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   10354篇
  免费   538篇
  国内免费   23篇
耳鼻咽喉   80篇
儿科学   304篇
妇产科学   283篇
基础医学   1810篇
口腔科学   212篇
临床医学   981篇
内科学   1839篇
皮肤病学   169篇
神经病学   1092篇
特种医学   471篇
外科学   1242篇
综合类   88篇
一般理论   3篇
预防医学   891篇
眼科学   131篇
药学   686篇
中国医学   29篇
肿瘤学   604篇
  2022年   65篇
  2021年   143篇
  2020年   92篇
  2019年   128篇
  2018年   157篇
  2017年   121篇
  2016年   159篇
  2015年   209篇
  2014年   268篇
  2013年   379篇
  2012年   639篇
  2011年   676篇
  2010年   391篇
  2009年   357篇
  2008年   604篇
  2007年   631篇
  2006年   614篇
  2005年   634篇
  2004年   576篇
  2003年   512篇
  2002年   527篇
  2001年   96篇
  2000年   57篇
  1999年   91篇
  1998年   124篇
  1997年   91篇
  1996年   80篇
  1995年   85篇
  1994年   67篇
  1993年   63篇
  1992年   42篇
  1991年   58篇
  1990年   44篇
  1989年   43篇
  1985年   45篇
  1984年   51篇
  1983年   42篇
  1982年   45篇
  1981年   40篇
  1974年   44篇
  1933年   71篇
  1932年   59篇
  1931年   57篇
  1930年   52篇
  1929年   44篇
  1928年   45篇
  1927年   52篇
  1926年   54篇
  1925年   49篇
  1924年   52篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
OBJECTIVE: Somatization is prevalent in primary care and is associated with substantial functional impairment and healthcare utilization. However, instruments for identifying and monitoring somatic symptoms are few in number and not widely used. Therefore, we examined the validity of a brief measure of the severity of somatic symptoms. METHODS: The Patient Health Questionnaire (PHQ) is a self-administered version of the PRIME-MD diagnostic instrument for common mental disorders. The PHQ-15 comprises 15 somatic symptoms from the PHQ, each symptom scored from 0 ("not bothered at all") to 2 ("bothered a lot"). The PHQ-15 was administered to 6000 patients in eight general internal medicine and family practice clinics and seven obstetrics-gynecology clinics. Outcomes included functional status as assessed by the 20-item Short-Form General Health Survey (SF-20), self-reported sick days and clinic visits, and symptom-related difficulty. RESULTS: As PHQ-15 somatic symptom severity increased, there was a substantial stepwise decrement in functional status on all six SF-20 subscales. Also, symptom-related difficulty, sick days, and healthcare utilization increased. PHQ-15 scores of 5, 10, 15, represented cutoff points for low, medium, and high somatic symptom severity, respectively. Somatic and depressive symptom severity had differential effects on outcomes. Results were similar in the primary care and obstetrics-gynecology samples. CONCLUSIONS: The PHQ-15 is a brief, self-administered questionnaire that may be useful in screening for somatization and in monitoring somatic symptom severity in clinical practice and research.  相似文献   
52.
53.
Correlation of MRT imaging with real-time axiography of TMJ clicks   总被引:2,自引:0,他引:2  
There is a series of tools useful for gathering diagnostic information on patients with temporomandibular joint disorders. Tracings of the joint movement (axiography) provide useful information about the motion of the joints. Since the availability of electronic axiographic tracers, the movement of the condyles can be resolved with high resolution both in space and in time. In order to obtain information about the anatomical relation of the joint surfaces and the disc, magnetic resonance tomography imaging (MRI) is routinely carried out. It is common practice to take MR images of the joints with the mouth closed and fully open. In order to correlate the MR images with the axiographic tracings, a series of images can provide much more information. In this study we examined patients with distinct temporomandibular joint (TMJ) clicks. In one case, the click occurs once a day, while in the other case the click happens every time the mouth is opened. In order to obtain information about both motion and anatomical relation of the TMJ at and around the position where the clicks occur, we recorded a series of MRI scans with the mouth gradually opened and before and after joint clicks. Real-time axiographic tracings during the click were taken with an optimized system where the polar moments were reduced as much as possible to follow the movement during the click. These tracings were correlated with the MRI scans to determine the exact internal conditions of the TMJ and the changes during the click. In particular cases, the additional information provided by this procedure can be useful in deciding whether and which therapeutic intervention is advisable.  相似文献   
54.
