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   176501篇
  免费   21497篇
  国内免费   2440篇
耳鼻咽喉   5434篇
儿科学   5708篇
妇产科学   2919篇
基础医学   4532篇
口腔科学   1755篇
临床医学   28177篇
内科学   50375篇
皮肤病学   7667篇
神经病学   16361篇
特种医学   6996篇
外国民族医学   2篇
外科学   42802篇
综合类   502篇
现状与发展   72篇
一般理论   14篇
预防医学   8613篇
眼科学   3711篇
药学   1989篇
中国医学   19篇
肿瘤学   12790篇
  2024年   794篇
  2023年   5153篇
  2022年   1557篇
  2021年   3318篇
  2020年   6154篇
  2019年   2404篇
  2018年   7638篇
  2017年   7518篇
  2016年   8640篇
  2015年   8635篇
  2014年   15802篇
  2013年   16091篇
  2012年   6192篇
  2011年   6238篇
  2010年   10733篇
  2009年   14570篇
  2008年   6433篇
  2007年   4780篇
  2006年   7260篇
  2005年   4559篇
  2004年   3770篇
  2003年   2700篇
  2002年   2719篇
  2001年   4123篇
  2000年   3364篇
  1999年   3561篇
  1998年   3813篇
  1997年   3605篇
  1996年   3487篇
  1995年   3311篇
  1994年   2040篇
  1993年   1670篇
  1992年   1615篇
  1991年   1641篇
  1990年   1294篇
  1989年   1378篇
  1988年   1207篇
  1987年   1037篇
  1986年   1094篇
  1985年   920篇
  1984年   696篇
  1983年   664篇
  1982年   618篇
  1981年   494篇
  1980年   440篇
  1979年   467篇
  1978年   438篇
  1977年   509篇
  1975年   385篇
  1972年   398篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Biliary tract obstruction in a 30-year-old man was found to be caused by a malignant melanoma in the common bile duct. Melanin pigment was demonstrated by immunohistochemistry and electron microscopy. Extensive search for a primary malignant melanoma elsewhere was unsuccessful. No pigmented lesions had been removed previously. There were junctional changes in the mucosa of the common bile duct close to the tumor. The malignant melanoma in the common bile duct therefore is considered to be primary. Only one other case of primary malignant melanoma in the common bile duct has been described in the literature, whereas metastases to the major bile ducts in one autopsy study of malignant melanoma in the more common locations were found with a frequency of 6 per cent.  相似文献   
992.
The presence of a significant organ dysfunction does not immediately exclude patients from consideration for treatment with a left ventricular assist system (LVAS). However, in treating morbid circulatory shock patients with multiple organ failure, it is important to know the preoperative and postoperative factor or factors related to the recovery of the damaged organ function. In this study, we retrospectively analyzed patients receiving a LVAS at our institution and tried to determine the important factors related to the survival of patients with multisystem failure. Twenty-seven patients who underwent LVAS placement at Saitama Medical School Hospital between 1993 and 2003 were included in this study. The preoperative risk factors analyzed were renal dysfunction, respiratory dysfunction, hepatic dysfunction, the existence of active infection, and the combination of all four factors. As a postoperative factor, the pump flow index (mean LVAS pump flow during the first 2 weeks after LVAS surgery divided by the body surface area) was analyzed. None of the analyzed preoperative factors could predict survival after LVAS surgery, but a pump flow index of less than 2.5 l/min/m2 had a significant relationship with death after LVAS surgery. Further analysis revealed that all the patients with a pump flow index of 3.0 l/min/m2 or more could overcome preoperative organ dysfunction. Congestive heart failure patients with multisystem failure need luxury pump flow for successful LVAS surgery; this factor could be especially important in device selection and postoperative management.  相似文献   
993.
