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   1201篇
  免费   44篇
  国内免费   1篇
  2024年   1篇
  2023年   25篇
  2022年   18篇
  2021年   28篇
  2020年   21篇
  2019年   14篇
  2018年   31篇
  2017年   35篇
  2016年   58篇
  2015年   46篇
  2014年   70篇
  2013年   119篇
  2012年   96篇
  2011年   92篇
  2010年   70篇
  2009年   57篇
  2008年   79篇
  2007年   50篇
  2006年   64篇
  2005年   58篇
  2004年   62篇
  2003年   67篇
  2002年   41篇
  2001年   7篇
  2000年   7篇
  1999年   3篇
  1998年   6篇
  1997年   3篇
  1996年   3篇
  1995年   1篇
  1994年   5篇
  1993年   1篇
  1992年   2篇
  1991年   2篇
  1989年   1篇
  1984年   1篇
  1979年   1篇
  1977年   1篇
排序方式: 共有1246条查询结果,搜索用时 31 毫秒
1.
Typha latifolia L. from aquatic plants is widely found throughout Kehli Stream (Elazig, Turkey). This study examined the uptake of some metals by T. latifolia and the transfer from roots to other plant parts. The accumulation of Mn in T. latifolia L. can be suggested as a tolerance strategy due to its transfer factor higher than 1.0. The enrichment coefficients in the leaves of T. latifolia L. were higher than 1.0 for Zn and Mn and often lower than 1.0 for other metals. Similarly, the enrichment coefficients of all metals, except for Cr, in roots of T. latifolia L. were higher than 1.0. This study demonstrated that T. latifolia L. could be considered as either a bio-indicator or a bio-accumulator for sediments and water polluted by metals.  相似文献   
2.
Allopatric isolation in glacial refugia has caused differentiation and speciation in many taxa globally. In this study, we investigated the nuclear and mitochondrial genetic differentiation of the long fingered bat, Myotis capaccinii during the ice ages in south-eastern Europe and Anatolia. The mitochondrial DNA (mtDNA) analyses indicated a suture zone similar to those recorded in other animal species, including bats, suggesting the association of more than one refugium with the region. Contrary to most of the other species where a suture zone was seen in Anatolia, for M. capaccinii the geographical location of the genetic break was in south-eastern Europe. This mitochondrial differentiation was not reflected in the nuclear microsatellites, however, suggesting that the lack of contact during the ice ages did not result in reproductive isolation. Hence taxonomically, the two mitochondrial clades cannot be treated as separate species.  相似文献   
3.
Molecular and Cellular Biochemistry - Excitation–contraction coupling in normal cardiac function is performed with well balanced and coordinated functioning but with complex dynamic...  相似文献   
4.
Zusammenfassung Die Fortpflanzungsperiode der Palmtaube (Streptopelia s. senegalensis L.) fängt in Diyarbakir/Türkei (37°55N/40°12E) schon Anfang Februar an und kann bis Mitte November dauern. In diesem Zeitraum kann ein Paar bis zu sieben Bruten beginnen (Tab. 1). Nach der Paarbildung fangen die Kopulationen an, die vor allem in der Woche vor der Eiablage stark zunehmen. Während des Brütens und der ersten Woche der Jungenaufzucht sind sie dagegen nicht zu beobachten. Sie werden vom im allgemeinen mit sog. Flügeltippen bzw. Scheinputzen eingeleitet. Nach der Begattung paradiert das um das , das auf der Stelle verharrt. Vor dem Tretakt fällt das dagegen in infantiles Verhalten und bettelt unter Flügelzittern den Partner um Futter an. Es bekommt auch tatsächlich Futter. Die Palmtauben sind zumindest für eine Fortpflanzungssaison monogam. U. a. spielen wechselseitige Gefiederpflege und Anschlußbruten sowie die Fütterung des durch das eine wichtige Rolle für das Zusammenleben und -bleiben der Partner. Der Nistplatz wird vom gezeigt, aber vom gewählt. Das Nistmaterial wird vom eingetragen und im allgemeinen vom alleine in das Nest eingefügt. Nur während des Brutwechsels bringt auch das hin und wieder Nistmaterial, das aber wahrscheinlich nur für den Partner, nicht für das Nest dient. In den späteren Phasen des Brütens gilt dies wahrscheinlich auch für das . 1–4 Tage nach dem Nestbaubeginn wird gegen Abend das erste Ei gelegt, womit auch das Brüten anfängt. Das zweite Ei folgt dann rund 38 Stunden später.
On the reproductive behaviour of the Laughing Dove (Streptopelia senegalensis): pair-formation to egg-laying
Summary In Diyarbakr/Turkey, the reproductive season of the Laughing Dove begins in early February and lasts til mid November. One pair may start with breeding up to seven times a year. The frequency of copulations which could be observed only after pair formation increased considerably in the week before incubation starts. During incubation and during the first week of the nestling period no copulations could be observed. Usually copulations are initiated by the male pecking behind its folded wings (displacement-preening). Before mating, the female turns into infantile behaviour begging food from its partner by wing-twitching. Food is then delivered by the male. After mating the female parades around the male which stays motionless. Paired birds stay together at least during one reproductive season. Reinforcement of the pair bond will be achieved by mutual preening, courtship feeding of the female by the male, and successive broods. The male indicates the nest site which is successively chosen by the female. The nest material is brought by the male and usually placed by the female at the nest site. Only during change-overs the female sometimes brings nesting material, too. However, this material probably is for the partner, not actually for the nest. The same may be true for similar behaviour of the male in late stages of incubation. One to four days after nest building has started the first egg is laid, mostly in late afternoon. Incubation starts with the first egg; the second egg is laid about 38 hours later.
  相似文献   
5.
