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881.
There are various different detectors, which can be used for radiotherapy measurements, and more are about to be adopted. Hybrid pixel detectors (HPD) have been originally developed for the high energy physics. However, over the last few years they also expanded in the medical physics. Novel 2D detector Pantherpix is a HPD designed specifically for the radiotherapy. In this article, its properties are characterised and an assessment of its use in radiotherapy photon beams is provided. Properties such as response stability, response linearity, angular dependence and energy dependence were studied. In order to prove sufficient clinical quality for relative dosimetry, further measurements were undertaken (i.e. dose profiles and collimator scatter factors). Acquired results were compared with ion chamber and gafchromic film results. Namely the applicability of PhPix for cobalt beam therapy, which is still widely used (and will be used in near future) in economically less developed countries, is considered. 相似文献
882.
The mechanism for the oxidation of catechol by catechol oxidase has been studied using B3LYP hybrid density functional theory.
On the basis of the X-ray structure of the enzyme, the molecular system investigated includes the first-shell protein ligands
of the two metal centers as well as the second-shell ligand Cys92. The cycle starts out with the oxidized, open-shell singlet
complex with oxidation states Cu2(II,II) with a μ-η2:η2 bridging peroxide, as suggested experimentally, which is obtained from the oxidation of Cu2(I,I) by dioxygen. The substrate of each half-reaction is a catechol molecule approaching the dicopper complex: the first
half-reaction involves Cu(I) oxidation by peroxide and the second one Cu(II) reduction. The quantitative potential energy
profile of the reaction is discussed in connection with experimental data. Since no protons leave or enter the active site
during the catalytic cycle, no external base is required. Unlike the previous density functional theory study, the dicopper
complex has a charge of +2. 相似文献
883.
Giuliano F. Panza Ivanka Paskaleva Petia Dineva Cristina La Mura 《Rendiconti Lincei》2009,20(2):91-116
The study solves 2D elastodynamic model for seismic in-plane wave propagation in laterally inhomogeneous geological profiles
situated in a vertically inhomogeneous half-space with a seismic source. For the aim, an efficient hybrid Modal Summation-Boundary
Integral Equation Method (MSM-BIEM) is applied. The MSM is used as a tool for the simulation of wave propagation from the
source position to the local multilayered laterally inhomogeneous geological profile, where the BIEM is applied. The BIEM
is based on the frequency-dependent fundamental solution of the governing equation in elastodynamics and the hybrid method
works in the frequency domain. The inverse FFT solution is applied to obtain time histories. The hybrid tool is applied to
several models for the investigation of local site effects due to: (a) the impedance contrasts between soil layers, (b) surface
topography and lateral inhomogeneity, (c) the seismic source properties and (d) the existence of water saturation in soils.
The application of the modeling tool is a contribution to the seismic risk analysis of Sofia city. 相似文献
884.
885.
Biologically produced alcohols are of great current interest for renewable solvents and liquid transportation fuels. While bioethanol is now produced on a massive scale, butanol has superior fuel characteristics and an additional value as a solvent and chemical feedstock. Butanol production has been demonstrated at ambient temperatures in metabolically-engineered mesophilic organisms, but the ability to engineer a microbe for in vivo high-temperature production of commodity chemicals has several distinct advantages. These include reduced contamination risk, facilitated removal of volatile products, and a wide temperature range to modulate and balance both the engineered pathway and the host׳s metabolism. We describe a synthetic metabolic pathway assembled from genes obtained from three different sources for conversion of acetyl-CoA to 1-butanol, and 1-butanol generation from glucose was demonstrated near 70 °C in a microorganism that grows optimally near 100 °C. The module could also be used in thermophiles capable of degrading plant biomass. 相似文献
886.