Cicatricial conjunctivitis may be a sequel to systemic disorders (eg, Stevens-Johnson syndrome, cicatricial pemphigoid) or local disorders such as chemical burns. The cicatrisation is often associated with corneal epithelial changes that cause visual loss. These have been attributed to encroachment of the conjunctival epithelium over the cornea. However, the epithelial anomalies are poorly understood. We investigated the corneal epithelial changes in cicatricial conjunctivitis with an immunohistochemical study of intermediate filaments in normal and pathological specimens. Our results show that the normal corneal epithelium is immunoreactive for cytokeratin 3 (CK 3) but not cytokeratin 19 (CK 19), whereas normal conjunctival epithelium is CK 3 negative and CK 19 positive. Conjunctiva artificially transposed over the cornea (after therapeutic conjunctival flap reconstruction) retained the normal pattern of conjunctival cytokeratin expression (CK 3 negative, CK 19 positive). Conversely, the entire corneal epithelium exhibited the normal cytokeratin pattern (CK 3 positive, CK 19 negative) in 82% of Stevens-Johnson, 80% of cicatricial pemphigoid, and 69% of chemical burns specimens. The findings suggest that conjunctival encroachment is not responsible for the changes at the corneal surface in cicatricial conjunctivitis and that the abnormal corneal epithelium is derived from native corneal cells in these diseases.  相似文献   
994.
A previously validated small mammal trauma model, hind-limb ischemia secondary to infrarenal aortic ligation in the rat, was utilized to investigate the effects of traumatic injury on hepatic glucuronidation activity. As was previously observed with hepatic oxidative drug metabolism, model trauma resulted in a significant decrease in the in vivo glucuronidation of chloramphenicol, with a 23% drop in clearance of this drug. The effect on in vivo pharmacokinetics appeared to result from a complex interaction between trauma's differential influences on conjugating enzyme(s), deconjugating enzyme(s), and hepatic UDP-glucuronic acid levels, as well as the relative physiological importance of these variables. Hepatic UDP-glucuronyltransferase activities towards both p-nitrophenol and chloramphenicol were elevated (44-54%) after model injury when measured in native hepatic microsomes. However, microsomes which had been "activated" by treatment with Triton X-100 showed no significant difference between control and traumatized animals. Serum beta-glucuronidase activities were elevated by 58%, while hepatic beta-glucuronidase rose by about 16%. Nevertheless, in vivo deconjugation showed no significant change. Model trauma also resulted in a 46% decrease in hepatic UDP-glucuronic acid content. Thus, the observed post-traumatic depression of in vivo chloramphenicol glucuronidation could be due either to a diminished availability of a necessary cofactor (UDP-glucuronic acid) or to an alteration in enzyme kinetics or function in vivo.  相似文献   
995.
The effect of exogenous bile salts on plasma concentrations of secretin was studied by infusion of chenodeoxycholate, cholate, glycocholate, and taurocholate into the duodenum of normal subjects. The effect of endogenous bile on plasma secretin was studied by ingestion of a liquid test meal, by reinfusion of postprandial duodenal aspirates with known contents of bile salts, and by stimulation of gallbladder contraction by cholecystokinin. Each experiment was performed in groups of seven subjects. The relative secretin-releasing potencies of glycocholate, cholate, taurocholate and chenodeoxycholate (2.25 mmol) were 1.01.31.93.2. Hydrochloric acid (0.5 mmol) was, on a molar basis, approximately ten times more potent than sodium cholate. The effect of taurocholate was diminished when a liquid meal was used as vehicle instead of saline. Endogenous bile did, in no circumstance, elicit release of secretin. It is concluded that although bile salts have the ability to stimulate secretin release, endogenous secretin release is of minor, if any, importance for secretin release when physiological conditions are approached.This study was supported by grants from the Danish Hospital Foundation for Medical Research, Region of Copenhagen, The Faroe Islands and Greenland (J.nr. 78/45 and 79/48) and Borgen Legatet.  相似文献   
996.
At the Mayo Clinic, from 1970 through 1979, 84 patients (52 males and 32 females) had abdominal exploration for primary gastric lymphoma. All patients were observed a minimum of 5 years or until death. The histologic findings for all 84 patients were reviewed. Forty-four patients had "curative resection," and 40 patients had either biopsy alone or a palliative procedure. The probability of surviving 5 years was 75% for patients after potentially curative resection and 32% for patients after biopsy and palliation (p less than 0.001). The operative mortality rate was 5% overall and 2% after potentially curative resection. Increased tumor size (p less than 0.02), increased tumor penetration (p less than 0.01), and lymph node involvement (p less than 0.02) decreased the probability of survival, whereas histologic classification did not affect survival. Radiation therapy after surgery did not significantly affect the survival rate for the entire group or the survival rate for patients who had potentially curative resection. Resectability was associated with increased patient survival--independent of other prognostic factors--when our experience was analyzed by the Cox proportional-hazards model (p less than 0.005). It was concluded that an aggressive surgical attitude in the treatment of primary gastric lymphoma is warranted. The role of radiotherapy remains in question.  相似文献   
997.
