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941.
Sebastian Kuntze 《ZDM》2006,38(5):413-421
Video technology offers the possibility to make instructional situations available for discussion in teacher learning projects. For the confrontation with videotaped instructional situations, the teachers' rating of characteristics for instructional quality plays an imminent role. As criteria for instructional quality are often linked to the goals of the teacher learning project, the teachers' views offer possibilities to evaluate these projects. For the example of instructional situations in german classrooms concerning geometrical proof, differences in judgements on instructional quality are analysed. The study focuses on data of a cluster analysis showing initial divergencies in the rating of videotaped instructional situations and it describes how the teachers'views evolve. 相似文献
942.
Jennifer Baas Sebastian Bieringer Corazon Frias Jerico Frias Carolina Soehnchen Corinna Urmann Steffi Ritter Herbert Riepl Aram Prokop 《Molecules (Basel, Switzerland)》2022,27(15)
Isatis tinctoria and its indigo dyes have already provided highly active anti-leukaemic lead compounds, with the focus mainly being on indirubin, whereas indigo itself is inactive. There are many more indigoids to find in this plant extract, for example, quingdainone, an indigoid derived from tryptanthrin. We present here a new synthesis of hitherto neglected substituted quingdainones, which is very necessary due to their poor solubility behaviour, and a structure-dependent anti-leukaemic activity study of a number of compounds. Substituted α-phenylaminoacrylic acid was synthesised by hydrogen sulfide extrusion from an analogue mercaptoacetic acid, available from the condensation of rhodanin and a substituted tryptanthrin. It is shown that just improving water solubility does not increase anti-leukaemic activity, since a quingdainone carboxylic acid is inactive compared to dihydroxyquingdainone. The most effective compound, dihydroxyquingdainone with an AC50 of 7.5 µmole, is further characterised, revealing its ability to overcome multidrug resistance in leukaemia cells (Nalm-6/BeKa) with p-glycoprotein expression. 相似文献
943.
944.
The discovery of vibrant excited-state dynamics and distinctive photochemistry has established nitrated polycyclic aromatic hydrocarbons as an exhilarating class of organic compounds. Herein, we report the atypical photorearrangement of nitro-perylenediimide (NO2-PDI) to nitrito-perylenediimide (ONO-PDI), triggered by visible-light excitation and giving rise to linkage isomers in the polar aprotic solvent acetonitrile. ONO-PDI has been isolated and unambiguously characterized using standard spectroscopic, spectrometric, and elemental composition techniques. Although nitritoaromatic compounds are conventionally considered to be crucial intermediates in the photodissociation of nitroaromatics, experimental evidence for this has not been observed heretofore. Ultrafast transient absorption spectroscopy combined with computational investigations revealed the prominence of a conformationally relaxed singlet excited-state (SCR1) of NO2-PDI in the photoisomerization pathway. Theoretical transition state (TS) analysis indicated the presence of a six-membered cyclic TS, which is pivotal in connecting the SCR1 state to the photoproduct state. This article addresses prevailing knowledge gaps in the field of organic linkage isomers and provides a comprehensive understanding of the unprecedented photoisomerization mechanism operating in the case of NO2-PDI.The unprecedented photorearrangement of nitro-perylenediimide (NO2-PDI) to nitrito-perylenediimide (ONO-PDI) is shown to occur through a cyclic six-membered transition state triggered by visible-light excitation. 相似文献
945.
Sebastian Raubitzek Thomas Neubauer Jan Friedrich Andreas Rauber 《Entropy (Basel, Switzerland)》2022,24(5)
We present a novel method for interpolating univariate time series data. The proposed method combines multi-point fractional Brownian bridges, a genetic algorithm, and Takens’ theorem for reconstructing a phase space from univariate time series data. The basic idea is to first generate a population of different stochastically-interpolated time series data, and secondly, to use a genetic algorithm to find the pieces in the population which generate the smoothest reconstructed phase space trajectory. A smooth trajectory curve is hereby found to have a low variance of second derivatives along the curve. For simplicity, we refer to the developed method as PhaSpaSto-interpolation, which is an abbreviation for phase-space-trajectory-smoothing stochastic interpolation. The proposed approach is tested and validated with a univariate time series of the Lorenz system, five non-model data sets and compared to a cubic spline interpolation and a linear interpolation. We find that the criterion for smoothness guarantees low errors on known model and non-model data. Finally, we interpolate the discussed non-model data sets, and show the corresponding improved phase space portraits. The proposed method is useful for interpolating low-sampled time series data sets for, e.g., machine learning, regression analysis, or time series prediction approaches. Further, the results suggest that the variance of second derivatives along a given phase space trajectory is a valuable tool for phase space analysis of non-model time series data, and we expect it to be useful for future research. 相似文献
946.
