全文获取类型
收费全文 | 247547篇 |
免费 | 3782篇 |
国内免费 | 612篇 |
专业分类
化学 | 130683篇 |
晶体学 | 3535篇 |
力学 | 10729篇 |
综合类 | 5篇 |
数学 | 29672篇 |
物理学 | 77317篇 |
出版年
2021年 | 2106篇 |
2020年 | 2402篇 |
2019年 | 2583篇 |
2018年 | 3630篇 |
2017年 | 3338篇 |
2016年 | 5173篇 |
2015年 | 3593篇 |
2014年 | 4899篇 |
2013年 | 11737篇 |
2012年 | 10336篇 |
2011年 | 11855篇 |
2010年 | 7909篇 |
2009年 | 7435篇 |
2008年 | 10617篇 |
2007年 | 10797篇 |
2006年 | 10092篇 |
2005年 | 9203篇 |
2004年 | 8381篇 |
2003年 | 7244篇 |
2002年 | 6871篇 |
2001年 | 7191篇 |
2000年 | 5577篇 |
1999年 | 4252篇 |
1998年 | 3388篇 |
1997年 | 3364篇 |
1996年 | 3215篇 |
1995年 | 2877篇 |
1994年 | 2770篇 |
1993年 | 2654篇 |
1992年 | 3029篇 |
1991年 | 2958篇 |
1990年 | 2867篇 |
1989年 | 2660篇 |
1988年 | 2664篇 |
1987年 | 2667篇 |
1986年 | 2459篇 |
1985年 | 3291篇 |
1984年 | 3533篇 |
1983年 | 2840篇 |
1982年 | 3079篇 |
1981年 | 3055篇 |
1980年 | 2878篇 |
1979年 | 2968篇 |
1978年 | 3047篇 |
1977年 | 2999篇 |
1976年 | 3125篇 |
1975年 | 2883篇 |
1974年 | 2857篇 |
1973年 | 2980篇 |
1972年 | 1854篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
M. G. Voronkov S. G. D’yachkova I. P. Lebedeva A. V. Evart L. G. Shagun 《Russian Journal of General Chemistry》2007,77(4):604-606
Alkylthiochloroacetylenes react with geminal (in ether) and vicinal (in THF) dithiols to form, respectively, functional 1,3-dithiolenes (yield 43%) or 1,3-dithiolanes (yield 34%). 相似文献
992.
The present report describes a method suitable for the indirect assay of hydroxyl radical (OH.), which is likely to be produced during reperfusion of ischemic myocardium. Isolated rat heart perfused by the Langendorff technique was subjected to 30 min of ischemia, followed by 30 min of reperfusion. Salicylic acid (2 mM) was added to the perfusion circuit to trap any OH. radical generated during the experiment. 2,5- and 2,3-dihydroxybenzoic acids (hydroxylated products of salicylic acid) were identified by authentic standards as well as by pure OH.-generating system using high-performance liquid chromatography with electrochemical detection. In addition to serving as a chemical trap for the detection of OH., salicylate attenuated myocardial reperfusion injury as evidenced by reduced formation of creatine kinase, decreased lipid peroxidation, and improved myocardial contractile functions during reperfusion. These results thus provide direct evidence for the presence of OH. in heart and link it to the myocardial reperfusion injury. 相似文献
993.
Kh. D. Ikramov 《Journal of Mathematical Sciences》2007,141(6):1633-1638
It is shown that the coneigenvalues of a matrix, when properly defined (in a way different from the one commonly used in the
literature), obey relations similar to the classical inequalities between the (ordinary) eigenvalues and singular values.
Several interesting spectral properties of conjugate-normal matrices are indicated. This matrix class plays the same role
in the theory of unitary congruences as the class of normal matrices plays in the theory of unitary similarities. Bibliography:
5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 334, 2006, pp. 111–120. 相似文献
994.
V. D. Zhuravlev 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(5):681-685
A technique for calculating the bond ionicity of crystalline materials using electronegativities of elements and taking into account the structure of polyhedra of the complex-oxide structure is proposed. 相似文献
995.
A. D. Lapin 《Acoustical Physics》2007,53(1):11-15
The problem of scattering of a Rayleigh wave by a chain of identical closely spaced monopole-dipole resonators with friction is considered. The values of resonator parameters that provide the rejection of the Rayleigh wave are found. The conditions under which the Rayleigh wave is much more efficiently reflected by the dipole resonators than by the monopole ones are determined. 相似文献
996.
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
997.
S. F. Dubinin V. E. Arkhipov Yu. G. Chukalkin S. G. Teploukhov V. D. Parkhomenko Ya. M. Mukovskiĭ 《Physics of the Solid State》2007,49(2):308-314
The magnetic structure and transport properties of partially disordered crystals of two-dimensional manganites La2?2x Sr1+2x Mn2O7 (x = 0.3, 0.4) are studied over a wide range of temperatures. The crystals are transformed into an atomically disordered state under irradiation with fast neutrons at a dose of 2 × 1019 cm?2. The average concentration of substitutional defects in the crystal is ≈4%. It is found that substitutional defects are responsible for the transition of these manganites from the ferromagnetic metal state to the insulator state with a spin glass structure. The results obtained are discussed in terms of the ratio between the kinetic energy of charge carriers and the exchange energy of localized spins. 相似文献
998.
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
999.
T. Ramanathan S. Stankovich D. A. Dikin H. Liu H. Shen S. T. Nguyen L. C. Brinson 《Journal of Polymer Science.Polymer Physics》2007,45(15):2097-2112
Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ~10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007 相似文献
1000.
J. M. Criado L. A. Pérez-Maqueda M. J. Diánez P. E. Sánchez-Jiménez 《Journal of Thermal Analysis and Calorimetry》2007,87(1):297-300
The SCTA method implies to control the temperature in such a way that
the reaction rate changes with the time according to a function previously
defined by the user. Constant Rate Thermal Analysis (CRTA) is one of the most
commonly used SCTA methods and implies achieving a temperature profile at
which the reaction rate remains constant all over the process at a value previously
selected by the user. This method permits to minimize the influence of heat
and mass transfer phenomena on the forward reaction. The scope of this work
is to develop a universal CRTA temperature controller that could be adapted
to any thermoanalytical device. The thermoanalytical signal is programmed
to follow a preset linear trend by means of a conventional controller that
at the time controls a second conventional temperature programmer that forces
the temperature to change for achieving the trend programmed for the thermoanalytical
signal. Examples of the performance of this control system with a Thermobalance
and a Thermomechanical Analyser (TMA) are given. 相似文献