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961.
Steffen Kudis Günter Helmchen 《Angewandte Chemie (International ed. in English)》1998,37(21):3047-3050
Mechanistic considerations made a decisive contribution to the development of new chiral P,N ligands L* containing tricarbonylcyclopentadienylmanganese (cymantrene). These ligands induce very high enantioselectivities (>99:1) in allylic substitutions of cyclic substrates 1 with formation of 2 (2-Bp=2-biphenylyl). 相似文献
962.
The reductive coupling of chlorotris(diorganylamino)silanes 1 with chlorotrimethylsilane by the action oflithium in THF provides for steric reasons, an easy access to unsymmetrical aminosubstituted disilanes (R2N)3Si-SiMe3 3. Similarly, cross-coupling to give pentakis(diethylamino)disilane 4 is observed between 1a and bis(diethylamino)chloro-hydridosilane 2a on treatment with lithium. In reactions of the less bulky bis(diorganylamino)chlorohy-dridosilanes 2 with ClSiMe3 and Li, however, thesymmetrical coupling is preferred and affords SiH-functional substituted (R2N)32HSi-SiH(NR2)2 5. Aminosubstituted disilanes 3–5 are useful starting materials for modification of disilanes or syntheses ofsilicon heterocycles via generation and trapping of aminosilylenes, as exemplified by diethylaminosilacyclopent-3-ene 6a. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:311–316, 1998 相似文献
963.
964.
The structure of tetraethyleneglycoldimethylether magnesium bromide has been determined by direct methods. The crystal is monoclinic, space group Cc with a = 15.1276(5) Å, b = 21.5603(8) Å, c = 11.0552(4) Å, β = 118.76(1)° and Z = 8. The structure contains two symmetrically independent molecules in the unit cell and sevenfold coordinated Mg atoms in the center of the tetraethyleneglycoldimethylether ligands. 相似文献
965.
Stanislav Kúdela Steffen Oswald Stanislav Kúdela Jr. Stefan Baunack Klaus Wetzig 《Mikrochimica acta》2000,133(1-4):29-34
Fibre/matrix interfaces in δ-Al2O3/Mg8Li and δ-Al2O3/Mg composites have been investigated using XPS and SIMS analysis of extracted δ-Al2O3 fibres in context with previous XRD observations. Results obtained indicate that in MgLi based composites lithium enters
preferentially the interfacial redox reactions producing Li+ ions that occupy vacant cation positions in the defect δ-Al2O3 lattice which results in a strong fibre/matrix interfacial bond. On the other hand, in Mg matrix composites the magnesium
oxide appears to be the final reaction product that does not enter the solid state reaction with adjacent δ-Al2O3 fibre during the melt infiltration process, so that only relatively weak interfacial bond is created. 相似文献
966.
967.
Christensen H Schjøth-Eskesen C Jensen M Sinning S Jensen HH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(38):10618-10627
We describe a novel approach for the synthesis of a series of 3,7-difunctionalised symmetric and unsymmetrical analogues of the tricyclic antidepressant (TCA) imipramine, which uses a key palladium-catalysed amination/cyclisation of an ester-functionalised dibromide. Of the ester, methyl, hydroxymethyl and methoxymethyl disubstituted compounds prepared, 3,7-dimethyl-imipramine was found to be the most potent against the human serotonin transporter (hSERT). The inhibitory potency of 3,7-dimethyl imipramine was found to be at least as high as the parent imipramine. This novel TCA also exhibits an increased selectivity (relative to imipramine) in binding to hSERT versus the human norepinephrine transporter (hNET). Even higher selectivity could be obtained with 3,7-dihydroxymethyl imipramine, which was found to be 167-fold more selective for hSERT over hNET, representative of a 120-fold gain in selectivity relative to the parent imipramine. These results further validate our previous model for the binding of imipramine and high-affinity analogues of imipramine to the central binding site of hSERT. 相似文献
968.
Mona AbdelTawab Ute Bahr Bruno Danieli Steffen Gebhardt Michael Karas Sergio Riva Manfred Schubert‐Zsilavecz 《Helvetica chimica acta》2000,83(4):739-747
The ginsenosides Rb1 ( 3 ) and Rg1 ( 4 ) isolated from Panax ginseng were enzymatically modified with galactosyltransferase to furnish new derivatives carrying galactose units in one or both sugar chains at position C(20) and/or C(3) or C(6) of the protopanaxadiol and protopanaxatriol aglycones 1 and 2 , respectively. To determine the linkage position(s) of the introduced galactose unit(s), an electrospray‐ionization MS analysis with consecutive fragmentation steps (ESI‐MSn) was carried out using an ion‐trap mass spectrometer (Figs. 2 and 3). It was shown that both sugar moieties, located at different positions of the protopanaxadiol and protopanaxatriol aglycone, can be easily differentiated and analyzed in the subsequent fragmentation steps. Collision‐induced dissociation (CID) of the Na+‐ionized molecule (MS2) leads to cleavage of the most labile O−C(20) glycosidic bond, liberating the C(20) oligosaccharide fragment ion that can be analyzed in a subsequent fragmentation step (MS3). MS3 of the C(20) monodeglycosylated ginsenoside leads to cleavage of the second sugar moiety, allowing structure analysis of this fragment ion (MS4). By this method, the linkages of the monosaccharides and branching positions can be rapidly determined using only a few μl of a 10−5 M sample solution. 相似文献
969.
The performance of a home-built tunable diode laser (TDL) spectrometer, aimed at multi-line detection of carbon dioxide, has been evaluated and optimized. In the regime of the (30(0)1)(III) <-- (000) band of (12)CO(2) around 1.6 microm, the dominating isotope species (12)CO(2), (13)CO(2), and (12)C(18)O(16)O were detected simultaneously without interference by water vapor. Detection limits in the range of few ppmv were obtained for each species utilizing wavelength modulation (WM) spectroscopy with balanced detection in a long-path absorption cell set-up. High sensitivity in conjunction with high precision -- typically +/-1 (per thousand) and +/-6 (per thousand) for 3% and 0.7% of CO(2), respectively -- renders this experimental approach a promising analytical concept for isotope-ratio determination of carbon dioxide in soil and breath gas. For a moderate (12)CO(2) line, the pressure dependence of the line profile was characterized in detail, to account for pressure effects on sensitive measurements. 相似文献
970.
[reaction: see text] Suitably substituted heteroaromatic compounds such as indole and pyrrole derivatives are excellent acceptor units for intramolecular couplings of samarium ketyls. They furnish highly functionalized indole derivatives with very good diastereoselectivities additionally. Intermediate samarium enolates can be trapped by electrophiles, allowing efficient tandem reactions. 相似文献