Fractal properties in time series of human behavior and physiology are quite ubiquitous, and several methods to capture such properties have been proposed in the past decades. Fractal properties are marked by similarities in statistical characteristics over time and space, and it has been suggested that such properties can be well-captured through recurrence quantification analysis. However, no methods to capture fractal fluctuations by means of recurrence-based methods have been developed yet. The present paper takes this suggestion as a point of departure to propose and test several approaches to quantifying fractal fluctuations in synthetic and empirical time-series data using recurrence-based analysis. We show that such measures can be extracted based on recurrence plots, and contrast the different approaches in terms of their accuracy and range of applicability. 相似文献
947.
Bicyclo[1.1.1]pentanes (BCPs), utilized as sp3-rich bioisosteres for tert-butyl- and aryl groups as well as internal alkynes, have gained considerable momentum in drug development programs. Although many elegant methods have been developed to access BCP amines and BCP aryls efficiently, the methods used to construct BCP ketones directly are relatively underdeveloped. In particular, the preparation of unsymmetrical 1,3-disubstituted-BCP ketones remains challenging and still requires multiple chemical steps. Herein, a single-step, multi-component approach to versatile disubstituted BCP ketones via nickel/photoredox catalysis is reported. Importantly, installing a boron group at the carbon position adjacent to the BCP structure bypasses the limitation to tertiary BF3K coupling partners, thus expanding the scope of this paradigm. Further transformation of disubstituted-BCP ketones into a variety of other BCP derivatives demonstrates the synthetic value of this developed method.Bicyclo[1.1.1]pentanes (BCPs), utilized as sp3-rich bioisosteres for tert-butyl- and aryl groups as well as internal alkynes, have gained considerable momentum in drug development programs.Three-dimensional (3D) molecular scaffolds have received considerable attention in drug molecular design to improve physicochemical properties of drug candidates.1 Among the promising 3D scaffolds in this area are the bicyclo[1.1.1]pentanes (BCPs), which serve as bioisosteres of aromatic rings as well as tert-butyl- and alkyne groups in medicinal chemistry.2 In Stepan''s pioneering work,2a the replacement of the fluorinated aryl ring of a gamma secretase inhibitor with a BCP moiety resulted in improved permeability and kinetic solubility. Since this landmark work, the number of patents published with BCP-containing drugs has skyrocketed. Despite considerable interest from the medicinal chemistry community, the incorporation of BCPs into specific structural classes found in bioactive molecules remains an unsolved challenge.BCP ketones could be considered as bioisosteres of aryl ketones, which widely exist in FDA-approved drugs (Fig. 1A).3 They can also be used as vehicles for the synthesis of other important BCP derivatives, including BCP amides and BCP esters through efficient transformations. Nevertheless, the methods that are used to construct BCP ketones efficiently are relatively underdeveloped, especially compared with well-developed approaches to access amino BCPs and aryl BCPs (Fig. 1B).4 Specifically, the Wiberg,5a Walsh,5b and Pan5c groups have reported methods for acylation of [1.1.1]propellane with aldehydes to form monosubstituted-BCP ketones. In contrast, the preparation of unsymmetrically 1,3-disubstituted-BCP ketones remains challenging and still requires multiple chemical steps. For example, Wills and coworkers reported a method for the synthesis of BCP ketones by reacting [1.1.1]propellane and Grignard reagents, followed by addition to an aldehyde and oxidation with MnO2 (Fig. 2A).6a This method requires the use of metal reagents and multiple synthesis steps, which are incompatible with the construction of complex targets containing sensitive functional groups. The Knochel group developed a similar two-step strategy to construct 1,3-disubstituted BCP ketones by opening the [1.1.1]propellane with allylzinc halides, followed by addition to acyl chlorides (Fig. 2A).6b However, this method is only suitable for some special