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   2231篇
  免费   174篇
  国内免费   117篇
耳鼻咽喉   4篇
儿科学   32篇
妇产科学   17篇
基础医学   203篇
口腔科学   7篇
临床医学   72篇
内科学   180篇
皮肤病学   12篇
神经病学   159篇
特种医学   70篇
外科学   106篇
综合类   113篇
预防医学   199篇
眼科学   11篇
药学   960篇
中国医学   321篇
肿瘤学   56篇
  2024年   17篇
  2023年   82篇
  2022年   83篇
  2021年   123篇
  2020年   105篇
  2019年   94篇
  2018年   96篇
  2017年   99篇
  2016年   70篇
  2015年   87篇
  2014年   91篇
  2013年   162篇
  2012年   93篇
  2011年   82篇
  2010年   61篇
  2009年   58篇
  2008年   65篇
  2007年   60篇
  2006年   55篇
  2005年   48篇
  2004年   49篇
  2003年   48篇
  2002年   26篇
  2001年   27篇
  2000年   32篇
  1999年   18篇
  1998年   26篇
  1997年   23篇
  1996年   25篇
  1995年   46篇
  1994年   25篇
  1993年   26篇
  1992年   23篇
  1991年   32篇
  1990年   38篇
  1989年   27篇
  1988年   29篇
  1987年   27篇
  1986年   29篇
  1985年   35篇
  1984年   57篇
  1983年   20篇
  1982年   40篇
  1981年   35篇
  1980年   26篇
  1979年   18篇
  1978年   12篇
  1977年   27篇
  1976年   15篇
  1973年   9篇
排序方式: 共有2522条查询结果,搜索用时 62 毫秒
101.
1.?Safrole is the main component of the volatile oil in Xixin, which has a strong antifungal effect. However, safrole has been shown to be associated with the development of hepatocellular carcinoma. Methylenedioxyphenyl and allyl-benzene substructures of safrole may cause a mechanism-based inhibition (MBI) of CYP450 enzymes (CYPs) and produce reactive metabolites (RMs), resulting in inhibition of enzyme activity and toxic effects.

2.?Based on the experiments of CYPs cocktail screening, glutathione (GSH) capture and the IC50 data, we found that safrole had an inhibitory effect on CYP1A2. The test of enzyme activity recovery when adding GSH may help to verify the MBI of safrole.

3.?Two metabolites, 1,2-dihydroxy-4-allylbenzene (M1) and 1′-hydroxy safrole (M2) could be captured by GSH. The ultra performance liquid chromatography - tandem mass spectrometer (UPLC-MS/MS) method was used to identify the RMs through a detailed characterization of the safrole cleavage processes and the GSH-M1 adduct. The RMs identified are quinone and its tautomer. Thus, preliminary conclusion can be obtained that safrole is a mechanism-based inhibitor of CYP1A2.

4.?The cleavage process of the GSH-M1/M2 adduct was analyzed in further detail. We believe the safrole hepatotoxicity mechanism is related to the RMs mediated by CYP1A2. This work provides important information on predicting in vivo drug induced liver injury.  相似文献   
102.
1.?Physalin A is a bioactive withanolide isolated from the natural plant Physalis alkekengi var. franchetii (Solanaceae), a common traditional Chinese herbal medicine. This study aims to investigate the metabolites of physalin A in vivo.

2.?Two metabolites (M1 and M2) were characterized as sulfonate metabolites in the feces obtained from rats treated with physalin A orally at a dose of 15?mg/kg/day for 3 days, by application of a UPLC-Q/TOF-MS method. Furthermore, formation of the two sulfonate metabolites was verified by chemical synthesis and NMR, including 1H NMR, 13C NMR and two-dimensional NMR. The structures of M1 and M2 were identified to be 3α-sulfo-2,25β,27-trihydrophysalin A and 3α,27-disulfo-2,25α-dihydrophysalin A, respectively.