Chandrasekhar Reddy Gade Nagendra K. Sharma 《Bioorganic & medicinal chemistry letters》2017,27(24):5424-5428
This report describes the synthesis of C-rich sequence, cytosine pentamer, of aep-PNA and its biophysical studies for the formation of hybrid DNA:aep-PNAi-motif structure with DNA cytosine pentamer (dC5) under acidic pH conditions. Herein, the CD/UV/NMR/ESI-Mass studies strongly support the formation of stable hybrid DNA i-motif structure with aep-PNA even near acidic conditions. Hence aep-PNA C-rich sequence cytosine could be considered as potential DNA i-motif stabilizing agents in vivo conditions. 相似文献
887.
A. G. Stephenson C. N. Hayes M. H. Jóhannsson J. A. Winsor 《Sexual plant reproduction》2001,14(1-2):77-83
Inbreeding reduces the level of heterozygosity, thereby exposing deleterious recessives to selection and simultaneously reducing
the number of loci expressing heterosis (overdominance). In contrast, hybridization increases the level of heterozygosity,
thereby masking deleterious recessives and simultaneously increasing the number of loci expressing heterosis. Most studies
of inbreeding depression/hybrid vigor have focused on sporophytic performance such as survivorship, vegetative growth rates,
fruit and seed production and (rarely) pollen production. Because the genetic mechanisms that underlie inbreeding depression/hybrid
vigor are relevant only to the diploid stage of the life cycle, most studies have tacitly assumed that they have no effects
on pollen performance (pollen germination, pollen tube growth rate, ability to achieve fertilization under conditions of pollen
competition). However, we reasoned that because pollen is dependent upon the sporophyte for the resources necessary to develop,
germinate and initiate tube growth, the level of heterozygosity (vigor) in the pollen-producing parent can affect pollen performance
by affecting the ability of the sporophyte to provision its pollen. In a series of studies conducted under field conditions
over 7 years, we experimentally varied the level of heterozygosity in wild gourd (Cucurbita pepo) plants (four levels of inbreeding, f = 0.75, 0.50, 0.25, 0 and a zucchini × wild gourd F1). We found that sporophytic vigor (e.g., flower and fruit production)
increased with the level of heterozygosity and that the level of heterozygosity of the sporophyte affects the in vitro and
in vivo performance of the microgametophytes it produces. These findings are analogous to the ”maternal environmental effects”
frequently observed in seeds.
Received: 29 October 2000 / Accepted: 3 May 2001 相似文献
888.
F. -X. Oury P. Brabant P. Bérard P. Pluchard 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,100(1):96-104
Multi-environmental experimentation made it possible to compare 311 hybrids and their 59 parental lines for five characters:
yield, two yield components (number of grains per m2 and 1000-grain weight), height and date of heading. At all three sites, average high-parent heterosis exceeded 6%, and our
results confirm that hybrids in general head as early as the earlier parent does and are as high as the taller parent. For
the five characters studied ecovalences were significantly lower in the F1 than in the parents, indicating a higher level
of homeostasis for hybrids. The experimental model, based on a ”top-cross” design comprised of 55 lines used as females and
four testers, made it possible to implement different hybrid-value prediction models. For yield, by far the most important
character to predict, the predictor based on the general combining ability and the per se value of the parents, appears to be the most interesting. The prediction remains, however, imperfect as specific combining
ability (SCA) has a strong impact for this character. Attempting to take account of SCA in the prediction, by using a multiplicative
model for ”male×female” interaction modelling, did not prove convincing.
Received: 15 February 1999 / Accepted: 25 July 1999 相似文献
889.
890.
W. M. Zhou K. Yoshida Y. Shintaku G. Takeda 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,82(5):657-661
Summary Flowering hybrid plants were obtained from reciprocal crosses between N. tabacum L. (2n=48) and N. repanda Willd. (2n = 48), in which cross incompatibility and hybrid inviability were manifested. Stylar pollination and ovule culture were used to overcome the cross incompatibility of stylar barriers and ovular death. It was shown that application of 2 mg/l indole-3-acetic acid (IAA) during the growth period, from the fiveto six-leaf stage to the flowering stage, is a useful and easy method to overcome hybrid inviability. 相似文献