全文获取类型
收费全文 | 1126篇 |
免费 | 55篇 |
国内免费 | 6篇 |
专业分类
化学 | 837篇 |
晶体学 | 5篇 |
力学 | 14篇 |
数学 | 157篇 |
物理学 | 174篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 42篇 |
2020年 | 32篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 29篇 |
2016年 | 39篇 |
2015年 | 38篇 |
2014年 | 42篇 |
2013年 | 70篇 |
2012年 | 73篇 |
2011年 | 82篇 |
2010年 | 49篇 |
2009年 | 43篇 |
2008年 | 60篇 |
2007年 | 54篇 |
2006年 | 58篇 |
2005年 | 53篇 |
2004年 | 46篇 |
2003年 | 28篇 |
2002年 | 26篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1997年 | 7篇 |
1996年 | 19篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1969年 | 4篇 |
1961年 | 5篇 |
1934年 | 3篇 |
1932年 | 3篇 |
1912年 | 3篇 |
1906年 | 3篇 |
排序方式: 共有1187条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
The present paper contributes to the development of new efficient solutions aimed at improving vehicle functional safety through the implementation of new transmission diagnostic methods. The study focuses on a new perspective of the diagnostic frequency range for hypoid gear condition monitoring, using acoustic emission and vibro-acoustic signal measurements and the Discrete Wavelet Transform for data analysis. The identification of the most sensitive diagnostic parameters and determination of frequency intervals using the Discrete Wavelet Transform, in which the most significant increase in the values of diagnostic parameters can be seen, has been presented. In addition, the identification of the sensitivity of the above-introduced non-destructive methods is presented. Diagnostic results in the extended frequency range were compared with the results of the classical method, and it was found that the selected parameter in the proposed measuring range could better characterize the condition of the gear unit. 相似文献
995.
996.
Andrej Staško Viktor Milata Zuzana Barbieriková Vlasta Brezová 《Magnetic resonance in chemistry : MRC》2014,52(1-2):22-26
4‐Oxoquinoline derivatives (quinolones) represent heterocyclic compounds with a variety of biological activities, along with interesting chemical reactivity. The quinolone derivatives possessing secondary amino hydrogen at the nitrogen of the enaminone system are oxidized with 3‐chloroperbenzoic acid to nitroxide radicals in the primary step while maintaining their 4‐pyridone ring. Otherwise, N‐methyl substituted quinolones also form nitroxide radicals coupled with the opening of the 4‐pyridone ring in a gradual oxidation of the methyl group via the nitrone–nitroxide spin‐adduct cycle. This was confirmed in an analogous oxidation using N,N‐dimethylaniline as a model compound. N‐Ethyl quinolones in contrast to its N‐methyl analog form only one nitroxide radical without a further degradation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
997.
Viktor O. Iaroshenko Sajid AliTariq Mahmood Babar Sergii DudkinSatenik Mkrtchyan Nasim Hasan RamaAlexander Villinger Peter Langer 《Tetrahedron letters》2011,52(3):373-376
4-Chloro-3-(trifluoroacetyl)coumarin was synthesized for the first time via direct TMSCl-mediated acylation of 4-hydroxycoumarin with TFAA followed by the treatment with POCl3. The reaction of 4-chloro-3-(trifluoroacetyl)coumarin with commercially available anilines is a two-step method, which affords a set of 7-(trifluoromethyl)-6H-chromeno[4,3-b]quinolin-6-ones in good to excellent yields. 相似文献
998.
Viktor Todorov 《Stochastic Processes and their Applications》2019,129(2):419-451
We develop a nonparametric estimator for the spectral density of a bivariate pure-jump Itô semimartingale from high-frequency observations of the process on a fixed time interval with asymptotically shrinking mesh of the observation grid. The process of interest is locally stable, i.e., its Lévy measure around zero is like that of a time-changed stable process. The spectral density function captures the dependence between the small jumps of the process and is time invariant. The estimation is based on the fact that the characteristic exponent of the high-frequency increments, up to a time-varying scale, is approximately a convolution of the spectral density and a known function depending on the jump activity. We solve the deconvolution problem in Fourier transform using the empirical characteristic function of locally studentized high-frequency increments and a jump activity estimator. 相似文献
999.
Tatyana A. Stroganova Viktor M. Red'kin Vladimir K. Vasilin Gennady D. Krapivin 《Journal of heterocyclic chemistry》2013,50(4):854-858
New Mannich bases were synthesized through an interaction of fused pyrrolo[1,2‐a][1,4]diazepines with secondary amines and formaldehyde. The reaction appears to be regioselective, yielding the monosubstituted products bearing N,N‐dialkylaminomethyl group at position 2 of the pyrrolodiazepine moiety. 相似文献
1000.
Juraj Zajac Vojtech Novohradsky Lenka Markova Viktor Brabec Jana Kasparkova 《Angewandte Chemie (International ed. in English)》2020,59(8):3329-3335
To design an anticancer drug capable of inhibiting not only the proliferation of the differentiated tumor cells but also reducing the tumorigenic capability of cancer stem cells (CSCs), the new PtIV prodrugs with axial cinnamate ligands were synthesized. We demonstrate their superior antiproliferative activity in monolayer and 3D spheroid antiproliferative activity tests using panel of cancer cell lines. An outstanding activity was found against rhabdomyosarcoma cells, one of the most problematic and poorly treatable pediatric tumors. The results also suggest that the released PtII compound inhibits antiproliferative activity of cancer cells by DNA‐damage mediated mechanism; the released cinnamic acid can trigger processes leading to differentiation, making the CSCs more sensitive to killing by the platinum part of the complex. PtIV complex with axial cinnamate ligands is the first PtIV prodrug capable of overcoming CSCs resistance and induce death in both CSCs and bulk cancer. 相似文献