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   599篇
  免费   26篇
  2023年   3篇
  2022年   4篇
  2021年   6篇
  2020年   5篇
  2019年   10篇
  2018年   14篇
  2017年   7篇
  2016年   8篇
  2015年   17篇
  2014年   29篇
  2013年   39篇
  2012年   51篇
  2011年   28篇
  2010年   28篇
  2009年   18篇
  2008年   19篇
  2007年   23篇
  2006年   29篇
  2005年   28篇
  2004年   32篇
  2003年   21篇
  2002年   19篇
  2001年   13篇
  2000年   15篇
  1999年   11篇
  1998年   7篇
  1996年   4篇
  1995年   6篇
  1994年   3篇
  1992年   8篇
  1991年   8篇
  1990年   5篇
  1989年   4篇
  1988年   4篇
  1987年   6篇
  1985年   7篇
  1984年   3篇
  1983年   3篇
  1982年   6篇
  1980年   4篇
  1979年   6篇
  1977年   9篇
  1976年   7篇
  1975年   6篇
  1974年   4篇
  1973年   4篇
  1972年   4篇
  1971年   4篇
  1970年   6篇
  1922年   3篇
排序方式: 共有625条查询结果,搜索用时 15 毫秒
81.
The objectives were to study the association between metabolic genes involved in alcohol metabolism (CYP2E1 RsaI, CYP2E1 DraI, ADH1C, NQO1) and alcohol consumption in a large sample of healthy controls. Healthy subjects were selected from the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC). Subjects with information on both alcohol consumption and at least one of the studied polymorphisms were included in the analysis (n=2224). Information on the amount of alcohol consumption was available for a subset of subjects (n=844). None of the studied genes was significantly associated with drinking habits. A significant heterogeneity with age was observed when studying the association between CYP2E1 RsaI and alcohol drinking. CYP2E1 RsaI polymorphism was significantly associated with being a never drinker at older ages (odds ratio [OR] 2.4, 95% confidence interval [CI] 1.2-4.8; at ages above 68 years), while the association was reversed at ages below 47 years (OR 0.5, 95% CI 0.2-1.4). For subjects with detailed information on alcohol intake, no association between alcohol quantity and polymorphisms in metabolic genes was observed; subjects carrying the NQO1 polymorphism tended to drink more than subjects carrying the wild-type alleles. Therefore, no significant association between CYP2E1 RsaI, CYP2E1 DraI, ADH1C, NQO1 polymorphisms and alcohol consumption was observed in healthy controls.  相似文献   
82.
Coregonine fish represent the most successful evolutionary lineage of salmonids with Coregonus as the most speciose salmonid genus inhabiting numerous postglacial lakes across the northern hemisphere. We isolated and characterized 31 polymorphic microsatellite loci in Coregonus clupeaformis with an average number of 5.3 alleles per locus (range three to eight) and an overall expected heterozygosity of 0.74 ± 0.11. Two loci revealed significant linkage associations through analyses of mapping families. Six additional salmonid taxa assessed for cross‐species amplification revealed between 18 and 26 positive amplifications and between two and 12 polymorphic loci per species.  相似文献   
83.
The biosynthetic enzyme peptidylglycine alpha-amidating monooxygenase catalyzes the formation of a variety of biologically active alpha-amidated peptides from respective COOH-terminal glycine-extended peptide precursors. Peptidylglycine alpha-amidating monooxygenase activity is dependent on copper, ascorbate, and molecular oxygen and is inhibited by the relatively selective copper chelator N,N-diethyldithiocarbamate or its disulfide dimer disulfiram (Antabuse). In the present study, chronic disulfiram treatment (100 mg/kg/day, for 12-25 days) resulted in significant changes in several neurochemical parameters in the mouse central nervous system, including levels of substance P-like, unamidated substance P-Gly-like, and protease-generated substance P-Gly-Lys-like immunoreactivities (SP-LI, SP-G-LI, and SP-G-K-LI, respectively). Combined high performance liquid chromatography/radioimmunoassay analyses of the extracted SP-LI, SP-G-LI, and SP-G-K-LI species indicated very similar chromatographic and immunochemical behavior as demonstrated for chemically authentic peptide standards. Additionally, changes in levels of monoamines and their metabolites were observed after drug administration. Complementary immunohistochemical analyses using affinity-purified anti-SP-G sera localized these drug-induced changes in levels of immunoreactive unamidated precursor to neural elements that normally express SP. As a functional corollary to alterations in neurochemical parameters, we observed significant disulfiram-induced increases in pain thresholds, potentiated by capsaicin treatment. Overall, our results indicate that the observed changes in steady state levels of immunoreactive SP and of the immature COOH-terminal extended forms of SP may reflect compensatory biosynthetic and posttranslational processing events in SP-containing neural systems after pharmacological challenge.  相似文献   
84.
The Escherichia coli endonuclease RNase E plays a key role in rRNA maturation and mRNA decay. In particular, it controls the decay of its own mRNA by cleaving it within the 5'-untranslated region (UTR), thereby autoregulating its synthesis. Here, we report that, when the synthesis of an RNase E substrate is artificially induced to high levels in vivo, both the rne mRNA concentration and RNase E synthesis increase abruptly and then decrease to a steady-state level that remains higher than in the absence of induction. Using rne-lacZ fusions that retain or lack the rne 5'UTR, we show that these variations reflect a transient mRNA stabilization mediated by the rne 5'UTR. Finally, by putting RNase E synthesis under the control of an IPTG-controlled promoter, we show that a similar, rne 5'UTR-mediated mRNA stabilization can result from a shortage of RNase E. We conclude that the burst in substrate synthesis has titrated RNase E, stabilizing the rne mRNA by protecting its 5'UTR. However, this stabilization is self-correcting, because it allows the RNase E pool to expand until its mRNA is destabilized again. Thus, autoregulation allows RNase E to adjust its synthesis to that of its substrates, a behaviour that may be common among autoregulated proteins. Incidentally, this adjustment cannot occur when translation is blocked, and we argue that the global mRNA stabilization observed under these conditions originates in part from this defect.  相似文献   
85.
86.
Abstract

