全文获取类型
收费全文 | 936篇 |
免费 | 69篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 17篇 |
2021年 | 32篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 25篇 |
2017年 | 29篇 |
2016年 | 28篇 |
2015年 | 67篇 |
2014年 | 59篇 |
2013年 | 75篇 |
2012年 | 89篇 |
2011年 | 73篇 |
2010年 | 43篇 |
2009年 | 44篇 |
2008年 | 64篇 |
2007年 | 49篇 |
2006年 | 56篇 |
2005年 | 41篇 |
2004年 | 58篇 |
2003年 | 25篇 |
2002年 | 38篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1994年 | 5篇 |
1992年 | 1篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1005条查询结果,搜索用时 31 毫秒
151.
Background: Helicobacter pylori infection is difficult to diagnose in children, especially in developing countries where noninvasive methods such as urea breath test are often not available. We evaluate the sensitivity and specificity of a new monoclonal antibody-based antigen-in-stool enzyme immunoassay (Premier Platinum HpSA PLUS) for diagnosis of H. pylori infection in Vietnamese children.
Materials and Methods: Sensitivity of the antigen-in-stool test was evaluated in 232 children, 3–15 years of age, who were positive for H. pylori infection by culture from biopsies. For evaluation of the specificity 98 children of similar age with nongastrointestinal conditions and who were negative for H. pylori infection by serologic assays were included with blood and stool samples.
Results: Of the 232 culture-positive children, 224 were also positive by Premier Platinum HpSA PLUS. Of the 98 control children, 93 were H. pylori negative also in the stool test. The sensitivity of Premier Platinum HpSA PLUS was thus 96.6% (95% CI 93.3–98.5) and the specificity was 94.9% (95% CI 88.5–98.3).
Conclusions: The findings have demonstrated Premium Platinum HpSA PLUS to be a reliable method for detection of H. pylori infection also in children in our area. 相似文献
Materials and Methods: Sensitivity of the antigen-in-stool test was evaluated in 232 children, 3–15 years of age, who were positive for H. pylori infection by culture from biopsies. For evaluation of the specificity 98 children of similar age with nongastrointestinal conditions and who were negative for H. pylori infection by serologic assays were included with blood and stool samples.
Results: Of the 232 culture-positive children, 224 were also positive by Premier Platinum HpSA PLUS. Of the 98 control children, 93 were H. pylori negative also in the stool test. The sensitivity of Premier Platinum HpSA PLUS was thus 96.6% (95% CI 93.3–98.5) and the specificity was 94.9% (95% CI 88.5–98.3).
Conclusions: The findings have demonstrated Premium Platinum HpSA PLUS to be a reliable method for detection of H. pylori infection also in children in our area. 相似文献
152.
The genus Laranda has six described species and is confined to South and Southeast of Brazil. We describe a new species and discuss the biology and distribution of the genus. The new species can be distinguished from its known congeners by the following characteristics: absence of yellow spots on pronotum and base of posterior tibiae; female copulatory papilla: sclerotization in dorsal view forming opposing acute angles, apical lobes narrow and small; male genitalia: pseudepiphallic median process short and wide; pseudepiphallic paramere with apex incurved and ectophallic fold surpassing apex of the parameres. The genus is distributed within the Atlantic Forest biome; the new species is found on tree trunks, as well as on forest leaf litter. 相似文献
153.
Riveiro ME Moglioni A Vazquez R Gomez N Facorro G Piehl L de Celis ER Shayo C Davio C 《Bioorganic & medicinal chemistry》2008,16(5):2665-2675
In the present study, we sought to establish the effect of diverse structural-related hydroxycoumarins on the proliferation, cytotoxicity, and induction of apoptosis in promonocytic leukemic cells (U-937). The dihydroxylated coumarins, 7,8-dihydroxy-coumarin and esculetin, induced DNA fragmentation as well as characteristic morphological changes of programmed cell death in U-937 cells. With the aim to perform a structure-activity relationship study, the correlation between the physicochemical properties of the molecules and their pro-apoptotic activity was carried out. Results showed that the presence of two adjacent phenolic hydroxyl groups was the most important factor in terms of the SAR. The exposure of leukemic cells to 7,8-dihydroxy-coumarin evoked a phenoxyl radical generation that was detected by electron spin resonance spectroscopy. The present study suggests that reactive oxygen species generation plays a critical role in dihydroxycoumarin-induced apoptosis in U-937 cells. These findings further suggest that these compounds may have a potential therapeutic role in the treatment of hematological malignancies. 相似文献
154.
