全文获取类型
收费全文 | 2826篇 |
免费 | 216篇 |
国内免费 | 1篇 |
出版年
2023年 | 19篇 |
2022年 | 22篇 |
2021年 | 80篇 |
2020年 | 54篇 |
2019年 | 60篇 |
2018年 | 88篇 |
2017年 | 83篇 |
2016年 | 112篇 |
2015年 | 127篇 |
2014年 | 155篇 |
2013年 | 207篇 |
2012年 | 217篇 |
2011年 | 234篇 |
2010年 | 168篇 |
2009年 | 132篇 |
2008年 | 168篇 |
2007年 | 189篇 |
2006年 | 186篇 |
2005年 | 125篇 |
2004年 | 125篇 |
2003年 | 103篇 |
2002年 | 106篇 |
2001年 | 29篇 |
2000年 | 16篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1967年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有3043条查询结果,搜索用时 673 毫秒
991.
Aleksey Y. Malyshev Pavel M. Balaban 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(1):25-32
Bilaterally symmetrical pair of serotonergic cells, named C1 in Clione, has been described in the cerebral ganglia of all gastropod species. Here we describe a new role of C1 cells in gastropod
mollusks: control of activity of ciliated epithelium in the foregut. Detailed morphological investigation of C1 neurons in
the pteropod mollusk Clione
limacina revealed that these cells among other destinations send their neurites into foregut where they produce intense arborization
with large varicosities along the processes. Intracellular stimulation of a single C1 induced pronounced activation (often
followed by inhibition) of cilia lining the foregut. This activation was substantially reduced by serotonin antagonist mianserin.
Bath application of serotonin also induced transient increase in ciliary transport rate, followed by inhibition of ciliary
activity up to its full cessation in some areas of isolated foregut. These data suggest that C1 in Clione may use serotonin to influence cilia in the foregut. Taking into account high homology of serotonergic cerebral cells across
studied species we can speculate that these cells may be involved in the neural control of cilia in the foregut in other gastropod
mollusks. 相似文献
992.
Tong J Dolezal P Selkrig J Crawford S Simpson AG Noinaj N Buchanan SK Gabriel K Lithgow T 《Molecular biology and evolution》2011,28(5):1581-1591
The evolution of mitochondria from ancestral bacteria required that new protein transport machinery be established. Recent controversy over the evolution of these new molecular machines hinges on the degree to which ancestral bacterial transporters contributed during the establishment of the new protein import pathway. Reclinomonas americana is a unicellular eukaryote with the most gene-rich mitochondrial genome known, and the large collection of membrane proteins encoded on the mitochondrial genome of R. americana includes a bacterial-type SecY protein transporter. Analysis of expressed sequence tags shows R. americana also has components of a mitochondrial protein translocase or "translocase in the inner mitochondrial membrane complex." Along with several other membrane proteins encoded on the mitochondrial genome Cox11, an assembly factor for cytochrome c oxidase retains sequence features suggesting that it is assembled by the SecY complex in R. americana. Despite this, protein import studies show that the RaCox11 protein is suited for import into mitochondria and functional complementation if the gene is transferred into the nucleus of yeast. Reclinomonas americana provides direct evidence that bacterial protein transport pathways were retained, alongside the evolving mitochondrial protein import machinery, shedding new light on the process of mitochondrial evolution. 相似文献
993.
The best available approach of biological sample preparation for transmission electron microscopy currently includes cryoimmobilization
by high-pressure freezing (HPF) followed by freeze-substitution (FS). This method has been well established for interphase
cells; however, a reliable and easy procedure is still missing for mitotic cells especially because of their fragility and
sensitivity to treatments. Here, we present a fast and effective method for HPF/automated FS and LR White embedding of mitotic
cells which allows for their controlled and reproducible quality processing. It should be useful in various ultrastructural
studies on mitotic cells especially in combination with immunocytochemistry. 相似文献
994.