Zusammenfassung Es wird anhand einer konsekutiven Serie über eine modifizierte fortlaufende Nahttechnik am Colon berichtet, die gerade bei älteren Patienten eine sichere und rasche Methode der Anastomosierung darstellt. Die klinisch relevante Insuffizienzrate sowie auch die Letalitätsrate betrugen in dieser Serie je 2%, wobei die Ursachen für die Letalität aber keine Folge der Insuffizienz waren. Die Komplikationsrate betrug 11%, die urologischen Komplikationen mit 6% standen hierbei im Vordergrund.
A consecutive series of 100 resections of the colon using a modified technique of continuous (running away) suture
Summary Based on a consecutive series it is reported about a modified type of continuous suture on the colon, used especially in elderly patients for being a secure and prompt method of anastomosing. The rate of insufficiency and mortality, as far as the clinical relevance is concerned, turns out to be 2% each and there was no relation between mortality and insufficient anastomosis. The complication rate was 11%, whereby the urological complications predominated with 6% of the total.
  相似文献   
998.
A fibronectin substrate will significantly enhance the strength of endothelial cell attachment on grafts constructed of polyester elastomer (PE) and polytetrafluoroethylene (e-PTFE). This experiment was undertaken to determine the short-termin vivo stability of endothellum on these fibronectin coated surfaces. Eight mongrel dogs underwent bilateral carotid artery replacement with both graft materlals. All grafts were inoculated with 2,000 cells/mm2 using cultured autogenous venous endothelium labelled with Indium-111-oxine. The Indium-111 label in the grafts was measured immediately prior to implantation, after 1 hour ofin vivo perfusion, and at explantation after 24 hours. The percentage of inoculated cells attached to the grafts before perfusion was simillar for both materials, 93.3±3.0% versus 92.2±7.2%, for PE and e-PTFE respectively. All grafts were patent at one hour after implantation. PE grafts were found to have 93.8±3.9 % of the attached cells present at one hour while e-PTFE grafts had only 54.5 ± 10.8 % remaining, p<.001. After 24 hours, 5/8 (62.5%) e-PTFE grafts and 2/8 (25.0 %) PE grafts remained patent, p=.13. Of the patent grafts however, endothelial cell retention was still superior on the PE grafts with 78.0±0.6% of the attached cells remaining compared to only 24.5±6.1% on e-PTFE, p<.001. Occluded PE grafts had fewer cells remaining at 24 hours than patent ones, 78.0±0.6% versus 31.1±32.8%, respectively, p=.13. Histologically, patent PE grafts demonstrated nearly confluent endothelial monolayers while e-PTFE had patches of endothelial cells surrounded by, a platelet-fibrin carpet. We conclude that short-term patency appears to be determined by the extent of endothelial retention on PE but not e-PTFE.  相似文献   
999.
One of the early diamond crimped knitted polyester (Dacron) grafts was surgically excised after implantation for 25 years in the aorto-billiac position because of false aneurysm formation at the three anastomotic sites. The sutures were no longer visible. While the areas around the false aneurysm were poorly incorporated, the graft limbs were well encapsulated with some endothelial-like cells on the luminal surface. The integrity of the graft was well preserved despite mild fraying and the disruption of one stitch.  相似文献   
1000.
From July 1979 to December 1985 we observed 51 patients with traumatic lesions of the descending thoracic aorta. Twenty-nine had acute ruptures, mostly accompanied by multiple injuries, and 27 had to be operated upon immediately. Twenty-two patients (19 males, 3 females) had chronic traumatic aneurysms of the descending thoracic aorta (more than six weeks after trauma). Mean age at the time of trauma was 24 years. Mean age at time of surgery was 36.5 years. Twelve patients were symptomatic. All were treated surgically. At surgery, complete aortic disruption was found in 15 patients and partial rupture in seven. We did not use aortic shunting of any kind, only aortic cross-clamping. Hypertension was controlled by intravenous drug infusion. The ruptured aortic segment was replaced in all cases by prosthetic Dacron graft. There were no operative deaths. One patient (age 77) died 11 weeks after surgery from multiple organ failure. One case of postoperative paraplegia was observed. This patient recovered almost completely from his neurological deficit.  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