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   14124篇
  免费   1213篇
  国内免费   32篇
耳鼻咽喉   190篇
儿科学   545篇
妇产科学   445篇
基础医学   1709篇
口腔科学   118篇
临床医学   1597篇
内科学   2493篇
皮肤病学   270篇
神经病学   1564篇
特种医学   421篇
外科学   1501篇
综合类   130篇
一般理论   20篇
预防医学   2128篇
眼科学   325篇
药学   819篇
  1篇
中国医学   17篇
肿瘤学   1076篇
  2024年   49篇
  2023年   317篇
  2022年   480篇
  2021年   936篇
  2020年   544篇
  2019年   798篇
  2018年   879篇
  2017年   585篇
  2016年   614篇
  2015年   586篇
  2014年   744篇
  2013年   898篇
  2012年   1274篇
  2011年   1253篇
  2010年   616篇
  2009年   507篇
  2008年   798篇
  2007年   737篇
  2006年   557篇
  2005年   510篇
  2004年   434篇
  2003年   359篇
  2002年   285篇
  2001年   63篇
  2000年   39篇
  1999年   37篇
  1998年   70篇
  1997年   42篇
  1996年   31篇
  1995年   32篇
  1994年   32篇
  1993年   35篇
  1992年   12篇
  1991年   12篇
  1990年   8篇
  1989年   19篇
  1988年   10篇
  1987年   9篇
  1986年   13篇
  1985年   9篇
  1984年   9篇
  1983年   13篇
  1982年   19篇
  1981年   9篇
  1980年   12篇
  1979年   7篇
  1978年   14篇
  1977年   6篇
  1976年   7篇
  1975年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.

Background  

Although regulatory compliance in academic research is enforced by law to ensure high quality and safety to participants, its implementation is frequently hindered by cost and logistical barriers. In order to decrease these barriers, we have developed a Web-based application, Duke Surgery Research Central (DSRC), to monitor and streamline the regulatory research process.  相似文献   
42.
Mycobacterium avium complex (MAC) is a significant cause of opportunistic infection in patients with acquired immunodeficiency syndrome. Although the major route of entry of MAC is via the gastrointestinal tract, MAC can infect humans through the respiratory tract and eventually encounter alveolar macrophages within the lung. Once in the lung, MAC can potentially interact with surfactant protein A (SP-A), an important component of the pulmonary innate-immune response. Previous work on other pulmonary pathogens including Mycobacterium bovis Bacillus Calmette-Guerin (BCG) suggests that SP-A participates in promoting efficient clearance of these organisms by alveolar macrophages. In the present study, we investigated the role of SP-A in clearance of MAC by cultured rat macrophages. SP-A bound to MAC organisms and enhanced the ingestion of the mycobacteria by macrophages. Infection of macrophages with SP-A-MAC complexes induced the production of nitric oxide (NO) and tumor necrosis factor-alpha. However, intracellular survival of MAC was not altered by preopsonization with SP-A. In addition, inhibitors of inducible NO synthase did not alter MAC clearance. These results suggest that SP-A can bind to and enhance the uptake of MAC by alveolar macrophages, similar to previous findings with BCG and Mycobacterium tuberculosis.However, unlike BCG and other pulmonary pathogens that are cleared effectively in the presence of SP-A via a NO-dependent pathway, macrophage-mediated clearance of MAC is not enhanced by SP-A.  相似文献   
43.
To the best of our knowledge, there are no published data on the historical and recent use of CGM in clinical trials of pharmacological agents used in the treatment of diabetes. We analyzed 2,032 clinical trials of 40 antihyperglycemic therapies currently on the market with a study start date between 1 January 2000 and 31 December 2019. According to ClinicalTrials.gov, 119 (5.9%) of these trials used CGM. CGM usage in clinical trials has increased over time, rising from <5% before 2005 to 12.5% in 2019. However, it is still low given its inclusion in the American Diabetes Association’s latest guidelines and known limitations of A1C for assessing ongoing diabetes care.

