全文获取类型
收费全文 | 1511篇 |
免费 | 34篇 |
国内免费 | 5篇 |
专业分类
化学 | 1117篇 |
晶体学 | 9篇 |
力学 | 34篇 |
综合类 | 1篇 |
数学 | 197篇 |
物理学 | 192篇 |
出版年
2023年 | 13篇 |
2022年 | 30篇 |
2021年 | 49篇 |
2020年 | 42篇 |
2019年 | 33篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 47篇 |
2015年 | 35篇 |
2014年 | 51篇 |
2013年 | 84篇 |
2012年 | 91篇 |
2011年 | 101篇 |
2010年 | 67篇 |
2009年 | 60篇 |
2008年 | 86篇 |
2007年 | 89篇 |
2006年 | 68篇 |
2005年 | 74篇 |
2004年 | 66篇 |
2003年 | 41篇 |
2002年 | 51篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 14篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1985年 | 4篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1970年 | 4篇 |
1955年 | 3篇 |
排序方式: 共有1550条查询结果,搜索用时 15 毫秒
31.
Coppens P Vorontsov II Graber T Kovalevsky AY Chen YS Wu G Gembicky M Novozhilova IV 《Journal of the American Chemical Society》2004,126(19):5980-5981
Using a stroboscopic technique, in which the molecule is repeatedly excited and the structural change is probed more than 5000 times per second immediately after excitation, we performed a 16 K time-resolved single-crystal study of the microsecond lifetime triplet state of the Cu(I)phenanthroline derivative[Cu(I)(dmp)(dppe)][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane). The geometry changes on excitation differ for the two symmetry-independent molecules, but are in the same direction as calculated for an isolated reference molecule, although the flattening distortion in the crystal is significantly smaller, implying that the reorganization energy is greatly affected by the confining medium. 相似文献
32.
In this paper the 4-state latch bridge model proposed by Rembold and Murphy is expanded; first by incorporation of the analytical expression of Ca2+ dependent MLCK activation from the work of Kato et al. and second, by inclusion of the myosin dephosphorylation based on the Michaelis-Menten kinetics. The analysis of the proposed model and the comparison with the original model results as well as with the experimental data is presented. The model is able to predict the steady-state isometric stress and the myosin phosphorylation in dependence on steady cytosolic [Ca2+] as well as the temporal evolution of the system in dependence on the input Ca2+ signal in the form of biphasic transient, whereby our model results are in several aspects in better agreement with experimental observations. 相似文献
33.
Jan Vorlíek Milan Fara Frantiek Vydra 《Fresenius' Journal of Analytical Chemistry》1968,241(5):314-318
Summary Conditions for the magnesium determination in alkaline solution by EDTA titration with biamperometric indication were examined. The most preferable pH range was found to be above 9.6. A reliable determination can be carried out in the presence of Ca, Ni, Cu and Co up to the ratio of 11. In the case of higher concentrations of Cu and Ni masking with potassium cyanide can be used. In this case, however, a change of the titration curves occurs.A new method for the determination of water-hardness by biamperometric indication is proposed. It is rapid and accurate and meets the requirements of routine and research work (error: ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
Zusammenfassung Die Bedingungen für die Magnesiumbestimmung in alkalischer Lösung durch Titration mit ÄDTA bei biamperometrischer Endpunktsanzeige wurden untersucht. Der günstigste pH-Bereich liegt über 9,6. Zuverlässige Bestimmungen können in Gegenwart von Ca, Ni, Cu und Co bis zum Verhältnis 11 ausgeführt werden. Höhere Konzentrationen an Cu oder Ni können mit KCN maskiert werden, wobei allerdings eine Umkehrung der Kurven auftritt.Ein Verfahren zur Wasserhärtebestimmung mit biamperometrischer Indikation wird vorgeschlagen, das schnell durchzuführen ist und genaue Werte liefert (Fehler ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
34.
35.
