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131.
Mette Kristensen Francesco Savorani Gitte Ravn-Haren Morten Poulsen Jaroslaw Markowski Flemming H. Larsen Lars O. Dragsted Søren B. Engelsen 《Metabolomics : Official journal of the Metabolomic Society》2010,6(1):129-136
Risk of cardiovascular disease is related to cholesterol distribution in different lipoprotein fractions. Lipoproteins in
rodent model studies can only reliably be measured by time- and plasma-consuming fractionation. An alternative method to measure
cholesterol distribution in the lipoprotein fractions in rat plasma is presented in this paper. Plasma from two rat studies
(n = 68) was used in determining the lipoprotein profile by an established ultracentrifugation method and proton nuclear magnetic
resonance (NMR) spectra of replicate samples was obtained. From the ultracentrifugation reference data and the NMR spectra,
an interval partial least-square (iPLS) regression model to predict the amount of cholesterol in the different lipoprotein
fractions was developed. The relative errors of the prediction models were between 12 and 33% and had correlation coefficients
(r) between 0.96 and 0.84. The models were tested with an independent test set giving prediction errors between 19 and 46%
and r between 0.96 and 0.76. Prediction of High, Low and Very Low Density Lipoprotein (HDL, LDL and VLDL) and total cholesterol
was conducted in a study where rats had been supplemented with two doses of air-dried apple-powder. No significant difference
in LDL, VLDL and total cholesterol was observed between the groups. The high apple-powder (20%) group had significantly lower
HDL cholesterol (11%, P = 0.0452) than the control group. It is concluded that the iPLS approach yielded excellent regression models and thus univocal
established chemometric analysis of NMR spectra of rat plasma as a strong and efficient way to quantify lipoprotein fractions
in rat studies. 相似文献
132.
We consider a three-variable forest pest model, proposed by Rinaldi & Muratori (1992) [Rinaldi, S., Muratori, S., 1992. Limit cycles in slow–fast forest–pest models. Theor. Popul. Biol. 41, 26–43]. The model allows relaxation oscillations where long pest-free periods are interspersed with outbreaks of high pest concentration. For small values of the timescale of the young trees, the model can be reduced to a two-dimensional model. By a geometrical analysis we identify a canard explosion in the reduced model, that is, a change over a narrow parameter interval from outbreak dynamics to small oscillations around an endemic state. For larger values of the timescale of the young trees the two-dimensional approximation breaks down, and a broader parameter interval with mixed-mode oscillations appear, replacing the simple canard explosion. The analysis only relies on simple and generic properties of the model, and is expected to be applicable in a larger class of multiple timescale dynamical models. 相似文献
133.
J E Morten 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1986,49(3):485-493
Retinoblastoma may be hereditary or non-hereditary. The hereditary form involves either a predisposing gene transmissible as an autosomal dominant or a deletion at chromosome 13q14. An abnormal cellular response to ionizing radiation was suggested by the occurrence of secondary neoplasms within the field of therapeutic radiation in hereditary retinoblastoma patients. Hereditary retinoblastoma patients also show a predisposition to second neoplasms not related to therapy. In vitro studies on the radiation response of cells from retinoblastoma patients have generated conflicting results. Some laboratories, including our own, find that survival following ionizing irradiation of fibroblasts is within the normal range, other laboratories find an abnormal decrease in cell survival. X-ray-induced chromosome damage in G0-irradiated lymphocytes was slightly elevated compared to control subjects. Recent studies using chromosome 13 genetic markers suggest that retinoblastoma tumour cells are homo- or hemi-zygous for the mutant retinoblastoma gene. It seems unlikely that the mutant gene causes sensitivity to ionizing radiation but any tendency to chromosomal rearrangement in a gene carrier would increase the probability of tumour development. 相似文献
134.
The validity of the Michaelis–Menten–Briggs–Haldane approximation for single enzyme reactions has recently been improved by
the formalism of the total quasi-steady-state approximation. This approach is here extended to fully competitive systems,
and a criterion for its validity is provided. We show that it extends the Michaelis–Menten–Briggs–Haldane approximation for
such systems for a wide range of parameters very convincingly, and investigate special cases. It is demonstrated that our
method is at least roughly valid in the case of identical affinities. The results presented should be useful for numerical
simulations of many in vivo reactions. 相似文献
135.
