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   4608篇
  免费   8篇
  国内免费   1篇
电工技术   3篇
综合类   6篇
化学工业   138篇
金属工艺   21篇
机械仪表   7篇
建筑科学   11篇
矿业工程   1篇
能源动力   8篇
轻工业   21篇
水利工程   3篇
石油天然气   1篇
无线电   29篇
一般工业技术   97篇
冶金工业   4246篇
原子能技术   2篇
自动化技术   23篇
  2023年   5篇
  2022年   7篇
  2021年   9篇
  2020年   8篇
  2019年   13篇
  2018年   8篇
  2016年   7篇
  2015年   5篇
  2014年   7篇
  2013年   19篇
  2012年   15篇
  2011年   34篇
  2010年   12篇
  2009年   16篇
  2008年   17篇
  2007年   10篇
  2006年   17篇
  2005年   12篇
  2004年   10篇
  2003年   14篇
  2002年   9篇
  2001年   18篇
  2000年   12篇
  1999年   147篇
  1998年   1423篇
  1997年   787篇
  1996年   519篇
  1995年   259篇
  1994年   235篇
  1993年   257篇
  1992年   37篇
  1991年   42篇
  1990年   39篇
  1989年   50篇
  1988年   51篇
  1987年   30篇
  1986年   26篇
  1985年   27篇
  1984年   4篇
  1983年   11篇
  1982年   13篇
  1981年   22篇
  1980年   38篇
  1978年   4篇
  1977年   86篇
  1976年   193篇
  1975年   7篇
  1972年   4篇
  1971年   4篇
  1965年   4篇
排序方式: 共有4617条查询结果,搜索用时 31 毫秒
951.
We describe a 31-year-old man who developed sudden painful loss of vision in the right eye and was found to have a retrobulbar optic neuropathy. Magnetic resonance (MR) imaging gave normal results, and a diagnosis of retrobulbar optic neuritis was made. The patient was treated with oral prednisone, but he continued to lose vision in the right eye and then began to lose vision in the left eye. Repeat MR imaging performed eight weeks after the initial study showed a giant intracranial aneurysm compressing the right and left optic nerves. Cerebral angiography revealed that the aneurysm arose from the origin of the right ophthalmic artery. Treatment of the aneurysm by a trapping procedure resulted in improvement in vision in the left eye but no change in vision in the right eye. This report emphasizes the difficulty in imaging intracranial aneurysms of various sizes, the rapidity with which intracranial aneurysms can enlarge, and the importance of continued follow-up examinations in patients thought to have idiopathic optic neuritis.  相似文献   
952.
Based on the Tesla‐type turbomachinery principle of operation, a fan consisting of flat, round discs arranged in between two separate channels, which generate two air flows in opposite directions, is investigated. Simulations of a model with one disc as well as a five‐channel model at different grids were performed. With almost unthrottled operation, secondary flows could be determined at velocity magnitudes of up to 20 % of the mean main flow velocity, with secondary currents reaching up to 50 % in throttled operation. Besides high dissipation and recirculation, these secondary currencies are found to be capable of reducing the overall efficiency of the system. Thus, topic of further investigations is the potential of increasing efficiency by means of straighteners and geometric adaptions.  相似文献   
953.
Epidemiological aspects of bovine viral diarrhoea virus (BVDV) infections were studied longitudinally in a large dairy herd for three years. At the start of the study, practically all the cows more than four years old had BVDV antibody titres, whereas the younger stock were almost all seronegative. The spread of the virus was monitored in a part of the population that contained only transiently viraemic cattle and in another part that contained persistently viraemic calves. Among the lactating cows the virus circulated for two-and-a-half years, although they had no direct contact with persistently viraemic cattle during this period. The highest transmission rate occurred when a large number of susceptible heifers was added to the population of cows that contained transiently viraemic cattle. The circulation of BVDV among the lactating cows ceased while 27 seronegative cows were still present. Both findings are in accordance with predictions from simple epidemic models. The susceptibility of the cows that remained seronegative was confirmed experimentally. In contrast with the limited circulation of BVDV caused by transiently viraemic cattle, virtually all susceptible cattle that came into contact with a persistently viraemic calf became seropositive within three months. Transplacental BVDV infections were not detected in the calves born to cows that had antibodies against the virus due to an infection that had occurred at least four years earlier. Transplacental transmission of BVDV did not occur in most of the pregnant cows that were infected before approximately the 60th day of gestation, but when cows became infected later in gestation the virus virtually always invaded the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
954.
