全文获取类型
收费全文 | 2979篇 |
免费 | 65篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 37篇 |
综合类 | 2篇 |
化学工业 | 460篇 |
金属工艺 | 65篇 |
机械仪表 | 31篇 |
建筑科学 | 14篇 |
矿业工程 | 3篇 |
能源动力 | 90篇 |
轻工业 | 73篇 |
水利工程 | 15篇 |
石油天然气 | 18篇 |
无线电 | 241篇 |
一般工业技术 | 403篇 |
冶金工业 | 1356篇 |
原子能技术 | 2篇 |
自动化技术 | 242篇 |
出版年
2023年 | 10篇 |
2022年 | 32篇 |
2021年 | 39篇 |
2020年 | 29篇 |
2019年 | 35篇 |
2018年 | 56篇 |
2017年 | 45篇 |
2016年 | 42篇 |
2015年 | 29篇 |
2014年 | 64篇 |
2013年 | 156篇 |
2012年 | 78篇 |
2011年 | 94篇 |
2010年 | 70篇 |
2009年 | 62篇 |
2008年 | 73篇 |
2007年 | 85篇 |
2006年 | 47篇 |
2005年 | 53篇 |
2004年 | 40篇 |
2003年 | 54篇 |
2002年 | 45篇 |
2001年 | 30篇 |
2000年 | 32篇 |
1999年 | 63篇 |
1998年 | 386篇 |
1997年 | 234篇 |
1996年 | 160篇 |
1995年 | 119篇 |
1994年 | 92篇 |
1993年 | 108篇 |
1992年 | 30篇 |
1991年 | 43篇 |
1990年 | 51篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 38篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 29篇 |
1980年 | 27篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 49篇 |
1976年 | 85篇 |
1975年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有3052条查询结果,搜索用时 15 毫秒
41.
42.
It was for the first time that of the fifth year of monitoring of Plantago lanceolata L., reproduced within the thirty-kilometer zone of Chernobyl NPP disaster, the authors discovered high incidence of seedlings with various morphological abnormalities. It is suggested that the damages observed are related to the cumulative effect of radiation. 相似文献
43.
GC Borgia P Fantazzini C Palmonari G Timellini 《Canadian Metallurgical Quarterly》1996,14(7-8):899-901
NMR Relaxation and Imaging have been applied to study preparation processes of ceramic porous samples. Relaxation analysis gives a clear characterization of the materials, with high sensitivity. Differences in the method of preparation and steps as low as 25 degrees C in the firing temperatures are well detectable. Furthermore, the images permit distinguishing the different samples. The effects of the contrast in relaxation times dominate those due to the different porosities of the samples. Scanning Electron Microscopy confirms the interpretation that the changes in relaxation times are due to different pore space structures associated with the different firing temperatures. The higher the firing temperature, the larger are the pores and the higher is the amount of compact, sintered matrix, leading to higher relaxation times. 相似文献
44.
OBJECTIVES: Injury is the leading cause of death in the male working population of Brazil. An important fraction of these deaths are work related. Very few cohort studies of steel workers, and none from developing countries, have reported on mortality from injuries. This paper analyses mortality from work and non-work related injuries among Brazilian steel workers. METHODS: Deaths during employment from 1 January 1977 to 30 November 1992 were analysed in a cohort of 21,816 male steel workers. Mortality rates specific for age and calendar year among the workers were compared with those of the male population of the state where the plant is located. Work related injuries were analysed by comparing the mortality rates for different subgroups of the cohort. RESULTS: The number of deaths (391) was less than half that expected based on death rates of the general population. Over 60% (242) of deaths were due to injuries. Mortality from most causes was substantially below that in the general population, but that from unintentional injury, was 50% above that of the general population. Standardised mortality ratios (SMRs) were highest for the youngest and the oldest employees and for labourers and clerical workers. Mortality from motor vehicle injury was twice that expected from population rates (SMR = 209, 95% confidence interval (95% CI) 176-244). There was a 67% fall in the age adjusted mortality from occupational injuries in the study period. CONCLUSION: The healthy worker effect in this cohort was greater than that commonly found in studies of occupational groups in developed countries, probably because of a greater socioeconomic gap between employed and unemployed populations in Brazil, and unequal distribution of health care resources. Mortality was especially high for motor vehicle injuries. The fall in mortality from occupational injuries during the study period was probably due to improvement in safety standards, increased automation, and better medical care. There is a need to investigate risk factors for unintentional injuries among steel workers, especially those due to motor vehicle injuries. Prevention of occupational and nonoccupational injuries should be a main priority in Brazil. 相似文献
45.
HB Joshi 《Canadian Metallurgical Quarterly》1997,88(9):197-198
46.
GC Viscomi 《Canadian Metallurgical Quarterly》1997,10(1):59-86
Type I IFNs constitute a family of proteins exhibiting high homology in primary, secondary, and tertiary structures. They interact with the same receptor and transmit signals to cellular nucleus through a similar mechanism, eliciting roughly homogeneous biological activity. Nevertheless, the members of that family, IFN alpha species, IFN beta and IFN omega, due to local differences in the structure sometime show distinct properties. From the reported data it results that even minute changes or differences in the primary sequences could be responsible for a significant variety of biological actions, thus inducing to the hypothesis that Type I IFNs, rather than to be the result of a redundant replication during the evolution play definite roles in the defense of living organisms to foreign agents. 相似文献
47.
The production of the cognitive internal state word know by four 2- to 5-year-old children and their parents was examined. The levels of meaning of cognitive words can be categorized hierarchically along the dimensions of conceptual difficulty and abstractness (see Booth & Hall, 1995). The present study found that children and their parents expressed low levels of meaning less frequently, whereas they expressed high levels of meaning more frequently as a function of age. The children's use of know was also correlated positively with (1) their number of different words produced suggesting that cognitive words are related to more general semantic processes, and (2) with parental use of those same cognitive words suggesting that parental linguistic input may be an important mechanism in cognitive word acquisition. Finally, young children tended to use know more to refer to themselves than to refer to others, whereas their parents tended to use know equally to refer to self and others. The importance of cognitive words in a theory of language acquisition is discussed. 相似文献
48.
Although long-term clinical studies have shown no excessive risk of lymphoma in rheumatoid arthritis (RA) patients treated with methotrexate (MTX), an increasing number of reports of this association continue to appear. We describe two cases, review the cases in the world's literature, and summarize their important characteristics. Possible oncogenic mechanisms are discussed. Most lymphoproliferation cases presented here have features of immunosuppression-associated lymphoma. The immunosuppressed state is attributable to a combination of factors, such as RA itself and the actions of MTX. The risk factors for RA patients to develop lymphoma while on MTX include severe disease, intense immunosuppression, genetic predisposition, and an increased frequency of latent infection with prooncogenic viruses such as Epstein-Barr virus (EBV). The spontaneous remission of lymphomas in eight RA patients after MTX was stopped highlights the likely causative role of the drug in the development of these malignancies. If the clinical situation permits, a period of observation for spontaneous remission after MTX is stopped is advisable. The physicians caring for RA patients on MTX should maintain a high surveillance for signs and symptoms suggestive of lymphoma. 相似文献
49.
50.