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1.
Renny Mathew Karolina A. Uchman Lydia Gkoura Chris J. Pickard Maria Baias 《Magnetic resonance in chemistry : MRC》2020,58(11):1018-1025
A combined experimental and computational approach was used to distinguish between different polymorphs of the pharmaceutical drug aspirin. This method involves the use of ab initio random structure searching (AIRSS), a density functional theory (DFT)-based crystal structure prediction method for the high-accuracy prediction of polymorphic structures, with DFT calculations of nuclear magnetic resonance (NMR) parameters and solid-state NMR experiments at natural abundance. AIRSS was used to predict the crystal structures of form-I and form-II of aspirin. The root-mean-square deviation between experimental and calculated 1H chemical shifts was used to identify form-I as the polymorph present in the experimental sample, the selection being successful despite the large similarities between the molecular environments in the crystals of the two polymorphs. 相似文献
2.
In the tree approximation, the critical relaxational dynamics of 2n with quenched random fields is calculated by renormalization near the upper critical dimensiond
u=4+2/(n–1). Although the relation between the characteristic frequency
c
q and the wave-numberq is as usual,unusual results are obtained for the asymptotic decay of the order-parameter correlation functionS(q,t).Dedicated to Prof. Dr. W. Döring on the occasion of his 75th birthday 相似文献
3.
Lydia J. Martinez Robert H. Sik Colin F. Chignell† 《Photochemistry and photobiology》1998,67(4):399-403
The fluoroquinolone antibacterial agents possess photo-sensitizing properties that lead to phototoxic responses in both human and animal subjects. The phototoxicity order reported in humans is: fleroxacin > lomefloxacin, pefloxacin > ciprofloxacin ? enoxacin, norfloxacin and ofloxacin. Studies both in vivo and in vitro have related this phototoxicity to the generation of reactive oxygen species including hydrogen peroxide and the hydroxyl radical. We determined the quantum yields of singlet oxygen generation (φΔ,) by detection of the singlet oxygen (1O2) luminescence at 1270 tun for several fluoroquinolones, naphthyridines and other structurally related compounds. All the fluoroquinolones examined have low φΔ values ranging from 0.06 to 0.09 in phosphate buffer at pD 7.5. We also determined the 1O2 quenching constants for these compounds and their values were on the order of 106M?1 s1, except for lomefloxacin whose rate constant was 1.8 × 107M?1 s?1. The φΔ values were significantly decreased in a solvent of lower polarity such as methanol (0.007 ≤φΔ≤ 0.02). The production of 1O2 by these antibiotics did not correlate with the order reported for their phototoxicity. We also measured the photogeneration (λ > 300 nm) of superoxide by these antibacterials in dimethylsulfoxide using electron paramagnetic resonance and the spin trap 5,5-dimethyl-l-pyrroiine N-oxide. Although there is not a one-to-one correspondence between the relative rates of superoxide generation and the phototoxicity ranking of the fluoroquinolones, the more phototoxic compounds tended to produce superoxide at a faster rate. Nevertheless, the magnitudes of the observed differences do not appear sufficient to explain the range of fluoroquinolone phototoxicity potencies in human and animal subjects in general and the high activity of fleroxacin and lomefloxacin in particular. For these latter drugs the photoinduced loss of the F8 atom as fluoride and the concomitant generation of a highly reactive carbene at C-8 provide a more plausible mechanism for their potent phototoxic and photocarcinogenic properties. 相似文献
4.
PHOTOINACTIVATION OF CATALASE 总被引:6,自引:0,他引:6
Abstract— Inactivation of catalase with visible light (>400nm) has been studied in purified bovine liver catalase and in peroxisomal catalase in the mitochondrial fraction of rat liver. Light corresponding to that of maximal absorbance of the heme site (405 nm) was most effective in inactivation. Although photoinactivation is O2 dependent, scavengers of OH radical, 1 O2 and O− 2 did not protect against loss of activity in either system. Superoxide dismutase partially protected purified catalase added into the mitochondrial fraction system. However, complete protection of catalase was afforded by low concentrations of substrates such as formic acid or methanol which rapidly convert Compound I to Ferricatalase. 相似文献
5.
