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   17874篇
  免费   1651篇
  国内免费   51篇
耳鼻咽喉   145篇
儿科学   516篇
妇产科学   272篇
基础医学   2422篇
口腔科学   667篇
临床医学   2090篇
内科学   3298篇
皮肤病学   293篇
神经病学   1502篇
特种医学   441篇
外科学   1840篇
综合类   435篇
一般理论   9篇
预防医学   2723篇
眼科学   377篇
药学   1356篇
中国医学   39篇
肿瘤学   1151篇
  2023年   158篇
  2022年   217篇
  2021年   427篇
  2020年   291篇
  2019年   452篇
  2018年   430篇
  2017年   392篇
  2016年   424篇
  2015年   480篇
  2014年   595篇
  2013年   828篇
  2012年   1186篇
  2011年   1252篇
  2010年   711篇
  2009年   605篇
  2008年   967篇
  2007年   975篇
  2006年   936篇
  2005年   916篇
  2004年   868篇
  2003年   753篇
  2002年   755篇
  2001年   462篇
  2000年   395篇
  1999年   350篇
  1998年   200篇
  1997年   208篇
  1996年   140篇
  1995年   118篇
  1994年   124篇
  1993年   130篇
  1992年   190篇
  1991年   197篇
  1990年   229篇
  1989年   198篇
  1988年   159篇
  1987年   168篇
  1986年   164篇
  1985年   136篇
  1984年   116篇
  1983年   115篇
  1982年   80篇
  1981年   62篇
  1979年   87篇
  1978年   70篇
  1977年   54篇
  1976年   64篇
  1974年   61篇
  1973年   66篇
  1970年   57篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A multicenter, randomized placebo-controlled double-blind trial of nimodipine in poor-grade aneurysm patients was carried out in 17 Canadian hospitals. Of 188 patients enrolled in the trial, 32 were excluded for protocol violations and two were excluded due to statistical considerations, leaving 154 patients for valid outcome analysis. Nimodipine treatment was associated with a significantly better outcome (p less than 0.001): 21 (29.2%) of 72 nimodipine-treated patients had a good outcome at 3 months after subarachnoid hemorrhage (SAH) compared to eight (9.8%) of 82 placebo-treated patients. Delayed ischemic deficits from vasospasm alone were significantly less frequent in the nimodipine group (p less than 0.05) with permanent deficits occurring in five nimodipine-treated patients (6.9%) and in 22 placebo-treated patients (26.8%). Improvement in the good outcome rate and reduction in delayed ischemic deficits from vasospasm alone occurred in both Grade 3 and 4 patients, with no difference between nimodipine- and placebo-treated patients being found in Grade 5 patients. Repeat angiography after Day 4 was carried out in 124 patients. There was no significant difference in the incidence of moderate or severe diffuse spasm, which was seen in 64.3% of nimodipine-treated patients and 66.2% of placebo-treated patients. The authors conclude that nimodipine treatment in poor-grade patients with SAH results in an increase in the number of good outcomes and a reduction in the incidence of delayed neurological deterioration due to vasospasm. This effect occurs by a mechanism other than prevention of large-vessel spasm as visualized on angiography.  相似文献   
52.
目的 了解变形链球菌表面蛋白和葡糖基转移酶基因疫苗单独及联合免疫对定菌鼠唾液变链菌和牙面菌斑的影响。方法  2 8d龄 Wistar大鼠 3 6只 ,随机分为 pc DNA3 - pac组、pc DNA3 - gtf B组、pc DNA3 - pac联合pc DNA 3 - gtf B组、变形链球菌灭活全菌组、pc DNA3空载体组和 PBS液组 ,进行三次双侧颌下腺腺周注射免疫 ,建立定菌鼠模型 ,作诱龋实验 3个月。唾液变链菌计数和菌斑计分。结果 唾液变链菌菌落计数和牙面菌斑计分在 pc D-NA3与 PBS组最高 ,其次为单基因疫苗免疫组 ,联合基因疫苗和灭活全菌细胞免疫组最低 ,各组间有显著性差异 ( P<0 .0 5 )。结论  pc DNA3 - gtf B和 pc DNA3 - pac具有明显的免疫抑菌作用 ,联合基因疫苗免疫优于单基因疫苗  相似文献   
53.
