全文获取类型
收费全文 | 12330篇 |
免费 | 119篇 |
国内免费 | 12篇 |
专业分类
教育 | 7906篇 |
科学研究 | 2178篇 |
各国文化 | 89篇 |
体育 | 997篇 |
综合类 | 6篇 |
文化理论 | 86篇 |
信息传播 | 1199篇 |
出版年
2021年 | 102篇 |
2020年 | 161篇 |
2019年 | 266篇 |
2018年 | 317篇 |
2017年 | 293篇 |
2016年 | 246篇 |
2015年 | 184篇 |
2014年 | 227篇 |
2013年 | 2255篇 |
2012年 | 247篇 |
2011年 | 240篇 |
2010年 | 213篇 |
2009年 | 183篇 |
2008年 | 196篇 |
2007年 | 225篇 |
2006年 | 165篇 |
2005年 | 161篇 |
2004年 | 151篇 |
2003年 | 150篇 |
2002年 | 149篇 |
2001年 | 184篇 |
2000年 | 202篇 |
1999年 | 171篇 |
1998年 | 93篇 |
1997年 | 96篇 |
1996年 | 122篇 |
1994年 | 106篇 |
1993年 | 108篇 |
1992年 | 144篇 |
1991年 | 151篇 |
1990年 | 153篇 |
1989年 | 172篇 |
1988年 | 128篇 |
1987年 | 120篇 |
1986年 | 173篇 |
1985年 | 164篇 |
1984年 | 138篇 |
1983年 | 143篇 |
1982年 | 128篇 |
1981年 | 107篇 |
1980年 | 109篇 |
1979年 | 146篇 |
1978年 | 126篇 |
1977年 | 111篇 |
1976年 | 104篇 |
1975年 | 89篇 |
1974年 | 112篇 |
1973年 | 99篇 |
1972年 | 88篇 |
1971年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Seema Gupta Rajesh Pandey Ranjan Katyal H. K. Aggarwal R. P. Aggarwal S. K. Aggarwal 《Indian journal of clinical biochemistry : IJCB》2005,20(1):67-71
The present study was conducted to evaluate some of the components of antioxidant defense system and oxidative damage in 20
male patients of alcoholic liver disease (ALD). The results were compared with 20 healthy male smokers and 20 healthy male
non-smokers volunteers. Patients were subjected to detailed clinical examination and laboratory investigations. Blood samples
were collected for estimating reduced glutathione (GSH), total thiols (T-SH) malondialdehyde (MDA), transaminases (AST, ALT),
glutathione-S-transferease (GST) and gammaglutamyl transferase (GGT). Serum aspartate amino transferase (AST)/alanine amino
transferase (ALT) ratio was significantly (p<0.01) reduced in ALD patients as compared to the controls. However, the core
of utility of MDA and GST was found to be significantly (p<0.01) increased in ALD patients compared to controls. There was
a significant negative correlation of MDA with both GSH and TSH. Plasma GGT levels were significantly (p<0.01) increased in
alcoholics and the enzyme showed a significant positive correlation with MDA. These results give enough evidence of increased
oxidative stress and compromised antioxidant defense system in patients with ALD. 相似文献
962.
H. Stead 《Research Policy》1976,5(1):2-9
Since its publication in 1967, the estimates of the US Panel on Invention and Innovation (“Charpie” Panel) on the cost structure of technological innovation have been widely quoted and almost universally accepted. However, two later studies, by Edwin Mansfield and by Statistics Canada, have found that R&D accounts for a far greater proportion of total innovation costs than that suggested by the Charpie Panel. The Canadian study may be particularly interesting for medium-sized industrial nations since it is likely that the costs of commercializing the results of R&D are affected by the size of the potential market or field of utilization of the innovation. The results of Mansfield and Statistics Canada imply that governments, in their encouragement of innovation by supporting R&D, have been following a better strategy than perhaps they knew. 相似文献
963.
964.
965.
