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61.
Ramos PH Coumans RG Deutman AB Smits JM de Gelder R Elemans JA Nolte RJ Rowan AE 《Journal of the American Chemical Society》2007,129(17):5699-5702
The threading behavior of a zinc analogue of a previously reported processive manganese porphyrin catalyst onto a series of polymers of different lengths is reported. It is demonstrated that the speed of the threading process is determined by the opening of the cavity of the toroidal porphyrin host, which can be tuned with the help of axial ligands that coordinate to the metal center in the porphyrin. 相似文献
62.
van Bommel MR Berghe IV Wallert AM Boitelle R Wouters J 《Journal of chromatography. A》2007,1157(1-2):260-272
Chromatographic and spectroscopic techniques are evaluated for the analysis of early synthetic dyes. The research focuses on the analysis of dyestuffs that were developed and used in the period 1850-1900, which has not been well investigated so far. The aim of this study was to develop and evaluate techniques that can be applied in the field of culture and art. A selection of 65 synthetic dyestuffs was chosen to investigate the usefulness of the analytical techniques applied. As a case study three embroideries, designed by the well-known 19th century French painter Emile Bernard, were investigated to obtain more information about the use and behaviour of synthetic dyes. 相似文献
63.
Rene Hornung Mathias K. Fehr Jill Monti-Frayne Tatiana B. Krasieva Bruce J. Tromberg Michael W. Berns Yona Tadir 《Photochemistry and photobiology》1999,70(4):624-629
Photodynamic therapy (PDT) uses light to activate a photosensitizer that has been absorbed or retained preferentially by cancer cells after systemic administration. The first pegylated photosensitizer, tetrakis-(m-methoxypolyethylene glycol) derivative of 7,8-dihydro-5,10,15,20-tetrakis(3-hydroxyphenyl)-21,23-[H]-porphyrin (PEG-m-THPC), was evaluated to target selectively unresectable pelvic ovarian cancer bulks. Our goals were two-fold: (1) to establish an ovarian cancer model suitable for the development of debulking techniques and (2) to characterize the pharmacokinetics and tumor selectivity of PEG-m-THPC by fluorescence microscopy. NuTu-19 ovarian cancer cells were injected into the caudal part of the right psoas muscle of Fisher rats. Five weeks later, 30 mg/kg body weight of PEG-m-THPC was injected intravenously. Necropsy was performed between 4 and 10 days following drug application, and fluorescence of the tumor and various abdominal organs was measured. All rats developed bulky pelvic tumors with an average diameter of 2.6 cm (+/- 0.6 SD). Tumor masses were encompassing and infiltrating pelvic organs in a similar manner to ovarian cancers in humans. Fluorescence of cancer tissue was maximal 8-10 days following drug application. At 8 days, the tumor-to-tissue ratio was 40:1 (+/- 12 SE) for most abdominal organs. We conclude that this tumor model may be used for the study of new pelvic debulking techniques, and that the tumor selectivity of PEG-m-THPC is exceptionally high 8 days after drug application. Based on these data, we are currently developing a PDT-based minimally invasive debulking technique for advanced ovarian cancer. 相似文献
64.
65.
Viktor A. Tafeenko Olga V. Kaukova Rene Peschar Aleksandr V. Petrov Leonid A. Aslanov 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(10):m421-m423
The crystal structure of the title potassium salt, K+·C8HN4O2−, of the organic anion 3‐cyano‐4‐(dicyanomethylene)‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate shows that the dicyanomethylene moiety is able to accept an electron in the same way as does tetracyanoethylene, to yield the novel product. The organic anion is nearly planar, with deviations caused by steric crowding among the exocyclic cyano groups. The K+ cations lie within tricapped trigonal prisms that stack to form channels. The three‐dimensional structure is completed by the formation of hydrogen‐bonded chains by the anions. 相似文献
66.
67.
