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61.
Contributions to the Chemistry of Transition Metal Alkyl Compounds. XLVI. Polarographic Properties of Dibenzyl and Diphenyl Titanium in Aprotic Solvents The polarographic properties of dibenzyl and diphenyl titanium were investigated using acetonitrile (AN), dimethylformamide (DMF), and dimethylsulfoxide (DMSO) as solvents. Both compounds are reduced irreversibly at very negative potentials in a two-electron step with formation of titanium. The half-wave potentials depend on the donor strength of the solvents. With increasing donor number the half-wave potentials are shifted to more negative values. The fact that the limiting currents turned out to be diffusion controlled suggests a monomeric structure of the titanium diorganyls in AN, DMF, and DMSO. 相似文献
62.
Florence Babonneau Christine Toutou Stéphanie Gavériaux 《Journal of Sol-Gel Science and Technology》1997,8(1-3):553-556
17O NMR experiments using enriched water were performed to followthe hydrolysis-condensation process of dimethyldiethoxysilanetetraethoxysilane and a 1/1 mixture of dimethyldiethoxysilane andtetraethoxysilane (H2O/OEt = 0.5; pH = 2). The spectrarecorded over several hours time period were simulated to followquantitatively the variations of residual water, hydroxyl groups(Si–17
H) and oxo bridges (Si–17
–Si). Presence of a resonance signal due oxo bridges between di- andtetrafunctional Si units clearly demonstrates that co-condensationreactions occur to a large extent between the two alkoxides, and that thesebonds are stable during the aging period. 相似文献
63.
Christine Walton 《Accreditation and quality assurance》2004,9(11-12):662-665
Safety issues related to the design, production and distribution of simulated specimens for microbiology external quality assessment (EQA) have occupied scheme organisers for many years. Since the anthrax attacks in Washington, USA in October 2001, there has been heightened awareness in the public domain regarding the transport of infectious substances. For instance, in direct response to the anthrax incident in the US, microbiology institutes in the UK that handle dangerous pathogens (like the Health Protection Agency) are registered with the national police force and are inspected regularly to ensure compliance with current legislation covering the control of these pathogens. The fear of a complete ban on the movement of infectious substances following the anthrax incident has not yet been realised, but remains a serious risk. Many countries such as the UK, USA, and Australia have introduced measures for the control, transportation, and health and safety aspects of handling and distribution of infectious materials. The national postal services of many countries do not accept infectious materials by mail. There are a limited number of courier services willing to transport dangerous goods, especially division 6.2 (infectious substances) and these services are costly. Measures can be implemented by scheme organisers to ensure best practice; for instance, by having sufficient and trained staff, with knowledge, expertise and use of computerised systems in the shipping/export department. Ensuring compliance with national and international health and safety legislation by providing safety data sheets and by carrying out product risk assessments is required to ensure transparency and to demonstrate duty of care. Organisers of microbiology EQA face uncertainty about the future survival of schemes in the current climate. It is imperative that practices and procedures are put into place that meet with the legislation and enable us to continue to support quality in laboratory medicine. 相似文献
64.
G. Eckert 《Fresenius' Journal of Analytical Chemistry》1956,153(4):261-267
Zusammenfassung Es wird ein Verfahren zur colorimetrischen Bestimmung kleiner Aluminiumgehalte (0,1–0,002% Al) in Nickellegierungen für Oxydkathoden beschrieben. Die Trennung des Aluminiums von dem großen Nickelüberschuß und anderen Schwermetallen wird durch negative Extraktion der Diäthyldithiocarbaminate in bestimmten Halogenkohlenwasserstoffen erreicht. Anschließend kann Aluminium mit dem Ammoniumsalz der Aurintricarbonsäure photometrisch bestimmt werden. Der Einfluß verschiedener Elemente auf die Farblackbildung wurde quantitativ untersucht.Das beschriebene Verfahren ist auch für die Aluminiumbestimmung in Eisen und Eisenlegierungen geeignet.Bei der Durchführung der beschriebenen Untersuchungen wurde ich von Frl. E. Bauersachs unterstützt. Herrn Dr. W. Schmidt, Röhrenfabrik der Siemens u. Halske AG, danke ich für wertvolle Diskussionen. 相似文献
65.
Christine Culot Magdalena Dory Francois Durant Daniel P. Vercauteren 《International journal of quantum chemistry》1993,46(1):211-225
Conformational analyses of large molecules as fatty acids and triglycerides are usually amenable by molecular mechanics. A correct evaluation of the electrostatic energy term is thus crucial in determining reliable results. In this contribution, we have considered the most abundant fatty acids in biomembranes, i.e., lauric, stearic, oleic, and elaidic acid, and the corresponding triglycerides, i.e., trilaurin, tristearin, triolein, and trielaidin, and estimated the Mulliken and potential-derived charges both at the semiempirical AM 1 and ab initio HF MO STO -3G level. Atomic charges obtained by the Mulliken population analysis do not take into account the full geometry of the molecule. On the contrary, the change of conformation, due to different chains length or the presence of a trans or cis double bond, greatly influences the repartition of the potential-derived charges. A systematic comparative analysis shows that charges calculated by AM 1 are not suitable because as they do not reproduce potential-derived charges obtained by ab initio. © 1993 John Wiley & Sons, Inc. 相似文献
66.
