全文获取类型
收费全文 | 289552篇 |
免费 | 1337篇 |
国内免费 | 452篇 |
专业分类
化学 | 131913篇 |
晶体学 | 4481篇 |
力学 | 16802篇 |
综合类 | 10篇 |
数学 | 44995篇 |
物理学 | 93140篇 |
出版年
2020年 | 2037篇 |
2019年 | 2604篇 |
2018年 | 11115篇 |
2017年 | 11771篇 |
2016年 | 8390篇 |
2015年 | 3040篇 |
2014年 | 4416篇 |
2013年 | 8726篇 |
2012年 | 10697篇 |
2011年 | 19011篇 |
2010年 | 12623篇 |
2009年 | 12972篇 |
2008年 | 17015篇 |
2007年 | 20144篇 |
2006年 | 6904篇 |
2005年 | 11493篇 |
2004年 | 8487篇 |
2003年 | 8257篇 |
2002年 | 6515篇 |
2001年 | 5771篇 |
2000年 | 4465篇 |
1999年 | 3193篇 |
1998年 | 2743篇 |
1997年 | 2793篇 |
1996年 | 2733篇 |
1995年 | 2323篇 |
1994年 | 2433篇 |
1993年 | 2326篇 |
1992年 | 2609篇 |
1991年 | 2735篇 |
1990年 | 2635篇 |
1989年 | 2713篇 |
1988年 | 2638篇 |
1987年 | 2657篇 |
1986年 | 2499篇 |
1985年 | 3137篇 |
1984年 | 3226篇 |
1983年 | 2709篇 |
1982年 | 2668篇 |
1981年 | 2635篇 |
1980年 | 2438篇 |
1979年 | 2844篇 |
1978年 | 2830篇 |
1977年 | 2915篇 |
1976年 | 2956篇 |
1975年 | 2739篇 |
1974年 | 2676篇 |
1973年 | 2821篇 |
1972年 | 2139篇 |
1971年 | 1996篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
V. E. Zubov A. D. Kudakov N. L. Levshin 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(11):1548-1549
It is established that reversible adsorption of water and methyl alcohol molecules, occurring via formation of hydrogen bonds, changes the dynamic properties of domain walls in the surface region of soft ferromagnets, as well as their initial static magnetic susceptibility. A mechanism is proposed for the effects revealed. 相似文献
962.
The effect of variation of the scattered light intensity in a magnetic fluid with aggregates of magnetite particles several microns in size under the action of a magnetic field is studied. The effect relaxation times are determined when the magnetic field is turned on and off. This effect is found to be caused by the orientation of anisotropically magnetized aggregates. Experimental data are used to calculate the average anisotropy of the magnetic susceptibility of the aggregate and estimate its magnetic permeability. 相似文献
963.
Within the framework of the kinetic theory of strength, relations for estimation of durability of thermoplastic materials
under stationary and non-stationary thermomechanical impacts are obtained It is shown that durability decreases linearly with
increase in the natural (Napierian) logarithm of the mean size of microcracks formed during manufacturing of polymer products.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–6, July, 2007. 相似文献
964.
A model for the interaction of near-infrared laser pulses with metal powders in selective laser sintering 总被引:4,自引:0,他引:4
P. Fischer N. Karapatis V. Romano R. Glardon H.P. Weber 《Applied Physics A: Materials Science & Processing》2002,74(4):467-474
A thermal model of the interaction of pulsed near-infrared laser radiation from a Nd:YAG laser was made, taking the measured
powder properties such as reflectance, optical penetration depth and thermal conductivity into account. It allows an estimation
of the evolution of two different temperatures: the average temperature of the powder (taken over the grains in a volume given
by the laser beam diameter and the optical penetration depth) and the temperature distinction within a single grain. It showed
that in pulsed mode consolidation can be achieved at much lower average power as the surface of the powder particles are molten
but their cores remain at nearly room temperature. This leads to a much lower average temperature and therefore a dramatic
decrease in residual thermal stresses in the finished piece. The results of the model were experimentally tested and confirmed.
Received: 26 July 2001 / Accepted: 23 November 2001 / Published online: 23 January 2002 相似文献
965.
This paper presents an application in the automotive industry where a combination of electronic speckle-pattern interferometry and laser doppler velocimetry were used at a critical stage in the design process of an internal combustion engine. Combined deformation and surface relief measurements were used to study the phase and amplitude of deformation of a vibrating engine. The relief data was combined with the interferometer geometry and used to geometrically correct the deformation data, in an effort to improve accuracy. The measurements allowed rapid identification and quantification of design weaknesses, particularly those causing undesirable resonances. This led to a significant reduction in the design time and lowering of costs, when compared with existing design optimisation methods. 相似文献
966.
