全文获取类型
收费全文 | 3490篇 |
免费 | 16篇 |
国内免费 | 5篇 |
专业分类
化学 | 1714篇 |
晶体学 | 53篇 |
力学 | 307篇 |
数学 | 275篇 |
物理学 | 1162篇 |
出版年
2022年 | 39篇 |
2021年 | 52篇 |
2020年 | 51篇 |
2019年 | 69篇 |
2018年 | 117篇 |
2017年 | 119篇 |
2016年 | 142篇 |
2015年 | 45篇 |
2014年 | 115篇 |
2013年 | 163篇 |
2012年 | 134篇 |
2011年 | 156篇 |
2010年 | 155篇 |
2009年 | 145篇 |
2008年 | 158篇 |
2007年 | 153篇 |
2006年 | 97篇 |
2005年 | 85篇 |
2004年 | 71篇 |
2003年 | 81篇 |
2002年 | 87篇 |
2001年 | 106篇 |
2000年 | 63篇 |
1999年 | 42篇 |
1998年 | 41篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 29篇 |
1994年 | 21篇 |
1993年 | 29篇 |
1992年 | 29篇 |
1991年 | 45篇 |
1990年 | 32篇 |
1989年 | 47篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 37篇 |
1985年 | 40篇 |
1984年 | 36篇 |
1982年 | 39篇 |
1981年 | 32篇 |
1980年 | 41篇 |
1979年 | 28篇 |
1978年 | 45篇 |
1977年 | 39篇 |
1975年 | 36篇 |
1974年 | 28篇 |
1973年 | 38篇 |
1972年 | 39篇 |
1971年 | 25篇 |
排序方式: 共有3511条查询结果,搜索用时 15 毫秒
61.
Lisachenko A. A. Kuznetsov V. N. Zakharov M. N. Mikhailov R. V. 《Kinetics and Catalysis》2004,45(2):189-197
A combined study of intrinsic structural defects in reduced TiO2 was performed using mass spectrometry, optical diffuse-reflectance spectroscopy, and UV photoelectron spectroscopy (UPS). It was found that the reduction of TiO2 resulted in the appearance of absorption in the region 0.50 h 3.50 eV (400 2500 nm), which is formed by absorption due to free electrons (a continuum at h 1.50 eV), local centers—Ti3+ ions (a band at 2.00 eV), and oxygen vacancies (bands at 1.17, 2.81, and 2.55 eV). The spectrum of induced occupied electronic states in the forbidden gap and the position of oxygen vacancy levels with respect to the Fermi level were determined by UPS. The absorption of reduced TiO2 was stable on the sample to T = 800 K in a vacuum; however, it weakened in contact with O2, NO, and N2O molecules beginning at T = 300 K (surface sites) and T 400 K (subsurface sites) as a result of filling oxygen vacancies with atomic oxygen in the course of dissociative adsorption. The adsorption complexes formed by the interaction of O2, NO, and N2O with defects were analyzed by temperature-programmed desorption. The distribution of sites over the energies of oxygen binding was found with the use of a nonuniform surface model, and specific oxygen adsorption species were revealed. It was found that the irradiation of TiO2 activates the formation and decay of sites and results in the formation of specific O2 and N2O adsorption species. 相似文献
62.
The paper presents a comparative analysis of the possibilities and characteristic features of the application of various polyhedral boron compounds, viz., the closo-decaborate anion [B10H10]2–, the closo-dodecaborate anion [B12H12]2–, the carba-closo-dodecaborate anion [CB11H12]–, carboranes C2B10H12, and the bis(dicarbollide) complexes [M(C2B9H11)2]– (M = Fe, Co, or Ni), in boron neutron capture therapy (BNCT) for cancer. The requirements on compounds used in BNCT are formulated and the advantages of the application of the closo-dodecaborate anion are considered. The data on the synthesis of various derivatives of the closo-dodecaborate anion, which either already found use in BNCT or are most promising in this field, are summarized. The possibilities of the application of agents derived from the closo-dodecaborate anion in medical diagnostics are discussed. 相似文献
63.
The charging of an illuminated silicon surface discovered by Abkevich [1] is of considerable interest for a number of practical applications (for example, semiconductor photography [2] and gas analysis). The present paper gives the results of investigations aimed at establishing the possibility of controlling the optical charge memory on the silicon surface by adsorption methods.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 92–96, January, 1981.We thank V. F. Kiselev for discussing the work and for helpful comments. 相似文献
64.
Silicon-silicon dioxide structures obtained by thermal, anodic, and chemical oxidation of silicon are studied by the photocharge and photoinjection current methods. It is shown that the extent of the fluctuation state tails" near the edges of the SiO2 forbidden zone is small (0.2 eV). The threshold for negative photocharging of anodic oxide traps is found to decrease with increase in oxide thickness, a fact related to the existence of a nonstoichiometric transition layer between the silicon and silicon dioxide. The effect of hydration and dehydration on negative optical charge of oxide traps is studied, and it is shown that the basis of electron traps is formed by the most hydrated and deformed SiO4Hn tetrahedra. The possibility of creating electron and hole traps in the oxide layer by doping with metal ions from a solution is demonstrated. It is found that the corresponding defects are also adsorption centers for water molecules by a coordination mechanism.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–7, July, 1981.In conclusion, the authors thank V. F. Kiselev for his interest in the study and valuable remarks. 相似文献
65.