54.
In depressed patients as well as healthy controls, a positive relationship between hippocampal volume and trait anxiety has been reported. This study sought to explore the possible inter-relation between hippocampal volume and trait anxiety further. Magnetic resonance imaging at 7 T was used to measure hippocampal volumes in a rat model of extremes in trait anxiety (experiment 1) and in a Wistar population with normal anxiety-related behavior (experiment 2). In addition to anxiety-related behavior, potentially confounding factors (depression-like, exploratory, and locomotor behavior) were assessed. Experiment 1 globally supported the hypothesis of a positive relationship between hippocampus volume and trait anxiety but did not allow for ruling out possible confounds arising from cosegregation of other behavioral traits. Experiment 2 yielded strong evidence for a negative relationship which was specific for trait anxiety. Thus, the relationship between hippocampal volume and anxiety may be more complex than expected. Interestingly, anxiety-related behavior in experiment 2 had a stronger influence on hippocampal volume than depression-like behavior. In the light of hippocampal volume loss in anxiety disorder and frequent comorbidity of anxiety and depression, this finding suggests that further research into the relationship between anxiety and hippocampal volume may be critical for understanding hippocampal contributions to normal and pathological behavior.  相似文献   
55.
OBJECTIVE--To determine the efficacy and dose requirements of captopril to reduce functional mitral regurgitation in patients with dilated heart failure. DESIGN--A randomised double blind placebo controlled parallel arm trial. Incremental daily doses of 25 mg, 50 mg and 100 mg captopril used for a four week period each for a total of 12 weeks preceded by a two week placebo washout. Twenty eight ambulatory patients (mean age 72) New York Heart Association (NYHA) class II or III with apparently controlled ischaemic dilated heart failure (ejection fraction 29% (0.04%)) on digoxin, diuretics, and nitrates were randomised. All had at least grade 2/4 functional mitral regurgitation (> 5 cm2 regurgitant area on colour flow Doppler). RESULTS--Twenty three patients completed the study (13 on placebo and 10 on captopril). Significant improvements were confined to the captopril group. Compared with placebo the following improvements were noted in the captopril treated group: mitral regurgitant area decreased from a threshold at 50 mg/day (p < 0.05, mean (95% confidence interval (95% CI)) 3.1 (0.2 to 6.0) cm2), with a further decrease at 100 mg/day (p < 0.01, mean (95% CI) 5.3 (3.1 to 7.5) cm2). Significant improvements in all the other measurements were noted only after 100 mg/day. Stroke volume increased (p < 0.01, mean (95% CI) 11, (1.4 to 21) ml), systemic vascular resistance decreased (p < 0.05, mean (95% CI) 414 (35 to 793) dyn s cm5), left atrial area decreased (p < 0.05, mean (95% CI) 4.3 (0.03 to 8.6) cm2), and deceleration time increased (p < 0.01, mean (95% CI) 52 ms (7 to 98) ms). Left ventricular diameter decreased marginally (p = 0.06, mean (95% CI) 4 (-0.05 to 9 mm). Duke activity index score increased (p < 0.001, median (95% CI) 6.8 (4.5 to 12) points). Heart rate, mean arterial blood pressure, serum creatinine, and serum potassium did not change with either placebo or captopril. No patient was withdrawn directly due to the side effects of captopril. In an open phase nine placebo patients given captopril in rapid increments reaching 100 mg/day in the fourth week showed similar improvements. CONCLUSION--Captopril is efficacious in reducing functional mitral regurgitation in dilated heart failure. Patients require and must tolerate high doses (50-100 mg/day) for additive effects over supervised conventional treatment to occur.  相似文献   
56.
