全文获取类型
收费全文 | 1195篇 |
免费 | 93篇 |
专业分类
1288篇 |
出版年
2023年 | 14篇 |
2022年 | 31篇 |
2021年 | 29篇 |
2020年 | 27篇 |
2019年 | 22篇 |
2018年 | 37篇 |
2017年 | 27篇 |
2016年 | 32篇 |
2015年 | 33篇 |
2014年 | 57篇 |
2013年 | 76篇 |
2012年 | 108篇 |
2011年 | 70篇 |
2010年 | 41篇 |
2009年 | 36篇 |
2008年 | 43篇 |
2007年 | 65篇 |
2006年 | 38篇 |
2005年 | 36篇 |
2004年 | 46篇 |
2003年 | 35篇 |
2002年 | 47篇 |
2001年 | 34篇 |
2000年 | 38篇 |
1999年 | 33篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 22篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 5篇 |
排序方式: 共有1288条查询结果,搜索用时 15 毫秒
91.
In this paper, we have made a comparative evaluation of the cytotoxicity and pathophysiological effects of mainstream smoke
from cellulose acetate (CA)-filtered cigarettes with that of charcoal-filtered cigarettes developed in our laboratory. Previously,
we had demonstrated that the mainstream smoke from an Indian CA-filtered commercial cigarette contains p-benzosemiquinone
(p-BSQ), a major, highly toxic, long-lived water-soluble radical. Here, we have examined 16 brands of different CA-filtered
cigarettes including Kentucky research cigarettes, and observed that mainstream smoke from all the cigarettes contains substantial
amounts of p-BSQ (100–200 μg/cigarette). We also show that when the CA filter is replaced by a charcoal filter, the amount
of p-BSQ in the mainstream smoke is reduced by 73–80%, which is accompanied by a reduction of carbonyl formation in bovine
serum albumin to the extent of 70–90%. The charcoal filter also prevented cytotoxicity in A549 cells as evidenced by MTT assay,
apoptosis as evidenced by FACS analysis, TUNEL assay, overexpression of Bax, activation of p53 and caspase 3, as well as emphysematous
lung damage in a guinea pig model as seen by histology and morphometric analysis. The results indicate that the charcoal filter
developed in our laboratory may protect smokers from cigarette smoke-induced cytotoxity, protein modification, apoptosis and
emphysema. 相似文献
92.
Biswajit Mishra Vipul Kumar Srivastava Rama Chaudhry Rishi Kumar Somvanshi Abhay Kumar Singh Kamaldeep Gill Ramesh Somvanshi Ishan Kumar Patro Sharmistha Dey 《Amino acids》2010,39(5):1493-1505
Anti-bacterial drug resistance is one of the most critical concerns among the scientist worldwide. The novel antimicrobial
decapeptide SD-8 is designed and its minimal inhibitory concentration and therapeutic index (TI) was found in the range of
1–8 μg/ml and 45–360, respectively, against major group of Gram positive pathogens (GPP). The peptide was also found to be
least hemolytic at a concentration of 180 μg/ml, i.e., nearly 77 times higher than its average effective concentration. The
kinetics assay showed that the killing time is 120 min for methicillin-sensitive Staphylococcus aureus (MSSA) and 90 min for methicillin-resistant S. aureus (MRSA). Membrane permeabilization is the cause of peptide antimicrobial activity as shown by the transmission electron microscopy
studies. The peptide showed the anti-inflammatory property by inhibiting COX-2 with a K
D and K
i values of 2.36 × 10−9 and 4.8 × 10−8 M, respectively. The peptide was also found to be effective in vivo as derived from histopathological observations in a Staphylococcal
skin infection rat model with MRSA as causative organism. 相似文献
93.
Ranadhir Dey Claudio Meneses Poonam Salotra Shaden Kamhawi Hira L. Nakhasi Robert Duncan 《Molecular microbiology》2010,77(2):399-414
Leishmaniasis is caused by the dimorphic protozoan parasite Leishmania. Differentiation of the insect form, promastigotes, to the vertebrate form, amastigotes, and survival inside the vertebrate host accompanies a drastic metabolic shift. We describe a gene first identified in amastigotes that is essential for survival inside the host. Gene expression analysis identified a 27 kDa protein‐encoding gene (Ldp27) that was more abundantly expressed in amastigotes and metacyclic promastigotes than in procyclic promastigotes. Immunofluorescence and biochemical analysis revealed that Ldp27 is a mitochondrial membrane protein. Co‐immunoprecipitation using antibodies to the cytochrome c oxidase (COX) complex, present in the inner mitochondrial membrane, placed the p27 protein in the COX complex. Ldp27 gene‐deleted parasites (Ldp27?/?) showed significantly less COX activity and ATP synthesis than wild type in intracellular amastigotes. Moreover, the Ldp27?/? parasites were less virulent both in human macrophages and in BALB/c mice. These results demonstrate that Ldp27 is an important component of an active COX complex enhancing oxidative phosphorylation specifically in infectious metacyclics and amastigotes and promoting parasite survival in the host. Thus, Ldp27 can be explored as a potential drug target and parasites devoid of the p27 gene could be considered as a live attenuated vaccine candidate against visceral leishmaniasis. 相似文献
94.
