首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2052篇
  免费   140篇
  2024年   2篇
  2023年   10篇
  2022年   25篇
  2021年   41篇
  2020年   25篇
  2019年   37篇
  2018年   56篇
  2017年   45篇
  2016年   56篇
  2015年   72篇
  2014年   106篇
  2013年   151篇
  2012年   145篇
  2011年   136篇
  2010年   92篇
  2009年   82篇
  2008年   116篇
  2007年   130篇
  2006年   96篇
  2005年   112篇
  2004年   88篇
  2003年   76篇
  2002年   84篇
  2001年   32篇
  2000年   32篇
  1999年   27篇
  1998年   20篇
  1997年   13篇
  1996年   21篇
  1995年   18篇
  1994年   5篇
  1993年   12篇
  1992年   24篇
  1991年   22篇
  1990年   26篇
  1989年   26篇
  1988年   16篇
  1987年   14篇
  1986年   6篇
  1985年   11篇
  1984年   7篇
  1983年   6篇
  1982年   7篇
  1981年   8篇
  1980年   14篇
  1979年   8篇
  1978年   17篇
  1977年   3篇
  1976年   3篇
  1975年   2篇
排序方式: 共有2192条查询结果,搜索用时 15 毫秒
201.
The potential protective role of Tribulus terrestris in acetaminophen-induced hepatotoxicity in Oreochromis mossambicus was investigated. The effect of oral exposure of acetaminophen (500 mg/kg) in O. mossambicus at 24-h duration was evaluated. The plant extract (250 mg/kg) showed a remarkable hepatoprotective activity against acetaminophen-induced hepatotoxicity. It was judged from the tissue-damaging level and antioxidant levels in liver, gill, muscle and kidney tissues. Further acetaminophen impact induced a significant rise in the tissue-damaging level, and the antioxidant level was discernible from the enzyme activity modulations such as glutamate oxaloacetic transaminase, glutamate pyruvic transaminase, alkaline phosphatase, acid phosphatase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione S-transferase, lipid peroxidase and reduced glutathione. The levels of all these enzymes have significantly (p < 0.05) increased in acetaminophen-treated fish tissues. The elevated levels of these enzymes were significantly controlled by the treatment of T. terrestris extract (250 kg/mg). Histopathological changes of liver, gill and muscle samples were compared with respective controls. The results of the present study specify the hepatoprotective and antioxidant properties of T. terrestris against acetaminophen-induced toxicity in freshwater fish, O. mossambicus.  相似文献   
202.
In a previous paper, the first ever application of lytic bacteriophage (virus)-mediated biocontrol of biomass bulking in the activated sludge process using Haliscomenobacter hydrossis as a model filamentous bacterium was demonstrated. In this work we extended the biocontrol application to another predominant filamentous bacterium, Sphaerotilus natans, notoriously known to cause filamentous bulking in wastewater treatment systems. Very similar to previous study, one lytic bacteriophage was isolated from wastewater that could infect S. natans and cause lysis. Significant reduction in sludge volume index and turbidity of the supernatant was observed in batches containing S. natans biomass following addition of lytic phages. Microscopic examination confirmed that the isolated lytic phage can trigger the bacteriolysis of S. natans. This extended finding further strengthens our hypothesis of bacteriophage-based biocontrol of overgrowth of filamentous bacteria and the possibility of phage application in activated sludge processes, the world's widely used wastewater treatment processes.  相似文献   
203.
Sagili RR  Pankiw T  Metz BN 《PloS one》2011,6(2):e16785
Division of labor is a striking feature observed in honey bees and many other social insects. Division of labor has been claimed to benefit fitness. In honey bees, the adult work force may be viewed as divided between non-foraging hive bees that rear brood and maintain the nest, and foragers that collect food outside the nest. Honey bee brood pheromone is a larval pheromone that serves as an excellent empirical tool to manipulate foraging behaviors and thus division of labor in the honey bee. Here we use two different doses of brood pheromone to alter the foraging stimulus environment, thus changing demographics of colony division of labor, to demonstrate how division of labor associated with brood rearing affects colony growth rate. We examine the effects of these different doses of brood pheromone on individual foraging ontogeny and specialization, colony level foraging behavior, and individual glandular protein synthesis. Low brood pheromone treatment colonies exhibited significantly higher foraging population, decreased age of first foraging and greater foraging effort, resulting in greater colony growth compared to other treatments. This study demonstrates how division of labor associated with brood rearing affects honey bee colony growth rate, a token of fitness.  相似文献   
204.
Prostate cancer (PCa) is the most common type of cancer found in men and among the leading causes of cancer death in the western world. In the present study, we compared the individual protein expression patterns from histologically characterized PCa and the surrounding benign tissue obtained by manual micro dissection using highly sensitive two-dimensional differential gel electrophoresis (2D-DIGE) coupled with mass spectrometry. Proteomic data revealed 118 protein spots to be differentially expressed in cancer (n = 24) compared to benign (n = 21) prostate tissue. These spots were analysed by MALDI-TOF-MS/MS and 79 different proteins were identified. Using principal component analysis we could clearly separate tumor and normal tissue and two distinct tumor groups based on the protein expression pattern. By using a systems biology approach, we could map many of these proteins both into major pathways involved in PCa progression as well as into a group of potential diagnostic and/or prognostic markers. Due to complexity of the highly interconnected shortest pathway network, the functional sub networks revealed some of the potential candidate biomarker proteins for further validation. By using a systems biology approach, our study revealed novel proteins and molecular networks with altered expression in PCa. Further functional validation of individual proteins is ongoing and might provide new insights in PCa progression potentially leading to the design of novel diagnostic and therapeutic strategies.  相似文献   
205.