Zusammenfassung Tabakmosaikvirus hoher spezifischer Aktivität, das am Phosphor und/oder Kohlenstoff markiert war, wurde biosynthetisch hergestellt. Damit wurde jeweils ein Blatt einer Pflanze von Nicotiana tabacum infiziert und der etwaige Transport von intaktem Virus durch das Leitungssystem der Pflanzen dadurch weitgehend unterbunden, daß die Leitgefäße des behandelten Blattes durchtrennt wurden.Das aus den unbehandelten Blättern der Pflanze nach 17 1/2, 48 und 72 Stdn. isolierte Virus wies im Vergleich zum eingesetzten TMV einen viel geringeren Anteil an Gesamtradiokohlenstoff im Protein auf. Dies deutet darauf hin, daß das Virus der unbehandelten Blätter höchstens zu einem sehr geringen Teil aus intakt transportiertem TMV bestehen könnte.Die nicht im TMV enthaltenen Polynukleotide der unbehandelten Blätter enthalten 7 Stdn. nach der Infektion verhältnismäßig viel32P, doch tritt derselbe innerhalb 70 Stdn. zum allergrößten Teil in niedermolekulare Verbindungen über.Die in Puffer unlöslichen Polynukleotide der unbehandelten Blätter (Blattnukleinsäure) weisen ein mit der Zeit abnehmendes Verhältnis von32P/14C auf. Auch innerhalb der Nukleinsäure (NS) des TMV dieser Blätter nimmt dieses Verhältnis zunächst ab, steigt aber später wieder an.Die angeführten Ergebnisse stehen mit der Vorstellung im Einklang, daß das Virus NS abspaltet und sowohl die systemische Infektion der Pflanze wie auch die Virusvermehrung mindestens zum Teil durch diese freie NS bewirkt wird. Die aus dem Virus stammende freie NS unterliegt zum großen Teil lebhaftem Abbau, wobei ihre Komponenten wahrscheinlich dem Aufbau normaler Blattbestandteile dienen.Mit 3 Abbildungen 相似文献
6.
The crystal structure of the complex [U(tpa)(2)]I(3), 1 (tpa = tris[(2-pyridyl)methyl]amine), has been elucidated. The complex exists as only one enantiomer in the crystal leading to the chiral space group P2(1)2(1)2(1). The coordination geometry of the metal can be described as a distorted cube. Accidental oxidation of [U(tpa)(2)]I(3) led to the isolation of the unusual mononuclear bishydroxo complex of uranium(IV) [U(tpa)(2)(OH)(2)]I(2).3CH(3)CN, 2, which was structurally characterized. The controlled reaction of [U(tpa)(2)]I(3) with water resulted in the oxidation of the metal center and led to the formation of protonated tpa and of the trinuclear U(IV) oxo complex ([U(tpa)(mu-O)I](3)(mu(3)-I))I(2), 3. The solid state and solution structures of this trimer are reported. The pathway suggested for the formation of this complex is the oxidation of the [U(tpa)(2)]I(3) complex by H(2)O to form a U(IV) hydroxo complex which then decomposes, eliminating mono-protonated tpa. The comparison with the reported reaction with water of cyclopentadienyl derivatives points to a higher reactivity toward water reduction of the bis(tpa) complex with respect to the cyclopentadienyl derivatives. The reaction of U(III) with methanol in the presence of the supporting ligand tpa leads to formation of alkoxo complexes similarly to what is found for amide or cyclopentadienyl derivatives. The monomethoxide complex [U(tpa)I(3)(OMe)], 4, has been prepared in good yield by alcoholysis of the U(III) mono(tpa) complex. The crystal structure of this complex has been determined. The reaction of [U(tpa)(2)]I(3) with 2 equiv of methanol in acetonitrile allows the isolation of the bismethoxo complex of U(IV) [U(tpa)I(2)(OMe)(2)], 5, in 35-47% yield, which has been fully characterized. To account for the oxidation of U(III) to U(IV) the suggested mechanism assumes that hydrogen is evolved in both reactions. 相似文献
7.
