全文获取类型
收费全文 | 672篇 |
免费 | 51篇 |
国内免费 | 1篇 |
出版年
2021年 | 7篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 11篇 |
2015年 | 27篇 |
2014年 | 39篇 |
2013年 | 43篇 |
2012年 | 41篇 |
2011年 | 35篇 |
2010年 | 26篇 |
2009年 | 17篇 |
2008年 | 23篇 |
2007年 | 25篇 |
2006年 | 22篇 |
2005年 | 24篇 |
2004年 | 22篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 20篇 |
1998年 | 8篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1969年 | 4篇 |
1968年 | 5篇 |
1965年 | 4篇 |
排序方式: 共有724条查询结果,搜索用时 15 毫秒
71.
Lind H Sjögren J Gohil S Kenne L Schnürer J Broberg A 《FEMS microbiology letters》2007,271(2):310-315
Antifungal compounds from cultures of five type strains of dairy propionibacteria, as well as from the cultivation medium, were studied. Cell-free supernatants and medium were fractionated by C(18) solid phase extraction. The aqueous 95% acetonitrile fractions were analyzed by GC-MS or subjected to reversed-phase HPLC, to identify, quantify or isolate antifungal substances. The resulting HPLC fractions were screened for antifungal activity against the mold Aspergillus fumigatus and the yeast Rhodotorula mucilaginosa. Active fractions were further separated by HPLC and the structures of the compounds were determined by spectroscopic and chromatographic methods. All five strains produced 3-phenyllactic acid, at concentrations ranging from 1.0 microg mL(-1) (Propionibacterium freudenreichii ssp. shermanii) to 15.1 microg mL(-1) (Propionibacterium thoenii), and at L/D -ratios ranging from 2 : 3 (Propionibacterium acidipropionici) to 9 : 1 (Propionibacterium freudenreichii). A number of active compounds found in cultures of propionibacteria were also present in noninoculated growth medium: two antifungal diketopiperazines, cyclo(L-Phe-L-Pro) and cyclo(L-Ile-L-Pro), and seven antifungal linear peptides. Three of the linear peptides corresponded to sequences found in the medium component casein, suggesting their origin from this component, whereas the diketopiperazines were suggested to be formed from medium peptides by heat treatment. 相似文献
72.
Zhang Yang Catharina Steentoft Camilla Hauge Lars Hansen Allan Lind Thomsen Francesco Niola Malene B. Vester-Christensen Morten Fr?din Henrik Clausen Hans H. Wandall Eric P. Bennett 《Nucleic acids research》2015,43(9):e59
The nuclease-based gene editing tools are rapidly transforming capabilities for altering the genome of cells and organisms with great precision and in high throughput studies. A major limitation in application of precise gene editing lies in lack of sensitive and fast methods to detect and characterize the induced DNA changes. Precise gene editing induces double-stranded DNA breaks that are repaired by error-prone non-homologous end joining leading to introduction of insertions and deletions (indels) at the target site. These indels are often small and difficult and laborious to detect by traditional methods. Here we present a method for fast, sensitive and simple indel detection that accurately defines indel sizes down to ±1 bp. The method coined IDAA for Indel Detection by Amplicon Analysis is based on tri-primer amplicon labelling and DNA capillary electrophoresis detection, and IDAA is amenable for high throughput analysis. 相似文献
73.
74.
Martin I. Lind Kylie Yarlett Julia Reger Mauricio J. Carter Andrew P. Beckerman 《Proceedings. Biological sciences / The Royal Society》2015,282(1816)
Phenotypic plasticity is the ability of a genotype to produce more than one phenotype in order to match the environment. Recent theory proposes that the major axis of genetic variation in a phenotypically plastic population can align with the direction of selection. Therefore, theory predicts that plasticity directly aids adaptation by increasing genetic variation in the direction favoured by selection and reflected in plasticity. We evaluated this theory in the freshwater crustacean Daphnia pulex, facing predation risk from two contrasting size-selective predators. We estimated plasticity in several life-history traits, the G matrix of these traits, the selection gradients on reproduction and survival, and the predicted responses to selection. Using these data, we tested whether the genetic lines of least resistance and the predicted response to selection aligned with plasticity. We found predator environment-specific G matrices, but shared genetic architecture across environments resulted in more constraint in the G matrix than in the plasticity of the traits, sometimes preventing alignment of the two. However, as the importance of survival selection increased, the difference between environments in their predicted response to selection increased and resulted in closer alignment between the plasticity and the predicted selection response. Therefore, plasticity may indeed aid adaptation to new environments. 相似文献
75.
Lindén H Tetzlaff T Potjans TC Pettersen KH Grün S Diesmann M Einevoll GT 《Neuron》2011,72(5):859-872
The local field potential (LFP) reflects activity of many?neurons in the vicinity of the recording electrode and is therefore useful for studying local network dynamics. Much of the nature of the LFP is, however, still unknown. There are, for instance, contradicting reports on the spatial extent of the region generating the LFP. Here, we use a detailed biophysical modeling approach to investigate the size of the contributing region by simulating the LFP from a large number of neurons around the electrode. We find that the size of the generating region depends on the neuron morphology, the synapse distribution, and the correlation in synaptic activity. For uncorrelated activity, the LFP represents cells in a small region (within a radius of a few hundred micrometers). If the LFP contributions from different cells are correlated, the size of the generating region is determined by the spatial extent of the correlated activity. 相似文献
76.
