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   1941篇
  免费   118篇
  国内免费   5篇
  2023年   13篇
  2022年   53篇
  2021年   83篇
  2020年   37篇
  2019年   47篇
  2018年   64篇
  2017年   63篇
  2016年   74篇
  2015年   108篇
  2014年   125篇
  2013年   140篇
  2012年   180篇
  2011年   168篇
  2010年   95篇
  2009年   75篇
  2008年   101篇
  2007年   72篇
  2006年   81篇
  2005年   74篇
  2004年   58篇
  2003年   47篇
  2002年   39篇
  2001年   20篇
  2000年   21篇
  1999年   15篇
  1998年   10篇
  1997年   9篇
  1996年   7篇
  1995年   7篇
  1994年   8篇
  1993年   9篇
  1992年   13篇
  1991年   10篇
  1990年   11篇
  1989年   6篇
  1987年   8篇
  1986年   9篇
  1983年   8篇
  1982年   8篇
  1981年   5篇
  1980年   7篇
  1979年   5篇
  1978年   7篇
  1977年   7篇
  1973年   6篇
  1972年   4篇
  1970年   4篇
  1969年   5篇
  1967年   4篇
  1966年   5篇
排序方式: 共有2064条查询结果,搜索用时 15 毫秒
991.
Reaction of [MoO(2)(acac)(2)] (where, acac=acetyl acetone) and KVO(3) with 2-(salicylidieneimine) benzimidazole lead to form new complexes [MoO(2)(sal-BMZ)(2)] and K [VO(2)(sal-BMZ)(2)] [where, sal-BMZ=2-(salicylidieneimine) benzimidazole], which showed the monobasic bidentate nature of the ligand in which the phenolic oxygen and the imine nitrogen of the ligand are coordinated to the metal ion. These complexes were characterized along with nine other complexes of oxoperoxovanadium (V), molybdenum (Vl) and tungsten (Vl) with benzimidazole derivatives and screened in vitro by micro dilution technique for their amoebicidal activity with a view to search for a more effective agent against Entamoeba histolytica suggests that compound 2 and 3 might be endowed with important antiamoebic properties since they showed IC(50 )values in a microM range.  相似文献   
992.
993.
Patients with acute watery diarrhea caused by Vibrio cholerae O1 or enterotoxigenic Escherichia coli (ETEC) were analyzed for innate immune factors produced by the epithelium during the disease process. Duodenal biopsies were obtained from study participants at the acute (day 2) and convalescent (day 21) stages of disease. Levels of α-defensin (HD-5 and -6), β-defensin (hBD-1-4), and cathelicidin (LL-37) mRNAs were determined by real-time qRT-PCR. hBD-2, HD-5, LL-37 peptides were analyzed in duodenal epithelium by immunomorphometry. Concentration of hBD-2 in stool was determined by ELISA. Specimens from healthy controls were also analyzed. hBD-2 mRNA levels were significantly increased at acute stage of diarrhea; hBD-2 peptide was detected in fecal specimens but barely in duodenal epithelium at acute stage. Immunomorphometry analysis showed that Paneth cells contain significantly higher amounts of HD-5 pre/propeptide at convalescence (P<0.01) and in healthy controls (P<0.001) compared to acute stage, LL-37 peptide levels also decreased at acute stage while mRNA levels remained unchanged. mRNA expression levels of the other antimicrobial peptides remained unchanged with higher levels of α-defensins than β-defensins. V. cholerae induced an innate immune response at the acute stage of disease characterized by increased expression of hBD-2, and continued expression of hBD-1, HD-5-6, and LL-37.  相似文献   
994.
2-(1-[(4-Chloro/methylphenylsulfonylamino)alkyl]-5-thioxo-4,5-dihydro-1,3,4-oxadiazoles (4a-e) were synthesized, in four steps, via the sulfonyl derivatives of l-amino acids (l-alanine, l-methionine and l-phenylalanine) 1a-e, the esters 2a-e, the hydrazides 3a-e and finally the cyclization to 4a-e. Alkylation of 4a-e with 1.0 mole eq. of substituted benzyl halides furnished S-benzyl derivatives 5a-t, while 1.1 mole eq. yielded major 5a-t and minor amount of 6a-d. Alternatively, treatment of 4a-e with 2.0 mole eq. of substituted benzyl halides furnished 6a-d only. The structures of 5b and 5l were further confirmed by single crystal X-ray analysis. Compounds 5a-t and 6a-d showed no selective inhibition against HIV-1 and HIV-2 replication in MT-4 cells. However, 5f and 5j-5q exhibited some inhibitory activity against both types with EC(50) values (>11.50 - >13.00 μg/mL). These results suggest that the structural modifications of these compounds might lead to the development of new antiviral agents. The quantum structure-activity relationship of these novel structural congeners is discussed.  相似文献   
995.
996.
In the present study we report on the use of speed congenics to generate a C57BL/6J congenic line of HD-model R6/2 mice carrying 110 CAG repeats, which uniquely exhibits minimal intergenerational instability. We also report the first identification of the R6/2 transgene insertion site. The relatively stable line of 110 CAG R6/2 mice was characterized for the onset of behavioral impairments in motor, cognitive and psychiatric-related phenotypes as well as the progression of disease-related impairments from 4 to 10 weeks of age. 110Q mice exhibited many of the phenotypes commonly associated with the R6/2 model including reduced activity and impairments in rotarod performance. The onset of many of the phenotypes occurred around 6 weeks and was progressive across age. In addition, some phenotypes were observed in mice as early as 4 weeks of age. The present study also reports the onset and progression of changes in several molecular phenotypes in the novel R6/2 mice and the association of these changes with behavioral symptom onset and progression. Data from TR-FRET suggest an association of mutant protein state changes (soluble versus aggregated) in disease onset and progression.  相似文献   
997.
Syed MS  Kwang J 《PloS one》2011,6(11):e26428
White Spot Syndrome Virus (WSSV) is an infectious pathogen of shrimp and other crustaceans, and neither effective vaccines nor adequate treatments are currently available. WSSV is an enveloped dsDNA virus, and one of its major envelope proteins, VP28, plays a pivotal role in WSSV infection. In an attempt to develop a vaccine against WSSV, we inserted the VP28 gene into a baculovirus vector tailored to express VP28 on the baculovirus surface under the WSSV ie1 promoter (Bac-VP28). The Bac-VP28 incorporated abundant quantity (65.3 μg/ml) of VP28. Shrimp were treated by oral and immersion vaccination with either Bac-VP28 or wild-type baculovirus (Bac-wt). The treatment was followed by challenge with WSSV after 3 and 15 days. Bac-VP28 vaccinated shrimp showed significantly higher survival rates (oral: 81.7% and 76.7%; immersion: 75% and 68.4%) than Bac-wt or non-treated shrimp (100% mortality). To verify the protective effects of Bac-VP28, we examined in vivo expression of VP28 by immunohistochemistry and quantified the WSSV copy number by qPCR. In addition to that, we quantified the expression levels shrimp genes LGBP and STAT by real-time RT-PCR from the samples obtained from Bac-VP28 vaccinated shrimp at different duration of vaccine regime. Our findings indicate that oral vaccination of shrimp with Bac-VP28 is an attractive preventative measure against WSSV infection that can be used in the field.  相似文献   
998.
In systems biology, experimentally measured parameters are not always available, necessitating the use of computationally based parameter estimation. In order to rely on estimated parameters, it is critical to first determine which parameters can be estimated for a given model and measurement set. This is done with parameter identifiability analysis. A kinetic model of the sucrose accumulation in the sugar cane culm tissue developed by Rohwer et al. was taken as a test case model. What differentiates this approach is the integration of an orthogonal-based local identifiability method into the unscented Kalman filter (UKF), rather than using the more common observability-based method which has inherent limitations. It also introduces a variable step size based on the system uncertainty of the UKF during the sensitivity calculation. This method identified 10 out of 12 parameters as identifiable. These ten parameters were estimated using the UKF, which was run 97 times. Throughout the repetitions the UKF proved to be more consistent than the estimation algorithms used for comparison.  相似文献   
999.

