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961.
Carbon nanotubes (CNTs) show exceptional properties that render them attractive for incorporation in a new generation of high‐performance engineering composites with tailored properties. While a great deal of work has been done toward using CNTs as a reinforcing agent in polymer composites, the full potential of CNTs has yet to be reached. In this work, two case studies were proposed in order to analyze the effectiveness of CNTs and carbon fibers (CFs) as reinforcing agents. Micromechanics models for the stiffness and strength of hybrid composites, comprising CNTs and CFs are derived by considering the concept of effective fiber. In addition, the 2009 prices of commercially available CNTs are reviewed. The strongest, the stiffest, and the cheapest CFs commercially available are compared with single walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs). The simulated results from the micromechanics models show that the use of CFs makes the acquisition of composites with maximum tensile strengths of 4.18 GPa possible. Analysis of the cost versus property relation showed that CNTs are the most viable strengthening option for achieving composites with strengths of up to 11.61 GPa. It is also shown that CFs are the most viable stiffening option, making composites with Young's moduli of up to 383 GPa possible at the expense of the material's toughness. Moreover, it is shown that, in order to achieve CNT's true potential, several challenges have to be faced. CNTs have to be produced with higher purity, longer lengths, better integrity, in larger amounts, and at lower cost. Moreover, issues such as orientation of the CNTs, their concentration, interfacial adhesion, distribution, and dispersion have to be overcome.
962.
Proving the chaoticity of some dynamical systems is equivalent to solving the hardest problems in mathematics. Conversely, classical physical systems may "compute the hard or even the incomputable" by measuring observables which correspond to computationally hard or even incomputable problems. 相似文献
963.
** Email: walter.johnston{at}baesystems.com*** Email: j.quigley{at}strath.ac.uk**** Email: lesley.walls{at}strath.ac.uk This paper considers reliability planning for a concept designfor a new system where a portfolio of possible reliability developmenttasks exists; the goal is to find a selection and sequence oftasks to achieve reliability targets subject to time constraintsat minimal cost. This is non-trivial given that each task potentiallycan expose several different weaknesses and each weakness potentiallycan be exposed by several different tasks. We use a Bayesianpoint process model to estimate the system reliability. Theprior distribution maps to a fault register and relates directlyto a set of potential engineering modifications.The likely impactof each task can be assessed using the point process model.An integer programming approach is used to sequence and scheduletasks under the constraint that contractual reliability requirementsmust be met. An illustrative example is provided and an extensionto system availability is proposed. 相似文献
964.
Haiges R Boatz JA Schroer T Yousufuddin M Christe KO 《Angewandte Chemie (International ed. in English)》2006,45(29):4830-4835
965.
Hanrahan JR Mewett KN Chebib M Matos S Eliopoulos CT Crean C Kumar RJ Burden P Johnston GA 《Organic & biomolecular chemistry》2006,4(13):2642-2649
A divergent synthesis of both diastereoisomers of (+/-)-(3-aminocyclopentane)alkylphosphinic acid is described. Both diastereoisomers are obtained in 5 steps from the key (+/-)-(3-hydroxycyclopent-1-ene)alkylphosphinate esters which are prepared via a palladium catalysed C-P bond forming reaction. 相似文献
966.
The synthesis of a series of open U-shaped bis-porphyrin cavity molecules is described, with bridged bicyclic backbones to confer rigidity, and a pendant substituted aromatic probe unit suspended on the inside of the cavity. The dimensions and flexibility of the bis-zincporphyrin cavity were probed using several different techniques. Initially the molecular ruler concept was employed, using flexible bidentate ligands as guests with a range of possible linear dimensions. Secondly, NMR methods were employed with rigid bidentate ligand guests of fixed lengths, and thirdly diffusion based NMR methods were utilised. The range of inter-porphyrin distances estimated by these methods suggests that these types of open-cavity systems have a surprising degree of flexibility. 相似文献
967.
