全文获取类型
收费全文 | 445578篇 |
免费 | 37442篇 |
国内免费 | 1077篇 |
专业分类
484097篇 |
出版年
2018年 | 16289篇 |
2017年 | 15238篇 |
2016年 | 12416篇 |
2015年 | 5985篇 |
2014年 | 6511篇 |
2013年 | 9040篇 |
2012年 | 15016篇 |
2011年 | 25032篇 |
2010年 | 20856篇 |
2009年 | 16510篇 |
2008年 | 20602篇 |
2007年 | 23204篇 |
2006年 | 8885篇 |
2005年 | 9768篇 |
2004年 | 9284篇 |
2003年 | 9236篇 |
2002年 | 8980篇 |
2001年 | 18437篇 |
2000年 | 18631篇 |
1999年 | 14123篇 |
1998年 | 4234篇 |
1997年 | 4518篇 |
1996年 | 4318篇 |
1995年 | 4005篇 |
1994年 | 3946篇 |
1993年 | 3818篇 |
1992年 | 11505篇 |
1991年 | 11174篇 |
1990年 | 10684篇 |
1989年 | 10255篇 |
1988年 | 9497篇 |
1987年 | 8857篇 |
1986年 | 8077篇 |
1985年 | 7959篇 |
1984年 | 6398篇 |
1983年 | 5580篇 |
1982年 | 4116篇 |
1981年 | 3590篇 |
1980年 | 3353篇 |
1979年 | 6108篇 |
1978年 | 4568篇 |
1977年 | 4123篇 |
1976年 | 3759篇 |
1975年 | 4339篇 |
1974年 | 4497篇 |
1973年 | 4389篇 |
1972年 | 4755篇 |
1971年 | 4116篇 |
1970年 | 3174篇 |
1969年 | 2968篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
Postural sway was compared for humans touching an external object while standing on an immobile or slowly moving posturographic platform. When the platform moves, the central nervous system may interpret the movement of the point of the contact with the external object as the movement of the body relative to the support or as the movement of the support itself. Thus, the information concerning the body position that is provided by the touch becomes ambiguous. It was demonstrated that contact with an external object during standing on an unstable support leads to a decrease in support sway. When a subject stands on a moving platform, this decrease is smaller than in the case of an immobile platform. Contact with an external object causes a decrease in postural responses to shank muscle vibrations on an immobile platform. On a moving platform, this decrease is nonsignificant. The change in postural sway depending on the unambiguity of afferent information is discussed in terms of the interaction between afferent signals of different modalities on the basis of the body scheme in subjects maintaining balance.Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 59–65.Original Russian Text Copyright © 2005 by Kazennikov, Shlykov, Levik. 相似文献
123.
124.
Comparative tissue ascorbic acid studies in fishes 总被引:1,自引:0,他引:1
Comparative tissue ascorbic acid levels in four species of major carp viz., Labeo rohila, L. calbasu, Cirrhina tnrigala and Catla catla , were investigated. The ascorbic acid level was found to be the highest in the spleen in the four species studied (range 430–380 μg/g) followed by the anterior (adrenal) kidney, gonads, liver, renal kidney, brain and/or eye. Heart and blood had the lowest levels (range 26–18 μg/ml) amongst the tissues studied. Overall tissue ascorbic acid levels were the highest in L. rohita and the lowest in C. mrigala . Investigation on seasonal variations in blood and kidney ascorbic acid levels of Notopterus notopterus revealed peak levels in spring (February-April) and the lowest levels in the postspawning period (August-September). 相似文献
125.
Relation between D-glucose and L- and D-alanine in the initiation of germination of Bacillus subtilis spore 总被引:1,自引:0,他引:1
The rate of L-alanine-initiated germination of Bacillus subtilis spore was measured by both loss of heat resistance and loss of turbidity, and the effect of glucose on the germination response to a wide range of concentrations of the germinant was analyzed in the presence and absence of D-alanine, an inhibitor. Glucose stimulated L-alanine germination by means of a cooperative effect: glucose increased the affinity of L-alanine by about 3-fold and the rate of germination by about 1.3-fold. However, glucose had little effect on the binding affinity of D-alanine. The apparent binding constant of L-alanine to the spore, which was determined by the next measurable event in the trigger reaction, was 1.2 X 10(-5), that of D-alanine was 6 X 10(-6), and that of glucose was 5 X 10(-5). The relation between the binding site for glucose and those for L- and D-alanine on the spore is discussed. Effect of glucose analogs was also examined. 相似文献
126.
M J Ronis I Johansson K Hultenby J Lagercrantz H Glaumann M Ingelman-Sundberg 《European journal of biochemistry》1991,198(2):383-389
The regulation of CYP2E1 and 2B1 was studied by following mRNA levels, catalytic activities and the subcellular distribution of the apoproteins in rat liver 0, 6, 12, 24, 48 and 96 h after a single intragastric dose of acetone. No changes were observed in hepatic CYP2E1 mRNA levels at any time after acetone treatment, whereas rapid rises were observed in the microsomal amount of CYP2E1 protein and CYP2E1-catalyzed 4-nitrophenol hydroxylase and carbon-tetrachloride-initiated lipid-peroxidation activities. However, CYP2E1-dependent catalytic activities declined much faster than the immunodetectable CYP2E1 protein, suggesting that this cytochrome P-450 is inactivated prior to degradation. Similar results were seen in primary hepatocyte cultures. By contrast, concomitant changes in levels of CYP2B1 and CYP2B1-dependent O-depentylation of pentoxyresorufin were observed in the same microsomal preparations. Investigation of the degradative mechanism of both CYP2E1 and CYP2B1 by immunoquantitation of the proteins in lysosomes and by immunohistochemistry indicated their degradation via an autophagic-lysosomal pathway. The data suggest that CYP2E1 is acutely inactivated in the endoplasmic reticulum and that degradation of this isozyme occurs, at least in part, by the lysosomal route. By contrast, CYP2B1 is principally controlled at the level of synthesis. 相似文献
127.
128.
129.
X-IRRADIATION of mammalian cells in culture yields a survival curve of the threshold type (for review see ref. 1). It isjnter-esting to ask how one can enhance the radiation response by small changes of the physical environment of the cells, as can be done chemically, for example, by incorporation of 5-bromo-deoxyuridine into DNA1,2. Elevation of the temperature is a likely prospect for enhancement of radiosensitivity for the following reasons. It is known that proteins are heat labile and that temperature sensitive mutants of bacteria and phage can be obtained for many different enzymes3 which are operative at 37° C but not at 42° or 43°C. For example4, DNA polymerase is reversibly temperature sensitive; it is rendered inoperative above 42°C, but will be functional again when the temperature is lowered. It is not unreasonable to expect that temperature sensitive mutations for many enzymes occur frequently and that the use of temperatures somewhat higher than the normal range at which the cells grow might disclose sensitivities for specific enzymes in normal cells of higher organisms. 相似文献
130.
IN addition to its well known antiviral activity, interferon has recently been shown to inhibit the multiplication of tumour and mammalian cells in cell culture1–6. We report here the inhibition by interferon of DNA synthesis induced in mouse spleen lymphocytes by the non-viral stimuli phytohaemagglutinin (PHA) and allogeneic lymphocytes. These findings are in accord with our contention that interferon affects cell function and, furthermore, they suggest that by acting on lymphocytes, interferon plays a role in the immunological response of the host. 相似文献