全文获取类型
收费全文 | 10983篇 |
免费 | 584篇 |
国内免费 | 562篇 |
专业分类
化学 | 5940篇 |
晶体学 | 184篇 |
力学 | 322篇 |
综合类 | 51篇 |
数学 | 3138篇 |
物理学 | 2494篇 |
出版年
2023年 | 48篇 |
2022年 | 185篇 |
2021年 | 138篇 |
2020年 | 176篇 |
2019年 | 218篇 |
2018年 | 207篇 |
2017年 | 207篇 |
2016年 | 214篇 |
2015年 | 185篇 |
2014年 | 238篇 |
2013年 | 413篇 |
2012年 | 313篇 |
2011年 | 550篇 |
2010年 | 447篇 |
2009年 | 801篇 |
2008年 | 636篇 |
2007年 | 618篇 |
2006年 | 584篇 |
2005年 | 560篇 |
2004年 | 690篇 |
2003年 | 587篇 |
2002年 | 579篇 |
2001年 | 398篇 |
2000年 | 352篇 |
1999年 | 276篇 |
1998年 | 233篇 |
1997年 | 226篇 |
1996年 | 247篇 |
1995年 | 198篇 |
1994年 | 243篇 |
1993年 | 189篇 |
1992年 | 175篇 |
1991年 | 98篇 |
1990年 | 76篇 |
1989年 | 73篇 |
1988年 | 65篇 |
1987年 | 75篇 |
1986年 | 62篇 |
1985年 | 54篇 |
1984年 | 51篇 |
1983年 | 21篇 |
1982年 | 40篇 |
1981年 | 48篇 |
1980年 | 53篇 |
1979年 | 74篇 |
1978年 | 55篇 |
1977年 | 56篇 |
1976年 | 40篇 |
1974年 | 14篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 33 毫秒
991.
Niklas Beisert 《Comptes Rendus Physique》2004,5(9-10):1039
The dilatation operator measures scaling dimensions of local operator in a conformal field theory. Algebraic methods of constructing the dilatation operator in four-dimensional N=4 gauge theory are reviewed. These led to the discovery of novel integrable spin chain models in the planar limit. Making use of Bethe ansätze a superficial discrepancy in the AdS/CFT correspondence was found, we discuss this issue and give a possible resolution. To cite this article: N. Beisert, C. R. Physique 5 (2004).
Résumé
L'opérateur de dilatation mesure les dimensions d'échelles des opérateurs locaux des théories conformes des champs. Nous passons en revue les méthodes algébriques de construction de l'opérateur de dilatation pour la théorie de jauge N=4 en quatre dimensions. Ceci nous a conduit à découvrir, dans la limite planaire, de nouveaux modèles intégrables de chaînes de spin. En utilisant l'ansätze de Bethe une incompatibilité avec la correspondance AdS/CFT fut découverte, nous discutons ce problème et une résolution possible. Pour citer cet article : N. Beisert, C. R. Physique 5 (2004). 相似文献992.
993.
Sol-Gel Synthesis of Transparent Alumina Gel and Pure Gamma Alumina by Urea Hydrolysis of Aluminum Nitrate 总被引:2,自引:0,他引:2
Maria I. F. Macêdo Carla C. Osawa Celso A. Bertran 《Journal of Sol-Gel Science and Technology》2004,30(3):135-140
-Alumina was synthesized by a sol-gel method with the aluminum ion hydrolysis control performed by urea. The initial saturated Al3+/urea solution presented urea coordinated with the aluminum ion, as shown in the 13C NMR and 27Al NMR spectra and longitudinal relaxation times, T
1, from the latter. The substitution of water molecules in the Al3+ coordination shell by urea controlled the hydrolysis process and provided an extensive nucleation during the initial steps of the aluminum hydroxide formation due to urea thermolysis at 90°C. The resulting sol, composed of Al(OH)3 nanoparticles, coalesced and became a transparent gel permeated by a solution of urea and the polycation ion [Al13O4(OH)24(H2O)12]7+. The freshly prepared gel was transformed, under heating at 300°C, directly to -alumina, characterized by FTIR, 27Al-MAS-NMR and SBET techniques, without - or -phases, as a consequence of the high degree of homogeneity of the -alumina precursor. 相似文献
994.
