首页 | 官方网站   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   27548篇
  免费   1601篇
  国内免费   256篇
医药卫生   29405篇
  2024年   24篇
  2023年   271篇
  2022年   233篇
  2021年   1018篇
  2020年   585篇
  2019年   837篇
  2018年   1000篇
  2017年   727篇
  2016年   880篇
  2015年   898篇
  2014年   1218篇
  2013年   1497篇
  2012年   2281篇
  2011年   2164篇
  2010年   1251篇
  2009年   1201篇
  2008年   1873篇
  2007年   1815篇
  2006年   1706篇
  2005年   1693篇
  2004年   1591篇
  2003年   1360篇
  2002年   1225篇
  2001年   127篇
  2000年   124篇
  1999年   169篇
  1998年   208篇
  1997年   166篇
  1996年   156篇
  1995年   151篇
  1994年   123篇
  1993年   115篇
  1992年   86篇
  1991年   54篇
  1990年   63篇
  1989年   45篇
  1988年   40篇
  1987年   34篇
  1986年   42篇
  1985年   36篇
  1984年   34篇
  1983年   32篇
  1982年   47篇
  1981年   28篇
  1980年   27篇
  1979年   17篇
  1978年   16篇
  1976年   11篇
  1975年   8篇
  1974年   11篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
OBJECTIVE: It is not well established whether the blood flow of arterial composite Y-grafts can efficiently respond to the flow demand of the coronary system early postoperatively. The aim of this study was to evaluate if soon after the operation, arterial composite Y-grafts can increase blood flow in response to an increase in myocardial oxygen consumption (MVO2). METHODS: Twenty-seven patients who received complete arterial myocardial revascularization using the left internal thoracic artery (LITA) and the radial artery (RA) as composite Y-graft gave their consent to a pre-discharge coronary angiography and intravascular flow velocity measurements using a Doppler guide wire. Flow measurements were performed in the LITA main stem, the distal LITA and the RA, both at rest and during atrial pacing at the 85% of the patient age-predicted maximum. The heart rate-systolic blood pressure product was considered as an indirect index of MVO2. Hyperemic flow was determined after injection of adenosine. The flow reserve (FR) was defined as the ratio of blood flow during maximal hyperemia (Qmax) to baseline flow (Qbasal). RESULTS: Atrial pacing increased MVO2 significantly (P<0.000). None of the patients developed ischemic S-T segment modifications or complained of chest pain. Q(basal) increased significantly in the LITA main stem (P=0.001), distal LITA (P=0.041) and RA (P=0.004) while Qmax did not change significantly. As a consequence, the FR decreased in the LITA main stem (P=0.002), distal LITA (P<0.000) and RA (P<0.000) but was not completely exhausted. CONCLUSIONS: Soon after the operation, arterial composite Y-grafts can significantly increase blood flow in response to conditions of increased MVO2, keeping normal the myocardial O2 supply-to-demand ratio.  相似文献   
62.
Much research has shown that cognitive processes are largely guided by individuals' states of mind (Mancini & Gangemi, 2002a, in press; Smeets, de Jong, & Mayer, 2000). In this paper, we specifically consider a state of mind characterized by guilt for having acted irresponsibly. This state is currently considered the breeding ground for the obsessive–compulsive disorder (Rachman, 2002; Salkovskis & Forrester, 2002). Our aim is to examine the impact of this state of mind on decision under risk. We hypothesize that individuals' choices (risk seeking/risk aversion) depend on how they evaluate themselves, as guilty or as victims of a wrong, and thus on moral values. People who evaluate them‐selves as guilty are expected to show a risk‐averse preference. People who evaluate themselves as victims are expected to show a risk‐seeking preference. In two different experiments, we demonstrated that non‐clinical participants' aversion to risky choices and preference for risky choices vary as a function of their moral role (guilty/victim). As predicted, in both the experiments, participants experienced intolerance for risk, making more riskless choices, in the context of guilt. Thus, aversion to risk‐taking is actually affected by a mental state of guilt. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
63.
