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   2099篇
  免费   4篇
  国内免费   2篇
电工技术   2篇
综合类   1篇
化学工业   33篇
金属工艺   2篇
机械仪表   4篇
能源动力   6篇
轻工业   4篇
水利工程   11篇
无线电   9篇
一般工业技术   23篇
冶金工业   1993篇
原子能技术   1篇
自动化技术   16篇
  2023年   2篇
  2022年   4篇
  2021年   3篇
  2020年   1篇
  2019年   2篇
  2018年   2篇
  2017年   4篇
  2016年   5篇
  2015年   3篇
  2014年   5篇
  2013年   7篇
  2012年   2篇
  2011年   7篇
  2010年   13篇
  2009年   5篇
  2008年   6篇
  2007年   3篇
  2006年   4篇
  2005年   8篇
  2004年   3篇
  2003年   1篇
  2002年   4篇
  2001年   3篇
  2000年   4篇
  1999年   89篇
  1998年   581篇
  1997年   341篇
  1996年   206篇
  1995年   135篇
  1994年   113篇
  1993年   137篇
  1992年   12篇
  1991年   21篇
  1990年   20篇
  1989年   22篇
  1988年   34篇
  1987年   21篇
  1986年   17篇
  1985年   26篇
  1983年   3篇
  1982年   8篇
  1981年   13篇
  1980年   16篇
  1979年   4篇
  1978年   7篇
  1977年   50篇
  1976年   122篇
  1975年   2篇
  1973年   1篇
  1955年   3篇
排序方式: 共有2105条查询结果,搜索用时 15 毫秒
171.
BACKGROUND: Infection with cancer-linked human papillomavirus (HPV) types such as HPV type 16 (HPV16) is the most important risk factor in the development of cervical cancer. It has been shown that immunoglobulin G (IgG) antibody responses against HPV16 virus-like particles (VLPs) are specifically associated with genital HPV16 infection. PURPOSE: The aim of this study was to determine the temporal relationships between the presence of HPV16 VLP-specific IgGs, HPV16 infection patterns, and the course of premalignant cervical disease. METHODS: Plasma samples from 133 women who had been diagnosed originally with mild to moderate cervical dyskaryosis and enrolled in a prospective non-intervention cohort study conducted in Amsterdam, The Netherlands, from 1991 through 1996 were analyzed for the presence of HPV16 VLP-specific IgGs by use of an enzyme-linked immunosorbent assay. A detailed analysis was performed on 43 women with different HPV16 infection patterns during a follow-up period of 10-34 months. Progression or regression of cervical intraepithelial neoplasia (CIN) lesions was monitored by cytologic and colposcopic testing at intervals of 3-4 months. HPV typing in cervical smears was performed by use of a polymerase chain reaction-based assay. Statistical analysis of the serologic data was performed by use of the Mann-Whitney U test or 2 x 2 table analyses. RESULTS: The presence of HPV16 VLP-specific IgGs in the plasma of the patients was found to be associated with the presence of HPV16 DNA in the cervical smear. Significantly higher proportions of patients with persistent HPV16 infections (i.e., who were polymerase chain reaction positive in three to 11 consecutive tests) than of patients with cleared HPV16 infections were found to be positive for the presence of HPV16 VLP-specific IgGs (18 [69.2%] of 26 versus nine [28.1%] of 32, respectively; P = .003). HPV16 VLP-specific IgGs were consistently detected in all women (n = 11) who were persistently HPV16 DNA positive during follow-up and whose disease ultimately progressed to CIN III (histologically diagnosed severe dysplasia or carcinoma in situ). CONCLUSION: HPV16 VLP-specific IgG responses are present in the plasma of a majority of patients with persistent HPV16 infections and histologically confirmed high-grade lesions but only in a smaller subset of patients with cleared HPV16 infections and either normal cervical histology or low-grade CIN lesions. IMPLICATIONS: These results suggest that HPV16 VLP-specific antibodies are not responsible for the clearance of virally induced CIN lesions but that they might, in patients with persistent HPV16 infections, be indicative of an increased cervical cancer risk.  相似文献   
172.
173.
174.
