全文获取类型
收费全文 | 357篇 |
免费 | 16篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 14篇 |
2012年 | 36篇 |
2011年 | 38篇 |
2010年 | 15篇 |
2009年 | 17篇 |
2008年 | 26篇 |
2007年 | 22篇 |
2006年 | 37篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有373条查询结果,搜索用时 312 毫秒
31.
Hartmann B Castelo R Miñana B Peden E Blanchette M Rio DC Singh R Valcárcel J 《RNA (New York, N.Y.)》2011,17(3):453-468
In Drosophila melanogaster, female-specific expression of Sex-lethal (SXL) and Transformer (TRA) proteins controls sex-specific alternative splicing and/or translation of a handful of regulatory genes responsible for sexual differentiation and behavior. Recent findings in 2009 by Telonis-Scott et al. document widespread sex-biased alternative splicing in fruitflies, including instances of tissue-restricted sex-specific splicing. Here we report results arguing that some of these novel sex-specific splicing events are regulated by mechanisms distinct from those established by female-specific expression of SXL and TRA. Bioinformatic analysis of SXL/TRA binding sites, experimental analysis of sex-specific splicing in S2 and Kc cells lines and of the effects of SXL knockdown in Kc cells indicate that SXL-dependent and SXL-independent regulatory mechanisms coexist within the same cell. Additional determinants of sex-specific splicing can be provided by sex-specific differences in the expression of RNA binding proteins, including Hrp40/Squid. We report that sex-specific alternative splicing of the gene hrp40/squid leads to sex-specific differences in the levels of this hnRNP protein. The significant overlap between sex-regulated alternative splicing changes and those induced by knockdown of hrp40/squid and the presence of related sequence motifs enriched near subsets of Hrp40/Squid-regulated and sex-regulated splice sites indicate that this protein contributes to sex-specific splicing regulation. A significant fraction of sex-specific splicing differences are absent in germline-less tudor mutant flies. Intriguingly, these include alternative splicing events that are differentially spliced in tissues distant from the germline. Collectively, our results reveal that distinct genetic programs control widespread sex-specific splicing in Drosophila melanogaster. 相似文献
32.
Chawla R Arora R Kumar R Sharma A Prasad J Singh S Sagar R Chaudhary P Shukla S Kaur G Sharma RK Puri SC Dhar KL Handa G Gupta VK Qazi GN 《Molecular and cellular biochemistry》2005,273(1-2):193-208
Whole extract of rhizomes of Podophyllum hexandrum has been reported earlier by our group to render whole-body radioprotection. High-altitude P. hexandrum (HAPH) was therefore fractionated using solvents of varying polarity (non-polar to polar) and the different fractions were designated as, n-hexane (HE), chloroform (CE), alcohol (AE), hydro-alcohol (HA) and water (WE). The total polyphenolic content (mg% of quercetin) was determined spectrophotometrically, while. The major constituents present in each fraction were identified and characterized using LC-APCI/MS/MS. In vitro screening of the individual fractions, rich in polyphenols and lignans, revealed several bioactivities of direct relevance to radioprotection e.g. metal-chelation activity, antioxidant activity, DNA protection, inhibition of radiation (250 Gy) and iron/ascorbate-induced lipid peroxidation (LPO). CE exhibited maximum protection to plasmid (pBR322) DNA in the plasmid relaxation assay (68.09% of SC form retention). It also showed maximal metal chelation activity (41.59%), evaluated using 2,2-bipyridyl assay, followed by AE (31.25%), which exhibited maximum antioxidant potential (lowest absorption unit value: 0.0389± 0.00717) in the reducing power assay. AE also maximally inhibited iron/ascorbate-induced and radiation-induced LPO (99.76 and 92.249%, respectively, at 2000 g/ml) in mouse liver homogenate. Under conditions of combined stress (radiation (250 Gy) + iron/ascorbate), at a concentration of 2000 g/ml, HA exhibited higher percentage of inhibition (93.05%) of LPO activity. HA was found to be effective in significantly (p < 0.05) lowering LPO activity over a wide range of concentrations as compared to AE. The present comparative study indicated that alcoholic (AE) and hydro-alcoholic (HA) fractions are the most promising fractions, which can effectively tackle radiation-induced oxidative stress. 相似文献
33.
