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891.
Rudolf Podoba Igor Štubňa Viera Trnovcová Anton Trník 《Journal of Thermal Analysis and Calorimetry》2014,118(2):597-601
The samples from kaolin Sedlec were investigated by the help of DTA, TG, and temperature dependences of DC conductivity using Pt wire electrodes and linear heating up to 1,050 °C. After drying, the samples contained ~1.5 mass% of the physically bound water. DTA and TG reflected generally known facts about a release of the physically bound water, dehydroxylation, and metakaolinite → Si–Al spinel transformation. The results of electrical measurements showed the electric current passed over the maximum at 60 °C. The self-ionization of water results in the process H2O → H+ + OH? in the water layers on the crystal surfaces; consequently, OH? and H+ are the main charge carriers in the low-temperature region. The water molecules simultaneously evaporate from the sample which decreases the number of the charge carriers. When the physically bound water evaporates, the current is carried mostly by K+ and Na+ ions. During dehydroxylation, the hydroxyls OH? split into H+ and O2?. The ions H+ jump to the neighboring OH? groups creating the water molecules. The ions O2?remain bounded to the newly created metakaolinite lattice. Therefore, mobile protons contribute to the electric current. At the same time, this contribution gradually decreases because of the escape of H2O from the sample. The sharp current peak and DTA peak at 970 °C imply relatively fast metakaolinite → Si–Al spinel transformation. This DC current peak results from the shift of Al3+ and O2? ions into new positions. 相似文献
892.
Nina V. Kosova Evgeniya T. Devyatkina Arseny B. Slobodyuk Anton K. Gutakovskii 《Journal of Solid State Electrochemistry》2014,18(5):1389-1399
Single-phase LiVPO4F and LiVPO4F/Li3V2(PO4)3 nanostructured composite cathode materials were prepared by heating of the VPO4?+?LiF mechanochemically activated mixture to 700 °C and subsequent quick or slow cooling to room temperature, respectively. The formation of the composites was proved by a combination of different physico-chemical methods, including XRD, FTIR, 6Li and 31P NMR, SEM, TEM, and HRTEM. It has been shown that in the composites LiVPO4F and Li3V2(PO4)3 nanocrystals well inset into each other resulting in the nanodomain composite formation. Charge–discharge curves of the composites have a sloping profile both in the high-voltage (3.0–4.5 V) and in the low-voltage (1.3–2.5 V) ranges, noticeably different from plateaus for a phase-pure LiVPO4F, thus indicating a probable change of a two-phase regime of lithium intercalation for a single-phase one. Enhanced rate capability of the LiVPO4F/Li3V2(PO4)3 composites is associated with their microstructure and high ionic conductivity of Li3V2(PO4)3. 相似文献
893.
Stereospecific Cyclic Poly(methyl methacrylate) and Its Topology‐Guided Hierarchically Controlled Supramolecular Assemblies
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Jing Ming Ren Prof. Kotaro Satoh Dr. Tor Kit Goh Dr. Anton Blencowe Dr. Kanji Nagai Dr. Kenji Ishitake Dr. Andrew Joseph Christofferson Dr. George Yiapanis Prof. Irene Yarovsky Prof. Masami Kamigaito Prof. Greg Guanghua Qiao 《Angewandte Chemie (International ed. in English)》2014,53(2):459-464
In this study, the stereocomplexation between a novel stereospecific cyclic vinyl polymer, that is, cyclic syndiotactic poly(methyl methacrylate) (st‐PMMA), with the complementary linear isotactic (it‐) PMMA was investigated. Surprising new insight into the effects of the topology (i.e., end groups), size, and tacticity of the assembling components on stereocomplex formation was obtained. Characterization of the stereocomplexes revealed that the self‐assembly of cyclic st‐PMMAs and linear it‐PMMAs resulted in the formation of an unprecedented “polypseudorotaxane‐type” supramolecular assembly. This stereocomplex exhibited remarkably different physical properties as compared to the conventional PMMA triple‐helix stereocomplex as a result of the restricted topology imposed by the cyclic st‐PMMA assembling component. 相似文献
894.
