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   1836篇
  免费   81篇
  国内免费   1篇
  1918篇
  2024年   6篇
  2023年   17篇
  2022年   40篇
  2021年   62篇
  2020年   52篇
  2019年   52篇
  2018年   52篇
  2017年   61篇
  2016年   79篇
  2015年   83篇
  2014年   102篇
  2013年   121篇
  2012年   132篇
  2011年   146篇
  2010年   91篇
  2009年   73篇
  2008年   102篇
  2007年   107篇
  2006年   89篇
  2005年   79篇
  2004年   72篇
  2003年   51篇
  2002年   48篇
  2001年   21篇
  2000年   19篇
  1999年   21篇
  1998年   17篇
  1997年   5篇
  1996年   7篇
  1995年   4篇
  1994年   3篇
  1993年   3篇
  1992年   3篇
  1991年   4篇
  1990年   6篇
  1989年   3篇
  1988年   6篇
  1987年   3篇
  1986年   4篇
  1985年   9篇
  1984年   4篇
  1983年   3篇
  1982年   5篇
  1977年   3篇
  1975年   4篇
  1974年   6篇
  1973年   11篇
  1972年   3篇
  1971年   6篇
  1970年   5篇
排序方式: 共有1918条查询结果,搜索用时 15 毫秒
991.
In this study, we aimed to investigate the allelopathic effects ofsunflower and wheat root exudates on the common weeds such as wild mustardand white mustard in our region. The root exudates which were obtained bysoaking 8 weeks old sunflower and wheat seedlings (20 or 40 seedlings) in 100mL of distilled water for 3 days were applied to the leaves of wild mustard andwhite mustard. In order to compare the allelopathic effect, the recommendeddose (1 g.da-1) and twice the recommended dose (2 g.da-1) of Gromstor(Tribenuron-methyl), a herbicide preferred by farmers for the chemical control ofthese weeds was also applied. The allelopathy was performed for wild mustardand white mustard seedlings by the measurement of different physiological andbiochemical parameters, such as chlorophyll a, chlorophyll b, total chlorophyll,carotenoid, proline, total protein amounts and superoxide dismutase enzymeactivity. The amounts of total chl and carotenoid in wild mustard leavesdecreased in all treatment groups compared to control. The highest decrease intotal chl (50.93%) and carotenoid (46.69%) was oberved in the treatment of 40wheat seedlings. 100 mL-1 distilled water. In the white mustard leaves, theamount of total chl in all treatment groups except the treatment group ofGromstor 2 g.da-1 and carotenoid in all treatment groups increased compared tothe control. The highest increases again were observed in 40 wheat seedlings.100 mL-1 distilled water treatment. The proline amounts in wild mustard andwhite mustard increased in all treatment groups. The highest increase wasobserved for the treatment of 20 wheat seedlings. 100 mL-1 distilled water inwild mustard (459.69%) and 40 sunflower seedlings. 100 mL-1 distilled water inwhite mustard plant (104.70%). In superoxide dismutase enzyme activities,treatments decreased activity except treatment of 40 sunflower seedling rootexudate in wild mustard, while increased activity outside commercial herbicidetreatment in white mustard. The results showed that sunflower and wheat rootexudates have allelopathic effects on wild mustard and white mustard weeds. Itis thought that the study will be a reference for new studies that will enable theuse of plant root exudates as bioherbicides or foliar fertilizers and will contributeto the fight against weeds in organic agriculture.  相似文献   
992.
Genetic relationships among Turkish sheep breeds were analysed on the basis of 30 microsatellite markers. Phylogenetic analyses based on the estimation of genetic distances revealed the closest relationships for the Akkaraman, Morkaraman and Tuj breeds, which were clearly differentiated from the others in the dendrogram. Our pattern was completely confirmed by results from the Factorial Correspondence Analysis. All the results described analysing either population parameters or individuals revealed a clear separation between the fat-tailed group and the others. These results, based on nuclear DNA, are discussed along with those already reported for these breeds through the investigation of mitochondrial DNA, which had revealed the invaluable significance of the genetic background of these Turkish sheep.  相似文献   
993.
Achillea (Asteraceae) species have been traditionally used for their different therapeutical properties. In this study, phytochemical composition of aerial parts of A. sintenisii which is endemic in Turkey was determined with Liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS). To evaluate the wound healing potential, the cream formulation prepared from A. sintenisii was tested on the linear incision wound model in mice. In vitro enzyme inhibitory activity tests were performed on elastase, hyaluronidase, and collagenase. In the histopathological examination, angiogenesis and granulation tissue formation were significantly increased in A. sintenisii treatment groups compared to the negative control group. As a result of this study, it is thought that the enzyme inhibition and antioxidant activity of the plant may contribute to the wound healing process. According to LC/MS/MS analysis result, quinic acid (24.261 μg/mg extract) and chlorogenic acid (14.97 μg/mg extract) were identified as main constituents of the extract.  相似文献   
994.
