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991.
Harald Müller Michael Eggert Jürgen Czarske Lars Büttner Andreas Fischer 《Experiments in fluids》2007,43(2-3):223-232
The main advantage of the described Doppler global velocimeter (DGV) systems based on frequency modulation (FM) or frequency
shift keying (FSK) is that no reference detector is required. The frequency variation of the laser light during one modulation
period additionally allows an on-line calibration of the complete DGV system. Thus, the new method has the potential to reduce
the uncertainty of conventional DGV velocity measurements since time resolved velocity field measurements on a spinning disc
have shown standard deviations down to 0.02 m/s. On investigating flow fields, velocity components notably less than 0.5 m/s
were resolved. 相似文献
992.
Identification of viscoelastic properties by means of nanoindentation taking the real tip geometry into account 总被引:1,自引:0,他引:1
Motivated by recent progress in viscoelastic indentation analysis, the identification of viscoelastic properties from nanoindentation
test data taking the real tip geometry into account is presented in this paper. Based on the elastic solution of the indentation
problem, the corresponding viscoelastic solution is obtained by the application of the method of functional equations. This
general solution, which accounts for the real geometric properties of the indenter tip, is specialized for the case of a trapezoidal
load history, commonly employed in nanoindentation testing. Three deviatoric creep models, the single dash-pot, the Maxwell,
and the three-parameter model are considered. The so-obtained expressions allow us to determine viscoelastic model parameters
via back calculation from the measured load–penetration history. The presented approach is illustrated by the identification
of short-term viscoelastic properties of bitumen. Hereby, the influence of loading rate, maximum load, and temperature on
the model parameters is investigated. 相似文献
993.
Boryl (Hetero)aryne Precursors as Versatile Arylation Reagents: Synthesis through CH Activation and Orthogonal Reactivity 下载免费PDF全文
Dr. Emilien Demory Karthik Devaraj Dr. Andreas Orthaber Dr. Paul J. Gates Dr. Lukasz T. Pilarski 《Angewandte Chemie (International ed. in English)》2015,54(40):11765-11769
(Pinacolato)boryl ortho‐silyl(hetero)aryl triflates are presented as a new class of building blocks for arylation. They demonstrate unique versatility by delivering boronate or (hetero)aryne reactivity chemoselectively in a broad range of transformations. This approach enables the unprecedented postfunctionalization of fluoride‐activated (hetero)aryne precursors, for example, as substrates in transition‐metal catalysis, and offers valuable new possibilities for aryl boronate postfunctionalization without the use of specialized protecting groups. 相似文献
994.
Corrigendum: Crystallographic Snapshot of an Arrested Intermediate in the Biomimetic Activation of CO2 下载免费PDF全文
995.
Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution 下载免费PDF全文
Priv.‐Doz. Dr. Albena Lederer Prof. Dr. Walther Burchard Tobias Hartmann Johannes S. Haataja Dr. Nikolay Houbenov Andreas Janke Dr. Peter Friedel Dr. Ralf Schweins Dr. Peter Lindner 《Angewandte Chemie (International ed. in English)》2015,54(43):12578-12583
Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo‐dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high‐generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1–G4) pseudo‐dendrimers strongly resembles the behavior of dendrimers in higher generations (G5–G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano‐sphere with a smooth surface even in the first generation. 相似文献
996.
Chemical Synthesis Elucidates the Immunological Importance of a Pyruvate Modification in the Capsular Polysaccharide of Streptococcus pneumoniae Serotype 4 下载免费PDF全文
Dr. Claney L. Pereira Andreas Geissner Dr. Chakkumkal Anish Prof. Dr. Peter H. Seeberger 《Angewandte Chemie (International ed. in English)》2015,54(34):10016-10019
Carbohydrate modifications are believed to strongly affect the immunogenicity of glycans. Capsular polysaccharides (CPS) from bacterial pathogens are frequently equipped with a pyruvate that can be placed across the 4,6‐, 3,4‐, or 2,3‐positions. A trans‐2,3‐linked pyruvate is present on the CPS of the Gram‐positive bacterium Streptococcus pneumoniae serotype 4 (ST4), a pathogen responsible for pneumococcal infections. To assess the immunological importance of this modification within the CPS repeating unit, the first total synthesis of the glycan was carried out. Glycan microarrays containing a series of synthetic antigens demonstrated how antibodies raised against natural ST4 CPS specifically recognize the pyruvate within the context of the tetrasaccharide repeating unit. The pyruvate modification is a key motif for designing minimal synthetic carbohydrate vaccines for ST4. 相似文献
997.
Thomas Heuser Elisabeth Weyandt Dr. Andreas Walther 《Angewandte Chemie (International ed. in English)》2015,54(45):13258-13262
Switchable self‐assemblies respond to external stimuli with a transition between near‐equilibrium states. Although being a key to present‐day advanced materials, these systems respond rather passively, and do not display autonomous dynamics. For autonomous behavior, approaches must be found to orchestrate the time domain of self‐assemblies, which would lead to new generations of dynamic and self‐regulating materials. Herein, we demonstrate catalytic control of the time domain of pH‐responsive peptide hydrogelators in a closed system. We program transient acidic pH states by combining a fast acidic activator with the slow, enzymatic, feedback‐driven generation of a base (dormant deactivator). This transient state can be programmed over orders of magnitude in time. It is coupled to dipeptides to create autonomously self‐regulating, dynamic gels with programmed lifetimes, which are used for fluidic guidance, burst release, and self‐erasing rapid prototyping. 相似文献
998.
Metal‐Catalyzed β‐Functionalization of Michael Acceptors through Reductive Radical Addition Reactions 下载免费PDF全文
Dr. Jan Streuff Prof. Dr. Andreas Gansäuer 《Angewandte Chemie (International ed. in English)》2015,54(48):14232-14242
Transition‐metal‐catalyzed radical reactions are becoming increasingly important in modern organic chemistry. They offer fascinating and unconventional ways for connecting molecular fragments that are often complementary to traditional methods. In particular, reductive radical additions to α,β‐unsaturated compounds have recently gained substantial attention as a result of their broad applicability in organic synthesis. This Minireview critically discusses the recent landmark achievements in this field in context with earlier reports that laid the foundation for today′s developments. 相似文献
999.
1000.
Synthesis,Structure, and Properties of SrC(NH)3, a Nitrogen‐Based Carbonate Analogue with the Trinacria Motif 下载免费PDF全文
M. Sc. Ronja Missong M. Sc. Janine George Dr. Andreas Houben Dr. Markus Hoelzel Prof. Dr. Richard Dronskowski 《Angewandte Chemie (International ed. in English)》2015,54(41):12171-12175
Strontium guanidinate, SrC(NH)3, the first compound with a doubly deprotonated guanidine unit, was synthesized from strontium and guanidine in liquid ammonia and characterized by X‐ray and neutron diffraction, IR spectroscopy, and density‐functional theory including harmonic phonon calculations. The compound crystallizes in the hexagonal space group P63/m, constitutes the nitrogen analogue of strontium carbonate, SrCO3, and its structure follows a layered motif between Sr2+ ions and complex anions of the type C(NH)32?; the anions adopt the peculiar trinacria shape. A comparison of theoretical phonons with experimental IR bands as well as quantum‐chemical bonding analyses yield a first insight into bonding and packing of the formerly unknown anion in the crystal. 相似文献