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   10514篇
  免费   898篇
  国内免费   16篇
耳鼻咽喉   148篇
儿科学   380篇
妇产科学   259篇
基础医学   1308篇
口腔科学   236篇
临床医学   1342篇
内科学   1788篇
皮肤病学   234篇
神经病学   1358篇
特种医学   211篇
外科学   1071篇
综合类   64篇
一般理论   19篇
预防医学   1545篇
眼科学   106篇
药学   592篇
  3篇
中国医学   7篇
肿瘤学   757篇
  2024年   38篇
  2023年   229篇
  2022年   328篇
  2021年   652篇
  2020年   419篇
  2019年   607篇
  2018年   667篇
  2017年   423篇
  2016年   449篇
  2015年   427篇
  2014年   544篇
  2013年   710篇
  2012年   934篇
  2011年   875篇
  2010年   449篇
  2009年   361篇
  2008年   517篇
  2007年   457篇
  2006年   456篇
  2005年   383篇
  2004年   296篇
  2003年   253篇
  2002年   264篇
  2001年   65篇
  2000年   39篇
  1999年   60篇
  1998年   41篇
  1997年   28篇
  1996年   37篇
  1995年   25篇
  1994年   19篇
  1993年   25篇
  1992年   24篇
  1991年   25篇
  1990年   25篇
  1989年   27篇
  1988年   14篇
  1987年   19篇
  1986年   22篇
  1985年   27篇
  1984年   15篇
  1983年   10篇
  1982年   17篇
  1981年   8篇
  1980年   14篇
  1979年   14篇
  1977年   8篇
  1976年   9篇
  1975年   9篇
  1973年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Abstract

The purpose of this study was to investigate the strength of the relationships between self-efficacy and (i) functional exercise capacity and (ii) physical activity in chronic obstructive pulmonary disease (COPD), and whether self-efficacy assessment type (i.e., COPD symptoms, exercise-task, exercise-barrier, general, falls) and physical activity assessment type (i.e., self-report vs. objective) are moderators. A systematic search of COPD and self-efficacy concepts was conducted using eight databases from inception to 23 January 2019. Studies were included if they provided correlation coefficients of the relationship between self-efficacy and functional exercise capacity or physical activity, were conducted in adults diagnosed with COPD, and were published in English-language journals. A total of 14 correlation coefficients were included in the self-efficacy and functional exercise capacity meta-analysis, and 16 in the self-efficacy and physical activity meta-analysis. Data were screened, reviewed, and extracted independently by two reviewers, with discrepancies resolved by a third reviewer. Stronger self-efficacy was associated with better functional exercise capacity (weighted r?=?0.38, 95%CI [0.25, 0.50]), and greater physical activity (weighted r?=?0.25, 95%CI [0.17, 0.34]). Exercise-task self-efficacy had the strongest relationship to functional exercise capacity (weighted r?=?0.64, 95% CI [0.51, 0.73]). For physical activity, the type of self-efficacy most strongly related was inconclusive. In COPD, self-efficacy has a relationship to functional exercise capacity and physical activity, the strength of which is influenced by the choice of self-efficacy measure. An understanding of these relationships will assist clinicians in selecting the self-efficacy measure most closely related to the outcome of interest.  相似文献   
2.