A tetraketide synthase containing a loading module (LM), the extension modules erythromycin module 1, rapamycin module 2, and erythromycin module 2 (LM-Ery1-Rap2-Ery2-TE), when expressed in Saccharopolyspora erythraea strain JC2, produced as previously reported a mixture of tetraketide lactones (minor products) and triketide lactones (major products). Several alternative plausible mechanisms by which this "skipping" phenomenon might occur may be proposed. Site-directed mutagenesis of the ketosynthase (KS) and acylcarrier protein (ACP) domains in the interpolated module has shown that skipping within the hybrid PKS involves passage of the growing polyketide through the interpolated module, by direct ACP-to-ACP transfer of the polyketide chain. 相似文献
67.
Mark SS Sandhyarani N Zhu C Campagnolo C Batt CA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(16):6808-6817
We report here a multistep route for the immobilization of DNA and proteins on chemically modified gold substrates using fourth-generation NH(2)-terminated poly(amidoamine) dendrimers supported by an underlying amino undecanethiol (AUT) self-assembled monolayer (SAM). Bioactive ultrathin organic films were prepared via layer-by-layer self-assembly methods and characterized by fluorescence microscopy, variable angle spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR). The thickness of the AUT SAM base layer on the gold substrates was determined to be 1.3 nm from ellipsometry. Fluorescence microscopy and AFM measurements, in combination with analyses of the XPS/ATR-FTIR spectra, confirmed the presence of the dendrimer/biopolymer molecules on the multilayer sensor surfaces. Model proteins, including streptavidin and rabbit immunoglobulin proteins, were covalently attached to the dendrimer layer using linear cross-linking reagents. Through surface plasmon resonance measurements, we found that sensor surfaces containing a dendrimer layer displayed an increased protein immobilization capacity, compared to AUT SAM sensor surfaces without dendrimer molecules. Other SPR studies also revealed that the dendrimer-based surfaces are useful for the sensitive and specific detection of DNA-DNA interactions. Significantly, the multicomponent films displayed a high level of stability during repeated regeneration and hybridization cycles, and the kinetics of the DNA-DNA hybridization process did not appear to be influenced by surface mass transport limiting effects. 相似文献
68.
The reaction of N-(3,4-dichlorophenethyl)-N-methylamine (1) with 3-chloromethyl-5-phenyl-1,2,4-oxadiazole (2) was investigated. Employment of an equimolar amount of 1 and 2 in the presence of potassium carbonate led to the expected tertiary amine 3 (N-[(3,4-dichlorophenyl)ethyl]-N-methyl-N-[(5-phenyl-1,2,4-oxadiazol-3-yl)methyl]amine), whereas an excess of 1 and prolonged reaction time resulted in ring fission of the oxadiazole system in 3 and finally in the formation of N′-benzoyl-N-[(3,4-dichlorophenyl)ethyl]-N-methylguanidine (4) and N,N′-bis[(3,4-dichlorophenyl)ethyl]-N,N′-dimethylmethanediamine (5). The structures of products 3–5 were determined by means of 1H and 13C NMR-spectroscopy, mass spectrometry and IR-spectroscopy, for 3 (as picrate) and 4 also X-ray structure analysis was employed. A possible mechanism of the reaction pathway leading to compounds 4 and 5 is proposed. 相似文献
69.
New compounds obtained by enzymatic oxidation of phloridzin 总被引:1,自引:0,他引:1
Oxidation of phloridzin was studied in a model system in the presence of apple polyphenol oxidase. In addition to 3-hydroxy phloridzin, two major oxidation products were purified by reversed phase HPLC at the semi-preparative scale. Their structures were elucidated by UV, ESI-MSn and NMR spectroscopies. The first compound was a colourless product, whose novel structure strongly differs from its precursor showing a biphenyl moiety and a propionic acid chain. The second product was an oxidised form of the first one and corresponded to a stable yellow pigment with two isomeric forms. A mechanism of formation of these products, which implied successive oxidation and nucleophilic addition steps was proposed. 相似文献
70.
The hindered rotor transitions of H(2) adsorbed in the chemically related and prototypical porous metal-organic frameworks IRMOF-1, IRMOF-8, IRMOF-11, and MOF-177 were studied by inelastic neutron scattering to gain information on the specifics of H(2) binding in this class of adsorbents. Remarkably sharp and complex spectra of these materials signify a diversity of well-defined binding sites. Similarities in the spectral features as a function of H(2) loading and correlations with recent crystallographic studies were used to assign transitions ranging in rotational barrier from <0.04 to 0.6 kcal/mol as corresponding to localized adsorption sites on the organic and inorganic components of these frameworks. We find that binding of H(2) at the inorganic cluster sites is affected by the nature of the organic link and is strongest in IRMOF-11 in accord with our adsorption isotherm data. The sites on the organic link have lower binding energies, but a much greater capacity for increases in H(2) loading, which demonstrates their importance for hydrogen uptake by these materials. 相似文献