Andersson A Bossios A Malmhäll C Sjöstrand M Eldh M Eldh BM Glader P Andersson B Qvarfordt I Riise GC Lindén A 《American journal of physiology. Lung cellular and molecular physiology》2011,300(1):L43-L55
Chronic exposure to tobacco smoke leads to an increase in the frequency of infections and in the number of CD8(+) and CD4(+) cells as well as the CD4(+) chemoattractant cytokine IL-16 in the airways. Here, we investigated whether tobacco smoke depletes intracellular IL-16 protein and inhibits de novo production of IL-16 in CD8(+) cells from human airways and blood while increasing extracellular IL-16 and whether oxygen free radicals (OFR) are involved. Intracellular IL-16 protein in CD8(+) cells and mRNA in all cells was decreased in bronchoalveolar lavage (BAL) samples from chronic smokers. This was also the case in human blood CD8(+) cells exposed to water-soluble tobacco smoke components in vitro, in which oxidized proteins were markedly increased. Extracellular IL-16 protein was increased in cell-free BAL fluid from chronic smokers and in human blood CD8(+) cells exposed to water-soluble tobacco smoke components in vitro. This was not observed in occasional smokers after short-term exposure to tobacco smoke. A marker of activation (CD69) was slightly increased, whereas other markers of key cellular functions (membrane integrity, apoptosis, and proliferation) in human blood CD8(+) cells in vitro were negatively affected by water-soluble tobacco smoke components. An OFR scavenger prevented these effects, whereas a protein synthesis inhibitor, a β-adrenoceptor, a glucocorticoid receptor agonist, a phosphodiesterase, a calcineurin phosphatase, and a caspase-3 inhibitor did not. In conclusion, tobacco smoke depletes preformed intracellular IL-16 protein, inhibits its de novo synthesis, and distorts key cellular functions in human CD8(+) cells. OFR may play a key role in this context. 相似文献
77.
Alterations in the microenvironment collaborate with cell autonomous mutations during the transformation process. Indeed, cancer-associated fibroblasts and senescent fibroblasts stimulate tumorigenesis in xenograft models. Because senescent fibroblasts accumulate with age, these findings suggest that they contribute to age-related increases in tumorigenesis. Previously we showed that senescence-associated stromal-derived osteopontin contributes to preneoplastic cell growth in vitro and in xenografts, suggesting that it impacts neoplastic progression. Analysis of fibroblasts within premalignant and malignant skin lesions ranging from solar/actinic keratosis to squamous cell carcinoma revealed they express osteopontin. Given the stromal expression of osteopontin, we investigated how osteopontin impacts preneoplastic cell growth. We show that osteopontin promotes preneoplastic keratinocyte cellular proliferation and cell survival through the CD44 cell receptor and activation of the MAPK pathway. These data suggest that stromal-derived osteopontin impacts tumorigenesis by stimulating preneoplastic cell proliferation thus allowing expansion of initiated cells in early lesions. 相似文献
78.
Amy J. Lind Phillip Q. Spinks Gary M. Fellers H. Bradley Shaffer 《Conservation Genetics》2011,12(1):269-284
Genetic data are increasingly being used in conservation planning for declining species. We sampled both the ecological and
distributional limits of the foothill yellow-legged frog, Rana boylii to characterize mitochondrial DNA (mtDNA) variation in this declining, riverine amphibian. We evaluated 1525 base pairs (bp)
of cytochrome b and ND2 fragments for 77 individuals from 34 localities using phylogenetic and population genetic analyses. We constructed
gene trees using maximum likelihood and Bayesian inference, and quantified genetic variance (using AMOVA and partial Mantel
tests) within and among hydrologic regions and river basins. Several moderately supported, geographically-cohesive mtDNA clades
were recovered for R. boylii. While genetic variation was low among populations in the largest, most inclusive clade, samples from localities at the edges
of the geographic range demonstrated substantial genetic divergence from each other and from more central populations. Hydrologic
regions and river basins, which represent likely dispersal corridors for R. boylii, accounted for significant levels of genetic variation. These results suggest that both rivers and larger hydrologic and geographic
regions should be used in conservation planning for R. boylii. 相似文献
79.
Background: Helicobacter pylori colonize the mucus layer that covers the gastric epithelium and can cause gastritis, ulcers, and gastric cancer. Recently, Lactobacillus sp. have also been found to reside in this niche permanently. This study compares adhesive properties and proliferation of co‐isolated lactobacilli and H. pylori in the presence of mucins and investigates possibilities for lactobacilli‐mediated inhibition of H. pylori. Materials and methods: Binding and proliferation of four H. pylori and four Lactobacillus strains, simultaneously isolated after residing in the stomachs of four patients for >4 years, to human gastric mucins were investigated using microtiter‐based methods. Results: The H. pylori strains co‐isolated with lactobacilli exhibited the same mucin binding properties as demonstrated for H. pylori strains previously. In contrast, no binding to mucins was detected with the Lactobacillus strains. Proliferation of mucin‐binding H. pylori strains was stimulated by the presence of mucins, whereas proliferation of non‐binding H. pylori and Lactobacillus strains was unaffected. Associative cultures of co‐isolated H. pylori and Lactobacillus strains showed no inhibition of H. pylori proliferation because of the presence of whole bacteria or supernatant of lactobacilli. Conclusions: The presence of lactobacilli in the stomach did not select for different mucin binding properties of H. pylori, and Lactobacillus sp. did neither compete for binding sites nor inhibit the growth of co‐isolated H. pylori. The effects of human gastric mucins on H. pylori proliferation vary between strains, and the host–bacteria interaction in the mucus niche thus depends on both the H. pylori strain and the microenvironment provided by the host mucins. 相似文献
80.
Jacobsson JA Almén MS Benedict C Hedberg LA Michaëlsson K Brooks S Kullberg J Axelsson T Johansson L Ahlström H Fredriksson R Lind L Schiöth HB 《PloS one》2011,6(5):e20158