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:      
  示例: 沙坡头地区,人工植被区,变化  检索词用空格隔开表示必须包含全部检索词,用“,”隔开表示只需满足任一检索词即可!
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   174169篇
  免费   6703篇
  国内免费   2368篇
耳鼻咽喉   5222篇
儿科学   5330篇
妇产科学   2367篇
基础医学   2876篇
口腔科学   1459篇
临床医学   26497篇
内科学   47287篇
皮肤病学   7398篇
神经病学   14838篇
特种医学   6300篇
外科学   40687篇
综合类   226篇
现状与发展   72篇
预防医学   6916篇
眼科学   3316篇
药学   849篇
中国医学   6篇
肿瘤学   11594篇
  2024年   748篇
  2023年   5083篇
  2022年   1443篇
  2021年   3073篇
  2020年   5999篇
  2019年   2123篇
  2018年   7371篇
  2017年   7298篇
  2016年   8378篇
  2015年   8356篇
  2014年   15421篇
  2013年   15525篇
  2012年   5325篇
  2011年   5320篇
  2010年   10263篇
  2009年   14165篇
  2008年   5653篇
  2007年   3881篇
  2006年   6354篇
  2005年   3641篇
  2004年   2913篇
  2003年   1895篇
  2002年   1984篇
  2001年   3769篇
  2000年   2983篇
  1999年   3187篇
  1998年   3628篇
  1997年   3448篇
  1996年   3349篇
  1995年   3200篇
  1994年   1928篇
  1993年   1555篇
  1992年   1367篇
  1991年   1398篇
  1990年   1048篇
  1989年   1182篇
  1988年   1009篇
  1987年   846篇
  1986年   879篇
  1985年   710篇
  1984年   543篇
  1983年   517篇
  1982年   511篇
  1981年   398篇
  1980年   358篇
  1979年   305篇
  1978年   328篇
  1977年   396篇
  1975年   277篇
  1972年   302篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Background. For effective palliation of patients with malignant pleural effusion due to advanced neoplastic disease, any proposed treatment should have low procedure-related mortality and morbidity.

Methods. The clinical outcome of 119 thoracoscopies in 101 patients (56 women, 45 men), from 42 to 91 years of age (mean, 68 ± 9 years) with malignant pleural effusions was evaluated in a retrospective study. Video-assisted thoracoscopy (VATS) talc pleurodesis was done in 105 instances, and a pleuroperitoneal shunt was performed 14 times as an alternative when complete expansion of the lung could not be achieved due to tumor implants on the visceral pleura.

Results. The VATS talc pleurodesis resulted in clinically significant improvement of dyspnea in 92.2% of the patients. Thirty-day mortality was 2.8% and morbidity was 2.8%. The mean duration of postoperative survival was 6.7 months. Recurrent pleural effusion occurred in 5.7% of patients after a mean interval of 6 months. Clinical relief of dyspnea was obtained in 73% of the patients treated with pleuroperitoneal shunts. Thirty-day mortality in this group was 21% and morbidity was 14.3%. The mean duration of survival was 4.2 months.

Conclusions. The VATS talc pleurodesis is appropriate for palliation of patients with malignant pleural effusions and should be performed once the diagnosis has been confirmed. Patients with lungs trapped by visceral carcinomatosis may benefit from placement of a pleuroperitoneal shunt as an alternative.  相似文献   

992.
BACKGROUND:

The use of advanced technology, such as virtual environments and computer-based simulators (VR/CBS), in training has been well established by both industry and the military. In contrast the medical profession, including surgery, has been slow to incorporate such technology in its training. In an attempt to identify factors limiting the regular incorporation of this technology into surgical training programs, a survey was developed and distributed to all general surgery program directors in the United States.

STUDY DESIGN:

A 22-question survey was sent to 254 general surgery program directors. The survey was designed to reflect attitudes of the program directors regarding the use of computer-based simulation in surgical training. Questions were scaled from 1 to 5 with 1 = strongly disagree and 5=strongly agree.

