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   1819篇
  免费   106篇
  国内免费   3篇
  2024年   4篇
  2023年   56篇
  2022年   33篇
  2021年   68篇
  2020年   65篇
  2019年   54篇
  2018年   96篇
  2017年   93篇
  2016年   122篇
  2015年   90篇
  2014年   130篇
  2013年   199篇
  2012年   141篇
  2011年   171篇
  2010年   107篇
  2009年   107篇
  2008年   65篇
  2007年   54篇
  2006年   52篇
  2005年   46篇
  2004年   33篇
  2003年   19篇
  2002年   17篇
  2001年   17篇
  2000年   14篇
  1999年   5篇
  1998年   4篇
  1997年   7篇
  1996年   2篇
  1995年   5篇
  1993年   8篇
  1990年   7篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
  1986年   2篇
  1983年   1篇
  1982年   5篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   4篇
  1975年   1篇
  1974年   2篇
  1972年   1篇
  1967年   1篇
  1963年   2篇
  1962年   1篇
排序方式: 共有1928条查询结果,搜索用时 15 毫秒
941.
Three new iridoid glycosides, named involucratosides A – C ( 1  –  3 ), were isolated from the H2O subextract of crude MeOH extract prepared from the aerial parts of Asperula involucrata along with a known iridoid glycoside (adoxoside), three flavone glycosides (apigenin 7‐Oβ‐glucopyranoside, luteolin 7‐Oβ‐glucopyranoside, apigenin 7‐O‐rutinoside) as well as two phenolic acid derivatives (chlorogenic acid and ferulic acid 4‐Oβ‐glucopyranoside). Their chemical structures were established by UV, IR, 1D‐ (1H, 13C and JMOD) and 2D‐ (COSY, HSQC, HMBC and NOESY) NMR experiments and HR‐ESI‐MS. In addition, the crude extract, subextracts and isolates were evaluated for their xanthine oxidase inhibitory and antioxidant activities in in vitro tests. This is the first report on the chemical composition and bioactivities of Ainvolucrata.  相似文献   
942.
A series of 2-(4-substitutedmethylphenyl)propionic acid derivatives (6a–6m) were synthesized, characterized and evaluated for cyclooxygenase (COX) enzyme inhibitory and antimicrobial activity. Test compounds that exhibited good COX inhibition and antibacterial activity were further screened for their cytotoxicity and genotoxicity. Compounds 6h and 6l showed better COX-1 and COX-2 inhibition when compared to ibuprofen. Inhibition potency of these compounds against COX-2 was very close to that of nimesulide. The compounds 6d, 6h, 6l and 6m displayed promising antibacterial property when compared to chloramphenicol. However, the compound 6l was emerged as the best dual COX inhibitory-antibacterial agent in this study. The ADME prediction of the compounds revealed that they may have a good pharmacokinetic profile. Docking results of the compounds 6h and 6l with COX-1 (PDB ID: 1EQG) also exhibited a strong binding profile.

