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   2002篇
  免费   0篇
电工技术   1篇
化学工业   8篇
金属工艺   2篇
轻工业   3篇
无线电   8篇
一般工业技术   5篇
冶金工业   1972篇
自动化技术   3篇
  2021年   1篇
  2013年   2篇
  2011年   3篇
  2010年   1篇
  2008年   1篇
  2007年   2篇
  2004年   1篇
  2003年   4篇
  2000年   2篇
  1999年   73篇
  1998年   710篇
  1997年   384篇
  1996年   229篇
  1995年   116篇
  1994年   113篇
  1993年   114篇
  1992年   17篇
  1991年   21篇
  1990年   9篇
  1989年   18篇
  1988年   9篇
  1987年   15篇
  1986年   9篇
  1985年   15篇
  1984年   1篇
  1983年   2篇
  1982年   2篇
  1981年   7篇
  1980年   12篇
  1979年   1篇
  1978年   1篇
  1977年   32篇
  1976年   66篇
  1975年   4篇
  1966年   1篇
  1955年   1篇
  1954年   1篇
  1920年   2篇
排序方式: 共有2002条查询结果,搜索用时 15 毫秒
101.
The author indicates the similarity of a human tooth and an endoprosthesis in their action, which is the basis for developing a procedure of endoprosthesis and designing an endoprosthesis with dumping elements. The procedure has been developed during a long-term surgical experiment by examining the results by the following techniques: X-ray, bed testing, light and scanning electron microscope. Experimental results are convincing. For coating the prostheses, polytetrafluoroethylene velour is used in the experiment, but cauflene, the material of the same kind polytetrafluoroethylene, is employed in the clinical setting. The experiments yielded two inventions patented in the Russian Federation. This direction in their development seems to be fruitful in preventing the aseptic endoprosthetic instability that is the most common and severe complication after endoprosthesis and requires most frequently resurgery.  相似文献   
102.
In this thesis, Korean prisoners' health behavior and the characteristics of their medical utilization were surveyed and analysed. Because prisoners are inclined to be mediators of communicable diseases or unhealthy behaviors between prison institution and the outside world, health care for prisoners is directly related to the national population. Data were collected through a self-administered survey of 5 Korean prisons out of a total of 38 correctional facilities and analysed in accordance with a causal model based on a path frame, by serial multiple regressions on health behavior, health status, and medical utilization, etc. According to the survey analysis, while prisoners were generally concerned with their health much more than they were before imprisonment, they perceived that their health status had deteriorated after imprisonment, and that their need for health services was increasing gradually during their time in prison. In the path analysis on the causal relations among variables related to the prisoners' health status and medical utilization, the prisoners' characteristics affected their health concern and health behavior, and subsequently affected their health status and medical utilization, respectively. To sum up these exploratory studies on prisoners' health behavior and health service utilization, some efforts to organize a health care system embracing the correctional institution and health care administration should be made on the level of establishing a health care delivery system for special social groups like prisoners.  相似文献   
103.
BACKGROUND: As of May 1, 1995, the National Marrow Donor Program had a donor registry consisting of over 1.35 million HLA-typed volunteers recruited from most major cities and states in the United States. This registry represents the largest single HLA-typed pool of normal individuals in the world. METHODS: We analyzed the HLA-A, -B, -DR locus phenotypes of the National Marrow Donor Program donors in order to estimate gene and haplotype frequencies for major racial groups of the United States: Caucasian American, Asian American, African American, Latin American, and Native American. The large size of the database allowed us to calculate the frequencies of relatively rare antigens and haplotypes with more accuracy than previous studies. RESULTS: We observed 89,522 distinguishable HLA-A, -B phenotypes in 1,351,260 HLA-A, -B-typed donors and 302,867 distinguishable HLA-A, -B, -DR phenotypes in 406,503 HLA-A, -B, -DR-typed donors. Gene and haplotype frequencies differed remarkably among the five racial groups, with African Americans and Asian Americans having a large number of haplotypes that were specific to their racial groups, whereas Caucasian Americans, Latin Americans, and Native Americans shared a number of common haplotypes. CONCLUSIONS: These data represent an important resource for investigators in the fields of transplantation and population genetics. The gene and haplotype frequencies can be used to aid clinicians in advising patients about the probability of finding a match within a specific ethnic group, or to determine donor recruitment goals and strategies. The information is also a valuable resource for individuals who are interested in population genetics, selection and evolution of polymorphic human genes, and HLA-disease association.  相似文献   
104.