OBJECTIVE: Our purpose was to evaluate our experience with estrogen replacement in women with a history of early-stage endometrial cancer and to determine whether it increased the risk for recurrence or death. STUDY DESIGN: A retrospective review was performed of 123 women with surgical stage I and II endometrial adenocarcinoma treated between 1984 and 1994; 62 had received estrogen replacement therapy after cancer therapy. Sixty-one women received no estrogen. Variables analyzed included age parity, surgical stage, grade, depth of myometrial invasion, presence of intercurrent illnesses, duration of follow-up, and duration of estrogen replacement, if applicable. Outcome variables assessed included recurrence rate, time to recurrence, and disease-free interval. RESULTS: The estrogen replacement therapy group had earlier stage disease (p = 0.04) and less severe depth of invasion (p = 0.003); however, the total number of deaths in each group was not significantly different. The disease-free survival in the estrogen replacement therapy group did not differ significantly compared with those not receiving estrogen replacement therapy. The data are suggestive of improved disease-free survival in the estrogen replacement therapy group, which may be related to differences in age, stage, grade, and depth of invasion. The overall recurrence rate was 6.5%, with an overall death rate of 1.6%. CONCLUSIONS: There is no evidence to suggest that estrogen decreased the disease-free interval or increased the risk for recurrence in early-stage disease.  相似文献   
955.
956.
The authors report the occurrence of the first three clinical cases of Lyme disease in Mato Grosso do Sul State, including the first case of Lyme meningitis in Brazil. These were identified by clinical and laboratorial criteria. Anti-Borrelia burgdorferi antibody search was carried out through ELISA and Western Blotting techniques, the former providing identification of IgG class antibodies alone, in one only of those cases. Through Immunoblotting, the following features were found in serum: 5 IgG and 2 IgM bands for the first case; 7 IgG and 2 IgM bands for the second; and 5 IgG and 6 IgM bands for the third. In the latter, presence fo specific antibodies was searched in liquor, due to lymphomonocitary meningitis occurrence, and one IgM band was detected. After antibiotic therapy, all patients exhibited significant clinical and laboratorial improvement in their conditions along with symptom regression to the present moment.  相似文献   
957.
958.
959.
960.
OBJECTIVES: To evaluate if caregivers are reliable informants concerning memory deficits in patients with Alzheimer's disease (AD). DESIGN: Responses of caregivers of patients with probable AD and responses of healthy control subjects on a standardized memory questionnaire were compared with objective measures of cognition (Consortium to Establish a Registry for Alzheimer's Disease neuropsychological battery) and with clinical estimates of activities of daily living, depression, and psychopathology (Consortium to Establish a Registry for Alzheimer's Disease [CERAD] clinical assessment battery) using the Self-report Memory Questionnaire. SETTING: A federally funded AD research center. SUBJECTS: The referred sample included 117 patients with probable AD, their informants, and 41 healthy control subjects age-matched to the patients. Patients and control subjects were between the ages of 58 and 85 years, had between 9 and 19 years of education, and were in good health. EXCLUSIONS: Patients who did not meet NINCDS-ADRDA criteria of probable AD. MAIN OUTCOME MEASURE: The optimal number of questionnaire items yielding the best combination of sensitivity and specificity. RESULTS: An abbreviated version of the scale, renamed the Short-Memory Questionnaire, had excellent specificity and sensitivity for identifying dementia. Positive and negative predictive values were 63.5% and near 100%, respectively. The Short-Memory Questionnaire showed good reliability, internal consistency, and external validity. Caregiver appraisals of memory deficits significantly correlated with objective measures of memory and also with generalized cognitive dysfunction. CONCLUSIONS: Caregivers of patients with AD are reliable informants of their relatives' deficits. The Short-Memory Questionnaire is an easily administered, informant-based scale that may be useful in clinical settings or epidemiologic studies to screen out persons with memory difficulties.  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