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871.
Combination of the enantioselective properties of the two versatile gas-chromatographic chiral stationary phases (CSPs) octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-gamma-CD (Lipodex E) 1 and L-valine-diamide-based CSP Chirasil-Val-C11 2 has been realized by doping the chiral polymer 2 with the nonpolymeric selector 1. The resulting mixed-mode CSP Chirasil-Val(gamma-Dex) 3 was found to have a greatly improved enantioselectivity toward proline and aspartic acid (as N-trifluoroacetyl ethyl or methyl esters) in comparison to the single-mode CSP 2. The presence of the CD selector in 3 extended the scope of gas-chromatographic enantioseparations achievable on 2 to underivatized alcohols, terpenes, and other chiral compounds that are exclusively enantioseparated on 1. 相似文献
872.
We propose a nonequilibrium version of functional renormalization within the Keldysh formalism by introducing a complex-valued flow parameter in the Fermi or Bose functions of each reservoir. Our cutoff scheme provides a unified approach to equilibrium and nonequilibrium situations. We apply it to nonequilibrium transport through an interacting quantum wire coupled to two reservoirs and show that the nonequilibrium occupation induces new power law exponents for the conductance. 相似文献
873.
Andrew R. Awtry Brian T. Fisher Robert A. Moffatt Volker Ebert 《Proceedings of the Combustion Institute》2007,31(1):799-806
We designed a three-channel tunable diode laser absorption spectrometer to make simultaneous in situ measurements of oxygen, carbon monoxide and water vapor in fire environments to aid in the evaluation of water-based fire suppression systems. The instrument also provides simultaneous information on the liquid water content via optical density measurements by evaluation of the captured direct absorption waveforms. We evaluated the spectrometer in a 1350 L test enclosure containing a small propane flame and a piezoelectric generated water mist of sub-10 μm drops. Mist drop number densities were on the order of 106 cm−3 resulting in transmission losses of greater than 99.99% for a sample pathlength of 21.6 cm. We were able to detect and quantify oxygen from transmission levels of 100% down to 0.01% with uncertainties of 0.1 and 0.4 vol%, respectively. The water vapor concentration uncertainty never exceeded 0.06 vol% even during times of heavy mist loading. Carbon monoxide levels produced in the test enclosure were below the 250 ppm detection limit determined from analysis of the noise levels in our detected signals. The liquid water content uncertainty was less than for values that typically reached . 相似文献
874.
Far‐Red Emitting Fluorescent Dyes for Optical Nanoscopy: Fluorinated Silicon–Rhodamines (SiRF Dyes) and Phosphorylated Oxazines 下载免费PDF全文
Dr. Kirill Kolmakov Elke Hebisch Dr. Thomas Wolfram Lars A. Nordwig Dr. Christian A. Wurm Dr. Haisen Ta Dr. Volker Westphal Dr. Vladimir N. Belov Prof. Stefan W. Hell 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(38):13344-13356
Far‐red emitting fluorescent dyes for optical microscopy, stimulated emission depletion (STED), and ground‐state depletion (GSDIM) super‐resolution microscopy are presented. Fluorinated silicon–rhodamines (SiRF dyes) and phosphorylated oxazines have absorption and emission maxima at about λ≈660 and 680 nm, respectively, possess high photostability, and large fluorescence quantum yields in water. A high‐yielding synthetic path to introduce three aromatic fluorine atoms and unconventional conjugation/solubilization spacers into the scaffold of a silicon–rhodamine is described. The bathochromic shift in SiRF dyes is achieved without additional fused rings or double bonds. As a result, the molecular size and molecular mass stay quite small (<600 Da). The use of the λ=800 nm STED beam instead of the commonly used one at λ=750–775 nm provides excellent imaging performance and suppresses re‐excitation of SiRF and the oxazine dyes. The photophysical properties and immunofluorescence imaging performance of these new far‐red emitting dyes (photobleaching, optical resolution, and switch‐off behavior) are discussed in detail and compared with those of some well‐established fluorophores with similar spectral properties. 相似文献
875.
Andreas Kolmer Dr. Volker Schmidts Dr. Peter Monecke Prof. Dr. Stefan Hecht Prof. Dr. Christina M. Thiele 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14545-14554
Stimuli responsive compounds and materials are of high interest in synthetic chemistry and materials science, with light being the most intriguing stimulus due to the possibility to remote control the physicochemical properties of a molecule or a material. There is a constant quest to design photoswitches with improved switching efficiency and especially diarylethene‐type switches promise photo cyclization quantum yields up to unity. However, only limited attention has been paid towards the influence of the solution conformation on the switching efficiency. Here, we describe a detailed NMR spectroscopic investigation on the conformational distribution of bridge‐substituted dithienylcyclopentenes in solution. We could discriminate between several photoactive and photoinactive as well as two diastereomorphous conformations and show that the trends observed in the switching efficiency match the conformer populations obtained from state of the art NMR parameters in solution. 相似文献
876.