Background

Post kala-azar dermal leishmaniasis (PKDL), a sequel to visceral leishamaniasis (VL) in 5–15% cases, constitutes a parasite reservoir important in disease transmission. The precise immunological cause of PKDL outcome remains obscure. However, overlapping counter regulatory responses with elevated IFN-γ and IL-10 are reported.

Methodology/Principal Findings

Present study deals with ex-vivo mRNA and protein analysis of natural regulatory T cells (nTreg) markers (Foxp3, CD25 and CTLA-4) and IL-10 levels in lesion tissues of PKDL patients at pre and post treatment stages. In addition, correlation of nTreg markers and IL-10 with parasite load in tissue lesions was investigated. mRNA levels of nTreg markers and IL-10 were found significantly elevated in pre-treatment PKDL cases compared to controls (Foxp3, P = 0.0009; CD25 & CTLA-4, P<0.0001; IL-10, P<0.0001), and were restored after treatment. Analysis of nTreg cell markers and IL-10 in different clinical manifestations of disease revealed elevated levels in nodular lesions compared to macules/papules. Further, Foxp3, CD25 and IL-10 mRNA levels directly correlated with parasite load in lesions tissues.

Conclusion/Significance

Data demonstrated accumulation of nTreg cells in infected tissue and a correlation of both IL-10 and nTreg levels with parasite burden suggesting their role in disease severity in PKDL.  相似文献   
206.
Neff CP  Kurisu T  Ndolo T  Fox K  Akkina R 《PloS one》2011,6(6):e20209
For prevention of HIV infection many currently licensed anti-HIV drugs and new ones in the pipeline show potential as topically applied microbicides. While macaque models have been the gold standard for in vivo microbicide testing, they are expensive and sufficient numbers are not available. Therefore, a small animal model that facilitates rapid evaluation of potential candidates for their preliminary efficacy is urgently needed in the microbicide field. We previously demonstrated that RAG-hu humanized mouse model permits HIV-1 mucosal transmission via both vaginal and rectal routes and that oral pre-exposure chemo-prophylactic strategies could be tested in this system. Here in these proof-of-concept studies, we extended this system for topical microbicide testing using HIV-1 as the challenge virus. Maraviroc, a clinically approved CCR5 inhibitor drug for HIV treatment, was formulated as a microbicide gel at 5 mM concentration in 2.2% hydroxyl ethyl cellulose. Female RAG-hu mice were challenged vaginally with HIV-1 an hour after intravaginal application of the maraviroc gel. Our results showed that maraviroc gel treated mice were fully protected against vaginal HIV-1 challenge in contrast to placebo gel treated mice which all became infected. These findings highlight the utility of the humanized mouse models for microbicide testing and, together with the recent data from macaque studies, suggest that maraviroc is a promising candidate for future microbicide clinical trials in the field.  相似文献   
207.