Optic chiasmatic-hypothalamic gliomas (OCHGs) have been considered benign tumors and self-limiting in growth potential because of their histological appearance. Unfortunately, most clinical series have reported significant morbidity and mortality especially with the more extensive, posteriorly positioned tumors. The biological behavior of OCHGs is age-dependent, with patients younger than five years and older than 20 years typically having tumors that exhibit aggressive growth. There are no specific pathological features to help differentiate the clinical behavior of such tumors. The emergence of modern imaging techniques, including magnetic resonance imaging (MRI), has facilitated the monitoring of the natural history of the disease and the determination of the effects of therapy. Most patients with OCHGs survive for many years. While the natural history of an OCHG for any individual may be indeterminate, enough data are now available from large series to make recommendations for treatment. Our current treatment policy for patients with OCHGs in the context of NF-I without visual failure is a conservative one involving CSF shunting for hydrocephalus if present and medical therapy for endocrinologic dysfunction. Patients with or without NF-I with visual deterioration or progressive neurological deficits and a rapidly expanding suprasellar mass lesion are treated surgically. After tumor resection, patients whose vision is significantly compromised or who show progression of their disease on serial neuroimaging scans receive chemotherapy. If chemotherapy proves ineffective in disease stabilization, then considerations of radiation therapy are given to children over five years old.  相似文献   
175.
The authors present a new method to locate the tumor bed after lumpectomy. The method relies on accumulation of Ga-67 at the surgical site. This technique was useful in identifying the tumor bed in six candidates for breast conserving surgery and radiation therapy. This method may be applicable in other soft tissue malignancies that require postoperative radiation.  相似文献   
176.
BACKGROUND: There is circumstantial evidence that human sperm count may have declined during past decades. The purpose of this study was to identify the association between semen quality and year of birth. METHODS: The study comprised 8608 men consulting four Danish medical centres from 1968 to 1992 because of infertility. Data on semen quality and urogenital disorders were obtained from medical records while lifestyle data were collected from a subset of the population by a postal questionnaire (response 80%). Semen characteristics were analysed as a linear function of year of birth, centre, season and calendar year at time of semen examination, sexual abstinence and lifestyle factors. Effects of age were accounted for by restriction and stratified analysis. RESULTS: The sperm count declined with increasing year of birth at two of the four centres, but this association disappeared when confounders were adjusted for. Within the subset of men born 1950-1970 we revealed a decrease in the average sperm count by 1.9 mill/ml (95% confidence interval [CI]: 1.45, 2.27) per one advancing year of birth. This finding was consistent across centres even after adjustment for effects of covariates. The proportion of morphologically normal sperm cells changed in parallel with the sperm count, while semen volume did not decline in any time periods. CONCLUSIONS: We found a birth cohort effect on sperm count and morphology among Danish infertile men born after 1950 but not in men born in the first part of the century. The findings are compatible with an environmental impact during prenatal life but the evidence is far from unequivocal.  相似文献   
177.
AIM: Appendiceal air has been reported as both a sign of appendicitis and of a normal appendix both at plain radiography and computed tomography (CT). It is the aim of this investigation to determine the prevalence, range of appearances, and significance of appendiceal and peri-appendiceal air at CT. PATIENTS AND METHODS: Appendiceal CT scans of 100 patients with proven appendicitis and 100 patients with a normal appendix were reviewed for the presence of appendiceal and peri-appendiceal air. All cases were correlated with surgical and pathological findings or clinical follow-up. RESULTS: In 100 CT cases of appendicitis, appendiceal and/or peri-appendiceal air was present in one or more forms in 31% of cases. When present, it appeared as intraluminal air bubbles (38.7%) or air-fluid levels (22.6%), appendolith air (41.9%), intramural air (16.1%), peri-appendiceal air bubbles (12.9%), or extraluminal air-fluid level(s) (29.0%). Intramural and extraluminal air correlated with perforation in 60% and 100%, respectively. In 100 CT cases of a normal appendix, air was present in 57%. It was always intraluminal and appeared as small bubbles of air (52.6%), a tubular-shaped air collection (43.9%), or as an air-fluid level (3.5%). The appendiceal lumen was either airless (43%), or minimally (32%), moderately (18%), or completely filled with air (7%). CONCLUSION: Air is a common finding at appendiceal CT in both the normal and inflamed appendix. Intraluminal air is seen in both appendicitis and normal appendices, and cannot be presumed to indicate a patent lumen and thus a normal appendix. Appendolith, intramural and peri-appendiceal air appear diagnostic of appendicitis.  相似文献   
178.
179.
180.
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