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191.
Coombs TC Lee MD Wong H Armstrong M Cheng B Chen W Moretto AF Liebeskind LS 《The Journal of organic chemistry》2008,73(3):882-888
A unified strategy for the high-throughput synthesis of multigram quantities of the eta(3)-oxopyranyl- and eta(3)-oxopyridinylmolybdenum complexes TpMo(CO)(2)(eta(3)-oxopyranyl) and TpMo(CO)(2)(eta(3)-oxopyridinyl) is described (Tp = hydridotrispyrazolylborato). The strategy uses the oxa- and aza-Achmatowicz reaction for the preparation of these organometallic enantiomeric scaffolds, in both racemic and high enantiopurity versions. 相似文献
192.
Isabelle Kondolff Henri Doucet Maurice Santelli 《Journal of heterocyclic chemistry》2008,45(1):109-118
193.
Kütt A Movchun V Rodima T Dansauer T Rusanov EB Leito I Kaljurand I Koppel J Pihl V Koppel I Ovsjannikov G Toom L Mishima M Medebielle M Lork E Röschenthaler GV Koppel IA Kolomeitsev AA 《The Journal of organic chemistry》2008,73(7):2607-2620
A general route to functionalized pentakis(trifluoromethyl)phenyl (C6(CF3)5) derivatives, promising building blocks for designing novel stable carbenes, radical species, superacids, weakly coordinating anions and other practically and theoretically useful species, is presented. This pertrifluoromethylation route proceeds via conveniently pregenerated (trifluoromethyl)copper (CF3Cu) species in DMF, stabilized by addition of 1,3-dimethyl-2-imidazolidinone (DMI). These species react with hexaiodobenzene at ambient temperature to give the potassium pentakis(trifluoromethyl)phenoxide along with hexakis(trifluoromethyl)benzene and pentakis(trifluoromethyl)benzene in a combined yield of 80%. A possible reaction pathway explaining the formation of pentakis(trifluoromethyl)phenoxide is proposed. Pentakis(trifluoromethyl)phenol gives rise to easily functionalized pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)aniline. Pertrifluoromethylation of pentaiodochlorobenzene and pentaiodotoluene allows straightforward access to pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)toluene, respectively. XRD structures of several C6(CF3)5 derivatives were determined and compared with the calculated structures. Due to the steric crowding the aromatic rings in all C6(CF3)5 derivatives are significantly distorted. The gas-phase acidities (Delta Gacid) and pKa values in different solvents (acetonitrile (AN), DMSO, water) for the title compounds and a number of related compounds have been measured. The origin of the acidifying effect of the C6(CF3)5 group has been explored using the isodesmic reactions approach. 相似文献
194.
Dr. Michela Parafioriti Dr. Minghong Ni Maurice Petitou Dr. Courtney J. Mycroft-West Dr. Timothy R. Rudd Dr. Neha S. Gandhi Prof. Vito Ferro Prof. Jeremy E. Turnbull Dr. Marcelo A. Lima Dr. Mark A. Skidmore Prof. David G. Fernig Dr. Edwin A. Yates Dr. Antonella Bisio Dr. Marco Guerrini Dr. Stefano Elli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2023,29(1):e202202599
Infection of host cells by SARS-CoV-2 begins with recognition by the virus S (spike) protein of cell surface heparan sulfate (HS), tethering the virus to the extracellular matrix environment, and causing the subunit S1-RBD to undergo a conformational change into the ‘open’ conformation. These two events promote the binding of S1-RBD to the angiotensin converting enzyme 2 (ACE2) receptor, a preliminary step toward viral-cell membrane fusion. Combining ligand-based NMR spectroscopy with molecular dynamics, oligosaccharide analogues were used to explore the interactions between S1-RBD of SARS CoV-2 and HS, revealing several low-specificity binding modes and previously unidentified potential sites for the binding of extended HS polysaccharide chains. The evidence for multiple binding modes also suggest that highly specific inhibitors will not be optimal against protein S but, rather, diverse HS-based structures, characterized by high affinity and including multi-valent compounds, may be required. 相似文献
195.
The highly strained [5](2,4)quinolinophane system can be generated as an intermediate (2b), which is extremely susceptible towards the attack of both nucleophilic and electrophilic species. Addition of water at the carbon bridgehead C2 occurs rapidly and is followed by rearrangements to give a strain free product 10. An unusual carbene addition at the N1C2 bond of 2b is proposed to explain the formation of the strained ‘anti-Bredt’ type olefin 11. 相似文献
196.