The behaviour of FeII and FeIII ions in combination with the potential ligand 1,4‐bis(2‐pyridyl‐methyl)piperazine (BPMP) under anhydrous conditions has been investigated. BPMP has been reacted with FeCl2, FeCl3 and [Fe(OTf)2(MeCN)2]. This led to the isolation of four new complexes, which were fully characterized and structurally investigated by single crystal X‐ray diffraction. It turned out that in the presence of chloride co‐ligands FeIII favours the tetradentate coordination mode of BPMP with the piperazine unit in a boat configuration, like for instance in [BPMP(Cl)Fe(μ‐O)FeCl3] or [BPMP‐FeCl2][FeCl4], ( 1 ). However, the employment of FeCl2 leads to the formation of a coordination polymer [BPMP‐FeCl2]n, ( 2 ), containing the piperazine ring in a chair configuration binding to two iron centres each. 2 can only be dissolved in very polar solvents like dmf which is capable of breaking up the polymeric structure under formation of [Cl2(dmf)Fe(μ‐BPMP‐1κ2N,N:2κ2N,N))Fe(dmf)Cl2]·2 dmf, ( 3 ). In contrast, using [Fe(OTf)2(MeCN)2] instead of FeCl2 as the starting material leads to a mononuclear FeII complex with BPMP bound in the desirable tetradentate fashion: [BPMP‐Fe(OTf)2], ( 4 ). Unlike other complexes with tetradentate N/py ligands the two residual ligands in 4 are bound almost trans to each other with the potential to adopt a cis orientation under oxidising conditions, and it will be interesting to exploit its catalytic properties in future. 相似文献
8.
Lydia McGrew 《Acta Analytica》2014,29(4):491-505
I offer an account of ad hocness that explains why the adoption of an ad hoc auxiliary is accompanied by the disconfirmation of a hypothesis H. H must be conjoined with an auxiliary (or set of auxiliaries) a′, which is improbable antecedently given H, while ~H does not have this disability. This account renders it unnecessary to require, for identifying (bad) ad hocness, that either a′ or H have a posterior probability less than or equal to 0.5; there are also other reasons for abandoning that condition. I distinguish between formal ad hocness, which is bad in the probabilistic sense that it results in disconfirmation of H, and argumentative ad hocness, which actually involves bad reasoning on the part of a subject. The latter is what I call “not counting the cost.” This distinction allows us to see why the 0.5 condition appeared attractive in the first place. The concept of not counting the cost also has implications for other areas of research, including both a Bayesian concept of unfalsifiability and the classic epistemological question of the problem of the external world. 相似文献
9.
10.
Ioana Konz Beatriz Fernández M. Luisa Fernández Rosario Pereiro Héctor González Lydia Álvarez Miguel Coca-Prados Alfredo Sanz-Medel 《Analytical and bioanalytical chemistry》2013,405(10):3091-3096
Laser ablation coupled to inductively coupled plasma mass spectrometry has been developed for the elemental imaging of Mg, Fe and Cu distribution in histological tissue sections of fixed eyes, embedded in paraffin, from human donors (cadavers). This work presents the development of a novel internal standard correction methodology based on the deposition of a homogeneous thin gold film on the tissue surface and the use of the 197Au+ signal as internal standard. Sample preparation (tissue section thickness) and laser conditions were carefully optimized, and internal normalisation using 197Au+ was compared with 13C+ correction for imaging applications. 24Mg+, 56Fe+ and 63Cu+ distributions were investigated in histological sections of the anterior segment of the eye (including the iris, ciliary body, cornea and trabecular meshwork) and were shown to be heterogeneously distributed along those tissue structures. Reproducibility was assessed by imaging different human eye sections from the same donor and from ten different eyes from adult normal donors, which showed that similar spatial maps were obtained and therefore demonstrate the analytical potential of using 197Au+ as internal standard. The proposed analytical approach could offer a robust tool with great practical interest for clinical studies, e.g. to investigate trace element distribution of metals and their alterations in ocular diseases. Figure
Development of a new internal standard correction methodology for qualitative elemental imaging by LA-ICP-MS 相似文献