全文获取类型
收费全文 | 2554篇 |
免费 | 56篇 |
国内免费 | 8篇 |
专业分类
化学 | 1729篇 |
晶体学 | 23篇 |
力学 | 32篇 |
数学 | 565篇 |
物理学 | 269篇 |
出版年
2022年 | 17篇 |
2020年 | 45篇 |
2019年 | 29篇 |
2018年 | 17篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 68篇 |
2014年 | 52篇 |
2013年 | 92篇 |
2012年 | 92篇 |
2011年 | 99篇 |
2010年 | 75篇 |
2009年 | 58篇 |
2008年 | 119篇 |
2007年 | 110篇 |
2006年 | 95篇 |
2005年 | 102篇 |
2004年 | 79篇 |
2003年 | 63篇 |
2002年 | 50篇 |
2001年 | 22篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 30篇 |
1997年 | 22篇 |
1996年 | 22篇 |
1995年 | 26篇 |
1994年 | 27篇 |
1993年 | 35篇 |
1992年 | 28篇 |
1991年 | 18篇 |
1989年 | 25篇 |
1988年 | 30篇 |
1987年 | 30篇 |
1985年 | 34篇 |
1984年 | 46篇 |
1983年 | 26篇 |
1982年 | 20篇 |
1981年 | 31篇 |
1980年 | 38篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 26篇 |
1976年 | 22篇 |
1975年 | 26篇 |
1974年 | 26篇 |
1966年 | 16篇 |
1965年 | 16篇 |
1964年 | 16篇 |
1956年 | 24篇 |
排序方式: 共有2618条查询结果,搜索用时 26 毫秒
61.
The structure and thermodynamic properties of lanthanide complexes with a new tripodal ligand L2 have been elucidated using different physicochemical methods. At stoichiometric ratios, the tetrahedral three-dimensional complexes with lanthanide cations are formed in acetonitrile with good stabilities. Despite minor structural changes comparing to previously investigated tripodal ligands, the resulting assembly exhibits different features revealed with the crystal structure of [Eu(4)L2(4)](OH)(ClO(4))(11) (orthorhombic, Pbcn). Interestingly, the highly charged edifice contains an inner cage encapsulating a perchlorate anion. Such lanthanide mediated cage-like assemblies are rare, and may be of interest for different sensing applications. Indeed, the anionic guest can be exchanged with different anions. The related host-guest equilibria were investigated with NMR techniques. Various aspects of these reactions are qualitatively discussed. 相似文献
62.
Gonec T Bobal P Sujan J Pesko M Guo J Kralova K Pavlacka L Vesely L Kreckova E Kos J Coffey A Kollar P Imramovsky A Placek L Jampilek J 《Molecules (Basel, Switzerland)》2012,17(1):613-644
In this study, a series of thirty-five substituted quinoline-2-carboxamides and thirty-three substituted naphthalene-2-carboxamides were prepared and characterized. They were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Primary in vitro screening of the synthesized compounds was also performed against four mycobacterial species. N-Cycloheptylquinoline-2-carboxamide, N-cyclohexylquinoline-2-carboxamide and N-(2-phenylethyl)quinoline-2-carboxamide showed higher activity against M. tuberculosis than the standards isoniazid or pyrazinamide and 2-(pyrrolidin-1-ylcarbonyl)quinoline and 1-(2-naphthoyl)pyrrolidine expressed higher activity against M. kansasii and M. avium paratuberculosis than the standards isoniazid or pyrazinamide. The most effective antimycobacterial compounds demonstrated insignificant toxicity against the human monocytic leukemia THP-1 cell line. The PET-inhibiting activity expressed by IC(50) value of the most active compound N-benzyl-2-naphthamide was 7.5 μmol/L. For all compounds, the structure-activity relationships are discussed. 相似文献
63.
Beckers H Esser S Metzroth T Behnke M Willner H Gauss J Hahn J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(3):832-844
Sulfenic acid (HSOH, 1 ) has been synthesized in the gas‐phase by low‐pressure high‐temperature (1150 °C) pyrolysis of di‐tert‐butyl sulfoxide (tBu2SO, 2 ) and characterized by means of matrix isolation and gas‐phase IR spectroscopy. High‐level coupled‐cluster (CC) calculations (CCSD(T)/cc‐pVTZ and CCSD(T)/cc‐pVQZ) support the first identification of the gas‐phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix‐isolated 1 have been assigned, and its rotational‐resolved gas‐phase IR spectrum provides additional information on the O–H and S–H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrometry, matrix isolation, and gas‐phase FT‐IR spectroscopy reveal that, up to 500 °C, 2 decomposes selectively into tert‐butylsulfenic acid, (tBuSOH, 3 ), and 2‐methylpropene. The formation of the isomeric sulfoxide (tBu(H)SO, 3 a ) has been excluded. Transient 3 has been characterized by a comprehensive matrix and gas‐phase vibrational IR study guided by the predicted vibrational spectrum calculated at the density functional theory (DFT) level (B3LYP/6‐311+G(2d,p)). At higher temperatures, the intramolecular decomposition of 3 , monitored by matrix IR spectroscopy, yields short‐lived 1 along with 2‐methylpropene, but also H2O, and most probably sulfur atoms. In addition, HSSOH ( 6 ), H2, and S2O are found among the final pyrolysis products observed at 1150 °C in the gas phase owing to competing intra‐ and intermolecular decomposition routes of 3 . The decomposition routes of the starting compound 2 and of the primary intermediate 3 are discussed on the basis of experimental results and a computational study performed at the B3LYP/6‐311G* and second‐order Møller–Plesset (MP2/6‐311G* and RI‐MP2/QZVPP) levels of theory. 相似文献
64.
