全文获取类型
收费全文 | 4903篇 |
免费 | 0篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 24篇 |
金属工艺 | 9篇 |
建筑科学 | 1篇 |
矿业工程 | 1篇 |
能源动力 | 1篇 |
轻工业 | 7篇 |
无线电 | 5篇 |
一般工业技术 | 13篇 |
冶金工业 | 4805篇 |
自动化技术 | 35篇 |
出版年
2020年 | 1篇 |
2017年 | 1篇 |
2013年 | 5篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2010年 | 3篇 |
2009年 | 3篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 5篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 154篇 |
1998年 | 1496篇 |
1997年 | 870篇 |
1996年 | 564篇 |
1995年 | 326篇 |
1994年 | 255篇 |
1993年 | 305篇 |
1992年 | 44篇 |
1991年 | 64篇 |
1990年 | 60篇 |
1989年 | 74篇 |
1988年 | 61篇 |
1987年 | 70篇 |
1986年 | 56篇 |
1985年 | 64篇 |
1984年 | 3篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 38篇 |
1979年 | 1篇 |
1978年 | 7篇 |
1977年 | 91篇 |
1976年 | 187篇 |
1975年 | 9篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1966年 | 2篇 |
1964年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有4903条查询结果,搜索用时 15 毫秒
61.
Our research team is involved in ongoing research in both worksites and medical office settings. These settings offer great potential for reaching individuals who would not otherwise participate in health promotion, but they also place considerable constraints on assessment time and efforts, especially if one's goal is to attract a high and representative proportion of employees or patients. This paper reports on our experience with measures of dietary behavior in these two settings. We found it problematic to collect detailed assessments such as 4-day food records or comprehensive food frequency/history checklists in worksites or medical office settings using population-based samples. Instead, we recommend and provide data on the utility of a dietary-fat screening instrument, and on the Food Habits Questionnaire (FHQ-Kristal, Shattuck, & Henry, 1990), a brief measure of dietary behaviors associated with high-fat eating patterns. The FHQ, in particular, was found to correlate well with other more costly and time-consuming methods of assessment, to be reliable and responsive to intervention effects, and to provide behavioral targets for intervention. The strengths and limitations of these measures for tailoring intervention and assessing outcomes are discussed. 相似文献
62.
P Wesseling JA van der Laak M Link HL Teepen DJ Ruiter 《Canadian Metallurgical Quarterly》1998,29(4):352-358
BACKGROUND: Despite concerns about its prevalence and ramifications, harassment has not been well quantified among physicians. Previous published studies have been small, have surveyed only 1 site or a convenience sample, and have suffered from selection bias. METHODS: Our database is the Women Physicians' Health Study, a large (4501 respondents; response rate, 59%), nationally distributed questionnaire study. We analyzed responses concerning gender-based and sexual harassment. RESULTS: Overall, 47.7% of women physicians reported ever experiencing gender-based harassment, and 36.9% reported sexual harassment. Harassment was more common while in medical school (31% of gender-based and 20% for sexual harassment) or during internship, residency, or fellowship (29% for gender-based and 19% for sexual harassment) than in practice (25% for gender-based and 11% for sexual harassment). Respondents more likely to report gender-based harassment were physicians who were now divorced or separated and those specializing in historically male specialties, whereas those of Asian and other (nonwhite, nonblack, non-Asian, non-Hispanic) ethnicity, those living in the East, and those self-characterized as politically very conservative were less likely to report gender-based harassment. Being younger, born in the United States, or divorced or separated were correlated with reporting ever experiencing sexual harassment; those who were Asian or who were currently working in group or government settings were less likely to report it. Those who felt in control of their work environments, were satisfied with their careers, and would choose again to become physicians reported lower prevalences of ever experiencing harassment. Those with histories of depression or suicide attempts were more likely to report ever having been harassed. CONCLUSIONS: Women physicians commonly perceive that they have been harassed. Experiences of and sensitivity to harassment differ among individuals, and there may be substantial professional and personal consequences of harassment. Since reported rates of sexual harassment are higher among younger physicians, the situation may not be improving. 相似文献
63.
DJ Gordon 《Canadian Metallurgical Quarterly》1998,27(3):699-709, xi
Although it is well established that a low-circulating level of high-density lipoprotein (HDL) cholesterol is strongly associated with the likelihood of developing atherosclerotic coronary heart disease (CHD), the causal nature of this association has not been shown. Low levels of HDL cholesterol frequently are associated with other CHD risk factors, whose correction, often by hygienic means, may reduce CHD risk with minimal risk of adverse side-effects. However, other recommended hygienic interventions may lower HDL cholesterol levels. Specific safe and effective drugs for correcting a low HDL cholesterol level are not available and the potential value of specific pharmacologic treatment of this condition in the treatment or prevention of CHD remains unproven. Thus, while HDL measurement should be incorporated routinely in risk-assessment, intervention efforts should focus primarily on lowering low-density lipoprotein cholesterol. 相似文献
64.
Sialyltransferase (Stase) in Neisseria gonorrhoeae organisms (gonococci [GC]) transfers sialic acid (N-acetylneuraminic acid [NANA]) from cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA) mainly to the terminal galactose (Gal) residue in the Gal beta-1,4 N-acetylglucosamine (Gal-GlcNAc)-R lipooligosaccharide (LOS) structure. Sialylated GC resist killing by normal human serum, sometimes show reduced invasion of epithelial cells, and have reduced adhesion to and stimulation of human neutrophils. We questioned whether Stase itself modulates the interactions of GC with human epithelial cells and neutrophils in the absence of exogenous CMP-NANA. To that end, we treated strain F62 with ethyl methanesulfonate and grew approximately 175,000 colonies on CMP-NANA plates, and screened them with monoclonal antibody 1B2-1B7 (MAb 1B2). MAb 1B2 is specific for Gal-GlcNAc and reacts only with asialylated GC. We isolated 13 MAb 1B2-reactive mutants, including five null mutants, that had Stase activities ranging from barely detectable to fivefold less than that of wild-type (WT) F62. The LOS phenotype of Stase null mutants was identical to that of WT F62, yet the mutants could not sialylate their LOS when grown with CMP-NANA. The Stase null phenotype was rescuable to Stase+ by transformation with chromosomal DNA from WT F62. Stase null mutants remained serum sensitive even when grown with CMP-NANA. One Stase null mutant, ST94A, adhered to and invaded the human cervical epithelial cell line ME-180 at levels indistinguishable from that of WT F62 in the absence of CMP-NANA. In human neutrophil studies, ST94A stimulated the oxidative burst in and adhered to human neutrophils at levels similar to those of WT F62. ST94A and WT F62 were also phagocytically killed by neutrophils at similar levels. These results indicate that expression of Stase activity is not required for interaction of GC with human cells. 相似文献
65.
66.
The map displays project was undertaken to investigate techniques for the storage and display of geographical maps and related information and to develop the hardware and software required for a complete working system. Initially most of the project was concerned with the design of graphics hardware to be interfaced to a DEC LSI-11/03 micro-computer which was the main supply of computing power for the project. The development of one of the pieces of specialized hardware, the framestore display, is described. 相似文献
67.
68.
Spin-glass models of neural networks 总被引:1,自引:0,他引:1
69.
70.