The B cell functional response following ligation of surface(s) lgM is dependent upon the differentiation stage of the populationstudied: cross-linking slgM promotes proliferation of restingtonsillar follicular mantle (FM) B lymphocytes but induces apoptosisin the susceptible Epstein- Barr virus genome-negative Burkittlymphoma (BL) cell line Ramos (Ramos-BL). This study investigateswhether phosphatidylinositol-3-kinase (Pl3-kinase), which hasbeen reported to be intimately involved in the regulation ofcellular growth, plays a role in the regulation of these sig-promoted B cell responses, and uses the selective and irreversibleinhibitor of Pl3-kinase activity, wortmannin (Wm). In Ramos-BLB cells, at 8 h post-treatment, Wm triggers a transient increasein apoptosis of 16 ± 6.9% with a concomitant cellularloss of 16 ± 6.1% from the G1 phase of cell cycle; [3H]thymidineincorporation also decreases by 33 ± 5.0%, from 37,274c.p.m. ± 10% to 25,127 c.p.m. ± 4.0%. Moreover,at 72 h culture, Wm inhibits anti-lgM-induced FM B lymphocytelevels of [3H]thymidine incorporation typically by 47% and triggers80% apoptosis from the G0G1 phase of cell cycle. Ramos-BL Bcells exhibit high basal levels of Pl3-kinase activity, as determinedby immunoprecipitation with antibody to the p85 regulatory subunitof Pl3-kinase and 32P incorporation into phosphatidylinositol,which is not significantly affected by anti-lgM stimulation;by contrast, anti-lgM stimulates significant Pl3-kinase activityover negligible basal levels in FM B lymphocytes. Pre-treatmentwith Wm inhibits Pl3-kinase activity in both cell types. Takentogether these data indicate that in Ramos-BL B cells slgM-triggeredgrowth arrest and apoptosis is Pl3- kinase independent, whereasPl3-kinase activity is critical for slgM-triggered mitogenesisof FM B lymphocytes. Thus Pl3-kinase plays a pivotal role inthe regulation of both normal and neoplastic B lymphocyte progressionthrough the cell cycle, such that if this Pl3-kinase-dependentpathway is inhibited these cells default to apoptosis.  相似文献   
3.
Summary: This is the first report of the largest study of blood pressure measurement in pregnancy in a New Zealand population using standardized definitions and methodology. Over 3,800 women who delivered in an 8-month period in the Wellington region were included in the study. Blood pressure measurement and the presence of oedema and proteinuria were recorded from booking until delivery and in the puerperium. Only 2.7% of women were unable to be contacted after delivery for details on outcomes. The results established normal ranges for blood pressure throughout pregnancy. The data show that Mood pressure greater than 140/90 until 35 weeks' gestation is outside 2 standard deviations at all gestations and justifies using these measurements as the definition of hypertension in pregnancy. The fall in blood pressure in the 2nd trimester was less than 1 mm Ffg per week in both the systolic and diastolic pressures. This fall was smaller than previously recorded in other studies. Gestational hypertension was the commonest blood pressure abnormality occurring in 15.2% of the population. This represented 69% of the pregnant women with a hypertensive disorder. The overall incidence of both gestational hypertension and preeclampsia was 18.5% which is higher than reported in other parts of the world. In this study obesity was significantly associated with hypertensive disorders in pregnancy. An arm circumference of >33 cm, one of the measurements of obesity, was found in 6.8% of the study population. Even after the effect of arm circumference was taken into account, hypertensive disorders were also more common in Pacific Island women. Ankle oedema was significantly associated with the development of both gestational hypertension and preeclampsia but the incidence of oedema was noted in only 11.9% of the subjects.  相似文献   
4.
5.
While there is a burgeoning body of research linking smoking during pregnancy to problem behaviour in offspring, a major criticism of this work has been the crude measurement of exposure in these studies (e.g. retrospective, self-reported only) that could lead to biased estimates. To address this issue, we used a pregnancy cohort with repeated prospective measures of exposure as well as biological assays to generate estimates of exposure patterns using a range of modelling techniques. In this paper we report on the analytical approaches we have developed, including patterns of exposure over time and best-estimate approaches that combine self-report and cotinine measures, and compare their predictive value in relation to different dimensions of fetal growth as a first step towards examining the utility of greater precision of exposure measurement.
Surprisingly, in this sample the more complex assessments of exposure, including biological measures, generally did not perform better than simple indicators of exposure based on repeated self-report measures, with one exception: a combined self-report cotinine 'best estimate' of third trimester exposure was uniquely associated with lower brain : body ratio. Further study is needed using more sophisticated cotinine assays and testing prediction of a range of outcomes to ascertain whether these findings represent true differences or are specific to the sample, methods and outcomes used. Such research will inform the development of guidelines for adequate exposure characterisation in developmental studies.  相似文献   
6.
Edited by Lauren Dundes. Walnut Creek (CA): Altamira Press, 2003. 239 pages. $27.95, paperback, $75.00, hardback.  相似文献   
7.
