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   1846篇
  免费   1篇
电工技术   1篇
化学工业   6篇
能源动力   1篇
轻工业   2篇
无线电   1篇
一般工业技术   2篇
冶金工业   1832篇
自动化技术   2篇
  2017年   1篇
  2016年   1篇
  2014年   1篇
  2011年   1篇
  2010年   1篇
  2004年   1篇
  2003年   4篇
  2002年   1篇
  2001年   1篇
  1999年   54篇
  1998年   554篇
  1997年   312篇
  1996年   217篇
  1995年   97篇
  1994年   105篇
  1993年   122篇
  1992年   15篇
  1991年   21篇
  1990年   24篇
  1989年   20篇
  1988年   18篇
  1987年   16篇
  1986年   18篇
  1985年   13篇
  1983年   2篇
  1982年   8篇
  1981年   11篇
  1980年   12篇
  1979年   1篇
  1978年   3篇
  1977年   59篇
  1976年   124篇
  1975年   5篇
  1974年   1篇
  1955年   3篇
排序方式: 共有1847条查询结果,搜索用时 13 毫秒
981.
982.
983.
To assess the effectiveness of gadopentetate dimeglumine in the magnetic resonance (MR) imaging evaluation of soft-tissue masses without osseous involvement, 30 patients underwent MR imaging before and after administration of contrast material (0.1 mmol/kg). Of the 30 lesions, 22 were benign and eight were malignant; histologic confirmation was available in all lesions except one benign lesion. Overall, enhancement was detected in 26 (87%) of 30 lesions: 18 (82%) of the 22 benign lesions and eight (100%) of eight malignant lesions. Enhancement was characterized as homogeneous (two [11%] benign lesions, two [25%] malignant lesions), inhomogeneous (11 [61%] benign lesions, six [75%] malignant lesions), or peripheral (five [28%] benign lesions, no malignant lesions). Of the 19 lesions assessed for a change in enhancement over time, seven (37%) showed an increase and two (11%) showed a decrease in signal intensity. The authors conclude that benign and malignant soft-tissue lesions could not be differentiated solely on the basis of enhancement (pattern, degree, or time course).  相似文献   
984.
985.
OBJECTIVE: In 1995, we presented our experience in hysteroscopic resection of hemorrhagic submucous fibroids in 196 patients. The objective of the present work was to analyze functional outcome three years later. PATIENTS: One hundred ninety-six patients with abnormal uterine bleeding were treated between 1987 and 1993. Equipment, techniques, characteristics of the procedures and early results were detailed in the previous article. RESULTS: With a mean follow-up of 73 months (range 50,104), results were: 13.8% of the patients were lost to follow-up; 68.4% had symptomatic improvement and failure was observed in 17.8% (subsequent hysterectomy in 12.7%). Forty-nine patients had repeat resection in this series; 61 became menopausal after surgery, and 21 were taking hormone replacement therapy with good results. CONCLUSION: Developed as an alternative to hysterectomy, operative hysteroscopy has proven to be a safe and effective procedure. This treatment modality appears to give satisfactory long-term results, with a low rate of complications.  相似文献   
986.
987.
To determine the effect of age on the regulation of intestinal nutrient absorption, we fed young (7.6-mo-old) and aged (24.8-mo-old) C57BL mice diets designed to stimulate in vitro sugar or amino acid uptake in the isolated small intestine. In each age group, diet had no effect on feeding rates and body weights. D-Glucose and D-fructose uptakes by the small intestine each increased by about two times in young and 1.5 times in aged mice fed high carbohydrate diets as compared with those fed no carbohydrate. Adaptive increases in uptake by the aged group were not only reduced but also restricted to more proximal regions of the small intestine. In both age groups, diet-stimulated increases in D-glucose transport were accompanied by parallel increases in number of Na(+)-D-glucose cotransporters as estimated by specific phlorizin binding. Diet had no effect on transporter Kd for phlorizin, turnover rate of each transporter, mucosal mass or mucosal permeability. A high protein diet stimulated the uptake of L-aspartate and L-proline in young mice and of only L-aspartate in aged mice. Uptake of essential amino acids and of nonessential amino acids sharing transporters with essential ones were not regulated. Although aged mice possess adaptive mechanisms to diet that are similar to those in young mice, the effectiveness of these mechanisms may be impaired with age and may result in malabsorption symptoms so prevalent in the elderly.  相似文献   
988.
989.
We evaluated the fluorescein angiographic features of full-thickness macular holes before and after vitrectomy, fluid-gas exchange, and instillation of transforming growth factor beta-2 in 43 eyes in a masked fashion to evaluate the angiographic characteristics of macular holes preoperatively and the changes that occur with successful and unsuccessful closure of the macular hole. Hyperfluorescence was present in the base of the macular hole preoperatively in 34 of 43 eyes (79.1%), was questionable in eight of 43 eyes (18.6%), and was definitely absent in only one of 43 eyes (2.3%). The hyperfluorescence in the base of the macular hole disappeared in 19 of 20 eyes (95%) with successful closure of the macular hole (P < .00001) and appeared to be caused by blocked fluorescence at the site of the macular hole. The photographic features of eyes with unsuccessful closure of the macular hole changed little, except that the size of the cuff of neurosensory detachment around the hole increased and was associated with decreased postoperative visual acuity. These angiographic changes support the presence of a glial tissue plug bridging a small defect in the fovea of eyes with successful closure of a macular hole.  相似文献   
990.
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