全文获取类型
收费全文 | 571篇 |
免费 | 43篇 |
专业分类
614篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 22篇 |
2015年 | 31篇 |
2014年 | 45篇 |
2013年 | 34篇 |
2012年 | 54篇 |
2011年 | 60篇 |
2010年 | 33篇 |
2009年 | 32篇 |
2008年 | 37篇 |
2007年 | 30篇 |
2006年 | 20篇 |
2005年 | 27篇 |
2004年 | 21篇 |
2003年 | 25篇 |
2002年 | 17篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
1956年 | 2篇 |
1955年 | 1篇 |
1952年 | 1篇 |
1950年 | 1篇 |
1949年 | 1篇 |
1939年 | 1篇 |
1935年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有614条查询结果,搜索用时 0 毫秒
121.
Ralf Salzer Martin Herzberg Dietrich H. Nies Friederike Joos Barbara Rathmann Yvonne Thielmann Beate Averhoff 《The Journal of biological chemistry》2014,289(44):30343-30354
The traffic AAA-ATPase PilF is essential for pilus biogenesis and natural transformation of Thermus thermophilus HB27. Recently, we showed that PilF forms hexameric complexes containing six zinc atoms coordinated by conserved tetracysteine motifs. Here we report that zinc binding is essential for complex stability. However, zinc binding is neither required for pilus biogenesis nor natural transformation. A number of the mutants did not exhibit any pili during growth at 64 °C but still were transformable. This leads to the conclusion that type 4 pili and the DNA translocator are distinct systems. At lower growth temperatures (55 °C) the zinc-depleted multiple cysteine mutants were hyperpiliated but defective in pilus-mediated twitching motility. This provides evidence that zinc binding is essential for the role of PilF in pilus dynamics. Moreover, we found that zinc binding is essential for complex stability but dispensable for ATPase activity. In contrast to many polymerization ATPases from mesophilic bacteria, ATP binding is not required for PilF complex formation; however, it significantly increases complex stability. These data suggest that zinc and ATP binding increase complex stability that is important for functionality of PilF under extreme environmental conditions. 相似文献
122.
Yoanne D. Mouwenda Madeleine E. Betouke Ongwe Friederike Sonnet Koen A. Stam Lucja A. Labuda Sophie De Vries Martin P. Grobusch Frejus J. Zinsou Yabo J. Honkpehedji Jean-Claude Dejon Agobe David J. Diemert Remko van Leeuwen Maria E. Bottazzi Peter J. Hotez Peter G. Kremsner Jeffrey M. Bethony Simon P. Jochems Ayola A. Adegnika Marguerite Massinga Loembe Maria Yazdanbakhsh 《PLoS neglected tropical diseases》2021,15(10)
Two hookworm vaccine candidates, Na-GST-1 and Na-APR-1, formulated with Glucopyranosyl Lipid A (GLA-AF) adjuvant, have been shown to be safe, well tolerated, and to induce antibody responses in a Phase 1 clinical trial (Clinicaltrials.gov ) conducted in Gabon. Here, we characterized T cell responses in 24 Gabonese volunteers randomized to get vaccinated three times with Na-GST-1 and Na-APR-1 at doses of 30μg (n = 8) or 100μg (n = 10) and as control Hepatitis B (n = 6). Blood was collected pre- and post-vaccination on days 0, 28, and 180 as well as 2-weeks after each vaccine dose on days 14, 42, and 194 for PBMCs isolation. PBMCs were stimulated with recombinant Na-GST-1 or Na-APR-1, before (days 0, 28 and 180) and two weeks after (days 14, 42 and 194) each vaccination and used to characterize T cell responses by flow and mass cytometry. A significant increase in Na-GST-1 -specific CD4+ T cells producing IL-2 and TNF, correlated with specific IgG antibody levels, after the third vaccination (day 194) was observed. In contrast, no increase in Na-APR-1 specific T cell responses were induced by the vaccine. Mass cytometry revealed that, Na-GST-1 cytokine producing CD4+ T cells were CD161+ memory cells expressing CTLA-4 and CD40-L. Blocking CTLA-4 enhanced the cytokine response to Na-GST-1.In Gabonese volunteers, hookworm vaccine candidate, Na-GST-1, induces detectable CD4+ T cell responses that correlate with specific antibody levels. As these CD4+ T cells express CTLA-4, and blocking this inhibitory molecules resulted in enhanced cytokine production, the question arises whether this pathway can be targeted to enhance vaccine immunogenicity. NCT02126462相似文献
123.
Carsten Mei?ner Reinhold Deppisch Friederike Hug Matthias Schulze Eberhard Ritz Horst Ludwig Gertrud M. H?nsch 《Glycoconjugate journal》1995,12(5):632-638
Contact of mononuclear human leukocytes with cellulose dialysis membranes may result in complement-independent cell activation, i.e. enhanced synthesis of cytokines, prostaglandins and an increase in 2-microglobulin synthesis. Cellular contact activation is specifically inhibited by the monosaccharidel-fucose suggesting that dialysis membrane associatedl-fucose residues are involved in leukocyte activation. In this study we have detected and quantitatedl-fucose on commercially-available cellulose dialysis membranes using two approaches. A sensitive enzymatic fluorescence assay detectedl-fucose after acid hydrolysis of flat sheet membranes. Values ranged from 79.3±3.6 to 90.2±5.0 pmol cm–2 for Hemophan® or Cuprophan® respectively. Enzymatic cleavage of terminal -l-fucopyranoses with -l-fucosidase yielded 7.7±3.3 pmoll-fucose per cm2 for Cuprophan. Enzymatic hydrolysis of the synthetic polymer membranes AN-69 and PC-PE did not yield detectable amounts ofl-fucose. In a second approach, binding of the fucose specific lectins ofLotus tetragonolobus andUlex europaeus (UEAI) demonstrated the presence of biologically accessiblel-fucose on the surface of cellulose membranes. Specific binding was observed with Cuprophan®, and up to 2.6±0.3 pmoll-fucose per cm2 was calculated to be present from Langmuir-type adsorption isotherms. The data presented are in line with the hypothesis that surface-associatedl-fucose residues on cellulose dialysis membranes participate in leukocyte contact activation. 相似文献
124.
