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991.
Pragst F 《Analytical and bioanalytical chemistry》2007,388(7):1393-1414
Solid-phase microextraction (SPME) is a miniaturized and solvent-free sample preparation technique for chromatographic–spectrometric
analysis by which the analytes are extracted from a gaseous or liquid sample by absorption in, or adsorption on, a thin polymer
coating fixed to the solid surface of a fiber, inside an injection needle or inside a capillary. In this paper, the present
state of practical performance and of applications of SPME to the analysis of blood, urine, oral fluid and hair in clinical
and forensic toxicology is reviewed. The commercial coatings for fibers or needles have not essentially changed for many years,
but there are interesting laboratory developments, such as conductive polypyrrole coatings for electrochemically controlled
SPME of anions or cations and coatings with restricted-access properties for direct extraction from whole blood or immunoaffinity
SPME. In-tube SPME uses segments of commercial gas chromatography (GC) capillaries for highly efficient extraction by repeated
aspiration–ejection cycles of the liquid sample. It can be easily automated in combination with liquid chromatography but,
as it is very sensitive to capillary plugging, it requires completely homogeneous liquid samples. In contrast, fiber-based
SPME has not yet been performed automatically in combination with high-performance liquid chromatography. The headspace extractions
on fibers or needles (solid-phase dynamic extraction) combined with GC methods are the most advantageous versions of SPME
because of very pure extracts and the availability of automatic samplers. Surprisingly, substances with quite high boiling
points, such as tricyclic antidepressants or phenothiazines, can be measured by headspace SPME from aqueous samples. The applicability
and sensitivity of SPME was essentially extended by in-sample or on-fiber derivatization. The different modes of SPME were
applied to analysis of solvents and inhalation narcotics, amphetamines, cocaine and metabolites, cannabinoids, methadone and
other opioids, fatty acid ethyl esters as alcohol markers, γ-hydroxybutyric acid, benzodiazepines, various other therapeutic drugs, pesticides, chemical warfare agents, cyanide, sulfide
and metal ions. In general, SPME is routinely used in optimized methods for specific analytes. However, it was shown that
it also has some capacity for a general screening by direct immersion into urine samples and for pesticides and other semivolatile
substance in the headspace mode. 相似文献
992.
Fritz C Cross I Moore BC Woodhouse J 《The Journal of the Acoustical Society of America》2007,122(6):3640-3650
This study is the first step in the psychoacoustic exploration of perceptual differences between the sounds of different violins. A method was used which enabled the same performance to be replayed on different "virtual violins," so that the relationships between acoustical characteristics of violins and perceived qualities could be explored. Recordings of real performances were made using a bridge-mounted force transducer, giving an accurate representation of the signal from the violin string. These were then played through filters corresponding to the admittance curves of different violins. Initially, limits of listener performance in detecting changes in acoustical characteristics were characterized. These consisted of shifts in frequency or increases in amplitude of single modes or frequency bands that have been proposed previously to be significant in the perception of violin sound quality. Thresholds were significantly lower for musically trained than for nontrained subjects but were not significantly affected by the violin used as a baseline. Thresholds for the musicians typically ranged from 3 to 6 dB for amplitude changes and 1.5%-20% for frequency changes. Interpretation of the results using excitation patterns showed that thresholds for the best subjects were quite well predicted by a multichannel model based on optimal processing. 相似文献
993.
Tailoring RuII Pyridine/Triazole Oxygenation Catalysts and Using Photoreactivity to Probe their Electronic Properties
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Fritz Weisser Hendrik Stevens Johannes Klein Margarethe van der Meer Dr. Stephan Hohloch Prof. Dr. Biprajit Sarkar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(24):8926-8938
Tuning of ligand properties is at the heart of influencing chemical reactivity and generating tailor‐made catalysts. Herein, three series of complexes [Ru(L)(Cl)(X)]PF6 (X=DMSO, PPh3, or CD3CN) with tripodal ligands (L1–L5) containing pyridine and triazole arms are presented. Triazole‐for‐pyridine substitution and the substituent at the triazole systematically influence the redox behavior and photoreactivity of the complexes. The mechanism of the light‐driven ligand exchange of the DMSO complexes in CD3CN could be elucidated, and two seven‐coordinate intermediates were identified. Finally, tuning of the ligand framework was applied to the catalytic oxygenation of alkanes, for which the DMSO complexes were the best catalysts and the yield improved with increasing number of triazole arms. These results thus show how click‐derived ligands can be tuned on demand for catalytic processes. 相似文献
994.