The availability of reliable continuous glucose monitoring (CGM) systems has proven to be a major innovation in diabetes management and research. Most current CGM systems are approved for 7- to 14-day use and use a wire-tipped glucose oxidase sensor inserted in subcutaneous tissue to monitor glucose concentrations in interstitial fluid. One implanted CGM system is approved for longer-term use (90–180 days); it operates with fluorescence-based technology. CGM sensors record a glucose data point every 1–15 minutes (depending on the system), collecting far more granular data and information on glycemic patterns than self-monitoring of blood glucose (SMBG) alone. Real-time CGM or intermittently scanned CGM systems send data continuously or intermittently to dedicated receivers or smartphones, whereas professional CGM systems provide retrospective data, either blinded or unblinded, for analysis and can be used to identify patterns of hypo- and hyperglycemia. Professional CGM can be helpful to evaluate patients when other CGM systems are not available to the patient or the patient prefers a blinded analysis or a shorter experience with unblinded data.In the 20 years since CGM systems first became available to people with diabetes, technological improvements, particularly pertaining to accuracy and form factor, have made CGM increasingly viable for both patient use and clinical investigation (1,2). Average sensor MARD (mean absolute relative difference; a summary accuracy statistic) has decreased from >20 to <10% (310), including two systems that do not require fingerstick calibrations and three that are approved to be used for insulin dosing (11). Concurrently, size, weight, and cost of CGM systems have all decreased, while user-friendliness and convenience have increased (12).To encourage use of CGM-derived data, researchers and clinicians have worked to develop a standard set of glycemic metrics beyond A1C. In 2017, two international groups of leading diabetes clinical and research organizations published consensus definitions for key metrics, including clinically relevant glycemic cut points for hypoglycemia (<70 and <54 mg/dL), hyperglycemia (>180 and >250 mg/dL), and time in range (TIR; 70–180 mg/dL) (13,14).CGM-derived metrics provide far greater precision and granularity than is possible with SMBG or A1C data alone (Table 1), enabling clinicians and investigators to better represent inter- and intraday glycemic differences with metrics such as TIR, glycemic variability, and time in hypoglycemia and hyperglycemia (15). Crucially, CGM also allows for the accurate measurement and detection of nocturnal glycemia (16). The use of these metrics enables a more comprehensive understanding of glycemic management that can facilitate individualized treatment for people with diabetes or prediabetes. Although A1C is a useful estimate of mean glucose over the previous 2–3 months, especially when evaluating population health, it is important to include other glycemic outcomes in clinical trials. Furthermore, there is emerging evidence suggesting that TIR predicts the development of microvascular complications at least as well as A1C (17,18).TABLE 1Benefits of CGM Compared With A1C Alone in Assessing Glycemia
CGMA1C Alone
Facilitates real-time readings of blood glucose levelsRequires SMBG
Provides information on glucose variability, including duration of hypo- and hyperglycemia and nocturnal glycemiaDoes not provide information on acute glycemic excursions and time in biochemical hypoglycemia and hyperglycemia
Correlates strongly with 3 months of mean glucose, TIR, and hyperglycemia metricsMeasures average glucose during the past 2–3 months
Provides information on direction of and rate of change in glucose levelsDoes not provide information on direction of or rate of change in glucose levels
Provides TIR data (time spent between 70 and 180 mg/dL)Does not have TIR measurement capability
Open in a separate windowDespite recent standardization of metrics and an emerging consensus around the importance of including CGM-derived outcomes in clinical trials, to our knowledge, there has been no attempt to estimate the historical and current use of CGM in clinical trials of pharmacological agents for diabetes. We sought to analyze the use of CGM in trials of currently available pharmaceutical agents for the treatment of diabetes.  相似文献   
44.