Puckett JL Liu J Bhalla V Kravetz D Krinsky ML Hassanein T Mittal RK 《American journal of physiology. Gastrointestinal and liver physiology》2005,288(5):G914-G919
We report our experience with an ultrasound system to measure esophageal varix pressure in an in vitro model. The ultrasound system consists of a 12.5 MHz frequency intraluminal ultrasound probe, a water infusion catheter, and a manometry catheter, all contained within a nondistensible latex bag. Esophagi and external jugular veins were harvested from five pigs. The vein and ultrasound system were placed inside the esophagus. One end of the vein was connected to a water reservoir to modulate its pressure; the other end was connected in two different ways to simulate hydrodynamic and hydrostatic flow conditions. The bag was inflated with water until vein occlusion was discernible on the ultrasound images. The influences of vein pressure, vein cross-sectional area and esophageal elasticity on the ultrasound measurement of vein pressure were assessed. A total of 108 trials were performed at nine different vein pressures. Complete vein occlusion occurred when the bag pressure was slightly greater (1.4 +/- 0.7 mmHg) than the vein pressure. For a vein pressure of 25 mmHg, the average occlusion and opening pressures were 27 +/- 0.2 and 25.7 +/- 0.3 mmHg, respectively (P < .05) suggesting that the vein opening pressure on the ultrasound images is more accurate than the vein closing pressure. In conclusion, the ultrasound technique can accurately measure intravariceal pressure in vitro. The bag pressure at the point of vein reopening is the best determinant of the vein pressure. 相似文献
34.
Flinn B Rothwell C Griffiths R Lägue M DeKoeyer D Sardana R Audy P Goyer C Li XQ Wang-Pruski G Regan S 《Plant molecular biology》2005,59(3):407-433
To help develop an understanding of the genes that govern the developmental characteristics of the potato (Solanum tuberosum), as well as the genes associated with responses to specified pathogens and storage conditions, The Canadian Potato Genome
Project (CPGP) carried out 5′ end sequencing of regular, normalized and full-length cDNA libraries of the Shepody potato cultivar,
generating over 66,600 expressed sequence tags (ESTs). Libraries sequenced represented tuber developmental stages, pathogen-challenged
tubers, as well as leaf, floral developmental stages, suspension cultured cells and roots. All libraries analysed to date
have contributed unique sequences, with the normalized libraries high on the list. In addition, a low molecular weight library
has enhanced the 3′ ends of our sequence assemblies. Using the combined assembly dataset, unique tuber developmental, cold
storage and pathogen-challenged sequences have been identified. A comparison of the ESTs specific to the pathogen-challenged
tuber and foliar libraries revealed minimal overlap between these libraries. Mixed assemblies using over 189,000 potato EST
sequences from CPGP and The Institute for Genomics Research (TIGR) has revealed common sequences, as well as CPGP- and TIGR-unique
sequences.
Electronic Supplementary Material Electronic Supplementary material is available for this article at
and accessible for authorised users. 相似文献
35.
