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891.
Summary Water extracts of foliage ofAster macrophyllus, Lonicera tatarica, Solanum dulcamara, Solidago gigantea, Prunus serotina, andRubus idaeus var.strigosus, collected from the ground vegetation of a red pine (Pinus resinosa Ait.) plantation, were tested for potential allelopathic effects on seed germination, radicle elongation, and growth of red pine seedlings. Seed germination was not significantly affected by extracts, but radicle elongation of newly germinated seeds was reduced by up to 48% compared to controls. All extracts variously inhibited height growth, formation of secondary needles, and dry weight increment of young red pine seedlings during a seven-week experiment. Total dry weight of seedlings treated with Lonicera extract was only 46% that of control plants. Phosphorus concentration in needles treated with Lonicera or Solidago extracts was significantly lower than that of controls. Growth inhibition was not mediated by pH effects or osmotic potentials of the extracts. The data suggest that allelopathic inhibition of red pine is possible, but additional field experiments are needed to evaluate the significance of allelopathy in red pine plantations.Research conducted by the College of Agricultural and Life Sciences. University of Wisconsin-Madison. 相似文献
892.
Jeroen den Hertog Ineke Stulen Freek Posthumus Hendrik Poorter 《Physiologia plantarum》1998,103(4):451-460
To assess the interactions between concentration of atmospheric CO2 and N supply, the response of Plantago major ssp. pleiosperma Pilger to a doubling of the ambient CO2 concentration of 350 µl l?1 was investigated in a range of exponential rates of N addition. The relative growth rate (RGR) as a function of the internal plant nitrogen concentration (Ni), was increased by elevated CO2 at optimal and intermediate Ni. The rate of photosynthesis, expressed per unit leaf area and plotted versus Ni. was increased by 20-30% at elevated CO2 for Ni above 30 mg N g?1 dry weight. However, the rate of photosynthesis, expressed on a leaf dry matter basis and plotted versus Ni, was not affected by the CO2 concentration. The allocation of dry matter between shoot and root was not affected by the CO2 concentration at any of the N addition rates. This is in good agreement with theoretical models. based on a balance between the rate of photosynthesis of the shoot and the acquisition of N by the roots. The concentration of total nonstructural carbohydrates (TNC) was increased at elevated CO2 and at N limitation, resulting in a shift in the partitioning of photosynthates from structural to nonstructural and, in terms of carbon balance, unproductive dry matter. The increase in concentration of TNC led to a decrease in both specific leaf area (SLA) and Ni at all levels of nutrient supply, and was the cause of the increased rate of photosynthesis per unit leaf area. Correction of the relationship between RGR and Ni for the accumulation of TNC made the effect of elevated CO2 on the relationship between RGR and Ni disappear. We conclude that the shift in the relationship between RGR and Ni was due to the accumulation of TNC and not due to differences in physiological variables such as photosynthesis and shoot and root respiration, changes in leaf morphology or allocation of dry matter. 相似文献
893.
Oil and eicosapentaenoic acid production by the diatom Phaeodactylum tricornutum cultivated outdoors in Green Wall Panel (GWP®) reactors 下载免费PDF全文
Liliana Rodolfi Natascia Biondi Alessia Guccione Niccolò Bassi Massimo D'Ottavio Gimena Arganaraz Mario R. Tredici 《Biotechnology and bioengineering》2017,114(10):2204-2210
894.
