全文获取类型
收费全文 | 29083篇 |
免费 | 360篇 |
国内免费 | 96篇 |
专业分类
化学 | 15525篇 |
晶体学 | 594篇 |
力学 | 781篇 |
综合类 | 7篇 |
数学 | 3354篇 |
物理学 | 9278篇 |
出版年
2020年 | 258篇 |
2019年 | 299篇 |
2018年 | 332篇 |
2017年 | 375篇 |
2016年 | 654篇 |
2015年 | 476篇 |
2014年 | 655篇 |
2013年 | 1556篇 |
2012年 | 1048篇 |
2011年 | 1142篇 |
2010年 | 845篇 |
2009年 | 786篇 |
2008年 | 1131篇 |
2007年 | 1115篇 |
2006年 | 1019篇 |
2005年 | 901篇 |
2004年 | 773篇 |
2003年 | 683篇 |
2002年 | 629篇 |
2001年 | 814篇 |
2000年 | 633篇 |
1999年 | 503篇 |
1998年 | 435篇 |
1997年 | 397篇 |
1996年 | 370篇 |
1995年 | 442篇 |
1994年 | 393篇 |
1993年 | 354篇 |
1992年 | 387篇 |
1991年 | 453篇 |
1990年 | 407篇 |
1989年 | 419篇 |
1988年 | 390篇 |
1987年 | 389篇 |
1986年 | 382篇 |
1985年 | 519篇 |
1984年 | 532篇 |
1983年 | 384篇 |
1982年 | 389篇 |
1981年 | 424篇 |
1980年 | 390篇 |
1979年 | 398篇 |
1978年 | 378篇 |
1977年 | 349篇 |
1976年 | 375篇 |
1975年 | 327篇 |
1974年 | 314篇 |
1973年 | 328篇 |
1967年 | 342篇 |
1966年 | 288篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Summary Flow injection analysis associated with a gradient mixing technique can be used for the determination of free acidity and total acidity (sum of free and bonded hydrogen ions) in a few microliters by reaction with suitable acid/base indicators and UV/VIS-detection. A rapid analysis of the two parameters in single raindrops in dependence on their size is possible [1]. 相似文献
22.
23.
T. Geppert S.L. Schweizer U. Gösele R.B. Wehrspohn 《Applied Physics A: Materials Science & Processing》2006,84(3):237-242
We present a method to create at the same time trenches and ordered macropore arrays during photo-electrochemical etching of n-type silicon. This novel method allows in situ separation of single devices with a submicrometer precision. It also enables new device structures in macroporous silicon in the areas of photonics, sensing and electronics. The limits of this new process are simulated using electrostatic models and are verified experimentally. PACS 82.45.Yz; 81.16.-c 相似文献
24.
25.
The aim of this contribution is to study lanthanum containing fullerenes produced and treated under different conditions. The work was done using solid soot extract giving poorly resolved ESR spectra or separated lanthanofullerenes in solution showing well resolved ESR spectra. ESR experiments in connection with the mass spectrometry give information on the electronic states due to the electron transfer from the endohedral metal to the fullerene cage and the influence of oxygen on endohedral lanthanofullerene. The analysis of ESR spectra indicates the presence of up to nine octets of lanthanum containing fullerenes. These species have different stabilities. Furthermore, a very narrow single ESR line in the lanthanofullerene spectrum was detected having a linewidth ΔB=0.008 mT and ag-factor 2.0025. The electron transfer to the endohedral La@C82 molecule studied by voltammetry and electrochemicalin situ ESR experiments is described. The interaction of the lanthanofullerene with oxygen in solution is also studied. In different solvents the influence of oxygen on line broadening in the ESR spectra of La@C82 was observed. 相似文献
26.
H. Günther M. Foerste M. Kunze G. zu Putlitz U. von Stein 《Zeitschrift für Physik B Condensed Matter》1996,100(4):613-617
We review the previous conclusion [J.Y. Ryu, Y.C. Chung and S.D. Choi, Phys. Rev. B 32, 7769 (1984)] that the trace property Tr(ABC) = Tr(CAB) leads to two different cyclotron transition absorption formulae in the electron-phonon systems in the lowest order approximation. The pictorial expression and the calculated linewidths in Ge and Si show that the socalled EWC scheme is more seeming than the socalled MWC scheme. The difference is expected to disappear if we take into account all the higher order perturbation terms or start with the many body formalism in the complete scheme. 相似文献
27.
Paweł Grochulski Zdzisław Wawrzak Zdzisław Gałdecki Antoinette Viger Suzy Coustal 《Journal of chemical crystallography》1990,20(5):429-432
The crystal structure of 18-cyanoprogesterone was determined by X-ray diffraction methods:P212121
a=7.436(2),b=11.322(2),c=22.642(2) Å. The structure was solved usingShelx-86. Final conventionalR=0.054.R
w
=0.051 for 1841 reflections. TheA ring has an intermediate sofa-half-chair conformation with asymmetry parameters C
s
/1
=11.0, C
2
3,4
=14.9. The steroid skeleton exhibits a flattening of theA ring relative to the rest of the molecule. The progesterone side chain has a typical conformation, and the C16-C17-C20-O20 torsion angle is –19.0(6)°. 相似文献
28.
We investigate representations of classical noncompact Lie groups induced by representations of the maximal parabolic subgroup. Formulas are obtained for 5O0(2p, 2q)/U(p, q) and U(2p, 2q) Sp(p, q).Translated from Ukrainskii Mathematicheskii Zhurnal, Vol. 42, No. 1, pp. 128–131, January, 1990. 相似文献
29.
U. A. Baltaev 《Chemistry of Natural Compounds》1992,28(2):198-200
A new ecdysteroid, rhapisterone C, has been isolated from seeds of the plantRhaponticum carthamoides (Willd) Iljin (family Compositae). It has been shown that rhapisterone C is 23-ethylecdysterone.Institute of Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 231–233, March–April, 1992. 相似文献
30.
U. M. Dzhemilev A. G. Ibragimov A. B. Morozov R. R. Muslukhov G. A. Tolstikov 《Russian Chemical Bulletin》1991,40(7):1425-1427
A novel approach was developed for the stereoselective synthesis of trans-3,4-dialkyl-substituted aluminacyclopentanes from -olefins, metallic magnesium, and EtAlCl2 in the presence of catalytic amounts of Cp2ZrCl2. The hydrolysis and deuterolysis products of the 3,4-dialkyl-substituted aluminacyclopentanes obtained are only in the trans configuration.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1607–1609, July, 1991. 相似文献