全文获取类型
收费全文 | 557篇 |
免费 | 47篇 |
专业分类
604篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 13篇 |
2020年 | 7篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2017年 | 18篇 |
2016年 | 16篇 |
2015年 | 42篇 |
2014年 | 33篇 |
2013年 | 43篇 |
2012年 | 62篇 |
2011年 | 49篇 |
2010年 | 21篇 |
2009年 | 21篇 |
2008年 | 48篇 |
2007年 | 39篇 |
2006年 | 30篇 |
2005年 | 26篇 |
2004年 | 30篇 |
2003年 | 28篇 |
2002年 | 19篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1990年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有604条查询结果,搜索用时 15 毫秒
31.
We studied the colonisation rate of insects inhabiting fruiting bodies of the wood-decaying fungus Fomitopsis pinicola both within and at different distances (up to 1610 m) from an old-growth forest reserve. The colonisation rate of most species
was not affected by the distance from the reserve, and none of the species were affected by the size of local sources of fruiting
bodies in the managed forest. We suggest that many insect species inhabiting fruiting bodies of wood-decaying fungi can colonise
fruiting bodies at a high enough rate to persist in managed forests of Fennoscandia. However, the colonisation rates of the
fungivorous beetle Cis quadridens and the predatory fly Medetera apicalis were negatively affected by distance from the reserve. Cis quadridens is rare in many managed forests, but often quite common at sites with high substrate densities. The rarity of this species
may therefore be due to weak ability to colonize distant patches. The same may also be true for M. apicalis, but less is known about the biology of this species. Medetera apicalis was the most common insect predator in the old-growth forest, but it was rare at the largest distances from it in the managed
forest. Therefore, it seems likely that the overall pressure from natural enemies significantly declined with distance from
the reserve. 相似文献
32.
David C. Muller Mattias Johansson David Zaridze Anush Moukeria Vladimir Janout Ivana Holcatova Marie Navratilova Dana Mates ?ivind Midttun Per Magne Ueland Paul Brennan Ghislaine Scelo 《PloS one》2015,10(10)
Prospective cohort studies have found that prediagnostic circulating vitamin B6 is inversely associated with both risk of kidney cancer and kidney cancer prognosis. We investigated whether circulating concentrations of vitamin B6 at kidney cancer diagnosis are associated with risk of death using a case-cohort study of 630 renal cell carcinoma (RCC) patients. Blood was collected at the time of diagnosis, and vitamin B6 concentrations were quantified using LC-MS/MS. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox regression models. After adjusting for stage, age, and sex, the hazard was 3 times lower among those in the highest compared to the lowest fourth of B6 concentration (HR4vs1 0.33, 95% CI [0.18, 0.60]). This inverse association was solely driven by death from RCC (HR4vs1 0.22, 95% CI [0.11, 0.46]), and not death from other causes (HR4vs1 0.89, 95% CI [0.35, 2.28], p-interaction = 0.008). These results suggest that circulating vitamin B6 could provide additional prognostic information for kidney cancer patients beyond that afforded by tumour stage. 相似文献
33.
Gunnar Srensen Mattias Rickhag Damiana Leo Matthew D. Lycas Pernille Herrstedt Ridderstrm Pia Weikop Jamila H. Lilja Pedro Rifes Freja Herborg David Woldbye Gitta Wrtwein Raul R. Gainetdinov Anders Fink-Jensen Ulrik Gether 《The Journal of biological chemistry》2021,297(6)
The dopamine (DA) transporter (DAT) is part of a presynaptic multiprotein network involving interactions with scaffold proteins via its C-terminal PDZ domain–binding sequence. Using a mouse model expressing DAT with mutated PDZ-binding sequence (DAT-AAA), we previously demonstrated the importance of this binding sequence for striatal expression of DAT. Here, we show by application of direct stochastic reconstruction microscopy not only that the striatal level of transporter is reduced in DAT-AAA mice but also that the nanoscale distribution of this transporter is altered with a higher propensity of DAT-AAA to localize to irregular nanodomains in dopaminergic terminals. In parallel, we observe mesostriatal DA adaptations and changes in DA-related behaviors distinct from those seen in other genetic DAT mouse models. DA levels in the striatum are reduced to ∼45% of that of WT, accompanied by elevated DA turnover. Nonetheless, fast-scan cyclic voltammetry recordings on striatal slices reveal a larger amplitude and prolonged clearance rate of evoked DA release in DAT-AAA mice compared with WT mice. Autoradiography and radioligand binding show reduced DA D2 receptor levels, whereas immunohistochemistry and autoradiography show unchanged DA D1 receptor levels. In behavioral experiments, we observe enhanced self-administration of liquid food under both a fixed ratio of one and progressive ratio schedule of reinforcement but a reduction compared with WT when using cocaine as reinforcer. In summary, our data demonstrate how disruption of PDZ domain interactions causes changes in DAT expression and its nanoscopic distribution that in turn alter DA clearance dynamics and related behaviors. 相似文献
34.
