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181.
182.
Masatoshi Hasegawa Daiki Hirano Mari Fujii Misako Haga Eiichiro Takezawa Shinya Yamaguchi Atsushi Ishikawa Takashi Kagayama 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):575-592
This work presents novel colorless polyimides (PIs) derived from 1R,2S,4S,5R‐cyclohexanetetracarboxylic dianhydride (H″‐PMDA). Isomer effects were also discussed by comparing with PI systems derived from conventional hydrogenated pyromellitic dianhydride, that is, 1S,2R,4S,5R‐cyclohexanetetracarboxylic dianhydride (H‐PMDA). H″‐PMDA was much more reactive with various diamines than H‐PMDA, and the former led to PI precursors with much higher molecular weights. The results can be explained from the quite different steric structures of these isomers. The thermally imidized H″‐PMDA‐based films were colorless regardless of diamines because of inhibited charge‐transfer interaction. In particular, the H″‐PMDA/4,4′‐oxydianiline system simultaneously achieved a very high Tg exceeding 300 °C, high toughness (elongation at break > 70%), and good solution processability. In contrast, the H‐PMDA‐based counterparts were essentially insoluble. The outstanding solubility of the former probably results from disturbed chain stacking by its nonplanar steric structure. An advantage of chemical imidization process is also proposed. In some cases, a copolymerization approach with an aromatic tetracarboxylic dianhydride was effective to improve the thermal expansion property. The results suggest that the H″‐PMDA‐based PI systems can be promising candidates for novel high‐temperature plastic substrate materials in electronic paper displays. A potential application as optical compensation film materials in liquid crystal displays (LCD) is also proposed in this work. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
183.
Shunpei Ishikawa 《Tetrahedron》2010,66(1):297-10163
Hydroxylated oligoarene-type phosphines with various substitution patterns were synthesized. Such phosphines have potential as ligands for transition metal-catalyzed reactions. A successful route, which includes a repetitive Suzuki-Miyaura coupling-triflation sequence, reduction, and salt formation, was established starting from 2-bromophenyldicyclohexylphosphine oxide. Other key aspects of the method are the use of suitable triflation reagents and the formation of phosphines as HBF4 salts. Interesting information was obtained from careful analysis of the byproducts in the triflation and reduction steps, and the mechanisms for their formation were proposed. 相似文献
184.
A new approach to reduce the reverse current of Ge pin photodiodes on Si is presented, in which an i-Si layer is inserted between Ge and top Si layers to reduce the electric field in the Ge layer. Without post- growth annealing, the reverse current density is reduced to -10 mA/cm^2 at -1 V, i.e., over one order of magnitude lower than that of the reference photodiode without i-Si layer. However, the responsivity of the photodiodes is not severely compromised. This lowered-reverse-current is explained by band-pinning at the i-Si/i-Ge interface. Barrier lowering mechanism induced by E-field is also discussed. The presented "non-thermal" approach to reduce reverse current should accelerate electronics-photonics convergence by using Oe on the Si complementary metal oxide semiconductor (CMOS) platform. 相似文献
185.
Satoshi Ishikawa 《Journal of Functional Analysis》2003,204(1):50-100
We investigate the totally geodesic Radon transform which assigns a function to its integration over totally geodesic symmetric submanifolds in Riemannian symmetric spaces of noncompact type. Our main concern is focused on the injectivity and support theorem. Our approach is based on the projection slice theorem relating the totally geodesic Radon transform and the Fourier transforms on symmetric spaces. Our approach also uses the study of geometry concerned with the totally geodesic symmetric subvarieties in Riemannian symmetric spaces in terms of the cell structure of the Satake compactifications. 相似文献
186.
