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11.
Résumé. Nous montrons qu'une surface de la classe VII0 avec b
2 > 0 sur laquelle existe un champ de vecteurs non trivial contient exactement b
2 courbes rationnelles. Il s'ensuit par un théorème de I. Nakamura qu'une telle surface se déforme en une surface de Hopf primaire
éclatée. Ce résultat contribue ? la classification des surfaces complexes compactes avec champs de vecteurs.
Received: August 6, 1998 相似文献
12.
Irena Zupanič Pajnič Carlo Previderè Tomaž Zupanc Martina Zanon Paolo Fattorini 《Electrophoresis》2022,43(13-14):1521-1530
The recent introduction of polymerase chain reaction (PCR)-massively parallel sequencing (MPS) technologies in forensics has changed the approach to allelic short tandem repeat (STR) typing because sequencing cloned PCR fragments enables alleles with identical molecular weights to be distinguished based on their nucleotide sequences. Therefore, because PCR fidelity mainly depends on template integrity, new technical issues could arise in the interpretation of the results obtained from the degraded samples. In this work, a set of DNA samples degraded in vitro was used to investigate whether PCR-MPS could generate “isometric drop-ins” (IDIs; i.e., molecular products having the same length as the original allele but with a different nucleotide sequence within the repeated units). The Precision ID GlobalFiler NGS STR panel kit was used to analyze 0.5 and 1 ng of mock samples in duplicate tests (for a total of 16 PCR-MPS analyses). As expected, several well-known PCR artifacts (such as allelic dropout, stutters above the threshold) were scored; 95 IDIs with an average occurrence of 5.9 IDIs per test (min: 1, max: 11) were scored as well. In total, IDIs represented one of the most frequent artifacts. The coverage of these IDIs reached up to 981 reads (median: 239 reads), and the ratios with the coverage of the original allele ranged from 0.069 to 7.285 (median: 0.221). In addition, approximately 5.2% of the IDIs showed coverage higher than that of the original allele. Molecular analysis of these artifacts showed that they were generated in 96.8% of cases through a single nucleotide change event, with the C > T transition being the most frequent (85.7%). Thus, in a forensic evaluation of evidence, IDIs may represent an actual issue, particularly when DNA mixtures need to be interpreted because they could mislead the operator regarding the number of contributors. Overall, the molecular features of the IDIs described in this work, as well as the performance of duplicate tests, may be useful tools for managing this new class of artifacts otherwise not detected by capillary electrophoresis technology. 相似文献
13.
The study of D(?)-ribose complexing with calcium in aqueous solutions less than 1.64 × 10?1M by potentiometric measurements with a calcium selective electrode afforded the value of K1 = 1.70 liters × mole?1 (SD = 1.05 × 10?3). Numerical analysis indicated that complex species with 1:1 and 1:2 calcium to D(-)-ribose ratios are present simultaneously: k1 = 1.13 liters × mole?1 and K2 = 8.47 liters × mole?1 (SD = 0.95 × 10?3).In methanolic medium 1.24 × 10?2M with regard to calcium chloride both stoichiometric proportions were evidenced. A large error accompanying the stability constant K1 = 28 kg × mole?1 (RSD = 82%) renders unreasonable the K2 value obtained from the product K1 × K2 = 96.5 kg2 × mole?2.The results are discussed with respect to the data published for more concentrated (1.27 M) aqueous solutions obtained on the basis of 1H-NMR spectroscopic investigations. 相似文献
14.
15.
Formation of the plasma potential in a plasma that contains energetic electrons and is bounded by a floating collector that
emits electrons is studied theoretically. The problem is treated by a static. kinetic plasma-sheath model of Schwager and
Birdsall [Phys. Fluids B2 (1990) 1057], which we have extended in order to include additional energetic electron population. The distribution of these
electrons is assumed to be a high-temperature Maxwellian. They are called hot electrons. In the paper we study effects of
the density and temperature of the hot electrons on the formation of the plasma potential. The model shows that for certain
densities and temperatures of the hot electron population plasmas with two different plasma potentials can coexist in the
system. These two plasmas are separated spatially by a double layer. For the case when there is no emission of electrons from
the collector, results of the model are compared with computer simulation and very good agreement between the model and the
simulation is found. The simulation also confirms existence of two plasmas with two different potentials separated by a double
layer. 相似文献
16.