N. A. Cherepkov V. V. Kuznetsov 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,7(3):271-280
A general expression for the angular distribution of photoelectrons with defined spin polarization ejected from oriented molecules is derived in the electric-dipole approximation in the limit of a weak radiation field. An analysis of its geometrical part permits to draw definite conclusions without calculating matrix elements. For linear molecules it is shown that in Hund's cases (a) and (b) photoelectrons may be polarized only parallel to the molecular axis, while in Hund's case (c) they may be polarized in any direction. Appearance of a circular dichroism for nonchiral oriented molecules of relatively low symmetry is predicted. Dependence of a circular dichroism in the angular distribution of photoelectrons on the symmetry of molecules is demonstrated. The results may serve as the framework for studying molecules oriented on surfaces, in liquid crystals, or by molecular beam techniques. 相似文献
66.
N. I. Fainer M. L. Kosinova Yu. M. Rumyantsev F. A. Kuznetsov 《Journal of Structural Chemistry》2004,45(1):S65-S70
Nanocrystalline transparent films SiCxNy were obtained by plasma-enhanced chemical deposition within the temperature range 473–1173 K from low pressure gas phase from a mixture of hexamethyldisilazane vapor, ammonia, and helium. Physical chemical properties of the films obtained were studied by IR and Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron spectroscopy and synchrotron radiation powder diffaction. Voltage-capacity and voltage-current measurements were also made. The dependence of chemical and phase composition of the films on deposition conditions was determined, and the formation of approximately 2 nm sized spherical nanocrystals within the films was established. The nanocrystals are formed by a phase similar to usual α-Si3N4, with silicon atoms partially substituted by carbon ones. 相似文献
67.
An ion disposed near the interface of two immiscible liquids creates a protrusion of one solvent into the other, subject to hydrophobic or hydrophilic interaction with these solvents. Due to a finite relaxation time the protrusion may not be able to spontaneously follow the ion when it moves across the interface. This, as well as any improper thermal fluctuation of the protrusion, will cause slowdown of the ion transfer. Here we present the results of theoretical analysis in which the stochastic motions of the ion and protrusion are coupled and considered on the same footing. We show that if the equilibrium electrochemical potential for the ion has no barrier, the ion transport is purely diffusional with D
eff = k
B
T/{6[r + (4/3)(h
max/)2
L]} being the effective diffusion coefficient. Here, is the average viscosity of the liquids, r is the Stokes radius of an ion, L and h
max are the average lateral size and the maximal height of the protrusion, and is the half-width of the function h
eq(z) which characterizes the equilibrium ion-interface coupling [h
eq(z) is the height of the protrusion for a given distance of the ion to the unperturbed interface, if the ion had been infinitely slowly moving]. This function could be obtained from model calculations or molecular dynamic simulations. The second term in the denominator is the one that causes the slowdown of ion transfer across the interface. This expression can easily rationalize an order of magnitude slowdown, but hardly much more than that. This is not inconsistent with recent more careful claims on the true scale of the observed effect. Otherwise, one should invoke models that rest on the existence of the barrier in the electrochemical potential. 相似文献
68.
In (E+Rh)/Al2O3 catalysts (E=Sn, Pb, Mo and W) the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion change drastically. For modified rhodium the decrease in the hydrogenolysis rate of C–C bonds in paraffins leads to an increased yield of the products of non-destructive conversion of n-hexane.
(E+Rh)/Al2O3 (E:Sn, Pb, Mo, W) , , -. C–C -.相似文献
69.
V. V. Kuznetsov 《Journal of Analytical Chemistry》2002,57(5):388-398
It is shown that chemical, configurational, and informational properties of flow-injection systems can be interrelated with the use of the methodology of the graph theory. The main equation of the theory is derived using a mathematical expression of the transition paths from the analyte to the detection of a product of the analytical reaction. Examples of specific developments are discussed for redox reactions, ligand exchange reactions, and heterogeneous exchange reactions, with due regard to, the hidden peculiarities of their chemical mechanisms that are essential for flow analysis and also for on-line preconcentration by coprecipitation. It is also shown that the conditions obtained in a flow system correspond to the basic postulates of linear nonequilibrium thermodynamics, which provides a basis for a new approach to the theory of flow analysis. An example of a complexation reaction was used for discussing the possibility that a linear interrelation exists between flows and forces in a flow system, which corresponds to the Onsager reciprocal relation. 相似文献
70.
I. V. Shcherbakova O. E. Shelepin N. A. Klyuev G. N. Dorofeenko E. V. Kuznetsov 《Chemistry of Heterocyclic Compounds》1982,18(10):1072-1078
The synthesis of 6-oxodibenzo[a,g]quinolizinium perchlorate — an analog of the alkaloid berberine — and a number of its derivatives, including mesoionic compounds, was accomplished on the basis of a 1-unsubstituted 3-(2-methylenecarboxyaryl)-2-benzopyrylium salt. The interconversions of the compounds obtained in this research were studied.See [1] for communication 26.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1381–1387, October, 1982. 相似文献