J. Somlai G. Szeiler P. Szabó A. Várhegyi S. Tokonami T. Ishikawa A. Sorimachi S. Yoshinaga T. Kovács 《Journal of Radioanalytical and Nuclear Chemistry》2009,279(1):219-225
In the last few decades attention has been given to improve workplace conditions, primarily to reduce the different health
risks. In the air that accumulates in underground workplaces radon may constitute one of the health risks. The radon concentration
in the show cave in Tapolca is especially high in summer months, with the annual average in the year 2005 being 7227 Bq/m3, in 2006 8591 Bq/m3. The radon concentration was found to be independent on the location of the measurement. Its value was rather similar for
working hours and for the total period. The hours spent in the cave by the workers depend on the number of visitors. The radiation
dose, estimated on the basis of personal dosimeters, is significant for those working there especially, employed during the
whole year. Taking into consideration the actual working hours and the equilibrium factor, F = 0.4, given in the literature, it approaches and even exceeds the dose limit of 20 mSv/year. With a well organized work
schedule, as well as the employment of outside workers during the summer period, the dose limit of 20 mSv/year can probably
be maintained. However, on the basis of recent measurements, the actual equilibrium factor was determined to be F = 0.5, which in turn means a further 25% increase in the dose effect. 相似文献
187.
Belous K Shapkin M Sokolov A Abe K Abe K Adachi I Aihara H Anipko D Arinstein K Aulchenko V Aushev T Bakich AM Barberio E Bay A Bedny I Bitenc U Bizjak I Blyth S Bondar A Bozek A Bracko M Browder TE Chang MC Chen A Chen KF Chen WT Cheon BG Chistov R Choi Y Choi YK Cole S Dalseno J Drutskoy A Eidelman S Epifanov D Fratina S Fujikawa M Gabyshev N Gershon T Gokhroo G Golob B Ha H Haba J Hasegawa Y Hayasaka K Hayashii H Hazumi M Heffernan D Hokuue T Hoshi Y Hou S Hou WS Iijima T Ikado K Imoto A 《Physical review letters》2007,99(1):011801
The mass of the tau lepton has been measured in the decay mode tau-->3pinutau using a pseudomass technique. The result obtained from 414 fb-1 of data collected with the Belle detector is Mtau=[1776.61+/-0.13(stat)+/-0.35(sys)] MeV/c2. The upper limit on the relative mass difference between positive and negative tau leptons is |Mtau+-Mtau-|/Mtau<2.8 x 10-4 at 90% confidence level. 相似文献
188.
Strain rate and temperature effects on the flow stress of 304N stainless steel were investigated using data obtained from torsion tests on thin-walled tubular specimens, at given strain rates of between 10−3 and 10−1 with temperatures ranging from 83 to 296 K. Initially, the apparent strain rate sensitivity of the flow stress, obtained at test temperatures of 83, 153, 213, and 296 K, was examined. The strain dependence and the strain rate dependence of the mechanical threshold stress (the flow stress at O K) at strains less than 0.1 and at strain rates of 2.4 × 10−3 and 8.3 × 102 s−1, is also discussed. It was concluded from the experimental results that the mechanical threshold stress depends not only on the strain but also on the strain rate. 相似文献
189.
Reconstitution of Biosynthetic Machinery for the Synthesis of the Highly Elaborated Indole Diterpene Penitrem
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Dr. Chengwei Liu Koichi Tagami Dr. Atsushi Minami Tomoyuki Matsumoto Jens Christian Frisvad Hideyuki Suzuki Jun Ishikawa Katsuya Gomi Prof. Dr. Hideaki Oikawa 《Angewandte Chemie (International ed. in English)》2015,54(19):5748-5752
Penitrem A is one of the most elaborated members of the fungal indole diterpenes. Two separate penitrem gene clusters were identified using genomic and RNA sequencing data, and 13 out of 17 transformations in the penitrem biosynthesis were elucidated by heterologous reconstitution of the relevant genes. These reactions involve 1) a prenylation‐initiated cationic cyclization to install the bicyclo[3.2.0]heptane skeleton (PtmE), 2) a two‐step P450‐catalyzed oxidative processes forming the unique tricyclic penitrem skeleton (PtmK and PtmU), and 3) five sequential oxidative transformations (PtmKULNJ). Importantly, without conventional gene disruption, reconstitution of the biosynthetic machinery provided sufficient data to determine the pathway. It was thus demonstrated that the Aspergillus oryzae reconstitution system is a powerful method for studying the biosynthesis of complex natural products. 相似文献
190.
Cover Picture: Reconstitution of Biosynthetic Machinery for the Synthesis of the Highly Elaborated Indole Diterpene Penitrem (Angew. Chem. Int. Ed. 19/2015)
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