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   24906篇
  免费   1267篇
  国内免费   216篇
耳鼻咽喉   291篇
儿科学   576篇
妇产科学   314篇
基础医学   3172篇
口腔科学   337篇
临床医学   1531篇
内科学   7078篇
皮肤病学   456篇
神经病学   1989篇
特种医学   1079篇
外科学   4084篇
综合类   99篇
一般理论   1篇
预防医学   556篇
眼科学   447篇
药学   1397篇
中国医学   37篇
肿瘤学   2945篇
  2023年   164篇
  2022年   299篇
  2021年   659篇
  2020年   342篇
  2019年   428篇
  2018年   624篇
  2017年   479篇
  2016年   552篇
  2015年   596篇
  2014年   727篇
  2013年   920篇
  2012年   1449篇
  2011年   1686篇
  2010年   1004篇
  2009年   895篇
  2008年   1504篇
  2007年   1590篇
  2006年   1571篇
  2005年   1589篇
  2004年   1581篇
  2003年   1416篇
  2002年   1417篇
  2001年   374篇
  2000年   314篇
  1999年   362篇
  1998年   318篇
  1997年   259篇
  1996年   205篇
  1995年   192篇
  1994年   181篇
  1993年   168篇
  1992年   233篇
  1991年   219篇
  1990年   201篇
  1989年   208篇
  1988年   185篇
  1987年   168篇
  1986年   160篇
  1985年   145篇
  1984年   111篇
  1983年   108篇
  1982年   57篇
  1981年   76篇
  1980年   50篇
  1979年   58篇
  1978年   52篇
  1977年   49篇
  1975年   41篇
  1970年   38篇
  1969年   49篇
排序方式: 共有10000条查询结果,搜索用时 953 毫秒
51.
OBJECTIVES: To evaluate the accuracy of sonographic identification of the site of umbilical cord insertion (CI) at 18-20 weeks of gestation, to compare the sensitivities for detection of a velamentous cord insertion (VCI) secondary to a CI into the anterior, posterior or fundal wall, and to compare the intrapartum complications secondary to VCI into the upper, middle or lower third of the uterus. METHODS: As part of the routine ultrasound scan at 18-20 weeks' gestation we evaluated abnormal CI (VCI and marginal CI) and the location of the CI in the uterus in 3446 pregnancies. In cases of abnormal CI, the location of the CI was further classified as being in the upper, middle or lower third of the uterus. After delivery, the placenta and the umbilical cord were examined and intrapartum complications were compared with the location of the CI. RESULTS: The values for antenatal detection of VCI were: sensitivity, 25 of 40 (62.5%); positive predictive value, 25 of 25 (100%); and negative predictive value, 3406 of 3421 (99.6%). The sensitivity for cases in which the CI was located on the anterior wall was 12 of 13 (92.3%); when it was located on the posterior wall, the sensitivity was 11 of 22 (50.0%); and when it was fundal the sensitivity was 2 of 5 (40.0%). Variable decelerations were frequently observed with a VCI. In lower VCI cases, non-reassuring fetal heart rate patterns and emergency Cesarean sections occurred with a higher frequency than in cases with upper or middle VCI (P < 0.01). After delivery, the length of the aberrant vessels in cases of VCI by pathologic examination was 3.9 +/- 3.3 cm in the upper third, 4.7 +/- 4.6 cm in the middle third, and 10.6 +/- 6.8 cm in the lower third; thus, the aberrant vessel length was significantly greater when the CI was in the lower third of the uterus (P = 0.024). CONCLUSION: We have demonstrated that VCI with a lower CI site and with longer aberrant vessels is associated with various intrapartum complications. This finding has the potential for improving perinatal outcome.  相似文献   
52.
The effects of region of interest (ROI) selection and correction for Compton-scattered photons using a buildup factor on radionuclide left ventricular volumes calculated by the Links method were compared in 19 humans with contrast ventriculography and in phantoms. Three different methods of ROI selection were compared: a manual ROI, a second derivative ROI and a 50% count-threshold ROI. In phantoms without Compton scatter correction, volumes were overestimated by 30% (manual ROI), 20% (derivative ROI) and 1% (count threshold ROI). In subjects, results without Compton scatter correction were similar with overestimates of 50% (manual ROI) and 20% (derivative ROI) and an underestimate by 3% (count threshold method). Correction for Compton-scattered photons with the use of a phantom-derived buildup factor resulted in improved accuracy for the manual ROI (+15%) and the derivative ROI (0%). A 50% count threshold ROI following interpolative background subtraction allows the accurate calculation of cardiac volumes without the need for scatter correction, while a second derivative ROI method requires a correction for Compton scatter with the use of a buildup factor.  相似文献   
53.
We reported a case of photoleukomelanodermatitis (Kobori) type drug eruption due to afloqualone (Arofuto®). The patient was given afloqualone and imipramine hydrochloride (Chrytemin®) for cervical spondylosis from November of 1990. Edematous erythema with slight itching appeared on the sun-exposed areas in December of 1990. As drug eruption was suspected, drugs were ceased, and the cutaneous lesions almost disappeared but pigmentations and depigmentations developed in spots in sun-exposed areas in March of 1991. Photopatch and oral challenge tests were positive.  相似文献   
54.
