全文获取类型
收费全文 | 275543篇 |
免费 | 3361篇 |
国内免费 | 1568篇 |
专业分类
化学 | 147648篇 |
晶体学 | 4279篇 |
力学 | 12366篇 |
综合类 | 62篇 |
数学 | 30553篇 |
物理学 | 85564篇 |
出版年
2020年 | 2363篇 |
2019年 | 2586篇 |
2018年 | 3366篇 |
2017年 | 3370篇 |
2016年 | 4902篇 |
2015年 | 3064篇 |
2014年 | 4819篇 |
2013年 | 11250篇 |
2012年 | 8808篇 |
2011年 | 10651篇 |
2010年 | 7570篇 |
2009年 | 7310篇 |
2008年 | 9796篇 |
2007年 | 9895篇 |
2006年 | 9274篇 |
2005年 | 8423篇 |
2004年 | 7725篇 |
2003年 | 6959篇 |
2002年 | 6871篇 |
2001年 | 7499篇 |
2000年 | 5775篇 |
1999年 | 4536篇 |
1998年 | 3982篇 |
1997年 | 3934篇 |
1996年 | 3690篇 |
1995年 | 3443篇 |
1994年 | 3581篇 |
1993年 | 3245篇 |
1992年 | 3719篇 |
1991年 | 3724篇 |
1990年 | 3665篇 |
1989年 | 3501篇 |
1988年 | 3595篇 |
1987年 | 3484篇 |
1986年 | 3313篇 |
1985年 | 4374篇 |
1984年 | 4645篇 |
1983年 | 3886篇 |
1982年 | 4012篇 |
1981年 | 3940篇 |
1980年 | 3909篇 |
1979年 | 3877篇 |
1978年 | 4192篇 |
1977年 | 4109篇 |
1976年 | 4175篇 |
1975年 | 3851篇 |
1974年 | 3895篇 |
1973年 | 4052篇 |
1972年 | 2851篇 |
1971年 | 2379篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Summary The relative X-ray fluorescence (XRF) intensities for annular source and various annular specimen are measured with a Ge-Li
detection system and calculated by the Monte Carlo numerical techniques (MCNT).Kα X-ray intensities of annular specimens with different radii prepared from a pure-molybdenum foil are measured and it is
seen that the measured values are in good agreement with the values calculated by MCNT. The variation of the fluorescence
intensity due to the collimator radius is also studied. The differences between the MCNT and experimental results are discussed
in terms of the possible sources of errors. 相似文献
992.
The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X-ray probe has been used to measure the focused plasma electron temperature (Te). The experimental results and the calculations showed that Te is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied. 相似文献
993.
994.
An investigation was made of the resonance conditions in systems of one-dimensional potential barriers of a general kind. The types of systems are identified and the conditions determined which are necessary for observing a broad resonance in which the first three derivatives of the energy transmission coefficient are equal to zero. The conditions are found for observing an isolated resonance with complete transparency on a background of resonances with incomplete transparency.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 49–53, August, 1993. 相似文献
995.
N. G. Gachkevich 《Journal of Mathematical Sciences》1996,81(6):3121-3125
By using numerical methods we construct the solution of the problem of determining the stress-optimal regimes (by the criterion
of minimizing the maximal normal stresses) for heating a piecewise-homogeneous shell consisting of a cylindrical shell and
a conical shell coupled with it that is closed at the vertex.
Translated fromMatematichni Metody i Fiziko-Mekhanichni Polya, Vol. 38, 1995. 相似文献
996.
V. F. Balakirev S. Kh. Estemirova A. M. Yankin S. G. Titova 《Doklady Physical Chemistry》2007,416(1):240-242
997.
Electrochemical oxidation of thio/carbohydrazide and their hydrazone derivatives Benzaldehyde thiocarbohydrazone [BTCH] diacetylene
thiocarbohydrazone [DATCH] have been studied in Brit-ton Robinson buffer in aqueous and nonaqueous media at a glassy carbon
electrode. The effects of pH, sweep rate, concentration, temperature and surfactants have been studied. The complex bis (carbo/thiocabohydrazide) Zn(II) chloride was also subjected to voltammetric analysis in order to understand the reactivity
both in free and metal bound states. The reaction conditions were optimized for the determination of above compounds in micrograms
quantities by differential pulse voltammetry, analytical utility of this investigation is also highlighted. 相似文献
998.
Structural study of polycrystalline silicon carbide obtained by sublimation performed via X-ray luminescence and X-ray diffraction analysis. It is shown that chemical vapor deposition of silicon carbide results in the formation of grains with the (00.1), (01.1), and (12.3) crystallographic planes parallel to the growth surface. The grains with the (00.1) growth planes are characterized by perfect structure and by red luminescence. Domains with yellow luminescence have a mosaic structure with the (01.1) and (12.3) growth planes. 相似文献
999.
K.P.B. Moosad P. Krishnakumar G. Chandrashekar R.M.R. Vishnubhatla 《Applied Acoustics》2007,68(10):1280-1285
Class IV flextensional transducers (FTs) are the best-known FTs in literature. These are light-weight projectors (compared to the conventional Tonpilz designs) with capability for high power delivery at low frequencies. The resonance frequencies of this type of transducers are known to be dominantly dependent on the characteristics of the outer shell than on the driver stack. Consequently, the method of achieving fine-tuning of the transducer by modifying the characteristics of the stack, as practiced in the case of Tonpilz designs, is not very effective. This paper describes a method for fine-tuning of the frequency of a Class IV FT, which involves only a modification of a pair of small components used for coupling the stack to the transducer. The effectiveness of the method is examined by finite element modelling using the package ATILA, in the case of a 3 kHz aluminium shell transducer. Experimental results are also presented. 相似文献
1000.
I. A. Belogorokhov M. N. Martyshov E. V. Tikhonov M. O. Breusova V. E. Pushkarev P. A. Forsh A. V. Zoteev L. G. Tomilova D. R. Khokhlov 《JETP Letters》2007,85(12):655-657
The Raman spectra have been obtained and the temperature dependence of the conductivity of organic semiconductor structures based on butyl-substituted erbium monophthalocyanine and erbium triphthalocyanine has been studied. It has been found experimentally that the activation energy decreases dramatically and the Raman spectra exhibits four new peaks in the region of large Raman shifts as the molecular structure of the samples becomes more complicated. 相似文献