全文获取类型
收费全文 | 1054篇 |
免费 | 65篇 |
国内免费 | 1篇 |
出版年
2023年 | 13篇 |
2022年 | 32篇 |
2021年 | 56篇 |
2020年 | 23篇 |
2019年 | 22篇 |
2018年 | 41篇 |
2017年 | 42篇 |
2016年 | 41篇 |
2015年 | 77篇 |
2014年 | 70篇 |
2013年 | 96篇 |
2012年 | 105篇 |
2011年 | 96篇 |
2010年 | 54篇 |
2009年 | 48篇 |
2008年 | 57篇 |
2007年 | 52篇 |
2006年 | 45篇 |
2005年 | 33篇 |
2004年 | 31篇 |
2003年 | 30篇 |
2002年 | 30篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1120条查询结果,搜索用时 15 毫秒
951.
952.
Background
The current development of brain-machine interface technology is limited, among other factors, by concerns about the long-term stability of single- and multi-unit neural signals. In addition, the understanding of the relation between potentially more stable neural signals, such as local field potentials, and motor behavior is still in its early stages.Methodology/Principal Findings
We tested the hypothesis that spatial correlation patterns of neural data can be used to decode movement target direction. In particular, we examined local field potentials (LFP), which are thought to be more stable over time than single unit activity (SUA). Using LFP recordings from chronically implanted electrodes in the dorsal premotor and primary motor cortex of non-human primates trained to make arm movements in different directions, we made the following observations: (i) it is possible to decode movement target direction with high fidelity from the spatial correlation patterns of neural activity in both primary motor (M1) and dorsal premotor cortex (PMd); (ii) the decoding accuracy of LFP was similar to the decoding accuracy obtained with the set of SUA recorded simultaneously; (iii) directional information varied with the LFP frequency sub-band, being greater in low (0.3–4 Hz) and high (48–200 Hz) frequency bands than in intermediate bands; (iv) the amount of directional information was similar in M1 and PMd; (v) reliable decoding was achieved well in advance of movement onset; and (vi) LFP were relatively stable over a period of one week.Conclusions/Significance
The results demonstrate that the spatial correlation patterns of LFP signals can be used to decode movement target direction. This finding suggests that parameters of movement, such as target direction, have a stable spatial distribution within primary motor and dorsal premotor cortex, which may be used for brain-machine interfaces. 相似文献953.
Background
JAMA introduced a requirement for independent statistical analysis for industry-funded trials in July 2005. We wanted to see whether this policy affected the number of industry-funded trials published by JAMA.Methods and Findings
We undertook a retrospective, before-and-after study of published papers. Two investigators independently extracted data from all issues of JAMA published between 1 July 2002 and 30 June 2008 (i.e., three years before and after the policy). They were not blinded to publication date. The randomized controlled trials (RCTs) were classified as industry funded (IF), joint industry/non-commercial funding (J), industry supported (IS) (when manufacturers provided materials only), non-commercial (N) or funding not stated (NS). Findings were compared and discrepancies resolved by discussion or further analysis of the reports. RCTs published in The Lancet and NEJM over the same period were used as a control group. Between July 2002 and July 2008, JAMA published 1,314 papers, of which 311 were RCTs. The number of industry studies (IF, J or IS) fell significantly after the policy (p = 0.02) especially for categories J and IS. However, over the same period, the number of industry studies rose in both The Lancet and NEJM.Conclusions
After the requirement for independent statistical analysis for industry-funded studies, JAMA published significantly fewer RCTs and significantly fewer industry-funded RCTs. This pattern was not seen in the control journals. This suggests the JAMA policy affected the number of submissions, the acceptance rate, or both. Without analysing the submissions, we cannot check these hypotheses but, assuming the number of published papers is related to the number submitted, our findings suggest that JAMA''s policy may have resulted in a significant reduction in the number of industry-sponsored trials it received and published. 相似文献954.
Jain R Vangapandu S Jain M Kaur N Singh S Singh PP 《Bioorganic & medicinal chemistry letters》2002,12(13):1701-1704
We report in vitro antimalarial activities against chloroquine sensitive and resistant Plasmodium falciparum strains, and in vivo activities against Plasmodium berghei in mice for four series of ring-substituted-L-histidines and histamines. 相似文献
955.