Carvalho M Schwudke D Sampaio JL Palm W Riezman I Dey G Gupta GD Mayor S Riezman H Shevchenko A Kurzchalia TV Eaton S 《Development (Cambridge, England)》2010,137(21):3675-3685
The high sterol concentration in eukaryotic cell membranes is thought to influence membrane properties such as permeability, fluidity and microdomain formation. Drosophila cannot synthesize sterols, but do require them for development. Does this simply reflect a requirement for sterols in steroid hormone biosynthesis, or is bulk membrane sterol also essential in Drosophila? If the latter is true, how do they survive fluctuations in sterol availability and maintain membrane homeostasis? Here, we show that Drosophila require both bulk membrane sterol and steroid hormones in order to complete adult development. When sterol availability is restricted, Drosophila larvae modulate their growth to maintain membrane sterol levels within tight limits. When dietary sterol drops below a minimal threshold, larvae arrest growth and development in a reversible manner. Strikingly, membrane sterol levels in arrested larvae are dramatically reduced (dropping sixfold on average) in most tissues except the nervous system. Thus, sterols are dispensable for maintaining the basic membrane biophysical properties required for cell viability; these functions can be performed by non-sterol lipids when sterols are unavailable. However, bulk membrane sterol is likely to have essential functions in specific tissues during development. In tissues in which sterol levels drop, the overall level of sphingolipids increases and the proportion of different sphingolipid variants is altered. These changes allow survival, but not growth, when membrane sterol levels are low. This relationship between sterols and sphingolipids could be an ancient and conserved principle of membrane homeostasis. 相似文献
95.
Methyl-coenzyme M reductase (MCR) from methanogenic archaea catalyzes the terminal step in methanogenesis using coenzyme B (CoBSH) as the two-electron donor to reduce methyl-coenzyme M (methyl-SCoM) to form methane and the heterodisulfide, CoBS-SCoM. The active site of MCR contains an essential redox-active nickel tetrapyrrole cofactor, coenzyme F(430), which is active in the Ni(I) state (MCR(red1)). Several catalytic mechanisms have been proposed for methane synthesis that mainly differ in whether an organometallic methyl-Ni(III) or a methyl radical is the first catalytic intermediate. A mechanism was recently proposed in which methyl-Ni(III) undergoes homolysis to generate a methyl radical (Li, X., Telser, J., Kunz, R. C., Hoffman, B. M., Gerfen, G., and Ragsdale, S. W. (2010) Biochemistry 49, 6866-6876). Discrimination among these mechanisms requires identification of the proposed intermediates, none of which have been observed with native substrates. Apparently, intermediates form and decay too rapidly to accumulate to detectible amounts during the reaction between methyl-SCoM and CoBSH. Here, we describe the reaction of methyl-SCoM with a substrate analogue (CoB(6)SH) in which the seven-carbon heptanoyl moiety of CoBSH has been replaced with a hexanoyl group. When MCR(red1) is reacted with methyl-SCoM and CoB(6)SH, methanogenesis occurs 1000-fold more slowly than with CoBSH. By transient kinetic methods, we observe decay of the active Ni(I) state coupled to formation and subsequent decay of alkyl-Ni(III) and organic radical intermediates at catalytically competent rates. The kinetic data also revealed substrate-triggered conformational changes in active Ni(I)-MCR(red1). Electron paramagnetic resonance (EPR) studies coupled with isotope labeling experiments demonstrate that the radical intermediate is not tyrosine-based. These observations provide support for a mechanism for MCR that involves methyl-Ni(III) and an organic radical as catalytic intermediates. Thus, the present study provides important mechanistic insights into the mechanism of this key enzyme that is central to biological methane formation. 相似文献
96.