With a glucose-limited chemostat culture of Bacillus stearothermophilus, increasing the incubation temperature progressively from 45°C to 63°C led to a progressive marked increase in the maintenance rates of glucose and oxygen consumption. Hence, at a fixed low dilution rate the yield values with respect to glucose and oxygen decreased substantially with increased temperature. However, the apparent Y
glucose
max
and
values did not decrease but actually increased with temperature, being highest at 63°C (i.e., close to the maximum growth temperature). With glucose-sufficient cultures growing at a fixed low dilution rate (0.2 h–1) and at their optimum temperature (55°C), glucose and oxygen consumption rates invariably were higher than that of a corresponding glucose-limited culture. Cation (K+ or Mg2+)-limited cultures expressed the highest metabolic rates and with the K+ limited culture this rate was found to be very markedly temperature dependent. As the temperature was increased from 45°C to 63°C the rate of glucose consumption increased 1.8-fold, and that of oxygen consumption by 3.7-fold. The culture pH value also exerted a noticeable effect on the metabolic rate of a glucose-limited culture, particularly at the extremes of pH tolerance (5.5 and 8.5, respectively). A K+-limited culture was less affected with respect to metabolic rate by the culture pH value though the steady state bacterial concentration, and thus the cellular K+ content, changed substantially. These results are discussed in relation to previous findings of the behaviour of this organism in batch culture, and to the behaviour of other thermophilic Bacillus species in chemostat culture. 相似文献
895.
E. W. TAYLOR A. J. INNES 《Biological journal of the Linnean Society. Linnean Society of London》1988,34(3):229-247
The evolution of air-breathing in land crabs is associated with a progressive shift in the primary site of respiratory gas exchange from the diffusion-limited gills used for water-breathing, via a simple 'cutaneous' lung surface to the perfusion-limited, invaginated lung described in the mountain crab, Pseudothelphusa garmani. The reduced diffusion limitation over the lungs facilitates oxygen transfer from air to the tissues at lower ventilation rates but is associated with accumulation of carbon dioxide. A potential respiratory acidosis is buffered by the respiratory pigment haemocyanin and by elevation of haemolymph bicarbonate levels. These changes parallel those described in vertebrates but air-breathing crustaceans maintain relatively low carbon dioxide levels in the haemolymph, either by retaining an aquatic route for its elimination over the reduced gills or by blowing it off across the lung. Maintenance of low carbon dioxide levels may be associated with a limited capacity to buffer against an acidosis due to low levels of circulating haemocyanin (i.e. crustaceans lack red blood cells). This may ultimately limit their survival in air as an acidosis will reduce oxygen transport due to a marked Bohr effect on haemocyanin. The primary role of an invaginated lung may be to reduce rates of water loss in air. 相似文献
896.
Vertical distribution and release characteristics of phosphorus forms in the sediments from the river inflow area of Dianchi Lake,China 总被引:1,自引:0,他引:1
Columnar sediment samples were collected from five representative river inflow areas of Dianchi Lake, China. The vertical distribution of each form of P were tested. Results showed that the concentration of TP in the sediments from areas A, B, C, D and E in the order of D > B > A > C > E, and the average concentration of D, B, A, C and E were 2991, 2064, 1308, 879, and 759 mg?kg?1, respectively. The concentration of Ex-P, Fe/Al-P, Ca-P and Org-P all decreased with increasing depth. The release of Ex-P was significantly related to TP whereas the Fe/Al-P was not significantly related to TP in the samples from areas polluted by domestic sewage. However, the release of Ex-P and Fe/Al-P were both significantly related to TP in the samples from areas polluted by phosphate mining and phosphate fertilizer application. The results of equilibrium P concentration (EPC0) analysis showed that P in the sediments of areas A, D and E were the source of P in Dianchi Lake, and the P in the sediments of areas B and C were in relative equilibrium with the overlying water. 相似文献
897.
Mark R. Sullivan 《Critical reviews in biochemistry and molecular biology》2013,48(3):193-207
Proliferation requires that cells accumulate sufficient biomass to grow and divide. Cancer cells within tumors must acquire a variety of nutrients, and tumor growth slows or stops if necessary metabolites are not obtained in sufficient quantities. Importantly, the metabolic demands of cancer cells can be different from those of untransformed cells, and nutrient accessibility in tumors is different than in many normal tissues. Thus, cancer cell survival and proliferation may be limited by different metabolic factors than those that are necessary to maintain noncancerous cells. Understanding the variables that dictate which nutrients are critical to sustain tumor growth may identify vulnerabilities that could be used to treat cancer. This review examines the various cell-autonomous, local, and systemic factors that determine which nutrients are limiting for tumor growth. 相似文献
898.
