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121.
An intramolecular hetero-Diels-Alder cycloadduct of an acyl nitroso compound and a 9,10-dimethyl anthracene derivative was prepared as a potential nitroxyl (HNO) donor. This compound did not release HNO under any of the conditions tested. Treatment of this cycloadduct with excess MeMgCl resulted in the formation of a nitrone, whose structure was confirmed by X-ray crystallography. A mechanism where MeMgCl acts as a nucleophile, strong base, and Lewis acid possibly explains the formation of this product. 相似文献
122.
Timothy B. Patrick Cynthia Fianu Eric Pak Kasey Zaksas Bradley E. Neal 《Journal of fluorine chemistry》2006,127(7):861-864
Several fluorinated alkenes were prepared from known ethyl (R)-2-fluoro-4,5-dihydroxyisopropylidine-2-pentenoate (1). The fluoroalkenoates were tested as dienophiles with several dienes and showed cycloaddition only with the very reactive diene, 1,3-diphenylisobenzofuran (5). Fluorobutenolide 2 reacted with 5 to produce the endo-syn adduct 9 in a highly stereoselective manner. 相似文献
123.
Busin CS Lima AP de Almeida Prado CP Strüssmann C Júnior SS Recco-Pimentel SM 《Micron (Oxford, England : 1993)》2006,37(4):355-362
Cytogenetic analysis were done on specimens from two populations of Lysapsus limellus limellus, three of L. l. bolivianus and of one of Lysapsus caraya. All animals showed a diploid chromosomal number of 2n=24. The karyotypes of the two L. limellus subspecies were very similar, differing only by the larger amount of telomeric heterochromatin and a small pericentromeric C-band on the short arms of pair 2 in L. l. limellus specimens. The karyotype of L. caraya differed from those of the two L. limellus subspecies in terms of chromosomal morphology, C-banding pattern and location of the main NOR on chromosomes 7 and 6, respectively. The karyotype of the L. l. bolivianus population from Guajará-Mirim/RO differed from those of the other populations of the same subspecies in morphology and heterochromatin pattern of chromosomes 7 and 8. Additional NORs were detected by silver staining and confirmed by FISH in one of the homologues of pairs 1 and 8 in L. l. bolivianus and in pair 7 in L. caraya. These results suggest that a reassessment of the taxonomic status of L. limellus subspecies, especially of the L. l. bolivianus populations, may be necessary. 相似文献
124.
The ligand epitope map and the effect of nonspecific binding is assessed for lidocaine binding to α1-acid glycoprotein using the saturation transfer difference nuclear magnetic resonance experiment performed as a function
of the ligand/protein ratio. The experimental design tested two different approaches for preparing solutions with various
ligand/protein ratios; holding the protein concentration constant and increasing the ligand concentration; and holding the
ligand concentration constant while decreasing the protein concentration. Nonspecific binding effects were more prevalent
in experiments in which the ligand concentration was increased, although spectra with higher signal-to-noise ratios were obtained
under these conditions. The epitope map determined for achiral lidocaine is compared with previously determined results for
the (R)- and (S)-enantiomers of propranolol. The weaker binding affinity of lidocaine may be partially attributed to steric hindrance by the
lidocaine N-ethyl groups which may prevent close contact of the lidocaine amine with the negatively charged amino acids at the apex of
the protein binding pocket. 相似文献
125.
A clean-up method was developed to enable the determination of tri-decabrominated diphenyl ethers, isomer-specific hexabromocyclododecanes (HBCDs), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), decabromodiphenyl ethane (DBDPE), (2-ethylhexyl)tetrabromobenzoate (TBB), and bis(2-ethylhexyl)tetrabromophthalate (TBPH) in the same dust sample extract using reasonable amounts of solvents and without dividing the sample. After extraction, the sample was separated on a silica column into three fractions that were subsequently cleaned up individually. The polybrominated diphenyl ethers (PBDEs) and DBDPE were eluted in Fraction I, TBB, TBPH, and BTBPE in Fraction II, and HBCDs in Fraction III. Fractions I and II were analyzed using gas chromatography/mass spectrometry and Fraction III using liquid chromatography/mass spectrometry. The method gave good recoveries (60-120%), precise results using (13)?C-labelled internal standards and was accurate when comparing results to certified values (PBDEs in NIST SRM 2585). The method was applied to dust samples from the Stockholm (Sweden) area. All the emerging brominated flame retardants (BFRs) studied, except BTBPE, were present in all the samples in quantifiable concentrations, often higher than the PBDEs. BTBPE was quantified in only one sample. It is evident that emerging BFRs are present in Swedish homes, and these compounds should be included in the BFR analyses of indoor environments. 相似文献
126.