Kolárová L Holcapek M Jambor R Dostál L Nádvorník M Růzicka A 《Journal of mass spectrometry : JMS》2004,39(6):621-629
Electrospray ionization (ESI) mass spectrometry was applied to the structural analysis of 23 2,6-[bis(alkyloxy)methyl]phenyltin(IV) derivatives. The mass spectra were measured in both polarity modes and multistage tandem mass spectrometric (MS(n)) measurements were performed on the ion trap analyser for positively charged tin-containing ions. The sum of complementary ions observed in the positive-ion mode (i.e. [M-R(3)](+) ion) and in the negative-ion mode (i.e. [R(3)](-) ion) permits molecular mass determination in spite of the fact that the molecular adducts were often missing even in the first-order mass spectra. The subsequent fragmentation of [M-R(3)](+) ions studied by MS(n) and the correlation of observed fragment ions with the expected structures of synthesized organotin(IV) compounds allowed us to understand the fragmentation behaviour and the mechanism of the ion formation for studied compounds. The typical neutral losses are alkenes, alcohols and aldehydes. The fragmentation pattern of one selected compound was supported by MS(n) measurements of an isotopically labelled analogue to confirm unusual ion-molecule reactions of some fragment ions with water in the ion trap. 相似文献
36.
Kaushik Chanda Milan Ch. Dutta Enamul Karim Jai N. Vishwakarma 《Journal of heterocyclic chemistry》2004,41(4):627-631
1‐(Aralkyl/aryl)‐3‐(alkyyaralkyl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines ( 2a‐c ) have been synthesized by dethiomethylation of 5‐aroyl‐6‐methylthio‐1,2,3,4‐tetrahydropyrimidines ( 1a‐c ). An alternative one‐pot synthetic strategy has been developed for the title compounds 2a‐t by the reaction of enaminones 3 with pri mary amine and formaldehyde in refluxing methanol in good yields. 相似文献
37.
The synthesis and characterization of CuX2L; (X = CH3CH2COO?, ClCH2CH2COO?, CH3CHClCOO? or CH3CCl2COO?; and L = 4-acetylpyridine N-oxide) is reported. The characterization of these compounds was based on electronic, infrared and EPR spectra, as well as magnetic measurements over the temperature range. Several correlations between the spectral and magnetic data as well as pKa values of the respective acids were found and discussed. On the basis of spectral and magnetic data the structures of the compounds are discussed. 相似文献
38.
39.
We consider a characterization of proteomics maps based on an alternative kind of neighborhood graphs for the protein spots on 2-D gel. The novel approach considers for every protein spot only the nearest neighborhood consisting of protein spots of higher abundance. The approach has the simplicity and advantages of the recently introduced characterization of proteome maps based on considering the nearest neighborhoods of protein spots, but it also has important additional desirable computational features. The characterization of the nearest neighborhood graphs of 2-D gel proteomics maps is sensitive to the number of spots considered and may lead to changes in the degree of similarity of different maps when the number of points has been changed, thus imposing restrictions on the protocol used for comparison of maps. The novel approach presented in this work is less sensitive to the number of points used in the analysis because graphs are constructed in a stepwise process in which the role of more distant neighbors has been diminished by linking a new spot to the nearest spot that has been already part of the neighborhood graph. In this way a graph with N + 1 spots is obtained from the graph on N spots by adding a single new link, while in the case of the nearest neighborhood graphs adding a new spot introduces novel neighborhoods and generally results in a graph that may differ significantly from the neighborhood graph on N points. 相似文献
40.
Milo Kovaík und Milan Mouka 《Fresenius' Journal of Analytical Chemistry》1956,150(6):416-420
Zusammenfassung PyrogallolcarbonsÄure kann mit Vorteil als Indicator bei der direkten Titration von Calciumsalzlösungen mit 0,1 m Komplexon(III)-lösung benutzt werden. Es ergibt sich ein scharfer Farbumschlag von Violettrot nach Gelb; die Titrationsergebnisse stimmen auch in Anwesenheit von Magnesiumsalz sowohl untereinander als auch mit den Sollwerten sehr befriedigend überein.Die direkte Titration von Barium- oder Strontium-Ionen ist wegen des in diesen FÄllen undeutlichen Farbumschlages nicht zu empfehlen. Dagegen sind beide Metall-Ionen (und auch Ca-Ion) gut zu bestimmen, wenn man mit einem gemessenen Komplexonüberschu\ versetzt und den unverbrauchten Rest mit 0,1 m Bariumchloridlösung zurücktitriert. Der Farbumschlag des PyrogallolcarbonsÄure-Indicators von Gelb nach Violettrot ist scharf.Das gleiche indirekte Bestimmungsverfahren (Rücktitration mit 0,1 m BaCl2-Lösung) eignet sich auch zur Bestimmung von Blei-, Cadmium-, Aluminium- und Zink-Ionen. 相似文献