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   3511篇
  免费   260篇
  国内免费   16篇
耳鼻咽喉   25篇
儿科学   203篇
妇产科学   35篇
基础医学   471篇
口腔科学   234篇
临床医学   375篇
内科学   839篇
皮肤病学   59篇
神经病学   182篇
特种医学   318篇
外科学   275篇
综合类   69篇
预防医学   337篇
眼科学   38篇
药学   154篇
中国医学   16篇
肿瘤学   157篇
  2023年   22篇
  2022年   31篇
  2021年   79篇
  2020年   52篇
  2019年   64篇
  2018年   88篇
  2017年   71篇
  2016年   63篇
  2015年   104篇
  2014年   131篇
  2013年   156篇
  2012年   179篇
  2011年   199篇
  2010年   142篇
  2009年   160篇
  2008年   190篇
  2007年   198篇
  2006年   171篇
  2005年   144篇
  2004年   129篇
  2003年   107篇
  2002年   85篇
  2001年   87篇
  2000年   79篇
  1999年   68篇
  1998年   100篇
  1997年   61篇
  1996年   71篇
  1995年   52篇
  1994年   55篇
  1993年   51篇
  1992年   60篇
  1991年   36篇
  1990年   38篇
  1989年   53篇
  1988年   48篇
  1987年   38篇
  1986年   31篇
  1985年   17篇
  1984年   28篇
  1983年   26篇
  1982年   23篇
  1981年   26篇
  1980年   23篇
  1979年   21篇
  1978年   20篇
  1977年   22篇
  1976年   11篇
  1975年   22篇
  1971年   10篇
排序方式: 共有3787条查询结果,搜索用时 78 毫秒
991.
992.
One hundred and eight patients with cystic fibrosis were investigated over one year to determine whether an association existed between rhinovirus or other respiratory virus infection and clinical status. Forced expiratory volume in one second (FEV1), forced vital capacity (FVC), Shwachman score, Chrispin-Norman chest radiograph score, and percentage weight for height were recorded at the beginning and end of the study; days of intravenous antibiotics were noted. Nasopharyngeal aspirates were taken for viral studies during respiratory exacerbations. Serum was collected at enrollment and 2-6 weeks after each respiratory exacerbation. One hundred and fifty seven exacerbations occurred in 76 patients. Respiratory virus infection was detected in 44 exacerbations and rhinovirus was present in 16% (25/157) of exacerbations. Patients with one or more respiratory virus infections were compared with those who had none. When all respiratory virus infections were considered, patients had a significantly greater deterioration in Shwachman score and received significantly more days of intravenous antibiotics. When rhinovirus was considered separately, patients received significantly more days of intravenous antibiotics, but showed no deterioration in clinical status. However, patients infected with another respiratory virus had a significant decline in FEV1, with trends towards significance for decline in FVC and Shwachman score.  相似文献   
993.
994.
OBJECTIVE: To evaluate the frequency of transient neonatal tyrosinemia, with or without secondary hyperphenylalaninemia,observed through neonatal screening for metabolic disorders, andthe need of monitoration and intervention with drugs and/or specialdiet in selected cases. METHODS: 457.870 dried blood samples obtained by heel stickfrom 3 to 20 days old babies were qualitatively evaluated by aminoacid thin-layer chromatography. Positive cases were quantitativelyconfirmed in serum samples by fluorimetric measurement of tyrosineand phenylalanine. RESULTS: 1.231 dried blood samples displayed positive resultsfor tyrosine in the cromatographic evaluation. The fluorimetricserum analysis disclosed normal levels of tyrosine and phenylalaninein 822 patients. The remained 409 patients showed hightyrosine levels and were placed in three groups according to thetyrosine concentration. In 118 of these cases serum phenylalaninewas also increased. CONCLUCIONS: Transient neonatal tyrosinemia is a very frequentdisorder in neonates (1/372); in some cases very high levels werefound, not only of tyrosine but also phenylalanine. As this findingis not yet accepted as absolutely harmless, the monitoration of thissituation and the use of measures to lower the tyrosine and phenylalaninelevels should be considered by the pediatrician.  相似文献   
995.
Selective pulmonary arteriography, with superselective magnification views of the lung bases or other areas where abnormalities are shown on perfusion lung scans, performed within 24-48 hours after the onset of symptoms, can effectively rule out clinically significant pulmonary thromboembolism. One hundred and eighty consecutive patients (minimum follow up, six months) with suspected pulmonary embolism and negative pulmonary arteriograms were studied. Not one of the 167 untreated patients died as a result of thromboembolic disease during the acute illness (20 died from unrelated causes), and none of the 147 patients who survived suffered "recurrent embolism" during follow up.  相似文献   
996.

Background

Stopping antipsychotic treatment can interrupt improvement and exacerbate the illness. The reasons for discontinuing treatment during controlled clinical trials were analyzed to explore this phenomenon.

Methods

A post-hoc, pooled analysis was made of 4 randomized, double-blind clinical trials, 24–28 weeks in duration, involving 1627 patients with schizophrenia or a related disorder. Analyses combined all the atypical antipsychotic treatment groups in the studies.

Results

The majority of patients (53%) stopped their treatment at an early stage. Poor psychiatric response along with worsening symptoms was the most frequently given reason for discontinuing the course (36%), which was substantially more common than discontinuation due to poor tolerability of the medication (12%). This phenomenon was corroborated by less improvement in patients who discontinued treatment compared with those who completed, based on the PANSS total scores. Discontinuation due to poor response was, apparently, more predominantly linked to patient perception than to physicians' conclusions alone (80% vs. 20%). Discontinuation due to patient perception of poor response appeared to occur particularly early in the course of treatment. Patients who discontinued due to poor toleration of the medication responded in a more comparable manner with completers.

