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   210839篇
  免费   15279篇
  国内免费   743篇
耳鼻咽喉   2301篇
儿科学   5490篇
妇产科学   4305篇
基础医学   27128篇
口腔科学   4520篇
临床医学   20079篇
内科学   45056篇
皮肤病学   2760篇
神经病学   20386篇
特种医学   6966篇
外国民族医学   13篇
外科学   32961篇
综合类   3412篇
现状与发展   2篇
一般理论   291篇
预防医学   19089篇
眼科学   4390篇
药学   14422篇
  12篇
中国医学   376篇
肿瘤学   12902篇
  2023年   930篇
  2022年   1431篇
  2021年   3518篇
  2020年   2203篇
  2019年   3393篇
  2018年   3970篇
  2017年   3213篇
  2016年   3412篇
  2015年   4069篇
  2014年   6097篇
  2013年   8827篇
  2012年   13129篇
  2011年   14327篇
  2010年   8098篇
  2009年   7307篇
  2008年   13593篇
  2007年   14434篇
  2006年   13925篇
  2005年   14397篇
  2004年   13812篇
  2003年   12903篇
  2002年   12438篇
  2001年   1880篇
  2000年   1460篇
  1999年   2049篇
  1998年   2829篇
  1997年   2437篇
  1996年   2206篇
  1995年   1954篇
  1994年   1756篇
  1993年   1655篇
  1992年   1212篇
  1991年   1150篇
  1990年   1055篇
  1989年   952篇
  1988年   1015篇
  1987年   1020篇
  1986年   1001篇
  1985年   1087篇
  1984年   1478篇
  1983年   1462篇
  1982年   1816篇
  1981年   1640篇
  1980年   1555篇
  1979年   812篇
  1978年   958篇
  1977年   933篇
  1976年   831篇
  1975年   682篇
  1974年   666篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Objective: To meta-analytically assess the efficacy and tolerability of nonsteroidal anti-inflammatory drugs (NSAIDs) vs placebo in schizophrenia. Method: Searching PubMed, PsycINFO, ISI Web of Science, and the US National Institute of Mental Health clinical trials registry from database inception to December 31, 2012, we conducted a systematic review/meta-analysis of randomized placebo-controlled studies assessing the efficacy of adjunctive NSAIDs. Primary outcome was the change in Positive and Negative Syndrome Scale (PANSS) total score. Secondary outcomes included change in PANSS positive and negative subscores, all-cause discontinuation, and tolerability outcomes. Random effects, pooled, standardized mean changes (Hedges’ g) and risk ratios were calculated. Results: Across 8 studies, including 3 unpublished reports (n = 774), the mean effect size for PANSS total score was −0.236 (95% CI: −0.484 to 0.012, P = .063, I2 = 60.6%), showing only trend-level superiority for NSAIDs over placebo. The mean effect sizes for the PANSS positive and negative scores were −0.189 (95% CI: −0.373 to −0.005, P = .044) and −0.026 (95% CI: −0.169 to 0.117, P = .72), respectively. The relative risk for all-cause discontinuation was 1.13 (95% CI: 0.794 to 1.599, P = .503). Significant superiority of NSAIDs over placebo regarding PANSS total scores was moderated by aspirin treatment (N = 2, P = .017), inpatient status (N = 4, P = .029), first-episode status (N = 2, P = .048), and (in meta-regression analyses) lower PANSS negative subscores (N = 6, P = .026). Interpretation: These results indicate that adjunctive NSAIDs for schizophrenia may not benefit patients treated with first-line antipsychotics judged by PANSS total score change. NSAIDs may have benefits for positive symptoms, but the effect was minimal/small. However, due to a limited database, further controlled studies are needed, especially in first-episode patients.Key words: schizophrenia, inflammation, treatment resistance, augmentation, concomitant, nonsteroidal anti-inflammatory  相似文献   
992.
Narcotic analgesics cause addiction by poorly understood mechanisms, involving mu opoid receptor (MOR). Previous cell culture studies have demonstrated significant basal, spontaneous MOR signaling activity, but its relevance to narcotic addiction remained unclear. In this study, we tested basal MOR-signaling activity in brain tissue from untreated and morphine-pretreated mice, in comparison to antagonist-induced withdrawal in morphine-dependent mice. Using guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTP gamma S) binding and adenylyl cyclase activity assay in brain homogenates, we demonstrated that morphine pretreatment of mice enhanced basal MOR signaling in mouse brain homogenates and, moreover, caused persistent changes in the effects of naloxone and naltrexone, antagonists that elicit severe withdrawal in dependent subjects. Naloxone and naltrexone suppressed basal [(35)S]GTP gamma S binding (acting as "inverse agonists") only after morphine pretreatment, but not in drug-naive animals. Moreover, naloxone and naltrexone stimulated adenylyl cyclase activity in striatum homogenates only after morphine pretreatment, by reversing the inhibitory effects of basal MOR activity. After cessation of morphine treatment, the time course of inverse naloxone effects on basal MOR signaling was similar to the time course of naltrexone-stimulated narcotic withdrawal over several days. The neutral antagonist 6 beta-naltrexol blocked MOR activation without affecting basal signaling (G protein coupling and adenylyl cyclase regulation) and also elicited substantially less severe withdrawal. These results demonstrate long-lasting regulation of basal MOR signaling as a potential factor in narcotic dependence.  相似文献   
993.
994.
995.