Cancer cells elaborate metalloproteinases which may play a role in invasion and metastasis. The serum level of the M(r) 72,000 type IV collagenase (MMP-2) was measured in 87 lung cancer patients. Stage IV cancer levels were significantly elevated (P less than 0.0001) compared to normal sera. A significant difference (P less than 0.01) was found between enzyme levels in the presence versus the absence of distant metastasis. For 29 patients treated with combination chemotherapy, a positive relationship was noted between response failure and elevated enzyme levels. Serum metalloproteinase levels may provide information relevant to prognosis as well as treatment decisions.  相似文献   
64.
BACKGROUND: Sodium removal (NaR) may have a major impact on the survival of peritoneal dialysis patients. The dialysate/plasma sodium concentration ratio (D/P(Na)) is an indirect index of transcellular water transport by aquaporin channels, and thus of ultrafiltration. Sodium concentration can be assessed by means of flame photometry (F), and direct (D-ISE) or indirect ion-selective electrodes (I-ISE), but these methods have different properties. I-ISE is being used increasingly in clinical laboratories. The aim of this study was to evaluate NaR and D/P(Na) using the three different measurement methods. METHODS: We performed peritoneal equilibration tests (PETs) in 44 peritoneal dialysis patients and calculated the NaR. We also calculated D/P(Na) during the test; plasma and dialysate sodium concentrations were measured by F, D-ISE and I-ISE. RESULTS: NaR was lower (P<0.001) with D-ISE (69+/-29 mmol) than with F (81+/-29 mmol) or I-ISE (79+/-28 mmol). D/P(Na) was also lower at baseline (0.92+/-0.02 vs 0.95+/-0.02 and 0.95+/-0.02; P<0.001), after 60 min (0.87+/-0.03 vs 0.90+/-0.03 and 0.90+/-0.03; P<0.001) and at the end of PET (0.88+/-0.04 vs 0.92+/-0.04 and 0.92+/-0.04; P<0.001) when measured by D-ISE in comparison with F and I-ISE, respectively. CONCLUSIONS: NaR and D/P(Na) were lower when measured by the D-ISE method compared with the F and I-ISE methods. NaR and D/P(Na) were similar when measured by F or I-ISE. I-ISE can be used reliably in the evaluation of NaR and D/P(Na) in everyday clinical practice of peritoneal dialysis.  相似文献   
65.
66.
Schistosoma mansoni infection, both in humans and in animal models, is known to induce granulomas in the liver and intestine. It has also been reported that in humans the eggs of this parasite can reach the brain, causing psychiatric and neuropathological disorders. Whether this also occurs in rodents is unknown. To answer this question, mice were infected with this parasite and the central nervous system (CNS) examined at various time intervals. The results show that schistosomiasis induced granulomas in several regions of the CNS and increased nerve growth factor (NGF) levels in the cortex, hypothalamus and brain stem, but not in the hippocampus. The infection also caused paw hyperalgesia, as determined by the hot-plate test, and a local increase in NGF, but not in substance P. These findings indicate that the murine model of infection can be used for studying mechanisms leading to human neuroschistosomiasis and suggest that the neuropathological disorders and the sensory deficits observed in human schistosomiasis are associated with impaired levels of NGF in the peripheral and central nervous system. Received: 18 January 1996 / Revised, accepted: 16 April 1996  相似文献   
67.
Risk of death from acute pancreatitis   总被引:5,自引:0,他引:5  
Summary Conclusions The analysis of all the data available in 192 patients at 24 h from admission shows that only serum glucose above 250 mg/dL (13.88 mmol/L) and serum creatinine above 2 mg/dL (176.8 μmol/L) are prognostic factors of death (P<0.0001). When, however, pathological chest X-rays are also considered in a subset of 149 patients, these and serum creatinine are prognostic factors of death with odds ratios of 2.9 (95% CL 1.3–6.3) and 9.4 (95% CL 2.2–40.7), respectively (P<0.0001). Background In patients suffering from acute pancreatitis, neither Ranson scores nor Glasgow criteria evaluation at 24 h yield a sufficiently reliable prognosis of the risk of death from the first acute attack. Methods After excluding posttraumatic, postsurgical, and post-ERCP acute pancreatitis, we selected 192 consecutive patients admitted in the first instance to our center for a first attack, distinguishing between patients who died and patients who survived. We used Cox's model to analyze the prognostic weight of variables available within 24 h of admission (sex, age, alcohol intake, smoking habits, 17 biochemical tests, body mass index, chest X-rays, body temperature, and shock status). Results Seventeen (8.8%) patients died; mortality showed a decreasing trend over the period of years considered and was correlated, among other things, with necrotizing type of pancreatitis, idiopathic etiology, and shock status on admission.  相似文献   
68.