Background

Targeted analgesic dietary interventions are a promising strategy for alleviating pain and improving quality of life in patients with persistent pain syndromes, such as chronic daily headache (CDH). High intakes of the omega-6 (n-6) polyunsaturated fatty acids (PUFAs), linoleic acid (LA) and arachidonic acid (AA) may promote physical pain by increasing the abundance, and subsequent metabolism, of LA and AA in immune and nervous system tissues. Here we describe methodology for an ongoing randomized clinical trial comparing the metabolic and clinical effects of a low n-6, average n-3 PUFA diet, to the effects of a low n-6 plus high n-3 PUFA diet, in patients with CDH. Our primary aim is to determine if: A) both diets reduce n-6 PUFAs in plasma and erythrocyte lipid pools, compared to baseline; and B) the low n-6 plus high n-3 diet produces a greater decline in n-6 PUFAs, compared to the low n-6 diet alone. Secondary clinical outcomes include headache-specific quality-of-life, and headache frequency and intensity.

Methods

Adults meeting the International Classification of Headache Disorders criteria for CDH are included. After a 6-week baseline phase, participants are randomized to a low n-6 diet, or a low n-6 plus high n-3 diet, for 12 weeks. Foods meeting nutrient intake targets are provided for 2 meals and 2 snacks per day. A research dietitian provides intensive dietary counseling at 2-week intervals. Web-based intervention materials complement dietitian advice. Blood and clinical outcome data are collected every 4 weeks.

Results

Subject recruitment and retention has been excellent; 35 of 40 randomized participants completed the 12-week intervention. Preliminary blinded analysis of composite data from the first 20 participants found significant reductions in erythrocyte n-6 LA, AA and %n-6 in HUFA, and increases in n-3 EPA, DHA and the omega-3 index, indicating adherence.

Trial Registration

ClinicalTrials.gov (NCT01157208)
  相似文献   
1000.

Background

p66Shc, an isoform of Shc adaptor proteins, mediates diverse signals, including cellular stress and mouse longevity. p66Shc protein level is elevated in several carcinomas and steroid-treated human cancer cells. Several lines of evidence indicate that p66Shc plays a critical role in steroid-related carcinogenesis, and steroids play a role in its elevated levels in those cells without known mechanism.

Methods and Findings

In this study, we investigated the molecular mechanism by which steroid hormones up-regulate p66Shc protein level. In steroid-treated human prostate and ovarian cancer cells, p66Shc protein levels were elevated, correlating with increased cell proliferation. These steroid effects on p66Shc protein and cell growth were competed out by the respective antagonist. Further, actinomycin D and cyclohexamide could only partially block the elevated p66Shc protein level by steroids. Treatment with proteasomal inhibitors, but not lysosomal protease inhibitor, resulted in elevated p66Shc protein levels, even higher than that by steroids. Using prostate cancer cells as a model, immunoprecipitation revealed that androgens and proteasomal inhibitors reduce the ubiquitinated p66Shc proteins.

Conclusions

The data collectively indicate that functional steroid receptors are required in steroid up-regulation of p66Shc protein levels in prostate and ovarian cancer cells, correlating with cell proliferation. In these steroid-treated cells, elevated p66Shc protein level is apparently in part due to inhibiting its ubiquitination. The results may lead to an impact on advanced cancer therapy via the regulation of p66Shc protein by up-regulating its ubiquitination pathway.  相似文献   
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