Gosain AK  Yan JG  Aydin MA  Das DK  Sanger JR 《Plastic and reconstructive surgery》2002,110(7):1655-61; discussion 1662-3
The vascular supply of the tensor fasciae latae flap and of the lateral thigh skin was studied in 10 cadavers to evaluate whether the lateral thigh skin toward the knee could be incorporated into an extended tensor fasciae latae flap. Within each cadaver, vascular injection of radiopaque material preceded flap elevation in one limb and followed flap elevation in the contralateral limb. Flaps raised after vascular injection were examined radiographically to evaluate the vascular anatomy of the lateral thigh skin independent of flap elevation. When vascular injection was made into the profunda femoris, the upper two-thirds of the flaps was better visualized than the distal third. When the injection was made into the popliteal artery, the vasculature of the distal third of the flaps was better visualized. Flaps raised before vascular injection were examined radiographically to delineate the anatomical territory of the vascular pedicle that had been injected. In these flaps, consistent cutaneous vascular supply was only seen in the skin overlying the tensor fasciae latae muscle, confirming that musculocutaneous perforators are the predominant means by which the pedicle of the tensor fasciae latae flap supplies the skin of the lateral thigh. Extended tensor fasciae latae flaps were elevated bilaterally in one cadaver, and selective methylene blue injections were made into the lateral circumflex femoral artery on one side and into the superior lateral genicular artery on the contralateral side. Methylene blue was observed in the proximal and distal thirds of the skin paddles, respectively, leaving unstained midzones. The vascular network of the lateral thigh skin could be divided into three zones. The lateral circumflex femoral artery and the third perforating branches of the profunda femoris artery perfuse the proximal and middle zones of the lateral thigh skin, respectively. The superior lateral genicular artery branch of the popliteal artery perfuses the distal zone. The middle and distal zones meet 8 to 10 cm above the knee joint, where the skin paddle of the tensor fasciae latae flap becomes unreliable. These data indicate that if the aim is to incorporate the skin over the distal thigh in an extended tensor fasciae latae flap without resorting to free-tissue transfer, then either a carefully planned delay procedure or an additional anastomosis to the superior lateral genicular artery is required.  相似文献   
995.
Doxorubicin (DOX) is a chemotherapeutic agent used for treatment of different cancers and its clinical usage is hindered by the oxidative injury-related cardiotoxicity. This work aims to declare if the harmful effects of DOX on heart can be alleviated with the use of Coenzyme Q10 (CoQ10) or L-carnitine. The study was performed on seventy two female Wistar albino rats divided into six groups, 12 animals each: Control group; DOX group (10 mg/kg); CoQ10 group (200 mg/kg); L-carnitine group (100 mg/kg); DOX + CoQ10 group; DOX + L-carnitine group. CoQ10 and L-carnitine treatment orally started 5 days before a single dose of 10 mg/kg DOX that injected intraperitoneally (IP) then the treatment continued for 10 days. At the end of the study, serum biochemical parameters of cardiac damage, oxidative stress indices, and histopathological changes were investigated. CoQ10 or L-carnitine showed a noticeable effects in improving cardiac functions evidenced reducing serum enzymes as serum interleukin-1 beta (IL-1 β), tumor necrosis factor alpha (TNF-α), leptin, lactate dehydrogenase (LDH), Cardiotrophin-1, Troponin-I and Troponin-T. Also, alleviate oxidative stress, decrease of cardiac Malondialdehyde (MDA), Nitric oxide (NO) and restoring cardiac reduced glutathione levels to normal levels. Both corrected the cardiac alterations histologically and ultrastructurally. With a visible improvements in α-SMA, vimentin and eNOS immunohistochemical markers. CoQ10 or L-carnitine supplementation improves the functional and structural integrity of the myocardium.  相似文献   
996.
