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   20684篇
  免费   1524篇
  国内免费   82篇
耳鼻咽喉   144篇
儿科学   513篇
妇产科学   376篇
基础医学   2951篇
口腔科学   632篇
临床医学   2304篇
内科学   4833篇
皮肤病学   304篇
神经病学   1934篇
特种医学   718篇
外科学   2611篇
综合类   338篇
一般理论   47篇
预防医学   1730篇
眼科学   566篇
药学   1148篇
中国医学   17篇
肿瘤学   1124篇
  2022年   121篇
  2021年   312篇
  2020年   195篇
  2019年   279篇
  2018年   310篇
  2017年   243篇
  2016年   298篇
  2015年   373篇
  2014年   484篇
  2013年   895篇
  2012年   1086篇
  2011年   1144篇
  2010年   672篇
  2009年   627篇
  2008年   1004篇
  2007年   1100篇
  2006年   1126篇
  2005年   1138篇
  2004年   1110篇
  2003年   1020篇
  2002年   1081篇
  2001年   230篇
  2000年   178篇
  1999年   248篇
  1998年   244篇
  1997年   233篇
  1996年   225篇
  1995年   189篇
  1994年   167篇
  1993年   187篇
  1992年   176篇
  1991年   162篇
  1990年   166篇
  1989年   165篇
  1988年   151篇
  1987年   155篇
  1986年   153篇
  1985年   175篇
  1984年   207篇
  1983年   191篇
  1982年   232篇
  1981年   207篇
  1980年   204篇
  1979年   145篇
  1978年   149篇
  1977年   142篇
  1976年   153篇
  1975年   147篇
  1974年   130篇
  1973年   114篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Derived indices on the Trail Making Test (TMT), a test often used to screen for cognitive impairment, were examined in a sample of 191 narcotic/other opiate abusers in drug abuse treatment programs. A mixed race sample was drawn from electronic files of data from the Drug Abuse Treatment Outcome Study (DATOS). The DATOS was a naturalistic, prospective cohort study that collected data from 1991-1993 in 96 programs in 11 cities in the United States. Data were analyzed to determine the effects of demographic variables on derived indices created by adding, subtracting, multiplying, and dividing parts A and B of the TMT in this large treatment sample of substance abusers. The variables of age, ethnicity, and education were statistically significant for the total score (A + B) and interaction score (A x B/100) derived indices of the TMT. In addition, the difference score (B - A) was statistically significant for education. The ratio score (B/A) was not significant for any demographic variable.  相似文献   
992.
The Trail Making Test (TMT) is often used for screening cognitive impairments in substance abusers. A possible limitation of the TMT in clinical settings is that substance abusers may malinger and give poor effort. In this study, previously validated cutting scores for malingering were applied to a sample of 7689 substance abusers (primary drug of abuse-number of subjects: Alcohol-1000, Marijuana-259, Hallucinogen-128, Cocaine/crack-4306, Heroin-1548, Narcotics/other opiates-191, Sedatives-72, Amphetamines-185) in drug abuse treatment programs. A mixed race sample was drawn from electronic files of data from the Drug Abuse Treatment Outcome Study (DATOS). The DATOS was a naturalistic, prospective cohort study that collected data from 1991-1993 in 96 programs in 11 cites in the United States. Data were analyzed to determine the number of substance abusers that fell beyond the preset malingering cutting scores on the TMT in this very large sample of substance abusing patients in treatment settings. The TMT variables of seconds to complete Part A and Part B, and the ratio score of Part B divided by Part A (B/A), ranged from no subjects beyond the preset cutting score for Part B to 2.28% (175 of 7689 subjects) for Part A to 9.74% (749 of 7689 subjects) for the ratio score. Most substance abusers fell within preset cutting score ranges, a finding that suggests that their scores are valid. Another interpretation of the data, however, is that the cutoff scores were not particularly sensitive to biased responding. Further research is indicated.  相似文献   
993.
