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991.
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
992.
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
993.
Miroslav Janicek Martina Polaskova Radek Holubar Roman Cermak 《Cellulose (London, England)》2014,21(6):4039-4048
Cellulose powders hydrophobized by surface esterification with carboxylic acids with different chain lengths (3, 10 and 18 carbons) were dispersed in a polypropylene matrix. Quality of the dispersion and nucleation activity of the filler were investigated by means of differential scanning calorimetry and optical microscopy. The results showed that the esterification decreases the crystallization rate in case of cellulose esterified with propionic or decanoic acid. On the other hand, the oleic acid ester demonstrated slightly higher crystallization rates than the unmodified cellulose, which was ascribed primarily to the newly arisen non-esterified surface after disintegration of the filler. Optical microscopy with hot stage showed the high nucleation ability of the natural cellulose fiber and its suppression in case of esterified surfaces. A complete inability to nucleate polypropylene crystallization was observed in case of decanoyl ester, while the other two retained some activity, but lower than that of the natural fiber. Finally, analysis of the filler dispersion and distribution revealed that the decanoyl and octadecanoyl esters disintegrate during melt mixing, while both dispersion and distribution of the fibers modified with propionic acid are poor. 相似文献
994.
995.
The photophysical and photovoltaic properties of three alternated fluorene–thiophene copolymers were studied. With similar structure the copolymers differed by the numbers of thiophene units linked to each fluorene group:one, two and three. The electronic properties were analyzed through mobility measurements and the overall properties pointed out to the one containing the three rings as the best material, as anticipated, due to the larger number of thiophene units. However, after thermal annealing the polymer containing two thiophene rings presented the best photovoltaic efficiency, seven fold greater than the pristine material. The morphology, studied by atomic force microscopy, revealed to be one of the key factors for the performance of the materials as solar cells. 相似文献
996.
We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO2) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO2 and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO2. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films. Figure
Illustration of the fabricated polystyrene/titania hybrids imprinted with 1-pyrenebutyric acid providing the interaction between the organic and inorganic components through the pyrene and carboxylic moieties 相似文献
997.
Jaromir Dmytrzyk Andrzej Kotarba Hanna Grabowska Roman Klimkiewicz 《Research on Chemical Intermediates》2004,30(4-5):337-342
The influence of gas-phase methylation of phenol on the state of the Fe-Si-Cr-K oxide catalyst surface was investigated by thermodesorption of K atoms and ions. Changes in potassium desorption energies, as determined from Arrhenius-like plots, varied from 3.07 eV to 1.21 eV for the atoms and from 2.59 eV to 2.89 eV for ion desorption from the active and deactivated samples, respectively. The results were discussed in terms of transformation of the catalyst surface and formation of β-ferrite. 相似文献
998.
999.
1000.
The paper deals with investigation of a self-excited vibrating system with dry friction. The system is composed of a mass connected by viscoelastic element with the referring frame and interacting with a moving belt by means of dry friction. An experimentally identified, multi-parametric dry friction model for the pair composed of soft and hard elements like steel–polyester pair, describing both the case of stick-slip and quasi-harmonic vibration, has been applied. Additionally, the system is influenced by external, two-frequency kinematic excitation. The results of computer simulation for different excitation conditions are submitted in the present paper. 相似文献