Palladium‐Catalyzed Chain‐Growth Polycondensation of AB‐type Monomers: High Catalyst Turnover and Polymerization Rates
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Dr. Roman Tkachov Dr. Volodymyr Senkovskyy Dr. Tetyana Beryozkina Dr. Kseniya Boyko Prof. Dr. Vasiliy Bakulev Dr. Albena Lederer Dr. Karin Sahre Prof. Dr. Brigitte Voit Dr. Anton Kiriy 《Angewandte Chemie (International ed. in English)》2014,53(9):2402-2407
Chain‐growth catalyst‐transfer polycondensations of AB‐type monomers is a new and rapidly developing tool for the preparation of well‐defined π‐conjugated (semiconducting) polymers for various optoelectronic applications. Herein, we report the Pd/PtBu3‐catalyzed Negishi chain‐growth polycondensation of AB‐type monomers, which proceeds with unprecedented TONs of above 100 000 and TOFs of up to 280 s?1. In contrast, related AA/BB‐type step‐growth polycondensation proceeds with two orders of magnitude lower TONs and TOFs. A similar trend was observed in Suzuki‐type polycondensation. The key impact of the intramolecular (vs. intermolecular) catalyst‐transfer process on both polymerization kinetics and catalyst lifetime has been revealed. 相似文献
895.
A New Reactivity Mode for the Diazo Group: Diastereoselective 1,3‐Aminoalkylation Reaction of β‐Amino‐α‐Diazoesters To Give Triazolines
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Alexey Kuznetsov Dr. Anton V. Gulevich Prof. Dr. Donald J. Wink Prof. Dr. Vladimir Gevorgyan 《Angewandte Chemie (International ed. in English)》2014,53(34):9021-9025
A novel mode of reactivity for the diazo group, the 1,3‐addition of a nucleophile and an electrophile to the diazo group, has been realized in the intramolecular aminoalkylation of β‐amino‐α‐diazoesters to form tetrasubstituted 1,2,3‐triazolines. The reaction exhibited a broad scope, good functional group tolerance, and excellent diastereoselectivity. In addition, a new Au‐catalyzed intramolecular transannulation reaction of the obtained propargyl triazolines to give pyrroles has been discovered. 相似文献
896.
Sergi Hernàndez‐Navarro Dr. Pietro Tierno Prof. Joan Anton Farrera Prof. Jordi Ignés‐Mullol Prof. Francesc Sagués 《Angewandte Chemie (International ed. in English)》2014,53(40):10696-10700
Different phoretic driving mechanisms have been proposed for the transport of solid or liquid microscopic inclusions in integrated chemical processes. It is now shown that a substrate that was chemically modified with photosensitive self‐assembled monolayers enables the direct control of the assembly and transport of large ensembles of micrometer‐sized particles and drops that were dispersed in a thin layer of anisotropic fluid. This strategy separates particle driving, which was realized by AC electrophoresis, and steering, which was achieved by elastic modulation of the nematic host fluid. Inclusions respond individually or in collective modes following arbitrary reconfigurable paths that were imprinted by irradiation with UV or blue light. Relying solely on generic material properties, the proposed procedure is versatile enough for the development of applications that involve either inanimate or living materials. 相似文献
897.
Rhodium‐Catalyzed NH Insertion of Pyridyl Carbenes Derived from Pyridotriazoles: A General and Efficient Approach to 2‐Picolylamines and Imidazo[1,5‐a]pyridines
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Yi Shi Dr. Anton V. Gulevich Prof. Dr. Vladimir Gevorgyan 《Angewandte Chemie (International ed. in English)》2014,53(51):14191-14195
A general and efficient NH insertion reaction of rhodium pyridyl carbenes derived from pyridotriazoles was developed. Various NH‐containing compounds, including amides, anilines, enamines, and aliphatic amines, smoothly underwent the NH insertion reaction to afford 2‐picolylamine derivatives. The developed transformation was further utilized in a facile one‐pot synthesis of imidazo[1,5‐a]pyridines. 相似文献
898.