This study aimed to investigate the protective effects of arbutin (ARB) against brain injury induced in rats with potassium bromate (KBrO3). The rats were divided into four groups as Group 1: Control (0.9% NaCl ml/kg/day p.), Group 2: KBrO3 (100 mg/kg (gavage), Group 3: ARB (50 mg/kg/day p.), and Group 4: KBrO3 + ARB (100 mg/kg (gavage) + 50 mg/kg/day p.). At the end of the fifth day of the study, the rats in all groups were killed, and their brain tissues were collected. In the collected brain tissues, malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) levels were measured, and routine histopathological examinations were made. The MDA levels in the group that was exposed to KBrO3 were significantly higher than those in the control group (p ˂ 0.001). In comparison to the KBrO3 group, the MDA levels in the KBrO3 + ARB group were significantly lower (p ˂ 0.001). It was observed that SOD and CAT enzyme activity levels were significantly lower in the KBrO3 group compared to the control group (p ˂ 0.001), while these levels were significantly higher in the KBrO3 + ARB group than in the KBrO3 group (p ˂ 0.001). Additionally, the group that was subjected to KBrO3 toxicity, as well as ARB administration, had much lower levels of histopathologic signs than the group that was subjected to KBrO3 toxicity only. Consequently, it was found that KBrO3 exposure led to injury in the brain tissues of the rats, and using ARB was effective in preventing this injury.  相似文献   
6.
Protoplasma - Watermelon and melon are members of the Cucurbitaceae family including economically significant crops in the world. The expansin protein family, which is one of the members of the...  相似文献   
7.
A thiol compound, glutathione, is essential for healthy cell defence against xenobiotics and oxidative stress. Glutathione reductase (GR) and glutathione S-transferase (GST) are two glutathione-related enzymes that function in the antioxidant and the detoxification systems. In this study, potential inhibitory effects of methyl 4-aminobenzoate derivatives on GR and GST were examined in vitro. GR and GST were isolated from human erythrocytes with 7.63 EU/mg protein and 5.66 EU/mg protein specific activity, respectively. It was found that compound 1 (methyl 4-amino-3-bromo-5-fluorobenzoate with Ki value of 0.325±0.012 μM) and compound 5 (methyl 4-amino-2-nitrobenzoate with Ki value of 92.41±22.26 μM) inhibited GR and GST stronger than other derivatives. Furthermore, a computer-aided method was used to predict the binding affinities of derivatives, ADME characteristics, and toxicities. Derivatives 4 (methyl 4-amino-2-bromobenzoate) and 6 (methyl 4-amino-2-chlorobenzoate) were estimated to have the lowest binding energies into GR and GST receptors, respectively according to results of in silico studies.  相似文献   
8.
In this work, the synthesis, characterization, and biological activities of a new series of 1,3,4-thiadiazole derivatives were investigated. The structures of final compounds were identified using 1H-NMR, 13C-NMR, elemental analysis, and HRMS. All the new synthesized compounds were then screened for their antimicrobial activity against four types of pathogenic bacteria and one fungal strain, by application of the MIC assays, using Ampicilin, Gentamycin, Vancomycin, and Fluconazole as standards. Among the compounds, the MIC values of 4 and 8 μg/mL of the compounds 3f and 3g , respectively, are remarkable and indicate that these compounds are good candidates for antifungal activity. The docking experiments were used to identify the binding forms of produced ligands with sterol 14-demethylase to acquire insight into relevant proteins. The MD performed about 100 ns simulations to validate selected compounds’ theoretical studies. Finally, using density functional theory (DFT) to predict reactivity, the chemical characteristics and quantum factors of synthesized compounds were computed. These results were then correlated with the experimental data. Furthermore, computational estimation was performed to predict the ADME properties of the most active compound 3f .  相似文献   
9.
In this study, we investigated the combined treatment of 5-fluorouracil (5-FU) and Anatolian propolis extract (PE) on colorectal cancer (CRC)using in vitro and in vivo studies. We exposed luciferase-transfected (Lovo-Luc CRC) cells and healthy colon cells (CCD-18Co) to varying concentrations of 5-FU and PE to assess their genotoxic, apoptotic, and cytotoxic effects, as well as their intracellular reactive oxygen species (iROS) levels. We also developed a xenograft model in nude mice and evaluated the anti-tumor effects of PE and 5-FU using various methods. Our findings showed that the combination of PE and 5-FU had selectivity against cancer cells, particularly at higher doses, and enhanced the anti-tumor effectiveness of 5-FU against colon CRC. The results suggest that PE can reduce side effects and increase the effectiveness of 5-FU through iROS generation in a dose-dependent manner.  相似文献   
10.
In this study, new chiral thiourea and 1,3-thiazolidine-4,5-dione derivatives were synthesized, it was aimed to evaluate the various biological activities and molecular docking of these compounds. Firstly, the new thioureas ( 1 – 16 ) were obtained by reacting 1-naphthylisothiocyanate with different chiral amines. Then, the chiral thioureas were cyclized with oxalyl chloride to obtain 1,3-thiazolidine-4,5-dione derivatives ( 17 – 32 ). All compounds were evaluated with several in vitro antioxidant and enzyme inhibition activities. Compound 30 was the most active compound against AChE, with a value of IC50=8.09±0.58 μM. On the other hand, all compounds were tested in silico absorption, distribution, metabolism, and excretion (ADME) assays to better understand their bioavailability. These physicochemical properties, pharmacokinetics, and drug-likeness of all compounds were calculated using SwissADME. Furthermore, according to molecular docking analyses compound 30 exhibited significant binding affinities for all enzymes. Based on our overall observations, compound 30 could be recommended as a potential lead for the therapuetic of Alzheimer's.  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