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991.
A new macrocyclic ligand, 1,3,5-triaza-2,4:7,8:16,17-tribenzo-9,12,15-trioxacyclooktadeca-1,5-dien (L) was synthesized by reaction of 2,6-diaminopyridine and 1,7-bis(2-formylphenyl)-1,4,7-trioxaheptane. Then, its Cu(II), Ni(II), Pb(II), Co(III) and La(III) complexes were synthesized by template effect by reaction of 2,6-diaminopyridine and 1,7-bis(2-formylphenyl)-1,4,7-trioxaheptane and Cu(NO3)2 · 3H2O, Ni(NO3)2 · 6H2O, Pb(NO3)2, Co(NO3)2 · 6H2O, La(NO3)3 · 6H2O, respectively. The ligand and its metal complexes have been characterized by elemental analysis, IR, 1H and 13C NMR, UV–Vis spectra, magnetic susceptibility, thermal gravimetric analysis, conductivity measurements, mass spectra and cyclic voltammetry. All complexes are diamagnetic and Cu(II) complex is binuclear. The Co(II) was oxidized to Co(III). The comparative electrochemical studies show that the nickel complex exhibited a quasi-reversible one-electron reduction process while copper and cobalt complexes gave irreversible reduction processes in DMSO solution. 相似文献
992.
Summary The solvolysis of trans-[Co(4-Etpy)4Cl2]+ (1) (Etpy=ethylpyridine) was investigated in water and in a wide range of water+methanol mixtures. The effect of temperature on the solvolysis was considered and the thermodynamic parameters of activation were calculated. The free energies of transfer of (1) in the initial state were calculated from the solubility of the complex [Co(4-Etpy)4Cl2]2[ReCl6]. The free energy of transfer of the cation (1) in the transition state was calculated using a free energy cycle. The effect of the solvent structure on (1) is dominant in the transition state, where –G
t
o
(1) transition >–G
t
o
(1) initial. Comparison of the present thermodynamic data with those obtained previously fortrans-[Co(4-Mepy)4Cl2]+, (2), andtrans-[Co(py4Cl2]+, (3) in the same solvent mixture, shows that the stability increases in the order: (1), (2)<(3) at low mole fraction of the co-solvent, contrary to expectation, while at high mole fraction the order of increasing stability is: (1)<(3)<(2). The results were interpreted on non-electrostatic grounds. 相似文献
993.
Ismail Ijjaali 《Journal of solid state chemistry》2004,177(3):760-764
The ternary selenides LnCuSe2 (Ln=La, Ce, Pr, Nd, Sm) have been synthesized by the reaction at 1173 K of Ln, Cu, and Se in a KBr or KI flux. The compounds, which are isostructural with LaCuS2, crystallize with four formula units in the space group P21/c of the monoclinic system. The structure may be thought of as consisting of layers of CuSe4 tetrahedra separated by double layers of LnSe7 monocapped trigonal prisms along the a-axis. Cell constants (Å or deg) at 153 K are: LaCuSe2, 6.8142(5), 7.5817(6), 7.2052(6), 97.573(1)°; CeCuSe2, 6.7630(5), 7.5311(6), 7.1650(6), 97.392(1)°; PrCuSe2, 6.740(1), 7.481(1), 7.141(1), 97.374(2)°; NdCuSe2, 6.7149(6), 7.4452(7), 7.1192(6), 97.310(1)°; SmCuSe2, 6.6655(6), 7.3825(7), 7.0724(6), 97.115(1)°. There are no Se-Se bonds in the structure of LnCuSe2; the formal oxidation states of Ln/Cu/Se are 3+/1+/2−. 相似文献
994.
Kite GC Ismail M Simmonds MS Houghton PJ 《Rapid communications in mass spectrometry : RCM》2003,17(14):1553-1564
Analysis of crude methanolic extracts of fresh khat (Catha edulis) by liquid chromatography/mass spectrometry (LC/MS) revealed the presence of 62 cathedulin alkaloids (compared with 15 published structures). Many cathedulins generated doubly protonated molecules following electrospray ionisation and the ratio of doubly to singly protonated species could be manipulated by adjusting the electrospray capillary position and source conditions. By selecting the doubly protonated species for serial mass spectrometric analysis (MS/MS), it was possible to use an ion trap mass spectrometer to observe singly charged product ions at lower m/z values than ion trap MS/MS analysis of [M+H](+) would have allowed. These spectra were particularly valuable in elucidating the acylation patterns of cathedulins where MS/MS analysis of [M+H](+) resulted in loss of a large neutral species to yield a small singly charged fragment below the lower limit for ion trapping. Acylation patterns for most of the 62 cathedulins are proposed from mass spectrometric analysis, and the data obtained for a major unreported cathedulin of mass 1001 Da suggest that it belongs to a new group of cathedulins having a cathate dilactone bridge but not an evoninate bridge. 相似文献
995.
Danuta Frackowiak Ismail Abdourakhmanov Roman Cegielski Roger M. Leblanc 《Photochemistry and photobiology》1993,57(5):877-884
Abstract— Polarized absorption, fluorescence and photoacoustic spectra of bacteriochlorophyll (BChl)-lipoprotein complexes from the purple bacterium Chromatium minutissimum oriented in stretched polyvinylalcohol films were measured at room temperature and 85 K. The preparations contain large amounts of the B800-820 antenna complexes. From polarized absorption spectra taken under various light beam incidence angles with respect to the film plane, conclusions concerning arrangement of pigment molecules in B800-820 complex are obtained. The transition moments of the BChl Qy band are not exactly parallel to the membrane plane. It seems that there are pools of differently oriented BChl chromophores absorbing in both 800 nm and 820 nm regions. Change in temperature strongly influences linear dichroism of carotenoids and BChl Qy bands. The reversible changes in absorption, linear dichroism and photoacoustic spectra caused by the variation in sample temperature suggest strongly the reversible twisting of carotenoid molecules, related probably to modification of the interactions between carotenoids and proteins. Various carotenoids exhibit different yield of thermal deactivation and this yield is also temperature dependent. 相似文献
996.