Coding sequences for a hammerhead ribozyme designed to cleave lexA mRNA in a targeted manner was cloned under phage T7 promoter and expressed in E. coli strain BL-21 (DE3) expressing T7 RNA polymerase under the control of IPTG-inducible lac UV-5 promoter. Ribozyme expression in vivo was demonstrated by RNase protection assay. Also, total RNA extracted from these transformed cells following induction by IPTG, displays site-specific cleavage of labeled lexA RNA in an In vitro reaction. The result demonstrates the active ribozyme in extracts of cell transformed with a recombinant cassette and goes beyond the earlier demonstration of the stability of In vitro synthesized ribozyme in cell extracts. The observed rise in lexA mRNA rules out any role for protease activity or resulting fragments of lexA protein in de-repression of RNA. (Mol Cell Biochem 271: 197–203, 2005)  相似文献   
208.
Accumulating data support the hypothesis that reactive oxygen species (ROS) play a critical role in the vascular complications observed in diabetes. However, the mechanisms of ROS-mediated vascular complications in diabetes are not clear. We tested the hypothesis that ROS-mediated increase in proapoptotic factor Bax expression leads to medial smooth muscle cell (SMC) apoptosis that is associated with neointima formation. We used a fructose-rich diet for 4 wk to model Type 2 diabetes in rats. SOD mimetic membrane-permeable 4-hydroxy-2,2,6,6,-tetramethylpiperidine-1-oxyl (Tempol, 1 mM) was administered in drinking water to scavenge superoxide starting 1 day before surgery and continued during the duration of the experiment. Vascular injury resulted in a significant increase in medial SMC apoptosis that was associated with neointima formation. The number of medial SMC positive for Bax immunostaining significantly increased in injured arteries compared with uninjured arteries. Superoxide scavenging by Tempol treatment inhibited both the Bax-positive index as well as the apoptotic index of medial SMC in response to vascular injury. Tempol treatment inhibited apoptotic loss of medial SMC, thus increasing their density in the injured arteries. These alterations in the media were associated with a marked decrease in neointima formation in injured arteries. We conclude that Bax expression may play an important role in vascular SMC apoptosis and, finally, that this regulatory mechanism is redox sensitive.  相似文献   
209.
Based on morphological analyses, extant members of the order Crocodylia are divided into three families, Alligatoridae, Crocodylidae, and Gavialidae. Gavialidae includes one species, the gharial, Gavialis gangeticus. In this study we have examined crocodilian relationships in phylogenetic analyses of seven mitochondrial genomes that have been sequenced in their entirety. The analyses did not support the morphologically acknowledged separate position of the gharial in the crocodilian tree. Instead the gharial joined the false gharial (Tomistoma schlegelii) on a common branch that was shown to constitute a sister group to traditional Crocodylidae (less Tomistoma). Thus, the analyses suggest the recognition of only two Crocodylia families, Alligatoridae and Crocodylidae, with the latter encompassing traditional Crocodylidae plus Gavialis/Tomistoma. A molecular dating of the divergence between Alligatoridae and Crocodylidae suggests that this basal split among recent crocodilians took place ≈140 million years before present, at the Jurassic/Cretaceous boundary. The results suggest that at least five crocodilian lineages survived the mass extinction at the KT boundary. [Reviewing Editor: Dr. Nicolas Galtier]  相似文献   
210.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号