877.
Carbon Nanodots: Supramolecular Electron Donor–Acceptor Hybrids Featuring Perylenediimides 下载免费PDF全文
Volker Strauss Johannes T. Margraf Konstantin Dirian Dr. Zois Syrgiannis Prof. Dr. Maurizio Prato Dr. Cordula Wessendorf Prof. Dr. Andreas Hirsch Prof. Dr. Timothy Clark Prof. Dr. Dirk M. Guldi 《Angewandte Chemie (International ed. in English)》2015,54(28):8292-8297
We describe the formation of charge‐transfer complexes that feature electron‐donating carbon nanodots (CND) and electron‐accepting perylenediimides (PDI). The functionalities of PDIs have been selected to complement those of CNDs in terms of electrostatic and π‐stacking interactions based on oppositely charged ionic head groups and extended π‐systems, respectively. Importantly, the contributions from electrostatic interactions were confirmed in reference experiments, in which stronger interactions were found for PDIs that feature positively rather than negatively charged head groups. The electronic interactions between the components in the ground and excited state were characterized in complementary absorption and fluorescence titration assays that suggest charge‐transfer interactions in both states with binding constants on the order of 8×104 M ?1 (25 L g?1). Selective excitation of the two components in ultrafast pump probe experiments gave a 210 ps lived charge‐separated state. 相似文献
878.
Dr. Volker L. Deringer Prof. Dr. Richard Dronskowski 《Angewandte Chemie (International ed. in English)》2015,54(51):15334-15340
Synthesis and utilization of nanocrystals are highly active fields of current research, but they require a thorough understanding of the underlying crystal surfaces. In this Minireview, we span the arc from surfaces to free nanocrystals, and onward to their chemical synthesis, using as examples lead selenide (PbSe), tin telluride (SnTe), and their direct chemical relatives. Besides experimental insights, we highlight the increasingly influential role played by quantum‐chemical simulations of surfaces and nanocrystals. What can theory do today, or possibly tomorrow; where are its limits? Answering these questions, and skillfully linking them to experiments, could open up new atomistically (that is, chemically) guided perspectives for nanosynthesis. 相似文献
879.
NHC-Stabilized Iridium Nanoparticles as Catalysts in Hydrogen Isotope Exchange Reactions of Anilines
Mégane Valero Dr. Donia Bouzouita Dr. Alberto Palazzolo Dr. Jens Atzrodt Dr. Christophe Dugave Dr. Simon Tricard Dr. Sophie Feuillastre Dr. Grégory Pieters Dr. Bruno Chaudret Dr. Volker Derdau 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3545-3550
The preparation of N-heterocyclic carbene-stabilized iridium nanoparticles and their application in hydrogen isotope exchange reactions is reported. These air-stable and easy-to-handle iridium nanoparticles showed a unique catalytic activity, allowing selective and efficient hydrogen isotope incorporation on anilines using D2 or T2 as isotopic source. The usefulness of this transformation has been demonstrated by the deuterium and tritium labeling of diverse complex pharmaceuticals. 相似文献
880.
Dr. Shuai Jiang Ming Xiao Prof. Wen Sun Dr. Daniel Crespy Prof. Volker Mailänder Prof. Xiaojun Peng Prof. Jiangli Fan Prof. Dr. Katharina Landfester 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20183-20191
The anticancer efficacy of photodynamic therapy (PDT) is limited due to the hypoxic features of solid tumors. We report synergistic PDT/chemotherapy with integrated tandem Fenton reactions mediated by ovalbumin encapsulation for improved in vivo anticancer therapy via an enhanced reactive oxygen species (ROS) generation mechanism. O2.− produced by the PDT is converted to H2O2 by superoxide dismutase, followed by the transformation of H2O2 to the highly toxic .OH via Fenton reactions by Fe2+ originating from the dissolution of co-loaded Fe3O4 nanoparticles. The PDT process further facilitates the endosomal/lysosomal escape of the active agents and enhances their intracellular delivery to the nucleus—even for drug-resistant cells. Cisplatin generates O2.− in the presence of nicotinamide adenine dinucleotide phosphate oxidase and thereby improves the treatment efficiency by serving as an additional O2.− source for production of .OH radicals. Improved anticancer efficiency is achieved under both hypoxic and normoxic conditions. 相似文献