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991.
Kruk I Zajdel P van Beek W Bakaimi I Lappas A Stock C Green MA 《Journal of the American Chemical Society》2011,133(35):13950-13956
Na(0.40(2))MnO(2) belongs to a family of mixed Mn(3+) and Mn(4+) porous oxides that contains both octahedral and square pyramidal Mn-O units. Neutron and synchrotron radiation studies identify the presence of both sodium ordering (T(Na) ≈ 310 K) and Mn charge and orbital ordering. Below T(Na), the centrosymmetric Pbam structure adopts an (ab 4c) supercell of Pnnm symmetry that accommodates a coupled commensurate modulation down the c-axis channels of both Na position and occupancy with Mn valence. 相似文献
992.
Jeishla L. M. Matos Samantha A. Green Yuge Chun Vuong Q. Dang Russell G. Dushin Paul Richardson Jason S. Chen David W. Piotrowski Brian M. Paegel Ryan A. Shenvi 《Angewandte Chemie (International ed. in English)》2020,59(31):12998-13003
Preparative reactions that occur efficiently under dilute, buffered, aqueous conditions in the presence of biomolecules find application in ligation, peptide synthesis, and polynucleotide synthesis and sequencing. However, the identification of functional groups or reagents that are mutually reactive with one another, but unreactive with biopolymers and water, is challenging. Shown here are cobalt catalysts that react with alkenes under dilute, aqueous, buffered conditions and promote efficient cycloisomerization and formal Friedel–Crafts reactions. The constraining conditions of bioorthogonal chemistry are beneficial for reaction efficiency as superior conversion at low catalyst concentration is obtained and competent rates in dilute conditions are maintained. Efficiency at high dilution in the presence of buffer and nucleobases suggests that these reaction conditions may find broad application. 相似文献
993.
Sara E. Kern Lora A. Lin Frederick L. Fricke 《Journal of the American Society for Mass Spectrometry》2014,25(8):1482-1488
U.S. food imports have been increasing steadily for decades, intensifying the need for a rapid and sensitive screening technique. A method has been developed that uses foam disks to sample the surface of incoming produce. This work provides complimentary information to the extensive amount of published pesticide fragmentation data collected using LCMS systems (Sack et al. Journal of Agricultural and Food Chemistry, 59, 6383–6411, 2011; Mol et al. Analytical and Bioanalytical Chemistry, 403, 2891–2908, 2012). The disks are directly analyzed using transmission-mode direct analysis in real time (DART) ambient pressure desorption ionization coupled to a high resolution accurate mass-mass spectrometer (HRAM-MS). In order to provide more certainty in the identification of the pesticides detected, a library of accurate mass fragments and isotopes of the protonated parent molecular ion (the [M+H]+) has been developed. The HRAM-MS is equipped with a quadrupole mass filter, providing the capability of “data-dependent” fragmentation, as opposed to “all -ion” fragmentation (where all of the ions enter a collision chamber and are fragmented at once). A temperature gradient for the DART helium stream and multiple collision energies were employed to detect and fragment 164 pesticides of varying chemical classes, sizes, and polarities. The accurate mass information of precursor ([M+H]+ ion) and fragment ions is essential in correctly identifying chemical contaminants on the surface of imported produce. Additionally, the inclusion of isotopes of the [M+H]+ in the database adds another metric to the confirmation process. The fragmentation data were collected using a Q-Exactive mass spectrometer and were added to a database used to process data collected with an Exactive mass spectrometer, an instrument that is more readily available for this screening application. The commodities investigated range from smooth-skinned produce such as apples to rougher surfaces like broccoli. The minimal sample preparation and absence of chromatography has shortened the analysis time to about 15 min per sample, and the simplicity and robustness of the technique make it ideal for rapid screening. Figure
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994.
Cover Picture: Dinuclear Ruthenium(II) Complexes as Two‐Photon,Time‐Resolved Emission Microscopy Probes for Cellular DNA (Angew. Chem. Int. Ed. 13/2014)
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995.
Dinuclear Ruthenium(II) Complexes as Two‐Photon,Time‐Resolved Emission Microscopy Probes for Cellular DNA
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Elizabeth Baggaley Martin R. Gill Nicola H. Green David Turton Igor V. Sazanovich Stanley W. Botchway Carl Smythe John W. Haycock Julia A. Weinstein Jim A. Thomas 《Angewandte Chemie (International ed. in English)》2014,53(13):3367-3371
The first transition‐metal complex‐based two‐photon absorbing luminescence lifetime probes for cellular DNA are presented. This allows cell imaging of DNA free from endogenous fluorophores and potentially facilitates deep tissue imaging. In this initial study, ruthenium(II) luminophores are used as phosphorescent lifetime imaging microscopy (PLIM) probes for nuclear DNA in both live and fixed cells. The DNA‐bound probes display characteristic emission lifetimes of more than 160 ns, while shorter‐lived cytoplasmic emission is also observed. These timescales are orders of magnitude longer than conventional FLIM, leading to previously unattainable levels of sensitivity, and autofluorescence‐free imaging. 相似文献
996.
An efficient approach for the synthesis of a new class of triazolophanes by 1,3-dipolar cycloaddition reaction of highly reactive organic azides with dialkynes using Cu(I)-catalyzed azide–alkyne cycloaddition methodology (“click chemistry”) has been developed. All the compounds were characterized by spectral and elemental analyses. 相似文献
997.
A new synthetic approach to the synthesis of some epimeric C‐4‐hydroxy‐benzo[c]pyrans is described. A key step in their formation is stereoisomerisation of a nonconjugated ortho alkenylphenylketone and ‐ester using palladium bisacetonitrile [bisacetonitriledichloropalladium(II)] to give the corresponding conjugated E stereoisomers which cyclize on treatment with meta‐chloroperbenzoic acid (m‐CPBA) to afford the target compounds. 相似文献
998.
Ghias Uddin Ala Ud Din Amna Khurshid Frederick A. Valeriote M. Iqbal Choudhary 《中国化学会会志》2013,60(1):92-96
The significant inhibition and selectivity for human solid tumor cell by oily fraction of Maytenus royleanus, was subjected to GC‐MS analysis for determination of its chemical constituents. GC‐MS profile of methyl ester derivatives of fatty acids, showed that Palmitic acid (35.41%), Oleic acid (10.91%), Stearic acid (5.31%), Margaric acid (5.13%), Behenic acid (5.18%) and Hexanoic acid (4.97%) were the major components in the isolated oily fraction, while rest of the other fatty acids were present in minor concentration. The literature revealed that no such work has been done for the determination of fatty acids in M. royleanus stem oil. 相似文献
999.
Aluminium(III) chloride is shown to cause (reversible) cis-trans stereoisomerisations in some benzo[c]- and naphtho[2,3-c]pyrans at ambient temperature. 相似文献
1000.
Racemic hongconin 1 has been synthesized from adduct 2 formed by reaction between 1-methoxycyclohexa-1,4-diene and benzoquinone. The synthetic strategy includes Fries and Claisen rearrangements, base and cerium(IV) initiated pyran ring formation, C-4 pyran ring hydroxylation and silver(II) mediated oxidation. 相似文献