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91.
Dinda E Rashid MH Biswas M Mandal TK 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):17568-17580
We describe a general one-step facile method for depositing gold nanoparticle (GNP) thin films onto any type of substrates by the in situ reduction of AuCl(3) using a newly designed redox-active ionic liquid (IL), tetrabutylphosphonium citrate ([TBP][Ci]). Various substrates such as positively charged glass, negatively charged glass/quartz, neutral hydrophobic glass, polypropylene, polystyrene, plain paper, and cellophane paper are successfully coated with a thin film of GNPs. This IL ([TBP][Ci]) is prepared by the simple neutralization of tetrabutylphosphonium hydroxide with citric acid. We also demonstrate that the [TBP][Ci] ionic liquid can be successfully used to generate GNPs in an aqueous colloidal suspension in situ. The deposited GNP thin films on various surfaces are made up of mostly discrete spherical GNPs that are well distributed throughout the film, as confirmed by field-emission scanning electron microscopy. However, it seems that some GNPs are arranged to form arrays depending on the nature of surface. We also characterize these GNP thin films via UV-vis spectroscopy and X-ray diffractometry. The as-formed GNP thin films show excellent stability toward solvent washing. We demonstrate that the thin film of GNPs on a glass/quartz surface can be successfully used as a refractive index (RI) sensor for different polar and nonpolar organic solvents. The as-formed GNP thin films on different surfaces show excellent catalytic activity in the borohydride reduction of p-nitrophenol. 相似文献
92.
Clayborne PA Gupta U Reber AC Melko JJ Khanna SN Castleman AW 《The Journal of chemical physics》2010,133(13):134302
Three-dimensional aromaticity is shown to play a role in the stability of deltahedral Zintl clusters and here we examine the connection between aromaticity and stability. In order to gain further insight, we have studied Zintl analogs comprised of bismuth doped tin clusters with photoelectron spectroscopy and theoretical methods. To assign aromaticity, we examine the ring currents induced around the cage by using the nucleus independent chemical shift. In the current study, BiSn(4)(-) is a stable cluster and fits aromatic criteria, while BiSn(5)(-) is found to fit antiaromatic criteria and has reduced stability. The more stable clusters exhibit an aromatic character which originates from weakly interacting s-states and bonding orbitals parallel to the surface of the cluster, while nonbonding lone pairs perpendicular to the surface of the cluster account for antiaromaticity and reduced stability. The effect of three-dimensional aromaticity on the electronic structure does not result in degeneracies, so the resulting variations in stability are smaller than those seen in conventional aromaticity. 相似文献
93.
Kinsuk Das Tarak Nath Mandal Somnath Roy Samik Gupta Anil Kumar Barik Partha Mitra Arnold L. Rheingold Susanta Kumar Kar 《Polyhedron》2010
The varying coordination modes of the title ligand, L [5-methyl-1-(pyridin-2-yl)-N′-[pyridin-2-ylmethylidene]pyrazole-3-carbohydrazide] towards the different metal centers is reported by preparation and characterization of Cu(II), Zn(II) and Cd(II) complexes, [Cu(L)NO3.H2O](NO3) (1) [Zn(L)2](ClO4)2·2DMF (2) and [Cd(L)(I)2] (3) respectively. In 1, the neutral ligand serves as tetradentate 4 N donor where both pyridine and pyrazole nitrogen atoms of pyridyl–pyrazole part are coordinatively active, leaving the carbonyl oxygen of the carbohydrazide part inactive. The same pyridine and pyrazole N atoms remain abstained from the coordination process towards the Zn(II) and Cd(II) metal centers. For 2 and 3 the ligand behaves as a tridentate NNO donor where the two nitrogen atoms come from azomethine, pyridine of pyridine-2-carbaldehyde parts and O from carbonyl oxygen atoms (carbohydrazide part). The complex 1 and 2 are distorted octahedral while complex 3 adopts distorted square pyramidal geometry. All the complexes are X-ray crystallographically characterized. 相似文献
94.
We have investigated the localization and environment of tryptophan residues in different quaternary and conformational states
(tetrameric, dimeric, monomeric and unfolded) of metallized and demetallized concanavalin A (ConA) by selective chemical modification,
fluorescence, and phosphorescence. ConA has four tryptophan residues (Trp 40, Trp 88, Trp 109 and Trp 182) per subunit. The
pattern of oxidation by N-bromosuccinimide (NBS) shows that NBS modifies, in dimer, only Trp 182 which remains inaccessible
in tetramer, two (Trp 88 along with Trp 182) in monomer, all four in unfolded form in presence of EDTA, and three (possibly
Trp 40 along with Trp 88 and Trp 182) in unfolded form from native or remetallized ConA. Utilizing wavelength-selective fluorescence
approach, we have observed a red edge excitation shift (REES) of 6–8 nm for tetramer and dimer. A more pronounced REES (11 nm)
is observed for oxidized monomer compared to REES (3 nm) for unoxidized species. Acrylamide quenching shows the Stern-Volmer
constant (KSV) for dimer, monomer, unfolded ConA and unfolded apo-ConA being 3.8, 5.2, 12.8, 14.0 M−1, respectively. Phosphorescence studies at 77 K give more structured spectra, with two (0,0) bands at 406.2 (weak) and 413.2 nm
for tetramer. However, a single (0,0) band appears at 413.2 for dimer and 412.6 nm for monomer, while the (0,0) band of the
oxidized monomer is red shifted to 414.4 nm. These results may provide important insight into subtlety of organization and
environment of tryptophans in the context of folding and structural studies of oligomeric proteins including lectins. 相似文献
95.
