全文获取类型
收费全文 | 6508篇 |
免费 | 638篇 |
国内免费 | 1篇 |
专业分类
7147篇 |
出版年
2023年 | 32篇 |
2022年 | 89篇 |
2021年 | 129篇 |
2020年 | 84篇 |
2019年 | 106篇 |
2018年 | 139篇 |
2017年 | 134篇 |
2016年 | 182篇 |
2015年 | 288篇 |
2014年 | 316篇 |
2013年 | 424篇 |
2012年 | 523篇 |
2011年 | 507篇 |
2010年 | 325篇 |
2009年 | 287篇 |
2008年 | 336篇 |
2007年 | 377篇 |
2006年 | 348篇 |
2005年 | 327篇 |
2004年 | 294篇 |
2003年 | 295篇 |
2002年 | 288篇 |
2001年 | 120篇 |
2000年 | 91篇 |
1999年 | 113篇 |
1998年 | 95篇 |
1997年 | 69篇 |
1996年 | 62篇 |
1995年 | 56篇 |
1994年 | 66篇 |
1993年 | 53篇 |
1992年 | 44篇 |
1991年 | 54篇 |
1990年 | 38篇 |
1989年 | 46篇 |
1988年 | 33篇 |
1987年 | 26篇 |
1986年 | 35篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 14篇 |
1978年 | 20篇 |
1977年 | 22篇 |
1975年 | 14篇 |
1974年 | 14篇 |
1972年 | 17篇 |
排序方式: 共有7147条查询结果,搜索用时 0 毫秒
1.
Cynthia L. Deitrick Richard E. Katholi David J. Huddleston Kathy Hardiek Lucienne Burrus 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,751(2)
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation. 相似文献
2.
Injection of manganese into the rat corpus striatum causes a rapid fall in the biopterin and dopamine (DA) content ipsilateral to the lesion. Two weeks after the lesion both biopterin and DA are partially recovered. Controls, injected with saline or magnesium, do not show alterations in their DA or cofactor levels. It is proposed that the fall in DA levels results from a rapid displacement of the amine from its storage sites by manganese followed by a decrease in the rate of DA synthesis causes by the drop in cofactor levels. 相似文献
3.
4.
5.
6.
Alfalfa (Medicago sativa L. cv. Vernal) nodules were separatedinto host plant fractions and fractions of rhizobial originby differential centrifugation and sedimentation equilibriumcentrifugation. Both NAD- and NADP-linked isocitrate dehydrogenase(70%, 90%) and glutamate dehydrogenase activities (90%, 83%)were located primarily (percent total nodule activity) in thefractions of plant origin and their specific activities werehighest in the fractions of plant origin. More than 50% of thenodules' total activity of both glutamine synthetase and NAD-glutamatesynthase and greater than 90% of the total glutamate oxaloacetatetransaminase activity was located in plant fractions. However,the fractions of rhizobial origin had the highest specific activitiesof glutamine synthetase and glutamate synthase. (Received September 5, 1981; Accepted December 7, 1981) 相似文献
7.
Jorge E. Ramos Gretta T. Pecl Natalie A. Moltschaniwskyj Jan M. Strugnell Rafael I. León Jayson M. Semmens 《PloS one》2014,9(8)
Understanding the response of any species to climate change can be challenging. However, in short-lived species the faster turnover of generations may facilitate the examination of responses associated with longer-term environmental change. Octopus tetricus, a commercially important species, has undergone a recent polewards range shift in the coastal waters of south-eastern Australia, thought to be associated with the southerly extension of the warm East Australian Current. At the cooler temperatures of a polewards distribution limit, growth of a species could be slower, potentially leading to a bigger body size and resulting in a slower population turnover, affecting population viability at the extreme of the distribution. Growth rates, body size, and life span of O. tetricus were examined at the leading edge of a polewards range shift in Tasmanian waters (40°S and 147°E) throughout 2011. Octopus tetricus had a relatively small body size and short lifespan of approximately 11 months that, despite cooler temperatures, would allow a high rate of population turnover and may facilitate the population increase necessary for successful establishment in the new extended area of the range. Temperature, food availability and gender appear to influence growth rate. Individuals that hatched during cooler and more productive conditions, but grew during warming conditions, exhibited faster growth rates and reached smaller body sizes than individuals that hatched into warmer waters but grew during cooling conditions. This study suggests that fast growth, small body size and associated rapid population turnover may facilitate the range shift of O. tetricus into Tasmanian waters. 相似文献
9.
10.