全文获取类型
收费全文 | 229013篇 |
免费 | 5635篇 |
国内免费 | 2966篇 |
专业分类
化学 | 119844篇 |
晶体学 | 3612篇 |
力学 | 10786篇 |
综合类 | 113篇 |
数学 | 25332篇 |
物理学 | 77927篇 |
出版年
2022年 | 2083篇 |
2021年 | 2608篇 |
2020年 | 2796篇 |
2019年 | 2978篇 |
2018年 | 3514篇 |
2017年 | 3323篇 |
2016年 | 4946篇 |
2015年 | 3441篇 |
2014年 | 4936篇 |
2013年 | 10847篇 |
2012年 | 9578篇 |
2011年 | 11065篇 |
2010年 | 7565篇 |
2009年 | 7362篇 |
2008年 | 9478篇 |
2007年 | 9517篇 |
2006年 | 9020篇 |
2005年 | 8009篇 |
2004年 | 7233篇 |
2003年 | 6272篇 |
2002年 | 6071篇 |
2001年 | 6825篇 |
2000年 | 5325篇 |
1999年 | 4288篇 |
1998年 | 3448篇 |
1997年 | 3465篇 |
1996年 | 3229篇 |
1995年 | 2959篇 |
1994年 | 2765篇 |
1993年 | 2562篇 |
1992年 | 2914篇 |
1991年 | 2866篇 |
1990年 | 2768篇 |
1989年 | 2536篇 |
1988年 | 2542篇 |
1987年 | 2552篇 |
1986年 | 2366篇 |
1985年 | 3040篇 |
1984年 | 3262篇 |
1983年 | 2671篇 |
1982年 | 2834篇 |
1981年 | 2789篇 |
1980年 | 2648篇 |
1979年 | 2737篇 |
1978年 | 2827篇 |
1977年 | 2821篇 |
1976年 | 2895篇 |
1975年 | 2680篇 |
1974年 | 2647篇 |
1973年 | 2779篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A method is proposed for evaluating the resistance of a flywheel rim to radial stresses in free rotation. The method is based on loading a rim segment in pure bending and calculating the limiting moment and the corresponding limiting angular velocity. Applicability of the method is substantiated theoretically by investigating the similarity of the radial stress diagrams in rotation and pure bending. The method is verified experimentally for the strained state of a rim segment in pure bending.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 4, pp. 521–526, July–August, 1993. 相似文献
112.
Composition of corrosion layers on steel 20 in aerated solutions with hydrazine concentrations less than 11 ppm was studied at 50, 60, and 80°C in dynamic conditions by transmission Mössbauer spectroscopy and X-ray diffraction as supplementary technique. Corrosion rates were determined by gravimetric method. A comparison with corrosion in water at 80°C was made. The observed layers have not any protective character. For 0.1 m/s linear velocity, they are composed by nonstoichiometric magnetite, (Fe3?x O4,x=0.02–0.04) with lepidocrocite (γ-FeOOH) as secondary phase at 50°C. Haematite (α-Fe2O3) is observed at 60 and 80°C with a 19 nm particle size. It becomes smaller for higher velocity (0.7 m/s). 相似文献
113.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. L. Seaman Y. Dalichaouch M. B. Maple J. D. Garrett 《Hyperfine Interactions》1991,64(1-4):517-522
We have performed both zero field and high transverse field measurements at dilution refrigerator temperatures on a number of heavy electron systems, examining the superconducting and magnetic properties of these interesting materials. Among the materials studied to date are UBe13, URu2Si2 and U6Fe. The magnetic field penetration depth in the superconducting state of UBe13 is greater than 10000 Å, as no increase in the transverse field relaxation rate is observed belowT c . A sharp increase in the precession frequency is seen, starting atT c . This frequency shift shows little temperature dependence at low temperature; we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we have observed relaxation in high transverse field due to the formation of a flux lattice in U6Fe, a material where the electron effective mass is rather lighter than in other heavy fermion systems. The relaxation exhibits a sharp onset atT c=3.9 K, and is flat at low temperatures as expected for a conventional superconductor. 相似文献
114.
115.
Let M be a symplectic manifold with a Hamiltonian circle action with isolated fixed points. We prove that σ (M) = b0(M) − b2(M) + b4(M) − b6(M) + … where σ (M) is the signature of M and bi(M) is the ith Betti number of M. 相似文献
116.
D. I. Moldavanskii 《Ukrainian Mathematical Journal》1991,43(12):1569-1571
Necessary and sufficient conditions for the isomorphism of two groups, each defined by a single relation of the type a–1bma=bn, are obtained.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 12, pp. 1684–1686, December, 1991. 相似文献
117.
A. K. Shahani N. Korve K. P. Jones D. J. Paynton 《The Journal of the Operational Research Society》1994,45(8):916-926
Asthma is one of the major chronic diseases in many countries. At present there is no cure for asthma, but medical advances can help to reduce the chances of attacks of the condition. Efficient care for asthma involves complexity, uncertainty, variability and the use of scarce resources, and these are the same conditions that indicate a possible use for the modelling approach of operational research. This paper is concerned with a pilot model that was developed through joint work by medical professionals and operational researchers. The development of the model is explained and illustrative results indicate the potential value of the modelling approach for the care of asthma in the community. 相似文献
118.
String theory at nonzero temperature is reviewed. A bosonic string at nonzero temperature is studied and the calculation of its free energy in both the one-loop approximation and the case of arbitrary genus (multiloop analysis) is discussed. A string at nonzero temperature is compared with a string compacted on a one-dimensional torus. The properties of modular invariance and dual symmetry are discussed at both the one-loop and multiloop levels. The thermodynamics of superstrings, including also superstrings compactified on a torus, is also studied. Possible cosmological applications are briefly considered. It is shown that many features of string thermodynamics (in particular, the existence of the Hagedorn temperature and dual symmetry) also occur in the theory of noncritical strings.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–49, December, 1991. 相似文献
119.
X. H. Sun 《Acta Mathematica Hungarica》1994,65(3):229-236
120.
M.S. Anagnostou I. Panagiotopoulos A. Kostikas D. Niarchos G. Zouganelis 《Journal of magnetism and magnetic materials》1994,130(1-3):57-62
From the analysis of Mössbauer data for Y2Fe17 and Y2Fe17N3−δ at various temperatures the hyperfine fields for 4f, 6g, 12j, 12k iron sites were estimated as a function of temperature. The reduced magnetizations calculated from the values of the hyperfine fields are fitted with a mean field model for four interacting sublattices using a computer program. The estimated exchange interaction from the fitting procedure between the 4f sites is found strongly negative (antiferromagnetic) in Y2Fe17 whereas in Y2Fe17N3−δ it increases and becomes weak negative following a modified Slater-Néel curve. The rest of the exchange interactions are found positive or weak negative depending on the distances between the Fe atoms. 相似文献