全文获取类型
收费全文 | 3382篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 1篇 |
化学工业 | 37篇 |
金属工艺 | 7篇 |
机械仪表 | 9篇 |
建筑科学 | 21篇 |
能源动力 | 3篇 |
轻工业 | 12篇 |
水利工程 | 3篇 |
石油天然气 | 9篇 |
无线电 | 23篇 |
一般工业技术 | 46篇 |
冶金工业 | 3176篇 |
原子能技术 | 1篇 |
自动化技术 | 35篇 |
出版年
2021年 | 4篇 |
2020年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2013年 | 15篇 |
2012年 | 9篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 3篇 |
2007年 | 12篇 |
2006年 | 7篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2003年 | 12篇 |
2002年 | 7篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 110篇 |
1998年 | 979篇 |
1997年 | 574篇 |
1996年 | 345篇 |
1995年 | 205篇 |
1994年 | 167篇 |
1993年 | 183篇 |
1992年 | 20篇 |
1991年 | 47篇 |
1990年 | 36篇 |
1989年 | 44篇 |
1988年 | 57篇 |
1987年 | 48篇 |
1986年 | 35篇 |
1985年 | 24篇 |
1984年 | 3篇 |
1983年 | 7篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 30篇 |
1979年 | 6篇 |
1978年 | 18篇 |
1977年 | 77篇 |
1976年 | 162篇 |
1975年 | 5篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1966年 | 2篇 |
1965年 | 6篇 |
1963年 | 4篇 |
1962年 | 2篇 |
排序方式: 共有3386条查询结果,搜索用时 31 毫秒
11.
Although enthusiasm for measuring health-related quality of life (HRQL) in clinical trials exists, information is limited on the meaning of scores. We examined the relation between scores from the 34-item Medical Outcomes Study HIV Health Survey (MOS-HIV) and the more detailed HIV Overview of Problems-Evaluation System (HOPES) using the responses of 318 HIV-infected outpatients being treated in Los Angeles and Baltimore. With the HOPES problem statements as independent variables, statistically significant predictors of the variation in MOS-HIV scores for the Physical Function, Mental Health, and Energy/Fatigue scales were identified using stepwise regression. Approximately 60% to 70% of the variation in each of the scores was explained by five to seven different HOPES problem statements, with a single item explaining 47% to 59% of the variation. We created illustrative profiles for each of the three MOS-HIV scales using the HOPES items identified in the regressions. Independent of the scale, persons scoring in the top MOS-HIV quartile tended to report few if any problems, whereas a decline in score to the next quartile was characterized by functional difficulties (e.g., "HIV interferes with work"). The onset of specific problems might trigger further evaluation and potential intervention from health care providers to help maintain patient functioning. 相似文献
12.
The present review has attempted to summarize the classic symptoms and signs of aortic valve stenosis, especially in an adult. It is emphasized that all the classic signs rarely are present and their absence may mislead an unwary clinician. The diagnostic help provided by noninvasive tests, including echocardiography and phonocardiography, has been emphasized. A need for cardiac catheterization and angiography in most patients prior to corrective surgery is stressed. The natural history of the disease without operative intervention is dim and a significant risk of sudden death exists. The current surgical approach with immediate and long-term results is summarized. Finally, attention has been drawn to the special clinical circumstances when the aortic valve stenosis provides a strinkingly different clinical picture. We cannot find a better way to end this review than by quoting a warning note given by Thomas Lewis in 1920: "It is the faint cry of an anguished and fast failing muscle, which, when it comes, all should strain to hear, for it is not long repeated. A few months, a few years at most, and the end comes." 相似文献
13.
I. M. Lerner G. I. Il’in 《Journal of Communications Technology and Electronics》2010,55(12):1385-1390
Transient processes at the output of an isolated oscillatory circuit caused by stepwise phase changes at the circuit input
are studied in the time and frequency domains. A mathematical model of this type of transient processes in the form of a narrowband
process is presented. Analytical expressions describing the behavior of the transient process in the time and frequency domains
are obtained. New features of this type of transient processes are revealed. 相似文献
14.
15.
16.
17.
The average gastrointestinal uptake 4 h after an intragastric dose of 400 nmol of cadmium chloride labeled with 109CdCl2 in iron-deficient mice, 25%, was significantly greater than the result, 16%, in iron-normal animals, and more cadmium entered the body of the former, 3.8%, than the latter, 2% (P less than 0.05). Between 4 and 72 h, gastrointestinal radioactivity declined without further increase in body activity; however, more radiocadmium remained in the duodenum of iron-deficient than iron-normal animals (P less than 0.05). The radiocadmium sequestered in the duodenum was bound to a protein with a molecular weight of about 12,000. After subcutaneous injection of radiocadmium, the rate of excretion of radioactivity from the body was similar in iron-normal and iron-deficient mice; however, a greater proportion of the injected dose accumulated in the duodenum of the iron-deficient animals (P less than 0.05). Thus, the intestinal adapative response to iron deficiency may enhance cadmium toxicity, whereas sequestration and subsequent excretion of cadmium by the intestinal mucosa serves to protect the body against toxic effects. The duodenum, particularly in iron-deficient mice, is especially vulnerable to the toxic effects of cadmium. 相似文献
18.
19.
20.
The effects of increasing and decreasing activity in sympathetic neurons on light (D420 = 1.05) and heavy (D420 = 1.15) populations of adrenergic vesicles have been determined. Norepinephrine (NE) was used as a marker for the soluble contents of the vesicles, and dopamine beta-hydroxylase was used as a marker for the vesicle membranes. Cold exposure was used to increase activity in the sympathetic nervous system. A 40% decrease in the NE content of the rat heart with no change in the activity of dopamine beta-hydroxylase was observed after 70 minutes at 5 degrees C. The fall in NE content was completely blocked by pretreating the animals with chlorisondamine. Separation of light and heavy populations of vesicles was achieved with linear sucrose density gradients. Cold stress of 70 minutes duration led to a marked decrease in the NE content of the light vesicles. Blocking adrenergic nerve impulses with chlorisondamine resulted in an increase in total NE in the heart but had no effect on dopamine beta-hydroxylase activity. The initial effect of chlorisondamine was to increase the NE content of the light vesicles. The administration of alpha-methyl-p-tyrosine for 6 hours caused an approximately equal loss of NE from both vesicle populations. The decrease in total heart NE was about 25% and could be prevented by pretreating the animals with chlorisondamine. These results suggest that the light vesicle fraction is involved in the rapid or short-term responses to changes in nerve impulse frequency. Changes in the NE content of the heavy vesicles in rat heart were seen only after longer times, suggesting that these particles may function only as auxiliary storage sites for the neurotransmitter. 相似文献