全文获取类型
收费全文 | 233852篇 |
免费 | 2511篇 |
国内免费 | 671篇 |
专业分类
化学 | 126045篇 |
晶体学 | 3601篇 |
力学 | 11022篇 |
综合类 | 10篇 |
数学 | 27187篇 |
物理学 | 69169篇 |
出版年
2021年 | 2371篇 |
2020年 | 2501篇 |
2019年 | 3035篇 |
2018年 | 4016篇 |
2017年 | 4030篇 |
2016年 | 5615篇 |
2015年 | 3043篇 |
2014年 | 5082篇 |
2013年 | 10253篇 |
2012年 | 8624篇 |
2011年 | 10262篇 |
2010年 | 7547篇 |
2009年 | 7597篇 |
2008年 | 9532篇 |
2007年 | 9510篇 |
2006年 | 8569篇 |
2005年 | 7660篇 |
2004年 | 7122篇 |
2003年 | 6449篇 |
2002年 | 6362篇 |
2001年 | 5978篇 |
2000年 | 4512篇 |
1999年 | 3471篇 |
1998年 | 3017篇 |
1997年 | 3094篇 |
1996年 | 2995篇 |
1995年 | 2538篇 |
1994年 | 2604篇 |
1993年 | 2477篇 |
1992年 | 2780篇 |
1991年 | 2868篇 |
1990年 | 2747篇 |
1989年 | 2819篇 |
1988年 | 2753篇 |
1987年 | 2746篇 |
1986年 | 2588篇 |
1985年 | 3368篇 |
1984年 | 3432篇 |
1983年 | 2831篇 |
1982年 | 2866篇 |
1981年 | 2835篇 |
1980年 | 2625篇 |
1979年 | 2978篇 |
1978年 | 2913篇 |
1977年 | 3086篇 |
1976年 | 3070篇 |
1975年 | 2867篇 |
1974年 | 2804篇 |
1973年 | 2912篇 |
1972年 | 2168篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Conclusion The proposed model of formation of the reinforcing framework in the manufacture of an axisymmetric shell by the CPW method makes it possible to numerically determine the thicknesses and rates of filling the layers, reinforcement angles as a function of the main parameters of the technological process, geometry of the mandrel, and characteristics of the reinforcing filament. It was established that the thicknesses of the layers, reinforcement rates and angles, and, as a consequence, the effective stiffness characteristics of the composite are substantially variable both along the meridian and over the thickness of the shell.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 609–617, September–October, 1992.The authors thank V. A. Frolov for the experimental results. 相似文献
902.
903.
V. D. Fedotov N. P. Obuchov R. A. Zadikhanov J. Spěváček J. Straka 《Applied magnetic resonance》1993,4(4):491-511
The combined analysis of1H and13C NMR relaxation data in solid lysozyme and some typical homopolypeptides was carried out by using “model-free” approach. Three types of relaxation transitions (γ’, γ and β) were revealed in the temperature range investigated. The microdynamical parameters of these motions were determined. From the comparison of these parameters with those of selected synthetic polymers it follows that the molecular motions in proteins and synthetic polymers are of the same nature. All these motions show pronounced anisotropic character. In the investigated temperature range no molecular motions corresponding to α-relaxation (liquid-like) transition were revealed. The hydration effects on parameters of the motions in proteins were considered. The most pronounced effect takes place for β-transition. The effect of Brownian rotation of protein molecule in solution on measured correlation function of local motions was also discussed. 相似文献
904.
B. M. Dzhagarov N. N. Kruk N. V. Konovalova A. A. Solodunov I. I. Stepuro 《Journal of Applied Spectroscopy》1995,62(2):285-289
Presented at the XV IUPAC Symposium on Photochemistry, Prague, July 17–22, 1994. 相似文献
905.
The present paper gives a more complete treatment of the scattering from a two-dimensional random surface than previous works. Reciprocal theorems for the stochastic wave field and the incoherent scattering distribution (bistatic cross section) are derived and the presence of backscattering enhancement in the case of a slightly random Neumann surface is demonstrated. A physical interpretation of the backscattering enhancement associated with the presence of anomalous scattering on a slightly random Neumann surface is given. Some numerical calculations are performed to show the incoherent scattering distribution and the backscattering enhancement. 相似文献
906.
Gabor Schmera Adi Bulsara David Pierson Frank Moss Enrico Di Cera 《Journal of statistical physics》1993,71(5-6):1179-1190
We consider the class of experiments which can be characterized by a Fokker-PIanck dynamics corresponding to the overdamped motion of a state point in a suitable stochastic potential. We assume that the general form of the potential is known (or can be guessed with reasonable accuracy), but that its parameters are to be determined experimentally by measurements made with a noisy instrument. This possible method for determining the potential parameters, which exploits the system's own internal stochastic motion in order to explore rapidly its available parameter space, is substantially more efficient than traditional methods involving time averages of single point measurements, and yet does not appear to have been previously considered. The method could be important when, for example, the experiment must be completed in a limited time owing either to the expense of the experimental materials or to the temporary stationarity of the preparation, situations which are commonly encountered in experimental biochemistry and biology. 相似文献
907.
A model of an expanding and rotating universe is constructed in the framework of general relativity. The parameters of the model are compared with the fundamental observables and shown to be in good agreement.Kaluzhsk Branch, N. É. Bauman Moscow State Technical University (MGTU). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 71–77, June, 1993. 相似文献
908.
G. N. Stratopoulos W. J. Zakrewski 《Zeitschrift fur Physik C Particles and Fields》1993,59(2):307-312
We look at the recently proposed scheme of approximating a sine-Gordon soliton by an expression derived from two dimensional instantons. We point out that the scheme of Sutcliffe in which he uses two dimensional instantons can be generalised to higher dimensions and that these generalisations produce even better approximations than the original approximation. We also comment on generalisations to other models. 相似文献
909.
Cun Feng Fan David A. Waldman Shaw Ling Hsu 《Journal of Polymer Science.Polymer Physics》1991,29(2):235-246
Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface. 相似文献
910.
The reaction of CH3 with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 1013 cm3/mol-s was measured for removal of OH by CH3. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (?75%) for the removal of OH by CH3 at these conditions is their combination to form CH3OH. Rate coefficients of (5.3 ± 0.8) × 1012 and (9.0 ± 1.4) × 1012 cm3/mol-s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure. 相似文献