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991.
Australian science has made rapid advances in the last decade in understanding eutrophication processes in inland waters and
estuaries. The freshwater research on which these advances are based was triggered by well-publicised blooms of cyanobacteria
during the 1980s and early 1990s, particularly a 1000 km long bloom on the Darling River. In estuaries the study which greatly
enhanced our understanding but simultaneously served to stimulate further research into estuarine eutrophication, the Port
Phillip Bay Study, was initially designed to address perceived problems of toxicants in the Bay but provided profound insights
into drivers for, and ecosystem responses to, eutrophication. Subsequent estuarine research has largely been stimulated by
management questions arising from Australia’s increasing coastal development for residential purposes. The research has shown
that some of the beliefs extant at the time of the blooms were incorrect. For example, it is now clear that stratification
and light penetration, not nutrient availability, are the triggers for blooms in the impounded rivers of southeastern Australia,
although nutrient exhaustion limits the biomass of blooms. Again, nitrogen seems to play as important a role as phosphorus
does in controlling the biomass of these freshwater blooms. The research has also shown that aspects of eutrophication, such
as nutrient transport, are dominated by different processes in different parts of Australia. Many of the biophysical processes
involved in eutrophication have now been quantified sufficiently for models to be developed of such processes as sediment-nutrient
release, stratification, turbidity and algal growth in both freshwater and estuarine systems. In some cases the models are
reliable enough for the knowledge gained in particular waterbodies to be applied elsewhere. Thus, there is now a firm scientific
foundation for managers to rely upon when managing algal blooms. Whilst these findings have already been presented to managers
and communities throughout Australia, there is still a considerable way to go before they are absorbed into their modus operandi. 相似文献
992.
Climatic and hydrological variability is usually high in the Pampa Plain (Argentina). However it has not studied yet how this
variability may affect the phytoplankton and zooplankton biomass and community structure in aquatic systems of this region.
The main purpose of this study was to assess flushing effects on nutrient and plankton dynamics in two interconnected very
shallow lakes of the Pampa Plain. In order to study the impact of hydrology on the plankton biomass and community structure,
we compared the summer plankton community among three consecutive years with contrasting hydrological characteristics. Water
residence time varied an order of magnitude among years and this variability was correlated to strong changes in physicochemical
and biological lake characteristics. Depending on the water discharge level, the hydrological regime within the lakes ranged
from lentic to more lotic conditions. Nutrient and phytoplankton biomass were positively related to water discharges. During
high flushing periods, nutrients import from intensive agriculture lands leads to a dramatic increase in trophic conditions.
On the other hand, macrozooplankton biomass was positively related to water residence time and showed a dramatic decrease
during high flushing years. Rotifers biomass was not affected by interannual water discharge variability during the study
period. Our results support that in case of lakes with high flushing rates, zooplankton development is dependent on water
residence time and that hydrology may have stronger effects on macrozooplankton biomass than top-down control by planktivores. 相似文献
993.
Mäkinen TM Raatikka VP Rytkönen M Jokelainen J Rintamäki H Ruuhela R Näyhä S Hassi J 《International journal of biometeorology》2006,51(1):27-36
The extent of outdoor exposure during winter and factors affecting it were examined in a cross-sectional population study in Finland. Men and women aged 25–74 years from the National FINRISK 2002 sub-study (n=6,591) were queried about their average weekly occupational, leisure-time and total cold exposure during the past winter. The effects of gender, age, area of residence, occupation, ambient temperature, self-rated health, physical activity and education on cold exposure were analysed. The self-reported median total cold exposure time was 7 h/week (8 h men, 6 h women),<1 h/week (2 h men, 0 h women) at work, 4 h/week (5 h men, 4 h women) during leisure time and 1 h/week (1 h men, 1.5 h women) while commuting to work. Factors associated with increased occupational cold exposure among men were: being employed in agriculture, forestry and industry/mining/construction or related occupations, being less educated and being aged 55–64 years. Factors associated with increased leisure-time cold exposure among men were: employment in industry/mining/construction or related occupations, being a pensioner or unemployed, reporting at least average health, being physically active and having college or vocational education. Among women, being a housewife, pensioner or unemployed and engaged in physical activity increased leisure-time cold exposure, and young women were more exposed than older ones. Self-rated health was positively associated with leisure time cold exposure in men and only to a minor extent in women. In conclusion, the subjects reported spending 4% of their total time under cold exposure, most of it (71%) during leisure time. Both occupational and leisure-time cold exposure is greater among men than women. 相似文献
994.
We have previously shown the usefulness of historical data for fermentation process optimization. The methodology developed includes identification of important process inputs, training of an artificial neural network (ANN) process model, and ultimately use of the ANN model with a genetic algorithm to find the optimal values of each critical process input. However, this approach ignores the time-dependent nature of the system, and therefore, does not fully utilize the available information within a database. In this work, we propose a method for incorporating time-dependent optimization into our previously developed three-step optimization routine. This is achieved by an additional step that uses a fermentation model (consisting of coupled ordinary differential equations (ODE)) to interpret important time-course features of the collected data through adjustments in model parameters. Important process variables not explicitly included in the model were then identified for each model parameter using automatic relevance determination (ARD) with Gaussian process (GP) models. The developed GP models were then combined with the fermentation model to form a hybrid neural network model that predicted the time-course activity of the cell and protein concentrations of novel fermentation conditions. A hybrid-genetic algorithm was then used in conjunction with the hybrid model to suggest optimal time-dependent control strategies. The presented method was implemented upon an E. coli fermentation database generated in our laboratory. Optimization of two different criteria (final protein yield and a simplified economic criteria) was attempted. While the overall protein yield was not increased using this methodology, we were successful in increasing a simplified economic criterion by 15% compared to what had been previously observed. These process conditions included using 35% less arabinose (the inducer) and 33% less typtone in the media and reducing the time required to reach the maximum protein concentration by 10% while producing approximately the same level of protein as the previous optimum. 相似文献
995.