Purpose

This paper shows the long-term benefits of total/near-total resection of complex spinal cord lipomas and meticulous reconstruction of the neural placode, and specifically, its advantage over partial resection, and over non-surgical treatment for the subset of children with asymptomatic virgin lipomas.

Methods

The technique of total resection and placode reconstruction, together with technical nuances, are described in detail. We added 77 patients with complex lipomas to our original lipoma series published in 2009 and 2010, to a total of 315 patients who had had total or near-total resection and followed for a span of 20 years. Long-term outcome is measured by overall progression-free survival (PFS) with the Kaplan–Meier analysis, and by subgroup Cox proportional recurrence hazard analysis for the influence on outcome of 4 predictor variables of lipoma type, presence of symptoms, prior surgery, and post-operative cord–sac ratio. These results are compared to an age-matched, lesion-matched series of 116 patients who underwent partial lipoma resection over 11 years. The results for total resection is also compared to two large published series of asymptomatic lipomas followed without surgery over 9 to 10 years, to determine whether prophylactic total resection confers better long-term protection over conservative treatment for children with asymptomatic lipomas..

Results

The PFS after total resection for all lipoma types and clinical subgroups is 88.1 % over 20 years versus 34.6 % for partial resection at 10.5 years (p?<?0.0001). Culling only the asymptomatic patients with virgin (previously unoperated) lipomas, the PFS for prophylactic total resection for this subgroup rose to 98.8 % over 20 years, versus 67 % at 9 years for one group of non-surgical treatment and 60 % at 10 years for another group of conservative treatment. Our own as well as other published results of partial resection also compare poorly to non-surgical treatment for the subset of asymptomatic virgin lipomas. Multivariate subgroup analyses show that cord–sac ratio is the only independent variable that predicts outcome, with a 96.9 % PFS for ratio <30 % (loosest sac), 86.2 % for ratio between 30 and 50 %, and 78.3 % for ratio >50 % (tightest sac), and a threefold increase in recurrence hazard for high ratios (p?=?0.0009). Pre-operative patient profiling using multiple correspondence analysis shows the ideal patient for total resection is a child less than 2 years old with a virgin asymptomatic lipoma, who, with a PFS of 99.2 %, is virtually cured by total resection.