Crosson GS Choi S Chorover J Amistadi MK O'Day PA Mueller KT 《The journal of physical chemistry. B》2006,110(2):723-732
The weathering of a specimen kaolinite clay was studied over the course of 369 d via solid-state 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and high-field 27Al MAS NMR. The chosen baseline solution conditions (0.05 mol kg-1 of Al, 2 mol kg-1 of Na+, 1 mol kg-1 of NO3-, 1 mol kg-1 of OH-, and pH approximately 13.8) approximate those of solutions leaking from waste tanks at the Hanford Site in Richland, WA. Nonradioactive Cs and Sr cations were added to this synthetic tank waste leachate (STWL) solution at concentrations of 10(-3), 10(-4), and 10(-5) molal (m) to represent their radionuclide counterparts. The transformations of silicon- and aluminum-containing solid phase species were monitored quantitatively by using NMR spectroscopy, with the resulting spectra directly reporting the influence of the initial Cs and Sr on formation and transformation of the neo-formed solids. At the lowest concentration of Cs and Sr employed (10(-5) m in each cation) peaks consistent with the formation of zeolite-like minerals were detected via 29Si and 27Al MAS NMR as early as 33 d. At concentrations of 10(-3) m in each cation, new silicon species are not detected until 93 d, although neophases containing four-coordinate aluminum were detectable at earlier reaction times via 27Al MAS NMR. At the highest magnetic field strengths employed in this NMR study, deconvolutions of resonances detected in the tetrahedral region of the 27Al MAS spectra yielded multiple components, indicating the existence of at least four new aluminum-containing phases. Two of these phases are identified as sodalite and cancrinite through comparison with diffuse-reflectance infrared (DRIFT) spectra and powder X-ray diffraction (XRD) results, while a third phase may correlate with a previously detected aluminum-rich chabazite phase. All measurable solid reaction products have been quantified via their 27Al MAS resonances acquired at high magnetic field strengths (17.6 T), and the quantitative nature of the 27Al NMR data shows that cancrinite growth increases while sodalite reaches a steady state with respect to total aluminum in the solid phases. The data also relate the coupling of Cs sorption to the ripening of feldspathoid phases in this heterogeneous system as a function of time, and illustrate the important influence of co-contaminants on the environmental reaction kinetics studied here. 相似文献
968.
Manaviazar S Frigerio M Bhatia GS Hummersone MG Aliev AE Hale KJ 《Organic letters》2006,8(20):4477-4480
A new enantioselective synthesis of Masamune's AB fragment (1) for bryostatin 7 is described. Key steps in the new route include a Meerwein-Ponndorf-Verley reduction to set the O(7) stereocenter and an alkylative union between the dithiane 6 and iodide 5 to construct the C(9)-C(10) bond. Because we have previously published a synthesis of Masamune's C-ring phenyl sulfone 2, our new route to 1 constitutes a formal total synthesis of bryostatin 7; it also corrects the previously reported spectral data for 1 in CDCl3. 相似文献
969.
Allodi MA Dunn ME Livada J Kirschner KN Shields GC 《The journal of physical chemistry. A》2006,110(49):13283-13289
It has been speculated that the presence of OH(H2O)n clusters in the troposphere could have significant effects on the solar absorption balance and the reactivity of the hydroxyl radical. We have used the G3 and G3B3 model chemistries to model the structures and predict the frequencies of hydroxyl radical/water clusters containing one to five water molecules. The reaction between hydroxyl radical clusters and methane was examined as a function of water cluster size to gain an understanding of how cluster size affects the hydroxyl radical reactivity. 相似文献
970.
Pickard FC Shepherd RL Gillis AE Dunn ME Feldgus S Kirschner KN Shields GC Manoharan M Alabugin IV 《The journal of physical chemistry. A》2006,110(7):2517-2526
We present a detailed theoretical study of geometries, electronic structure, and energies of transition states and intermediates completing the full Bergman cycloaromatization pathway of ortho-substituted enediynes with a focus on polar and steric contributions to the kinetics and thermodynamics of hydrogen abstraction. This study provides a rare unambiguous example of remote substitution that affects reactivity of a neutral reactive intermediate through an sigma framework. 相似文献