The green alga Chlamydomonas reinhardtii Dangeard CW-15 exhibited very low rates of plasma-membrane Fe(III) reductase activity when grown under Fe-sufficient conditions.
After switching the medium to an Fe-free formulation, both ferricyanide reductase and ferric chelate reductase activities
rapidly increased, reaching a maximum after 3 d under iron-free conditions. Both of the Fe(III) reductase activities increased
in parallel over time, they exhibited similar K
m values (approximately 10 μM) with respect to Fe(III), displayed the same pH profile of activity, and both exhibited the same
degree of light stimulation which could be inhibited by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU). Furthermore, ferricyanide
competitively inhibited ferric chelate reduction by iron-limited cells. These results indicate that both Fe(III) reductase
activities were mediated by the same iron-limitation-induced plasma-membrane reductase. No evidence was found for the presence
of Fe(III)-reducing substances in the culture medium, or for the involvement of active oxygen species in the process of Fe(III)
reduction. Chlamydomonas reinhardtii appears to respond to iron limitation in a manner similar to Strategy I higher plants.
Received: 24 June 1997 / Accepted: 2 August 1997 相似文献
899.
Transparent exopolymer particle production and aggregation by a marine planktonic diatom (Thalassiosira weissflogii) at different growth rates 下载免费PDF全文
Transparent exopolymer particles (TEP) play an important role in the ocean carbon cycle as they are sticky and affect particle aggregation and the biological carbon pump. We investigated the effect of growth rate on TEP production in nitrogen limited semi‐continuous cultures of the diatom Thalassiosira weissflogii (Grunow) G. Fryxell & Hasle. Steady‐state diatom concentrations and other indicators of biomass (chl a, and total carbohydrate) were inversely related to growth rate, while individual cell volume increased with growth rate. There was no change in total TEP area with growth rate; however, individual TEP were larger at high growth rates and the number of individual TEP particles was lower. TEP concentration per cell was higher at higher growth rates. SYTOX Green staining showed that <5% of the diatom population had permeable cell membranes, with the proportion increasing at low growth rates. However, TEP production rates were greater at high growth rates, refuting our hypothesis that TEP formation is dependent on dying cells with compromised cell membranes in a diatom population. Measurements of particle size distribution in the cultures using laser scattering showed that they were most aggregated at high growth rates. These results indicate a coupling between TEP production and growth rate in diatoms under N limitation, with fast growing T. weissflogii producing more TEP and aggregates. 相似文献
900.
Gabriela Zuquim Flávia R. C. Costa Jefferson Prado Ricardo Braga-Neto 《Biodiversity and Conservation》2009,18(1):151-166
Extrapolation of local abundance–environment relationships to broader scales provides species distribution models used for
conservation planning. We investigated the importance of environmental heterogeneity and geographic distance on pteridophyte
species spatial distribution on 38 plots of 250 × 2.5 m distributed over 90 km2 in Central Amazon. Inclusion of canopy openness in our models increased the capacity of predicting community composition
even under the narrow range of canopy openness found in our plots. Nevertheless, there was still a large amount of unexplained
variance (55–65%). The response of the community to the light gradient was hierarchical and we did not find evidences of light
partitioning. Most species were concentrated in low light plots but a few common and abundant occurred along the entire gradient.
Soil properties were the major determinants of community composition. Contrary to similar studies, slope was not a good predictor
of pteridophyte community composition, indicating that this relationship may be site-specific. There was no correlation between
floristic distances and geographic distances. We concluded that mesoscale turnover is low, although locally environmental
variation determines high turnover of species. Studies among different Amazonian physiognomies tend to find high levels of
beta-diversity. However, coarse comparisons can not reveal subtle patterns that are relevant for biodiversity conservation
planning. This study found some important changes on pteridophyte community within the same type of forest, mainly related
to environmental heterogeneity, even in narrow ranges of environmental variation. 相似文献