The palladium-tetraphosphine catalyzed arylation of an alkylidenecyclopropane gives a simple and direct access to 1-aryl-2-methyl-1-(2,2,3,3-tetramethylcyclopropylidene)propenes. This reaction tolerates several functional groups on the aryl bromides. Even heteroaryl bromides have been used successfully. This reaction probably proceeds via a classical oxidative addition of the aryl bromide to palladium, insertion of the CCMe2 bond in the Ar-Pd bond followed by β-elimination to give the dienes. 相似文献
197.
198.
C-H bond activation has been extensively studied with (Cp*)M(L)n (M = Ir, Rh), but cobalt, the third member of this triad, has not previously been shown to activate sp3 C-H bonds. Further, practical functionalization of the metal alkyl products of oxidative addition has not been fully explored. Toward these ends, we have developed catalytic dehydrogenation of alkyl amines with a Co(I) catalyst. Amine substrates are protected with vinyl silanes, followed by catalytic transfer hydrogenation, to yield a broad range of stable protected enamines and 1,2-diheteroatom-substituted alkenes, including several unprecedented heterocycles. (Cp*)Co(VTMS)2 catalyzes transfer hydrogenation under surprisingly mild conditions with high chemo-, regio-, and diastereoselectivity, while tolerating additional functionality. 相似文献
199.
Analysis of trace levels of pesticides in rainwater by SPME and GC-tandem mass spectrometry after derivatisation with PFFBr 总被引:2,自引:0,他引:2
Scheyer A Briand O Morville S Mirabel P Millet M 《Analytical and bioanalytical chemistry》2007,387(1):359-368
Solid-phase microextraction (SPME) was used for the analysis of some pesticides (bromoxynil, chlorotoluron, diuron, isoproturon,
2,4-MCPA, MCPP and 2,4-D) in rainwater after derivatisation with PFBBr and gas chromatography-ion trap mass spectrometry.
The derivatisation procedure was optimized by testing different methods: direct derivatisation in the aqueous phase followed
by SPME extraction, on-fibre derivatisation and derivatisation in the injector. The best result was obtained by headspace
coating the PDMS/DVB fibre with PFBBr for 10 min followed by direct SPME extraction for 60 min at 68 °C (pH 2 and 75% NaCl).
Good detection limits were obtained for all the compounds: these ranged between 10 and 1,000 ng L−1 with a relatively high uncertainty due to the combination of derivatisation and SPME extraction steps. The optimized procedure
was applied to the analysis of pesticides in rainwater and results obtained shows that this method is a fast and simple technique
to assess the spatial and temporal variations of concentrations of pesticides in rainwater. 相似文献
200.
Lottmann A Cadé E Geagea ML Delhomme O Grand C Veilleraud C Rizet AL Mirabel P Millet M 《Analytical and bioanalytical chemistry》2007,387(5):1855-1861
In to order increase sensitivity and to reduce the background induced by matrix effects, a method was developed that uses
flash chromatography to separate various compounds present in atmospheric aerosol samples prior to their analysis with different
analytical techniques (GC–MS, GC–FID, HPLC). For this purpose, flash chromatography using a 4 g silica gel column crossed
by eluent at a flow rate of 20 mL min−1 was used. An eluent with enhanced polarity is needed to separate nonpolar (linear and branched alkanes), semipolar (PAH,
nitro-PAH and cholesterol) and polar (methoxyphenols, alkanoic acids, and levoglucosan) compounds. Three combinations of solvents
were used: hexane for the nonpolar fraction (F1), toluene/hexane for the semipolar fraction (F2) and dimethylformamide for
the polar fraction (F3). The use of different eluents for each fraction allows separation of the sample to be accomplished
with good repeatability and satisfying yields [85 ± 5% for F1, 81 ± 8% (PAHs), 89 ± 6% (nitro-PAHs) and 74 ± 7% (cholesterol)
for F2 and 79 ± 7% (n-alkanoic acids), 40 ± 11% (methoxyphenols) and 77 ± 6% (levoglucosan) for F3]. The methoxyphenol yields were low due to losses
during the concentration/evaporation step. This method was then applied to analyse the organic composition of particles collected
at an urban site in Strasbourg (France). 相似文献