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   22683篇
  免费   1779篇
  国内免费   33篇
耳鼻咽喉   195篇
儿科学   774篇
妇产科学   621篇
基础医学   2804篇
口腔科学   397篇
临床医学   2764篇
内科学   4041篇
皮肤病学   395篇
神经病学   2094篇
特种医学   701篇
外科学   3292篇
综合类   362篇
一般理论   38篇
预防医学   2368篇
眼科学   546篇
药学   1598篇
  3篇
中国医学   12篇
肿瘤学   1490篇
  2022年   156篇
  2021年   373篇
  2020年   221篇
  2019年   409篇
  2018年   466篇
  2017年   335篇
  2016年   376篇
  2015年   397篇
  2014年   591篇
  2013年   898篇
  2012年   1328篇
  2011年   1443篇
  2010年   750篇
  2009年   679篇
  2008年   1159篇
  2007年   1207篇
  2006年   1205篇
  2005年   1103篇
  2004年   1043篇
  2003年   1024篇
  2002年   903篇
  2001年   511篇
  2000年   542篇
  1999年   461篇
  1998年   250篇
  1997年   173篇
  1996年   186篇
  1995年   182篇
  1994年   142篇
  1993年   161篇
  1992年   420篇
  1991年   367篇
  1990年   379篇
  1989年   349篇
  1988年   359篇
  1987年   326篇
  1986年   307篇
  1985年   333篇
  1984年   260篇
  1983年   219篇
  1982年   149篇
  1981年   126篇
  1980年   121篇
  1979年   237篇
  1978年   172篇
  1977年   124篇
  1976年   116篇
  1974年   119篇
  1973年   128篇
  1970年   116篇
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
992.
993.
OBJECTIVES: Acetylcysteine in patients undergoing computerized tomography with intravenous contrast reduces the incidence of acute renal dysfunction. We examined the effect of N-acetylcysteine in patients undergoing coronary angiography. METHODS: Fifty-five consecutive patients receiving 3 doses of N-acetylcysteine prior to cardiac catheterization were compared to 55 historical controls. All patients in both groups had baseline serum creatinine > 1.2 mg/dl and received intravenous hydration before and after the procedure. Serum creatinine levels at baseline and 48 hours after the procedure were compared. RESULTS: Univariate analysis of clinical variables revealed no significant differences between the groups except for a higher baseline creatinine in the treatment group (2.0 0.7 vs. 1.8 0.4 mg/dl; p = 0.04). There was no difference in the amount or type of contrast used. The mean change in creatinine after 48 hours was -0.4 0.3 versus +0.1 0.3 mg/dl for treatment and control groups (p < 0.001). In patients with baseline creatinine > 2 mg/dl, the benefit was larger (-0.4 0.4 vs. +0.5 0.3 mg/dl; p < 0.001). Multivariate analysis confirmed pre-treatment with N-acetylcysteine as an independent predictor of renal protection (p < 0.001). CONCLUSIONS: Prophylactic use of acetylcysteine prevented reduction of renal function after coronary angiography. The benefit was greater in patients with baseline serum creatinine > 2 mg/dl.  相似文献   
994.
995.
SIR, Behçet's disease is a chronic, relapsing inflammatorydisorder that causes ocular inflammation in up to 70% of patients[1, 2]. Despite intensive immunosuppressive therapy, relapsingocular inflammation can lead to permanent loss of vision [2].Infliximab, a monoclonal chimeric antibody to tumour necrosisfactor (TNF), is a novel therapy used in the management of Behçet'spanuveitis that is unresponsive to established immunosuppressivetreatment. Initialshort-term experience in six patients withBehçet's panuveitis has resulted in a rapid and effectiveresolution of ocular inflammation with no side-effects [3, 4].Long-term safety data obtained in patients taking infliximabfor rheumatoid arthritis (RA) and Crohn's disease report an  相似文献   
996.