Summary Turning a rabbit on a turn-table for a few degrees induces compensatory eye-movements and results in an asymmetry of tonus in the optomotor system. If the visual input is discontinued (darkness), this asymmetry decays and the eyes drift back to the mid-position within 12–18 sec. The equalization of such asymmetries of tonus under normal conditions and under curare is described. Tonus asymmetries induced by tilting the animals about the longitudinal axis are neither compensated under visual, nor under non-visual, conditions. Recordings were taken from oculomotor neurons, and changes of their firing frequencies were used as a measure for eye movements.A preliminary report was given at the spring meeting of the German Physiological Society 1973.Supported by the Deutsche Forschungsgemeinschaft, SFB 33.  相似文献   
55.
Conversion of ADP to ATP in crude and purified brain and liver mitochondrial preparations from dilute and non-dilute strains of mice was studied. ATP production was found to be appreciably greater in brain mitochondria from 14-, 21-, and 35-day old dilute mice; maximum differences were observed at 21 days. No significant differences in conversion of ADP to ATP in liver mitochondrial preparations were found. The differences in brain mitochondria from these mice seemed not to be due to decreased ATPase activity in dilute mice. Dilute 21-day old DBA/2J mice were found to have approximately 25% more ATP in whole brain homogenates than 21-day old non-dilute C57BL/6J mice. These findings suggest a correlation between oxidative phosphorylation and seizure susceptibility in mice of dilute genotypes. Since similar differences in ATP production were found between the DBA/2J and C57BL/6J strains, and between dilute lethal (d1/d1) and littermate non-lethal controls (D/d1), thed locus would seem to be implicated.This research was partially supported by Research Grant No. MH-13026 from the National Institute for Mental Health and Grant No. GM-14547 from National Institute of General Medical Science.  相似文献   
56.
57.
Three methods by which to determine absolute total cerebral hemoglobin concentration (tHb in micromol/L) by near-infrared spectrophotometry (NIRS) have evolved: (1) tHbo, requiring oxygenation changes and arterial oxygen saturation measurements as a reference using a relative NIRS algorithm, (2) tHbg, using a geometrical multidistance principle and (3) tHbgo, a combination of both. The aim of this study was to compare the three methods quantitatively. Sixteen clinically stable preterm infants with a mean gestational age of 29.6 (range of 25.1-36.4) weeks, birthweight of 1386 (680-2820) g and a postnatal age of 2.5 (0.5-6) days, who needed supplemental oxygen, were enrolled. The mean+/-standard deviation tHbg was 150.2+/-41.8 micromol/L (range of 61.6-228.9 micromol/L), the tHbo was 62.1+/-27.2 micromol/L (26.0-110.8 micromol/L) and the tHbgo was 89.3+/-45.6 micromol/L (26.5-195.9 micromol/L). The correlation coefficient among the three methods were tHbg and tHbgo r=0.736; tHbo and tHbgo r=0.938; tHbg and tHbo r=0.598. A multiple regression with variable selection by Mellow's C(p) showed, that tHbg was correlated to the birthweight, the postnatal age, the heart rate and the pCO2 (r(2)=0.588), tHbo and tHbgo were associated with the hemoglobin concentration in the blood, the mean arterial blood pressure and the pCO2 (r(2)=0.493 and 0.406, respectively). The three methods (tHbg, tHbo, and tHbgo) give systematically different tHb readings and large intersubject variability.  相似文献   
58.