Kumar A Singh BK Tyagi R Jain SK Sharma SK Prasad AK Raj HG Rastogi RC Watterson AC Parmar VS 《Bioorganic & medicinal chemistry》2005,13(13):4300-4305
Our earlier observations led to the identification of a microsomal enzyme termed as acetoxy drug: protein transacetylase (TAase) catalyzing the transfer of acetyl groups from acetylated polyphenols to the receptor proteins. TAase was conveniently assayed by the irreversible inhibition of cytosolic glutathione S-transferase (GST) by the model acetoxycoumarin, 7,8-diacetoxy-4-methylcoumarin (1). The specificities of the acetoxy group on the benzenoid ring and position of the pyran carbonyl group of the coumarin with respect to oxygen heteroatom for the catalytic activity of TAase were also reported earlier. In this communication, we have demonstrated that the acetoxy coumarins and acetoxy dihydrocoumarins having a methyl group instead of a phenyl ring at the C-4, when used as the substrates, resulted in enhancement of TAase activity, while the saturation of double bond at C-3 and C-4 position had no effect on TAase activity. A comparison of the optimized structures of 1 and 7,8-diacetoxy-4-phenylcoumarin (2) suggested that the observed influence may be due to out of plane configuration of the phenyl ring at C-4. Further, the TAase-catalyzed activation of NADPH cytochrome c reductase and inhibition of aflatoxin B1 (AFB1)-DNA binding by acetoxy 4-phenylcoumarins and dihydrocoumarins were significantly lower as compared to those caused by acetoxy 4-methylcoumarins. 相似文献
956.
Chintan Kapadia Alaa Alhazmi Nafisa Patel Basem H. Elesawy R.Z. Sayyed Fatema Lokhandwala Shafiul Haque Rahul Datta 《Saudi Journal of Biological Sciences》2021,28(8):4164-4172
Enteric fever caused by Salmonella typhi has been the most crucial health issue in rural people, especially in Southeast Asia and Africa. Another disease, Salmonellosis, caused by a large group of bacteria of the genus Salmonella, cause substantial economic loss resulting from mortality and morbidity. Higher concentration and repeated use of antibiotics to treat these diseases will likely develop antibiotic resistance among the microbes. The nanoparticle has good penetration power and can kill microbes. Combining two strategies by using nanoparticles with antibiotics kills microbes and reduces the chances of the development of antibiotics resistance. Silver, Nickel, Copper, and Zinc oxide Nanoparticles were chemically synthesized and characterized in this study. Silver nanoparticles at a concentration of 10 µg/ml inhibit all the strains under study.In comparison, silver nanoparticles (16.90 µg/ml), Nickel nanoparticles (83 µg ml?1), Copper nanoparticles (249 µg ml?1), and Zinc oxide (1614 µg ml?1) along with 50 µg/ml cefixime gave maximum zone of inhibition of 35 mm, 19 mm, 31 mm and 23 mm respectively. The antimicrobial assay showed that silver nanoparticles presented good antibacterial performance against all multi-drug-resistant pathogenic Salmonella sp alone as well as in combinations. The present study proved that silver nanoparticles at the lowest concentration along with cefixime could be a possible alternative to control the multi-drug-resistant pathogens. 相似文献
957.
Elisabetta Barresi Rahul Ravichandran Lorenzo Germelli Andrea Angeli Emma Baglini Silvia Salerno Anna Maria Marini Barbara Costa Eleonora Da Pozzo Claudia Martini Federico Da Settimo Claudiu Supuran Sandro Cosconati Sabrina Taliani 《Journal of enzyme inhibition and medicinal chemistry》2021,36(1):1783
Carbonic Anhydrase Activators (CAAs) could represent a novel approach for the treatment of Alzheimer’s disease, ageing, and other conditions that require remedial achievement of spatial learning and memory therapy. Within a research project aimed at developing novel CAAs selective for certain isoforms, three series of indole-based derivatives were investigated. Enzyme activation assay on human CA I, II, VA, and VII isoforms revealed several effective micromolar activators, with promising selectivity profiles towards the brain-associated cytosolic isoform hCA VII. Molecular modelling studies suggested a theoretical model of the complex between hCA VII and the new activators and provide a possible explanation for their modulating as well as selectivity properties. Preliminary biological evaluations demonstrated that one of the most potent CAA 7 is not cytotoxic and is able to increase the release of the brain-derived neurotrophic factor (BDNF) from human microglial cells, highlighting its possible application in the treatment of CNS-related disorders. 相似文献
958.
