全文获取类型
收费全文 | 148103篇 |
免费 | 1506篇 |
国内免费 | 405篇 |
专业分类
化学 | 81000篇 |
晶体学 | 2421篇 |
力学 | 6102篇 |
综合类 | 3篇 |
数学 | 13746篇 |
物理学 | 46742篇 |
出版年
2021年 | 1064篇 |
2020年 | 1216篇 |
2019年 | 1275篇 |
2018年 | 1667篇 |
2017年 | 1720篇 |
2016年 | 2591篇 |
2015年 | 1588篇 |
2014年 | 2394篇 |
2013年 | 6129篇 |
2012年 | 4921篇 |
2011年 | 6010篇 |
2010年 | 4228篇 |
2009年 | 4249篇 |
2008年 | 5771篇 |
2007年 | 5568篇 |
2006年 | 5434篇 |
2005年 | 4990篇 |
2004年 | 4489篇 |
2003年 | 4151篇 |
2002年 | 4034篇 |
2001年 | 5553篇 |
2000年 | 3984篇 |
1999年 | 3087篇 |
1998年 | 2116篇 |
1997年 | 2216篇 |
1996年 | 2079篇 |
1995年 | 1923篇 |
1994年 | 1923篇 |
1993年 | 1737篇 |
1992年 | 2225篇 |
1991年 | 2308篇 |
1990年 | 2144篇 |
1989年 | 2113篇 |
1988年 | 2085篇 |
1987年 | 2098篇 |
1986年 | 1918篇 |
1985年 | 2383篇 |
1984年 | 2407篇 |
1983年 | 1919篇 |
1982年 | 1921篇 |
1981年 | 1765篇 |
1980年 | 1764篇 |
1979年 | 2043篇 |
1978年 | 2115篇 |
1977年 | 2062篇 |
1976年 | 1992篇 |
1975年 | 1866篇 |
1974年 | 1848篇 |
1973年 | 1880篇 |
1972年 | 1239篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
81.
82.
E. N. Yurchenko G. E. Kramareva N. G. Zubritskaya T. P. Gaidei 《Reaction Kinetics and Catalysis Letters》1995,55(2):425-432
In the Russian Scientific Center Applied Chemistry catalysts have been developed for the gas-phase fluorination of organics, including chlorine-containing substances, hydrogenation and reductive amination of organic substances, decomposition of liquid substances to gases, complete oxidation and reduction, suitable for environment at protection. 相似文献
83.
T. A. Beu 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,27(3):263-266
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented. 相似文献
84.
J.V.P. de OliveiraA.V. Cardona M.T. VilhenaR.C. Barros 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,73(1):55-62
We describe a semi-analytical numerical method for coherent isotropic scattering time-dependent radiative transfer problems in slab geometry. This numerical method is based on a combination of two classes of numerical methods: the spectral methods and the Laplace transform (LTSN) methods applied to the radiative transfer equation in the discrete ordinates (SN) formulation. The basic idea is to use the essence of the spectral methods and expand the intensity of radiation in a truncated series of Laguerre polynomials in the time variable and then solve recursively the resulting set of “time-independent” SN problems by using the LTSN method. We show some numerical experiments for a typical model problem. 相似文献
85.
Y Sonoda K Ichinose T Yoshimura Y Sato T Sasaki 《Chemical & pharmaceutical bulletin》1991,39(1):100-103
Lanosterol derivatives with a functional group at C-32 have been synthesized from 3 beta-acetoxylanostan-7 alpha-ol. The key reaction of the synthesis is the hypoiodite reaction of 3 beta-acetoxylanostan-7 alpha-ol. In vitro antitumor activity testing of the lanosterol derivatives revealed that 3 beta-hydroxylanost-7-en-32-oic acid has antineoplastic activity. 相似文献
86.
A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans. 总被引:12,自引:0,他引:12
L T Cohen F W Rickards G M Clark 《The Journal of the Acoustical Society of America》1991,90(5):2467-2479
Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation. 相似文献
87.
Partially supported by NSF Grants. 相似文献
88.
89.
90.
Let V be a hypersurface with an isolated singularity at the origin in ? n+1. It is a natural question to ask when V is defined by weighted homogeneous polynomial or homogeneous polynomial up to biholomorphic change of coordinates. In 1971, a beautiful theorem of Saito gives a necessary and sufficient condition for V to be defined by a weighted homogeneous polynomial. For a two-dimensional isolated hypersurface signularity V, Xu and Yau found a coordinate free characterization for V to be defined by a homogeneous polynomial. Recently Lin and Yau gave necessary and sufficient conditions for a 3-dimensional isolated hypersurface singularity with geometric genus bigger than zero to be defined by a homogeneous polynomial. The purpose of this paper is to prove that Lin-Yau’s theorem remains true for singularities with geometric genus equal to zero. 相似文献