全文获取类型
收费全文 | 7443篇 |
免费 | 123篇 |
国内免费 | 22篇 |
专业分类
化学 | 3944篇 |
晶体学 | 91篇 |
力学 | 195篇 |
数学 | 1108篇 |
物理学 | 2250篇 |
出版年
2023年 | 44篇 |
2022年 | 136篇 |
2021年 | 172篇 |
2020年 | 141篇 |
2019年 | 197篇 |
2018年 | 231篇 |
2017年 | 193篇 |
2016年 | 245篇 |
2015年 | 159篇 |
2014年 | 208篇 |
2013年 | 420篇 |
2012年 | 325篇 |
2011年 | 442篇 |
2010年 | 287篇 |
2009年 | 295篇 |
2008年 | 349篇 |
2007年 | 359篇 |
2006年 | 322篇 |
2005年 | 282篇 |
2004年 | 246篇 |
2003年 | 214篇 |
2002年 | 187篇 |
2001年 | 137篇 |
2000年 | 115篇 |
1999年 | 91篇 |
1998年 | 90篇 |
1997年 | 79篇 |
1996年 | 73篇 |
1995年 | 40篇 |
1994年 | 51篇 |
1993年 | 56篇 |
1992年 | 43篇 |
1991年 | 59篇 |
1990年 | 49篇 |
1989年 | 54篇 |
1988年 | 44篇 |
1987年 | 44篇 |
1986年 | 52篇 |
1985年 | 60篇 |
1984年 | 73篇 |
1983年 | 53篇 |
1982年 | 58篇 |
1981年 | 60篇 |
1980年 | 46篇 |
1979年 | 63篇 |
1978年 | 44篇 |
1977年 | 65篇 |
1976年 | 43篇 |
1975年 | 42篇 |
1973年 | 38篇 |
排序方式: 共有7588条查询结果,搜索用时 15 毫秒
61.
Conditions for converting a set of five standard proteins to electrochemically active sodium dodecylsulfate (SDS) complexes were worked out with the aim of using such complexes for conductivity detection with a a chip electrophoresis system. The results obtained were compared with standard capillary electrophoresis (37 cm (effective length 30 cm)×75 μm I.D. capillary, 10 kV, negative polarity at the inlet). The chip separations were run at 500 V per chip (100 V/cm) as compared to the standard capillary arrangement, which was run at 266.6 V/cm. For the capillary set-up the protein complexes were prepared in aqueous solution (Milli-Q water) made 10 mM with respect to SDS. If the SDS concentration was increased to 50 mM, the separation in the capillary was incomplete. On the other hand with the chip system both approaches yielded acceptable results. The chip separations were slightly (but not distinctly) shorter and offered better separations than the standard set-up. The concentration of the surfactant used for the preparation the complexes results in alternations of the elution sequence, which is preserved if the chip separation is used instead of the capillary set-up. Apparently the full capacity of protein–SDS binding is not exploited for the preparation of the adducts. 相似文献
62.
L’ubica Triščíková Ivan Potočňák Jozef Chomič Peter Baran 《Transition Metal Chemistry》2006,31(4):504-515
The new mixed-valence mixed-metal complex Cu(py)6Cu2Ag2(CN)6 (py = pyridine) possesses a three dimensional polymeric crystal structure. The Cu(I) atom is tetrahedrally coordinated by
two nitrogen atoms of pyridine molecules, by one nitrogen atom of the dicyanoargentate anion and by one carbon atom of the
cyano group. Both the dicyanoargentate anion and the cyano group bridge the Cu(I) atom with neighboring Cu(II) atoms. These
are hexacoordinated in the form of an elongated tetragonal bipyramid. The equatorial plane is formed by two nitrogen atoms
from two pyridine molecules and two nitrogen atoms from bridging cyano groups. Axial positions are occupied by nitrogen atoms
of the bridging [Ag(CN2]− anions. Correlation between structures of the title compound and seven other dicyanoargentates with their i.r. spectra has
been studied. The coordination mode of [Ag(CN2]− anions in compounds Cu8-xAgx(tn)3(CN)10 x = 0.25, Cu(3-Mepy)2Ag2(CN)4, Cu(py)2Ag2(CN)4 and Cu(py)4Ag2(CN)4 (tn is 1,3-diaminopropane, 3-Mepy is 3-methylpyridine) is predicted based on this correlation. 相似文献
63.
64.
65.
L. I. Vereshchagin A. V. Petrov V. N. Kizhnyaev F. A. Pokatilov A. I. Smirnov 《Russian Journal of Organic Chemistry》2006,42(7):1049-1055
Nonfused bis-1,3,4-oxadiazoles were synthesized by reaction of 5-substituted mono-and bis-tetrazoles with mono-and dicarboxylic acid chlorides. The results of kinetic studies showed that the transformation of tetrazoles into 1,3,4-oxadiazoles is accelerated by 1 to 2 orders of magnitude on addition of a catalytic amount of dimethylformamide, triethylamine, or pyridine. 相似文献
66.
García-Orozco I López-Cortés JG Ortega-Alfaro MC Toscano RA Penieres-Carrillo G Alvarez-Toledano C 《Inorganic chemistry》2004,43(26):8572-8576
The paper describes the synthesis and structural characterization of four novel copper(I) complexes [CuL(PPh(3))(2)] (L = 3-hydroxy-3-(p-R-phenyl)-2-propenedithioate). In addition, a tautomeric equilibrium in solution was found and Hammett correlations with (13)C NMR parameters were studied. The structure of one complex was fully established by X-ray diffraction analysis. 相似文献
67.
The first example of the formation of hydrogen-deficient radical cations of the type [M + H](.2+) is demonstrated to occur through a one-electron-transfer mechanism upon low-energy collision-induced dissociation (CID) of gas-phase triply charged [Cu(II)(terpy)(M + H)](.3+) complex ions (where M is an angiotensin III or enkephalin derivative; terpy = 2,2':6',2'-terpyridine). The collision-induced dissociation of doubly charged [M + H](.2+) radical cations generates similar product ions to those prepared through hot electron capture dissociation (HECD). Isomeric isoleucine and leucine residues were distinguished by observing the mass differences between [z(n) + H](.+) and w(n)(+) ions (having the same residue number, n) of the Xle residues. The product ion spectrum of [z(n) + H](.+) reveals that the w(n)(+) ions are formed possibly from consecutive fragmentations of [z(n) + H](.+) ions. Although only the first few [M + H](.2+) species have been observed using this approach, these hydrogen-deficient radical cations produce fragment ions that have more structure-informative patterns and are very different from those formed during the low-energy tandem mass spectrometry of protonated peptides. 相似文献
68.
Increased structural complexity leads to higher activity: peptides as efficient and versatile catalysts for asymmetric aldol reactions 总被引:3,自引:0,他引:3
[reaction: see text] Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure. 相似文献
69.
Cesare Oliva Anatoli V. Vishniakov Ivan E. Mukovozov Giorgio Termignone Lucio Forni 《Radiation Physics and Chemistry》1995,45(6):945-948
Evidence of quantum spin fluid and of quantum spin glass behaviour has been detected by extended EPR analysis in some La-cuprate catalysts of general formula La2−xEuxCuO4 + δ. Some features of the EPR spectrum, appearing in a few cases, are also discussed and attributed to a pseudo Jahn-Teller effect due to a particular coordination of up to five oxygen ions around surface copper ions at low temperature. 相似文献
70.