RESULTS:

A total of 139 responses (55%) were returned. The majority of respondents (58%) had seen VR/CBS, but only 19% had “hands-on” experience with these systems. Respondents strongly agreed that there is a need for learning opportunities outside of the operating room and a role for VR/CBS in surgical training. Respondents believed both staff and residents would support this type of training. Concerns included VR/CBS’ lack of validation and potential requirements for frequent system upgrades.

CONCLUSIONS:

Virtual environments and computer-based simulators, although well established training tools in other fields, have not been widely incorporated into surgical education. Our results suggest that program directors believe this type of technology would be beneficial in surgical education, but they lack adequate information regarding VR/CBS. Developers of this technology may need to focus on educating potential users and addressing their concerns.  相似文献   

993.
A 76-yr-old man with bilateral total hip arthroplasties was referred for a baseline bone mineral density (BMD) measurement. The L1-L4 lumbar bone density revealed a density above the upper expected value for a young individual (i.e., T-score > 2.5) with large intervertebral variation, while the forearm study revealed an osteoporotic measurement. Lumbar spine radiographs demonstrated abundant, flowing ossification of the anterior spinal ligament, predominantly at L3, consistent with diffuse idiopathic skeletal hyperostosis, which accounted for the increased BMD.  相似文献   
994.
Background. The outcome of valvular heart operations in patients with previous mediastinal radiation therapy was studied.

Methods. This is a single center retrospective study of 60 patients (37 females, 23 males) with a mean age of 62 ± 15 years (28 to 88 years old) operated on from January 1976 to December 1998. Valvular heart operations performed included aortic valve replacements (n = 26), mitral valve procedures (n = 16), tricuspid valve procedures (n = 6), and multiple valve procedures (n = 12). A total of 264 clinical, hemodynamic, electrocardiographic and echocardiographic variables were analyzed.

Results. Total follow-up was 199 patient-years with a mean of 3.3 ± 3.1 years and a range of 0 to 12.4 years old. Early mortality was 7 patients (12%). Early mortality in patients with constrictive pericarditis was 40% (4 of 10) compared with 6% (3 of 50) in patients without constrictive pericarditis. By univariate analysis, early mortality was associated with constrictive pericarditis (p = 0.011), reduced preoperative ejection fraction (p = 0.015), and longer cardiopulmonary bypass times (p = 0.037). A total of 14 patients (23%) required permanent pacemaker placement before (n = 7), during (n = 1), or early (n = 6) after valvular heart operations. There were 19 late deaths (malignancies, 7; heart failures, 5; other cardiac, 4; and other noncardiac, 3). Overall survival and freedom from late cardiac death and cardiac reoperation at 5 years for hospital survivors were 66% ± 8%, 82% ± 7%, and 93% ± 4%, respectively. By univariate analysis, late cardiac death was associated with low ejection fraction (p = 0.002), New York Heart Association (NYHA) functional class IV (p = 0.004), preoperative congestive heart failure (p = 0.02), and preoperative atrial fibrillation (p = 0.038). Eighty-five percent of the discharged patients were in NYHA functional class I or II at follow-up.

Conclusions. Early results of valve replacement after mediastinal radiation therapy were good except in the presence of constrictive pericarditis. Long-term outcome was limited by malignancy and heart failure. Early surgical intervention is recommended before the development of risk factors for late death, namely, severe symptoms, left ventricular dysfunction, and atrial fibrillation.  相似文献   