Hector Rene Vega-Carrillo M. R. Martinez-Blanco Victor Martin Hernandez-Davila Jose Manuel Ortiz-Rodriguez 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(3):615-618
Artificial neural networks have been applied to unfold the neutron spectra and to calculate the effective dose, the ambient equivalent dose, and the personal dose equivalent for 252Cf, 241Am–Be, and 239Pu–Be neutron sources. The count rates that these neutron sources produce in a Bonner Sphere Spectrometer with a 6LiI(Eu) were utilized as input in both artificial neural networks. Spectra and the ambient dose equivalent were also obtained with BUNKIUT code and the UTA4 response matrix. With both procedures spectra and ambient dose equivalent agrees in less than 10%. The Artificial neural network technology is an alternative procedure to unfold neutron spectra and to perform neutron dosimetry. 相似文献
68.
Moran AM Maddox JB Hong JW Kim J Nome RA Bazan GC Mukamel S Scherer NF 《The Journal of chemical physics》2006,124(19):194904
Optoelectronic properties of a polyphenylenevinylene-based oligomer and its paracylophane-linked dimer are studied using a variety of experimental and theoretical techniques. Despite the symmetrical structure and redshifted absorption of the dimer versus the monomer, an exciton picture is not the most appropriate. Electronic structure calculations establish changes in charge density upon optical excitation and show localized excitations that cannot be accounted for by a simple Frenkel exciton model. Visible frequency pump-probe anisotropy measurements suggest that the dimer should be considered as a three-level system with a fast, approximately 130 fs, internal conversion from the higher to lower energy excited electronic state. Signatures of nuclear relaxation processes are compared for electric field-resolved transient grating and two-dimensional photon echo spectra. These measurements reveal that nuclear relaxation occurs on similar time scales for the monomer and dimer. The connection between the spectral phase of four-wave mixing signals and the time dependent width of a nuclear wave packet is discussed. Semiempirical electronic structure and metropolis Monte Carlo calculations show that the dominant line broadening mechanisms for the monomer and dimer are associated with inter-ring torsional coordinates. Together, the theoretical calculations and electric field-resolved four-wave mixing experiments suggest that while the structure of dimer is more rigid than that of monomer, the difference in their rigidities is not sufficient to slow down excited state relaxation of dimer with respect to the monomer. 相似文献
69.
Uttiya?SenguptaEmail author Hassan?Nemati Bendiks?J.?Boersma Rene?PecnikEmail author 《Flow, Turbulence and Combustion》2017,99(3-4):909-931
This work investigates fully developed turbulent flows of carbon-dioxide close to its vapour-liquid critical point in a channel with a hot and a cold wall. Two direct numerical simulations are performed at low Mach numbers, with the trans-critical transition near the channel centre and the cold wall, respectively. An additional simulation with constant transport properties is used to selectively investigate the effect of the non-linear equation of state on turbulence. Compared to the case where the pseudo-critical transition occurs in the channel center, the case with the pseudo-critical transition close to the cold wall reveals that compressibility effects can exist in the near-wall region even at low Mach numbers. An analysis of the velocity streaks near the hot and the cold walls also indicates a greater degree of streak coherence near the cold wall. A comparison between the constant and variable viscosity cases at the same Reynolds number, Mach number and having the same isothermal wall boundary conditions reveals that variable viscosity increases turbulence near the cold wall and also causes higher velocity gradients near the hot wall. We also show that the extended van Driest transformation results in a better agreement of the velocity profile with the log-law of the wall compared to the standard van Driest transformation. The semi-locally scaled turbulent velocity fluctuations and the turbulent kinetic energy budgets on the hot and the cold sides of the channel collapse on top of each other, thereby establishing the validity of Morkovin’s hypothesis. 相似文献
70.
Sandpile-based models have successfully shed light on key features of nonlinear relaxational processes in nature, particularly the occurrence of fat-tailed magnitude distributions and exponential return times, from simple local stress redistributions. In this work, we extend the existing sandpile paradigm into an inter-sandpile cascade, wherein the avalanches emanating from a uniformly-driven sandpile (first layer) is used to trigger the next (second layer), and so on, in a successive fashion. Statistical characterizations reveal that avalanche size distributions evolve from a power-law p(S)≈S−1.3 for the first layer to gamma distributions p(S)≈Sαexp(−S/S0) for layers far away from the uniformly driven sandpile. The resulting avalanche size statistics is found to be associated with the corresponding waiting time distribution, as explained in an accompanying analytic formulation. Interestingly, both the numerical and analytic models show good agreement with actual inventories of non-uniformly driven events in nature. 相似文献