BACKGROUND: Clarithromycin is postulated to possess immunomodulatory properties in addition to its antimicrobial activity. OBJECTIVE: To evaluate the effect of clarithromycin on serum and nasopharyngeal cytokine and chemokine concentrations in children with an acute exacerbation of recurrent wheezing. METHODS: Children with a history of recurrent wheezing or asthma and who presented with an acute exacerbation of wheezing were enrolled in a double-blind, randomized trial of clarithromycin vs placebo. Concentrations of tumor necrosis factor alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin-1beta (IL-1beta), IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor, RANTES, eotaxin, macrophage inflammatory protein 1alpha, macrophage inflammatory protein 1beta, and monocyte chemoattractant protein 1 were measured in serum and/or nasopharyngeal aspirates before, during, and after therapy. Mycoplasma pneumoniae and Chlamydophila pneumoniae infection were evaluated for by polymerase chain reaction and serologic testing. RESULTS: Nasopharyngeal concentrations of TNF-alpha, IL-1beta, and IL-10 were significantly and persistently lower in children treated with clarithromycin compared with placebo. There tended to be a greater effect of clarithromycin on nasopharyngeal cytokine concentrations in patients with evidence of M. pneumoniae or C. pneumoniae infection. No significant differences were detected in serum cytokines for children treated with clarithromycin compared with placebo. CONCLUSION: Clarithromycin therapy reduces mucosal TNF-alpha, IL-1beta, and IL-10 concentrations in children with an acute exacerbation of recurrent wheezing.  相似文献   
59.
BACKGROUND: Hepatitis B virus (HBV) DNA often remains detectable in serum despite clinical recovery and loss of HBsAg. OBJECTIVE: To study whether coinfection with HIV and HCV influence the chance of detecting HBV DNA in sera with markers of past hepatitis B. STUDY DESIGN AND RESULTS: The test panel included 160 anti-HBc-positive/HBsAg-negative sera collected in the diagnostic setting. The following parameters were determined in the sera: anti-HIV (32% positive), anti-HCV (34% positive), HCV RNA (18% positive), and anti-HBs (37% positive). A highly sensitive PCR (90%-detection limit 100 copies/ml) amplifying the terminal protein (TP) region of HBV was established and HBV DNA was detected in 12.5% of the samples. In 70% of these samples, the HBV DNA concentration was below 500 copies/ml as measured by real-time PCR in the S gene. Logistic regression analysis revealed that the chance of detecting HBV DNA was increased by a positive HCV serostatus (odds ratio 5.0, 95%-CI 1.6-15.7), whereas HIV coinfection (odds ratio 2.0, 95%-CI 0.7-5.8), anti-HBs (odds ratio 0.9, 95%-CI 0.3-2.6), and HCV RNA status (odds ratio 0.4, 95%-CI 0.1-1.7) had no statistically significant influence. In contrast, the chance of detecting HCV RNA in the subgroup of anti-HCV-positive sera was increased by HIV coinfection (odds ratio 4.5, 95%-CI 1.2-17.4). Sequencing of the TP PCR products revealed neither a specific phylogenetic origin of the circulating HBV DNA nor clustering of uncommon mutations in the TP region. CONCLUSIONS: The prevalence of HBV DNA in serum of anti-HBc-positive/HBsAg-negative subjects correlates with HCV rather than HIV serostatus.  相似文献   
60.
Natural killer (NK) cells and cytotoxic T lymphocytes (CTL), the functional coordination of which are governed by various signal substances, are crucial in the body’s defense of tumor and virus-infected cells. We investigated the role of various neurotransmitters and hormones on the regulation of functional parameters, including NK cell cytotoxicity, and the migration of NK cells and CTL within a three-dimensional collagen lattice. Using peripheral blood CTL and NK cells, we show that the neurotransmitters endorphin, histamine and substance P increase NK cell cytotoxicity, while norepinephrine inhibits cytotoxicity. Moreover, substance P reduces migratory activity, while norepinephrine increases NK cell and CTL migration. Furthermore, all three steroid hormones which were investigated, namely cortisone, testosterone, and estradiol, had regulatory influence on both cytotoxicity and migration of NK cells. These results further specify the functional basis of the complex interconnection between the immune and neuro-endocrine systems.  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