全文获取类型
收费全文 | 30905篇 |
免费 | 1068篇 |
国内免费 | 110篇 |
专业分类
电工技术 | 374篇 |
综合类 | 228篇 |
化学工业 | 5080篇 |
金属工艺 | 627篇 |
机械仪表 | 588篇 |
建筑科学 | 969篇 |
矿业工程 | 94篇 |
能源动力 | 932篇 |
轻工业 | 3886篇 |
水利工程 | 240篇 |
石油天然气 | 152篇 |
武器工业 | 6篇 |
无线电 | 2240篇 |
一般工业技术 | 4099篇 |
冶金工业 | 8607篇 |
原子能技术 | 237篇 |
自动化技术 | 3724篇 |
出版年
2024年 | 50篇 |
2023年 | 150篇 |
2022年 | 494篇 |
2021年 | 789篇 |
2020年 | 532篇 |
2019年 | 603篇 |
2018年 | 692篇 |
2017年 | 769篇 |
2016年 | 728篇 |
2015年 | 551篇 |
2014年 | 852篇 |
2013年 | 1413篇 |
2012年 | 1257篇 |
2011年 | 1583篇 |
2010年 | 1153篇 |
2009年 | 1210篇 |
2008年 | 1097篇 |
2007年 | 958篇 |
2006年 | 772篇 |
2005年 | 832篇 |
2004年 | 902篇 |
2003年 | 812篇 |
2002年 | 786篇 |
2001年 | 688篇 |
2000年 | 536篇 |
1999年 | 603篇 |
1998年 | 2820篇 |
1997年 | 1778篇 |
1996年 | 1188篇 |
1995年 | 757篇 |
1994年 | 612篇 |
1993年 | 675篇 |
1992年 | 225篇 |
1991年 | 298篇 |
1990年 | 252篇 |
1989年 | 216篇 |
1988年 | 229篇 |
1987年 | 183篇 |
1986年 | 194篇 |
1985年 | 193篇 |
1984年 | 128篇 |
1983年 | 91篇 |
1982年 | 121篇 |
1981年 | 124篇 |
1980年 | 126篇 |
1979年 | 91篇 |
1978年 | 78篇 |
1977年 | 181篇 |
1976年 | 329篇 |
1975年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
SL Kamholz RJ Brewer G Grijalva J Burack MJ Del Rio M Vaynblatt N Lawson S Squinto WL Fodor AJ Norin 《Canadian Metallurgical Quarterly》1997,21(9):951-955
The lack of sufficient suitable human donor lungs for the many patients requiring pulmonary transplantation as life-saving therapy for end-stage lung diseases has generated extensive interest in cross-species lung transplantation. Ethical concerns and those of animal rights advocates have prompted studies of nonprimate species as potential solid organ donors for humans. This paper provides an overview of some of the laboratory studies of cross-species pulmonary transplantation performed over the past 20 years and focuses, in particular, on more recent work (from our laboratory and others) in the area of porcine-to-primate pulmonary xenotransplantation. 相似文献
52.
A chromosomally integrated Bradyrhizobium japonicum hoxA mutant is unable to oxidize hydrogen in free-living conditions. Derepressing conditions that induce hydrogenase activity in free-living, wild-type B. japonicum cells cannot induce expression of the hydrogenase structural genes in the hoxA mutant. The DNA-binding capacity of HoxA at the hup promoter region was studied by means of gel retardation. Both heterotrophically growing cells and cells induced to express hydrogenase activity contain a protein that specifically binds to the hup promoter region. Crude protein extracts isolated from a B. japonicum hoxA mutant do not contain this binding compound. The HoxA protein was overexpressed in E. coli and isolated in the form of a maltose-binding protein (MBP)-HoxA fusion. The MBP-HoxA hybrid protein specifically bound to a 50 bp region of the hupSL promoter known to be important for regulation of hupSL expression. 相似文献
53.
