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981.
It is timely to evaluate the role of protozoa as model organisms given their diversity, abundance and versatility as well as the economic and ethical pressures placed on animal-based experimentation. We first define the term model organism and then examine through examples why protozoa make good models. Our examples reflect major issues including evolution, ecology, population and community biology, disease, the role of organelles, ageing, space travel, toxicity and teaching. We conclude by recognising that although protozoa may in some cases not completely mimic tissue- or whole-animal-level processes, they are extremely flexible and their use should be embraced. Finally, we offer advice on obtaining emergent model protozoa. 相似文献
982.
983.
The Fe content in animal feeds is highly variable. The availability of Fe in feeds varies with the feed and the form in which Fe is present. The present study reports the effect of the addition of different concentrations of Fe from yeast biomass on Fe bioavailability and Fe level in rat liver, compared with a diet containing Fe-sulphate (Fe-sulphate) addition (control) and with a diet without any addition of Fe. Male Wistar rats were fed ad libitum for 10 days a diet with different levels of Fe-enriched yeast biomass (20, 35 and 50 mg of Fe), or Fe-sulphate diet (50 mg of Fe) or without Fe addition. Faeces and urine were collected for Fe analyses during the last 5 days of the test period. The results clearly showed a highly significant (P < 0.001) better bioavailability of Fe from Fe-enriched yeast biomass, independent of the level of Fe in the diet. This was on average 36% higher than the availability of Fe from the Fe-sulphate-enriched diet. Liver Fe storage depended on the level of Fe in the diet from yeast biomass. A significantly lower amount of Fe was found to be incorporated in the liver in the group with an inorganic source of Fe (Fe-sulphate) in the diet. 相似文献
984.
Sykorová B Kuresová G Daskalova S Trcková M Hoyerová K Raimanová I Motyka V Trávnícková A Elliott MC Kamínek M 《Journal of experimental botany》2008,59(2):377-387
The manipulation of cytokinin levels by senescence-regulated expression of the Agrobacterium tumefaciens ipt gene through its control by the Arabidopsis SAG12 (senescence-associated gene 12) promoter is an efficient tool for the prolongation of leaf photosynthetic activity which potentially can affect plant productivity. In the present study, the efficiency of this approach was tested on wheat (Triticum aestivum L.)-a monocarpic plant characterized by a fast switch from vegetative to reproductive growth, and rapid translocation of metabolites from leaves to developing grains after anthesis. When compared with the wild-type (WT) control plants, the SAG12::ipt wheat plants exhibited delayed chlorophyll degradation only when grown under limited nitrogen (N) supply. Ten days after anthesis the content of chlorophyll and bioactive cytokinins of the first (flag) leaf of the transgenic plants was 32% and 65% higher, respectively, than that of the control. There was a progressive increase in nitrate influx and nitrate reductase activity. However, the SAG12::ipt and the WT plants did not show differences in yield-related parameters including number of grains and grain weight. These results suggest that the delay of leaf senescence in wheat also delays the translocation of metabolites from leaves to developing grains, as indicated by higher accumulation of ((15)N-labelled) N in spikes of control compared with transgenic plants prior to anthesis. This delay interferes with the wheat reproductive strategy that is based on a fast programmed translocation of metabolites from the senescing leaves to the reproductive sinks shortly after anthesis. 相似文献
985.
Polgár C Orosz Z Kahán Z Gábor G Jani N Cserni G Hadijev J Kulka J Sulyok Z Boross G Lázár G László Z Diczházi C Udvarhelyi N Szabó E Péntek Z Major T Fodor J 《Magyar onkologia》2008,52(3):269-277
The aim of this work is to report the preliminary results of the Hungarian multicentric randomised DCIS study. Between 2000 and 2007, 278 patients with ductal carcinoma in situ (DCIS) treated by breast-conserving surgery were randomised according to predetermined risk groups. Low/intermediate-risk patients (n=29) were randomised to 50 Gy whole-breast irradiation (WBI) or observation. High-risk cases (n=235) were allocated to receive 50 Gy WBI vs. 50 Gy WBI plus 16 Gy tumour bed boost. Very high-risk patients (patients with involved surgical margins; n=14) were randomised to 50 Gy WBI plus 16 Gy tumour bed boost or reoperation (reexcision plus radiotherapy or mastectomy alone). Immunohistochemistry (IHC) was performed to detect the expression of potential molecular prognostic markers (ER, PR, Her2, p53, Bcl-2 and Ki-67). At a median follow-up of 36 months no recurrence was observed in the low/intermediate- and very high-risk patient groups. In the high-risk group, 4 (1.7%) local recurrences and 1 (0.4%) distant metastasis occurred. No patient died of breast cancer. In the high-risk group of patients, the 3- and 5-year probability of local recurrence was 1.1% and 3.1%, respectively. The positive immunostaining for Her2 (38%), p53 (37%) and Ki-67 (44%) correlated with a high nuclear grade. Significant inverse correlation was found between the expression of ER (77%), PR (67%), Bcl-2 (64%) and grade. Preliminary results suggest that breast-conserving surgery followed by radiotherapy yields an annual local recurrence rate of less than 1% in patients with DCIS. IHC of molecular prognostic markers can assist to gain insight into the biologic heterogeneity of DCIS. 相似文献
986.
