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   8807篇
  免费   575篇
  国内免费   57篇
耳鼻咽喉   61篇
儿科学   200篇
妇产科学   123篇
基础医学   837篇
口腔科学   173篇
临床医学   775篇
内科学   2236篇
皮肤病学   80篇
神经病学   1182篇
特种医学   285篇
外科学   1636篇
综合类   21篇
一般理论   1篇
预防医学   356篇
眼科学   207篇
药学   458篇
中国医学   13篇
肿瘤学   795篇
  2023年   110篇
  2022年   175篇
  2021年   391篇
  2020年   230篇
  2019年   301篇
  2018年   309篇
  2017年   238篇
  2016年   271篇
  2015年   285篇
  2014年   414篇
  2013年   497篇
  2012年   763篇
  2011年   709篇
  2010年   364篇
  2009年   363篇
  2008年   544篇
  2007年   537篇
  2006年   554篇
  2005年   461篇
  2004年   417篇
  2003年   362篇
  2002年   314篇
  2001年   74篇
  2000年   64篇
  1999年   71篇
  1998年   45篇
  1997年   44篇
  1996年   49篇
  1995年   30篇
  1994年   35篇
  1993年   28篇
  1992年   42篇
  1991年   39篇
  1990年   31篇
  1989年   41篇
  1988年   23篇
  1987年   18篇
  1986年   20篇
  1985年   17篇
  1984年   28篇
  1983年   22篇
  1982年   13篇
  1981年   17篇
  1980年   8篇
  1979年   13篇
  1978年   5篇
  1977年   5篇
  1975年   6篇
  1974年   10篇
  1973年   6篇
排序方式: 共有9439条查询结果,搜索用时 218 毫秒
61.
Bordetella bronchiseptica is closely related to Bordetella pertussis, which produces respiratory disease primarily in mammals other than humans. However, its importance as a human pathogen is being increasingly recognized. Although a large amount of research on Bordetella has been generated regarding protein virulence factors, the participation of the surface lipopolysaccharide (LPS) during B. bronchiseptica infection is less understood. To get a better insight into this matter, we constructed and characterized the behavior of an LPS mutant with the deepest possible rough phenotype. We generated the defective mutant B. bronchiseptica LP39 on the waaC gene, which codes for a heptosyl transferase involved in the biosynthesis of the core region of the LPS molecule. Although in B. bronchiseptica LP39 the production of the principal virulence determinants adenylate cyclase-hemolysin, filamentous hemagglutinin, and pertactin persisted, the quantity of the two latter factors was diminished, with the levels of pertactin being the most greatly affected. Furthermore, the LPS of B. bronchiseptica LP39 did not react with sera obtained from mice that had been infected with the parental strain, indicating that this defective LPS is immunologically different from the wild-type LPS. In vivo experiments demonstrated that the ability to colonize the respiratory tract is reduced in the mutant, being effectively cleared from lungs within 5 days, whereas the parental strain survived at least for 30 days. In vitro experiments have demonstrated that, although B. bronchiseptica LP39 was impaired for adhesion to human epithelial cells, it is still able to survive within the host cells as efficiently as the parental strain. These results seem to indicate that the deep rough form of B. bronchiseptica LPS cannot represent a dominant phenotype at the first stage of colonization. Since isolates with deep rough LPS phenotype have already been obtained from human B. bronchiseptica chronic infections, the possibility that this phenotype arises as a consequence of selection pressure within the host at a late stage of the infection process is discussed.  相似文献   
62.
Cytotoxicity, morphological neoplastic transformation, cellularuptake and metabolic reduction were determined in BALB/3T3 CIA31-1-1 cells for trivalent arsenic (sodium arsenite, As3+)and for pentavalent arsenic (sodium arsenate, As5+). The levelsof cellular uptake of73As-labelled sodium arsenite and arsenatewere dose-dependent and highest in the first hour. At equimolarconcentration (3 x 10–6 M), cellular uptake was 4-foldhigher for As3+ than for As5+. Cytotoxicity was higher for As3+than for As5+, but when correlated to total As cell burden itshowed no significant difference for the two forms. Morphologicaltransformation focus assays showed transforming activity forboth As3+ and As5+, with relative transformation frequenciesalso of 4:1. Recovery from the cytosol after exposure for 1–24h was >90% for either form of absorbed As. Exposure to As3+yielded 100% as As3+ in cytosol, but exposure to As5+ yielded>70% as As3+, showing a high rate of intracellular metabolicreduction. No methylated metabolites were detected by ion-exchangechromatography. After 24-h incubation in cell-free medium, oxidationof As3+ to As5+ occurred up to 30% of the dose, but incubationin the presence of cells lowered the oxidation level to 4%.As5+ was recovered unchanged from cell-free medium (24-h incubation),but in the presence of the cells it yielded up to 5% as As3+within 24 h and the cumulative release of As3+ by cells exposedto As5+ was dose-dependent. Glutathione depletion by diethylmaleateinhibited reduction of As5+ to As3+ by these cells up to 25%of controls, showing that As5+ reduction is partly dependenton glutathione. These results suggest that As3+ is the formresponsible for the cytotoxic and transforming effects, independentlyof the valence state of the inorganic arsenic in the culturemedium.  相似文献   
63.