OBJECTIVE: To describe the dieting histories of bariatric surgery candidates. RESEARCH METHODS AND PROCEDURES: One hundred seventy-seven individuals with extreme obesity who sought bariatric surgery completed the Weight and Lifestyle Inventory, a self-report instrument that assesses several variables, including weight and dieting history. Patients' dieting histories were further explored with an aided recall during a preoperative behavioral/psychological evaluation performed by a mental health professional. RESULTS: Participants who completed the Weight and Lifestyle Inventory reported an average of 4.7 +/- 2.9 successful dieting attempts, defined as those that resulted in a loss of 10 lbs (4.5 kg) or more. These individuals reported a mean total lifetime weight loss of 61.1 +/- 41.3 kg. Despite these efforts, their weight increased from 89.4 +/- 27.4 kg at the time of their first diet (age 21.2 +/- 10.1 years) to 144.5 +/- 30.8 kg at the time they underwent their behavioral/psychological evaluation (age 43.0 +/- 11.0 years). Results of the aided recall revealed that participants had made numerous other efforts to lose weight that were unsuccessful. Self-directed diets and commercial programs were used more frequently. DISCUSSION: Individuals who sought bariatric surgery reported an extensive history of dieting, beginning in adolescence, that was not successful in halting progressive weight gain. Thus, the recommendation often made by insurance companies that patients delay surgery to attempt more conservative treatment options may be unwarranted, particularly in the presence of significant obesity-related comorbidities. Weight loss histories should be routinely examined during a behavioral evaluation to determine whether additional attempts at non-surgical weight loss are advisable. Future studies also are needed to explore the potential relationship between dieting history and postoperative outcome.  相似文献   
8.
The mitochondrial theory of aging proposes that mitochondrial DNA (mtDNA) accumulates mutations with age, and that these mutations contribute to physiological decline in aging and degenerative diseases. Although a great deal of indirect evidence supports this hypothesis, the aggregate burden of mtDNA mutations, particularly point mutations, has not been systematically quantified in aging or neurodegenerative disorders. Therefore, we directly assessed the aggregate burden of brain mtDNA point mutations in 17 subjects with Alzheimer's disease (AD), 10 elderly control subjects and 14 younger control subjects, using a PCR-cloning-sequencing strategy. We found that brain mtDNA from elderly subjects had a higher aggregate burden of mutations than brain mtDNA from younger subjects. The average aggregate mutational burden in elderly subjects was 2 x 10(-4) mutations/bp. The bulk of these mutations were individually rare point mutations, 60% of which changed an amino acid. Control experiments ensure that these results were not due to artifacts arising from PCR error, mistaken identification of nuclear pseudogenes or ex vivo oxidation. Cytochrome oxidase activity correlated negatively with increasing mutational burden. These findings significantly bolster the mitochondrial theory of aging.  相似文献   
9.
Neurophysiological analysis of spontaneous and reflex-triggered myoclonus in a case of epilepsia partialis continua is reported. A central positive wave (P1), part of the high voltage evoked potential and of the spontaneous spike, is held to be responsible for the myoclonic jerk. It is demonstrated that P1 is a distinct phenomenon from both the evoked potential and the epileptic spike, and so should be identified as a myoclonus-related potential (MRP).  相似文献   
10.
Sequential salivary gland scintigraphy with 99mTc-technetium pertechnetate (Tc-99) is a safe, minimally invasive test for study of major salivary glands. However, its relationship to salivary function has not been investigated in detail. We have investigated the relationship between major salivary gland flow rates and Tc-99 scans and developed a new rating scale using scans of a control group with normal salivary function. Salivary flow rates and Tc-99 scans were obtained from healthy, non-medicated subjects (n = 33) and from xerostomic patients (n = 22). There were significant differences between the groups for salivary flow rates and Tc-99 ratings. Significant correlations were found between salivary flow rates and Tc-99 ratings in the control and xerostomic groups. The Tc-99 rating scale proved reliable in assessing salivary dysfunction, and showed a high inter-examiner correlation. These results demonstrate the usefulness of salivary gland scintigraphy in assessing major salivary gland flow rates and the utility of a new rating scale.  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