全文获取类型
收费全文 | 383篇 |
免费 | 55篇 |
专业分类
438篇 |
出版年
2023年 | 2篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 9篇 |
2015年 | 21篇 |
2014年 | 14篇 |
2013年 | 17篇 |
2012年 | 26篇 |
2011年 | 25篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 26篇 |
2007年 | 22篇 |
2006年 | 16篇 |
2005年 | 18篇 |
2004年 | 18篇 |
2003年 | 14篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有438条查询结果,搜索用时 0 毫秒
1.
The current examination was intended to observe the defensive impacts of embelin against paraquat‐incited lung damage in relationship with its antioxidant and anti‐inflammatory action. Oxidative stress marker, like malondialdehyde (MDA), antioxidative enzymes, for example, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH Px), inflammatory cytokines, such as interleukin‐1β (IL‐1β), tumor necrosis factor‐α, and IL‐6, histological examination, and nuclear factor kappa B/mitogen‐activated protein kinase (NF‐κB/MAPK) gene expression were evaluated in lung tissue. Embelin treatment significantly decreased MDA and increased SOD, CAT, and GSH Px. Embelin significantly reduced levels of inflammatory cytokines in paraquat‐administered and paraquat‐intoxicated rats. In addition, embelin suggestively decreased relative protein expression of nuclear NF‐κB p65, p‐NF‐κBp65, p38 MAPK, and p‐p38 MAPKs in paraquat‐intoxicated rats. The outcomes show the impact of embelin inhibitory action on NF‐κB and MAPK and inflammatory cytokines release, and the decrease of lung tissue damage caused by paraquat. 相似文献
2.
Topoisomerases are essential ubiquitous enzymes, falling into two distinct classes. A number of eubacteria including Escherichia coli, typically contain four topoisomerases, two type I topoisomerases and two type II topoisomerases viz. DNA gyrase and topoisomerase IV. In contrast several other bacterial genomes including mycobacteria, encode for one type I topoisomerase and a DNA gyrase. Here we describe a new type II topoisomerase from Mycobacterium smegmatis which is different from DNA gyrase or topoisomerase IV in its characteristics and origin. The topoisomerase is distinct with respect to domain organization, properties and drug sensitivity. The enzyme catalyses relaxation of negatively supercoiled DNA in an ATP-dependent manner and also introduces positive supercoils to both relaxed and negatively supercoiled substrates. The genes for this additional topoisomerase are not found in other sequenced mycobacterial genomes and may represent a distant lineage. 相似文献
3.
MARIA JOSÉ ASINS IRENE VILLALTA MOHAMED M. ALY RAQUEL OLÍAS PAZ ÁLVAREZ DE MORALES RAÚL HUERTAS JUN LI NOELIA JAIME‐PÉREZ ROSARIO HARO VERÓNICA RAGA EMILIO A. CARBONELL ANDRÉS BELVER 《Plant, cell & environment》2013,36(6):1171-1191
The location of major quantitative trait loci (QTL) contributing to stem and leaf [Na+] and [K+] was previously reported in chromosome 7 using two connected populations of recombinant inbred lines (RILs) of tomato. HKT1;1 and HKT1;2, two tomato Na+‐selective class I‐HKT transporters, were found to be closely linked, where the maximum logarithm of odds (LOD) score for these QTLs located. When a chromosome 7 linkage map based on 278 single‐nucleotide polymorphisms (SNPs) was used, the maximum LOD score position was only 35 kb from HKT1;1 and HKT1;2. Their expression patterns and phenotypic effects were further investigated in two near‐isogenic lines (NILs): 157‐14 (double homozygote for the cheesmaniae alleles) and 157‐17 (double homozygote for the lycopersicum alleles). The expression pattern for the HKT1;1 and HKT1;2 alleles was complex, possibly because of differences in their promoter sequences. High salinity had very little effect on root dry and fresh weight and consequently on the plant dry weight of NIL 157‐14 in comparison with 157‐17. A significant difference between NILs was also found for [K+] and the [Na+]/[K+] ratio in leaf and stem but not for [Na+] arising a disagreement with the corresponding RIL population. Their association with leaf [Na+] and salt tolerance in tomato is also discussed. 相似文献
4.
Ranging from dwarfs to giants, the species of honeybees show remarkable differences in body size that have placed evolutionary constrains on the size of sensory organs and the brain. Colonies comprise three adult phenotypes, drones and two female castes, the reproductive queen and sterile workers. The phenotypes differ with respect to tasks and thus selection pressures which additionally constrain the shape of sensory systems. In a first step to explore the variability and interaction between species size-limitations and sex and caste-specific selection pressures in sensory and neural structures in honeybees, we compared eye size, ommatidia number and distribution of facet lens diameters in drones, queens and workers of five species (Apis andreniformis, A. florea, A. dorsata, A. mellifera, A. cerana). In these species, male and female eyes show a consistent sex-specific organization with respect to eye size and regional specialization of facet diameters. Drones possess distinctly enlarged eyes with large dorsal facets. Aside from these general patterns, we found signs of unique adaptations in eyes of A. florea and A. dorsata drones. In both species, drone eyes are disproportionately enlarged. In A. dorsata the increased eye size results from enlarged facets, a likely adaptation to crepuscular mating flights. In contrast, the relative enlargement of A. florea drone eyes results from an increase in ommatidia number, suggesting strong selection for high spatial resolution. Comparison of eye morphology and published mating flight times indicates a correlation between overall light sensitivity and species-specific mating flight times. The correlation suggests an important role of ambient light intensities in the regulation of species-specific mating flight times and the evolution of the visual system. Our study further deepens insights into visual adaptations within the genus Apis and opens up future perspectives for research to better understand the timing mechanisms and sensory physiology of mating related signals. 相似文献
5.