Zanek MC Reyes CA Cervera M Peña EJ Velázquez K Costa N Plata MI Grau O Peña L García ML 《Plant cell reports》2008,27(1):57-66
Citrus psorosis is a serious viral disease affecting citrus trees in many countries. Its causal agent is Citrus psorosis virus (CPsV), the type member of genus Ophiovirus. CPsV infects most important citrus varieties, including oranges, mandarins and grapefruits, as well as hybrids and citrus
relatives used as rootstocks. Certification programs have not been sufficient to control the disease and no sources of natural resistance have been found.
Pathogen-derived resistance (PDR) can provide an efficient alternative to control viral diseases in their hosts. For this
purpose, we have produced 21 independent lines of sweet orange expressing the coat protein gene of CPsV and five of them were
challenged with the homologous CPV 4 isolate. Two different viral loads were evaluated to challenge the transgenic plants,
but so far, no resistance or tolerance has been found in any line after 1 year of observations. In contrast, after inoculation
all lines showed characteristic symptoms of psorosis in the greenhouse. The transgenic lines expressed low and variable amounts
of the cp gene and no correlation was found between copy number and transgene expression. One line contained three copies of the cp gene, expressed low amounts of the mRNA and no coat protein. The ORF was cytosine methylated suggesting a PTGS mechanism,
although the transformant failed to protect against the viral load used. Possible causes for the failed protection against
the CPsV are discussed. 相似文献
155.
Fialho Lda S Guimarães VM Callegari CM Reis AP Barbosa DS Borges EE Moreira MA de Rezende ST 《Phytochemistry》2008,69(14):2579-2585
Tachigali multijuga Benth. seeds were found to contain protein (364 mg g(-1)dwt), lipids (24 mg g(-1)dwt), ash (35 mg g(-1)dwt), and carbohydrates (577 mg g(-1)dwt). Sucrose, raffinose, and stachyose concentrations were 8.3, 3.0, and 11.6 mg g(-1)dwt, respectively. alpha-Galactosidase activity increased during seed germination and reached a maximum level at 108 h after seed imbibition. The alpha-galactosidase purified from germinating seeds had an M(r) of 38,000 and maximal activity at pH 5.0-5.5 and 50 degrees C. The enzyme was stable at 35 degrees C and 40 degrees C, but lost 79% of its activity after 30 min at 50 degrees C. The activation energy (E(a)) values for p-nitrophenyl-alpha-d-galactopyranoside (pNPGal) and raffinose were 13.86 and 4.75 kcal mol(-1), respectively. The K(m) values for pNPGal, melibiose, raffinose, and stachyose were 0.45, 5.37, 39.62 and 48.80 mM, respectively. The enzyme was sensitive to inhibition by HgCl(2), SDS, AgNO(3), CuSO(4), and melibiose. d-Galactose was a competitive inhibitor (K(i)=2.74 mM). In addition to its ability to hydrolyze raffinose and stachyose, the enzyme also hydrolyzed galactomannan. 相似文献
156.
Chemosensory neurons in the olfactory epithelium (OE) project axonal processes to the olfactory bulb (OB) of the brain. During
embryonic stages, on their trajectory to the OB, the outgrowing axons traverse the so-called cribriform mesenchyme, which
is located between the OE and the OB. The molecular cues guiding these axons through the cribriform mesenchyme are largely
unknown. To identify molecules influencing the axonal trajectory in the murine cribriform mesenchyme, we performed microarray
analyses focusing on extracellular matrix (ECM) proteins present in this tissue. Thereby, the ECM protein Reelin turned out
to be an interesting candidate. Reelin was found to be expressed by numerous cells in the cribriform mesenchyme during the
embryonic stages when the first axons navigate from the OE to the OB. These cells were closely associated with olfactory axons
and apparently lack glial and neuronal markers. In the mesenchyme underlying the OE, localization of the Reelin protein was
not confined to the Reelin-expressing cells, but it was also observed to be widely distributed in the ECM—most prominently
in regions traversed by olfactory axons. Importantly, these axons were found to be endowed with the Reelin receptor very-low-density
lipoprotein receptor (VLDLR). Finally, Reelin expression was also detectable in neuronal cells of the OB, which are contacted
by VLDLR-positive olfactory axons. In summary, the results of the present study suggest that a Reelin/VLDLR signaling pathway
might contribute to the formation of olfactory projections to the OB and the establishment of initial contacts between the
incoming axons and neurons in the OB.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Funding: This work was supported by the Deutsche Forschungsgemeinschaft. 相似文献
157.