Munzir M. E. Ahmed J. A. S. Al-Obosi H. M. Osman M. E. Shayoub 《Indian journal of clinical biochemistry : IJCB》2016,31(2):162-170
Acetaminophen (APAP) a commonly used drug for decrease the fever and pain but is capable to induced hepatotoxicity at over dose. This study was carried out to investigate the effect of APAP on the expression of anti-apoptotic and antioxidative defense genes, and whether aldose reductase over-expressing plasmid capable to protect against APAP-induced oxidative stress and cell death. APAP treatment induced oxidative stress and hepatotoxicity, and significantly increased aldose reductase mRNA and protein expression in mouse hepatocyte (AML-12). Unexpectedly, AML-12 cells over-expressing aldose reductase augmented APAP-induced reduction in cell viability, reactive oxygen species (ROS) production, glutathione (GSH) depletion and glutathione S-transferase A2 expression. Moreover, over-expression of aldose reductase potentiated APAP induced reduction on proliferating cell nuclear antigen, B cell lymphoma-extra large (bcl-xL), catalase, glutathione peroxidase-1 (GPx-1) and abolished APAP-induced B-cell lymphoma 2 (bcl-2) inductions. Further, over-expression of aldose reductase significantly abolished AMP activated protein kinase (AMPK) activity in APAP-treated cells and induced p53 expression. This results demonstrate that APAP induced toxicity in AML-12, increased aldose reductase expression, and over-expression of aldose reductase render this cell more susceptible to APAP induced oxidative stress and cell death, this probably due to inhibition AMPK or bcl-2 activity, or may due to competition between aldose reductase and glutathione reductase for NADPH. 相似文献
966.
Akila V. Prashant H. Harishchandra Vivian D'souza Benedicta D'souza 《Indian journal of clinical biochemistry : IJCB》2007,22(1):131-134
Advanced age is associated with an accumulation of free radical damage, which leads to physiological and clinical modifications.
Age related changes resulting from free radical reactions include increasing levels of lipid peroxides, alterations in enzyme
activities and greater osmotic fragility. The present study was conducted to estimate the level of lipid peroxidation product-Malondialdehyde
and antioxidants Catalase and Glutathione in elderly people. An increase in lipid peroxidation and decrease in antioxidants
was observed in normal elderly people. Highly significant increase in MDA and decrease in antioxidants was observed in elderly
people when complicated with diabetes and hypertension. Supplementation of antioxidants may prevent further oxidative injury
in elderly people. 相似文献
967.
Simple as the outflow clock principle may seem for the measurement of time, its translation into an accurate clock raises formidable technical and conceptual problems. An attempt is made here to reconstruct the Egyptians' consciousness of these problems, and the success of their solutions. 相似文献
968.
Andrew H. Wilson 《Research Policy》1974,2(4):364-379
As a country with a relatively small international reputation for manufacturing and, apparently, with an even smaller one for technology-based product and process innovation in manufacturing, Canada has a long way to go to develop its manufacturing and innovative activities to the stage reached by most European countries. Recently, however, a number of science and research policy studies have been made to examine problems associated with innovation in manufacturing. This present paper deals with two important elements associated with these studies, namely, the organization of the public sector in Canada and the roles and responsibilities of the public sector agencies with regard to the encouragement of technology-based innovation in manufacturing. As pointed out in the paper, the federal structure and the agencies within it may at present frustrate as well as encourage innovation. However, assuming that the appropriate policy objectives can be articulated and accepted, the removal of the principal public sector frustrations will be dependent upon better divisions of responsibility and labour between the three levels of government. 相似文献
969.
970.
During the period 1952 to 1965, there were strenuous world-wide efforts to produce an automated cotton spinning mill. These attempts, which involved the use of concepts developed outside the textile machinery industry (i.e. automatic transfer systems), were motivated by the need to reduce the very great amount of manual handling of packages between successive operations in the yarn manufacturing process.The case is unusual in that, while many of the developments were ‘technically successful’ in that installations were made which functioned satisfactorily in the mill), they were, without exception, commercially unsuccessful from the point of view of the machinery manufacturer and mill operator. This paper describes the economic forces which led to the attempts at automation, and explains why, after an expenditure in excess of £ 25 mill/on worldwide, commercial success was not achieved.The prime reason for failure lay in minor and major developments of existing individual machines, which had continued independently of automation research, and which had, to a great extent, obviated the economic need for automation. The surprising thing (in retrospect at least), is that, as production rates were increased step by step, development engineers working to produce automated systems saw, in the increasing speeds, only a challenge to their ingenuity — not a disappearance of the need for automatic transfer devices.A secondary reason for failure in the particular case of the Shirley Institute's automated card room sequence lay in the fact that the research was directed by a committee whose terms of reference were limited to pursuance of a defined goal — the development of an automated card room. The committee had no mandate to question the soundness of its objectives, and the work continued until a technically successful system was finally produced. 相似文献