Friederike Behmenburg Marianne Dorsch Ragnar Huhn David Mally André Heinen Markus W. Hollmann Marc M. Berger 《PloS one》2015,10(12)
Background
Mitochondrial large-conductance Ca2+-sensitive potassium (mBKCa) channels are involved in myocardial ischemic preconditioning. Their role in sildenafil-induced cardioprotection is unknown. We investigated whether sildenafil-induced acute cardioprotection is mediated by activation of mBKCa channels in the rat heart in vitro.Methods
Male Wistar rats (n = 8 per group) were randomized and anesthetized with pentobarbital (90 mg/kg). Hearts were isolated, mounted on a Langendorff system and perfused with Krebs-Henseleit buffer at a constant pressure of 80 mmHg. Hearts underwent 30 min of global ischemia followed by 60 min of reperfusion. At the end of the experiments infarct size was determined by TTC staining. In the control group rats were not further treated. Sildenafil (3 μM) was administered over 10 min before the beginning of ischemia. The mBKCa channel inhibitor paxilline (1 μM) was administered with and without sildenafil before the onset of ischemia. The pathway underlying sildenafil-induced cardioprotection was further investigated with the protein kinase G blocker KT5823 (1 μM). Myocardial cGMP concentration was measured by ELISA. Data (mean±SD) were analysed with a one and two-way analysis of variance as appropriate.Results
In control animals infarct size was 52±8%. Sildenafil increased cGMP concentration and reduced infarct size to 35±6% (P<0.05 vs. control). Paxilline and KT5823 completely blocked sildenafil-induced cardioprotection (paxilline+sildenafil: 50±8%, KT5823+sildenafil: 45±8%; both P<0.05 vs. sildenafil). Functional heart parameters and coronary flow were not different between the study groups.Conclusion
This study shows that in male rats protein kinase G-dependent opening of mBKCa channels plays a pivotal role in sildenafil-induced cardioprotection. 相似文献125.
126.
127.
Friederike Althoff Ivana Viktorinov Johanna Kastl Christian F. Lehner 《Developmental biology》2009,333(2):263-272
Enteric neural crest-derived cells (ENCCs) migrate along the intestine to form a highly organized network of ganglia that comprises the enteric nervous system (ENS). The signals driving the migration and patterning of these cells are largely unknown. Examining the spatiotemporal development of the intestinal neurovasculature in avian embryos, we find endothelial cells (ECs) present in the gut prior to the arrival of migrating ENCCs. These ECs are patterned in concentric rings that are predictive of the positioning of later arriving crest-derived cells, leading us to hypothesize that blood vessels may serve as a substrate to guide ENCC migration. Immunohistochemistry at multiple stages during ENS development reveals that ENCCs are positioned adjacent to vessels as they colonize the gut. A similar close anatomic relationship between vessels and enteric neurons was observed in zebrafish larvae. When EC development is inhibited in cultured avian intestine, ENCC migration is arrested and distal aganglionosis results, suggesting that ENCCs require the presence of vessels to colonize the gut. Neural tube and avian midgut were explanted onto a variety of substrates, including components of the extracellular matrix and various cell types, such as fibroblasts, smooth muscle cells, and endothelial cells. We find that crest-derived cells from both the neural tube and the midgut migrate avidly onto cultured endothelial cells. This EC-induced migration is inhibited by the presence of CSAT antibody, which blocks binding to β1 integrins expressed on the surface of crest-derived cells. These results demonstrate that ECs provide a substrate for the migration of ENCCs via an interaction between β1 integrins on the ENCC surface and extracellular matrix proteins expressed by the intestinal vasculature. These interactions may play an important role in guiding migration and patterning in the developing ENS. 相似文献
128.
129.
Summary The recombinagenic pathway of DNA repair in yeast was characterized by the effect of different inhibitors on the temperature-dependent survival after-irradiation in haploid cells of the thermoconditional mutantrad54-3. Blocking protein synthesis with cycloheximide in replicating cells caused partial inhibiton of theRAD54 dependent function but some repair activity remained detectable. This indicates that-rays can induceRAD54 activity above some constitutive level of function. Inhibition of DNA replication by hydroxyurea efficiently blocked theRAD54 dependent function in stationary-phase cells but not in logarithmic-phase cells. In logarithmic-phase cells, we found a strong inhibitory effect of caffeine on theRAD54 mediated repair process. 相似文献
130.
Hiltrud Brauch Takeshi Kishida Damjan Glavac Fan Chen Friederike Pausch Heinz Höfler Farida Latif Michael I. Lerman Berton Zbar Hartmut P. H. Neumann 《Human genetics》1995,95(5):551-556
We identified a germline missense mutation at nucleotide 505 (T to C) of the VHL tumor suppressor gene in 14, apparently unrelated, VHL type 2A families from the Black Forest region of Germany. This mutation was previously identified in two VHL 2A families living in Pennsylvania (USA). All affected individuals in the 16 families shared the same VHL haplotype indicating a founder effect. This missense mutation at codon 169 (Tyr to His) would probably cause an alteration in the structure of the putative VHL protein. The association of this distinct mutation with the pheochromocytoma phenotype in VHL may help to elucidate the genetic mechanism of carcinogenesis in this multi tumor cancer syndrome. 相似文献