3.?In summary, this study indicated that physalin A could be biotransformed to sulfonate metabolites with strong polarity, which contributed to the elimination of physalin A. A rare metabolic pathway has been revealed in this study.  相似文献   
103.
Simple and facile methods for the synthesis of deuterium‐labeled obeticholic acid and its 2 metabolites, glycine and taurine conjugates of obeticholic acid, are described herein. The 3 deuterated compounds were applicable for use as internal standards in drug development.  相似文献   
104.
甲氨蝶呤(MTX)被广泛用于治疗骨肉瘤、急性淋巴细胞白血病、恶性淋巴瘤、类风湿性关节炎和炎性肠道疾病等。由于MTX个体差异大和不良反应较严重,同时其在体内代谢迅速,主要以多聚谷氨酸化代谢物的形式长期存在,因此,监测MTX及其代谢物的血药浓度显得尤为重要。本文对已发表的相关文献进行了分析,结合笔者在临床药物浓度监测实践中的经验和体会,从样品采集、样品保存、样品前处理方法、分离条件、检测方法等方面,探讨了MTX及其代谢物血药浓度测定中的细节问题,以期实现MTX的精准医疗,确保其用药安全性。  相似文献   
105.
目的 研究浙江普陀岛海泥来源真菌Penicillium sp. wqh-572的次级代谢产物及其抑菌活性。方法 将菌株进行大规模发酵,乙酸乙酯萃取,采用小孔树脂MCI柱和半制备型高效液相色谱等分离纯化方法,通过核磁(1H NMR和13C NMR)和质谱(MS)等波谱分析方法,并与相关文献比较,鉴定化合物结构。结果 从该真菌发酵液的乙酸乙酯萃取相中分离得到6个化合物,鉴定结果分别为physcion (1)、emodin (2)、7-hydroxy-2-(2-hydroxypropyl)-5-methylchromone (3)、isorhodoptilometrin (4)、2-(2’, 4’, 6’-trihydroxyphenyc)-(7-hydroxy-5-methyc) chromone (5)及(Z)-N-(4-hydroxy styryl) formamide (6)。其中,其中化合物5为首次从青霉属真菌中分离得到。化合物1对3种植物病原菌均具有抑制作用。  相似文献   
106.
目的 对分离自西沙隋氏蒂壳海绵共附生真菌Penicilliumchrysogenum的次级代谢产物进行化学成分及其生物活性研究,以期发现结构特异并且活性良好的次级代谢产物。方法 对隋氏蒂壳海绵共附生真菌Penicilliumchrysogenum用真菌2号培养基发酵,发酵后的菌丝体采用溶剂提取、萃取和现代色谱分离纯化手段,再运用现代核磁波谱技术并结合高分辨质谱鉴定化合物结构。基于微阵列技术的表面等离子体共振成像(SPRi)系统,检测化合物与肿瘤相关蛋白的相互作用,并提供化合物与肿瘤相关蛋白的结合动力学数据。结果 通过分离隋氏蒂壳海绵共附生真Penicilliumchrysogenum的菌丝体提取物,从中分离鉴定了7个单体化合物,鉴定结果为conidiogenone(1)、2-acetylquinazolin-4(3H)-one(2)、15β-hydroxyl-(22E,24R)-ergosta-3,5,8,22-tetraen-on(3)、ergosta-4,6,8(14),22-tetraen-3-one(4)、 2-((2E,4E)-hexa-2,4-dienoyl)-5,6-dihydroxy-4,6-dimethylcyclohex-4-ene-1,3-dione(5)、(22E)-5α,8α-epidioxyergosta-6,22-dien-3β-ol(6)、2-(1-hydroxyethyl)quinazolin-4(3H)-one(7)。结论 化合物3和6是从Penicillium属内第一次分离得到,化合物4是从真菌Penicilliumchrysogenum中第一次分离得到,化合物5与肿瘤蛋白VEGFR-1、FGFR有亲和作用,KD的数值分别为7.78×10-3和1.44×10-1 μmol/L。  相似文献   
107.
Abstract