Carina Nielsen Maximilian Casteel Andrea Didier Richard Dietrich Erwin Märtlbauer 《Mycotoxin Research》2009,25(2):77-84
Trichothecene cytotoxicity of type A (T-2 toxin and HT-2 toxin), type B (deoxynivalenol, DON, and nivalenol, NIV), and type
D (satratoxins G and H) compounds was determined comparatively by using eight permanent human cell lines (Hep-G2, A549, CaCo-2,
HEp-2, A204, U937, RPMI 8226, and Jurkat). Viability of cells was measured by a water-soluble tetrazolium (WST-1) reagent
cell proliferation assay assessing mitochondrial metabolic activity. Toxicity was expressed as the toxin concentration inhibiting
50% of cell viability (IC50). Depending on the chemotype of the tested trichothecenes, relative cytotoxic activity differed by a factor of 100–1,000,
and the corresponding IC50 values were in the range from 2.2 nmol/l (satratoxin H on Jurkat and U937 cells) to 4,900 nmol/l (deoxynivalenol on HEp-2
cells). In contrast, the specific toxicity of each individual mycotoxin towards different cell lines was within remarkable
close limits, and between-cell line differences were much smaller than previously reported. For the cell lines tested, IC50 values were 4.4–10.8 nmol/l for T-2 toxin, 7.5–55.8 mol/l for HT-2 toxin, 600–4,900 nmol/l for DON, 300–2,600 nmol/l for
NIV, and 2.2–18.3 nmol/l for satratoxins G/H. In addition, for the first time, the toxic activity of trichothecenes on primary
cell culture of human endothelial cells (HUVEC) was tested. The susceptibility of this cell line was comparable to the other
cell lines tested, with IC50 values ranging from 16.5 nmol/l (T-2 toxin) to 4,500 nmol/l (DON). The results suggest that the current focus of cytotoxicological
studies on trichothecenes on lymphoid cell lines may lead to an underestimate of their potential on other target cell systems. 相似文献
158.
Carina Klein Anja Grahnert Aliaa Abdelrahman Christa E. Müller Sunna Hauschildt 《Cell calcium》2009,46(4):263-272
Extracellular nicotinamide adenine dinucleotide (NAD+) is known to increase the intracellular calcium concentration [Ca2+]i in different cell types and by various mechanisms. Here we show that NAD+ triggers a transient rise in [Ca2+]i in human monocytes activated with lipopolysaccharide (LPS), which is caused by a release of Ca2+ from IP3-responsive intracellular stores and an influx of extracellular Ca2+. By the use of P2 receptor-selective agonists and antagonists we demonstrate that P2 receptors play a role in the NAD+-induced calcium response in activated monocytes. Of the two subclasses of P2 receptors (P2X and P2Y) the P2Y receptors were considered the most likely candidates, since they share calcium signaling properties with NAD+. The identification of P2Y1 and P2Y11 as receptor subtypes responsible for the NAD+-triggered increase in [Ca2+]i was supported by several lines of evidence. First, specific P2Y1 and P2Y11 receptor antagonists inhibited the NAD+-induced increase in [Ca2+]i. Second, NAD+ was shown to potently induce calcium signals in cells transfected with either subtype, whereas untransfected cells were unresponsive. Third, NAD+ caused an increase in [cAMP]i, prevented by the P2Y11 receptor-specific antagonist NF157. 相似文献
159.
Júlio César Bicca-Marques Carina Barboza Muhle Helissandra Mattjie Prates Sabine Garcia de Oliveira Cláudia Calegaro-Marques 《International journal of primatology》2009,30(5):743-748
Species response to habitat loss, fragmentation, or alteration ranges from intolerance and extinction to tolerance and population
growth. An ability to increase trophic niche breadth is likely to play a key role in promoting tolerance to habitat change
in many species. Howlers (Alouatta spp.) are good examples of these tolerant species. Researchers have related their capacity to thrive well in disturbed habitats
to their ability to exploit an eclectic vegetarian diet. Despite >50,000 h of observation of habituated free-ranging groups
throughout the distribution of Alouatta, no case of intentional ingestion of animal matter has ever been observed. Here, we report an unexpected trophic niche broadening
for free-ranging groups of black-and-gold howlers (Alouatta caraya) living in small (≤2 ha) impoverished habitat islands in the State of Rio Grande do Sul, Brazil. We studied 3 isolated social
groups (15–17, 12–14, and 5 individuals) and observed 1 of them preying on birds’ nests. We recorded 19 events of egg-eating
during 2274 h of observation in 1 group and 2 suspected cases in another. Our findings highlight the dietary flexibility that
characterize howlers and contrast with the widely held view that they observe a strictly vegetarian diet. 相似文献
160.