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971.
Dr. Nitika Grover Gemma M. Locke Dr. Keith J. Flanagan Michael H. R. Beh Prof. Alison Thompson Prof. Dr. Mathias O. Senge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(11):2405-2416
Connecting two porphyrin units in a rigid linear fashion, without any undesired electron delocalization or communication between the chromophores, remains a synthetic challenge. Herein, a broad library of functionally diverse multi-porphyrin arrays that incorporate the non-traditional rigid linker groups cubane and bicyclo[1.1.1]pentane (BCP) is described. A robust, reliable, and versatile synthetic procedure was employed to access porphyrin-cubane/BCP-porphyrin arrays, representing the largest non-polymeric structures available for cubane/BCP derivatives. These reactions demonstrate considerable substrate scope, from utilization of small phenyl moieties to large porphyrin rings, with varying lengths and different angles. To control conformational flexibility, amide bonds were introduced between the bridgehead carbon of BCP/cubane and the porphyrin rings. Through varying the orientation of the substituents around the amide bond of cubane/BCP, different intermolecular interactions were identified through single crystal X-ray analysis. These studies revealed non-covalent interactions that are the first-of-their-kind including a unique iodine-oxygen interaction between cubane units. These supramolecular architectures indicate the possibility to mimic a protein structure due to the sp3 rigid scaffolds (BCP or cubane) that exhibit the essential conformational space for protein function while simultaneously providing amide bonds for molecular recognition. 相似文献
972.
Kevinjeorjios Pellumbi Mathias Smialkowski Dr. Daniel Siegmund Prof. Dr. Ulf-Peter Apfel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):9938-9944
The electrochemical reduction of CO2 is an attractive strategy towards the mitigation of environmental pollution and production of bulk chemicals as well as fuels by renewables. The bimetallic sulfide Fe4.5Ni4.5S8 (pentlandite) was recently reported as a cheap and robust catalyst for electrochemical water splitting, as well as for CO2 reduction with a solvent-dependent product selectivity. Inspired by numerous reports on monometallic sulfoselenides and selenides revealing higher catalytic activity for the CO2 reduction reaction (CO2RR) than their sulfide counterparts, the authors investigated the influence of stepwise S/Se exchange in seleno-pentlandites Fe4.5Ni4.5S8-YSeY (Y=1–5) and their ability to act as CO2 reducing catalysts. It is demonstrated that the incorporation of higher equivalents of selenium favors the CO2RR with Fe4.5Ni4.5S4Se4 revealing the highest activity for CO formation. Under galvanostatic conditions in acetonitrile, Fe4.5Ni4.5S4Se4 generates CO with a Faradaic Efficiency close to 100 % at applied current densities of −50 mA cm−2 and −100 mA cm−2. This work offers insight into the tunability of the pentlandite based electrocatalysts for the CO2 reduction reaction. 相似文献
973.
Mathias Steiner Frank Schleifenbaum Clemens Stupperich Antonio Virgilio Failla Achim Hartschuh Alfred Johann Meixner 《Chemphyschem》2005,6(10):2190-2196
We present for the first time cavity-controlled fluorescence spectra and decay curves of single dipole emitters interacting at room temperature with the first longitudinal mode of a Fabry-Perot microcavity offering a lambda/2-spacing between its silver mirrors. The spontaneous emission rate of individual dye molecules was found to be enhanced by the Purcell effect by up to three times compared to the rate in free space, in agreement with theoretical predictions. Moreover, our new microcavity design was found to provide long-term stability and single-molecule sensitivity under ambient conditions for several months without noticeable reduction of the cavity-Q value. We consider this as a significant advance for single-photon sources operating at room temperature. 相似文献
974.
Mathias O. Senge Kevin M. Smith 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(9):o537-o541
The crystal and molecular structures of 4‐ethyl‐3,5‐dimethylpyrrole‐2‐carbaldehyde, C10H15NO, (I), benzyl 3,5‐dimethylpyrrole‐2‐carboxylate, C14H15NO2, (II), benzyl 4‐acetyl‐3,5‐dimethylpyrrole‐2‐carboxylate, C16H17NO3, (III), dimethyl 3,5‐dimethylpyrrole‐2,4‐dicarboxylate, C10H13NO4, (IV), 4‐ethyl‐3,5‐dimethyl‐2‐(p‐tosylacetyl)pyrrole, C17H21NO3S, (V), and ethyl 4‐(2‐ethoxycarbonyl‐2‐hydroxyacryloyl)‐3,5‐dimethylpyrrole‐2‐carboxylate, C15H19NO6, (VI), were determined at 130 K. Compounds (I), (II), (IV), (V) and (VI) form hydrogen‐bonded dimers [N—H⋯O=C = 1.97 (2)–2.03 (3) Å]. Four dimers, viz. (I) and (IV)–(VI), have inversion symmetry, while the dimer of (II) has twofold symmetry. Only (III) forms polymeric chains involving hydrogen bonds between the pyrrole H atom and the acetyl carbonyl group [H⋯O = 1.97 (2) Å] and is further stabilized by CH3⋯O interactions (C—H⋯O = 2.28–2.49 Å). Compound (VI) was found to occur as the enol ether in the crystal. 相似文献
975.
976.
Mathias Jungen 《NoDEA : Nonlinear Differential Equations and Applications》2006,13(4):469-483
By variational methods, we establish the existence of an infinite number of self-similar wave maps which evolve from smooth,
compactly supported data and develop a singularity in finite time. 相似文献
977.
978.
Mathias Zessin 《Indagationes Mathematicae》2007,18(2):305-325
In this paper, we introduce a geometric structure called top, which is a trivialized bundle of plane pencils over a Riemannian 3-manifold, defined as the set of kernels of a circle of l-forms (e.g., of contact and integrable forms) with particular properties with respect to the metric. We classify the manifolds which admit tops and we describe the associated metrics. 相似文献
979.
980.
Gema González Werner Stracke Zoraya Lopez Ulrike Keller Andrea Ricker Rudolf Reichelt 《Microscopy and microanalysis》2004,10(2):224-235
High-resolution transmission (HRTEM) and high-resolution scanning electron microscopy as well as atomic force microscopy (AFM), X-ray diffraction, and electron diffraction were used for studying the zeolites MFI, MEL, and the MFIMEL intergrowth system. All three zeolites consisted of individual particles having a size in the range of approximately 0.5 m to 5 m. The particle habits varied from rather cubelike to almost spherelike with many intermediate habits. Typically, the particles of these three zeolites were assembled by many individual blocks that differed in the dimension from about 25 nm to 140 nm as well as in the shape from very frequently almost rectangular (for MFI, MEL, and MFIMEL) to sometimes roundish or irregular habits (mainly for MFIMEL). An estimate shows that some 104 up to more than 106 densely packed blocks typically may assemble each individual zeolite particle or, related to the corresponding unit cell dimension, about 108 up to 1010 unit cells. The fine surface structure of zeolite particles was terracelike with steps between adjacent terraces typically in the range of 20 nm to 60 nm; the minimum step measured was approximately 4 nm. A detailed study of the surface topography was performed by AFM, detecting organic molecules at the block intersections. The presence of topological defects was observed by HRTEM and electron diffraction. 相似文献