organozinc reagents, which limits the diversity of the BCP ketones. Chemists at SpiroChem also reported a two-step method for construction of 1,3-disubstituted BCP ketones through a process involving radical addition to [1.1.1]propellane, followed by engagement with different arylmetal reagents (Fig. 2A).6c In this case, the other substituent on the BCP ring is limited to an ester functional group. Furthermore, there are some individual examples showing that disubstituted BCP ketones can be obtained from the corresponding BCP redox active ester. Specifically, the Ohmiya group developed the N-heterocyclic carbene-catalyzed acylation of BCP redox active ester, but the yield was only 20% (Fig. 2A).6d The Yuan group also conducted the cross-coupling of BCP redox active esters with pyridyl esters to access BCP ketones (Fig. 2A).6e Considering the five-step synthesis of BCP ketones from [1.1.1]propellane, these methods cannot meet the requirements of rapid synthesis of a library of products in the medicinal chemistry setting. Clearly, the drawbacks of stepwise synthetic approaches to 1,3-disubstituted BCP ketones hamper the broad application of bicyclo[1.1.1]pentanes. Thus, more efficient methods for the preparation of disubstituted BCP ketones are urgently needed.Open in a separate windowFig. 1(A) Examples of bioactive diaryl ketones. (B) Representative BCP derivatives.Open in a separate windowFig. 2(A) Previous strategies to access unsymmetrically 1,3 disubstituted BCP ketones. (B) Research reported herein. HE = Hantzsch ester; RAE = Redox active ester [N-(acyloxy)phthalimide]; NHC = N-heterocyclic carbene; CzIPN = 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene.Multicomponent reactions (MCRs) that allow one-step access to complex and diverse disubstituted BCP products are synthetically advantageous to current stepwise approaches to BCP derivatives. However, achieving such a transformation is still challenging because of competing two-component coupling or propellane oligomerization. Uchiyama,7a MacMillan,7b and our group7c,d have successfully developed multi-component approaches to versatile BCP derivatives based on the differentiated reactivity of BCP radicals and substrate alkyl radicals. In our previous report,7d we successfully took advantage of the slow capture of tertiary radicals by Ni species as a key mechanistic aspect to achieve a one-step, multicomponent reaction for the synthesis of BCP-aryl derivatives. Meanwhile, our group has successfully developed an efficient photoredox/Ni dual catalysis paradigm for transition metal-catalyzed cross-couplings of alkylboron- or alkylsilicon reagents with various electrophiles, including aryl halides, acyl chlorides, alkenyl halides, and isocyanates based on a single-electron transfer (SET) transmetalation pathway.8 Inspired by these results, we questioned whether acyl chlorides or other electrophiles could also serve as partners in the three-component radical coupling of [1.1.1]propellane to access a diverse array of BCP derivatives of high importance in the pharmaceutical industry. Herein we report a one-step, three-component radical coupling of [1.1.1]propellane to afford diversely functionalized bicycles using various electrophiles.To determine the chemoselectivity of the proposed MCR pathway, the reactivity of tertiary alkyl and BCP radicals in the nickel/photoredox-catalyzed cross-couplings with acyl chlorides was first examined (Fig. 3). The results indicated that BCP bridgehead radicals engage the nickel catalyst to enter the cross-coupling catalytic cycle, generating the product BCP ketone, while acyclic tertiary radicals do not take part in this catalytic cycle. Encouraged by this promising reactivity pattern, we explored the possibility of achieving a multi-component reaction forging two C–C bonds in a single operation using [1.1.1]propellane.Open in a separate windowFig. 3Control experiments.Initial investigations utilized t-BuBF3K, [1.1.1]propellane, and benzoyl chloride as a model reaction to optimize the reaction conditions ( Entry Deviation from standard conditions NMR yield (%) 1 None 63 2 No base 32 3 0.01 M 52 4 0.025 M 55 5 427 mm 25 6 2 mol% [Ir] cat. 10 mol% [Ni] 49 7 2 mol% [Ir] cat. 20 mol% [Ni] 58 8 No [Ni] catalyst 0 9 No [Ir] catalyst 0 10 No light 0 11 t-BuCOOCs, instead of 1 0