Gaston Bocaz-BeneventiRosa Latorre Marta FarkováJosef Havel 《Analytica chimica acta》2002,452(1):47-63
The application of the combination of experimental design (ED) and artificial neural networks (ANNs) for the quantification of overlapped peaks in capillary zone electrophoresis is described. When the total separation cannot be achieved by separation techniques, the use of ED-ANN can be a suitable approach. The unstability of EOF causes peak shift that has to be corrected in order to apply ED-ANN methods. In this work, normalization procedure of electropherograms with consequent application of ANNs for quantification purpose was developed. Both, spectra and electropherograms can be used as multivariate data. In general, both kinds of data were found to be suitable for unresolved peaks quantification by ED-ANN approach. 相似文献
65.
Olaf Kunert Ernst Haslinger Martin G. Schmid Josef Reiner Franz Bucar Efrem Mulatu Dawit Abebe Asfaw Debella 《Monatshefte für Chemie / Chemical Monthly》2000,131(2):195-204
Summary. Three bisdesmosidic saponins, 20-hydroxyecdysone, and quercetin-3-O-β-D-galactoside were isolated from the methanol extract of the aerial parts of Achyranthes aspera L. (Amaranthaceae). Their structures were established on the basis of NMR spectroscopic analysis; the complete 1H and 13C assignments of the compounds were achieved by means of 2D NMR studies.
Received July 21, 1999. Accepted August 26, 1999 相似文献
66.
67.
Karásek P Planeta J Varad'ová Ostrá E Mikesová M Goliás J Roth M Vejrosta J 《Journal of chromatography. A》2003,1002(1-2):13-23
Direct supercritical fluid extraction (SFE) of wines with carbon dioxide was compared to SFE of the sorbent used for solid-phase extraction of the same wine samples (SPE-SFE). Compared to SPE-SFE, the direct SFE results in amore specific and representative gas chromatographic fingerprint of the wine sample. The multivariate statistical processing of the direct SFE-GC data provides a clear-cut and sharp discrimination among the individual wine varieties while the discrimination based on the SPE-SFE-GC data is relatively poor. This finding reflects the adverse effects of additional analyte-sorbent interactions and sorption/desorption steps involved in SPE-SFE. 相似文献
68.
The microwave spectrum of 1-thia-closo-dodecaborane(11), 1-SB(11)H(11), has been investigated in the 23-62 GHz spectral region. The molecule is found to have C(5v) symmetry. The spectra of several isotopomers have been assigned and a precise substitution structure of the non-hydrogen atoms has been determined. The structure is in quite good agreement with the one determined previously by electron diffraction. Density functional theory calculations at the B3LYP/cc-pVTZ level were found to predict a structure that is in good agreement with the substitution structure. 相似文献
69.
Alexander Kastner Isabella Poetsch Josef Mayr Jaroslav V. Burda Alexander Roller Petra Heffeter Bernhard K. Keppler Christian R. Kowol 《Angewandte Chemie (International ed. in English)》2019,58(22):7464-7469
Due to their high kinetic inertness and consequently reduced side reactions with biomolecules, PtIV complexes are considered to define the future of anticancer platinum drugs. The aqueous stability of a series of biscarboxylato PtIV complexes was studied under physiologically relevant conditions. Unexpectedly and in contrast to the current chemical understanding, especially oxaliplatin and satraplatin complexes underwent fast hydrolysis in equatorial position (even in cell culture medium and serum). Notably, the resulting hydrolysis products strongly differ in their reduction kinetics, a crucial parameter for the activation of PtIV drugs, which also changes the anticancer potential of the compounds in cell culture. The discovery that intact PtIV complexes can hydrolyze at equatorial position contradicts the dogma on the general kinetic inertness of PtIV compounds and needs to be considered in the screening and design for novel platinum‐based anticancer drugs. 相似文献
70.