Moreno JA Betancur MJ Buitrón G Moreno-Andrade I 《Biotechnology and bioengineering》2006,94(4):803-814
Discontinuous bioreactors may be further optimized for processing inhibitory substrates using a convenient fed-batch mode. To do so the filling rate must be controlled in such a way as to push the reaction rate to its maximum value, by increasing the substrate concentration just up to the point where inhibition begins. However, an exact optimal controller requires measuring several variables (e.g., substrate concentrations in the feed and in the tank) and also good model knowledge (e.g., yield and kinetic parameters), requirements rarely satisfied in real applications. An environmentally important case, that exemplifies all these handicaps, is toxicant wastewater treatment. There the lack of online practical pollutant sensors may allow unforeseen high shock loads to be fed to the bioreactor, causing biomass inhibition that slows down the treatment process and, in extreme cases, even renders the biological process useless. In this work an event-driven time-optimal control (ED-TOC) is proposed to circumvent these limitations. We show how to detect a "there is inhibition" event by using some computable function of the available measurements. This event drives the ED-TOC to stop the filling. Later, by detecting the symmetric event, "there is no inhibition," the ED-TOC may restart the filling. A fill-react cycling then maintains the process safely hovering near its maximum reaction rate, allowing a robust and practically time-optimal operation of the bioreactor. An experimental study case of a wastewater treatment process application is presented. There the dissolved oxygen concentration was used to detect the events needed to drive the controller. 相似文献
996.
With regard to adaptation of green ash (Fraxinus pennsylvanica
Marshall) to ecological conditions in Croatia, pollen germination and pollen tube length after 2, 4 and 6 hours were examined in vitro at 10, 15, 20 and 25°C during two years 2001 and 2002. Narrow leaved ash (F. angustifolia
Vahl) pollen served as a control in 2002. The year, time and temperature, and the interaction between time and temperature were
significant for both germination percentage and pollen tube length. Interactions year × temperature and year × time were significant
for pollen tube length only. The highest germination percentage (17.86% in 2001 and 19.40% in 2002) of green ash pollen was
at 15°C after 6 hours. The pollen tube length was greatest at 20°C (393.46 μm) in 2001 and 25°C (899.50 μm) in 2002 after
6 hours. Narrow leaved ash pollen had the highest germination percentage (19.22%) at 20°C after 6 hours and was significantly
reduced at 25°C. The pollen tube length was greatest at 25°C (518.90 μm) after 6 hours. It can be concluded that green ash
pollen has satisfactory germination in ecological conditions in Croatia and that the optimum temperature for pollen germination
is higher than 20°C. 相似文献
997.
Estimates of annual survival are essential for addressing topics in evolutionary and conservation ecology. However, most demographic studies of land birds are based on north temperate species, and few robust estimates of survival based on mark–recapture statistics are available for continental South American birds. We used time‐since‐marking models to estimate apparent survival of adult birds from 7 yr of mist netting data in the Colonche Hills. This site is one of few remaining large tracts of premontane forest in southwestern Ecuador, and an area of high priority for avian conservation. Species with sufficient data for analysis included three hummingbirds (Adelomyia melanogenys, Heliodoxa jacula, Phaethornis baroni), a cotinga (Schiffornis turdinus), and a wren (Henicorhina leucophrys). Our parameter estimates had reduced precision because the number of recaptures was small. Probability of recapture was low in three species , and moderate in two others . Adelomyia and Phaethornis had moderate apparent survival (; probability that a bird neither died nor emigrated from our survey area in a given year). Adults of Adelomyia moved seasonally, and it is possible that permanent emigration from our survey area contributed to low estimates of apparent survival. The other three species had relatively high estimates of adult apparent survival ranging from in Heliodoxa and Schiffornis to a high of in Henicorhina. 相似文献
998.
999.
Abdel-Mottaleb Y Clynen E Jalali A Bosmans F Vatanpour H Schoofs L Tytgat J 《FEBS letters》2006,580(26):6254-6258
The very first member of K(+) channels toxins from the venom of the Iranian scorpion Odonthobuthus doriae (OdK1) was purified, sequenced and characterized physiologically. OdK1 has 29 amino acids, six conserved cysteines and a pI value of 4.95. Based on multiple sequence alignments, OdK1 was classified as alpha-KTx 8.5. The pharmacological effects of OdK1 were studied on six different cloned K(+) channels (vertebrate Kv1.1-Kv1.5 and Shaker IR) expressed in Xenopus laevis oocytes. Interestingly, OdK1 selectively inhibited the currents through Kv1.2 channels with an IC50 value of 183+/-3 nM but did not affect any of the other channels. 相似文献
1000.
Multidrug resistance protein (MRP) 1 belongs to the 'C' branch of the ABC transporter superfamily. MRP1 is a high-affinity transporter of the cysteinyl leukotriene C(4) and is responsible for the systemic release of this cytokine in response to an inflammatory stimulus. However, the substrate specificity of MRP1 is extremely broad and includes many organic anion conjugates of structurally unrelated endo- and xenobiotics. In addition, MRP1 transports unmodified hydrophobic compounds, such as natural product type chemotherapeutic agents and mutagens, such as aflatoxin B(1). Transport of several of these compounds has been shown to be dependent on the presence of reduced glutathione (GSH). More recently, GSH has also been shown to stimulate the transport of some conjugated compounds, including sulfates and glucuronides. Here, we summarize current knowledge of the substrate specificity and modes of transport of MRP1 and discuss how the protein may recognize its structurally diverse substrates. 相似文献