El-Hawiet A Kitova EN Kitov PI Eugenio L Ng KK Mulvey GL Dingle TC Szpacenko A Armstrong GD Klassen JS 《Glycobiology》2011,21(9):1217-1227
The binding of recombinant fragments of the C-terminal cell-binding domains of the two large exotoxins, toxin A (TcdA) and toxin B (TcdB), expressed by Clostridium difficile and a library consisting of the most abundant neutral and acidic human milk oligosaccharides (HMOs) was examined quantitatively at 25°C and pH 7 using the direct electrospray ionization mass spectrometry (ES-MS) assay. The results of the ES-MS measurements indicate that both toxin fragments investigated, TcdB-B1 and TcdA-A2, which possess one and two carbohydrate binding sites, respectively, bind specifically to HMOs ranging in size from tri- to heptasaccharides. Notably, five of the HMOs tested bind to both toxins: Fuc(α1-2)Gal(β1-4)Glc, Gal(β1-3)GlcNAc(β1-3)Gal(β1-4)Glc, Fuc(α1-2)Gal(β1-3)GlcNAc(β1-3)Gal(β1-4)Glc, Gal(β1-3)[Fuc(α1-4)]GlcNAc(β1-3)Gal(β1-4)Glc and Gal(β1-4)[Fuc(α1-3)]GlcNAc(β1-3)Gal(β1-4)Glc. However, the binding of the HMOs is uniformly weak, with apparent affinities ≤10(3?)M(-1). The results of molecular docking simulations, taken together with the experimental binding data, suggest that a disaccharide moiety (lactose or lactosamine) represents the core HMO recognition element for both toxin fragments. The results of a Verocytotoxicity neutralization assay reveal that HMOs do not significantly inhibit the cytotoxic effects of TcdA or TcdB. The absence of protection is attributed to the very weak intrinsic affinities that the toxins exhibit towards the HMOs. 相似文献
995.
Ji?í Reif Pavel Marhoul Old?ich ?í?ek Martin Konvi?ka 《Biodiversity and Conservation》2011,20(14):3645-3662
The European landscape is under pervasive attack of massive land use changes, such as agricultural intensification, urbanization
and land abandonment. These changes resulted in population decline of birds living in open habitats. Despite a good understanding
on the effects of these driving forces on bird populations, effective conservation actions are difficult to conduct as these
forces are closely connected with socioeconomic development of particular countries and thus almost impossible to reverse.
It is hence necessary to conserve refuge sites with a limited influence of these negative factors. We surveyed birds in 42
abandoned military training sites (AMTS) in a central European country, the Czech Republic, and we have found these sites
are valuable, and to date overlooked, refuges for bird conservation. Birds of high conservation concern and open habitats
birds (such as Miliaria calandra, Saxicola torquata or Lullula arborea) were more abundant in AMTS than predicted by their total population size in the Czech Republic. The most important characteristics
predicting attractiveness of AMTS for birds of conservation concern were low altitude, low proportion of forest/dense scrubland,
high proportion of sparse scrubland/bare ground and large area. Former military activity was beneficial for declining open
habitat birds by maintaining moderate disturbance levels, which are rarely found elsewhere in current landscapes. Owing to
reduction of armed forces across Europe AMTS provide continental-wide network of high-quality sites for bird conservation.
Nevertheless, AMTS are subject to pressure from building activities or loss of openness due to overgrowth of forest or scrub
plant communities. 相似文献
996.
Dong LF Jameson VJ Tilly D Prochazka L Rohlena J Valis K Truksa J Zobalova R Mahdavian E Kluckova K Stantic M Stursa J Freeman R Witting PK Norberg E Goodwin J Salvatore BA Novotna J Turanek J Ledvina M Hozak P Zhivotovsky B Coster MJ Ralph SJ Smith RA Neuzil J 《Free radical biology & medicine》2011,50(11):1546-1555
997.
Dorr CR Yemets S Kolomitsyna O Krasutsky P Mansky LM 《Bioorganic & medicinal chemistry letters》2011,21(1):542-545
Triterpene derivatives were analyzed for anti-HIV-1 activity and for cellular toxicity. Betulinic aldehyde, betulinic nitrile, and morolic acid derivatives were identified to have anti-HIV-1 activity. These derivatives inhibit a late step in virus replication, likely virus maturation. 相似文献
998.