DNA matrices are prepared by electrochemically directed copolymerization of pyrrole-modified oligonucleotides and pyrrole.  相似文献   
87.
The National Committee for Clinical Laboratory Standards (NCCLS) has published a tentative standard for leukocyte differential counting, by means of which a manual or automated method for leukocyte differential counting can be compared with a manual reference method. The performance of the Technicon H6000 system was evaluated using the standard at Stamford and Overlook Hospitals. A total of 502 patient samples were analyzed: 315 from Overlook and 187 from Stamford. The H6000 system was found to be approximately four times more precise than the 200-cell manual reference method for each cell type. Correlation of the H6000 system with the manual method was good, with correlation coefficients of 0.98 for neutrophils and lymphocytes, 0.96 for eosinophils, 0.72 for monocytes, and 0.5 for basophils. The clinical sensitivity of the H6000 system, measured in terms of false normals and false abnormals, was similar to that of the manual reference method when measured against itself. There were no clinically significant discrepancies in results from the H6000 system, except for possibly one case where a patient was already on antibiotic therapy. The NCCLS standard was found to be a useful but rather complex and involved method for evaluating the performance of the H6000 system, the major problem being the amount of work needed to count manually the number of cells required for the manual reference method.  相似文献   
88.
Synthesis and biological evaluation of a series of novel indole derivatives as anticancer agents is described. A bisindolylmaleimide template has been derived as a versatile pharmacophore with which to pursue chemical diversification. Starting from maleimide, the introduction of an oxygen to the headgroup (hydroxymaleimide) was initially investigated and the bioactivity assessed by screening of kinase inhibitory activity, identifying substituent derived selectivity. Extension of the hydroxymaleimide template to incorporate substitution of the indole nitrogens was next completed and assessed again by kinase inhibition identifying unique selectivity patterns with respect to GSK-3 and CDK kinases. Subsequently, the anticancer activity of bisindolylmaleimides were assessed using the NCI-60 cell screen, disclosing the discovery of growth inhibitory profiles towards a number of cell lines, such as SNB-75 CNS cancer, A498 and UO-31 renal, MDA MB435 melanoma and a panel of leukemia cell lines. The potential for selective kinase inhibition by modulation of this template is evident and will inform future selective clinical candidates.  相似文献   
89.
90.

Introduction

Although it is still at a very early stage compared to its mass spectrometry (MS) counterpart, proton nuclear magnetic resonance (NMR) lipidomics is worth being investigated as an original and complementary solution for lipidomics. Dedicated sample preparation protocols and adapted data acquisition methods have to be developed to set up an NMR lipidomics workflow; in particular, the considerable overlap observed for lipid signals on 1D spectra may hamper its applicability.

Objectives

The study describes the development of a complete proton NMR lipidomics workflow for application to serum fingerprinting. It includes the assessment of fast 2D NMR strategies, which, besides reducing signal overlap by spreading the signals along a second dimension, offer compatibility with the high-throughput requirements of food quality characterization.

Method

The robustness of the developed sample preparation protocol is assessed in terms of repeatability and ability to provide informative fingerprints; further, different NMR acquisition schemes—including classical 1D, fast 2D based on non-uniform sampling or ultrafast schemes—are evaluated and compared. Finally, as a proof of concept, the developed workflow is applied to characterize lipid profiles disruption in serum from β-agonists diet fed pigs.

Results

Our results show the ability of the workflow to discriminate efficiently sample groups based on their lipidic profile, while using fast 2D NMR methods in an automated acquisition framework.

Conclusion

This work demonstrates the potential of fast multidimensional 1H NMR—suited with an appropriate sample preparation—for lipidomics fingerprinting as well as its applicability to address chemical food safety issues.
  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