Hydrosilylation Induced by N→Si Intramolecular Coordination: Spontaneous Transformation of Organosilanes into 1‐Aza‐Silole‐Type Molecules in the Absence of a Catalyst
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Miroslav Novák Dr. Libor Dostál Dr. Mercedes Alonso Prof. Frank De Proft Dr. Aleš Růžička Prof. Antonín Lyčka Dr. Roman Jambor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(9):2542-2550
Our attempts to synthesize the N→Si intramolecularly coordinated organosilanes Ph2L1SiH ( 1 a ), PhL1SiH2 ( 2 a ), Ph2L2SiH ( 3 a ), and PhL2SiH2 ( 4 a ) containing a CH?N imine group (in which L1 is the C,N‐chelating ligand {2‐[CH?N(C6H3‐2,6‐iPr2)]C6H4}? and L2 is {2‐[CH?N(tBu)]C6H4}?) yielded 1‐[2,6‐bis(diisopropyl)phenyl]‐2,2‐diphenyl‐1‐aza‐silole ( 1 ), 1‐[2,6‐bis(diisopropyl)phenyl]‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 2 ), 1‐tert‐butyl‐2,2‐diphenyl‐1‐aza‐silole ( 3 ), and 1‐tert‐butyl‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 4 ), respectively. Isolated organosilicon amides 1 – 4 are an outcome of the spontaneous hydrosilylation of the CH?N imine moiety induced by N→Si intramolecular coordination. Compounds 1–4 were characterized by NMR spectroscopy and X‐ray diffraction analysis. The geometries of organosilanes 1 a – 4 a and their corresponding hydrosilylated products 1 – 4 were optimized and fully characterized at the B3LYP/6‐31++G(d,p) level of theory. The molecular structure determination of 1 – 3 suggested the presence of a Si?N double bond. Natural bond orbital (NBO) analysis, however, shows a very strong donor–acceptor interaction between the lone pair of the nitrogen atom and the formal empty p orbital on the silicon and therefore, the calculations show that the Si?N bond is highly polarized pointing to a predominantly zwitterionic Si+N? bond in 1 – 4 . Since compounds 1 – 4 are hydrosilylated products of 1 a – 4 a , the free energies (ΔG298), enthalpies (ΔH298), and entropies (ΔH298) were computed for the hydrosilylation reaction of 1 a – 4 a with both B3LYP and B3LYP‐D methods. On the basis of the very negative ΔG298 values, the hydrosilylation reaction is highly exergonic and compounds 1 a – 4 a are spontaneously transformed into 1 – 4 in the absence of a catalyst. 相似文献
899.
Katharina Buddrus-Schiemann Martin Rieger Marlene Mühlbauer Maria Vittoria Barbarossa Christina Kuttler Burkhard A. Hense Michael Rothballer Jenny Uhl Juliano R. Fonseca Philippe Schmitt-Kopplin Michael Schmid Anton Hartmann 《Analytical and bioanalytical chemistry》2014,406(25):6373-6383
In this interdisciplinary approach, the dynamics of production and degradation of the quorum sensing signal 3-oxo-decanoylhomoserine lactone were studied for continuous cultures of Pseudomonas putida IsoF. The signal concentrations were quantified over time by use of monoclonal antibodies and ELISA. The results were verified by use of ultra-high-performance liquid chromatography. By use of a mathematical model we derived quantitative values for non-induced and induced signal production rate per cell. It is worthy of note that we found rather constant values for different rates of dilution in the chemostat, and the values seemed close to those reported for batch cultures. Thus, the quorum-sensing system in P. putida IsoF is remarkably stable under different environmental conditions. In all chemostat experiments, the signal concentration decreased strongly after a peak, because emerging lactonase activity led to a lower concentration under steady-state conditions. This lactonase activity probably is quorum sensing-regulated. The potential ecological implication of such unique regulation is discussed. 相似文献
900.
Recently, S. Grivaux showed that there exists a rank one perturbation of a unitary operator in a Hilbert space which is hypercyclic. Another construction was suggested later by the first and the third authors. Here, using a functional model for rank one perturbations of singular unitary operators, we give yet another construction of hypercyclic rank one perturbation of a unitary operator. In particular, we show that any countable union of perfect Carleson sets on the circle can be the spectrum of a perturbed (hypercyclic) operator. 相似文献