Derived indices on the Trail Making test (TMT), a test often used for screening for cognitive impairment, were examined in a sample of hallucinogen abusers in drug abuse treatment programs. A mixed race sample (N = 128) was drawn from electronic files of data from the Drug Abuse Treatment Outcome Study (DATOS). The DATOS was a naturalistic, prospective cohort study that collected data from 1991 to 1993 in 96 programs in 11 cities in the United States. Data were analyzed to determine the effects of demographic variables on derived indices created by adding, subtracting, multiplying, and dividing Parts A and B of the TMT in this large treatment sample of hallucinogen abusers. The variables of sex and age were not statistically significant for derived indices of the TMT. The variable of ethnicity was significant for the all derived indices except the ratio score (divide Part B by Part A) and the variable of education was significant for the interaction score (multiply Part A by Part B and divide by 100).  相似文献   
994.
995.
996.
Triphenyl phosphite (TPP) has been examined extensively in our lab to assess its degenerative effects on the visual pathway of the European ferret. Tanaka et al. [Fundam. Appl. ToxicoL 22 (1994) 577; J. Toxicol. Environ. Health 58 (1999) 215] reported an age-related pattern of fiber and cell body degeneration progressing from retinal axons and lateral geniculate nucleus (LGN) neurons to the visual cortex. These studies, however, did not address whether TPP exposure results in retinal ganglion cell (RGC) degeneration, nor did they quantify the degenerative effects in the LGN. The purpose of this study was to quantify the effects of TPP on RGCs and LGN neurons. We administered single subcutaneous injections of TPP (1184 mg/kg) to 13 ferrets for histological analysis. The retinae were examined as whole-mounts and the brains sectioned parasagittally (50 microm). RGC countsfrom matched areas of nasal retina showed significantly fewer (21%) neurons in the TPP-treated ferrets (Sd = 282 +/- 52S.D.; 7d = 284 +/- 12S.D.) compared with control (359 +/- 42S.D.). No significant difference in cell number was found in temporal retina, even though this region contained, on average, 13% fewer ganglion cells in TPP-treated ferrets (Sd = 3344 +/- 44S.D.; 7d = 357 +/- 39S.D. versus control = 394 +/- 72S.D.). The mean soma sizes and RGC cell size distributions for nasal and temporal retinae were not significantly different for any group. LGN neurons were significantly smaller (28%) than control in the TPP-treated ferrets (Sd = 155 microm2 +/- 23S.D.; 7d = 152 microm2 +/- 28S.D. versus control = 214 microm2 +/- 9S.D.). Cell size distributions for LGN neurons were shifted toward smaller cell sizes in both TPP-treated groups compared to control.  相似文献   
997.
This study evaluated the prevalence, risk factors and morbidity associated with specific phobia of illness. Subjects were from a random, community telephone survey of 500 persons age 40 to 65 who lived in Johnson County, Iowa, USA. Forty-three subjects reported that illness fears substantially bothered them personally or affected their medical care, work, or social life. Twenty-one of these subjects could be contacted and agreed to a semistructured interview designed to diagnose specific phobia of illness and screen for other common psychiatric disorders. Based on the interview, 10 subjects met the criteria for specific phobia of illness, 10 for major depressive disorder, 5 for obsessive-compulsive disorder, 5 for generalized anxiety disorder, 4 for hypochondriasis, 4 for panic disorder and 4 for specific phobia other than illness. Assuming subjects not interviewed were similar to subjects who were, the community prevalence of specific phobia of illness is 4.0%. Among the 10 subjects with specific phobia of illness, 7 had prior negative experiences with illness and 8 had comorbid Axis I disorders. The phobia interfered with medical care as well as social functioning for many subjects. These results suggest a prevalence rate and risk factors that will be useful for additional studies of illness phobia.  相似文献   
998.
