims to find out the variations and adaptation in Chlorophytum borivillianum under two different doses of UV-B radiation; ambient + low (3.2 kJm−2 d−1) and high (7.2 kJm−2 d−1) UV-B dose, denoted as LD and HD, respectively. Reduction in photosynthetic rate was higher at HD, while plants receiving LD displayed nonsignificant variation. During vegetative and reproductive stage, significant reduction (P ≤ 0.001) in stomatal conductance was obtained when exposed to HD-eUV-B. Fv/Fm showed more reductions in HD-eUV-B (12.6%) followed by LD-eUV-B (7.9%). Low and high doses of UV-B enhanced the anthocyanin content but the increase was significant in HD, indicates epidermal protection strategy by the plants. Under LD-eUV-B, the content of saponin, a major phytochemical constituent was enhanced by 26%. Phytochemical analysis of roots revealed reduction mostly in fatty acid components whereas the steroidal components (stigmasterol and sarsasapogenin) showed enhancement in response to LD. The study suggests the importance of LD-eUV-B in the stimulation of medicinal compounds in C. borivillianum. 相似文献
28.
Results of the scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoconductivity (PC), and
photoluminescence (PL) studies for the CdSSe:CdCl2,Ho films are presented in this paper. The SEM studies of different CdSSe films show a layered growth structure. A crystalline
nature of the films is observed in the XRD studies. The regions with stacking fault were also observed in the X-ray diffractograms.
The optical absorption spectra of these films show variations corresponding to the band gaps and the grain-sizes obtained
under various deposition conditions and also with annealing. The effect of flux, impurities and annealing on the saturated
photo to dark current ratio Ipc/Idc is observed in the PC rise and decay studies. The maximum value of Ipc/Idc ∼107 is obtained for the impurity doped annealed films. The PL emission spectra of CdSSe films show two emission peaks associated
with the annihilation of free excitons and the transitions between shallow donor and deep acceptor states. In CdSSe:CdCl2,Ho films, two PL emission peaks are observed at 495 nm and 545 nm corresponding to the transitions 5S2→5I8 and 5F3→5I8, respectively, in Ho. The effect of pH on PL and grain size is also included in the present studies. 相似文献
29.
30.
Nondispersive wavelength-division sampling 总被引:1,自引:0,他引:1
We propose and demonstrate a new wavelength-division-sampling technique with high temporal resolution. A discrete-time true-time delay generates multiwavelength near-transform-limited pulses from a supercontinuum source. Pulses sample the analog signal in an electro-optic modulator and are subsequently demultiplexed in a wavelength-division-multiplexing filter. A 100-Gsample/s experimental demonstration of this concept is presented. 相似文献