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161.
Ki Mann Jee Dong Chul Park 《International Journal of Infrared and Millimeter Waves》2003,24(12):2105-2117
A spurious-suppressed transversal filter using the multiple-coupled line is proposed. The frequency characteristics of the multiple-coupled line are analyzed in detail. In order to compare the performances, the novel spurious-suppressed transversal filter using triple-coupled half-wavelength directional couplers is designed at 30 GHz. The spurious-suppression characteristics of the proposed transversal filter are verified by the full wave analysis and the measurement. The spurious response of the fabricated filter is effectively suppressed and the large attenuation is obtained in the stopband. 相似文献
162.
Dr. Luke A. Clifton Dr. Stephen A. Holt Dr. Arwel V. Hughes Dr. Emma L. Daulton Dr. Wanatchaporn Arunmanee Dr. Frank Heinrich Dr. Syma Khalid Damien Jefferies Dr. Timothy R. Charlton Dr. John R. P. Webster Dr. Christian J. Kinane Prof. Jeremy H. Lakey 《Angewandte Chemie (International ed. in English)》2015,54(41):11952-11955
Gram‐negative bacteria are an increasingly serious source of antibiotic‐resistant infections, partly owing to their characteristic protective envelope. This complex, 20 nm thick barrier includes a highly impermeable, asymmetric bilayer outer membrane (OM), which plays a pivotal role in resisting antibacterial chemotherapy. Nevertheless, the OM molecular structure and its dynamics are poorly understood because the structure is difficult to recreate or study in vitro. The successful formation and characterization of a fully asymmetric model envelope using Langmuir–Blodgett and Langmuir–Schaefer methods is now reported. Neutron reflectivity and isotopic labeling confirmed the expected structure and asymmetry and showed that experiments with antibacterial proteins reproduced published in vivo behavior. By closely recreating natural OM behavior, this model provides a much needed robust system for antibiotic development. 相似文献
163.
164.
Detecting changes in arabidopsis cell wall composition using time‐of‐flight secondary ion mass spectrometry
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Alex Yi‐Lin Tsai Robyn E. Goacher Emma R. Master 《Surface and interface analysis : SIA》2015,47(5):626-631
Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was previously used to characterize lignocellulosic materials, including woody biomass. ToF‐SIMS can acquire both rapid spectral and spatial information about a sample's surface composition. In the present study, ToF‐SIMS was used to characterize the cell walls of stem tissue from the plant model organism, Arabidopsis thaliana. Using principal component analyses, ToF‐SIMS spectra from A. thaliana wild‐type (Col‐0), cellulose mutant (irx3), and lignin mutant (fah1) stem tissues were distinguished using ToF‐SIMS peaks annotated for wood‐derived lignocellulose, where spectra from the irx3 and fah1 were characterized by comparatively low polysaccharide and syringyl lignin content, respectively. Spatial analyses using ToF‐SIMS imaging furthermore differentiated interfascicular fiber and xylem vessels based on differences in the lignin content of corresponding cell walls. These new data support the applicability of ToF‐SIMS peak annotations based on woody biomass for herbaceous plants, including model plant systems like arabidopsis. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
165.
166.
Dr. Yan Li Dr. Yuk-Chi Chan Bi-Xiang Leong Dr. Yongxin Li Dr. Emma Richards Indu Purushothaman Dr. Susmita De Dr. Pattiyil Parameswaran Dr. Cheuk-Wai So 《Angewandte Chemie (International ed. in English)》2017,56(26):7573-7578
The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAACMe] (cAACMe=:C(CMe2)2(CH2)NAr, Ar=2,6-iPr2C6H3) with H2SiI2 in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAACMe)2Si:.]+I− ( 1 ), which features a cationic cAAC–silicon(I) radical, and [cAACMe−H]+I−. In addition, the reaction of the NHC–iodosilicon(I) dimer [IAr(I)Si:]2 (IAr=:C{N(Ar)CH}2) with 4 equiv of IMe (:C{N(Me)CMe}2), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(IMe)2SiH]+I− ( 2 ) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the CAr−H bond activation product [1-F-2-IMe-C6H4]+I− ( 3 ). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1 . Compounds 1 – 3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography. 相似文献
167.
Dynamics of milling processes with variable time delays 总被引:5,自引:0,他引:5
A milling-process model with a variable time delay associated with each cutting tooth is presented in this article. The source
of this variable time delay is the feed rate. The effect of the feed motion on the entry cutting angle, the exit cutting angle,
and the amplitude of feed mark is also discussed. Loss-of-contact effects are also considered. The system dynamics is described
by a set of delay differential equations with periodic coefficients and variable time delays. A semi-discretization scheme
is presented for analyzing the stability of periodic orbits of this system. The analysis provides evidence of period-doubling
bifurcations and secondary Hopf bifurcations. Good agreement is found between the numerical results obtained from this work
and the results of related experimental studies. 相似文献
168.