Normal‐to‐Abnormal NHC Rearrangement of AlIII,GaIII, and InIII Trialkyl Complexes: Scope,Mechanism, Reactivity Studies,and H2 Activation
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Dr. Gilles Schnee Prof. Olalla Nieto Faza Dr. David Specklin Dr. Béatrice Jacques Dr. Lydia Karmazin Prof. Richard Welter Prof. Carlos Silva López Dr. Samuel Dagorne 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17959-17972
The present contribution reports experimental and theoretical mechanistic investigations on a normal‐to‐abnormal (C2‐to‐C4‐bonded) NHC rearrangement processes occurring with bulky group 13 metal NHC adducts, including the scope of such a reactivity for Al compounds. The sterically congested adducts (nItBu)MMe3 (nItBu=1,3‐di‐tert‐butylimidazol‐2‐ylidene; M=Al, Ga, In; 1 a – c ) readily rearrange to quantitatively afford the corresponding C4‐bonded complexes (aItBu)MMe3 ( 4 a – c ), a reaction that may be promoted by THF. Thorough experimental data and DFT calculations were performed on the nNHC‐to‐aNHC process converting the Al‐nNHC ( 1 a ) to its aNHC analogue 4 a . A nItBu/aItBu isomerization is proposed to account for the formation of the thermodynamic product 4 a through reaction of transient aItBu with THF–AlMe3. The reaction of benzophenone with (nItBu)AlMe3 afforded the zwitterionic species (aItBu)(CPh2‐O‐AlMe3) ( 6 ), reflecting the unusual reactivity that such bulky adducts may display. Interestingly, the nItBu/Al(iBu)3 Lewis pair behaves like a frustrated Lewis pair (FLP) since it readily reacts with H2 under mild conditions. This may open the way to future reactivity developments involving commonly used trialkylaluminum precursors. 相似文献
995.
L-selectin is a protein with potential importance for numerous diseases and clinical disorders. In this paper, we present a new aptamer-based luminescent assay developed to detect L-selectin. The sensing system working principle is based on Förster Resonance Energy Transfer (FRET) from a donor terbium complex (TbC) to an acceptor cyanine dye (Cy5). In the present approach, the biotinylated aptamer is combined with Cy5-labelled streptavidin (Cy5-Strep) to yield an aptamer-based acceptor construct (Apta-Cy5-Strep), while L-selectin is conjugated using luminescent TbC. Upon aptamer binding to the TbC-labelled L-selectin (L-selectin-TbC), permanent donor-acceptor proximity is established which allows for radiationless energy transfer to occur. However, when unlabelled L-selectin is added, it competes with the L-selectin-TbC and the FRET signal decreases as the L-selectin concentration increases. FRET from the TbC to Cy5 was observed with time-gated time-resolved luminescence spectroscopy. A significant change in the corrected luminescence signal was observed in the dynamic range of 10–500 ng/mL L-selectin, the concentration range relevant for accelerated cognitive decline of Alzheimer's disease, with a limit of detection (LOD) equal to 10 ng/mL. The aptasensor-based assay is homogeneous and can be realized within one hour. Therefore, this method has the potential to become an alternative to tedious heterogeneous analytical methods, e.g. based on enzyme-linked immunosorbent assay (ELISA). 相似文献
996.
Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex
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M. Sc. Lydia M. Peschel Prof. Dr. Ferdinand Belaj Prof. Dr. Nadia C. Mösch‐Zanetti 《Angewandte Chemie (International ed. in English)》2015,54(44):13018-13021
The synthesis and characterization of a biomimetic system that can reversibly bind acetylene (ethyne) is reported. The system has been designed to mimic catalytic intermediates of the tungstoenzyme acetylene hydratase. The thiophenyloxazoline ligand S‐Phoz (2‐(4′,4′‐dimethyloxazolin‐2′‐yl)thiophenolate) is used to generate a bioinspired donor environment around the W center, facilitating the stabilization of W–acetylene adducts. The featured complexes [W(C2H2)(CO)(S‐Phoz)2] ( 2 ) and [WO(C2H2)(S‐Phoz)2] ( 3 ) are extremely rare from a synthetic and structural point of view as very little is known about W–C2H2 adducts. Upon exposure to visible light, 3 can release C2H2 from its coordination sphere to yield the 14‐electron species [WO(S‐Phoz)2] ( 4 ). Under light‐exclusion 4 re‐activates C2H2 making this the first fully characterized system for the reversible activation of acetylene. 相似文献
997.
Dr. Guillaume Ernouf Dr. Egor Chirkin Dr. Lydia Rhyman Dr. Ponnadurai Ramasami Dr. Jean-Christophe Cintrat 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(7):2640-2644
A new photoredox-catalyzed decarboxylative radical addition approach to functionalized cyclobutanes is described. The reaction involves an unprecedented formal Giese-type addition of C(sp3)-centered radicals to highly strained bicyclo[1.1.0]butanes. The mild photoredox conditions, which make use of a readily available and bench stable phenyl sulfonyl bicyclo[1.1.0]butane, proved to be amenable to a diverse range of α-amino and α-oxy carboxylic acids, providing a concise route to 1,3-disubstituted cyclobutanes. Furthermore, kinetic studies and DFT calculations unveiled mechanistic details on bicyclo[1.1.0]butane reactivity relative to the corresponding olefin system. 相似文献
998.
Xiang-Zhao Kong Markus Holzner Fritz Stauffer Wolfgang Kinzelbach 《Experiments in fluids》2011,50(6):1659-1670
The main goal of this work is to implement and validate a visualization method with a given temporal/spatial resolution to
obtain the dynamic three-dimensional (3D) structure of an air plume injected into a deformable liquid-saturated porous medium.
The air plume develops via continuous air injection through an orifice at the bottom of a loose packing of crushed silica
grains. The packing is saturated by a glycerin-water solution having the same refractive index and placed in a rectangular
glass container. By using high-speed image acquisition through laser scanning, the dynamic air plume is recorded by sequential
tomographic imaging. Due to the overlap between adjacent laser sheets and the light reflection, air bubbles are multiply exposed
in the imaging along the scanning direction. Four image processing methods are presented for the removal of these redundant
pixels arising from multiple exposure. The respective results are discussed by comparing the reconstructed air plume volume
with the injected one and by evaluating the morphological consistency of the obtained air plume. After processing, a 3D dynamic
air flow pattern can be obtained, allowing a quantitative analysis of the air flow dynamics on pore-scale. In the present
experimental configuration, the temporal resolution is 0.1 s and the spatial resolution is 0.17 mm in plane and about 1 mm
out of plane of the laser sheet. 相似文献
999.
Riederer SK Bechlars B Herrmann WA Kühn FE 《Dalton transactions (Cambridge, England : 2003)》2011,40(1):41-43
A facile and straightforward synthetic procedure for the preparation of new chiral bis-1,2,4-triazolium salts and their corresponding rhodium(I) biscarbene complexes are reported. It is widely applicable for the synthesis of 1,2,4-triazolium salts. The new chiral biscarbenes represent promising ligands for transition metal-catalyzed asymmetric syntheses. Their first successful application is demonstrated by the rhodium-catalyzed hydrogenation of dimethylitaconate and methyl-2-acetamidoacrylate which yielded enantioselectivities of up to 61% ee. 相似文献
1000.