This study was performed to investigate the relative role of noradrenaline (NA) and dopamine (DA) carrier blockade in the effects of psychostimulants on DA transmission in the rat prefrontal cortex (PFCX). To this end, changes of extracellular DA and NA in the PFCX and of extracellular DA in the nucleus accumbens (NAc) were measured following the administration of amphetamine and cocaine, which are known to bind to both DA and NA carriers, or GBR 12909, a selective DA carrier blocker. After non-intravenous injection, amphetamine (0.25 and 0.5 mg/kg, s.c.) and cocaine (5 and 10 mg/kg, i.p.) increased extracellular DA in the PFCX to a larger extent than in the NAc, while the reverse applied to GBR 12909 (2.5 and 5 mg/kg, i.p.). These differences were obtained in spite of the fact that the three drugs elicited at each dose level a similar peak increase of extracellular DA in the NAc. Amphetamine and cocaine also increased extracellular NA in the PFCX and this effect was quantitatively similar to that on extracellular DA in the same area. Intravenous doses of cocaine and GBR 12909, corresponding to those which maintain self-administration in the rat, while equieffective in raising extracellular DA in the NAG, had different effects on extracellular DA in the PFCX. In fact, in contrast to cocaine, GBR 12909 increased extracellular DA in the PFCX to a lesser extent than in the NAc or did not modify it at all. The peak increase of extracellular DA in the PFCX was highly correlated to that of NA in the same area but was poorly correlated to the increase of extracellular DA in the NAc. These results suggest that amphetamine and cocaine increase extracellular DA in the PFCX largely through the blockade of the NA carrier. Direct evidence for this hypothesis was provided by the observation that, when the NA carrier was blocked by reverse dialysis of the PFCX with desipramine (1 μM), cocaine and GBR 12909 lost their differences in the ability to increase extracellular DA in the PFCX.  相似文献   
69.
Purpose The goal of the study is to evaluate utility of contrast enhanced ultrasound (US) with carbon dioxide microbubbles in evaluation of hepatic lesions.Methods Twenty eight patients with single or multiple t hepatic lesions (11 hepatocellular carcinoma, 8 hemangiomas, 5 metastases, 1 adenoma, 1 focal nodular hyperplasia, 2 regenerative nodules) were examined. US exam was performed during intraarterial injection of 10 ml of CO2 through the same catheter employed for liver arteriography. The US exam was videotaped in its salient phases. Characteristics of enhancement were evaluated and correlated with histological findings or patient follow up.Results Sonographic angiography clearly demonstrated vascularization of the lesions. Hepatocellular carcinoma, hemangioma, metastases, focal nodular hyperplasia, and regenerative nodules had very characteristic patterns. The injection of CO2 allowed detection of small additional nodules.Conclusion Sonographic angiography can improve characterization and staging of hepatic tumors. Low cost and the simplicity of the technique should encourage further experimentation.  相似文献   
70.
OBJECTIVE: The aim of this paper was to describe our surgical technique for the treatment of nasal septal perforations. STUDY AND DESIGN: We studied 31 patients with nasal septal perforation treated with an endoscope-assisted technique, based on a bilateral dissection of monopedicled mucosal flaps from the nasal fossa floor, sutured at the edge of the perforation previously unstuck, without any graft interposed between the two mucosal layers. RESULTS: In our experience with 31 patients, the use of this technique led to the persistent closing (with follow-up for at least one year) of 96.3% of the perforations smaller than 3 cm. CONCLUSIONS: Our technique has the advantage of an endonasal approach, without any external incision, and the use of monopedicled flaps from the nasal fossa floor without any graft interposition, avoiding any other surgical procedure and morbidity in the donor site of the graft. The use of nasal endoscopy permits superior precision in all surgical steps. SIGNIFICANCE: The high success rate in perforations smaller than 3 cm seems to confirm the effectiveness of this technique.  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-23

京公网安备 11010802026262号