Kuntal Dey Tapati Chakraborti Soumitra Roy Biswarup Ghosh Pulak Kar Sajal Chakraborti 《Life sciences》2010,86(13-14):473-481
AimsWe sought to identify, purify and partially characterize a protein inhibitor of Na+/K+-ATPase in cytosol of pulmonary artery smooth muscle.Main methods(i) By spectrophotometric assay, we identified an inhibitor of Na+/K+-ATPase in cytosolic fraction of pulmonary artery smooth muscle; (ii) the inhibitor was purified by a combination of ammonium sulfate precipitation, diethylaminoethyl (DEAE) cellulose chromatography, hydroxyapatite chromatography and gel filtration chromatography; (iii) additionally, we have also purified Na+/K+-ATPase α2β1 and α1β1 isozymes for determining some characteristics of the inhibitor.Key findingsWe identified a novel endogenous protein inhibitor of Na+/K+-ATPase having an apparent mol mass of ~ 70 kDa in the cytosolic fraction of the smooth muscle. The IC50 value of the inhibitor towards the enzyme was determined to be in the nanomolar range. Important characteristics of the inhibitor are as follows: (i) it showed different affinities toward the α2β1 and α1β1 isozymes of the Na+/K+-ATPase; (ii) it interacted reversibly to the E1 site of the enzyme; (iii) the inhibitor blocked the phosphorylated intermediate formation; and (iv) it competitively inhibited the enzyme with respect to ATP. CD studies indicated that the inhibitor causes an alteration of the conformation of the enzyme. The inhibition study also suggested that the DHPC solubilized Na+/K+-ATPase exists as (αβ)2 diprotomer.SignificanceThe inhibitor binds to the Na+/K+-ATPase at a site different from the ouabain binding site. The novelty of the inhibitor is that it acts in an isoform specific manner on the enzyme, where α2 is more sensitive than α1. 相似文献
97.
Stage-specific integration of maternal and embryonic peroxisome proliferator-activated receptor delta signaling is critical to pregnancy success 总被引:1,自引:0,他引:1
Wang H Xie H Sun X Tranguch S Zhang H Jia X Wang D Das SK Desvergne B Wahli W DuBois RN Dey SK 《The Journal of biological chemistry》2007,282(52):37770-37782
98.
Trosky JE Li Y Mukherjee S Keitany G Ball H Orth K 《The Journal of biological chemistry》2007,282(47):34299-34305
The bacterial pathogen Vibrio parahemeolyticus manipulates host signaling pathways during infections by injecting type III effectors. One of these effectors, Vibrio outer protein A (VopA), inhibits MAPK signaling via a novel mechanism, distinct from those described for other bacterial toxins, that disrupts this signaling pathway. VopA is an acetyltransferase that potently inhibits MAPK signaling pathways not only by preventing the activation of MAPK kinases (MKKs) but also by inhibiting the activity of activated MKKs. VopA acetylates a conserved lysine found in the catalytic loop of all kinases and blocks the binding of ATP, but not ADP, on the MKKs, resulting in an inactive phosphorylated kinase. Acetylation of this conserved lysine inhibits kinase activity by a new mechanism of regulation that has not been observed previously. Identifying the target of VopA reveals a way that the reversible post-translational modification of lysine acetylation can be used to regulate the activity of an enzyme. 相似文献
99.
Gupta A Chattopadhyay I Dey S Nasipuri P Das SK Gangopadhyay PK Ray K 《Cellular and molecular neurobiology》2007,27(8):1023-1033
Aims We aim to identify the molecular defects in the ATP7B, the causal gene for Wilson disease (WD), in eastern Indian patients and attempt to assess the overall mutation spectrum
in India for detection of mutant allele for diagnostic purposes. Methods Patients from 109 unrelated families and their first-degree relatives comprising 400 individuals were enrolled in this study
as part of an ongoing project. Genomic DNA was prepared from the peripheral blood of Indian WD patients. PCR was done to amplify
the exons and flanking regions of the WD gene followed by sequencing, to identify the nucleotide variants. Results In addition to previous reports, we recently identified eight mutations including three novel (c.3412 + 1G > A, c.1771 G > A,
c.3091 A > G) variants, and identified patients with variable phenotype despite similar mutation background suggesting potential
role of modifier locus. Conclusions So far we have identified 17 mutations in eastern India including five common mutations that account for 44% of patients.
Comparative study on WD mutations between different regions of India suggests high genetic heterogeneity and the absence of
a single or a limited number of common founder mutations. Genotype–phenotype correlation revealed that no particular phenotype
could be assigned to a particular mutation and even same set of mutations in different patients showed different phenotypes. 相似文献
100.
Human eosinophil-derived neurotoxin (EDN) or RNase 2, found in the non-core matrix of eosinophils is a ribonuclease belonging
to the Ribonuclease A superfamily. EDN manifests a number of bioactions including neurotoxic and antiviral activities, which
are dependent on its ribonuclease activity. The core of the catalytic site of EDN contains various base and phosphate-binding
subsites. Unlike many members of the RNase A superfamily, EDN contains an additional non-catalytic phosphate-binding subsite,
P−1. Although RNase A also contains a P−1 subsite, the composition of the site in EDN and RNase A is different. In the current study we have generated site-specific
mutants to study the role of P−1 subsite residues Arg36, Asn39, and Gln40 of EDN in its catalytic activity. The individual mutation of Arg36, Asn 39, and Gln40 resulted in a reduction in the catalytic activity of EDN on poly(U) and poly(C). However, there was no change in the activities
on yeast tRNA and dinucleotide substrates. The study shows that the P−1 subsite is crucial for the ribonucleolytic activity of EDN on polymeric RNA substrates.
Deepa Sikriwal and Divya Seth contributed equally to this work. 相似文献