全文获取类型
收费全文 | 2993篇 |
免费 | 114篇 |
国内免费 | 6篇 |
专业分类
化学 | 2364篇 |
晶体学 | 27篇 |
力学 | 39篇 |
数学 | 283篇 |
物理学 | 400篇 |
出版年
2023年 | 14篇 |
2022年 | 45篇 |
2021年 | 90篇 |
2020年 | 46篇 |
2019年 | 71篇 |
2018年 | 40篇 |
2017年 | 44篇 |
2016年 | 96篇 |
2015年 | 91篇 |
2014年 | 100篇 |
2013年 | 146篇 |
2012年 | 180篇 |
2011年 | 182篇 |
2010年 | 136篇 |
2009年 | 117篇 |
2008年 | 204篇 |
2007年 | 175篇 |
2006年 | 155篇 |
2005年 | 192篇 |
2004年 | 141篇 |
2003年 | 126篇 |
2002年 | 109篇 |
2001年 | 53篇 |
2000年 | 39篇 |
1999年 | 41篇 |
1998年 | 23篇 |
1997年 | 43篇 |
1996年 | 35篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 24篇 |
1992年 | 17篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 19篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1972年 | 4篇 |
排序方式: 共有3113条查询结果,搜索用时 93 毫秒
111.
Rosa Caballol Josep M. Ribó Francesc R. Trull Asunción Vallés 《Monatshefte für Chemie / Chemical Monthly》1987,118(8-9):993-1010
The applicability of the MINDO/3 method is evaluated for calculations on dipyrrolic partial structures of bile pigments. It is shown that this method cannot be used for an accurate conformational analysis. However, when applying the frontier orbital model for reactivity parameters, a good picture of the HOMO and the LUMO distribution can be obtained in this type of molecules.
Reaktivität von Pyrrolpigmenten, 9. Mitt. MINDO/3-Rechnungen von dipyrrolischen Partialmodellen von Gallenpigmenten
Zusammenfassung Es werden die Einsatzmöglichkeiten von MINDO/3 für den Fall dipyrrolischer Partialstrukturen der Gallenpigmente aufgezeigt. Die Methode ist für eine genaue Konformationsanalyse nicht geeignet. Unter Verwendung der Reaktionsparameter des Frontier-Orbital-Modells läßt sich jedoch ein gutes Bild der HOMO- und LUMO-Verteilung für diesen Verbindungstyp gewinnen.相似文献
112.
Ciminiello P Dell'Aversano C Fattorusso E Forino M Magno S Di Rosa M Ianaro A Poletti R 《Journal of the American Chemical Society》2002,124(44):13114-13120
A detailed analysis of the causative toxins contained in the hepatopancreas of toxic mussels from the northern Adriatic sea has been carried out. Along with some DSP (diarrhetic shellfish poisoning) type toxins, such as okadaic acid, yessotoxin, and their derivatives, which are involved in a number of human intoxications throughout the world, we have now isolated a new cytotoxin, a polychlorinated sulfolipid 1, whose gross structure has been elucidated by spectral analysis, including various 2D NMR techniques. The relative stereochemistry of 1 was elucidated by successful application of the J-based configuration analysis developed for acyclic compounds using carbon-proton spin-coupling constants ((2,3)J(C,H)) and proton-proton spin-coupling constants ((3)J(H,H)); its absolute stereochemistry was established by the Mosher method. Compound 1 possesses in vitro cytotoxicity against WEHI 164 and RAW 264.7 cells. 相似文献
113.
A method for determining cadmium and lead in urine and other biological samples by graphite-furnace atomic-absorption spectrometry is reported. Samples were analysed after wet or dry ashing and without extraction or matrix-modification techniques, in laminar-flow clean-room; negligible blank contributions were found. Matrix interference effects were observed only for lead and were resolved by the method of standard additions. Five NBS biological reference materials were used as internal quality-control standards. The urinary levels for non-exposed volunteers ranged from 0.16 +/- 0.01 to 1.65 +/- 0.20 and from 6 +/- 1 to 31 +/- 6 ng/ml for cadmium and lead, respectively; this corresponds to 0.15 +/- 0.02 to 2.01 +/- 0.16 and 7 +/- 1 to 31 +/- 3 mug/day. The average relative standard deviation for 60 urine samples was 10% for cadmium and 13% for lead. 相似文献
114.
Villagomez-Guzman Ana K. Rodriguez-Garcia Gabriela del Rio Rosa E. Oliveros Ortiz Antonio J. Cerda-Garcia-Rojas Carlos M. Joseph-Nathan Pedro Gomez-Hurtado Mario A. 《Chemistry of Natural Compounds》2021,57(2):319-322
Chemistry of Natural Compounds - A known kaurenoic acid (1), together with a new kaurane derivative named 3α-isobutyryloxykaurenoic acid (2), was isolated from the roots of Lasianthaea aurea,... 相似文献
115.
116.
The synthesis of several new pyrrolidine based asymmetric organocatalysts derived from tartaric, glyceric acids and a pyrrolidine moiety is described with a study of their application in the development of an enantioselective aldol protocol. The influence of different proton donor groups, such as a primary hydroxyl or a carboxylic acid group, or their absence, on the efficiency of the organocatalyst was studied. The configuration of the tartrate derived catalysts and the presence of the rigid butane-2,3-diacetal were found to have a strong influence on the stereoselective outcome of the aldol reaction. 相似文献
117.
Karla G. Gutiérrez-Cuevas Rosa Julia Rodríguez-González Bertrand Donnio Damaso Navarro-Rodríguez 《Liquid crystals》2013,40(4):534-545
In this article, we report on the synthesis and thermotropic behaviour of methacrylic polymers containing 4′-(4-alkyloxyphenyl)azobenzene mesogens attached to the backbone through n-alkyloxy spacers of 6 or 10 methylene groups. Polymerisations were carried out via free radicals using azobisisobutyronitrile (AIBN) as initiator. Chemical structures of polymers and their precursors were characterised by 1H NMR spectroscopy. Thermogravimetric analysis showed that azopolymers are thermally stable up to temperatures around 300°C. The thermotropic liquid-crystalline (LC) behaviour was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). Results indicate that all synthesised mesogens, monomers and polymers developed two or more orthogonal LC phases in wide temperature ranges. Mesogens and monomers developed nematic and smectic phases, whereas polymers exhibited only smectic phase. In polymers, the arrangement of mesogens depends on the relative length of the spacer and the terminal flexible chain; two distinct structural models were proposed based on chemical interactions and steric constrains. The trans–cis photoisomerisation of monomers and polymers in solution was also studied. High cis-isomer contents (>80%) were reached in relative short irradiation times despite the steric constrains imposed by the polymer backbone. 相似文献
118.
Domenico Grasso Carmelo La Rosa Antonio Raudino Felice Zuccarello 《Liquid crystals》2013,40(12):1699-1705
Abstract Scanning dilatometric and calorimetric measurements were performed in order to obtain information on correlations between various phenomena involving a lipid vesicle. Scanning dilatometry has been shown to be a fast and reliable tool which gives complementary information to that obtained using differential scanning calorimetry and also, provides a means with which to follow dynamic processes without the introduction of perturbing probes into the lipid matrix. The systems examined were vesicles built up from mixtures of neutral and charged lipids in the presence of mono- and divalent inorganic cations. The studied processes were the gel-liquid crystal transition, lateral phase separation in mixed lipid vesicles and fusion between vesicles. 相似文献
119.