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   41183篇
  免费   2331篇
  国内免费   70篇
医药卫生   43584篇
  2023年   218篇
  2022年   182篇
  2021年   630篇
  2020年   376篇
  2019年   671篇
  2018年   1147篇
  2017年   823篇
  2016年   794篇
  2015年   979篇
  2014年   1023篇
  2013年   1604篇
  2012年   2748篇
  2011年   2682篇
  2010年   1331篇
  2009年   1113篇
  2008年   2454篇
  2007年   2536篇
  2006年   2391篇
  2005年   2457篇
  2004年   2374篇
  2003年   2180篇
  2002年   2125篇
  2001年   1167篇
  2000年   1226篇
  1999年   966篇
  1998年   261篇
  1997年   189篇
  1996年   187篇
  1995年   195篇
  1994年   145篇
  1993年   146篇
  1992年   553篇
  1991年   499篇
  1990年   494篇
  1989年   462篇
  1988年   423篇
  1987年   406篇
  1986年   385篇
  1985年   367篇
  1984年   251篇
  1983年   211篇
  1982年   121篇
  1979年   178篇
  1974年   136篇
  1973年   122篇
  1972年   119篇
  1971年   126篇
  1970年   113篇
  1969年   138篇
  1968年   117篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Hypercalcaemia and pancreatic ultrastructure in cats.   总被引:3,自引:0,他引:3  
OBJECTIVE--To study the effects of local and systemic infusions of calcium on the ultrastructure of the pancreas in cats. DESIGN--Controlled study. INTERVENTIONS--Three groups of four cats each had local infusions (into the splenic artery) of calcium gluconate 0.6 mmol/kg.hour or potassium chloride 1.1 mmol/kg.hour, or sodium chloride 0.9%, for three hours. Two groups of eight cats each had systemic infusions (into the jugular vein) of either calcium gluconate 0.6 mmol/kg.hour or sodium chloride 0.9%, for twelve hours. In the group that was given calcium, the infusion rate was reduced after three hours to 0.3 mmol/kg.hour to maintain the hypercalcaemic state for a further nine hours. RESULTS--Local infusion of calcium caused destruction of acinar cells with hydropic degeneration of nuclei, discharge of cell organelles into the interstitial spaces, and extravasation of red blood cells but no apparent damage to the capillaries. There were no ultrastructural changes of any importance in the groups that received potassium or sodium chloride. Systemic infusion of calcium resulted in a 1.8 fold increase in the ionised calcium concentration in the serum, progressive signs of overstimulation of the Golgi apparatus with hypertrophy, fusion of condensing vacuoles, and disruption of the acinar cell polarization. This was followed by clumping of nuclear chromatin and destruction of acinar cells. CONCLUSION--Acute pancreatitis in cats can result from stimulation and destruction of acinar cells by hypercalcaemia.  相似文献   
92.
Pleural mesotheliomas are rare, and their diagnosis and treatment not clear. The case observed in our Department leads us to an analysis of the literature. This showed that differential diagnosis with pulmonary carcinoma is very difficult, even in cases of parietal mesothelioma; however local treatment may be performed even in malignant mesothelioma.  相似文献   
93.
Sera from BDIX rats inoculated with 2 tumor clones derived from a single syngeneic colon carcinoma were assayed by Western blotting for the presence of antibodies against the grafted tumor. The PROb clone is progressive and produces metastases. We observed that rats bearing this tumor developed antibodies against an unglycosylated water-soluble protein of 105 kDa. The magnitude of this humoral response, as assessed by the intensity of the signal on immunoblots, was inversely correlated with survival of the rats. Furthermore, rats inoculated with the REGb clone, which is immunologically rejected, never developed detectable antibodies against the tumor. Antisera from rats injected with PROb tumor detected p105 antigen in cellular extracts from the REGb clone and from a series of rat and human cell lines. This protein was also detected in variable amounts in some normal adult and fetal tissues. Treatment of PROb or REGb cells by either interferon-gamma or heat shock did not significantly alter the expression of the p105 auto-antigen.  相似文献   
94.