A comparison has been made of the in vitro light-activated drug cytotoxicities of two different porphyrin compounds, Photofrin II and TPPS4. An early passage human colon adenocarcinoma cell line, WiDr, has been exposed to either drug for 24 h, the excess drug washed from the cells and the cells irradiated with light using quartz-tungsten-halogen lamps. Neither light nor drug alone under the experimental conditions employed was toxic to WiDr cells. Together, considerable cytotoxicity could be seen and the shapes of the cell survival curves following exposure to either drug then irradiation with light, were similar. For equal amounts of drug in the medium, Photofrin II was a more efficient photosensitizer of WiDr cells than TPPS4, and differences in cellular uptake could only partly explain this. When the experimental procedure was changed by reducing the temperature of irradiation, a reduction in photosensitizing efficiency could be demonstrated. This was more pronounced for Photofrin II, and was seen as a change in the slope of the final portion of the survival curve; and as a change in the shoulder for TPPS4. Two different batches of the two drugs were compared and shown to give slightly different results for Photofrin II (change in shoulder) but not to differ for TPPS4.  相似文献   
57.
58.
pHo is an important determinant of vascular tone in cerebral blood vessels. We investigated the effects of changes in pHo on isolated smooth muscle cells from the basilar artery of the guinea pig. Single cells contracted rapidly in response to an elevation in pHo (constant CO2), and contraction was blocked by nifedipine, suggesting a role for dihydropyridine-sensitive Ca2+ channels. In whole-cell patch-clamp experiments, changes in pHo (pHo 5.7-8.1, pHi 7.2 with 10 mM HEPES) strongly affected the amplitude of the peak Ca2+ channel current (10 mM Ba2+, +15 mV, holding potential of -55 mV), with an apparent pK of 6.9. The current-voltage curves were minimally shifted, indicating no important effect of surface charge. To separate the slowly inactivating L-type Ca2+ channel current from the more rapidly inactivating B-type current, the decaying portions of inward currents from cells studied with repetitive 1-second pulses (+15 mV, holding potential of -55 mV) were fit to a two-component model. Titration curves for the L-type and B-type currents indicated maximum increases by factors of 3.65 and 1.28 at alkaline pHo and gave apparent pK values of 7.71 and 6.47 (Hill coefficient unity). The time constant of inactivation for the B-type current at +15 mV was little affected by pHo, whereas that for the L-type current increased somewhat with increasing pHo. Additional experiments showed no significant effect of pHo on holding current or on voltage-activated outward currents (pCai 7 with 11 mM EGTA). Our results provide additional evidence for participation of Ca2+ channels in regulating basal tone in cerebral smooth muscle and indicate that pHo regulates current through slowly inactivating, dihydropyridine-sensitive L-type Ca2+ channels.  相似文献   
59.
60.
OBJECTIVE: To examine response decrement of the recently reported inspiratory skin conductance response (SCR) [Lim CL, Seto-Poon M, Clouston PD, Morris JG. Sudomotor nerve conduction velocity and central processing time of the skin conductance response. Clin Neurophysiol 2003;114:2172-80]. METHODS: Twelve healthy adult volunteers performed 3 tasks (A) a control task of maintaining tidal breathing and then two randomized tasks, (B) a deep inspiration to a target oral pressure and (C) tapping with a finger. Each task was performed 30 times on cue every 20s in 3 runs with 5 min of rest between runs. The SCR, oral pressure, airflow, inspired volume and cue signal were recorded continuously and analysed offline. SCR amplitude was logarithmically transformed and then statistically analysed, using a linear mixed effects model, as a function of run number, trial number and absolute error between target and actual oral pressures. RESULTS: Inspiratory efforts elicited exponentially decreasing SCR amplitude with increasing trial number during each run (P < 0.0001). After adjusting for trial number, the mean SCR amplitude of the second and the third run were, respectively, 24.2 (95% CI (0.175, 0.336), P < 0.001) and 14.4% (95% CI (0.104, 0.200), P < 0.001) of the first run amplitude. CONCLUSIONS: Volitional deep inspiration reliably activates an SCR that exhibits response decrement with repetition, which may be habituation. SIGNIFICANCE: The volitional inspiratory SCR may assist in the assessment of sympathetic autonomic status in patients with peripheral afferent neuropathy.  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