The meat production industry is one of the leading contributors of greenhouse gas emissions. Cultured meat presents itself as a potential eco- and animal-friendly meat substitute which has the potential to eradicate animal cruelty and reduce both the environmental footprint and the risk of zoonotic illnesses, while delivering a nutrient-dense product. The purpose of this study was to investigate how consumers perceive cultured meat and if the frequency of meat consumption is related to their intention of trying or purchasing cultured meat. Data were collected online in 2020 from Croatia, Greece, and Spain. Among the 2007 respondents, three segments were identified according to meat consumption and variety, plus an a priori identified group of “non-meat eaters”. Sixty percent perceived cultured meat as kind to animals, 57% as unnatural, 45% as healthy and environmentally-friendly, 21% as disgusting, and only 16% as tasty. Although 47% of the respondents had not heard of cultured meat before, 47% would taste it and 41% would purchase it for the same price as conventional meat. This indicates that consumers from Croatia, Greece and Spain might be likely to purchase cultured meat if sold at an affordable price.  相似文献   
64.
Metabolic- (dysfunction) associated fatty liver disease (MAFLD) represents the predominant hepatopathy and one of the most important systemic, metabolic-related disorders all over the world associated with severe medical and socio-economic repercussions due to its growing prevalence, clinical course (steatohepatitis and/or hepatocellular-carcinoma), and related extra-hepatic comorbidities. To date, no specific medications for the treatment of this condition exist, and the most valid recommendation for patients remains lifestyle change. MAFLD has been associated with metabolic syndrome; its development and progression are widely influenced by the interplay between genetic, environmental, and nutritional factors. Nutrigenetics and nutrigenomics findings suggest nutrition’s capability, by acting on the individual genetic background and modifying the specific epigenetic expression as well, to influence patients’ clinical outcome. Besides, immunity response is emerging as pivotal in this multifactorial scenario, suggesting the interaction between diet, genetics, and immunity as another tangled network that needs to be explored. The present review describes the genetic background contribution to MAFLD onset and worsening, its possibility to be influenced by nutritional habits, and the interplay between nutrients and immunity as one of the most promising research fields of the future in this context.  相似文献   
65.
A proportion of men are infertile despite having normal medical history/physical examination and normal semen analysis. We aimed to assess whether normal sperm parameters per se account for male factor fertility. 1,957 infertile men were compared with 103 age-comparable fertile controls. Semen analysis was based on 2010 World Health Organization reference criteria. Of all, 12.1% of infertile men and 40.8% of fertile men presented with normal sperm parameters. Among fertile men, 36.9% had isolated sperm abnormalities and 22.3% men showed two or more concomitant sperm abnormalities. Serum total testosterone was higher in infertile men with normal sperm parameters compared to those with ≥2 sperm abnormalities or azoospermia, but similar to those with isolated sperm abnormalities (p ≤ .001). Circulating hormones were similar among sperm parameters groups in fertile men. At multivariable analyses, testicular volume (OR 1.12, p ≤ .001) and FSH (OR 0.8, p ≤ .001) were associated with normal sperm parameters. Overall, the longer the infertility period, the greater the number of sperm parameters abnormalities (p < .01). In conclusion, we found that 12% of infertile men and only 41% of fertile men present with normal sperm parameters. Normal sperm parameters per se do not reliably account for fertility in the real-life setting.  相似文献   
66.