We investigated the effect of sex hormones on the sex-dependent response of rat kidney ornithine decarboxylase (ODC) activity to cadmium (Cd) administration and the involvement of the renin-angiotensin system in mediating stimulation of the liver enzyme by the metal. The response of renal ODC to Cd, which occurs in intact adult males but not in females, is also detectable in prepubertal and castrated males. Upon treatment with 17 beta-estradiol, the basal levels of enzyme activity in intact or castrated adult males were enhanced and Cd administration failed to increase them further. In adult females the kidney enzyme became responsive after ovariectomy. Also, in prepubertal females renal ODC was induced by Cd, and this was prevented by treatment with 17 beta-estradiol. Under the same conditions, changes in the levels of Cd accumulation within the kidney, that might account for variations in the response of ODC activity, did not occur. Cd caused an increase in renin activity starting minutes after its injection. Captopril, which specifically inhibits the conversion of angiotensin I to angiotensin II, prevented completely the induction of liver ODC by this metal; stimulation of the enzyme by Co was not affected by the drug. A similar inhibitory effect was exerted by propranolol. Adrenalectomy had no influence on the response of hepatic ODC to Cd; the decarboxylase was unaffected by aldosterone administration. It is suggested that Cd may induce liver ODC through the increase in angiotensin II following stimulation of renin by the metal.  相似文献   
95.
Background: Percutaneous coronary intervention (PCI) is performed in patients with coronary artery disease who are undergoing major noncardiac procedures to reduce perioperative cardiac morbidity and mortality. However, the impact of this approach on postoperative outcome remains controversial.

Methods: The authors analyzed a cohort of 1,152 patients after abdominal aortic surgery in which 78 patients underwent PCI. A propensity score analysis was performed. Also, using a logistic regression model, the authors determined variables associated with a severe postoperative coronary event or a death in patients without PCI. Then, in patients with PCI, they compared the expected and observed outcome.

Results: Five variables (age > 75 yr, blood transfusion > 3 units, repeated surgery, preoperative hemodialysis, and previous cardiac failure) independently predicted (with 94% correctly classified) a severe postoperative coronary event, and five variables (age > 75 yr, repeated surgery, previously abnormal ST segment/T waves, previous hypertension, and previous cardiac failure) independently predicted (with 97% correctly classified) postoperative death. In the PCI group, the observed percentages of patients with a severe postoperative coronary event (9.0% [95% confidence interval, 4.4-17.4]) or death (5.1% [95% confidence interval, 2.0-12.5]) were not significantly different from the expected percentages (8.2 and 6.9%, respectively). When all patients were pooled together, the odds ratios of PCI were not significant. The propensity score analysis provided a similar conclusion.  相似文献   

96.
A number of studies have shown that ultrasound has an advantage over physical examination in the diagnosis of acute appendicitis. Most of these studies were conducted by experts in the field of ultrasonography. In this study the influence of experience on the results of the sonography of actue appendicitis were evaluated. All 203 patients admitted to our unit between December 1990 and December 1992 were examined physically and sonographically by a team of surgeons consisting of one experienced sonographer and six inexperienced surgical trainees. Laparotomy was performed in 136 patients (46%). Appendicitis was demonstrated histologically in 119 cases (39.4%). Initial clinical findings were positive in 87 (28.8%). Sonography was positive in 119 patients (39.4%). The 163 patients not operated on demonstrated other pathology on ultrasound in 60 cases (19.9%). The rate of negative laparotomies amounted to 7.2% in our study. Sensitivity and specificity for the sonographic diagnosis were 92% and 95%, respectively. They were only 81% and 80% for physical examination. Overall accuracy was 92% for sonography. Sensitivity and specificity for the inexperienced surgeons were 87% and 93%, respectively, while the experienced surgeon reached values of 97% and 98%, respectively. The results of both groups are comparable with values in the literature, suggesting that ultrasound evaluation of appendicitis is not a diagnostic tool limited to a few experienced sonographers.  相似文献   
97.