Pragathi B. Shridhar Lance W. Noll Xiaorong Shi Natalia Cernicchiaro David G. Renter J. Bai T. G. Nagaraja 《PloS one》2016,11(3)
Escherichia coli O104:H4, an hybrid pathotype of Shiga toxigenic and enteroaggregative E. coli, involved in a major foodborne outbreak in Germany in 2011, has not been detected in cattle feces. Serogroup O104 with H type other than H4 has been reported to cause human illnesses, but their prevalence and characteristics in cattle have not been reported. Our objectives were to determine the prevalence of E. coli O104 in feces of feedlot cattle, by culture and PCR detection methods, and characterize the isolated strains. Rectal fecal samples from a total of 757 cattle originating from 29 feedlots were collected at a Midwest commercial slaughter plant. Fecal samples, enriched in E. coli broth, were subjected to culture and PCR methods of detection. The culture method involved immunomagnetic separation with O104-specific beads and plating on a selective chromogenic medium, followed by serogroup confirmation of pooled colonies by PCR. If pooled colonies were positive for the wzxO104 gene, then colonies were tested individually to identify wzxO104-positive serogroup and associated genes of the hybrid strains. Extracted DNA from feces were also tested by a multiplex PCR to detect wzxO104-positive serogroup and associated major genes of the O104 hybrid pathotype. Because wzxO104 has been shown to be present in E. coli O8/O9/O9a, wzxO104-positive isolates and extracted DNA from fecal samples were also tested by a PCR targeting wbdDO8/O9/O9a, a gene specific for E. coli O8/O9/O9a serogroups. Model-adjusted prevalence estimates of E. coli O104 (positive for wzxO104 and negative for wbdDO8/O9/O9a) at the feedlot level were 5.7% and 21.2%, and at the sample level were 0.5% and 25.9% by culture and PCR, respectively. The McNemar’s test indicated that there was a significant difference (P < 0.01) between the proportions of samples that tested positive for wzxO104 and samples that were positive for wzxO104, but negative for wbdDO8/O9/O9a by PCR and culture methods. A total of 143 isolates, positive for the wzxO104, were obtained in pure culture from 146 positive fecal samples. Ninety-two of the 143 isolates (64.3%) also tested positive for the wbdDO8/O9/O9a, indicating that only 51 (35.7%) isolates truly belonged to the O104 serogroup (positive for wzxO104 and negative for wbdDO8/O9/O9a). All 51 isolates tested negative for eae, and 16 tested positive for stx1 gene of the subtype 1c. Thirteen of the 16 stx1-positive O104 isolates were from one feedlot. The predominant serotype was O104:H7. Pulsed-field gel electrophoresis analysis indicated that stx1-positive O104:H7 isolates had 62.4% homology to the German outbreak strain and 67.9% to 77.5% homology to human diarrheagenic O104:H7 strains. The 13 isolates obtained from the same feedlot were of the same PFGE subtype with 100% Dice similarity. Although cattle do not harbor the O104:H4 pathotype, they do harbor and shed Shiga toxigenic O104 in the feces and the predominant serotype was O104:H7. 相似文献
6.
Oral pathogens have created a menace in recent years due to biofilm formation and antimicrobial drug resistance. The current treatment strategy works well with antibiotics. However, constant use of antibiotics creates a selective pressure, which increases adaptability of the pathogens. Therefore, it is of interest to analyze the potential targets of genistein in dental pathogens using computer aided prediction tools. 相似文献
7.
Amal A. Alotaibi Asmatanzeem Bepari Rasha Assad Assiri Shaik Kalimulla Niazi Sreenivasa Nayaka Muthuraj Rudrappa Shashiraj Kareyellapa Nagaraja Meghashyama Prabhakara Bhat 《Current issues in molecular biology》2021,43(2):1114
Background and Objectives: Saussurea lappa (S. lappa) is an important species of the Asteraceae family with several purposes in traditional medicine. This study intended to explore the cytotoxic effect of S. lappa on HepG2 cancer cell proliferation. Materials and Methods: The effects of an S. lappa n-butanol extract on the induction of apoptosis were investigated by flow cytometry and mitochondrial cytochrome C-releasing apoptosis assay. Additionally, real-time PCR was employed to confirm apoptosis initiation. Further, qualitative estimation of the active constituent of S. lappa was done by gas chromatography–mass spectroscopy (GC–MS). Results: The cell viability study revealed that the n-butanol extract of S. lappa demonstrated potent cytotoxicity against HepG2 cancer cells, with an IC50 value of 56.76 μg/mL. Cell morphology with dual staining of acridine orange (AO)-ethidium bromide (EB) showed an increase in orange/red nuclei due to cell death by S. lappa n-butanol extract compared to control cells. Apoptosis, as the mode of cell death, was also confirmed by the higher release of cytochrome C from mitochondria, the increased expression of caspase-3 and bax, along with down regulation of Bcl-2. Conclusion: These findings conclude that S. lappa is a cause of hepatic cancer cell death through apoptosis and a potential natural source suggesting furthermore investigation of its active compounds that are responsible for these observed activities. 相似文献
8.
9.
Background
Annotation of sequences that share little similarity to sequences of known function remains a major obstacle in genome annotation. Some of the best methods of detecting remote relationships between protein sequences are based on matching sequence profiles. We analyse the superfamily specific performance of sequence profile-profile matching. Our benchmark consists of a set of 16 protein superfamilies that are highly diverse at the sequence level. We relate the performance to the number of sequences in the profiles, the profile diversity and the extent of structural conservation in the superfamily. 相似文献10.