Glucuronidation is an important and popular metabolic reaction in vivo of drugs. The further evaluation of biological activity and toxicity of glucuronides is necessary in the course of the drug research and development. However, the synthesis of glucuronides is limited by the lack of efficient approach. Herein, we have developed a new glucuronide synthesis method using plant uridine diphosphate-dependent glucuronosyltransferases (UGTs), UGT88D4, UGT88D7, and EpGT8, enabling the convenient preparation for corresponding O-glucuronide metabolites (1a, 2a, 3a, and 3b) in milligram scale of two neurological active agents, IMM-H004 (1) and FLZ (2). Their structures were characterized by spectroscopic data analyses.  相似文献   
108.
Context: Plants of the genus Echinacea (Asteraceae) are among the most popular herbal supplements on the market today. Recent studies indicate there are potential new applications and emerging markets for this natural health product (NHP).

Objective: This review aims to synthesize recent developments in Echinacea biotechnology and to identify promising applications for these advances in the industry.

Methods: A comprehensive survey of peer-reviewed publications was carried out, focusing on Echinacea biotechnology and impacts on phytochemistry. This article primarily covers research findings since 2007 and builds on earlier reviews on the biotechnology of Echinacea.

Results: Bioreactors, genetic engineering and controlled biotic or abiotic elicitation have the potential to significantly improve the yield, consistency and overall quality of Echinacea products. Using these technologies, a variety of new applications for Echinacea can be realized, such as the use of seed oil and antimicrobial and immune boosting feed additives for livestock.

Conclusions: New applications can take advantage of the well-established popularity of Echinacea as a NHP. Echinacea presents a myriad of potential health benefits, including anti-inflammatory, anxiolytic and antibiotic activities that have yet to be fully translated into new applications. The distinct chemistry and bioactivity of different Echinacea species and organs, moreover, can lead to interesting and diverse commercial opportunities.  相似文献   

109.
Mycotoxins, including zearalenone (ZEA), can occur worldwide in cereals. They can enter the food chain and cause several health disorders. ZEA and its derivatives (α-zearalenol, α-ZOL and β-zearalenol, β-ZOL) have structural analogy to estrogen, thus they can bind to estrogen receptors (ERs). In order to characterize the estrogenic activity of ZEA, α-ZOL and β-ZOL, the proliferation of ER-positive human breast cancer cells (MCF-7) exposed to these mycotoxins was measured. After exposure at levels ranging from 6.25 to 25?µM, cell proliferation was evaluated by using the E-Screen bioassay. In accordance with previous studies, our results show the estrogenic activity of ZEA, α-ZOL and β-ZOL in MCF-7 cells. This effect is related to ZEA and its metabolites being flexible enough to bind to mammalian ERs. The relative proliferative effect (RPE) ranged from 10% to 91%. The α-ZOL induced the highest proliferative effect due to its higher affinity for the ERs compared to the other mycotoxins.  相似文献   
110.
In the fight against doping, the introduction of alternative markers to the steroid profile can be considered as an effective approach to improve the screening capabilities for the detection of testosterone (T) misuse. The aim of this study was to evaluate the potential of several T metabolites (cysteinyl conjugated and glucuronoconjugated resistant to enzymatic hydrolysis) to detect both the transdermal and the intramuscular administration of T. In Part I of the study, we studied the potential of these metabolites for the detection of T transdermal administration. Results revealed that resistant glucuronides can be a suitable complement to the current steroid profile. In this, Part II, dedicated to the intramuscular administration, we studied the potential of cysteinyl conjugated, resistant glucuronoconjugated and 1‐cyclopentenoylglycine (1‐CPG) for the detection of a single intramuscular injection of T cypionate. Possible differences in the excretion profile of all markers were explored between individuals with low basal (n=6) and medium basal (n=6) values of the testosterone/epitestosterone ratio (T/E). The results showed that all tested markers presented low intra‐individual stability in basal conditions. Despite this, all glucuronoconjugated markers and 1‐CPG, but not the cysteinyl conjugated markers, provided detection windows that were similar or longer than those obtained by markers currently included in the steroid profile. Based on the results obtained from the 2 parts of this study and from previously reported data, the potential applicability and the limitations of including these markers in the steroid profile are discussed.  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