995.
Aims nduction characteristics of sevoflurane were compared with isoflurane and halothane in 45 acyanotic infants undergoing surgery for congenital heart disease. Methods Infants were randomized into three groups of 15 each. None of them received premedication. In group I induction was done with 8% sevoflurane in 100% oxygen, in group II with 5% isoflurane in 100% oxygen and in group III with 4% halothane in 100% oxygen. Induction time, intubation time, haemodynamic variables and side effects like coughing, laryngospasm, breatholding and excessive crying were noted. Results The mean induction time taken as loss of eyelash reflex was significantly lower in sevoflurane group (52.80±8.5 seconds) as compared to isoflurane (196.80±49.13 seconds) and halothane groups (168.72±9.1 seconds) (p value <0.001). The mean intubation time in sevoflurane group was 2.97±0.48 minutes followed by halothane group (5.10±2.9 minutes) and isoflurane group (6.70±1.77 minutes) (p value < 0.001). The incidence of coughing and laryngospasm was observed in 6% (1 in 15), each in sevoflurane and halothane groups and 20% (3 in 15) cases in isoflurane group. Haemodynamics were comparable in both sevoflurane and isoflurane groups. However in halothane group significant decrease in mean arterial pressure was observed. Conclusion Sevoflurane anaesthesia is a better alternative for induction in infants undergoing cardiac surgery as compared to isoflurane and halothane. (Ind J Thorac Cardiovasc Surg, 2001; 17:233-237)  相似文献   
996.
Surgical intervention for neck and back pain in elderly patients without significant comorbidities can significantly improve a patient's symptoms and quality of life when more conservative therapies fail. Current spine literature strongly supports the paradigm of treating elderly patients with stable, chronic neck or back pain with conservative therapies first in order to optimize the risks and benefits of all available treatment options. If less-invasive methods fail to achieve satisfactory outcomes, more aggressive surgical options can, at that time, typically be implemented with excellent results in elderly patients without significant comorbidities. Clinical scenarios threatening to result in spine instability or nerve root or spinal cord compression require immediate intervention, especially in elderly patients, who, in general, have a higher risk of developing such conditions either through falls or trauma or acquired degenerative disease processes or malignancies. When an elderly patient enters a physician's office and asks "doctor, I've had pain for years, but it's getting worse. At my age, is it really worth having surgery?" The answer is a qualified "yes," if conservative treatments have failed and if the patient is otherwise in reasonably good health. Because the vast majority of these patients first interact with the medical system through their primary care doctors and neurologists, early recognition of situations requiring immediate attention, and those requiring referrals to spine specialists, can greatly expedite the appropriate use of scarce healthcare resources. Furthermore, knowledge of the various treatment options available to elderly patients complaining of the very common symptoms of neck or back pain can significantly improve patient care, especially in this new century when older patients will increasingly become a larger and more active force in all aspects of our society.  相似文献   
997.
BACKGROUND: Long-term success in the treatment of truncal and significant branch leg varicosities, when the saphenofemoral junction (SFJ) and the greater saphenous vein (GSV) are involved, depends on the elimination of the highest point of reflux and the incompetent venous segment, and is best achieved by surgical ligation and stripping. Minimally invasive alternatives in the treatment of varicose veins with SFJ and GSV incompetence have been tried over the years to increase patient comfort, reduce cost and risk, and allow implementation by a wide variety of practitioners resulting in varying degrees of success depending on the fulfillment of the above two premises and the effectiveness of the method used. OBJECTIVE: To demonstrate a novel way to use laser energy through an endoluminal laser fiber for the minimally invasive treatment of truncal varicosities that eliminates the highest point of reflux and the incompetent segment. METHODS: Patients were treated with 810 nm diode laser energy administered endovenously through a bare-tipped laser fiber (400-750 microm). Vein access for endoluminal placement of the fiber through a catheter was achieved by means of percutaneous or stab wound incision under ultrasound guidance and local anesthesia. Exact placement of the fiber was determined by direct observation of the aiming beam through the skin and by ultrasound confirmation. RESULTS: Preliminary short-term postprocedure results (up to 1 year, 2 months after treatment) in the endovenous laser treatment of 40 greater saphenous veins in 33 patients indicate a 100% rate of closure with no significant complications. In addition, a 2-year experience of 80 cases of isolated branch varicosities (Giacomini, anterolateral branch, etc.) also shows a 100% rate of closure. CONCLUSION: Early results of our endoluminal laser methodology indicate a very effective and safe way to eliminate SFJ incompetence and close the GSV. With proper patient selection, the ease of methodology and the reduced risk and cost associated with endovenous laser treatment may make it a successful minimally invasive alternative for a wide group of patients that previously would have required ligation and stripping.  相似文献   