Conclusion

Total/near-total resection of complex lipomas and complete reconstruction of the neural placode achieves far better long-term protection against symptomatic recurrence than partial resection for all lesions; and for the subset of asymptomatic virgin lipomas, also better than non-surgical treatment. Partial resection in many cases produces worse outcome than conservative treatment for asymptomatic lesions.  相似文献   
996.
Chronic metabolic acidosis occurs commonly in chronic renal failure (CRF). The proximal renal tubular cell is the site in the kidney of high oxidative metabolic activity and in CRF is associated with adaptive hypertrophy and hypermetabolism. We hypothesised that chronic acidosis may lead to increased generation of reactive oxygen species due to increased oxidative activity. We developed a novel model of chronic acidosis in LLC-PK1 cells and measured markers of oxidative stress and metabolism. Acidosis led to a reduction in cellular total glutathione and protein thiol content and an increase in glutathione peroxidase activity and NH3 generation. The expression of constitutively expressed heat stress protein (HSP) HSC70 and HSP60 increased at pH 7.0.  相似文献   
997.
998.
Rifampin has concentration-dependent activity against Mycobacterium tuberculosis. However, marked intersubject variation of rifampin concentrations occurs. In this study, we evaluated rifampin pharmacokinetics in relation to tuberculosis, geographic region, race, and single nucleotide polymorphisms of the human transporter genes SLCO1B1, SLCO1B3, and MDR1. Seventy-two adults with pulmonary tuberculosis from Africa, North America, and Spain were evaluated during multidrug intensive-phase therapy, and their results were compared to those from 16 healthy controls from North America. Rifampin pharmacokinetic values were similar between tuberculosis patients and controls (geometric mean [GM] area under the concentration-time curve from 0 to 24 h [AUC0-24] of 40.2 versus 40.9 μg·h/ml; P = 0.9). However, in multivariable analyses, the rifampin AUC0-24 was significantly affected by rifampin dosage (in mg/kg of body weight), polymorphisms in the SLCO1B1 gene, and the presence of tuberculosis by geographic region. The adjusted rifampin AUC0-24 was lowest in patients with tuberculosis from Africa compared to that in non-African patients or control subjects. The adjusted rifampin AUC0-24 was also 36% lower among participants with SLCO1B1 genotype c.463CA than that among participants with SLCO1B1 genotype c.463CC (adjusted GM, 29.8 versus 46.7 μg·h/ml; P = 0.001). Polymorphisms in the SLCO1B1 gene associated with lower rifampin exposure were more frequent among black subjects. In conclusion, marked intersubject variation of the rifampin AUC0-24 values was observed, but the mean values of the AUC0-24 did not significantly vary between patients with tuberculosis and healthy controls. Lower rifampin exposure was associated with the polymorphism of the SLCO1B1 c.463C>A gene. When adjusted for the patient mg/kg dosage and transporter gene polymorphisms, rifampin exposure was lower in patients with tuberculosis, which suggests that additional absorption or metabolic processes affect rifampin exposure with tuberculosis disease.Rifamycins have consistently demonstrated concentration-dependent activity against Mycobacterium tuberculosis in both in vitro and in vivo models (14, 17, 18, 24). There is marked intersubject variation of rifamycin concentrations among patients on standard tuberculosis therapy, and the basis for variation is not well characterized. Advanced HIV infection has been associated with low rifampin concentrations, but marked differences in rifampin concentrations are also found among tuberculosis patients without HIV infection and between patient groups (7, 21, 27, 29). Low rifamycin exposures can have clinical significance. In a treatment trial of rifabutin in patients with HIV-associated tuberculosis, low rifabutin exposure (area under the concentration-time curve [AUC]) was associated with treatment failure or relapse with acquired rifamycin-resistant M. tuberculosis (33). In treatments with intermittent rifamycin-containing regimens (with lower total rifamycin exposure per week), increases in relapse rates were observed (5, 20).Two recent Tuberculosis Trials Consortium (TBTC) clinical trials demonstrated a decreased initial response to therapy (by 2-month culture conversion) among patients enrolled at African sites rather than non-African sites (3, 9). Possible explanations for the decreased response include differences in severity of tuberculosis, morbidity due to HIV infection, differences in microbiologic techniques between sites, or the pharmacokinetics of antitubercular drugs, particularly rifampin.Our primary study objectives were the comparison of rifampin pharmacokinetics among patients with tuberculosis and healthy controls and between regions (Africa versus non-Africa) and races (black versus all other races). Different human phenotypes may result from alternative forms of a gene at the same physical location (called alleles), and gene polymorphisms are reported to vary among races. Because organic anion transporter peptides (OATP) play key roles in transport and disposition of xenobiotics in the gastrointestinal tract and liver, the secondary objectives of the study were to determine the relationships between rifampin pharmacokinetics and human genetic polymorphisms of drug influx and efflux transporter genes (anion-transporting polypeptides [SLCO1B1 and SLCO1B3] and P-glycoprotein [MDR1]).Rifampin pharmacokinetic data of healthy controls were previously described (32).(Some of the pharmacokinetic and pharmacogenetic data for patients with tuberculosis were previously reported at the Second International Workshop on Clinical Pharmacology of Tuberculosis Drugs in 2009 [30] and as abstract A791 at the American Thoracic Society International Conference in 2008 [31].)  相似文献   
999.

