全文获取类型
收费全文 | 5524篇 |
免费 | 341篇 |
国内免费 | 36篇 |
专业分类
化学 | 3890篇 |
晶体学 | 70篇 |
力学 | 189篇 |
数学 | 854篇 |
物理学 | 898篇 |
出版年
2023年 | 32篇 |
2022年 | 109篇 |
2021年 | 149篇 |
2020年 | 106篇 |
2019年 | 202篇 |
2018年 | 161篇 |
2017年 | 121篇 |
2016年 | 271篇 |
2015年 | 173篇 |
2014年 | 261篇 |
2013年 | 508篇 |
2012年 | 324篇 |
2011年 | 347篇 |
2010年 | 246篇 |
2009年 | 227篇 |
2008年 | 255篇 |
2007年 | 245篇 |
2006年 | 248篇 |
2005年 | 188篇 |
2004年 | 190篇 |
2003年 | 185篇 |
2002年 | 211篇 |
2001年 | 96篇 |
2000年 | 134篇 |
1999年 | 82篇 |
1998年 | 48篇 |
1997年 | 61篇 |
1996年 | 41篇 |
1995年 | 42篇 |
1994年 | 39篇 |
1993年 | 46篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 18篇 |
1989年 | 30篇 |
1988年 | 35篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 38篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 30篇 |
1980年 | 19篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 16篇 |
1975年 | 17篇 |
1974年 | 13篇 |
排序方式: 共有5901条查询结果,搜索用时 15 毫秒
31.
Mousa Z. Al-Noaimi Raid J. Abdel-Jalil Mustafa M. El-Abadelah Salim F. Haddad Younis N. H. Baqi Wolfgang Voelter 《Monatshefte für Chemie / Chemical Monthly》2006,37(12):745-750
In the presence of RuCl3, N-phenylamidrazone underwent oxidative cyclization into 1,4-dihydro-1-phenyl-1,2,4-benzotriazine, the structure of which is
established by spectral and X-ray diffraction data. 相似文献
32.
E.H. El Abdalaoui F. Parreau A.A. Prikhod'ko 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2006,42(6):671-681
It is shown that for any family of probability measures in Ornstein type constructions, the corresponding transformation has almost surely a singular spectrum. This is a new generalization of Bourgain's theorem [J. Bourgain, On the spectral type of Ornstein class one transformations, Israel J. Math. 84 (1993) 53–63], same result is proved for Rudolph's construction [D. Rudolph, An example of a measure-preserving map with minimal self-joining and applications, J. Anal. Math. 35 (1979) 97–122]. 相似文献
33.
M. N. El Tarazi 《BIT Numerical Mathematics》1990,30(3):484-489
The interpolation problem at uniform mesh points of a quadratic splines(x
i)=f
i,i=0, 1,...,N ands(x
0)=f0 is considered. It is known that s–f=O(h
3) and s–f=O(h
2), whereh is the step size, and that these orders cannot be improved. Contrary to recently published results we prove that superconvergence cannot occur for any particular point independent off other than mesh points wheres=f by assumption. Best error bounds for some compound formulae approximatingf
i
andf
i
(3)
are also derived. 相似文献
34.
35.
F. El Akkad H. F. Ragaie M. Abdel Naby 《Applied Physics A: Materials Science & Processing》1989,48(5):493-495
Zn
x
Cd1–x
S thin films (0x0.20) were prepared using rf sputtering in argon atmosphere and characterized using X-ray diffraction, optical transmission, electrical resistivity and photoconductive decay measurements. The films were found to possess hexagonal structure. The crystallite size and degree of preferential orientation were found to decrease with the increase ofx and to improve upon annealing in vacuum at 250 °C. The transmission edge shifted towards shorter wavelengths with the increase ofx in agreement with the expected shift in the energy band gap. The films were found to exhibit room temperature resistivity in the range 100–1000 cm. The obtained values of long wavelength transmission (70–80%) and minority carrier diffusion length (30 m) are high enough for the application of these films in the field of solar cells. 相似文献
36.
37.
38.
Ricardo Baggio Juan Carlos Muoz Mireille Perec 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(10):m498-m500
The title compound, [Dy2(C2H3O2)6(H2O)4]·4H2O, crystallizes in the form of dimeric units related by an inversion centre. Each cation is nine‐coordinate, binding to two water molecules and three acetate groups, two of which are bidentate and the third tridentate. This last acetate group acts as a bridge between neighbouring metal atoms, leading to an intradimer Dy?Dy separation of 4.170 (1) Å. 相似文献
39.
E. O. Chukhadzhyan K. G. Shakhatuni El. O. Chukhadzhyan N. T. Gevorkyan 《Chemistry of Heterocyclic Compounds》1999,35(3):343-347
Quaternary ammonium salts containing propargyl and 3-(2-methyltetrazol-5-yl)propargyl groups undergo base-catalyzed cyclization at room temperature with self heating to form condensed heterocyclic systems containing the tetrazole ring. Heating at 90–92°C for 2 h is necessary to cyclize the allyl analogs of the starting salts.Communication 234 of the series Research on Amines and Ammonium Compounds. For 233, see [1].Institute of Organic Chemistry, National Academy of Sciences of the Republic of Armenia, Erevan 375094. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 390–394, March, 1999. 相似文献
40.
Omar El Tall Nicole Jaffrezic‐Renault Monique Sigaud Olivier Vittori 《Electroanalysis》2007,19(11):1152-1159
Boron‐doped Diamond (BDD) electrode has become one of the important tools for heavy metal detection. By studying some analytical parameters of DPASV method, like deposition time and potential in different electrolyte concentrations (acetate buffer), the conditions for detecting very low metal ion levels (Zn, Cd, Pb, and Cu) could be chosen. Diluted electrolyte (0.01 M buffer) was one of the factors favoring low detection and quantification limits, but its quantification range is short in comparison to more concentrated media. For ?1.7 V deposition potential, the detection of single metal at ppb levels was reached in 60 s deposition time. Understanding different metal‐metal interactions shows the limits to the simultaneous determination of heavy metals at BDD. Quantification was possible for the simultaneous determination of Zn, Cd and Pb despite the overlapping of Zn and Cd peaks. The performance of the BDD was compared with that of another C‐based solid electrode: the glassy carbon electrode (without mercury plating). A lower base line current, wider potential range, higher sensitivity (3 to 5 times higher than GC) and longevity of the material were noticed for the BDD. 相似文献