全文获取类型
收费全文 | 1721篇 |
免费 | 10篇 |
专业分类
电工技术 | 2篇 |
综合类 | 1篇 |
化学工业 | 47篇 |
金属工艺 | 1篇 |
机械仪表 | 8篇 |
建筑科学 | 17篇 |
能源动力 | 3篇 |
轻工业 | 43篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 11篇 |
一般工业技术 | 26篇 |
冶金工业 | 1494篇 |
原子能技术 | 4篇 |
自动化技术 | 68篇 |
出版年
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 29篇 |
2012年 | 4篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 18篇 |
2008年 | 8篇 |
2007年 | 18篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 16篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 2篇 |
2000年 | 10篇 |
1999年 | 32篇 |
1998年 | 415篇 |
1997年 | 281篇 |
1996年 | 157篇 |
1995年 | 105篇 |
1994年 | 78篇 |
1993年 | 95篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 14篇 |
1980年 | 23篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 60篇 |
1976年 | 131篇 |
1975年 | 4篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1959年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有1731条查询结果,搜索用时 15 毫秒
61.
WH Utian 《Canadian Metallurgical Quarterly》1977,2(6086):577-578
The most controversial issue related to prolonged estrogen therapy is the possible relationship of this therapy to the etiology and pathogenesis of breast and uterine cancer. The imprecise nature of the relevant data does not allow full definition of the rish. To maintain proper perspective, smoking 20 cigarettes a day increases the risk of death from lung cancer 17 times; the risk from estrogens is less than that. There is no controversy over the use of estrogens for short-term relief of menopausal symptoms. The Mulley and Mitchell paper referred to was opinion based on no direct research and an inadequate knowledge of the literature. The early symptoms of estrogen dificiency, hot flushes and atrophic vaginitis, respond to short-term estrogen therapy, which in addition, provides a "mental tonic" effect. It is not justifiable to withhold such therapy from the normal informed patient requesting it, provided no contraindications exist. The patient should be reevaluated at frequent intervals, and the proper selection of drug, dosage, and therepeutic regimen administered. This can be accomplished, including research, through a menopause clinic. 相似文献
62.
As the sensitivity of the new in vitro cancer detection techniques increases, a larger number of "false positive" results can be expected from control populations apparently free from malignant disease at the time of the test. An attempt is made to predict the number of unexplained positives, together with the expected age and sex distribution, using published cancer registration statistics. The predicted numbers are compared with the observed numbers of unexplained positives in two clinical trials of the MEM test. 相似文献
63.
Urinary amino acid excretion was determined in 31 leukemic patients and 29 normal individuals by rapid gas chromatographic analysis of 16 amino acids as their N-acetyl-n-propyl esters. The leukemic patients were concurrently undergoing, or had recently completed, chemotherapy. It was found that aspartic acid, threonine, and serine were of significance in distinguishing between patients "on" therapy and those "off" therapy. Patients with advanced disease have the greatest aminoaciduria, although both the normal and leukemic populations have wide individual ranges. Within both populations, men excrete a greater variety and quantity of amino acids than women. It is concluded that analysis of urinary amino acids represents a history of complex metabolic events, which is potentially useful for evaluating patient response to chemotherapy in leukemia. 相似文献
64.
For several months prior to birth a major portion of a family's attention, conversation, thought, and often worry, is directed toward the idea of a new child. This prolonged attention and anticipation contribute to making childbirth an emotionally charged experience. In psychological terms, it is therefore a critical period of peak motivation for learning, and a time to peak susceptibility to reinforcement. Theory, reason, and scientific evidence indicate thng with childbirth and early postpartum experiences, can significantly affect subsequent parental behaviors, the child's central environment influence. Evidence strongly suggests that these parental attitudes and behaviors so crucial to the child's ultimate well-being are learned rather than derived instinctually, and therefore they are malleable and can be taught, directed, and corrected. Through education and reinforcement it is possible to encourage parental behaviors and child interactions which are products of feelings of control, competence, accomplishment, understanding, and caring. Similarly we can recognize and work toward replacing attitudes, feelings, and behaviors that express fear, worry, and insecurity about the child. Over the past 50 years major changes have occurred in the practice of obstetrics and newborn pediatrics. Other major changes will necessarily occur as we move toward perinatal regionalization. Changes instigated solely on physiologic data can have unrecognized collateral effects on the psychological component of the childbirth experience. All concerned health care personnel, especially obstetricians and pediatricians, can insist that the importance of desirable mother-father-child interactions be recognized and that practices fostering them be afforded a high priority. I would like to endorse a comment from a recent article by Richmond concerning the advent of behavioral pediatrics by adding that behavioral obstetrics is also "an idea whose time has arrived". 相似文献
65.
66.
Cliff Guy 《Planning Theory & Practice》2013,14(3):319-330
This article examines how major retailers, in their attempts to secure sites for very large stores (over 7000 m2 sales area), have had to adopt new strategies in order to overcome resistance from local authority and central government retail planning policy. These strategies include recycling of old retail developments with ‘open A1 consent’, participation in urban regeneration projects and development or redevelopment of ‘district shopping centres’ in urban areas. Discussion of these strategies reveals weaknesses and inconsistencies in retail planning policy in the UK. 相似文献
67.
Cliff Win Jr. 《电子技术应用》2007,33(11):10-13
首先简要介绍了复合NSTC/PAL视频,并阐述差分增益与差分相位的重要性,随后,重点讨论了如何理解规格表中的各种规格及各种重要的DG/DP测量方法。 相似文献
68.
The potential for the use of possibility theory in the qualitative model-based diagnosis of spacecraft systems is described. The first sections of the paper briefly introduce the Model-Based Diagnostic approach to spacecraft fault diagnosis, Qualitative Modeling methodologies, and the concepts of possibilistic modeling in the context of Generalized Information Theory. Then the necessary conditions for the applicability of possibilistic methods to qualitative model-based diagnosis, and a number of potential directions for such an application, are described. 相似文献
69.
70.
The influence of operating conditions such as reheat, intercooling, ambient temperature and pressure ratio are analyzed from a second law perspective on the performance of a natural gas‐fired gas turbine cogeneration system. The effect of these operating parameters on carbon dioxide emissions is also discussed. The second law efficiency of gas turbine cogeneration system increases markedly with reheat option. Higher pressure ratios lead to decreased second law cogeneration efficiency but this effect can be reduced with a higher level of reheat option. The effect of intercooling on second law efficiency is strongly related to pressure ratio with higher pressure ratios significantly decreasing efficiency. The second law efficiency is not so sensitive to the environment temperature for levels of reheat or intercooling greater than 50%. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献