全文获取类型
收费全文 | 278780篇 |
免费 | 1603篇 |
国内免费 | 802篇 |
专业分类
化学 | 127855篇 |
晶体学 | 4139篇 |
力学 | 16873篇 |
综合类 | 10篇 |
数学 | 53272篇 |
物理学 | 79036篇 |
出版年
2021年 | 1971篇 |
2020年 | 2011篇 |
2019年 | 2569篇 |
2018年 | 13890篇 |
2017年 | 13703篇 |
2016年 | 10755篇 |
2015年 | 3149篇 |
2014年 | 4564篇 |
2013年 | 8860篇 |
2012年 | 10486篇 |
2011年 | 18260篇 |
2010年 | 11941篇 |
2009年 | 12532篇 |
2008年 | 14021篇 |
2007年 | 16093篇 |
2006年 | 6874篇 |
2005年 | 7146篇 |
2004年 | 7092篇 |
2003年 | 7068篇 |
2002年 | 6124篇 |
2001年 | 5828篇 |
2000年 | 4411篇 |
1999年 | 3268篇 |
1998年 | 2878篇 |
1997年 | 2895篇 |
1996年 | 2730篇 |
1995年 | 2322篇 |
1994年 | 2399篇 |
1993年 | 2318篇 |
1992年 | 2572篇 |
1991年 | 2705篇 |
1990年 | 2601篇 |
1989年 | 2679篇 |
1988年 | 2589篇 |
1987年 | 2608篇 |
1986年 | 2469篇 |
1985年 | 3079篇 |
1984年 | 3143篇 |
1983年 | 2632篇 |
1982年 | 2605篇 |
1981年 | 2565篇 |
1980年 | 2380篇 |
1979年 | 2751篇 |
1978年 | 2705篇 |
1977年 | 2888篇 |
1976年 | 2888篇 |
1975年 | 2681篇 |
1974年 | 2613篇 |
1973年 | 2736篇 |
1972年 | 2102篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A. N. Kochubei 《Ukrainian Mathematical Journal》1992,44(7):836-840
A manifold M with semi-Riemannian almost product structure invariant relative to a transformation group G is considered. A connection with special G-invariance property is constructed in the corresponding bundle of frames.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 7, pp. 926–931, July, 1992. 相似文献
92.
93.
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
94.
95.
The mechanism of ozone formation has been studied using 16O and 18O2. High-resolution microwave spectroscopy was used to measure the amounts of the isotopomeric ozone species formed. The study is hampered by the very rapid exchange process between the reactants, that tends to scramble the isotopes and hence give a 2:1 statistical ratio between the two possible isotopomers. We have found a strategy to come around this difficulty and conclude that the mechanism is a simple end-on-addition. 相似文献
96.
A potential of mean torque is derived for a solute at infinite dilution in a uniaxial liquid crystal solvent, which contains terms originating from the dispersion interaction, and the electrostatic interaction between quadrupole moments on both molecules. It is shown that the electrostatic term is non-zero only if the solute-solvent vectors are distributed with lower than spherical symmetry. If this distribution has cylindrical symmetry then both the electrostatic and dispersion terms in the potential of mean torque are shown to depend on order parameters for the orientational distribution of the solute-solvent vectors, as well as on the order parameters of the solvent molecules. 相似文献
97.
A. S. Il'inskii S. V. Trubnikov N. A. Fedoseeva 《Computational Mathematics and Modeling》1994,5(3):195-202
Translated from Matematicheskie Modeli i Optimizatsiya Vychislitel'nykh Algoritmov, pp. 131–143, 1993. 相似文献
98.
We have devised a new method for bis(tributyltin)oxide (TBTO) determination in marine sediments and mussels. This technique involves an n-hexane/methylene chloride mixture extraction and extract purification with a sodium hydroxide wash in order to eliminate interfering compounds. TBTO is then extracted again by nitric acid and converted into an inorganic tin species; the analysis has been effected using Zeeman graphite furnace-atomic absorption spectrophotometry. The method detection limit for the matrices examined is 0.004 μg TBTO g?1 (wet weight) and is sufficient for the analysis in real samples. The percentage recovery of TBTO from sediments and mussels samples is higher than 85% and 95% respectively. This method has been applied to TBTO level determination in sediments and mussels (Mytilus galloprovincialis) sampled in the harbour area in Taranto, where mussel culture activities are much developed; the TBTO levels obtained in sediments and mussels were in the range 15-47 ng g?1 (wet weight) and 11-30 ng g?1 (wet weight) respectively. Such values are comparable with those found in other harbour areas in the Mediterranean Sea. 相似文献
99.
N. I. Usyukina 《Theoretical and Mathematical Physics》1991,88(1):683-685
Scientific-Research Institute of Nuclear Physics at the Moscow State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 88, No. 1, pp. 14–16, July, 1991. 相似文献
100.
We develop a lattice-dynamical model based on the screw symmetry of single-walled carbon nanotubes that allows for reducing the size of the dynamical matrix to six, for all tube chiralities. The model uses force constants derived from fitting to the phonon dispersion of 2D graphite. We present the calculation procedure in a clear and transparent way, making the model easier to follow. We calculate the phonon dispersions of a number of nanotubes of different chiralities. The splitting of two highest Raman active modes and the radial breathing mode frequency are studied by changing the tube diameter and chirality. 相似文献