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991.
A three-year survey (1997–99) was carried out on organically reared sheep flocks throughout Sweden. The aim was to determine the prevalence and intensity of nematode infections and to establish relationships between sheep management practices and parasite infections. Faecal samples from ewes and lambs were collected from 152 organic flocks around lambing-time and during the grazing-period for analysis. Results were compared with the different management practices that farmers use to prevent parasitism in their flocks. A high proportion of the flocks was infected with nematodes. The most prevalent species were Haemonchus contortus, Teladorsagia circumeincta, Trichostrongylus axei, T. colubriformis and Chabertia ovina and infections progressively increased during summer in lambs grazing on permanent pastures. Severity of parasitic infection in lambs was highly dependent on egg output from the ewes. H. contortus was found in 37% of the flocks, even at latitudes approximating the Polar Circle. Nematodirus battus was recorded for the first time in Sweden during the course of this study. Lambs turned out onto permanent pasture showed higher nematode faecal egg counts (epg) than lambs that had grazed on pastures, which had not carried sheep the previous year. This beneficial effect of lambs grazing non-infected pastures persisted if the ewes were treated with an anthelmintic before turn-out and if the lambs were kept on pastures of low infectivity after weaning. In lambs, the prevalence and the magnitude of their egg counts were higher during autumn in flocks where lambs were slaughtered after 8 months of age, compared with flocks where all lambs were slaughtered before this age. These results will be used in providing advice to farmers of ways to modify their flock management in order to minimise the use of anthelmintics, but at the same time efficiently produce prime lambs. 相似文献
992.
Using accelerometry to quantify prey attack and handling behaviours in piscivorous pike Esox lucius 下载免费PDF全文
M. Van Deurs A. Andersson J. Vinterstare A. Didenko A. Persson C. Brönmark P. A. Nilsson 《Journal of fish biology》2017,90(6):2462-2469
Accelerometer technology was used to evaluate behaviours in the teleost ambush predator pike Esox lucius foraging on crucian carp Carassius carassius. Automated rule‐based estimates of prey‐size determined handling time were obtained and are compared with video‐recorded behaviours. Solutions to tag attachment and the limitations imposed by battery‐time and data‐logging capacities are evaluated. 相似文献
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Eggs of mallard ducks ( Anas platyrhynchos ) and ring-necked pheasants ( Phasianus colchicus ) were incubated in clutches arranged to stimulate embryos to hatch earlier or later than normal. This manipulation of hatching time was achieved by combining eggs of different age in the same clutch. To ensure hatching synchrony, embryos communicate with each other during the last stage of incubation, resulting in either a delay or an acceleration of hatching. Embryos of both species that accelerated their hatching time suffered a higher mortality rate after hatching. Combining mortality with the proportion of hatchlings that suffered from leg deformities, impeding their movements, resulted in a cost also to pheasant chicks delaying their hatching. Chicks of both species accelerating hatching time had a lower minimum mass and a shorter tarsus length than control chicks, whereas chicks delaying hatching time either grew as well or slightly better than control chicks. Mallard chicks had better balance and mobility immediately after hatching the longer they stayed in the egg. This indicates that the period immediately before hatching, is an important period for muscular and organ maturity. Reducing this period results in costs affecting post-hatching survival. The strategy to assure synchronous hatching in mallards and pheasants probably reflect a trade-off between the negative effects of shifting the age at hatching away from normal and differences in predation risk during different stages of reproduction. 相似文献
996.
Alfred E. Szmidt Marie‐Charlotte Nilsson Elmer Briceo Olle Zackrisson Xiao‐Ru Wang 《植被学杂志》2002,13(5):627-634
Abstract. In late successions of the boreal forest of northern Sweden the evergreen dwarf shrub Empetrum hermaphroditum forms an extensive cover and is believed to spread mainly vegetatively through layering. To analyse the process of population establishment and the relative importance of sexual vs asexual reproduction and the spatial clonal distribution of this species we selected one mainland and two island sites of different post‐fire successional ages (145, 375 and 1720 yr since last fire, respectively). Using 61 polymorphic RAPD markers, we found 96 genotypes in a total of 133 samples. All three populations showed high levels of genetic variation. AMOVA analysis revealed that 33% of the total variation resided among sites, 26% resided among plots within sites and 41% was due to variation within plots. The youngest population had only 14% clonal fraction. In contrast, the oldest population had > 30% clonal fraction and many genets had dimensions of 10–40 m and were intermingled. It appears that E. hermaphroditum establishes by seeds to a larger extent than previously thought and that the clonal spread by layering is rather slow. 相似文献
997.