Stephen E Huang D Shaw JL Blake AJ Collison D Davies ES Edge R Howard JA McInnes EJ Wilson C Wolowska J McMaster J Schröder M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(37):10246-10258
The NiII complexes [Ni([9]aneNS2‐CH3)2]2+ ([9]aneNS2‐CH3=N‐methyl‐1‐aza‐4,7‐dithiacyclononane), [Ni(bis[9]aneNS2‐C2H4)]2+ (bis[9]aneNS2‐C2H4=1,2‐bis‐(1‐aza‐4,7‐dithiacyclononylethane) and [Ni([9]aneS3)2]2+ ([9]aneS3=1,4,7‐trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal NiIII products, which have been characterized by X‐ray crystallography, UV/Vis and multi‐frequency EPR spectroscopy. The single‐crystal X‐ray structure of [NiIII([9]aneNS2‐CH3)2](ClO4)6?(H5O2)3 reveals an octahedral co‐ordination at the Ni centre, while the crystal structure of [NiIII(bis[9]aneNS2‐C2H4)](ClO4)6?(H3O)3? 3H2O exhibits a more distorted co‐ordination. In the homoleptic analogue, [NiIII([9]aneS3)2](ClO4)3, structurally characterized at 30 K, the Ni? S distances [2.249(6), 2.251(5) and 2.437(2) Å] are consistent with a Jahn–Teller distorted octahedral stereochemistry. [Ni([9]aneNS2‐CH3)2](PF6)2 shows a one‐electron oxidation process in MeCN (0.2 M NBu4PF6, 293 K) at E1/2=+1.10 V versus Fc+/Fc assigned to a formal NiIII/NiII couple. [Ni(bis[9]aneNS2‐C2H4)](PF6)2 exhibits a one‐electron oxidation process at E1/2=+0.98 V and a reduction process at E1/2=?1.25 V assigned to NiII/NiIII and NiII/NiI couples, respectively. The multi‐frequency X‐, L‐, S‐, K‐band EPR spectra of the 3+ cations and their 86.2 % 61Ni‐enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6 %, 42.8 % and 37.2 % Ni character in [Ni([9]aneNS2‐CH3)2]3+, [Ni(bis[9]aneNS2‐C2H4)]3+ and [Ni([9]aneS3)2]3+, respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S‐thioether centres. EPR spectra for [61Ni([9]aneS3)2]3+ are consistent with a dynamic Jahn–Teller distortion in this compound. 相似文献
169.
Lupoli TJ Tsukamoto H Doud EH Wang TS Walker S Kahne D 《Journal of the American Chemical Society》2011,133(28):10748-10751
The β-lactams are the most important class of antibiotics in clinical use. Their lethal targets are the transpeptidase domains of penicillin binding proteins (PBPs), which catalyze the cross-linking of bacterial peptidoglycan (PG) during cell wall synthesis. The transpeptidation reaction occurs in two steps, the first being formation of a covalent enzyme intermediate and the second involving attack of an amine on this intermediate. Here we use defined PG substrates to dissect the individual steps catalyzed by a purified E. coli transpeptidase. We demonstrate that this transpeptidase accepts a set of structurally diverse D-amino acid substrates and incorporates them into PG fragments. These results provide new information on donor and acceptor requirements as well as a mechanistic basis for previous observations that noncanonical D-amino acids can be introduced into the bacterial cell wall. 相似文献
170.
Mann JA Rodríguez-López J Abruña HD Dichtel WR 《Journal of the American Chemical Society》2011,133(44):17614-17617
Single-layer graphene is a newly available conductive material ideally suited for forming well-defined interfaces with electroactive compounds. Aromatic moieties typically interact with the graphene surface to maximize van der Waals interactions, predisposing most compounds to lie flat on its basal plane. Here we describe a tripodal motif that binds multivalently to graphene through three pyrene moieties and projects easily varied functionality away from the surface. The thermodynamic and kinetic binding parameters of a tripod bearing a redox-active Co(II) bis-terpyridyl complex were investigated electrochemically. The complex binds strongly to graphene and forms monolayers with a molecular footprint of 2.3 nm(2) and a ΔG(ads) = -38.8 ± 0.2 kJ mol(-1). Its monolayers are stable in fresh electrolyte for more than 12 h and desorb from graphene 1000 times more slowly than model compounds bearing a single aromatic binding group. Differences in the heterogeneous rate constants of electron transfer between the two compounds suggest that the tripod projects its redox couple away from the graphene surface. 相似文献