Conclusion

Discontinuing treatment may lead to exacerbation of symptoms, undermining therapeutic progress. In these studies, poor response to treatment and worsening of underlying psychiatric symptoms, and to a lesser extent, intolerability to medication were the primary contributors to treatment being discontinued. Our findings suggest that adherence may be enhanced by effective symptom control, as objectively measured and as subjectively perceived. Such strategies may improve patients' willingness to undertake long-term therapy and increase the likelihood of a better prognosis.  相似文献   
997.
Many tandemly repeated minisatellite loci display extreme levels of length variation as a consequence of high rates of spontaneous germline mutation altering repeat copy number. Direct screening for new allele lengths by small-pool PCR has shown that instability at the human minisatellite locus MS205 (D16S309) is largely germline specific and usually results in the gain or loss of just a few repeat units. Structural analysis of the order of variant repeats has shown that these events occur preferentially at one end of the tandem array and can result in complex rearrangements including the inter-allelic transfer of repeat units. In contrast, putative mutants recovered from somatic DNA occur at a substantially lower rate and are simple and non- polar in nature. Germline mutation rates vary considerably between alleles, consistent with regulation occurring in cis. Although examination of DNA sequence polymorphisms immediately flanking the minisatellite reveals no definitive associations with germline mutation rate variation, differences in rate may be paralleled by changes in mutation spectrum. These findings help to explain the diversity of MS205 allele structures in modern humans and suggest a common mutation pathway with some other minisatellites.   相似文献   
998.
BACKGROUND: Recent data are lacking about the number of patients with angiotensin-converting enzyme inhibitor (ACEI)-induced angioedema who present to the emergency department (ED). Current management of the condition and clinical outcomes also are not known. OBJECTIVE: To describe the clinical epidemiology of ACEI-induced angioedema in patients who present to the ED. METHODS: We performed a medical record review of ACEI-induced angioedema in patients who presented to 5 EDs in the Emergency Medicine Network. A structured data abstraction form was used to collect each patient's demographic factors, medical history, and details about the angioedema that prompted the ED visit. The medical record review also focused on treatment provided in the ED and subsequent need for hospitalization. RESULTS: We identified a total of 220 patients with ACEI-induced angioedema. The frequency of ACEI-induced angioedema among all patients with angioedema who presented to the ED was 30% (95% confidence interval, 26%-34%). The annual rate of visits for ACEI-induced angioedema was 0.7 per 10,000 ED visits. The most frequent presenting signs were shortness of breath, lip and tongue swelling, and laryngeal edema. Most patients (58%) were sent home directly from the ED, whereas 12% were regular inpatient admissions, 11% were admitted to the intensive care unit, and 18% were admitted under observation status (<24 hours). Pharyngeal swelling and respiratory distress were independent predictors of hospital admission and longer length of stay. CONCLUSION: ACEI-induced angioedema accounted for almost one-third of angioedema treated in the ED, although it remains a rare ED presentation. A subgroup of these patients still needs inpatient hospitalization for management of upper airway angioedema.  相似文献   
999.
Mechanisms of immunity to respiratory syncytial virus in cotton rats.   总被引:18,自引:0,他引:18       下载免费PDF全文
Active immunity and maternally transmitted passive immunity to respiratory syncytial virus (RSV) were studied in cotton rats. Animals infected with respiratory syncytial virus developed complete resistance to pulmonary reinfection, which lasted at least 18 months. Nasal resistance was of shorter duration and began to diminish in 8 months. Pulmonary resistance was transferred by parabiosis, but nasal resistance was not. Adoptive transfer studies with fractionated convalescent blood showed that serum antibody, but not circulating lymphocytes, conferred pulmonary resistance. Immune females conferred antibody to their young prenatally and postnatally, with most of the antibody being transferred via colostrum and milk. Maternally transmitted immunity was more effective in the lungs than in the nose and was transient in both organs. Foster nursing experiments showed colostrum and milk to be the most important routes of immune transfer. Although resistance in infants generally correlated with serum neutralizing antibody levels, several exceptions to this correlation suggested that immune factors other than neutralizing antibody may also play an important role in maternal passive immunity.  相似文献   
1000.
Trypanosoma cruzi-infected mice show disturbance in the peripheral immune system such as polyclonal lymphocyte activation, autoantibody production, and immunosuppression of T lymphocytes. Previous observations in our laboratory showed that some stocks of T. cruzi can be contaminated with mouse hepatitis virus type 3 (MHV-3). Literature has shown that MHV-3 infection induces immunologic disorders characterized by thymic involution with marked cell depletion. However, the effects of interactions between MHV-3 and the parasite on the immune system are not well understood. In the present study specific-pathogen-free CBA mice were inoculated with MHV-3, alone or associated with different stocks of T. cruzi. Concurrent murine virus infection resulted in increased pathogenicity of T. cruzi infection shown by profound thymic atrophy; loss of cortical thymocytes; depletion of Thy1.2+, CD4+, and CD8+ cells; enhancement of in situ labeling of nuclear DNA fragmentation; and eventually, death of the animals. Such lines of evidence show that the mechanism underlying this thymic atrophy is associated with apoptosis. These results also suggest that MHV-3 can account for the increased immunosuppression observed during experimental infection with the parasite.  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