Yang Y Mijalis AJ Fu H Agosto C Tan KJ Batteas JD Bergbreiter DE 《Journal of the American Chemical Society》2012,134(17):7378-7383
Pendant groups on polymers that have lower-critical solution temperature (LCST) properties experience a water-like environment below the LCST where the polymer is soluble but are less hydrated above the LCST when the polymer phase separates from solution. When these pendant groups are amphoteric groups like carboxylate salts or ammonium salts, the change in solvation that accompanies the polymer precipitation event significantly changes these groups' acidity or basicity. These changes in acidity or basicity can lead to carboxylate salts forming carboxylic acid groups by capturing protons from the bulk solvent or ammonium salts reverting to the neutral amine by release of protons to the bulk solvent, respectively. When polymers like poly(N-isopropylacrylamide) that contain a sufficient loading of such comonomers are dissolved in solutions whose pH is near the pK(a) of the pendant acid or basic group and undergo an LCST event, the LCST event can change the bulk solution pH. These changes are reversible. These effects were visually followed using common indicators with soluble polymers and or by monitoring solution pH as a function of temperature. LCST events triggered by the addition of a kosmotropic salt lead to similar reversible solution pH changes. 相似文献
127.
Y He C Brown Y He J Fan CA Lundgren Y Zhao 《Chemical communications (Cambridge, England)》2012,48(62):7741-7743
Three-dimensional Cu-Si and Cu-SiO(2) nanorod arrays containing ~68 at% Cu have been fabricated by a glancing angle co-deposition technique. By selectively etching Cu in 0.05 M KCN methanol solution, porous nanorods with different shapes form, which are promising for applications in sensors, catalysts, and as medical capsules that are able to be loaded with functional materials. 相似文献
128.
Bourbon P Peng Q Ferraudi G Stauffacher C Wiest O Helquist P 《The Journal of organic chemistry》2012,77(6):2756-2762
The syntheses and photophysical/photochemical properties of two amide-tethered coumarin-labeled nicotinamides are described. Photochemical studies of 6-bromo-7-hydroxycoumarin-4-ylmethylnicotinamide (BHC-nicotinamide) revealed an unexpected solvent effect. This result is rationalized by computational studies of the different protonation states using TD-DFT with the M06L/6-311+G** method with implicit and explicit solvation models. Molecular orbital energies responsible for the λ(max) excitation show that the functionalization of the coumarin ring results in a strong red-shift from 330 to 370 nm when the pH of solution is increased from 3.06 to 8.07. From this MO analysis, a model for solvent interactions has been proposed. The BHC-nicotinamide proved to be photochemically stable, which is also interpreted in terms of NBO calculations. The results provide a set of principles for the rational design of either photostable labeling reagents or photolabile cage compounds. 相似文献
129.
Sides CR Liyanage R Lay JO Philominathan ST Matsushita O Sakon J 《Journal of the American Society for Mass Spectrometry》2012,23(3):505-519
Pairing limited proteolysis and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS)
to probe clostridial collagenase collagen binding domain (CBD) reveals the solution dynamics and stability of the protein,
as these factors are crucial to CBD effectiveness as a drug-delivery vehicle. MS analysis of proteolytic digests indicates
initial cleavage sites, thereby specifying the less stable and highly accessible regions of CBD. Modulation of protein structure
and stability upon metal binding is shown through MS analysis of calcium-bound and cobalt-bound CBD proteolytic digests. Previously
determined X-ray crystal structures illustrate that calcium binding induces secondary structure transformation in the highly
mobile N-terminal arm and increases protein stability. MS-based detection of exposed residues confirms protein flexibility,
accentuates N-terminal dynamics, and demonstrates increased global protein stability exported by calcium binding. Additionally,
apo- and calcium-bound CBD proteolysis sites correlate well with crystallographic B-factors, accessibility, and enzyme specificity.
MS-observed cleavage sites with no clear correlations are explained either by crystal contacts of the X-ray crystal structures
or by observed differences between Molecules A and B in the X-ray crystal structures. The study newly reveals the absence
of the βA strand and thus the very dynamic N-terminal linker, as corroborated by the solution X-ray scattering results. Cobalt
binding has a regional effect on the solution phase stability of CBD, as limited proteolysis data implies the capture of an
intermediate-CBD solution structure when cobalt is bound. 相似文献
130.
Saver C 《OR manager》2012,28(6):1, 6-1, 8