全文获取类型
收费全文 | 7848篇 |
免费 | 260篇 |
国内免费 | 61篇 |
专业分类
化学 | 5190篇 |
晶体学 | 41篇 |
力学 | 277篇 |
数学 | 1593篇 |
物理学 | 1068篇 |
出版年
2023年 | 47篇 |
2022年 | 50篇 |
2021年 | 187篇 |
2020年 | 155篇 |
2019年 | 162篇 |
2018年 | 139篇 |
2017年 | 114篇 |
2016年 | 276篇 |
2015年 | 234篇 |
2014年 | 240篇 |
2013年 | 443篇 |
2012年 | 530篇 |
2011年 | 594篇 |
2010年 | 361篇 |
2009年 | 352篇 |
2008年 | 517篇 |
2007年 | 485篇 |
2006年 | 486篇 |
2005年 | 411篇 |
2004年 | 352篇 |
2003年 | 279篇 |
2002年 | 292篇 |
2001年 | 99篇 |
2000年 | 73篇 |
1999年 | 67篇 |
1998年 | 79篇 |
1997年 | 82篇 |
1996年 | 91篇 |
1995年 | 54篇 |
1994年 | 74篇 |
1993年 | 53篇 |
1992年 | 52篇 |
1991年 | 41篇 |
1990年 | 53篇 |
1989年 | 47篇 |
1988年 | 39篇 |
1987年 | 40篇 |
1986年 | 29篇 |
1985年 | 44篇 |
1984年 | 61篇 |
1983年 | 39篇 |
1982年 | 45篇 |
1981年 | 31篇 |
1980年 | 40篇 |
1979年 | 29篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 14篇 |
1974年 | 15篇 |
1973年 | 14篇 |
排序方式: 共有8169条查询结果,搜索用时 171 毫秒
991.
Angelo Crugnola Antonio Longo Ferruccio Casabuona Paolo Lombardi 《Tetrahedron letters》1981,22(41):4141-4144
The synthesis of chiral “4,7-lactam“ has been accomplished starting from natural 6-aminopenicillanic acid. 相似文献
992.
993.
Summary When two immiscible fluids in a porous medium are in contact with one another, an interface is formed and the movement of
the fluids results in a free boundary problem for determining the location of the interface along with the pressure distribution
throughout the medium. The pressure satisfies a nonlinear parabolic partial differential equation on each side of the interface
while the pressure and the volumetric velocity are continuous across the interface. The movement of the interface is related
to the pressure through Darcy’s law. Two kinds of boundary conditions are considered. In Part I the pressure is prescribed
on the known boundary. A weak formulation of the classical problem is obtained and the existence of a weak solution is demonstrated
as a limit of a sequence of classical solutions to certain parabolic boundary value problems. In Part II the same analysis
is carried out when the flux is specified on the known boundary, employing special techniques to obtain the uniform parabolicity
of the sequence of approximating problems.
Entrata in Redazione il 29 novembre 1975.
This research was supported in part by the National Science Foundation, the Senior Fellowship Program of the North Atlantic
Treaty Organization, the Italian Consiglio Nazionale delle Ricerche, and the Texas Tech. University. 相似文献
994.
995.
Antonio Coniglio 《Physica A》1993,200(1-4):165-170
Recent work showing evidence for multiscaling in large two dimensional DLA clusters is reviewed. A connection between multiscaling and multifractality is also shown resulting in a weak localization of the growth sites (δ-sites) in shells around the cluster seed. 相似文献
996.
A convenient route to the daunomycinone precursor 18via a succession of Diels-Alder reactions from 2,7-dichloronaphthazarin (9) is described. In a similar manner, starting from 2,6-dichloronaphthazarin (19) compound 20, a regioisomer of 18,is synthesized. This methodology constitutes a regiospecific approach to (±)-daunomycinone and related anthracyclinones. 相似文献
997.