The effects of azadirachtin, salannin, nimbin, and 6-desacetylnimbin on ecdysone 20-monooxygenase (E-20-M) activity were examined in three insect species. Homogenates of wandering stage third instar larvae of Drosophila melanogaster, or abdomens from adult female Aedes aegypti, or fat body or midgut from fifth instar larvae of Manduca sexta were incubated with radiolabeled ecdysone and increasing concentrations (from 1 x 10(-8) to 1 x 10(-3) M) of the four compounds isolated from seed kernels of the neem tree, Azadirachta indica. All four neem tree compounds were found to inhibit, in a dose-dependent fashion, the E-20-M activity in three insect species. The concentration of these compounds required to elicit a 50% inhibition of this steroid hydroxylase activity in the three insect species examined ranged from approximately 2 x 10(-5) to 1 x 10(-3). 相似文献
54.
55.
Shoulder pain secondary to impingement of the rotator cuff tendons underneath the coracoacromial arch is a common problem seen in athletes who perform repetitive overhead activities. Shoulder impingement has been classified into primary and secondary types. Several factors contribute to impingement, including rotator cuff weakness, posterior capsule tightness, and subacromial crowding. Recently, it has been proposed that scapulothoracic muscle weakness could be a factor that contributes to impingement. Traditional rehabilitation protocols for shoulder impingement syndrome stress individualized rotator cuff strengthening. The authors propose that individualized scapulothoracic muscle strengthening should be a part of any protocol for nonoperative treatment of secondary shoulder impingement syndrome. 相似文献
56.
OD de Rada AC Villaro LM Montuenga A Martínez DR Springall JM Polak 《Canadian Metallurgical Quarterly》1993,162(1-2):121-124
The presence of nitric oxide synthase (NO-synthase), the enzyme responsible for the production of nitric oxide (NO) from L-arginine, is shown immunocytochemically in the intrinsic neurons of the human and porcine respiratory tract. NO-synthase immunoreactivity is demonstrated in a subpopulation of neurons of the microganglia present in the wall of the extra- and intrapulmonary bronchi as well as in the hilar region of the lung in relation to blood vessels. The immunostaining was also found in some nerve fibers of the respiratory nervous system. Human and porcine lung gave similar results. The possible involvement of NO in the nonadrenergic noncholinergic (NANC) nervous regulation of the lung is discussed. 相似文献
57.
Child care in the United States today 总被引:1,自引:0,他引:1
SL Hofferth 《Canadian Metallurgical Quarterly》1996,6(2):41-61
This article describes the consumers and providers of child care in the United States. It uses data from nationally representative surveys and research studies conducted from the late 1960s through 1995 to examine the child care arrangements parents select for their young children, comparing today's arrangements with those made by parents decades ago. It then discusses the availability of child care, examining both the number of child care spaces available and whether quality programs are available to suit the needs and resources of parents. The article concludes with speculation about how proposed new policies and continuing trends may lead to future changes in child care. 相似文献
58.
R de Franchis 《Canadian Metallurgical Quarterly》1998,10(12):1041-1044
Bleeding oesophageal varices (BOV), resulting from portal hypertension, can prove fatal. Not only is it important to stop the initial bleeding, which may lead to hypovolaemic shock, but also to treat this condition in the longer term, and, consequently, the prevention of rebleeding needs to be addressed. This review highlights the current findings on the haemostatic drug, terlipressin, focusing particular attention on the potential for longer-term treatment strategies in the prevention of rebleeding. The efficacy of terlipressin in treating acute BOV, its low incidence of severe side-effects (comparable to those of somatostatin) and its favourable comparison with sclerotherapy in the prevention of early rebleeds, all indicate the potential for terlipressin administration to be extended to 5 days in the longer-term treatment of BOV. In addition, terlipressin administration, in conjunction with sclerotherapy, can significantly reduce the likelihood of rebleeding compared with sclerotherapy alone and further supports its potential use in the longer-term treatment of BOV. 相似文献
59.
J Gálvez R García-Domenech C de Gregorio Alapont JV de Julián-Ortiz L Popa 《Canadian Metallurgical Quarterly》1996,14(5):272-276
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives. 相似文献
60.