Sulfate reduction rates and biogeochemical parameters of fish farm sediments across the Mediterranean were investigated in
the order to evaluate the potential effects of organic matter inputs on habitat quality for the common seagrass Posidonia oceanica. Four study sites were selected in Spain, Italy, Greece and Cyprus to represent the Mediterranean basin. P. oceanica was found in immediate vicinity of all the farms, which were located at physically exposed sites about 1 km from the shore
lines. Organic matter accumulation, sulfate reduction rates and sulfur pools were measured in depth profiles along transects
from the farms in both bare and vegetated sediments. Results show that although the organic matter accumulation was minor
at the sites (POC < 2.8% DW), the sulfate reduction rates were high, in particular at the largest farm in Italy (up to 212 mmol m−2 d−1), similar to rates found at shallower, temperate fish farm sites, where higher sedimentation rates can be expected. Sulfate
reducing bacteria in these low-organic, carbonate-rich Mediterranean sediments respond strongly to organic matter loadings
and cause habitat degradation. Sulfate reduction rates measured in the P. oceanica sediments were among the highest recorded (7.8–42.0 mmol m−2 d−1) similar to rates found in degrading meadows impacted by organic matter loadings. As sulfate reduction rates were correlated
with the sedimentation rates along the transects rather than organic matter pools this suggests mineralization processes were
controlled by organic matter loading in fish farm sediments. The vegetated sediments near the net cages were more reduced
due to accumulation of sulfides compared to control sites, which is a possible contributing factor to the observed seagrass
decline in the farm surroundings. It is recommended that Mediterranean fish farms are placed in areas with rapid dispersal
of particulate waste products to minimize organic matter loading of the sediments and thereby preserve habitat quality for
benthic fauna and flora. 相似文献
136.
A general feature of the demography of large ungulates is that many demographic traits are dependent on female body mass at
early ages. Thus, identifying the factors affecting body mass variation can give important mechanistic understanding of demographic
processes. Here we relate individual variation in autumn and winter body mass of moose calves living at low density on an
island in northern Norway to characteristics of their mother, and examine how these relationships are affected by annual variation
in population density and climate. Body mass increased with increasing age of their mother, was lower for calves born late
in the spring, decreased with litter size and was larger for males than for female calves. No residual effects of variation
in density and climate were present after controlling for annual variation in mother age and calving date. The annual variation
in adult female age structure and calving date explained a large part (71–75%) of the temporal variation in calf body mass.
These results support the hypotheses that (a) body mass of moose calves are affected by qualities associated with mother age
(e.g. body condition, calving date); and (b) populations living at low densities are partly buffered against temporal fluctuations
in the environment. 相似文献
137.
138.
Morten IJ Gosal WS Radford SE Hewitt EW 《The Journal of biological chemistry》2007,282(40):29691-29700
Dialysis related amyloidosis is a serious complication of long-term hemodialysis in which beta(2)-microglobulin (beta(2)m) forms amyloid fibrils that deposit predominantly in cartilaginous tissues. How these fibrils form in vivo, however, is poorly understood. Here we perform a systematic investigation into the role of macrophages in the formation and degradation of beta(2)m amyloid fibrils, building on observations that macrophages are found in association with beta(2)m amyloid deposits in vivo and that these cells contain intra-lysosomal beta(2)m amyloid. In live cell imaging experiments we demonstrate that macrophages internalize monomeric beta(2)m, whereupon it is sorted to lysosomes. At lysosomal pH beta(2)m self-associates in vitro to form amyloid-like fibrils with an array of morphologies as visualized by atomic force microscopy. Cleavage of the monomeric protein by both macrophages and lysosomal proteases isolated from these cells results in the rapid degradation of the monomeric protein, preventing amyloid formation. Incubation of macrophages with preformed fibrils revealed that macrophages internalize amyloid-like fibrils formed extracellularly, but in marked contrast with the monomeric protein, the fibrils were not degraded within macrophage lysosomes. Correspondingly beta(2)m fibrils were highly resistant to degradation by high concentrations of lysosomal proteases isolated from macrophages. Despite their enormous degradative capacity, therefore, macrophage lysosomes cannot ameliorate dialysis-related amyloidosis by degrading pre-existing amyloid fibrils, but lysosomal proteases may play a protective role by eliminating amyloid precursors before beta(2)m fibrils can accumulate in what may represent an otherwise fibrillogenic environment. 相似文献
139.
140.
A Wetland Change Model has been developed to identify the vulnerability of coastal wetlands at broad spatial (regional to
global (mean spatial resolution of 85 km)) and temporal scales (modelling period of 100 years). The model provides a dynamic
and integrated assessment of wetland loss, and a means of estimating the transitions between different vegetated wetland types
and open water under a range of scenarios of sea-level rise and changes in accommodation space from human intervention. This
paper is an overview of key issues raised in the process of quantifying broad-scale vulnerabilities of coastal wetlands to
forcing from sea-level rise discussing controlling factors of tidal range, sediment availability and accommodation space,
identification of response lags and defining the threshold for wetland loss and transition. 相似文献