BACKGROUND: Clinical factors related to suicide and suicide attempts have been studied much more extensively in unipolar depression compared with bipolar disorder. We investigated demographic and course-of-illness variables to better understand the incidence and potential clinical correlates of serious suicide attempts in 648 outpatients with bipolar disorder. METHOD: Patients with bipolar I or II disorder (DSM-IV criteria) diagnosed with structured interviews were evaluated using self-rated and clinician-rated questionnaires to assess incidence and correlates of serious suicide attempts prior to study entry. Clinician prospective ratings of illness severity were compared for patients with and without a history of suicide attempt. RESULTS: The 34% of patients with a history of suicide attempts, compared with those without such a history, had a greater positive family history of drug abuse and suicide (or attempts); a greater personal history of early traumatic stressors and more stressors both at illness onset and for the most recent episode; more hospitalizations for depression; a course of increasing severity of mania; more Axis I, II, and III comorbidities; and more time ill on prospective follow-up. In a hierarchical logistic regression, a history of sexual abuse, lack of confidant prior to illness onset, more prior hospitalizations for depression, suicidal thoughts when depressed, and cluster B personality disorder remained significantly associated with a serious suicide attempt. CONCLUSION: Our retrospective findings, supplemented by prospective follow-up, indicate that a history of suicide attempts is associated with a more difficult course of bipolar disorder and the occurrence of more psychosocial stressors at many different time domains. Greater attention to recognizing those at highest risk for suicide attempts and therapeutic efforts aimed at some of the correlates identified here could have an impact on bipolar illness-related morbidity and mortality.  相似文献   
997.
BACKGROUND: A number of recent longitudinal outcome studies have found substantial long-term morbidity in patients with bipolar disorder. The detailed course and pattern of illness emerging despite comprehensive treatment with mood stabilizers and adjunctive agents have previously not been well delineated. METHOD: 258 consecutive outpatients admitted from 1996 to 1999 to the Stanley Foundation Bipolar Network who had a full year of prospective daily clinician ratings on the National Institute of Mental Health-Life Chart Method were included in the analysis. Patients were diagnosed by the Structured Clinical Interview for DSM-IV, with the majority (76%) having bipolar I disorder. They completed a questionnaire on demographics and prior illness course, and variables associated with outcome were examined in a hierarchical multinomial logistic regression analysis. Patients were treated naturalistically with a mean of 4.1 psychotropic medications during the year. RESULTS: Despite comprehensive pharmacologic treatment, mean time depressed (33.2% of the year) was 3-fold higher than time manic (10.8%); 62.8% of patients had 4 or more mood episodes per year. Two thirds of the patients were substantially impacted by their illness; 26.4% were ill for more than three fourths of the year, and 40.7% were intermittently ill with major affective episodes. After logistic regression analysis, those who were ill most of the year, compared with the largely well group, had a significantly greater family history of substance abuse, 10 or more depressive episodes, and limited occupational functioning prior to Network entry. CONCLUSION: A majority of outpatients with bipolar illness, even with intense monitoring and treatment in specialty clinics, have a considerable degree of residual illness-related morbidity, including a 3-fold greater amount of time spent depressed versus time spent manic. A personal or family history of substance abuse, 10 or more prior depressions, and limited occupational functioning predicted the poorest outcomes. Additional interventions, particularly those targeted at treating depressive phases of bipolar illness, are greatly needed.  相似文献   
998.
Immunohistochemical expression in the neocortex, hippocampus and cerebellum of the alpha(1A) or alpha(1E) subunit of the voltage-sensitive Ca(2+) channel was examined in Long-Evans hooded rats on gestational day 18 and postnatal days 1, 4, 7, 10, 14, 21, 90, 360 and 720. On gestational day 18 and postnatal day 1, alpha(1A) immunoreactivity was more dense in the neocortex and hippocampus than the cerebellum. By postnatal day 7, levels of alpha(1A) immunoreactivity increased dramatically in the cerebellum, while in neocortex, alpha(1A) immunoreactivity became more sparse, which approached the more diffuse pattern of cellular staining in the mature brain. Expression of alpha(1E) in the neocortex, hippocampus and cerebellum was much less dense than alpha(1A) between gestational day 18 and postnatal day 4. There was also significant alpha(1E) immunoreactivity in the mossy fibers of the hippocampus and in dendrites of Purkinje cells of the cerebellum. Depolarization-dependent 45Ca(2+) influx was examined in rat brain synaptosomes on postnatal days 4, 7, 10, 14, 21 and >60. In neocortical and hippocampal synaptosomes, 45Ca(2+) influx increased steadily with age and reached adult levels by postnatal day 10. In cerebellar synaptosomes, 45Ca(2+) influx was constant across all ages, except for a spike in activity which was observed on postnatal day 21. In neocortical and hippocampal synaptosomes, 100 nM omega-conotoxin MVIIC significantly inhibited 45Ca(2+) influx on postnatal day 10 and 14, respectively, or after. In cerebellar synaptosomes, influx was inhibited by omega-conotoxin MVIIC only on postnatal day 10 or prior. On postnatal day 7, 45Ca(2+) influx was not inhibited in neocortical and hippocampal synaptosomes by a combination of 10 microM nifedipine, 1 microM omega-conotoxin GVIA and 1 microM omega-conotoxin MVIIC, suggesting that an 'insensitive' flux predominates at this age. Overall, the results suggest that expression of voltage-sensitive Ca(2+) channels during development is dynamic and is important in central nervous system development.  相似文献   
999.