Franta Z Sojka D Frantova H Dvorak J Horn M Srba J Talacko P Mares M Schneider E Craik CS McKerrow JH Caffrey CR Kopacek P 《International journal for parasitology》2011,41(12):1253-1262
Intracellular proteolysis of ingested blood proteins is a crucial physiological process in ticks. In our model tick, Ixodes ricinus, cathepsin L (IrCL1) is part of a gut-associated multi-peptidase complex; its endopeptidase activity is important in the initial phase of haemoglobinolysis. We present the functional and biochemical characterisation of this enzyme. We show, by RNA interference (RNAi), that cathepsin L-like activity that peaks during the slow feeding period of females is associated with IrCL1. Recombinant IrCL1 was expressed in bacteria and yeast. Activity profiling with both peptidyl and physiological protein substrates (haemoglobin and albumin) revealed that IrCL1 is an acidic peptidase with a very low optimum pH (3-4) being unstable above pH 5. This suggests an endo/lysosomal localisation that was confirmed by indirect fluorescence microscopy that immunolocalised IrCL1 inside the vesicles of digestive gut cells. Cleavage specificity determined by a positional scanning synthetic combinatorial library and inhibition profile indicated that IrCL1 has the ligand-binding characteristics of the cathepsin L subfamily of cysteine peptidases. A non-redundant proteolytic function was demonstrated when IrCL1-silenced ticks had a decreased ability to feed compared with controls. The data suggest that IrCL1 may be a promising target against ticks and tick-borne pathogens. 相似文献
999.
Ji?í?NeustupaEmail author Jan??t’astny Katarína?Nemjová Petra?Mazalová Emma?Goodyer Aloisie?Poulí?ková Pavel??kaloud 《Hydrobiologia》2011,667(1):223-239
Morphological species of freshwater microalgae often have broad geographic distribution. However, traditional species concepts
have been challenged by the results of molecular phylogenetic analyses that mostly indicate higher diversity than was previously
recognized by purely morphological approaches. A degree of phenotypic differentiation or different geographic distribution
of species defined by molecular data remains largely unknown. In this study, we analyzed a pair of well-known and widely distributed
desmid species (Micrasterias fimbriata and M. rotata) and tested for their phylogenetic and morphological homogeneity as well as their geographic distribution. Geometric morphometric
and morphological attributes of cells were used in combination with genetic analysis of the trnG
ucc
sequences of 30 strains isolated from a variety of European locations and obtained from culture collections. Micrasterias rotata proved to be phylogenetically homogenous across Europe while M. fimbriata turned out to be composed of two firmly delimited lineages, differing by molecular as well as by morphometric and morphological
data. Published records of traditional M. fimbriata were also included in the classification discrimination analysis and were placed into the newly identified lineages upon
comparison to the morphometric data collected from living material. Largely disparate geographic patterns were revealed within
traditional M. fimbriata. One phylogenetic lineage is frequent in central and eastern Europe, but occurs also in the British Isles. A second lineage
has been recorded in North America and in Western Europe, where its distribution is possibly limited to the west of the Rhine
River. Interestingly, the morphometric analyses of the published records illustrated that the geographic differences have
remained largely unchanged since the 1850s indicating a previously unknown distributional stability among microalgal species
groups such as the desmids. 相似文献
1000.
Hájková Z Bugajev V Dráberová E Vinopal S Dráberová L Janáček J Dráber P Dráber P 《Journal of immunology (Baltimore, Md. : 1950)》2011,186(2):913-923
Activation of mast cells by aggregation of the high-affinity IgE receptors (FcεRI) initiates signaling events leading to the release of inflammatory and allergic mediators stored in cytoplasmic granules. A key role in this process play changes in concentrations of intracellular Ca(2+) controlled by store-operated Ca(2+) entry (SOCE). Although microtubules are also involved in the process leading to degranulation, the molecular mechanisms that control microtubule rearrangement during activation are largely unknown. In this study, we report that activation of bone marrow-derived mast cells (BMMCs) induced by FcεRI aggregation or treatment with pervanadate or thapsigargin results in generation of protrusions containing microtubules (microtubule protrusions). Formation of these protrusions depended on the influx of extracellular Ca(2+). Changes in cytosolic Ca(2+)concentration also affected microtubule plus-end dynamics detected by microtubule plus-end tracking protein EB1. Experiments with knockdown or reexpression of STIM1, the key regulator of SOCE, confirmed the important role of STIM1 in the formation of microtubule protrusions. Although STIM1 in activated cells formed puncta associated with microtubules in protrusions, relocation of STIM1 to a close proximity of cell membrane was independent of growing microtubules. In accordance with the inhibition of Ag-induced Ca(2+) response and decreased formation of microtubule protrusions in BMMCs with reduced STIM1, the cells also exhibited impaired chemotactic response to Ag. We propose that rearrangement of microtubules in activated mast cells depends on STIM1-induced SOCE, and that Ca(2+) plays an important role in the formation of microtubule protrusions in BMMCs. 相似文献