The kinetics of the solvolytic aquation of trans-[Ru (3-Me Py)4Cl2] was studied spectrophotometrically in water – isopropanol in the range (30–90% v/v), and water acetonitrile in the range
(10–70% v/v), and in the temperature range 50–65 °C. Plots of log k versus the reciprocal of the relative permittivity and Grunwald–Winstien gave non-linear plots. This non-linearity is derived from
a large differential effect of solvent structure between the initial and transition states. The plot of log k versus water concentration was also non linear; evidence for the presence of a S
N
1
mechanism. However, extrema in the variation of enthalpy ΔH* and entropy ΔS* of activation correlate well with the extrema in physical properties of the mixtures which are related to changes in solvent
structure. Linear plots of ΔH* versus ΔS* were obtained and the iso- kinetic temperature indicates that the reaction is entropy controlled. 相似文献
997.
For L a second order linear elliptic differential operator on
, one is usually interested in finding positive solutions of the heat equation
where V is a nonnegative potential. But for L the Laplacian, it was discovered by [BG] in 1984 that positive solutions may not exist if V is too singular. We use Gaussian estimates to extend this result to the case when L is not symmetric.
Helmut H. Schaefer in memoriam 相似文献
998.
Alexandra Quek Nur Kartinee Kassim Amin Ismail Muhammad Alif Mohammad Latif Khozirah Shaari Dai Chuan Tan Pei Cee Lim 《Molecules (Basel, Switzerland)》2021,26(1)
The present study investigated the antidiabetic properties of the extracts and fractions from leaves and stem bark of M. glabra based on dipeptidyl peptidase-4 (DPP-4) and α-Amylase inhibitory activity assays. The chloroform extract of the leaves was found to be most active towards inhibition of DPP-4 and α-Amylase with IC50 of 169.40 μg/mL and 303.64 μg/mL, respectively. Bioassay-guided fractionation of the leaves’ chloroform extract revealed fraction 4 (CF4) as the most active fraction (DPP-4 IC50: 128.35 μg/mL; α-Amylase IC50: 170.19 μg/mL). LC-MS/MS investigation of CF4 led to the identification of trans-decursidinol (1), swermirin (2), methyl 3,4,5-trimethoxycinnamate (3), renifolin (4), 4′,5,6,7-tetramethoxy-flavone (5), isorhamnetin (6), quercetagetin-3,4′-dimethyl ether (7), 5,3′,4′-trihydroxy-6,7-dimethoxy-flavone (8), and 2-methoxy-5-acetoxy-fruranogermacr-1(10)-en-6-one (9) as the major components. The computational study suggested that (8) and (7) were the most potent DPP-4 and α-Amylase inhibitors based on their lower binding affinities and extensive interactions with critical amino acid residues of the respective enzymes. The binding affinity of (8) with DPP-4 (−8.1 kcal/mol) was comparable to that of sitagliptin (−8.6 kcal/mol) while the binding affinity of (7) with α-Amylase (−8.6 kcal/mol) was better than acarbose (−6.9 kcal/mol). These findings highlight the phytochemical profile and potential antidiabetic compounds from M. glabra that may work as an alternative treatment for diabetes. 相似文献
999.
Lukka Thuyavan Yogarathinam Juhana Jaafar Ahmad Fauzi Ismail Pei Sean Goh Mohd Hilmi Bin Mohamed Mohamad Fahrul Radzi Hanifah Arthanareeswaran Gangasalam Jerome Peter 《先进技术聚合物》2022,33(1):66-80
In direct methanol fuel cells (DMFC), methanol crossover is a major issue which has reduced the performance of polymer electrolyte membrane (PEM) for energy generation. In this study, graphene oxide (GO) and conductive polyaniline decorated GO (PANI-GO) were used as additives in fabrication of sulfonated poly(ether ether ketone) (SPEEK) nanocomposite PEM membrane to reduce methanol crossover. PANI-GO was synthesized by in situ polymerization method and the formation of PANI coated GO nanostructures was confirmed by surface morphology and crystallinity analysis. The membrane morphology and topography analysis confirmed that GO and PANI-GO were well dispersed on the surface of SPEEK membrane. 0.1 wt% PANI-GO modified SPEEK nanocomposite membrane exhibited the highest water uptake and ion exchange capacity of 40% and 1.74 meq g?1, respectively. The oxidative stability of the nanocomposite membranes also improved. Lower methanol permeability of 4.33 × 10?7 cm?2S?1 was noticed for 0.1 wt% PANI-GO modified SPEEK membrane. PANI-GO modified SPEEK membrane enhanced the proton conductivity, which was due to the existence of acidic and hydrophilic group present in PANI and GO. PANI-GO modified SPEEK membrane held higher selectivity of 1.94 × 104 S cm?3 s?1. Overall, these studies revealed that PANI-GO modified SPEEK membrane is a potential material for DMFC applications. 相似文献
1000.
Almanassra Ismail W. Zakaria Yahya Kochkodan Viktor Mroue Kamal Zekri Atef Atieh Muataz Ali Al-Ansari Tareq 《Journal of Thermal Analysis and Calorimetry》2022,147(21):11787-11803
Journal of Thermal Analysis and Calorimetry - In this study, the stability, thermal conductivity and viscosity of carbide-derived carbon antifreeze thermal fluids were explored. The study also... 相似文献