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   517篇
  免费   3篇
电工技术   2篇
化学工业   51篇
金属工艺   5篇
机械仪表   9篇
建筑科学   18篇
矿业工程   1篇
能源动力   5篇
轻工业   20篇
水利工程   4篇
无线电   25篇
一般工业技术   74篇
冶金工业   262篇
原子能技术   2篇
自动化技术   42篇
  2021年   1篇
  2019年   1篇
  2018年   3篇
  2016年   1篇
  2015年   6篇
  2014年   6篇
  2013年   15篇
  2012年   9篇
  2011年   17篇
  2010年   7篇
  2009年   6篇
  2008年   13篇
  2007年   12篇
  2006年   5篇
  2005年   11篇
  2004年   12篇
  2003年   7篇
  2002年   5篇
  2001年   7篇
  2000年   8篇
  1999年   18篇
  1998年   74篇
  1997年   52篇
  1996年   27篇
  1995年   22篇
  1994年   22篇
  1993年   15篇
  1992年   10篇
  1991年   8篇
  1990年   5篇
  1989年   5篇
  1988年   8篇
  1987年   11篇
  1986年   9篇
  1985年   7篇
  1984年   5篇
  1983年   3篇
  1982年   5篇
  1981年   7篇
  1980年   2篇
  1979年   3篇
  1977年   11篇
  1976年   26篇
  1975年   3篇
  1974年   1篇
  1973年   2篇
  1972年   2篇
  1971年   1篇
  1968年   2篇
  1967年   2篇
排序方式: 共有520条查询结果,搜索用时 15 毫秒
71.
72.
The hypothesis that prior experience, specifically a knowledge-based schema for typical house layouts, can compensate for age declines in spatial memory was evaluated in 4 experiments. Old and young adults explored and subsequently recalled house layouts presented 1 room at a time on a computer screen. The findings failed to support the compensation hypothesis in that schema-relevant layouts facilitated recall equivalently for the 2 age groups. Violation of a typical house schema had a more negative effect on recall of the older group. Individual differences in spatial visualization ability explained much of the age difference in performance but not the effects of schema manipulations. It was concluded that there is age invariance in the facilitatory effects of relevant prior knowledge on spatial memory but an age-related decrease in the ability to inhibit irrelevant prior knowledge. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
73.
Intracranial aneurysms are common extrarenal manifestations of autosomal dominant polycystic kidney disease (ADPKD). Although their natural history is not completely understood, small asymptomatic intracranial aneurysms in patients with ADPKD often are not treated but are followed with serial magnetic resonance (MR) angiography. The authors report the unique case of a patient with ADPKD who bled from a previously documented asymptomatic 3-mm intracranial aneurysm. This 42-year-old man with ADPKD suffered a subarachnoid hemorrhage (SAH) from a 7-mm left pericallosal artery aneurysm. This aneurysm was clipped and the patient made an excellent recovery. An irregular asymptomatic 3-mm right middle cerebral artery (MCA) aneurysm had also been demonstrated on angiography. While the patient was considering elective surgery for the MCA aneurysm, he suffered a hemorrhage from this lesion 10 weeks after the initial SAH. The aneurysm was clipped and the patient made a satisfactory recovery (he was moderately disabled). In this report the authors indicate that small asymptomatic intracranial aneurysms are not always innocuous in patients with ADPKD, and they suggest that treatment should be strongly considered for these lesions in this group of patients when there is a history of SAH or the aneurysm is irregular in appearance. Because MR angiography studies may not adequately define the configuration of small aneurysms and irregularity may easily be missed, conventional angiography is recommended for patients with ADPKD who are found to have an intracranial aneurysm on screening with MR angiography.  相似文献   
74.
75.
76.
Chronic obstructive pulmonary disease (COPD) is considered to be caused in part by smoking-induced inflammation, but it is unknown which inflammatory cells within the small airways are associated with the obstruction. We investigated the inflammatory infiltrate in the small airways of 16 current or ex-smokers with COPD (FEV1 < or = 75% predicted) and 15 without COPD (FEV1 > or = 85% predicted) in pneumectomy specimens that were removed for lung cancer. Mast cells, macrophages, neutrophils, eosinophils, T cells, and B cells were identified using immunohistochemistry on formalin-fixed, paraffin-embedded specimens. These cells were quantified in the epithelium and the remainder of the airway wall. The number of mast cells and macrophages in the epithelium, but not in the remainder of the airway wall, was significantly increased in patients with COPD. Neutrophil and T cell numbers did not differ between the groups. Only few B cells and eosinophils were present in both groups. Smoking history, perioperative steroid usage, tumor localization, or reversibility in the FEV1 to salbutamol could not account for the observed differences. We conclude that the number of epithelial mast cells and macrophages is increased in the bronchioli in smokers with airflow limitation, suggesting a role in development of COPD.  相似文献   
77.
78.
Three cases of metastatic basal-cell carcinoma are reported. All of the cases were relatively small when compared with other lesions reported in the literature. With early chemosurgical treatment of small recurrent carcinomas, metastasizing basal-cell carcinoma will be a condition of the past.  相似文献   
79.
In an effort to understand molecular mechanisms of intracellular lipid transport, we have focused upon specific events required for de novo aminophospholipid synthesis in the yeast Saccharomyces cerevisiae. A genetic system for examining the steps between phosphatidylserine (PtdSer) synthesis in the endoplasmic reticulum and its transport to and decarboxylation by PtdSer decarboxylase 2 in the Golgi/vacuole has been developed. We have isolated a mutant, denoted pstB1, that accumulates PtdSer and has diminished phosphatidylethanolamine formation despite normal PtdSer decarboxylase 2 activity. The lesion in PtdSer metabolism is consistent with a defect in interorganelle lipid transport. A genomic DNA clone that complements the mutation was isolated, and sequencing revealed that the clone contains the STT4 gene, encoding a phosphatidylinositol 4-kinase. The pstB1 mutant exhibits a defect in Stt4p-type phosphatidylinositol 4-kinase activity, and direct gene replacement indicates that STT4 is the defective gene in the mutant. Creation of an STT4 null allele (stt4Delta::HIS3) demonstrates the gene is essential. These results provide evidence that implicates phosphoinositides in the regulation of intracellular aminophospholipid transport.  相似文献   
80.
OBJECTIVE: to investigate whether there are differences between the cost of intrapartum care for women at low obstetric risk in a midwife-managed labour and delivery unit and that in a consultant-led labour and delivery ward. DESIGN: cost analysis based on the findings of a randomised controlled trial comparing two alternative types of intrapartum care. SETTING: Aberdeen Maternity Hospital, Grampian. SUBJECTS: the number of women 'booked' for care in the Midwives' Unit in a standard year and a comparable group of women cared for in the consultant-led labour ward. PRIMARY OUTCOME MEASURE: the cost 'outcome' is the extra (or reduced) cost per woman resulting from the introduction of a midwife-managed delivery unit. FINDINGS: the baseline extra cost of the introduction of the Midwives' Unit was found to be 40.71 pounds per woman. Depending on the scenario used, this ranged from a cost saving of 9.74 pounds per woman to an additional cost of 44.23 pounds per woman. CONCLUSIONS: this study has shown that, in terms of costs incurred during the intrapartum period, the marginal cost of caring for women at low obstetric risk alongside women at high obstetric risk in a standard labour ward is small. However, the impact of establishing a separate midwife-managed delivery unit, requiring an increase in midwifery staffing levels, can be significant.  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