98.
This study analysed the possibilities of returning to work of professional drivers after a cardiac event and rehabilitation. The population comprised 94 consecutive patients, all men, average age 48.8 years (range 30 to 63 years) referred after coronary bypass surgery (N = 39), myocardial infarction (N = 38), angina (N = 4) or valve replacement surgery (N = 13). Advice on professional reinsertion was given after the rehabilitation program, authorization to drive being given in the absence of cardiac symptoms, residual myocardial ischaemia, severe left ventricular dysfunction and serious ventricular arrhythmias. After 35 months, 4 patients were lost to follow-up; of the 90 remaining patients, the frequency of return to work (maximal at the 9th month) was 65.6% with 84.7% obtaining a renewal of their driving licence. In this series, 81% of patients were asymptomatic, 2 died, 16.7% had further cardiovascular complications. The morbidity and mortality were significantly greater in the group who had to stop driving (N = 40) (32.5% vs 8%, p < 0.001). Non complications occurred during work in those who resumed driving. This study confirms the safety of allowing low risk professional drivers, identified during cardiac rehabilitation by simple, reliable clinical and paraclinical criteria, to return to work.  相似文献   
99.
The highly sensitive and specific methods of molecular biology emphasize the frequency of subclinical infections in the genital tract tissues by the human papillomaviruses (HPVs). The purpose of this work was to investigate occult viral infections by the HPV type 6, 11, 16, and 18 in the gingival tissues. The Southern blot method with 32P-radiolabeled DNA probes applied under stringent conditions to 20 interproximal gingival papilla specimens revealed homologous viral sequences in 1 of 6 cases of adult periodontitis (HPV 16), 1 of 2 cases of rapidly progressive periodontitis (RPP) (HPV 6/HPV 11), 2 of 2 cases of acute gingivitis in psychiatric institutionalized patients (HPV 6; HPV 6/HPV 11), and 2 of 10 cases of acute gingivitis in AIDS patients (HPV 6/HPV 11/HPV 16; HPV 6). No periodontal or extra-periodontal specimen hybridized with the HPV 18 probe. Simultaneous hybridization with two or three HPV types was common (3/6 cases). The present detection of HPV 6, 11, 16 DNAs or related-DNAs in periodontal tissues without obvious clinical signs of viral infection suggests that the gingival epithelium may act as a reservoir.  相似文献   
100.
CASE REPORT: A pregnant woman who was a regular user of anxiolytics was admitted to the maternity ward at 38 weeks and 4 days amenorrhea after a massive overdose of clorazepate dipotassium, a benzodiazepine. The exact quantity ingested was undetermined. The infant, born at 39 weeks, presented no spontaneous breathing and tracheal intubation was necessary in the delivery room. The neonatal blood concentrations of the clorazepate metabolites were very high at delivery (26 mg/l nordiazepam and 3.5 mg/l oxazepam) and showed little change over the next 5 days (16 mg/l nordiazepam and 2.1 mg/l oxazepam, with an apparent half-life of 168 h for nordiazepam and 160 h for oxazepam). By day 6, the infant was still dependent on ventilator support and enterodialysis was begun with repeated doses of activated charcoal (1 g/kg every 6 h by gastric tube). Treatment was continued for 5 days and a spectacular diminution in the serum concentrations of the two metabolites was noted on day 11: 1.5 mg/l nordiazepam and less than 0.1 mg/l oxazepam. The nordiazepam and oxazepam half-lifes were reduced to 42 h and 30 h respectively. The concomitant clinical improvement authorized the weaning from ventilation on day 12. CONCLUSION: This is the first report of the use of enterodialysis to treat severe benzodiazepine poisoning in a neonate. Depuration of the toxin was accelerated and the duration of intensive care was shortened thanks to 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