105.
106.
This paper systematically reviews the results from epidemiologic studies investigating the hypothesis that breast cancer risk in postmenopausal women increases with increasing concentrations of estradiol in blood and with increasing urinary estrogen excretion rates. Data from 29 epidemiologic studies of endogenous hormones and postmenopausal breast cancer were used. The ratio of the average estrogen concentration in the women with breast cancer to that in the women without breast cancer (and its 95 percent confidence interval [CI]) was calculated for each study, and the results were summarized by calculating weighted averages of the log ratios. In six prospective studies of serum estradiol concentration, 329 women who subsequently developed breast cancer had, overall, a 15 percent (CI = 6-24 percent, P = 0.0003) higher mean concentration of estradiol in their blood than the 1,105 women who remained free of cancer. The results of these prospective studies did not differ significantly from each other (chi2 for heterogeneity = 8.7; degrees of freedom = 5; P > 0.1). Similar differences in mean estrogen levels were seen in the case-control studies which reported either estradiol concentrations in the blood or urinary estrogen excretion. However, the case-control studies showed significant heterogeneity among their results. The data from the prospective studies strongly suggest that breast cancer risk in postmenopausal women is associated with relatively high concentrations of endogenous estradiol.  相似文献   
107.
Parents' anxiety about their children's anesthesia may adversely affect the children's outcomes and compromise the quality of informed consent. Studies of these issues have been limited by the lack of validated measures of parental anxiety and knowledge surrounding anesthesia. In the present study, we evaluated psychometric properties of the Amsterdam Preoperative Anxiety and Information Scale (APAIS) and the Standard Anesthesia Learning Test (SALT) among 85 parents who participated in an evaluation of the effects of a videotape about pediatric anesthesia. The results supported the internal consistency, test-retest reliability, and concurrent validity of both instruments and documented the equivalence of two forms of the SALT. Factor analysis supported the previously demonstrated factor structure of the APAIS, further confirming its construct validity. We conclude that the APAIS and SALT are reliable and valid measures of parental anxiety and knowledge of pediatric anesthesia that can be used for clinical and research purposes. Implications: This study verified the reliability and validity of two questionnaires for measuring parents' knowledge and anxiety about pediatric anesthesia. These questionnaires can be used in further research on factors affecting parental anxiety and knowledge before their children's surgery.  相似文献   
108.
This paper presents an indoor localization system based on a frequency modulated continuous wave radar in the industrial–scientific–medical band at 5.8 GHz. An integrated active pulsed reflector behaves as a backscatter by regenerating the incoming phase with phase coherent startup at a constant frequency. The base station (BS) determines the distance to this reflector with a round-trip time-of-flight measurement. The active pulsed reflector is built around a switchable and tunable oscillator. The circuit has been fully integrated in a 0.18-$mu{hbox{m}}$ CMOS technology. Outdoor measurements revealed a positioning accuracy of 15 cm, while in a harsh multipath environment with omnidirectional antennas a positioning accuracy of 32.88 cm was measured. The localization system is capable of detecting multiple reflectors at the same time, and no synchronization between BSs is needed.   相似文献   
109.
The frog intermediate lobe consists of a single endocrine cell type, the melanotrope cells, which are under the tonic inhibitory control of dopamine. Separation of dispersed pars intermedia cells in a Percoll density gradient has revealed the existence of two melanotrope cell subpopulations, referred to as high-density (HD) and low-density (LD) cells. The aim of the present study was to investigate the effects of dopamine on each of these melanotrope cell subsets. Increasing doses of dopamine, ranging from 10(-9)-10(-6) M, inhibited the release of alpha-melanocyte-stimulating hormone (alpha-MSH) in LD (but not in HD) melanotrope cells. In addition, dopamine provoked a significant reduction of the rate of acetylation of alpha-MSH in LD cells but not in HD cells. Similarly, dopamine significantly decreased the accumulation of POMC messenger RNA in LD cells, whereas it did not affect POMC gene expression in the HD melanotrope subset. On the other hand, microfluorimetric studies revealed that dopamine induced a significant reduction of KCl-stimulated cytosolic free calcium concentration in both LD and HD cells. The present study provides additional evidence for functional heterogeneity of melanotrope cells in the frog pars intermedia. Because dopamine plays a pivotal role in the regulation of alpha-MSH secretion, these data suggest the involvement of cell heterogeneity in the physiological process of background color adaptation in amphibians.  相似文献   
110.
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