Background: The EXIT (ex utero intrapartum treatment) procedure, although initially designed for reversal of tracheal occlusion in fetuses with congenital diaphragmatic hernias (CDH), has been adapted to treat a variety of fetal conditions. Methods: A retrospective chart review of all consecutive EXIT procedures since 1996 was conducted. Results: Thirty-one women underwent the EXIT procedure, with an average maternal age of 29 years (range, 20 to 38), and average gestational age of 34 weeks (range, 29 to 40). The indication was airway obstruction from fetal neck mass in 13, and reversal of tracheal occlusion from in utero clipping in 13. Singular indications included an EXIT-to-ECMO (extracorporeal membrane oxygenation) procedure for a fetus with CDH and a cardiac defect (n = 1), congenital high airway obstruction syndrome (CHAOS, n = 1), resection of a very large congenital cystic adenomatoid malformation of the lung (CCAM) on uteroplacental bypass (n = 1), unilateral pulmonary agenesis (n = 1), and thoracoomphalopagus conjoined twins. The mean duration on uteroplacental bypass (from uterine incision to umbilical cord clamping) was 30.3 [plusmn] 14.7 minutes (range, 8 to 66). No fetus experienced hemodynamic instability during uteroplacental bypass as recorded by fetal heart rate (FHR), pulse oximeter, and fetal echocardiography, except for one instance of reversible bradycardia from umbilical cord compression. The mean FHR and fetal saturation were 153.0 [plusmn] 38.5 beats per minute and 71.2% [plusmn] 19.9%, respectively. Five fetuses required a tracheostomy. Only 1 death occurred during an EXIT procedure because of inability to secure the airway secondary to extensive involvement by a lymphangioma. The average cord pH and pCO2 were, respectively, 7.20 [plusmn] 0.11 and 63.2 [plusmn] 14.6. Two maternal complications occurred: bleeding from a hysterotomy site and dehiscence of an old hysterotomy scar noticed at a subsequent cesarean section. The average maternal blood loss was 848.3 [plusmn] 574.1 mL. Conclusion: The EXIT procedure was used successfully to ensure uteroplacental gas exchange and fetal hemodynamic stability during a variety of surgical procedures performed to secure the fetal airway or ensure successful transition to postnatal environment.  相似文献   
1000.
Background/Purpose: Accurate prenatal diagnosis of complex anatomic connections and associated anomalies has only been possible recently with the use of ultrasonography, echocardiography, and fetal magnetic resonance imaging (MRI). To assess the impact of improved antenatal diagnosis in the management and outcome of conjoined twins, the authors reviewed their experience with 14 cases. Methods: A retrospective review of prenatally diagnosed conjoined twins referred to our institution from 1996 to present was conducted. Results: In 14 sets of conjoined twins, there were 10 thoracoomphalopagus, 2 dicephalus tribrachius dipus, 1 ischiopagus, and 1 ischioomphalopagus. The earliest age at diagnosis was 9 weeks' gestation (range, 9 to 29; mean, 20). Prenatal imaging with ultrasonography, echocardiography, and ultrafast fetal MRI accurately defined the shared anatomy in all cases. Associated anomalies included cardiac malformations (11 of 14), congenital diaphragmatic hernia (4 of 14), abdominal wall defects (2 of 14), and imperforate anus (2 of 14). Three sets of twins underwent therapeutic abortion, 1 set of twins died in utero, and 10 were delivered via cesarean section at a mean gestational age of 34 weeks. There were 5 individual survivors in the series after separation (18%). In one case, in which a twin with a normal heart perfused the cotwin with a rudimentary heart, the ex utero intrapartum treatment procedure (EXIT) was utilized because of concern that the normal twin would suffer immediate cardiac decompensation at birth. This EXIT-to-separation strategy allowed prompt control of the airway and circulation before clamping the umbilical cord and optimized control over a potentially emergent situation, leading to survival of the normal cotwin. In 2 sets of twins in which each twin had a normal heart, tissue expanders were inserted before separation. Conclusions: Advances in prenatal diagnosis allow detailed, accurate evaluations of conjoined twins. Careful prenatal studies may uncover cases in which emergent separation at birth is lifesaving.  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