Lina Geng Tao Bo Huwei Liu Na Li Feng Liu Kean Li Junling Gu Ruonong Fu 《Chromatographia》2004,59(1-2):65-70
A new capillary coating of alternate -zirconium phosphate lysozyme fabricated for open-tubular electrochromatography enantioseparation. The chiral compounds D, L-tryptophan tested were enantiomerically resolved. The influences brought by experimental parameters, such as organic modifier, temperature, applied voltage and pH of running buffer on the performance of the column, were investigated. 相似文献
995.
4-Phenyl-3,4-dihydro--carboline was prepared using the Bischler—Napieralski reaction on -phenyltryptamine.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 486–487, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献
996.
Piaoping Yang Zhenlü Wang JianFeng Yu Qingsheng Liu Tonghao Wu 《Reaction Kinetics and Catalysis Letters》2004,83(1):129-136
A kinetic model is proposed to account for the effect of oxygen during catalyst premodification on the rate and enantioselectivity in hydrogenation of methyl pyruvate over cinchonidine modified platinum catalysts.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
997.
Eberhard?ReimannEmail author Christian?Ettmayr 《Monatshefte für Chemie / Chemical Monthly》2004,135(8):959-972
Summary. N-Alkylation of certain angularly substituted heterocycles by C2- and C3-units provided appropriate precursors to construct stereoselectively the erythrinanone and several erythrinanone type analogues by intramolecular Friedel-Crafts acylation. The resulting aromatic ketones were catalytically reduced affording the corresponding parent frameworks including the hitherto unknown tetracyclus A-norschelhammerane. On the other hand, the stereoselective reduction of the carbonyl moiety offered a convenient approach to 11-hydroxylated erythrinanes with the natural occurring -configuration. The structures and the stereochemistry of the target compounds were proved by NMR spectroscopy.Part of PhD thesis, LMU München, D 相似文献
998.
Javad?AzizianEmail author Ali R.?Karimi Hamedeh?Arefrad Ali A.?Mohammadi Mohammad R.?Mohammadizadeh 《Monatshefte für Chemie / Chemical Monthly》2004,135(6):729-733
Summary. We report on the addition of dialkyl acetylenedicarboxylate to 1-alkylisatins or tryptanthrine in the presence of triphenylphosphine which leads to highly functionalised novel unsaturated -spirolactones. 相似文献
999.
Specimens of the nickel base alloy IN 718 deformed at high strain rate (~10 s–1), as realized in a screw press, have higher strength than parts forged conventionally in a hydraulic press. Microstructure analyses in light and transmission electron microscopes reveal the precipitation of very small Ni3Nb particles (-phase) to be the reason for the increased hardness. Several processing routes are discussed and analyzed in relation to the TTT-diagram of IN 718. 相似文献
1000.
The effects of 17-ethinylestradiol (EE), an endocrine disruptor, on zoo- and phytoplankton were studied in outdoor 230-L still-water microcosms. Cell density and biomass, diversity, and community composition were analyzed. Five microcosms were treated by controlled release for six weeks, three by direct application of EE. To investigate recovery, sampling was continued for four weeks after treatment. Most characteristics of the zooplankton were not unambiguously affected by EE. Only the relative density of copepods, especially of their larvae, decreased significantly after EE application. For phytoplankton, no unambiguous concentration- or toxodose-correlated effects on any biotic characteristics could be found. However, most properties of the phytoplankton deviated from those of controls, i.e. tended to be smaller (number of species per microcosm, biomass, cell density) or covered a wider range (diversity, evenness). PCA indicated a shift of species structure in the treated microcosms. This was supported by the species scores calculated by the principal response curve method, although the principal response curve itself showed no clear EE-correlated shifts. High variability within the biocenosis between microcosms and over time, probably because of disturbance of the ecosystem before starting of the test, might have superimposed EE-dependent effects.Abbreviations
c
dt
Canonical coefficient
- CRD
Controlled-release device
-
E
Shannon–Wiener index for evenness
- EC10
Effect concentration for 10% of maximum effect
- EC50
Effect concentration for 50% of maximum effect
- EE
17-Ethinylestradiol
-
H
Shannon–Wiener index for diversity
- LPDE
Low density polyethylene
- NOEC
No observed effect concentration
- PCA
Principal component analysis
- PRC
Principal response curve
- RDA
Redundancy analysis
- SD
Standard deviation 相似文献