The genetic and environmental mediation of continuity and change in parent-reported ADHD symptoms were investigated in a cohort of over 6000 twin pairs at 2, 3 and 4 years of age. Genetic analyses of the cross-sectional data yielded heritability estimates of 0.78–0.81 at each age, with contrast effects. A common pathway model provided the best fit to the longitudinal data, indicating that genetic influences underlie 91% of the stable variance in ADHD symptomatology. In other words, what is stable for ADHD symptoms is largely genetic. Contrast effects acting in the same direction at different ages contributed to the observed continuity:longitudinal correlations were greater for dizygotic than monozygotic twins.The Twins Early Development Study is funded by the Medical Research Council.  相似文献   
45.
Sleep disturbance is prevalent in anxious youth and prospectively predicts poor emotional adjustment in adolescence. Study 1 examined whether anxiety treatment improves subjective and objective sleep disturbance in anxious youth. Study 2 examined whether a sleep intervention called Sleeping TIGERS can further improve sleep following anxiety treatment. Study 1 examined 133 youth (ages 9–14; 56% female; 11% ethnic/racial minority) with generalized, social, or separation anxiety over the course of anxiety treatment (cognitive behavioral treatment or client-centered treatment). Sleep-related problems (parent-, child-report) and subjective (diary) and objective (actigraphy) sleep patterns were assessed across treatment in an open trial design. Study 2 included 50 youth (ages 9–14; 68% female; 10% ethnic/racial minority) who continued to report sleep-related problems after anxiety treatment and enrolled in an open trial of Sleeping TIGERS. Pre- and postassessments duplicated Study 1 and included the Focal Interview of Sleep to assess sleep disturbance. Study 1 demonstrated small reductions in sleep problems and improvements in subjective sleep patterns (diary) across anxiety treatment, but outcomes were not deemed clinically significant, and 75% of youth stayed above clinical cutoff. Study 2 showed clinically significant, large reductions in sleep problems and small changes in some subjective sleep patterns (diary). Anxiety treatment improves, but does not resolve, sleep disturbance in peri-pubertal youth, which may portend risk for poor emotional adjustment and mental health. The open trial provides preliminary support that Sleeping TIGERS can improve sleep in anxious youth to a clinically significant degree.  相似文献   
46.
A rare benign condition of uncertain etiology and pathogenesis, Synovial Chondromatosis (SC) is most often seen intraarticularly in adults but only a handful of cases have been reported extraarticularly in children. Symptoms and physical signs consist of pain, swelling, and osteoarthritic changes related to a mass effect. Here we discuss the case of a 9-year-old boy with documented SC of the knee and critically review the Epidemiology, Clinical Presentation, Gross Anatomy and Microscopic Histopathologic Features as well as the role of Imaging Studies in Diagnosis. In addition, this paper reviews Current Pathogenetic Concepts including the infrequent but distinct possibility of malignant transformation.  相似文献   
47.
This study examined the relationship between indices of self-reported emotional distress and absolute versus change in cortisol levels. Fifty-four women attending a diagnostic breast clinic completed scales measuring stress, anxiety and depression and provided five saliva samples over the course of a single day for the measurement of cortisol. No significant relationships were evident between absolute cortisol levels and the distress measures. Analysis of the change in cortisol levels revealed a non-linear interaction effect between stress and anxiety and time of day. There was a non-linear relation between time of day and cortisol levels, but the extent of the non-linearity was dependent upon levels of stress and anxiety, not depression. A relationship was apparent between indices of distress and change in cortisol levels, but not absolute levels of the hormone.  相似文献   
48.
PURPOSE: Women have been postulated to be more responsible than men for the recent trend of lifestyle factors influencing the specialty choices of graduating U.S. medical students. The authors looked at the specialty choices of U.S. medical students between 1990 and 2003 to determine whether and to what degree women were responsible for the trends toward controllable lifestyle specialties. METHOD: Specialty preference was based on analysis of results from the American Association of Medical Colleges' Medical School Graduation Questionnaire. Specialty lifestyle (controllable vs. uncontrollable) was classified using a standard definition from prior research. A random effects regression model was used to assess differences between men and women in specialty choice over time and the proportion of variability in specialty preference from 1990 to 2003 explained by women. RESULTS: Overall, a greater proportion of women planned to pursue uncontrollable specialties compared with men in every year analyzed. Both women and men demonstrated a decreasing interest in uncontrollable lifestyle specialties by almost 20%. However, regression analysis found that women were more slightly more likely to choose an uncontrollable lifestyle specialty compared to men over time (p < .01). CONCLUSION: Among U.S. medical graduates, women were not more responsible than were men for the trend away from uncontrollable lifestyle specialties over the time period studied. Men and women expressed similar and significant rates of declining interest in specialties with uncontrollable lifestyles.  相似文献   
49.

