全文获取类型
收费全文 | 990篇 |
免费 | 49篇 |
国内免费 | 2篇 |
专业分类
化学 | 635篇 |
晶体学 | 6篇 |
力学 | 35篇 |
数学 | 80篇 |
物理学 | 285篇 |
出版年
2023年 | 11篇 |
2022年 | 24篇 |
2021年 | 19篇 |
2020年 | 22篇 |
2019年 | 34篇 |
2018年 | 23篇 |
2017年 | 27篇 |
2016年 | 46篇 |
2015年 | 32篇 |
2014年 | 43篇 |
2013年 | 76篇 |
2012年 | 86篇 |
2011年 | 88篇 |
2010年 | 41篇 |
2009年 | 48篇 |
2008年 | 45篇 |
2007年 | 53篇 |
2006年 | 32篇 |
2005年 | 49篇 |
2004年 | 41篇 |
2003年 | 28篇 |
2002年 | 25篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1961年 | 2篇 |
排序方式: 共有1041条查询结果,搜索用时 31 毫秒
941.
Parimal Kundu Samiran Mitra Sonjay Kumar Dilip Banerjee Ranga Lal Bhattacharya 《Transition Metal Chemistry》1995,20(5):417-422
Summary Double complex salts containing cationic CuII having cyclic ligand piperazine (pipz), N-methylpiperazine (mpipz) and N,N-dimethylpiperazine (dmpipz) and hexacyanoferrate(III) ion have been synthesized and characterized by elemental analyses, i.r. and electronic spectra, and magnetic moment measurements. Mössbauer spectra at room temperature and at 80 K, were recorded in order to evaluate the metal-metal charge transfer and the impact of the cyclic ligand present in cationic moiety of the double complex salt upon the Mössbauer spectra of the hexacyanoferrate(III) ion. Evidence for metal-metal charge transfer is supported by electronic spectra and magnetic susceptibilities. Variable temperature e.p.r. spectra were recorded in order to determine the distortion of crystal system. Thermally induced stereochemical studies have been carried out with the help of i.r. spectral data. Kinetics of thermochemical reactions have also been studied. Activation energies (E
infa
sup*
) and inception temperatures for the thermochemical reactions show the order of stability of the double complex salts follows the trend: dmpipz > mpipz > pipz, which indicates that the + I effect is more pronounced than steric effect. 相似文献
942.
Specific heat capacities and apparent molar heat capacities of aqueous nicotinamide have been determined from 25.0 to 55.0°C using microdifferential scanning calorimetry in the molality range of 0.07433 to 1.50124 mol-kg–1. Densities and apparent molar volumes have also been determined for aqueous nicotinamide from 10.30 to 34.98°C using a digital densimeter in the molality range 0.07804–2.02435 mol-kg–1. The results of these measurements have been used to calculate the following partial molar quantities and temperature derivatives for aqueous nicotinamide as a function of temperature: C
p,2,m
o, (C
p,2,m
o/T)p, (2Cp,2,m
o/T
2)p, V
2,m
o, ( V
2,m
o/T)p, and (2
V
2,m
2/T
2)p. The results are discussed in terms of the changes in the packing of nicotinamide molecules in the crystal, interactions in the aqueous form, and its structure-promoting ability with rise in temperature. 相似文献
943.
Krishna C. Majumdar Uday K. Kundu Swapan K. Samanta Nirmal K. Jana 《Monatshefte für Chemie / Chemical Monthly》2003,25(6):1137-1143
Two hitherto unreported pyrimidine annelated heterocycles were synthesized from 6-cyclopent-2-enyl-5-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and 5-cyclopent-2-enyl-6-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione by reaction with pyridine hydrotribromide or hexamethylenetetramine hydrotribromide. The first one was also obtained by reaction with concentrated sulfuric acid. 相似文献
944.
M. Chowdhury T. Chakraborty T. Kundu L. Kundu A. K. Banerjee D. Nath S. P. Bhattacharyya 《Journal of Chemical Sciences》1991,103(3):265-276
The complementarity of one- and two-photon spectroscopy has been utilised for throwing light on the following problems of
chemical interest: (1) Weak interaction between identical chromophores separated by insulating bridges gives rise to split
states of different symmetries. Two-photon spectroscopy (TPA), in conjunction with one-photon absorption (OPA), has been used
to identify the states and hence to estimate the magnitude of interaction in bimolecules and trimolecules. From the shifts
between the one- and the two-photon spectra, the splittings have been estimated. Calculations confirm that the dominant interaction
is the through-bond one. (2) The second type of problem is the identification ofg andu vibrations in molecules. We have initiated studies on three molecules in jet-cooled conditions: 9,10-dihydro-anthracene (DHA).
9,10-dihydro-phenanthrene (DHP) and octa-fluoronaph-thalene (OFN). Only the one-photon fluorescence excitation spectra have
so far been obtained by us and the TPA spectra are under investigation. (3) The third class of molecules discussed here are
the Ln3+ complexes wheref
n⇒ fn transitions are intrinsically two-photon allowed. We have studied two GD3+ single crystals. The CF-splittings, observed clearly in TPA, have been fitted with a parametric model. Some of our observations
on the variations of TPA intensity patterns from crystal to crystal, such as circular:linear polarisation ratios, relative
intensities of transitions to differentJ-states, do not quite fit in with the Axe-Judd-Downer model. The discrepancies call for a reappraisal of the role of ligand
in the TPA process. 相似文献
945.