Karin Westerberg Marcus Degerman Bernt Nilsson 《Bioprocess and biosystems engineering》2010,33(3):375-382
Preparative chromatographic columns that run at high loads are highly sensitive to batch-to-batch disturbances of the process parameters, placing high demands on the strategy used for pooling of the product fractions. A new approach to pooling control is presented in a proof-of-concept study. A model-based sensitivity analysis was performed identifying the critical process parameters to product purity and optimal cut points. From this, the robust fixed cut points were found and pooling control strategies for variations in the critical parameters were designed. Direct measurements and indirect measurements based on the UV detector signal were used as control signals. The method is demonstrated for two case studies of preparative protein chromatography: hydrophobic interaction and reversed phase chromatography. The yield improved from 88.18 to 92.88% when changing from fixed to variable pooling in hydrophobic interaction chromatography, and from 35.15 to 76.27% in the highly sensitive reversed phase chromatography. 相似文献
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999.
Snke Andres Anna Skoglund Christina Nilsson Margareta Krabbe Britta Bjrkholm Lars Engstrand 《Helicobacter》2010,15(2):114-125
Background: A remarkable variety of restriction‐modification (R‐M) systems is found in Helicobacter pylori. Since they encompass a large portion of the strain‐specific H. pylori genes and therefore contribute to genetic variability, they are suggested to have an impact on disease outcome. Type I R‐M systems comprise three different subunits and are the most complex of the three types of R‐M systems. Aims: We investigated the genetic diversity and distribution of type I R‐M systems in clinical isolates of H. pylori. Material and methods: Sixty‐one H. pylori isolates from a Swedish hospital based case‐control study and 6 H. pylori isolates of a Swedish population‐based study were analyzed using polymerase chain reaction for the presence of the three R‐M systems' subunits. Representative gene variants were sequenced. Results: Although the hsdM and hsdR genes appeared conserved in our clinical H. pylori isolates, the sequences of the hsdS loci were highly variable. Despite their sequence diversity, the genes per se were present at high frequencies. We identified a number of novel allelic hsdS variants, which are distinct from corresponding hsdS loci in the sequenced H. pylori strains 26695, J99 and HPAG1. In analyses of paired H. pylori isolates, obtained from the same individuals with a 4‐year interval, we observed genetic modifications of hsdS genes in patients with atrophic gastric mucosa. Discussion: We propose that the genetic variability of hsdS genes in a bacterial population will give rise to new specificities of these enzymes, which might lead to adaptation to an ever‐changing gastric environment. 相似文献
1000.
Juli Broggi Esa Hohtola Kari Koivula Markku Orell Jan-Åke Nilsson 《Evolutionary ecology》2010,24(1):177-184
Physiological changes due to aging are intensively studied as they have far-reaching implications for the mechanistic and evolutionary theories of senescence. In this respect, metabolic rate has been suggested to play a role for the deterioration and damage of cells and tissues with age, partly due to the generation of reactive oxygen species. To mitigate such damage, individuals can be predicted to reduce basal metabolic rate (BMR) with age. This prediction has been verified in humans and some laboratory animals but never in wild animal populations. We analyzed the change in BMR within individuals across years in two wild populations of great tit (Parus major) differing in BMR. Great tits, living under stressful conditions towards the northern limit of their distribution, decreased their BMR as they aged whereas no such decrease was found in a southern population. Thus, we found a clear decline only in the population with the highest BMR levels. This study provides the first evidence of an age-related decline in BMR for a wild homeotherm. 相似文献