We study two estimators of the long-range parameter of a covariance stationary linear process. We show that one of the estimators
achieve the optimal semiparametric rate of convergence, whereas the other has a rate of convergence as close as desired to
the optimal rate. Moreover, we show that the estimators are asymptotically normal with a variance, which does not depend on
any unknown parameter, smaller than others suggested in the literature. Finally, a small Monte Carlo study is included to
illustrate the finite sample relative performance of our estimators compared to other suggested semiparametric estimators.
More specifically, the Monte-Carlo experiment shows the superiority of the proposed estimators in terms of the Mean Squared
Error.
The first author research was funded by the Economic and Social Research Council (ESRC) reference number: R000238212. The
second author research was funded by the Ministry of Education, Culture, Sports and Technology of Japan, reference number:
09CE2002 and B(2)10202202. 相似文献
967.
968.
N. S. Oliveira J. Dorgan J. A. P. Coutinho A. Ferreira J. L. Daridon I. M. Marrucho 《Journal of Polymer Science.Polymer Physics》2007,45(5):616-625
The sorption of carbon dioxide in glassy Poly(lactic acid) (PLA) films was studied by quartz crystal microbalance (QCM) at high pressures. Two thermal treatments, melted and quenched, were performed in PLA with two different L:D contents, 80:20 and 98:2, films and compared with a third thermal protocol, annealed, and used in a previous work. The results obtained show that for pressures higher than 2 MPa, the carbon dioxide solubility is larger in PLA 80:20 than in PLA 98:2, indicating that the L:D plays a dominant role on this property. The thermal treatments only affect the gas solubility in PLA 98:2. Sorption isotherms at temperatures 303, 313, and 323 K, below the glass transition temperature of the polymer, and pressures up to 5 MPa were measured and analyzed with three different models, the dual‐mode sorption model, the Flory–Huggins equation, and a modified dual‐mode sorption model where the Henry's law term was substituted by the Flory–Huggins equation. This last model performs especially well for CO2 in PLA 80:20, due to the convex upward curvature of the solubility isotherms for that system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 616–625, 2007 相似文献
969.
A. V. Porfir’eva G. A. Evtyugin E. Yu. Podshivalina L. I. Anchikova G. K. Budnikov 《Journal of Analytical Chemistry》2007,62(12):1180-1186
A new technique is proposed for detecting interactions between DNA and DNA autoimmune antibodies using a potentiometric sensor based on a glassy-carbon electrode modified with polyaniline and native DNA from chicken erythrocytes. It is shown that the DNA-antibody interaction changes the rate of polyaniline doping in transferring the DNA sensor from an alkaline (pH 7.5) solution, which is optimum for the immunochemical reaction, to an acidic (pH 3.0) solution. The dynamics of the variation of the DNA sensor potential depends on the titer of antibodies and their origin. The dependence of the DNA sensor signal on the dilution of the blood sera from systemic lupus erythematosus and autoimmune thyroiditis patients shows that DNA antibodies can be diagnosed by the characteristic maximum in the dilution curve found in the range of serum dilutions from 1: 20 to 1: 50. 相似文献
970.
E. S. Voropai M. P. Samtsov K. N. Kaplevskii A. A. Maskevich V. I. Stepuro O. I. Povarova I. M. Kuznetsova K. K. Turoverov A. L. Fink V. N. Uverskii 《Journal of Applied Spectroscopy》2003,70(6):868-874
Comparative analysis of the absorption and fluorescence spectra and fluorescence excitation spectra of thioflavin T (ThT) in various solvents and in the composition of amyloid fibrils has shown that ThT, when excited in the region of the long-wavelength absorption band, fluoresces in the spectral region with a maximum at 478–484 nm. The appearance in aqueous and alcohol solutions of a fluorescence band with a maximum near 440 nm has been attributed to the presence in the composition of the ThT preparations of an impurity with an absorption band in the 340–350-nm range. The literature data showing that in glycerol ThT has a wide fluorescence spectrum with two maxima are due to the artifact connected with the use of a high concentration of the dye. It has been suggested that the cause of the low quantum yield of ThT aqueous and alcohol solutions is the breakage of the system of conjugated bonds due to the reorientation of the benzothiozole and benzaminic rings of ThT in the excited state with respect to one another. The main factor determining the high quantum yield of fluorescence of ThT incorporated in fibrils is the steric restriction of the rotation of the rings about one another under these conditions. The suggestions made have been verified by the quantum-chemical calculation of the ThT molecule geometry in the ground and excited states. 相似文献