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   997645篇
  免费   75078篇
  国内免费   2616篇
耳鼻咽喉   12968篇
儿科学   34465篇
妇产科学   28460篇
基础医学   145293篇
口腔科学   27714篇
临床医学   90270篇
内科学   193584篇
皮肤病学   22913篇
神经病学   79106篇
特种医学   38386篇
外国民族医学   305篇
外科学   149490篇
综合类   23738篇
一般理论   385篇
预防医学   77819篇
眼科学   22608篇
药学   71869篇
  3篇
中国医学   2029篇
肿瘤学   53934篇
  2018年   10559篇
  2017年   8237篇
  2016年   9375篇
  2015年   10598篇
  2014年   14415篇
  2013年   22005篇
  2012年   28984篇
  2011年   30832篇
  2010年   18492篇
  2009年   17438篇
  2008年   28795篇
  2007年   30464篇
  2006年   30961篇
  2005年   29642篇
  2004年   28930篇
  2003年   27799篇
  2002年   26814篇
  2001年   46926篇
  2000年   48034篇
  1999年   40268篇
  1998年   11183篇
  1997年   10097篇
  1996年   10161篇
  1995年   9776篇
  1994年   9091篇
  1993年   8480篇
  1992年   32248篇
  1991年   31458篇
  1990年   31007篇
  1989年   29874篇
  1988年   27167篇
  1987年   27325篇
  1986年   25434篇
  1985年   24602篇
  1984年   18397篇
  1983年   15515篇
  1982年   9288篇
  1981年   8375篇
  1979年   16859篇
  1978年   12217篇
  1977年   10314篇
  1976年   9754篇
  1975年   10178篇
  1974年   12317篇
  1973年   11843篇
  1972年   10884篇
  1971年   10113篇
  1970年   9375篇
  1969年   8724篇
  1968年   8104篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Urticaria is a common condition, seldom of allergic origin. It is however not always possible to find the provoking allergen. The aim of the present study was to analyze if there was a relationship between urticaria and sensitization to common airborne allergens. A representative sample of 402 12 to 13-yr-old children answered a questionnaire on allergic diseases, 397 were interviewed by the study nurse and 371 underwent skin prick tests to cat, dog, horse, birch, timothy-grass, house dust mites and Cladosporium mould. Specific IgE-antibodies were analyzed to birch pollen and cat dander. Urticaria was more common in sensitized children, but the relationship between urticaria and sensitization was only statistically significant for birch pollen sensitization (OR 1.99, 95% CL 1.04-3.83), when tested in a multiple logistic regression model with the specified allergens as independent variables. A similar pattern was seen for birch-specific IgE-antibody levels, which was higher in children reporting urticaria than in those without. IgE-levels to cat dander did not show such a difference. Urticaria was statistically significantly associated with sensitization to birch-pollen, but not to other common inhalant allergens. We propose that intake of birch-pollen cross-reactive food-stuffs may be a neglected cause of urticaria and relapsing urticaria, in birch-pollen sensitized subjects.  相似文献   
992.
Several metabolic and hormonal parameters were evaluated in blood of two human subjects during simulation of an extended saturation dive. Increases in creatine kinase and an upward trend in cholesterol and glucose were observed after decompression. The levels of TTH and thyroxin went up in both subjects during exposure. The significant changes in cortisol, ACTH, insulin and C-peptide were a fingerprint of stress-reaction. After eight days of recovery most of the parameters returned to baseline values. The investigation suggests that the recompression treatment table did not cause pathological changes in the biochemical and hormonal parameters of humans.  相似文献   
993.
Objectives: To determine interobserver agreement between radiologists for computed tomography (CT) angiography and venography. CT venography of the lower extremities combined with standard CT angiography of the chest may result in an increased overall diagnosis rate of venous thromboembolism (pulmonary embolism or deep venous thrombosis).
Methods: The study had a retrospective cohort design. The population consisted of emergency department patients who were evaluated for suspected pulmonary embolism. A random sample of 50 patients diagnosed and treated for venous thromboembolism and 50 age- and gender-matched patients whose CT angiograms and venograms were read as negative were enrolled. The original reading (R1) was compared with readings of two study radiologists: R2, a general radiologist, and R3, a radiologist with fellowship training in cross-sectional imaging. All readers were blinded to each other.
Results: Both R2 and R3 found both CT angiogram and venogram components technically adequate in 95% (95% CI = 89% to 98%) and 86% (95% CI = 78% to 92%) of studies, respectively. The agreement was very good for CT angiography (lowest agreement = 92%; lowest κ = 0.83) and was good for CT venography (85%, κ = 0.65). In nine cases, R1 read the CT angiogram as negative but the venogram as positive for DVT, whereas both R2 and R3 read both components as negative in four of these nine, suggesting a false-positive isolated DVT rate of 44% (95% CI = 19% to 73%). In no case did R1 read both scan components as negative when R2 and R3 agreed on presence of pulmonary embolism or DVT.
Conclusions: Diagnosis of pulmonary embolism on CT angiography is more reliable than diagnosis of isolated DVT on CT venography.  相似文献   
994.