998.
Laryngeal wound healing is essential following laryngotracheal surgery. Patients with poor wound healing develop poor epithelial closure and increased granulation tissue which cause a stenosis of the repaired airway. Transforming growth factor-beta3 has been shown to enhance wound healing in cutaneous wounds, but has never been used in the airway. This study utilized a rabbit laryngeal wound-healing model that has been shown to be reproducible with limited morbidity. Thirty-four rabbits underwent a cricoid-split operation with collagen sponge insertion. All animals were classified randomly into three groups: local administration of placebo (Group G1, n = 13), 0.18 microg transforming growth factor-beta3 (Group G2, n = 11) and of 1.0 microg transforming growth factor-beta3 (Group G3, n = 10). All animals survived the postoperative period without respiratory distress. The airway was harvested six days after surgery and assessed by light microscopy. Histologic evidence for healing was subjectively graded by two blinded, independent investigators, and the results were statistically analyzed for significance. A significant improvement in the epithelial closure (p < 0.01) and subepithelial connective tissue closure (p < 0.005) was found in the 1.0 microg transforming growth factor-beta3 group (G3) compared with the placebo group (G1). Analysis of the 0.18 microg transforming growth factor-beta3 group (G2) did not reveal any significant differences compared with the placebo group (G1). These results suggest an application for transforming growth factor-beta3 in accelerating wound healing in the larynx.  相似文献   
999.
BACKGROUND: Actin is largely responsible for cell motility and is only sparsely found in normal epithelial cells. An altered expression of actin in some malignancies may facilitate aggressive invasion. Micronodular basal cell carcinoma (BCC) has been shown to require more surgical stages, wider tissue margins, and deeper defects for extirpation during Mohs micrographic surgery relative to nodular BCC. OBJECTIVE: To provide preliminary data regarding a possible correlation between alpha-smooth muscle actin (alpha-SMA) expression within the cells or stroma of micronodular BCC and aggressive invasion. In addition, the incidence of alpha-SMA expression in micronodular, morpheaform, and nodular BCC is evaluated. METHODS: Nine micronodular basal cell carcinomas (7 primary, 2 recurrent) were evaluated for neural invasion, depth of tissue invasion, and alpha smooth muscle actin antibodies. The presence of alpha-smooth muscle actin antibodies was assessed using immunoperoxidase staining and compared with 13 morpheaform (13 primary, 0 recurrent) and 12 nodular (12 primary, 0 recurrent). RESULTS: Six of the nine micronodular (67%), eight of the 13 morpheaform (62%), and 0 of the 12 nodular (0%) BCCs stained positive for alpha-SMA. Of the six micronodular BCCs that stained positive for alpha-SMA, three invaded the fascia or muscle and three displayed neural invasion. In contrast, of the three micronodular BCCs that stained negative for alpha-SMA, none invaded the fascia or muscle and only one exhibited neural invasion. CONCLUSION: Actin was present in 66% of micronodular, 62% of morpheaform, and 0% of nodular BCC. The presence of actin in micronodular BCC may be a marker for aggressive invasion.  相似文献   
1000.
BACKGROUND: Eruptive syringomas are uncommon benign adnexal neoplasms. They are numerous and disseminated and often have a predilection for the neck, face, chest, and axillary fossae. Because they are persistent, usually numerous, and often on exposed sites, the lesions may be disfiguring and often pose significant cosmetic concerns for patients. Many treatment modalities such as dermabrasion, electrodesiccation with curettage, and scissors excision have been tried with some success, but more recently lasers have provided good to excellent results. OBJECTIVE: To describe an approach to the treatment of eruptive syringomas in an African American patient with a combination of trichloroacetic acid (TCA) and CO2 laser resurfacing, providing acceptable cosmetic results without significant side effects. METHODS: We describe an African American patient with eruptive syringomas of the face treated with a combination of TCA and CO2 laser resurfacing with good results. RESULTS: While the syringomas were not completely ablated, the combination of TCA and CO2 laser resurfacing provided acceptable cosmetic results without significant side effects. CONCLUSION: The TCA pretreatment probably removed some of the bulk of the surface of the lesions, thereby reducing the number of laser passes required to flatten the remainder of the lesions and thus lessening the potential for thermal damage at the treated sites and of surrounding normal skin.  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