  相似文献   

943.
Sulfonamides represent an important class of biologically active compounds. A sulfonamide possessing carbonic anhydrase (CA) inhibitory properties obtained from a pyrazole based sulfonamide, ethyl 1-(3-nitrophenyl)-5-phenyl-3-((5-sulfamoyl-1,3,4-thiadiazol-2-yl)carbamoyl)-1H-pyrazole-4-carboxylate (1), and its metal complexes with the Ni(II) for (2), Cu(II) for (3) and Zn(II) for (4) have been synthesized. The structures of metal complexes (24) were established on the basis of their elemental analysis, 1H NMR, IR, UV–Vis and MS spectral data. The inhibition of two human carbonic anhydrase (hCA, EC 4.2.1.1) isoenzymes I and II, with 1 and synthesized complexes (24) and acetazolamide (AAZ) as a control compound was investigated in vitro by using the hydratase and esterase assays. The complexes 2, 3 and 4 showed inhibition constant in the range 0.1460–0.3930?µM for hCA-I and 0.0740–0.0980?µM for hCA-II, and they had effective more inhibitory activity on hCA-I and hCA-II than corresponding free ligand 1 and than AAZ.  相似文献   
944.
The binding interaction between two dicationic styrylimidazo[1,2‐a]pyridinium dyes and human serum albumin (HSA) was investigated at physiological conditions using fluorescence, UV–vis absorption, and circular dichroism (CD) spectroscopies. Analysis of the fluorescence titration data at different temperatures suggested that the fluorescence quenching mechanism of HSA by these dyes was static. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) indicated that hydrogen bonding and van der Waals forces played a major role in the formation of the dye–HSA complex. Binding distances (r) between dyes and HSA were calculated according to Förster's non‐radiative energy transfer theory. Studies of conformational changes of HSA using CD measurements indicate that the α‐helical content of the protein decreased upon binding of the dyes. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
945.
Turner's syndrome (TS) is depicted as a total or partial absence of X chromosome, and occurs in approximately 1/2200 of live born females. Generally, mosaic patients are diagnosed following karyotype analysis due to recurrent pregnancy loss, repeated in vitro fertilization (IVF) failure, and a history of malformed babies. The purpose of this case report is to show that even a selection of normal karyotype embryos can result in abnormalities for those with mosaic TS. A 32-year old patient who underwent IVF after ICSI-PGD, and was diagnosed with 45X/46XX karyotype. At the 12-week scan, one of the fetuses had an upper limb hemimelia in one arm, and feticide was applied to that fetus. The patient delivered a healthy, 2980 g female baby at the thirty-eighth week. In mosaic TS pregnancies (even those obtained by ICSI-PGD), fetal anomaly risk is high. Therefore, careful prenatal scanning is needed for these pregnancies.  相似文献   
946.
947.
Use of chemical pesticides in agriculture harms humans, non-target organisms and environments, and causes increase resistance against chemicals. In order to develop an effective bio-pesticide against coleopterans, particularly against Agelastica alni (Coleoptera: Chrysomelidae) which is one of the serious pests of alder leaf and hazelnut, we tested the insecticidal effect of 21 Bacillus isolates against the larvae and adults of the pest. Bacillus thuringiensis var. tenebrionis-Xd3 (Btt-Xd3) showed the highest insecticidal effect based on screening tests. For toxin protein production and high sporulation of Xd3, the most suitable medium, pH and temperature conditions were determined as nutrient broth medium enriched with salts, pH 7 and 30?°C, respectively. Sporulated Btt-Xd3 in nutrient broth medium enriched with salts transferred to fermentation medium containing soybean flour, glucose and salts. After fermentation, the mixture was dried in a spray dryer, and spore count of the powder product was determined as 1.6?×?1010 c.f.u. g?1. Moisture content, suspensibility and wettability of the formulation were determined as 8.3, 86% and 21 s, respectively. Lethal concentrations (LC50) of formulated Btt-Xd3 were determined as 0.15?×?105 c.f.u. ml?1 for larvae at laboratory conditions. LC50 values were also determined as 0.45?×?106 c.f.u. ml?1 at the field condition on larval stage. Our results showed that a new bio-pesticide developed from B. thuringiensis tenebrionis (Xd3) (Btt-Xd3) may be valuable as a biological control agent for coleopteran pests.  相似文献   
948.
Introduction: Chronic obstructive pulmonary disease (COPD) is a progressive condition characterized by poorly reversible airflow limitations associated with an abnormal inflammatory response of the lung.

Methods: We investigated whether prolidase levels in serum, total antioxidant status, total oxidative status (TOS), and the oxidative stress index (OSI) were associated with the etiopathogenesis of COPD, and whether there is a relationship between prolidase activity and oxidative parameters and carotid artery intima-media thickness (CIMT) in patients with COPD. This study included 91 patients with COPD and 15 control cases. Routine haematological and biochemical parameters were determined in all patients. All subjects were fully informed about the study and provided consent.

Results: The mean age of the patients with COPD was 61.3?±?10.5 years and that of the control group was 56.2?±?12.1 years. The control group had a significantly higher plasma prolidase level than that in the COPD group. TOS and OSI levels in the control group were significantly lower than those in the COPD group. However, no significant differences were found in TALs or CIMT levels between the COPD and control groups. A negative correlation was detected between prolidase activity and age; however, no significant difference in age was observed between the two groups.

Conclusion: These results indicate that prolidase activity decreases in patients with COPD.  相似文献   
949.
We investigated effects of two doses of Tenoxicam, a type 2 cyclooxygenase inhibitor, administration on lipid peroxidation and antioxidant redox system in cortex of the brain in rats. Twenty-two male Wistar rats were randomly divided into three groups. First group was used as control. 10 and 20 mg/kg body weight Tenoxicam were intramuscularly administrated to rats constituting the second and third groups for 10 days, respectively. Both dose of Tenoxicam administration resulted in significant increase in the glutathione peroxidase activity, reduced glutathione and vitamins C and E of cortex of the brain. The lipid peroxidation levels in the cortex of the brain were significantly decreased by the administration. Vitamin A and β-carotene concentration was not affected by the administration. There was no statistical difference in all values between 10 and 20 mg Tenoxicam administrated groups. In conclusion, treatment of brain with 10 and 20 mg Tenoxicam has protective effects on the oxidative stress by inhibiting free radical and supporting antioxidant redox system.  相似文献   
950.
hSARS-CoV is the causative agent for SARS infection. Its spike glycoprotein (S) is processed by host furin enzyme to produce S1 and S2 fragments, the latter being crucial for fusion with the host membrane. This takes place via formation of a coiled coil 6-helix bundle involving N and C-terminal heptad repeat domains (HR-N and HR-C) of S2. Several fluorescent and non-fluorescent peptides from these domains were synthesized to examine their interactions by circular dichroism, thermal denaturation, native-page, mass spectrometry and fluorescence spectroscopy studies. Data revealed that HR-C domains (1153-1189), (1153-1172) and (1164-1184) all exhibit potent binding interactions with HR-N(892-931) domain. These peptides may find useful therapeutic applications in SARS intervention.  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