Alberto Castellón Serrano Antonio Fernández López Amable García Martín Cándido Martín González 《manuscripta mathematica》1996,90(1):479-487
In this paper, we use the known classification of the finite capacity simple alternative pairs and the version of the Litoff
Theorem for Jordan pairs to describe all the strongly prime alternative pairs with nonzero socle. We study the inheritance
of some properties (primeness, nondegenerancy,…) when passing from the original alternative pair to the symmetrized pair.
Thus, we can apply Jordan theoretical results to the alternative case.
This work has been partially supported by 1) the “Plan Andaluz de Investigación y Desarrollo Tecnológico” with project no.
1027 and 2) the DGICYT with project no. PB93-0990 相似文献
998.
Antonio Pasini 《Geometriae Dedicata》1996,60(3):225-236
It is well known that a geometry belonging to a disconnected diagram is the direct sum of geometries corresponding to the connected components of the diagram. On the other hand, chamber systems with a disconnected diagram exist which do not split as direct products of components of smaller rank. Many finite examples of this kind are discussed in Groups of Lie Type and their Geometries (CUP, 1995, pp. 185–214), but none of them is simply connected. In this article, we construct a simply connected finite example. 相似文献
999.
Javier Gamboa Félix Javier Jiménez-Jiménez Alberto Nieto Ignacio Cobeta Alberto Vegas Miguel Ortí-Pareja Teresa Gasalla José Antonio Molina Esteban García-Albea 《Journal of voice》1998,12(4):444-452
To quantify several acoustic features of the voice in patients with essentialtremor (ET), 28 patients and 28 age- and sex-matched controls were studied. ET severity was assessed with the rating scale for tremor of Fahn, Tolosa, and Marín. The Computerized Speech Lab 4300 program (Kay Elemetrics) was used. Two-second samples of a sustained /a/ and a sentence were captured with a microphone and laryngograph equipment. Measures included fundamental frequency (F0), frequency perturbation (fitter, Koike algorithm), intensity perturbation (shimmer, Horii algorithm), and harmonic-to-noise ratio (H/N, Yumoto algorithm) of the vowel /a/, and the frequency and intensity variability of the sentence, phonational range, and dynamic range at the natural frequency, maximum phonational time, and s/z ratio. All subjects underwent indirect laryngoscopy and/or laryngeal fibroscopy. When compared with controls, ET patients showed higher jitter, lower H/N ratio (the last one only with laryngographic signal), of the vowel /a/, lower frequency variability in the microphonc signal, lower intensity variability in the laryngographic signal of the sentence, and significantly lower dynamic range at natural frequency of phonation. ET patients reported higher frequency of the presence of high voice intensity, tremor, and struggle. Several acoustic parameters were influenced by the severity of the disease, including shimmer, jitter, H/N ratio, frequency variability of the sentence, and s/z ratio, although neither of the acoustic analysis values or the phonetometric measurements were affected by the presence of voice tremor or by a successful pharmacological treatment of ET. 相似文献
1000.
Antonio Raudino Franco Battaglia 《Journal of Electron Spectroscopy and Related Phenomena》1980,20(3):327-331
The He(II) spectra of the unsubstituted metallocenes {M(η-C5H5)2}, M V, Cr, Mn, Fe, Co, Ni and Ru, and of {Mn(η-C5H4Me)2} are reported; both He(I) and He(II) spectra of some decamethylmetallocenes {M(η-C5Me5)2}, where M Mg, V, Cr, Mn, Fe, Co and Ni, are also given. Intensity changes between the He(I) and He(II) spectra are shown to provide a reliable guide to band assignment. A ligand field treatment of the decamethylmanganocene cation, including limited configuration interaction, gives values for Δ2, B and C; these values are also in good agreement with the photoelectron spectra of {M(η-C5Me5)2} where M V, Cr and Fe. Overlap between the ligand and metal “d” band structures prevents complete assignment in the cases of Co and Ni. 相似文献