Abhijit Bandyopadhyay Mousumi de Sarkar Anil K. Bhowmick 《Journal of Polymer Science.Polymer Physics》2005,43(17):2399-2412
The effect of polymer–filler interaction on solvent swelling and dynamic mechanical properties of the sol–gel derived acrylic rubber (ACM)/silica, epoxidized natural rubber (ENR)/silica, and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites has been described for the first time. Tetraethoxysilane (TEOS) at three different concentrations (10, 30, and 50 wt %) was used as the precursor for in situ silica generation. Equilibrium swelling of the hybrid nanocomposites in respective solvents at ambient condition showed highest volume fraction of the polymer in the swollen gel in PVA/silica system and least in ACM/silica, with ENR/silica recording an intermediate value. The Kraus constant (C) also followed a similar trend. In dynamic mechanical analysis, the storage modulus dropped at higher strain (>1%), which indicated disengagement of polymer segments from the filler surfaces. This drop was maximum in ACM/silica, intermediate in ENR/silica, and minimum in PVA/silica, both at 50 and 70 °C. The drop in modulus with theoretical volume fraction of silica (ϕ) was interpreted with the help of a Power law model ΔE′ = a1ϕ, where a1 was a constant and b1 was primarily a filler attachment parameter. Strain dependence of loss modulus was observed in ACM/silica hybrid nanocomposites, while ENR/silica and PVA/silica nanocomposites showed almost strain‐independent behavior. The storage modulus showed sharp increase with increasing frequency in ACM/silica system, while that was lower in both ENR/silica (at higher frequency) and PVA/silica systems (in the entire frequency spectrum). The increase in modulus with ϕ also followed similar model ΔE′ = a2ϕ proposed in the strain sweep mode. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2399–2412, 2005 相似文献
946.
Coupled limit cycle oscillators with instantaneous mutual coupling offer a useful but idealized mathematical paradigm for
the study of collective behavior in a wide variety of biological, physical and chemical systems. In most real-life systems
however the interaction is not instantaneous but is delayed due to finite propagation times of signals, reaction times of
chemicals, individual neuron firing periods in neural networks etc. We present a brief overview of the effect of time-delayed
coupling on the collective dynamics of such coupled systems. Simple model equations describing two oscillators with a discrete
time-delayed coupling as well as those describing linear arrays of a large number of oscillators with time-delayed global
or local couplings are studied. Analytic and numerical results pertaining to time delay induced changes in the onset and stability
of amplitude death and phase-locked states are discussed. A number of recent experimental and theoretical studies reveal interesting
new directions of research in this field and suggest exciting future areas of exploration and applications. 相似文献
947.
A. Kundu 《Theoretical and Mathematical Physics》2007,151(3):831-842
We discover an operator-deformed quantum algebra using the quantum Yang-Baxter equation with the trigonometric R-matrix. This
novel Hopf algebra together with its q→1 limit seems the most general Yang-Baxter algebra underlying quantum integrable systems.
We identify three different directions for applying this algebra in integrable systems depending on different sets of values
of the deforming operators. Fixed values on the whole lattice yield subalgebras linked to standard quantum integrable models,
and the associated Lax operators generate and classify them in a unified way. Variable values yield a new series of quantum
integrable inhomogeneous models. Fixed but different values at different lattice sites can produce a novel class of integrable
hybrid models including integrable matter-radiation models and quantum field models with defects, in particular, a new quantum
integrable sine-Gordon model with defect.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 3, pp. 470–485, June, 2007. 相似文献
948.
Recently generalized exponential distribution has received considerable attentions. In this paper, we deal with the Bayesian
inference of the unknown parameters of the progressively censored generalized exponential distribution. It is assumed that
the scale and the shape parameters have independent gamma priors. The Bayes estimates of the unknown parameters cannot be
obtained in the closed form. Lindley’s approximation and importance sampling technique have been suggested to compute the
approximate Bayes estimates. Markov Chain Monte Carlo method has been used to compute the approximate Bayes estimates and
also to construct the highest posterior density credible intervals. We also provide different criteria to compare two different
sampling schemes and hence to find the optimal sampling schemes. It is observed that finding the optimum censoring procedure
is a computationally expensive process. And we have recommended to use the sub-optimal censoring procedure, which can be obtained
very easily. Monte Carlo simulations are performed to compare the performances of the different methods and one data analysis
has been performed for illustrative purposes.
This work was partially supported by a grant from the Department of Science and Technology, Government of India 相似文献
949.
Pintu K. Kundu 《Journal of organometallic chemistry》2009,694(3):382-8568
Reaction of dimethylsulfoxonium methylide with a β-silylmethylene malonate gives diversified products, cyclopropane, cyclobutane or allyl and homoallyl silanes depending upon the stoichiometry of the reactants and reaction conditions. Contrary to this, reaction of a β-arylmethylene malonate gives only the cyclopropane product. The product(s) formed are unique and the silicon group played a crucial role either by assisting and/or by participating in the process. 相似文献
950.
Benjamin Zimmerman Payel Kundu William D. Rooney Jacob Raber 《Molecules (Basel, Switzerland)》2021,26(11)
In both humans and animal models, consumption of a high-saturated-fat diet has been linked to vascular dysfunction and cognitive impairments. Laboratory animals provide excellent models for more invasive high-fat-diet-related research. However, the physiological differences between humans and common animal models in terms of how they react metabolically to high-fat diets need to be considered. Here, we review the factors that may affect the translatability of mechanistic research in animal models, paying special attention to the effects of a high-fat diet on vascular outcomes. We draw attention to the dissociation between metabolic syndrome and dyslipidemia in rodents, unlike the state in humans, where the two commonly occur. We also discuss the differential vulnerability between species to the metabolic and vascular effects of macronutrients in the diet. Findings from animal studies are better interpreted as modeling specific aspects of dysfunction. We conclude that the differences between species provide an opportunity to explore why some species are protected from the detrimental aspects of high-fat-diet-induced dysfunction, and to translate these findings into benefits for human health. 相似文献