The relationship between work rate () and time to exhaustion (t) during intense exercise is commonly described by either a hyperbolic function (NLin), t=W /(? cp), or by its linear equivalent (LinW) W lim =W + cp(t). The parameter <INF cp (critical power) has been described as an inherent characteristic of the aerobic energy system, while W?′ has been shown to be a ralid estimate of anaerobic work capacity. Recent studies have demonstrated that oral supplementation of creatine monohydrate (CrH2O) increases total muscle creatine stores, and have linked these increases to improved performances in intense intermittent exercise. This study was conducted to determine the effect of CrH2O supplementation on estimates of W?′ and <INF cp derived from the NLin and LinW equations, and to determine the effect of CrH2O on t in exhaustive constant power exercise of different intensities. Fifteen active but untrained university students completed three phases of testing on a cycle ergometer: (1) familiarization, three learning trials, (2) baseline determination of W?′ and <INF cp, four bouts performed at a selected to elicit fatigue in 90–600?s, and (3) experimental determination of W?′ and cp, four bouts performed at the same as baseline, but performed after 5 days of ingesting either a placebo (4?×?6?g of glucose/day) or CrH2O (4?×?5?g of CrH2O and 1?g glucose/day). Testing was administered in a double-blind manner. Analyses of covariance revealed a significant effect for CrH2O on both estimates of W?′ (NLin, P=0.04; LinW, P<0.01), but not on estimates of cp (NLin, P=0.37; LinW; P=0.30). Within groups, t was significantly different for only CrH2O at the two highest s (P=0.04). It is concluded that oral ingestion of CrH2O increases estimates of W?′ due to an improved t at the shorter, more intense exercise bouts.

  相似文献   
50.
PROBLEM: Previously we reported on the generation of experimental anti-phospholipid syndrome (APS) in mice. These models were employed to evaluate the efficacy of various novel therapeutic modalities including interleukin-3 (IL-3) and low dose aspirin. The efficacy of the latter was found to be interrelated. Low dose aspirin is capable of inhibiting the activity of the enzyme cyclooxygenase which is responsible for the metabolism of arachidonic acid towards the production of prostaglandins. This shifts the metabolism of arachidonic acid to the other pathway and leads to an overproduction of leukotrienes. The leukotrienes act as stimulators of IL-3 production, a positive cytokine in pregnancy which enhances placental and fetal development. In the current study we evaluated the IL-3 levels in pregnant women with APS and expanded our knowledge on the interrelationships between aspirin, arachidonic acid metabolites and IL-3 in the human system. METHODS: IL-3 levels were recorded in the serum of pregnant women with APS and compared to a control pregnant group. In addition peripheral blood mononuclear cells from healthy subjects were incubated with different concentrations of aspirin or with arachidonic acid metabolites (Leukotriene B4, C4 or PGE2), and IL-3 production in the culture fluids was evaluated. RESULTS: Serum level of IL-3 in pregnant patients with primary APS, APS secondary to SLE and SLE was lower in comparison to the control group. The in vitro studies revealed that only low dose aspirin (10 mg/μl) stimulated IL-3 production while higher doses of the drug failed to induce the cytokine generation. Leukotriene B4 and C4 were stimulatory whereas PGE2 acted as inhibitor of IL-3 production. CONCLUSIONS: The serum level of IL-3 is decreased to pregnant women with primary or secondary APS. Low dose aspirin is capable of stimulating EL-3 production in vitro most probably through an elevation of leukotriene production, which may explain its beneficial activity in preventing the manifestations of APS.  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