Here, we describe the draft genome sequence of Vibrio fischeri SR5, a squid symbiotic isolate from Sepiola robusta in the Mediterranean Sea. This 4.3-Mbp genome sequence represents the first V. fischeri genome from an S. robusta symbiont and the first from outside the Pacific Ocean. 相似文献
35.
Rahman S Magalhaes I Rahman J Ahmed RK Sizemore DR Scanga CA Weichold F Verreck F Kondova I Sadoff J Thorstensson R Spångberg M Svensson M Andersson J Maeurer M Brighenti S 《Molecular medicine (Cambridge, Mass.)》2012,18(1):647-658
To prevent the global spread of tuberculosis (TB) infection, a novel vaccine that triggers potent and long-lived immunity is urgently required. A plasmid-based vaccine has been developed to enhance activation of major histocompatibility complex (MHC) class I–restricted CD8+ cytolytic T cells using a recombinant Bacille Calmette-Guérin (rBCG) expressing a pore-forming toxin and the Mycobacterium tuberculosis (Mtb) antigens Ag85A, 85B and TB10.4 followed by a booster with a nonreplicating adenovirus 35 (rAd35) vaccine vector encoding the same Mtb antigens. Here, the capacity of the rBCG/rAd35 vaccine to induce protective and biologically relevant CD8+ T-cell responses in a nonhuman primate model of TB was investigated. After prime/boost immunizations and challenge with virulent Mtb in rhesus macaques, quantification of immune responses at the single-cell level in cryopreserved tissue specimen from infected organs was performed using in situ computerized image analysis as a technological platform. Significantly elevated levels of CD3+ and CD8+ T cells as well as cells expressing interleukin (IL)-7, perforin and granulysin were found in TB lung lesions and spleen from rBCG/rAd35-vaccinated animals compared with BCG/rAd35-vaccinated or unvaccinated animals. The local increase in CD8+ cytolytic T cells correlated with reduced expression of the Mtb antigen MPT64 and also with prolonged survival after the challenge. Our observations suggest that a protective immune response in rBCG/rAd35-vaccinated nonhuman primates was associated with enhanced MHC class I antigen presentation and activation of CD8+ effector T-cell responses at the local site of infection in Mtb-challenged animals. 相似文献
36.
Homozygosity is a commonly used summary of allele-frequency distributions at polymorphic loci. Because high-frequency alleles contribute disproportionately to the homozygosity of a locus, it often occurs that most homozygotes are homozygous for the most frequent allele. To assess the relationship between homozygosity and the highest allele frequency at a locus, for a given homozygosity value, we determine the lower and upper bounds on the frequency of the most frequent allele. These bounds suggest tight constraints on the frequency of the most frequent allele as a function of homozygosity, differing by at most 14 and having an average difference of 23 - pi(2)/18 approximately 0.1184. The close connection between homozygosity and the frequency of the most frequent allele-which we illustrate using allele frequencies from human populations-has the consequence that when one of these two quantities is known, considerable information is available about the other quantity. This relationship also explains the similar performance of statistical tests of population-genetic models that rely on homozygosity and those that rely on the frequency of the most frequent allele, and it provides a basis for understanding the utility of extended homozygosity statistics in identifying haplotypes that have been elevated to high frequency as a result of positive selection. 相似文献
37.
We have compared the basic organization of the primary olfactory centre, the antennal lobe (AL), in 4 hemipteran species representing the 2 major lineages in this order. The Homoptera were represented by the psyllid Trioza apicalis and its aphid relatives the grain aphid Sitobion avenae Fabricius and the rose-grain aphid Metopolophium dirhodum Walker, whereas the Heteroptera were represented by the pentatomid stink bug Euschistus heros Fabricius. The olfactory systems of psyllids and aphids are generally very small, with low numbers of afferents in comparison to other insect groups, and the smallest described so far belongs to T. apicalis, comprising less than 50 olfactory receptor neurons (ORNs). Originally, we tried to estimate numbers of olfactory glomeruli in the AL of T. apicalis, which in insects generally correspond closely to the number of different types of ORNs. Neither immunocytochemical staining nor anterograde staining of ORNs revealed any glomerular structures in the ALs of T. apicalis or the 2 aphids that were included for comparison. In contrast, the ALs of the pentatomid stink bug E. heros displayed numerous distinct and well-delineated glomeruli, showing that aglomerular ALs are not typical of all insects within the order Hemiptera. Glomeruli are hallmark features of olfactory lobes in many different phyla, and the absence of glomerular structures in psyllids and aphids appears to be unique in insects that depend on olfactory orientation. 相似文献
38.