BackgroundCOVID-19 covers a broad clinical spectrum, threatening global health. Although several studies have investigated various prognostic biochemical and hematological parameters, they generally lack specificity and are insufficient for decision-making. Beyond the neonatal period, NRBCs (nucleated red blood cells) in peripheral blood is rare and often associated with malignant neoplasms, bone marrow diseases, and other severe disorders such as sepsis and hypoxia. Therefore, we investigated if NRBCs can predict mortality in hypoxic ICU (Intensive Care Unit) patients of COVID-19.MethodsSeventy-one unvaccinated RT-PCR confirmed COVID-19 ICU patients was divided into those who survived (n=35, mean age=58) and died (n=36, mean age=75). Venous blood samples were collected in K3 EDTA tubes and analyzed on a Sysmex XN-1000 hematology analyzer with semiconductor laser flow cytometry and nucleic acid fluorescence staining method for NRBC analysis. NRBC numbers and percentages of the patients were compared on the first and seventh days of admission to the ICU. Results are reported as a proportion of NRBCs per 100 WBCs NRBCs/100 WBC (NRBC% and as absolute NRBC count (NRBC #, × 109/L).ResultsNRBC 7th-day count and % values were statistically higher in non-survival ones. The sensitivity for 7th day NRBC value <0.01 (negative) was 86.11%, the specificity was 48.57%, for <0.02; 75.00%, and 77.14%, for <0.03; 61.11%, and 94.60%.ConclusionsIn conclusion, our results indicate that NRBC elevation (>0.01) significantly predicts mortality in ICU hospitalized patients due to COVID-19. Worse, a high mortality rate is expected, especially with NRBC values of >0.03.  相似文献   
997.
Studying variations in behaviour at the individual or population level enables insight into the reproductive strategies within a species. We examined individual and geographical variation in the vocal and dive behaviour of male harbour seals, Phoca vitulina, which is associated with aquatic mating. This display behaviour was recorded in the Moray Firth, Scotland, from July 1994 to 1997, and in Orkney, Scotland, during July 1998. One vocalization type was apparent in the Moray Firth and two in Orkney. Time parameters (total and pulse duration) varied between males in the population in the Moray Firth. We used both frequency and time parameters in a discriminant analysis, which showed that 73.2% of individual male vocalizations could be correctly classified; 94.6% of male vocalizations from the Moray Firth and Orkney could be correctly classified according to their geographical areas. Therefore, vocal variation was greater between geographical areas than between individuals. No individual variation was apparent between dive and surface interval durations. However, individuals varied significantly in the percentage of short surface intervals. Male harbour seals showed substantial variability in the parameters affecting their vocal and dive behaviour during the mating season. We suggest that these variations may be indicative of adaptations to varying environmental challenges influencing the reproductive strategies of discrete populations. Copyright 2000 The Association for the Study of Animal Behaviour.  相似文献   
998.
Absract The plasmid stability of three wild type Lactococcus lactis strains and their mutants was investigated at different incubation time and temperatures in two different media [M17 broth and reconstituted skim milk (RSM)]. The results showed that both incubation times and temperature are effective on plasmid loss. The plasmid profiles of wild type strains exhibited 8 to 9 distinct plasmid species with molecular weights from 2.1 to 24.0 kb. Lactose fermentation ability was found to be encoded by 22.2 (strain U70), 23.6 (strain U29) and 24.0 (strain U52) kb plasmids in the wild type strains, respectively. The stabilities of the plasmids were explained by applying a second-order polynomial modeling system. Reasonable fittings were obtained for the model and the adjusted regression coefficients (R 2 adj) were between 0.76 and 0.99 for the overall data. Overall, it was found that incubation time had the most profound effect on plasmid stability, with plasmid loss occurring after 72 h, while temperatures in the range of 15–40°C also induced plasmid instability.  相似文献   
999.
Early acquisition of Pseudomonas aeruginosa is associated with a poorer prognosis in patients with cystic fibrosis. We investigated whether polymorphisms in CD14, the lipopolysaccharide receptor, increase the risk of early infection. Forty-five children with cystic fibrosis were investigated with annual bronchoalveolar lavage (BAL) and plasma sCD14 levels. Plasma sCD14 levels were significantly lower in children from whom P.aeruginosa was subsequently isolated (492.75 μg/ml vs. 1339.43 μg/ml, p = 0.018). Those with the CD14 -159CC genotype had a significantly increased risk of early infection with P.aeruginosa suggesting that CD14 C-159T plays a role in determining the risk of early infection with P.aeruginosa.  相似文献   
1000.
Major depression (MD) has a complex multifactorial aetiology with genetic and environmental factors contributing to this disorder. As with all antidepressant treatments, there is variability in drug response because of heredity, and this leads us to focus on the genetic polymorphism of the drug’s metabolising transporter genes. The serotonin transporter (5-HTT) gene is a particularly important candidate for genetic involvement in MD disorders owing to its key role in the regulation of serotonergic transmission and is therefore considered an interesting candidate in the mechanism of antidepressant drugs. Here, we studied the associations between genetic polymorphisms in two regions of the 5-HTT gene (5-HTTLPR and VNTR) to understand venlafaxine response. Venlafaxine was found to be effective in MD patients based on their HAM-D and CGI scores (p<0.05). Although the results did not yield a significant difference between the frequencies of the SS, LS, LL, 9/9, 10/10, 12/12 and 10/12 genotypes and venlafaxine response, venlafaxine dose was increased in patients with Stin2.12 and S alleles. These alleles might have a predisposition to mood disorders. Further studies with more patients are required to confirm this clinical association.  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