17.
Nives Galić Nataša Burić Renato Tomaš Leo Frkanec Vladislav Tomišić 《Supramolecular chemistry》2013,25(5):389-397
The fluorescent peptidocalixarenes, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,27-di(O-methyl)-26,28-bis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (2), were prepared by introducing tryptophan subunits at a lower calixarene rim. Coordination abilities of 1 and 2 towards Eu(III) and alkali metal cations were studied by spectrophotometric, spectrofluorimetric, conductometric and potentiometric titrations in acetonitrile at 25°C. Rather strong complexation was observed for smaller alkali metal cations Li+ and Na+ (log K Li1 >6, log K Li2 >6, log K Na1 = 8.25, log K Na2 = 6.94), and moderate for K+ (log K K1 = 5.09, log K K2 = 4.09). Larger Rb+ and Cs+ cations did not fit in the ion binding site of 1 so no complexation was detected, whereas the more flexible ligand 2 accommodated Rb+ cation (log K Rb2 = 3.44). The fluorescence of 1 (λex = 280 nm, λem = 340 nm) was remarkably quenched by Eu(III). Stability constant of 1:1 (Eu3+:1) complex determined spectrofluorimetrically amounted to log K Eu1 = 6.16. 相似文献
18.
The Pd-catalysed conjugate addition of arylboronic acids to α,β-unsaturated cyclic ketones was studied under controlled microwave irradiation conditions. A variety of catalysts, bases and
solvents was explored in order to achieve optimum yields in the shortest possible reaction time. Under optimised conditions
(Pd(OAc)2/2,2′-bipyridine and KF in a mixture of toluene, water, and acetic acid and 10 min microwave irradiation), a range of arylboronic
acids was successfully added to several cyclic enones. With chiral phosphane ligands, a promising enantioselectivity was obtained
(85 % ee). 相似文献
19.
A trinuclear bis(cyclohexanedioximate)(chloro)(nitrosyl)ruthenium(II) complex containing two (2,2-bipyridine)-copper(II) groups has been synthesized and its electronic and electrochemical properties investigated. According to ZINDO/S calculations, the electronic structure of the ruthenium(dioximate)(nitrosyl) moiety is strongly delocalized. The electrochemical behavior has been interpreted with the aid of spectroelectrochemical measurements. In the trinuclear complex, it has been shown that the copper(II) ions can promote the oxidation of the NO species generated electrochemically, and also mediate the redox reactions of the complex, under a dioxygen atmosphere. 相似文献
20.
Tomazela DM Gozzo FC Mayer I Engelmann FM Araki K Toma HE Eberlin MN 《Journal of mass spectrometry : JMS》2004,39(10):1161-1167
Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I-Va, bn+ (n = 1-4) formed by the coordination of [Ru(bipy)2Cl]+ to the pyridyl N-atoms of a series of meso-(phenyl)m-(meta or para-pyridyl)n-porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I-Va, bn+ are found to constitute also a new class of stable, long-lived multiply charged gas-phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b+ to IVa, b3+ facilitates in-source and tandem collision-induced dissociation (CID). However, for the quadruply charged ions Va, b4+, electrostatic repulsion is alleviated mainly by ion pairing with the CF3SO3- counterion forming the salt clusters [Va,b/CF3SO3]3+ and [Va,b/(CF3SO3)2]2+ with reduced charge states. Ion-pairing that yields [IVa,b/CF3SO3]2+ is also observed as a minor ESI process for the triply charged ions IVa, b3+. The gaseous ions I-Va, bn+ (n = 2, 3 or 4) dissociate by sequential 'charge partitioning' with the formation of two cationic fragments by the release of [Ru(bipy)2Cl]+. The meta (a) and para (b) isomers and the positional isomers II2+ and III2+ display nearly identical ESI-MS and ESI-MS/MS spectra. ESI-MS/MS of I-Va, bn+ shows that the Ru-py(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID. 相似文献