Objective: Evaluate a) the prevalence of developmental disabilities (DD) in children admitted to a general pediatrics inpatient unit, and b) the number of children admitted to the unit with previously undiagnosed developmental disability. Methods: Prevalence was evaluated through retrospective record review. Subjects: One hundred ninety children older than five months of age admitted to a general pediatric unit. Results: Of 190 children admitted, 155 (81.6%) had adequate developmental screening documented in the record. Forty-nine (25.7% of total, 31.6% of screened) had a developmental disability, 22 (12.1% of total, 14.8% of screened) had a previously unrecognized disability. Sample prevalence of DD was: cerebral palsy (6.8%), developmental delay or mental retardation (8.4%), language delay (4.6%), learning disability (8.2%), and hearing loss (1.5%). New diagnoses included: three children with probable mental retardation (MR), nine with learning disability (may include mild MR), seven with language delay, three with abnormal motor skills (fine and/or gross motor), one each of: neurofibromatosis type I, hearing loss, cerebral palsy, dysphagia. Some children had more than one new diagnosis. Conclusion: The prevalence of disabilities in a general pediatrics inpatient unit is much higher than the prevalence in the community. Because almost half of the disabilities were previously unrecognized, acute hospitalization is an excellent opportunity to conduct developmental screening.  相似文献   
995.
Coccidiosis of chickens, caused by species of Eimeria (Protozoa, Apicomplexa), is an intestinal disease of major economic importance worldwide. In the present study, the reproductive characteristics of a precocious line (designated E. tenella Rt3+15) from Australia were investigated in chicken embryos and the implications of the findings briefly discussed.  相似文献   
996.
997.
In this study, the relationship between mental training with biofeedback and swimmers' performance was investigated. The Wingate five-step approach was used as a mental preparation technique for enhancing the performance among 16-18 year-old pre-elite swimmers. Participants (n = 40) were randomly assigned to one of two conditions: (a) experimental--regular training plus the Wingate 5-step mental training program (adapted for swimming), and (b) control--regular training plus relaxing activities. After a baseline measurement, participants were tested on running and swimming five times during a 10-week period. Results indicated that the experimental group improved its performance over time on both running and swimming, with improvement being most substantial during transformation and realisation (steps 4 and 5). In contrast, the control group remained relatively stable on both dependent measures. Results are discussed in reference to previous work on the 5-step approach, including several methodological and theoretical aspects that are particularly relevant to the use of such interventions with other athletic tasks and populations.  相似文献   
998.
BACKGROUND: Ischemic preconditioning (IPC) has been found in animals to have a protective effect against future ischemic injury to muscle tissue. Such injury is unavoidable during some surgical procedures. To determine whether chronic ischemia in the lower extremities would imitate IPC and reduce ischemic injury during vascular surgery, we designed a controlled clinical study. PATIENTS AND METHODS: Two groups of patients at a university-affiliated medical centre with chronic lower-extremity ischemia served as models of IPC: 6 patients awaiting femoral distal bypass (FDB) and 4 scheduled for aortobifemoral (ABF) bypass grafting for aortoiliac occlusive disease. Seven patients undergoing elective open repair of an infrarenal abdominal aortic aneurysm (AAA) were chosen as non-IPC controls. Three hematologic indicators of skeletal-muscle injury, lactate dehydrogenase (LDH), creatine kinase (CK) and myoglobin, were measured before placement of the proximal clamp, during surgical ischemia, immediately upon reperfusion, 15 minutes after and 1 hour after reperfusion, and during the first, second and third postoperative days. RESULTS: Baseline markers of skeletal-muscle injury were similar in all groups. In postreperfusion samples, concentrations of muscle-injury markers were significantly lower in the 2 PC groups than in the control group. For example, at day 2, LDH levels were increased by about 30% over baseline measures in the elective AAA (control) group, whereas levels in the FDB and ABF groups remained statistically unchanged from baseline. Myoglobin in controls had increased by 977%, but only by 160% in the FDB and 528% in the ABF groups. CK levels, in a similar trend, were 1432% higher in the control group and only 111% (FDB) and 1029% (ABF) in the study groups. Taken together, these data represent a significant level of protection. CONCLUSIONS: Patients with chronic lower-extremity ischemia suffered less severe ischemic injury after a period of acute ischemia than those with acute ischemia alone. Ischemic preconditioning is one proposed mechanism to help explain this protective effect.  相似文献   
999.
PURPOSE: To compare measured visual field extent for a 6 degrees stimulus (typical size used in studies of infants) with a 1.5 degrees stimulus (similar to the largest size used in Goldmann perimetry) in young infants. METHODS: A total of 120 infants (60 each at 3.5 months and 7 months of age) and 24 adults were tested monocularly with a kinetic perimetry procedure using a black double-arc perimeter. Each subject was tested with either a 6 degrees or 1.5 degrees white sphere, which was mounted on a black wand and moved smoothly toward the intersection of the perimeter arms at 3.4 degrees /s. Visual field extent along each perimeter arm was defined as the median of 2 to 3 measurements of the position of the leading edge of the stimulus when the subject made an eye movement toward the stimulus. RESULTS: The 6 degrees stimulus produced larger measured visual field extent than the 1.5 degrees stimulus in 3.5-month olds (temporal field only) and in 7-month olds (nasal and temporal field), but not in adults. CONCLUSIONS: Using the testing conditions of the present study, increasing stimulus size beyond the largest used in a Goldmann perimeter (approximately 2 degrees) increases measured visual field extent in young infants, but not in adults. This may relate to differences in peripheral summation areas or to differences in attentional factors between infants and adults.  相似文献   
1000.
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