全文获取类型
收费全文 | 3971篇 |
免费 | 408篇 |
国内免费 | 1篇 |
出版年
2023年 | 17篇 |
2022年 | 30篇 |
2021年 | 83篇 |
2020年 | 51篇 |
2019年 | 71篇 |
2018年 | 91篇 |
2017年 | 60篇 |
2016年 | 103篇 |
2015年 | 158篇 |
2014年 | 178篇 |
2013年 | 241篇 |
2012年 | 287篇 |
2011年 | 250篇 |
2010年 | 177篇 |
2009年 | 181篇 |
2008年 | 209篇 |
2007年 | 187篇 |
2006年 | 183篇 |
2005年 | 162篇 |
2004年 | 148篇 |
2003年 | 119篇 |
2002年 | 137篇 |
2001年 | 78篇 |
2000年 | 76篇 |
1999年 | 66篇 |
1998年 | 44篇 |
1997年 | 27篇 |
1996年 | 30篇 |
1995年 | 28篇 |
1994年 | 33篇 |
1993年 | 40篇 |
1992年 | 74篇 |
1991年 | 55篇 |
1990年 | 48篇 |
1989年 | 49篇 |
1988年 | 48篇 |
1987年 | 36篇 |
1986年 | 40篇 |
1985年 | 41篇 |
1984年 | 21篇 |
1983年 | 34篇 |
1982年 | 16篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1973年 | 19篇 |
1972年 | 28篇 |
1971年 | 22篇 |
1967年 | 17篇 |
1966年 | 18篇 |
排序方式: 共有4380条查询结果,搜索用时 15 毫秒
1.
Oxygen inhibition of nitrate uptake is a general regulatory mechanism in nitrate respiration 总被引:8,自引:0,他引:8
It has recently been demonstrated that oxygen inhibits nitrate uptake by denitrifying Pseudomonas aeruginosa. The purpose of the present investigation was to determine if this novel mechanism of regulation is universal for the regulation of nitrate respiration in other widely divergent species of bacteria. Nitrate transport by whole cell suspensions was completely and reversibly inhibited in 11 out of 12 species tested, whereas nitrate reduction by cell-free extracts was not affected by oxygen or was only partially inhibited in some cases. These results indicate that oxygen inhibition of nitrate uptake is a general regulatory phenomenon. 相似文献
2.
3.
4.
5.
Protection of Mice against Lethal Coxsackievirus B3 Infection by Using DNA Immunization 总被引:27,自引:0,他引:27 下载免费PDF全文
Andreas Henke Elke Wagner J. Lindsay Whitton Roland Zell Axel Stelzner 《Journal of virology》1998,72(10):8327-8331
Vaccination with DNA and recombinant vaccinia viruses (rec.VV) has been studied with the coxsackievirus B3 (CVB3) model system. Plasmids encoding all structural proteins of CVB3, when injected intramuscularly, induced only low levels of virus-specific antibodies. However, DNA vaccination with the major structural protein VP1 protected 72.2% of mice from lethal challenge, whereas VP1 expressed by rec.VV was much less efficient. 相似文献
6.
7.
8.
Summary The effects of varying the pH of the cocultivation medium, additons of vir-inducing phenolic compounds and the strains of wild-type agrobacteria on transformation rates of a number of different varieties of Antirrhinum majus were studied. In general, optimal transformation was found with strains C58 or A281 and was favoured by low pH and the inclusion of acetosyringone in the co-cultivation medium. However, maximal transformation of the least susceptible variety was achieved at high pH and in the presence of syringaldehyde. This demonstrates the need for the optimization of a wide range of culture conditions when working with new genotypes and offers a rational approach towards the development of Agrobacterium-mediated transformation of new species or varieties.Abbreviations BAP
6-benzylaminopurine
- MS
Murashige and Skoog medium (Murashige and Skoog, 1962)
- NOA
naphthoxyacetic acid 相似文献
9.
Karen L. Lindsay Christian Hellmuth Olaf Uhl Claudia Buss Pathik D. Wadhwa Berthold Koletzko Sonja Entringer 《PloS one》2015,10(12)
Pregnancy is characterized by a complexity of metabolic processes that may impact fetal development and ultimately, infant health outcomes. However, our understanding of whole body maternal and fetal metabolism during this critical life stage remains incomplete. The objective of this study is to utilize metabolomics to profile longitudinal patterns of fasting maternal metabolites among a cohort of non-diabetic, healthy pregnant women in order to advance our understanding of changes in protein and lipid concentrations across gestation, the biochemical pathways by which they are metabolized and to describe variation in maternal metabolites between ethnic groups. Among 160 pregnant women, amino acids, tricarboxylic acid (TCA) cycle intermediates, keto-bodies and non-esterified fatty acids were detected by liquid chromatography coupled with mass spectrometry, while polar lipids were detected through flow-injected mass spectrometry. The maternal plasma concentration of several essential and non-essential amino acids, long-chain polyunsaturated fatty acids, free carnitine, acetylcarnitine, phosphatidylcholines and sphingomyelins significantly decreased across pregnancy. Concentrations of several TCA intermediates increase as pregnancy progresses, as well as the keto-body β-hydroxybutyrate. Ratios of specific acylcarnitines used as indicators of metabolic pathways suggest a decreased beta-oxidation rate and increased carnitine palmitoyltransferase-1 enzyme activity with advancing gestation. Decreasing amino acid concentrations likely reflects placental uptake and tissue biosynthesis. The absence of any increase in plasma non-esterified fatty acids is unexpected in the catabolic phase of later pregnancy and may reflect enhanced placental fatty acid uptake and utilization for fetal tissue growth. While it appears that energy production through the TCA cycle increases as pregnancy progresses, decreasing patterns of free carnitine and acetylcarnitine as well as increased carnitine palmitoyltransferase-1 rate and β-hydroxybutyrate levels suggest a concomitant upregulation of ketogenesis to ensure sufficient energy supply in the fasting state. Several differences in metabolomic profiles between Hispanic and non-Hispanic women demonstrate phenotypic variations in prenatal metabolism which should be considered in future studies. 相似文献
10.