Dibakar Sahoo Prosenjit Bhattacharya Hirak Kumar Patra Paulami Mandal Sankar Chakravorti 《Journal of nanoparticle research》2011,13(12):6755-6760
Change of α-helical structure of heme protein (Hb) to a β-sheet and random coil conformation because of the interaction of
glycine capped gold nanoparticles (20–60 nm) as observed from attenuation total reflectance, absorption, Fourier transform
infra red, and Circular Dichroism spectroscopy has been reported in this article. Upon interaction, protein takes a cylindrical
shape of length 12 μm and diameter 0.35 μm as revealed from scanning electron microscopy and transmission electron microscopy.
The Selected-Area Electron beam Diffraction pattern shows change of crystalline structure in GNP to amorphous nature with
the interaction of Hb. 相似文献
96.
D. Bhoi P. Mandal P. Choudhury S. Dash A. Banerjee 《Physica C: Superconductivity and its Applications》2011,471(7-8):258-264
The magnetization of the PrFeAsO0.60F0.12 polycrystalline sample has been measured as functions of temperature and magnetic field (H). The observed total magnetization is the sum of a superconducting irreversible magnetization and a paramagnetic magnetization. Analysis of dc susceptibility χ(T) in the normal state shows that the paramagnetic component of magnetization comes from the Pr3+ magnetic moments. The intragrain critical current density (JL) derived from the magnetization data is large. The JL(H) curve displays a second peak which shifts towards the high-field region with decreasing temperature. In the low-field region, a plateau up to a field H* followed by a power law H?5/8 behavior of JL(H) is the characteristic of the strong pinning. A vortex phase diagram for the present superconductor has been obtained from the magnetization and resistivity data. 相似文献
97.
Swades De Priyatosh Mandal Shyam S. Chakraborty 《Mathematical and Computer Modelling》2011,53(11-12):2093-2107
Standard analyses of wireless random access protocols that are available in the literature assume negligible propagation delay between any two nodes. This assumption holds good in reasonably short-range terrestrial RF (radio frequency) wireless networks. On the contrary, in wireless communications involving acoustic wave propagation, as in underwater wireless networks, even short distance propagation has appreciably large propagation delay. This observation has led to several recent simulation and experimental studies on underwater Aloha and slotted-Aloha (S-Aloha) protocols and also a few new proposals on random access protocols for underwater wireless ad hoc networks (UWN). To study the efficiency of more advanced multiaccess communication protocols for UWN, it is important to benchmark their performances with respect to the two basic random access protocols, Aloha and S-Aloha. This paper provides an analytic framework to capture the performance of Aloha and S-Aloha protocols in an underwater environment with high and random internodal signal propagation delay. The performance of underwater Aloha and S-Aloha are contrasted with those in short-range terrestrial RF wireless networks. The analysis shows that random internodal propagation delay has no effect on the underwater Aloha performance. It also sheds light on the throughput degradation of underwater S-Aloha with a slotting concept that achieves RF S-Aloha equivalent one-slot vulnerability. Additionally, a modified slotting concept is introduced where the slot size is judiciously reduced such that even by allowing some collisions the overall system throughput can be increased. Our calculations show that, with the modified slotting approach up to 17% throughput performance gain can be achieved over the naive (RF S-Aloha equivalent) slotting approach in UWN. Our analytic results are supported by discrete event simulations. 相似文献
98.
The uptake behavior of long-lived radionuclides such as 134Cs (2.06 years), 137Cs (30 years) or 133Ba (10.54 years) on calcium alginate (CA) beads have been investigated. The CA beads are able to remove 133Ba (92%) at pH 7 after 90 min of exposure from the binary mixture of two. The separation method of short-lived daughter 137Ba (2.55 min) from its long-lived parent 137Cs (30 years) using this CA beads have also been developed. 相似文献
99.
Dipak Ghosh Argha Deb Subrata Biswas Pasupati Mandal Asok Kumar Mallick Prabir Kumar Haldar 《Indian Journal of Physics》2009,83(10):1463-1485
This paper presents an investigation of compound hadrons (pions and protons) distribution emitted from 24Mg-AgBr and 12C-AgBr interactions both at 4.5 AGeV and 32S-AgBr interactions at 200 AGeV. The study includes azimuthal correlations (two particle and three particle), azimuthal asymmetry
and fractal behaviour. This paper reveals some interesting results. 相似文献
100.