BACKGROUND: Brief depression screens have recently been developed, but their use in older or minority populations has not been studied. To date, optimal depression screens and optimal cutpoints have not been identified for middle-aged and older Hispanic primary care patients. METHODS: This study compares multiple versions of four depression screening tools--Center for Epidemiologic Studies-Depression Scale (CES-D), Geriatric Depression Scale, Yale 1-question screen, and PRIME-MD 2-question screen--to the Composite International Diagnostic Interview (CIDI), the World Health Organization's diagnostic interview, which has been validated in adult Latino populations, to assess convergent validity. Three hundred and three Puerto Rican primary care patients age 50 and older completed all screens and the CIDI in a face-to-face interview. Sensitivity and specificity for each screen were calculated, and receiver operator characteristic curves were generated. RESULTS: Between 34% and 61% of patients screened positive for depression, depending on the measure, with 12% meeting DSM-IV criteria for major depression (CIDI). The 10-item CES-D worked best to identify major depression in this population, with a sensitivity of 84% and specificity of 64% using a cutpoint of 3. CONCLUSIONS: The 10-item CES-D, which takes about 2 minutes to administer, is a useful tool for identifying Puerto Rican patients in need of an in-depth mental health evaluation in a primary care setting. A lower cutpoint of 3 (instead of the conventional cutpoint of 4) is recommended for optimal sensitivity and specificity.  相似文献   
999.
BACKGROUND: This report describes the associations between sleep complaints and reported visual impairment in an urban community-residing older adult sample. METHODS: A total of 1118 volunteers from a biracial cohort participated in the study (mean age = 74 +/- 6; mean body mass index = 28 +/- 10). Volunteers were recruited using a stratified, cluster sampling technique. In a standard order, several questionnaires were administered, soliciting information on socioeconomic status, physical health, social support, and emotional experience. The physical health questionnaire included questions on whether or not the volunteer experienced sleep disorder, visual impairment, heart disease, respiratory disease, arthritis, and hypertension. In this report, we present data on the prevalence of reported sleep problems and visual impairment among older adults. RESULTS: Of the total sample, 9% used sleep medicine, 25% reported difficulty falling asleep, 52% indicated experiencing difficulty maintaining sleep, 28% reported waking up early in the morning, and 12% reported daytime sleep longer than 2 hours. Chi-square results showed greater sleep complaints for volunteers with visual impairment. Consistent with these results, analysis of variance revealed that visually impaired volunteers had a higher index rate of sleep disturbance (F((1, 1110)) = 35.32, p <.0001). CONCLUSIONS: These data provide evidence that older adults reporting visual impairment are also likely to report sleep complaints. This verifies laboratory findings of an association of ophthalmic diseases with sleep-wake problems and with circadian rhythm abnormalities.  相似文献   
1000.
Selenium (Se) is an essential micronutrient for human health. The biological roles of the essential micronutrient Se are attributed to its presence in a range of 20-30 selenoproteins including the cytosolic and phospholipid hydroperoxide glutathione peroxidases (GPX1 and GPX4). It has been suggested that GPX4 may play a role in regulation of leukotriene biosynthesis and thus inflammation. In eukaryotes Se is incorporated into selenoproteins as the amino acid selenocysteine in a process requiring a stem-loop within the 3' untranslated region (3'UTR) of the mRNA. In this study the region of the GPX4 gene corresponding to the 3'UTR was scanned for mutations in a group of 66 volunteers. The data show a T/C variant at position 718. The distribution of this SNP in our population was 34% CC, 25% TT and 41% TC; i.e., it is in Hardy-Weinberg equilibrium. Individuals of different genotypes exhibited significant differences in the levels of lymphocyte 5-lipoxygenase total products, with C718 showing increased levels of those products compared to T718 and T/C718 (36% and 44% increases, respectively). The data suggest that the SNP718 that we have identified has functional effects and support the hypothesis that GPX4 plays a regulatory role in leukotriene biosynthesis.  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