Here we describe, determine the prevalence, and examine the host-specificity of some parasitic nematode microfilariae in selected bird species from West and Central Africa. We used microscopy to determine the prevalence of microfilariae in 969 host individuals representing 121 rainforest bird species from Cameroon, Côte d’Ivoire and Equatorial Guinea. Thirteen (11%) of these potential host species harboured microfilariae, and 35 individuals (3.6%) were infected. From the 35 infected individuals, we identified eight distinct morphological microfilarial forms. Sixteen of the 35 infected individuals were of one host species, the Fire-crested Alethe (Alethe diademata), at a prevalence rate of 62%. To examine host and geographical specificity, we sequenced a portion of the LSU rDNA gene from representative microfilariae drawn from different hosts and collecting locations. Identical sequences of the nematode LSU rDNA gene were found in A. diademata collected from locations in Côte d’Ivoire and Equatorial Guinea, locations separated by the Dahomey Gap and associated with different hypothesized refugial areas. In contrast, several other bird species collected at the same sites harboured different microfilaria lineages. We sequenced the mitochondrial ATP synthase genes of the host species A. diademata, and found a 5.4% sequence divergence between the birds sampled in Côte d’Ivoire, and those from Cameroon. Thus, despite this split between the two populations, they harbour microfilariae with identical lineages. These data provide evidence that the microfilariae found in A. diademata may be highly host specific. This apparent specificity may have important implications for the evolutionary and ecological interactions between parasitic nematodes and their avian hosts. 相似文献
36.
Das B Ramu R Venkateswarlu K Rao YK Reddy MR Ramakrishna KV Harakishore K Murty US 《化学与生物多样性》2006,3(2):175-179
Two new ent-clerodane-type diterpenoids, compounds 1 and 2, were isolated from the aerial parts of Pulicaria wightiana, together with three known constituents. Their structures were established based on spectroscopic data, and their antibacterial activities were evaluated (Table 2). 相似文献
37.
Batish DR Singh HP Setia N Kaur S Kohli RK 《Zeitschrift für Naturforschung. C, Journal of biosciences》2006,61(9-10):709-714
BOA (2-benzoxazolinone) is a potent phytotoxin present in several graminaceous crops such as rye, maize and wheat. Due to its wide range of phytotoxicity, it is considered as a potential pesticide. A study was conducted to explore the impact of BOA on the radicle and plumule elongation of mung bean (Phaseolus aureus) and associated changes in the macromolecular content - proteins and carbohydrates - and activities of enzymes like amylases, proteases, polyphenol oxidases and peroxidases. BOA significantly reduced the radicle and plumule length of P. aureus, and the contents of proteins and carbohydrates in both root and leaf tissue. On the other hand, activities of hydrolytic enzymes - proteases, amylases, polyphenol oxidases and peroxidases - increased substantially in both root and leaf tissue of P. aureus upon BOA exposure. This indicated that BOA treatment induced stress in P. aureus and enhanced enzyme activities to counter the induced stress and continue the growth. In other words, BOA-induced stress altered the plant biochemical status and related enzyme activities resulting in increased metabolism that serves to provide protection against cellular injury. Such studies providing information about the biomolecular content and enzymatic activities in response to natural products serve as clues for furtherance of knowledge about the modes of action of natural compounds of commercial interest. 相似文献
38.
Vijayakumar S Merkx-Jacques A Ratnayake DB Gryski I Obhi RK Houle S Dozois CM Creuzenet C 《The Journal of biological chemistry》2006,281(38):27733-27743
Campylobacter jejuni produces glycoproteins that are essential for virulence. These glycoproteins carry diacetamidobacillosamine (DAB), a sugar that is not found in humans. Hence, the enzymes responsible for DAB synthesis represent potential therapeutic targets. We describe the biochemical characterization of Cj1121c, a putative aminotransferase encoded by the general protein glycosylation locus, to assess its role in DAB biosynthesis. By using overexpressed and affinity-purified enzyme, we demonstrate that Cj1121c has pyridoxal phosphate- and glutamate-dependent UDP-4-keto-6-deoxy-GlcNAc C-4 transaminase activity and produces UDP-4-amino-4,6-dideoxy-GlcNAc. This is consistent with a role in DAB biosynthesis and distinguishes Cj1121c from Cj1294, a homologous UDP-2-acetamido-2,6-dideoxy-beta-l-arabino-4-hexulose C-4 aminotransferase that we characterized previously. We show that Cj1121c can also use this 4-keto-arabino sugar indirectly as a substrate, that Cj1121c and Cj1294 are active simultaneously in C. jejuni, and that the activity of Cj1121c is preponderant under standard growth conditions. Kinetic data indicate that Cj1121c has a slightly higher catalytic efficiency than Cj1294 with regard to the 4-keto-arabino substrate. By site-directed mutagenesis, we show that residues Glu-158 and Leu-131 are not essential for catalysis or for substrate specificity contrary to expectations. We further demonstrate that a cj1121c knock-out mutant is impaired for flagella-mediated motility, for invasion of intestinal epithelial cells, and for persistence in the chicken intestine, clearly demonstrating that Cj1121c is essential for host colonization and virulence. Finally, we show that cj1121c is necessary for protein glycosylation by lectin Western blotting. Collectively, these results validate Cj1121c as a promising drug target and provide the means to assay for inhibitors. 相似文献
39.