BackgroundWe aim to evaluate the impact of multiparametric magnetic resonance imaging and fusion-target biopsy for early reclassification of patients with low-risk Prostate Cancer in a randomized trial.Materials and methodsBetween 2015 and 2018, patients diagnosed with Prostate Cancer after random biopsy fulfilling PRIAS criteria were enrolled and centrally randomized (1:1 ratio) to study group or control group. Patients randomized to study group underwent multiparametric magnetic resonance imaging at 3 months from enrollment: patients with positive findings (PIRADS-v2>2) underwent fusion-target biopsy; patients with negative multiparametric magnetic resonance imaging or confirmed ISUP - Grade Group 1 at fusion-target biopsy were managed according to PRIAS schedule and 12-core random biopsy was performed at 12 months. Patients in control group underwent PRIAS protocol, including a confirmatory 12-core random biopsy at 12 months. Primary endpoint was a reduction of reclassification rate at 12-month random biopsy in study group at least 20% less than controls. Reclassification was defined as biopsy ISUP Grade Group 1 in >2 biopsy cores or disease upgrading.ResultsA total of 124 patients were randomized to study group (n = 62) or control group (n = 62). Around 21 of 62 patients (34%) in study group had a positive multiparametric magnetic resonance imaging, and underwent fusion-target biopsy, with 11 (17.7%) reclassifications. Considering the intention-to-treat population, reclassification rate at 12-month random biopsy was 6.5% for study group and 29% for control group, respectively (P < 0.001).ConclusionsThe early employment of multiparametric magnetic resonance imaging for active surveillance patients enrolled after random biopsy consents to significantly reduce reclassifications at 12-month random biopsy.  相似文献   
67.
BackgroundIn severe cases of ankle and subtalar arthritis, arthrodesis of the subtalar joint is performed in combination with ankle arthroplasty. In these special cases gait analysis reveals real motion at the replaced tibiotalar joint.MethodsTwenty-three patients affected by ankle and subtalar arthritis, treated either with a 3-component or a 2-component prosthesis in combination with subtalar arthrodesis, were clinically evaluated preoperatively and at a minimum of 1-year follow-up. Gait analysis was performed postoperatively using a multi-segment foot protocol. Foot kinematics were compared to corresponding data from a healthy control group.ResultsClinical scores significantly improved from preoperative to follow-up. The clinically measured passive ankle dorsiflexion/plantarflexion significantly improved at the follow-up. Patients’ normalized walking speed and stride length were significantly lower than those in control. With exception of the ankle frontal-plane motion, sagittal-plane mobility of foot joints was about 50% than that in healthy joints.ConclusionsImprovement in clinical scores was found for both prostheses. Normal spatio-temporal parameters were not restored. In these patients, fusion of the subtalar joint appeared to be compensated by larger frontal-plane motion at the tibiotalar joint.Level of evidenceLevel III- retrospective comparative study.The study was approved by the local Ethics Committee as protocol MAT (protocol registration at clinicaltrials.gov NCT03356951).  相似文献   
68.
BackgroundThe aim of this study is to systematically review the literature on clinical outcomes of patients who have undergone autologous matrix-induced chondrogenesis (AMIC) for treatment of osteochondral lesions of the talus (OCL) and compare the studies’ outcomes.MethodsPubmed and Embase were searched in January 2020 for articles concerning OCL surgery. Studies were included if they had a minimum 1-year follow-up and the primary measures were functional outcomes. The meta-analysis compared the Visual Analogic Score (VAS), the American Orthopedic Foot and Ankle Score (AOFAS), and the Foot Function Index (FFI) between baseline and follow-up of 1?2 years, and 3?5 years. A random effects model was used to evaluate outcome changes.ResultsThe search returned 15 studies, with a total of 492 patients. The VAS improved 4.45 and 4.6 points from baseline to the 1?2 year and 3?5 year follow-up, respectively (p < 0.001). AOFAS improved 31.59 and 32.47 points from baseline to the 1?2 year and 3?5 year follow-up, respectively (p < 0.001). The FFI showed a significant improvement of 30.93 points from baseline to year 3?5 (p < 0.001). A total of 6 patients with revision surgeries have been reported within the follow up period. It was not possible to correlate clinical features like lesion size, surgical approach, and bone marrow stimulation technique to the reported outcome.ConclusionSurgical treatment of OCL via the AMIC procedure provided significant improvement in the functional outcome and pain scores when compared to the pre-operative values. Improvements were observed up to 5 years post-operatively.  相似文献   
69.
Notfall + Rettungsmedizin - Der Europäische Rat für Wiederbelebung hat diese Leitlinie –&nbsp;Basismaßnahmen zur Wiederbelebung&nbsp;– auf Grundlage des...  相似文献   
70.
Journal of Public Health - Neighbourhood composition is considered a social determinant of mental health that can be addressed by policymakers to improve outcomes. Deprived neighbourhoods typically...  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