全文获取类型
收费全文 | 6480篇 |
免费 | 65篇 |
国内免费 | 88篇 |
专业分类
系统科学 | 65篇 |
丛书文集 | 69篇 |
教育与普及 | 25篇 |
理论与方法论 | 15篇 |
现状及发展 | 2451篇 |
研究方法 | 303篇 |
综合类 | 3673篇 |
自然研究 | 32篇 |
出版年
2021年 | 48篇 |
2016年 | 47篇 |
2015年 | 66篇 |
2014年 | 75篇 |
2013年 | 128篇 |
2012年 | 189篇 |
2011年 | 209篇 |
2010年 | 108篇 |
2009年 | 92篇 |
2008年 | 171篇 |
2007年 | 206篇 |
2006年 | 160篇 |
2005年 | 133篇 |
2004年 | 152篇 |
2003年 | 118篇 |
2002年 | 128篇 |
2001年 | 220篇 |
2000年 | 186篇 |
1999年 | 142篇 |
1992年 | 119篇 |
1991年 | 76篇 |
1990年 | 89篇 |
1989年 | 74篇 |
1988年 | 75篇 |
1987年 | 86篇 |
1986年 | 59篇 |
1985年 | 103篇 |
1984年 | 94篇 |
1983年 | 81篇 |
1982年 | 63篇 |
1981年 | 58篇 |
1980年 | 74篇 |
1979年 | 188篇 |
1978年 | 147篇 |
1977年 | 124篇 |
1976年 | 116篇 |
1975年 | 126篇 |
1974年 | 162篇 |
1973年 | 134篇 |
1972年 | 139篇 |
1971年 | 176篇 |
1970年 | 212篇 |
1969年 | 160篇 |
1968年 | 172篇 |
1967年 | 141篇 |
1966年 | 148篇 |
1965年 | 113篇 |
1958年 | 68篇 |
1957年 | 47篇 |
1954年 | 47篇 |
排序方式: 共有6633条查询结果,搜索用时 46 毫秒
831.
Novel mutations in families with unusual and variable disorders of the skeletal muscle sodium channel. 总被引:11,自引:0,他引:11
A I McClatchey D McKenna-Yasek D Cros H G Worthen R W Kuncl S M DeSilva D R Cornblath J F Gusella R H Brown 《Nature genetics》1992,2(2):148-152
Mutations in the skeletal muscle sodium channel gene (SCN4A) have been described in paramyotonia congenita (PMC) and hyperkalaemic periodic paralysis (HPP). We have found two mutations in SCN4A which affect regions of the sodium channel not previously associated with a disease phenotype. Furthermore, affected family members display an unusual mixture of clinical features reminiscent of PMC, HPP and of a third disorder, myotonia congenita (MC). The highly variable individual expression of these symptoms, including in some cases apparent non-penetrance, implies the existence of modifying factors. Mutations in SCN4A can produce a broad range of phenotypes in muscle diseases characterized by episodic abnormalities of membrane excitability. 相似文献
832.
833.
The mechanics of chromosome movement, mitotic spindle assembly and spindle elongation have long been central questions of cell biology. After attachment in prometaphase of a microtubule from one pole, duplicated chromosome pairs travel towards the pole in a rapid but discontinuous motion. This is followed by a slower congression towards the midplate as the chromosome pair orients with each kinetochore attached to the microtubules from the nearest pole. The pairs disjoin at anaphase and translocate to opposite poles and the interpolar distance increases. Here we identify CENP-E as a kinesin-like motor protein (M(r) 312,000) that accumulates in the G2 phase of the cell cycle. CENP-E associates with kinetochores during congression, relocates to the spindle midzone at anaphase, and is quantitatively discarded at the end of the cell division. CENP-E is likely to be one of the motors responsible for mammalian chromosome movement and/or spindle elongation. 相似文献
834.
Lipid peroxidation and activities of antioxidative enzymes were studied in the brain cortex after short (15 min) cerebral ischemia and reperfusion (10 min) in rats. Conjugated dienes (CD) and thiobarbituric acid-reactive substances (TBARS) were significantly elevated in the group of rats with ischemia followed by reperfusion in comparison to the ischemic animals. Superoxide dismutase (SOD) activity significantly increased in the group of animals with ischemia and reperfusion. No significant changes in the activities of glutathione peroxidase (GP) were observed. Stobadine administered before ischemia or before reperfusion decreased the level of TBARS. Stobadine probably prevents malondialdehyde (MDA) formation from hydroperoxide or might elevate the activity of aldehyde dehydrogenase. In contradiction to the findings after long-lasting (4 h) ischemia and subsequent reperfusion, no decrease in the concentration of CD or in the activity of SOD or GP was found. 相似文献
835.
Cellular and Molecular Life Sciences - Ethyl acetate is utilizdd byDrosophila buzzatii adults under some physiological conditions, reducing mortality rate and body weight loss. Ethanol has similar... 相似文献
836.
Summary Rats can produce glycine from hydroxyproline and vice versa. After the injection, hydroxyproline is rapidly converted into glycine and then incorporated into collagen. Later the labelled amino acids in collagen are hydroxyproline, proline, serine, threonine, alanine, and glutamic acid. We suppose that all these labelled amino acids come from glycine. 相似文献
837.
Plasma progesterone, testosterone, total estrogens and immunoreactive gonadotropin were measured in nesting and non-nesting sea turtles, Chelonia mydas. Progesterone and gonadotropin concentrations were significantly higher in nesting than in non-nesting turtles, testosterone was not significantly different in either group and total estrogens appeared to be slightly in the nesting group. 相似文献
838.
839.
840.
Azotobacter cytochrome b557.5 is a bacterioferritin. 总被引:22,自引:0,他引:22