Mattias Lindberg Henrik Biverst?hl Astrid Gr?slund Lena M?ler 《European journal of biochemistry》2003,270(14):3055-3063
The Antennapedia homeodomain protein of Drosophila has the ability to penetrate biological membranes and the third helix of this protein, residues 43-58, known as penetratin (RQIKIWFQNRRMKWKK-amide) has the same translocating properties as the entire protein. The variant, RQI KIFFQNRRMKFKK-amide, here called penetratin (W48F,W56F) does not have the same ability. We have determined a solution structure of penetratin and investigated the position of both peptides in negatively charged bicelles. A helical structure is seen for residues Lys46 through Met54. The secondary structure of the variant penetratin(W48F,W56F) in bicelles appears to be very similar. Paramagnetic spin-label studies and analysis of NOEs between penetratin and the phospholipids show that penetratin is located within the bicelle surface. Penetratin (W48F,W56F) is also located inside the phospholipid bicelle, however, with its N-terminus more deeply inserted than that of wild-type penetratin. The subtle differences in the way the two peptides interact with a membrane in an equilibrium situation could be important for their translocating ability. As a comparison we have also investigated the secondary structure of penetratin(W48F,W56F) in SDS micelles and the results show that the structure is very similar in SDS and bicelles. In contrast, penetratin(W48F,W56F) and penetratin appear to be located differently in SDS micelles. This clearly shows the importance of using realistic membrane mimetics for investigating peptide-membrane interactions. 相似文献
39.
†Wiebke Sihver Karl-Johan Fasth Mattias Ögren ‡Håkan Bivehed Mats Bergström §Agneta Nordberg †Yasuyoshi Watanabe Bengt Långström 《Journal of neurochemistry》1998,71(4):1750-1760
Abstract: The binding characteristics of the novel 11C-labeled nicotinic ligands (R,S)-1-methyl-2-(3-pyridyl) azetidine (MPA) and (S)-3-methyl-5-(1-methyl-2-pyrrolidinyl)isoxazole (ABT-418) were investigated in comparison with those of (S)-[11C]nicotine in vitro in the rat brain to be able to predict the binding properties of the new ligands for positron emission tomography studies in vivo. The data from time-resolved experiments for all ligands indicated fast binding kinetics, with the exception of a slower dissociation of [11C]MPA in comparison with (S)-[11C]nicotine and [11C]ABT-418. Saturation experiments revealed for all ligands two nicotinic receptor binding sites with affinity constants (KD values) of 2.4 and 560 nM and binding site densities (Bmax values) of 65.5 and 223 fmol/mg of protein for (S)-[11C]nicotine, KD values of 0.011 and 2.2 nM and Bmax values of 4.4 and 70.7 fmol/mg of protein for [11C]MPA, and KD values of 1.3 and 33.4 nM and Bmax values of 8.8 and 69.2 fmol/mg of protein for [11C]ABT-418. In competing with the 11C-ligands, epibatidine was most potent, followed by cytisine. A different rank order of potencies was found for (?)-nicotine, (+)-nicotine, MPA, and ABT-418 displacing each of the 11C-ligands. Autoradiograms displayed a similar pattern of receptor binding for all ligands, whereby [11C]MPA showed the most distinct binding pattern and the lowest nonspecific binding. We conclude that the three 11C-labeled nicotinic ligands were suitable for characterizing nicotinic receptors in vitro. The very high affinity of [11C]MPA to nicotinic acetylcholine receptors, its low nonspecific binding, and especially the slower dissociation kinetics of the [11C]MPA from the putative high-affinity nicotinic acetylcholine receptor binding site compared with (S)-[11C]nicotine and [11C]ABT-418 raise the level of interest in [11C]MPA for application in positron emission tomography. 相似文献
40.
Music is a human universal, which suggests a biological adaptation. Several evolutionary explanations have been proposed, covering the entire spectrum of natural, sexual, and group selection. Here we consider the hypothesis that musical behaviour constitutes a reliable or even costly signal of fitness, and thus may have evolved as a human trait through sexual selection. We experimentally tested how musical performance quality (MPQ), in improvisations on the drums, saxophone, and violin, affects mate values and mate preferences perceived by a prospective partner. Swedish student participants (27 of each sex) saw a face of a person of the opposite sex and heard a piece of improvised music being played. The music occurred in three levels of MPQ and the faces in three levels of facial attractiveness (FA). For each parametric combination of MPG and FA, the participants rated four mate value scales (intelligence, health, social status, and parenting skill) and four mate preference scales (date, intercourse, and short- and long term relationship). Consistent with sexual selection theory, mate value ratings were generally increased by MPQ for raters of both sexes. Consistent with more specific hypotheses that follow from combining sexual selection and parental investment theory, women’s but not men’s preference for a long-term, but not short-term, relationship was significantly increased by MPQ, MPQ generally affected women’s ratings more than men’s, FA generally affected men’s ratings more than women’s, and women’s ratings of intelligence were even more influenced by MPQ than by FA. 相似文献