We reported an autopsy case of a 14-year-old girl with cardiac myxoma, presenting sudden onset of consciousness disturbance and right hemiplegia while running in an 800 meter race. Though CT scan showed no abnormal findings, cerebral angiogram revealed an embolic stenosis of the left middle cerebral artery, and abdominal aortogram showed complete obstruction of the bilateral common iliac artery. Histological study of emboli taken from obstructed femoral arteries showed systemic embolization of the cardiac myxoma. She died three days after admission. Autopsy was performed. Myxoma tissue was not found, but its stalk was left in the left atrial septum. The brain was very edematous, and a myxoma emboli was found in the left middle cerebral artery. Systemic embolization of myxoma to spleen, kidneys, liver, pancreas, etc. was found histologically. Left atrial myxoma is a rare but potentially treatable cause of stroke, and should be included in the differential diagnosis of cerebral vascular disease, especially in young patients.  相似文献   
55.
56.
To determine the prognostic factors for patients with pathological T1 (pT1) carcinoma of the ampulla of Vater, 36 consecutive patients with carcinoma of the ampulla of Vater who underwent surgery were retrospectively analyzed in terms of clinicopathological features. The overall 5-year Kaplan-Meier survival in all patients was 50.2%, and the median survival of all patients was 64.0 months. Factors favorably influencing a long-term outcome were the absence of lymph node metastasis (P<0.0001), the absence of ulcer formation of the tumor (P=0.0062), and the absence of tumor invasion into the duodenum (P = 0.0025) and the pancreas (P=0.0098). In a multivariate analysis, lymph node metastasis was the only predictor of survival (P=0.0023). In the pT1 stage patients, 20% of the patients had lymph node metastasis, and their survival was statistically poor compared to the pT1 patients without lymph node metastasis (P=0.017). As for survival after the operation, there was no significant difference between pancreatoduodenectomy and pylorus-preserving pancreatoduodenectomy.  相似文献   
57.
A 69-year-old man was admitted to hospital because of sustainedventricular tachycardia with right bundle branch block morphology.After abolition of ventricular tachycardia, an electrocardiogramshowed atrial fibrillation, complete right bundle  相似文献   
58.
Referenceless, or self-reference, thermometry is a technique for mapping temperature differences in the region of interest (ROI) using the baseline phase estimated by extrapolating the field in the surrounding region for estimation (RFE) and subtracting the estimated baseline from the measured field. In the present work a self-reference technique based on complex field estimation using 2D polynomials comprising complex-valued coefficients was proposed and optimized. Numerical simulations with a Gaussian-profiled phase distribution demonstrated that the ROI radius had to be 2.3-2.5 times the standard deviation (SD) of the Gaussian function in order to keep the error below 8% of the peak phase change. The area ratio between the ROI and the RFE had to be larger than 2.0 to maintain the error level. Based on the simulations, and phantom and volunteer experiments, the complex-based method with independently optimized polynomial orders for the two spatial dimensions was compared with the phase-based method using the similar-order optimization strategy. The complex-based method appeared to be useful when phase unwrapping was not removed. Otherwise, the phase-based method yielded equivalent results with less polynomial orders.  相似文献   
59.
We report a case of aspergilloma in an 80-year-old male patient who had no identifiable underlying disease before surgery for pneumothorax. He was hospitalized for left pneumothorax. A chest CT revealed a large bulla in the left lung apex with a nodule (diameter; 1.5 cm) at the edge of the bulla. After thoracodocesis, air leakage persisted and a large bulla and nodule were resected. Aspergillus was detected histopathologically in the nodule. Treatment with itraconazole 200 mg a day followed, and 4 months later he had no recurrent pneumothorax or Aspergillus infection.  相似文献   
60.
The diuretic and the antihypertensive actions of torasemide were examined in renal and genetic hypertensive rats and compared to the effects of furosemide. Oral administration of torasemide (1 and 3 mg/kg) elicited a dose-dependent increase in the excretion of urine and electrolytes and elevated the urinary Na/K ratio in both renal and genetic hypertensive rats. Torasemide and furosemide had a similar maximum diuretic effect in the normotensive Wistar rat and the spontaneously hypertensive rat (SHR). However, the diuretic activity of furosemide was weaker in the renal hypertensive rat (RHR). Torasemide showed approximately 30 times greater diuretic potency than furosemide. Torasemide and furosemide demonstrated hypotensive action in hypertensive rat models, but not in the normotensive Wistar rat. Especially in the RHR, torasemide exhibited a more potent hypotensive action than furosemide. These results show that the diuretic and antihypertensive activities of torasemide are effective in various rat models of hypertension, while the diuretic activity of furosemide is weak in certain hypertensive rat models. © 1992 Wiley-Liss, 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