A rapid, in-process assessment of virus replication is disired to quickly investigate the effects of process parameters on virus infection, and to monitor consistency of process in routine manufacturing of viral vaccines. Live virus potency assays are generally based on plaque formation, cytopathic effect, or antigen production (TCID50) and can take days to weeks to complete. Interestingly, when infected with viruses, cultured cells undergo changes in cellular metabolism that can be easily measured. These phenomena appear to be common as they has been observed in a variety of virus-host systems, e.g., in insect cells infected with baculovirus, Vero cells infected with Rotavirus, MRC-5 cells infected with Hepatitis A virus, and MRC-5 cells infected with the Varicella Zoster Virus (VZV). In this article, changes in glycolytic metabolism of MRC-5 cells as a result of CVZ infection are described. Both glucose consumption and lactate production in VZV infected MRC-5 cells are significantly elevated in comparison to uninfected cells. Based on this result, a rapid, in-process assay to follow VZV infection has been developed. The relative increase in lactate production in infected cells () increases as the infection progresses and then plateaus as the infection peaks. This plateau correlates with time of peak virus titer and could be used as a harvest triggering parameter in a virus production process.Xu = cell density of uninfected cellsXi = cell density of infected cellsXT = total cell densityLi = cumulative lactate production in infected culturesLu = cumulative lactate production in uninfected culturesqLi = specific lactate production of infected cellsqLu = specific lactate production of uninfected cellsk1, K2 = constantsList of Symbols 相似文献
959.
Mee-Rye Park Rahul Gauttam Bonnie Fong Yan Chen Hyun Gyu Lim Adam M. Feist Aindrila Mukhopadhyay Christopher J. Petzold Blake A. Simmons Steven W. Singer 《Environmental microbiology》2023,25(2):493-504
The Pseudomonas putida group in the Gammaproteobacteria has been intensively studied for bioremediation and plant growth promotion. Members of this group have recently emerged as promising hosts to convert intermediates derived from plant biomass to biofuels and biochemicals. However, most strains of P. putida cannot metabolize pentose sugars derived from hemicellulose. Here, we describe three isolates that provide a broader view of the pentose sugar catabolism in the P. putida group. One of these isolates clusters with the well-characterized P. alloputida KT2440 (Strain BP6); the second isolate clustered with plant growth-promoting strain P. putida W619 (Strain M2), while the third isolate represents a new species in the group (Strain BP8). Each of these isolates possessed homologous genes for oxidative xylose catabolism (xylDXA) and a potential xylonate transporter. Strain M2 grew on arabinose and had genes for oxidative arabinose catabolism (araDXA). A CRISPR interference (CRISPRi) system was developed for strain M2 and identified conditionally essential genes for xylose growth. A glucose dehydrogenase was found to be responsible for initial oxidation of xylose and arabinose in strain M2. These isolates have illuminated inherent diversity in pentose catabolism in the P. putida group and may provide alternative hosts for biomass conversion. 相似文献
960.
Akash Harish Vipin Kumar Rajneesh Kumar Mishra Jin Seog Gwag Rahul Singhal Anoop Kumar Mukhopadhyay Pushpendra Kumar 《Luminescence》2023,38(7):1297-1306
Here we report a simple, inexpensive, energy benign, yet novel pH-driven chemical precipitation technique to achieve microstructural and band gap engineering of calcium hydroxide nanoparticles (CHNPs). The chemical precipitation route involved the use of 0.4–1.6 M Ca(NO3)2.4H2O solutions as the precursor and 1 M NaOH solution as the precipitator. The simple variation in precursor molarity induces a pH change from about 12.4 to 11.3 in the reactant solution. The CHNPs characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and ultraviolet–visible (UV–Vis) spectroscopy techniques confirm a jump of nanocrystallite size from ~50–70 nm with a concomitant reduction of direct optical band gap energy from ~5.38–5.26 eV. The possible mechanisms that could be operative behind obtaining microstructurally tuned (MT)-CHNPS and band gap engineering (BGE) are discussed from both theoretical and physical process perspectives. Furthermore, the implications of these novel results for possible futuristic applications are briefly hinted upon. 相似文献