Background

Steroid use has prolonged ambulation in Duchenne muscular dystrophy (DMD) and combined with advances in respiratory care overall management has improved such that cardiac manifestations have become the major cause of death. Unfortunately, there is no consensus for DMD-associated cardiac disease management. Our purpose was to assess effects of steroid use alone or in combination with angiotensin converting enzyme inhibitors (ACEI) or angiotension receptor blocker (ARB) on cardiovascular magnetic resonance (CMR) derived circumferential strain (εcc).

Methods

We used CMR to assess effects of corticosteroids alone (Group A) or in combination with ACEI or ARB (Group B) on heart rate (HR), left ventricular ejection fraction (LVEF), mass (LVM), end diastolic volume (LVEDV) and circumferential strain (εcc) in a cohort of 171 DMD patients >5 years of age. Treatment decisions were made independently by physicians at both our institution and referral centers and not based on CMR results.

Results

Patients in Group A (114 studies) were younger than those in Group B (92 studies)(10 ± 2.4 vs. 12.4 ± 3.2 years, p < 0.0001), but HR, LVEF, LVEDV and LVM were not different. Although εcc magnitude was lower in Group B than Group A (-13.8 ± 1.9 vs. -12.8 ± 2.0, p = 0.0004), age correction using covariance analysis eliminated this effect. In a subset of patients who underwent serial CMR exams with an inter-study time of ~15 months, εcc worsened regardless of treatment group.

Conclusions

These results support the need for prospective clinical trials to identify more effective treatment regimens for DMD associated cardiac disease.  相似文献   
1000.
The Zucker rat is used as a model of genetic obesity, and while Zucker rats have been well studied for their reduced sensitivity to leptin signaling and subsequent weight gain, little work has examined their responses to environmental signals that are associated with “hedonic” feeding. This study evaluated the effects of a high‐fat food olfactory cue (bacon) in stimulating nose‐poke food‐seeking behavior on first exposure (novel) and after a period of access for consumption (familiar) in lean and obese Zucker rats at either 4 or 12 months of age, and under ad‐lib fed (unrestricted; U) or chronically food‐restricted (70% of ad‐lib; R) conditions. Baseline nose‐poke levels were comparable amongst all groups. At 4 months of age, only ObU rats displayed increased behavioral activation to familiar food cues. Twelve‐month‐old Ob rats, regardless of diet, exhibited substantially greater food‐seeking behavior when exposed to both the novel and familiar olfactory cues. A strong positive correlation between body weight and nose‐poke entries for the familiar food cue was observed at both ages, while this correlation for the novel food cue was significant in 12–month‐old rats only. Similarly, there were strong positive correlations between food intake and poke entries for the familiar food cue was observed at both ages, while this correlation for the novel food cue was significant in 12–month‐old rats only. Although it is possible that differences in olfactory sensitivity contribute to these behavioral effects, our findings support the interactions between food intake, obesity, and food‐seeking behavior and are consistent with leptin inhibiting the brain's reactivity to food cues and suggest that the enhanced sensitivity to the food cues with leptin deficiency is likely to contribute to overeating and weight gain. Synapse, 2013. © 2012 Wiley Periodicals, Inc.  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