全文获取类型
收费全文 | 146934篇 |
免费 | 1455篇 |
国内免费 | 394篇 |
专业分类
化学 | 80244篇 |
晶体学 | 2387篇 |
力学 | 6064篇 |
综合类 | 3篇 |
数学 | 13578篇 |
物理学 | 46507篇 |
出版年
2021年 | 1032篇 |
2020年 | 1181篇 |
2019年 | 1253篇 |
2018年 | 1642篇 |
2017年 | 1690篇 |
2016年 | 2542篇 |
2015年 | 1563篇 |
2014年 | 2352篇 |
2013年 | 6041篇 |
2012年 | 4850篇 |
2011年 | 5945篇 |
2010年 | 4184篇 |
2009年 | 4210篇 |
2008年 | 5734篇 |
2007年 | 5508篇 |
2006年 | 5383篇 |
2005年 | 4945篇 |
2004年 | 4453篇 |
2003年 | 4118篇 |
2002年 | 4009篇 |
2001年 | 5543篇 |
2000年 | 3974篇 |
1999年 | 3075篇 |
1998年 | 2109篇 |
1997年 | 2210篇 |
1996年 | 2069篇 |
1995年 | 1916篇 |
1994年 | 1912篇 |
1993年 | 1726篇 |
1992年 | 2215篇 |
1991年 | 2298篇 |
1990年 | 2137篇 |
1989年 | 2099篇 |
1988年 | 2078篇 |
1987年 | 2087篇 |
1986年 | 1912篇 |
1985年 | 2373篇 |
1984年 | 2397篇 |
1983年 | 1909篇 |
1982年 | 1915篇 |
1981年 | 1756篇 |
1980年 | 1737篇 |
1979年 | 2028篇 |
1978年 | 2102篇 |
1977年 | 2046篇 |
1976年 | 1975篇 |
1975年 | 1859篇 |
1974年 | 1843篇 |
1973年 | 1876篇 |
1972年 | 1235篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Whittum D.H. Ebihara K. Hiramatsu S. Kishiro J.-i. Monaka T. Ozaki T. Takayama K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):136-141
Studies of microwave amplification with an in-focused electron beam drawn from an induction injector are reported. A free-electron laser (FEL) operating at 9.4 GHz and employing ion-focusing within the interaction region has achieved power in excess of 30 MW at 9.4 GHz, with a beam energy of 0.8 MeV and current of 0.7 kA. Peak gain is 20 dB/m, with no saturation after 15 wiggler periods. Also reported are the first evolution and detuning data for an ion-channel laser/maser (ICL). Two shortcomings of the prematurely halted ICL studies are poor frequency discrimination and a large axial plasma gradient. Prospects for operation with an upgraded 1.6 MeV accelerator are discussed 相似文献
62.
63.
G. D. Krapivan N. I. Val'ter T. Ya. Kaklyugina V. G. Kul'nevich 《Chemistry of Heterocyclic Compounds》1994,30(3):289-295
Halogen in positions 3 and 5 of the furan ring in ftirfurylidenedioxanediones is readily replaced by dithiocarbonate, dithiocarbatnate, dithiophosphate, thiocyanate, and azide anions, and by thiourea, and secondary and tertiary amines. The conformation of the initial halogen derivative is retained in the substitution products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–334, March, 1994. 相似文献
64.
M. A. Mikhaleva B. M. Bolotin T. A. Kizner E. S. Serebrykova 《Chemistry of Heterocyclic Compounds》1994,30(1):79-81
We have synthesized 5-alkyl(alkoxy)-2-(o-lzydroxy-p-alkoxyphenyl)pyrimidines and considered the effect of the OH group on the inesomorphism. We have found that in binuclear o-hydroxyarylpyrimidines, an ortho OH group forming an intramolecular hydrogen bond increases Tmp, inhibits the appearance of nematic properties, and promotes the appearance of a smectic A.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 1, pp. 90–92, January, 1994. 相似文献
65.
N. I. Khamidov B. T. Kadyrov N. T. Ul'chenko A. Sh. Isamukhamedov A. I. Glushenkova 《Chemistry of Natural Compounds》1994,30(4):430-433
The phsicochemical indices and the fatty-acid and triacylglycerol compositions of cottonseed and palm oils, of cottonseed
oil hydrogenate, and of compositions based on them have been determined with the aid of IR and UV spectroscopies, GLC analysis,
and chemical transformations. The compositions and amounts of the main classes of lipids in the initial oils and the hydrogenate
have been studied. It has been found that in the process of hydrogenation the amount of oxygenated components falls.
The work was conducted with the financial support of the Uzbek Fund for Fundamental Investigations. 相似文献
66.
S. O. Kolusheva B. A. Salakhutdinov T. F. Aripov L. P. Vernon 《Chemistry of Natural Compounds》1994,29(4):523-525
It has been shown by the ESR of spin probes that thionin initially interacts with with negatively charged membranes electrostatically and then passes into the membranes to a depth comparable with the length of the hydrophobic sections of the protein loops.Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Brigham Young University, Provo, Utah, USA. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 594–597, July–August, 1993. 相似文献
67.
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
68.
Partially supported by NSF Grants. 相似文献
69.
70.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain
a decomposition of continuity. 相似文献