Growth form is one of the important life history traits ultimately influencing plant fitness. Potentilla palustris is a stoloniferous plant growing in a range of habitats from densely vegetated wet meadows to acidic transitional fens, and
its growth form varies according to habitat. In a four year multi-site comparative study, we investigated which biotic and
abiotic characteristics influence most its growth traits. Vegetation composition and physiognomy, as well as numerous abiotic
environmental variables, were recorded at 32 study sites located on an altitudinal gradient. Growth traits of P. palustris were best explained by the surrounding vegetation physiognomy and not by abiotic conditions, although the latter obviously
represents the factors indirectly influencing its growth. Stolon length traits and branching were positively correlated with
vegetation density and height, and negatively with altitude. Plants flowered more in taller vegetation, and leaf area was
greater in wetter sites with lower vegetation cover. Potentilla palustris appeared to be well adapted to transitional fens, but its vegetative growth was fastest in wet meadows and alluvial habitats
on highly organic humid soils. It produced more branches and larger leaves in alluvial habitats with open water, while it
had enhanced generative reproduction in wet meadows. Species composition was less important than vegetation physiognomy. In
less favorable habitat types, P. palustris prefers an escape strategy of linear growth. Internode length exhibited pronounced plasticity, increasing particularly in
tall dense vegetation of lower altitude, whereas internode number remained fairly constant over various habitats. It is evident
that both plastic low cost growth traits (internode elongation), and constant high cost traits (internode number) contribute
to the P. palustris escape strategy under tall dense vegetation. Phenotypic plasticity enhances the potential of P. palustris to grow in a wide range of habitats and so increases plant fitness on regional scale. 相似文献
987.
The chlorophyll fluorescence (F) temperature curves in a linear time-temperature heating/cooling regime were used to study
heat-induced irreversible F changes in primary green leaves of spring barley (Hordeum vulgare L. cv. Akcent). The leaf segments were heated in a stirred water bath at heating rates of 0.0083, 0.0166, 0.0333, and 0.0500
°C s−1 from room temperature up to maximal temperature T
m and then linearly cooled to 35 °C at the same rate. The F intensity was measured by a pulse-modulated technique. The results
support the existence of the two critical temperatures of irreversible F changes postulated earlier, at 45–48 and 53–55 °C.
The critical temperatures are slightly dependent on the heating rate. Two types of parameters were used to characterize the
irreversibility of the F changes: the coefficient of irreversibility μ defined as the ratio of F intensity at 35 °C at the
starting/ending parts of the cycle and the slopes of tangents of linear parts of the F temperature curve. The dependence of
μ on T
m revealed a maximum, which moved from 54 to 61 °C with the increasing heating/cooling rate v from 0.0083 to 0.0500 °C s−1, showing two basic phases of the irreversible changes. The Arrhenius and Eyring approaches were applied to calculate the
activation energies of the initial increase in μ. The values varied between 30 and 50 kJ mol−1 and decreased slightly with the increasing heating rate. 相似文献
988.
989.
The European ground squirrel (Spermophilus citellus) is considered an endangered species with declining numbers throughout Europe, most pronounced at the western margin of its
distribution area. Being extinct in Germany and Poland, the western margin of its distribution is in the Czech Republic. Here,
landscape fragmentation has restricted the ground squirrels into few and very isolated localities where local extinctions
still occur. In the present study we analysed European ground squirrels from six Czech and one Slovak localities using five
microsatellite loci as genetic marker. The results show a strong genetic differentiation among the investigated populations
(mean value of F
ST = 0.16) and high levels of inbreeding (values of F
IS ranged from 0.34 to 0.90). High level of inbreeding is generally considered to affect the viability of each population, which
could lead to extinction. One of the most important factors is the lack of migration due to the large distances between the
populations and the presence of migration barriers. Based on the results obtained we recommend a few suggestions for a conservation
management of this species. 相似文献
990.
The structure of pyrenetetrasulfonate intercalated with hydrotalcite, having the formula [Zn0.68Al0.32(OH)2][(C16H6O12S4)0.08 · x H2O], was proposed based on molecular simulations combined with experimental data (X-ray powder diffraction, thermogravimetry).
Calculations were done for samples kept at various relative humidities (0%, 84%, 98%). The appropriate models were selected
from comparison of calculated and measured diffraction patterns. Modelling revealed the arrangement of pyrenetetrasulfonate
anions, and the positions and the amount of water molecules in the interlayer space of the host structure. The results confirmed
a large variability in the arrangement of the guest species. In the sample without water molecules (0% RH), pyrenetetrasulfonate
anions formed a layer at the centre of the interlayer distance. For the sample kept at 84% RH, the anions formed two layers
at the thirds of the interlayer. For the sample kept at 98% RH, the anions became tilted with respect to the layered double
hydroxides (LDH) layers and are less organised. Water molecules were arranged in three distinct planes: one in the middle
and two at the quarters of interlayer distance. The number of water molecules obtained by the modelling basically agrees with
the water content as measured by thermogravimetry.
Figure Pyrenetetrasulfonate was intercalated into hydrotalcite and equilibrated at various relative humidities. Structural analysis
was performed using molecular simulations based on X-ray and thermogravimetric data 相似文献