Ravinder K. Kohli Daizy R. Batish H. P. Singh Kuldip S. Dogra 《Biological invasions》2006,8(7):1501-1510
Invasive weeds have threatened the integrity of ecosystems throughout the world. They affect not only the species diversity
of native areas but also their biological integrity. In India, a number of invasive exotic weeds have been reported but some
viz. Parthenium hysterophorus, Lantana camara and Ageratum conyzoides, especially those from tropical America are troublesome and have caused adverse ecological, economic and social impact. These
weeds can be seen growing in different landscapes but are luxuriantly localized in unattended forests and cultivated areas.
Parthenium hysterophorus (Asteraceae, commonly known as congress grass) is perhaps the most troublesome and noxious weed of urban and rural India.
Besides rapidly colonizing areas replacing the native vegetation, it is also known to cause a number of human health problems
such as skin allergy, rhinitis and irritation to eyes of the residents in the vicinity. Likewise, it causes fodder scarcity
in addition to being unpalatable and toxic to livestock. Lantana camara (Verbenaceae), another serious tropical American pest, has encroached upon large areas of land, especially the forests where
it has virtually replaced the forest floor vegetation and reduced tree growth. Also because of its bushy and spreading type
of growth it obstructs forest operations. The third weed, Ageratum conyzoides (Asteraceae, Billy goat weed) has invaded agricultural fields. It interferes with crops and causes yield reductions of major
staple crops of India. When it invades rangeland areas, it out competes native grasses causing scarcity of fodder. These weeds
have similar growth strategies such as fast growth rates, short life-cycles, greater reproductive potential, high competitive
abilities and allelopathy that make them successful invaders of native habitats. Mechanical, chemical, biological and cultural
control tactics have failed individually, though integrated approaches combining all these approaches along with community
participation and proper land management have been relatively successful. This paper presents various aspects of biology,
ecology, hazards and control measures of these weeds. 相似文献
40.
Singh S Ahmad R Mathur D Sagar RK Krishana B 《Indian journal of experimental biology》2006,44(9):699-704
Brain derived neurotrophic factor (BDNF) has been shown to exert trophic effects on dopaminergic neurons against 6-hydroxydopamine (6-OHDA) in young rat. Since the degeneration of substantia nigra dopaminergic neurons that occurs in Parkinson's disease is more often than not confined to elderly individuals, it is of interest to determine whether the effects of BDNF against 6 hydroxydopamine (6-OHDA) in young rats can be extended to aged animals. 6-hydroxydopamine was stereotaxically injected into the striatum of young (3-months) and aged (24-months) rats, which were treated two hours earlier with BDNF. 6-OHDA results in almost complete destruction of substantia nigra pars compacta dopaminergic neurons. BDNF injection significantly changed apomorphine induced rotations from 132 +/- 15 to 181 +/- 10, staircase test from 73 +/- 2% to 61 +/- 3%, initiation time from 7 +/- 2 to 12 +/- 1 sec, and disengage time from 80 +/- 7 to 90 +/- 5 sec in young and aged animals, respectively. It is concluded that BDNF causes the limited behavior recovery of striatal DA systems from 6-OHDA toxicity in aged animals. 相似文献