全文获取类型
收费全文 | 8661篇 |
免费 | 483篇 |
国内免费 | 6篇 |
专业分类
9150篇 |
出版年
2023年 | 77篇 |
2022年 | 122篇 |
2021年 | 254篇 |
2020年 | 151篇 |
2019年 | 170篇 |
2018年 | 233篇 |
2017年 | 214篇 |
2016年 | 273篇 |
2015年 | 357篇 |
2014年 | 406篇 |
2013年 | 563篇 |
2012年 | 583篇 |
2011年 | 554篇 |
2010年 | 334篇 |
2009年 | 274篇 |
2008年 | 388篇 |
2007年 | 348篇 |
2006年 | 337篇 |
2005年 | 332篇 |
2004年 | 270篇 |
2003年 | 223篇 |
2002年 | 230篇 |
2001年 | 201篇 |
2000年 | 179篇 |
1999年 | 164篇 |
1998年 | 60篇 |
1997年 | 56篇 |
1996年 | 65篇 |
1995年 | 52篇 |
1994年 | 59篇 |
1993年 | 37篇 |
1992年 | 117篇 |
1991年 | 117篇 |
1990年 | 88篇 |
1989年 | 95篇 |
1988年 | 88篇 |
1987年 | 90篇 |
1986年 | 87篇 |
1985年 | 92篇 |
1984年 | 82篇 |
1983年 | 50篇 |
1982年 | 48篇 |
1981年 | 42篇 |
1980年 | 48篇 |
1979年 | 78篇 |
1978年 | 58篇 |
1977年 | 49篇 |
1976年 | 42篇 |
1974年 | 39篇 |
1973年 | 44篇 |
排序方式: 共有9150条查询结果,搜索用时 15 毫秒
61.
Summary The critical role of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) in determining the rate of ethanol production is confirmed using PDC constitutive mutants. By deriving strains with altered levels of these two enzymes, it has been found that a high level of both PDC and ADH is necessary for faster ethanol production. 相似文献
62.
The uptake of nutrients was investigated in the renal cortical brush border membrane (BBM) vesicles at different stages of ascending pyelonephritis. There was significant difference (p less than 0.05) in the uptake of D-glucose, L-alanine, L-aspartate, L-lysine and L-proline 3 days postinfection and onwards in both right unobstructed and left obstructed experimental kidneys as compared to the sham operated control. The uptake of D-glucose, L-lysine and L-proline was found to be significantly decreased (p less than 0.05) during the course of infection. While uptake of L-alanine and L-aspartate increased (p less than 0.05) in early stages and decreased (p less than 0.05) in later stages of infection. The differential effect was attributed to the compensatory measure and different kinds of transport systems for different types of amino acids. 相似文献
63.
Vipin K. Paliwal Krishan K. Kohli Mridula Sharma Ravindra Nath 《Molecular and cellular biochemistry》1986,71(2):139-147
Metallothionein (MT) a low molecular weight, Cd-binding, cysteine rich, cytosolic protein has been isolated, purified and characterized from cadmium exposed Rhesus monkeys maintained on protein calorie malnourished (PCM) diet. Metallothionein was resolved into three isoforms i.e. MTa, MTb and MTVc. The ratio of Cd, Zn and Cu varied in these isometallothioneins. MTc was the major isometallothionein. UV Spectra of MTc revealed the presence of mercaptide bonds and absence of aromatic amino acids. These observations were further confirmed by amino acid analysis of MTc which demonstrated high cysteine content (22.6) followed by serine, glycine and lysine. The molecular weight of MTc as determined by gel filtration and amino acid analysis was 13000 and 6398 daltons respectively. This demonstrates that MTc is a non-globular ellipsoid polypeptide. MTc showed a unique property of binding selenium. Monkey liver metallothionein was immunologically identical with human metallothionein. All the characteristics of MTc obtained in the present study reveal a similarity between monkey and human metallothionein probably due to closer phylogenetic relationship between the two species. 相似文献
64.
The witches' broom disease has been recently observed on poplars in Paris and its suburbs. The incidence of the disease appeared to be considerably high along main roads. The electron microscopic examination of 350 nm thick sieve tube sections revealed the presence of wall-less mycoplasmalike organisms (MLOs) in diseased samples of Populus alba var. nivea Wesm. They could not be found in their healthy counterparts. 相似文献
65.
Underground and aboveground biomass and their ratios at flowering time in different natural stands of Typha angustata near Jaipur, India were studied in the field and experimentally over a period of eleven months (June to April). The underground biomass was 40–50% of the aboveground biomass in both natural and experimental conditions. 相似文献
66.
Sanjib Das Robindra N. Baruah Ram P. Sharma Jogendra N. Baruah Palaniappan Kulanthaivel Werner Herz 《Phytochemistry》1983,22(9):1989-1991
Cynaropicrin, 11βH-11,13-dihydrodesacylcynaropicrin, aguerins A and B, isoamberboin and the new guaianolides saussureolide and 11βH-11,13-dihydrodesacylcynaropicrin 8-β-d-glucoside were isolated from Saussurea affinis. 相似文献
67.
Methylation of transfer RNA during transformation of human lymphocytes by phytohemagglutinin 总被引:1,自引:0,他引:1
Methylation of transfer RNA during phytohemagglutinin induced transformation of human lymphocytes was studied by labeling the tRNA with (methyl-H3)-methionine and measuring the distribution of tritium in the methylated nucleotides. An alteration in the pattern of methylation occurred within hours after PHA-stimulation and this change was maintained through several cell generations. There was a 50 to 94% increase in the relative amount of methylated N2-methyl-guanine (1 to 3 hr) and a 40 to 59% decrease in the relative amount of 1-methyladenine (1 to 12 hr). Treatment of the stimulated cells with Actinomycin D prevented the subsequent methylation not tRNA. However, inhibition of protein synthesis by puromycin did not effect the early changes observed in the methylation of tRNA. 相似文献
68.
69.
Summary Of A. rubellum, already known as a diploid (2n=16), a triploid form has been collected from Pathankot. All the 24 chromosomes in the latter possess median to submedian kinetochores. Of these, 6 are nucleolar chromosomes, which do not represent 3 truly morphologically homologous pairs.Meiosis is characterised by the presence of quadrivalents, trivalents, bivalents and univalents. Out of these, trivalents are the most common and often as many as 8 were seen in a cell. Anaphase-I distribution is irregular and shows bridge-fragment configurations, lagging chromosomes and micronuclei. The subsequent course of meiosis is also not normal and results in sterility.In view of the high frequency of trivalents, the triploid form appears to be an autotriploid and the karyotypic heterozygosity points to an intervarietal origin. It maintains itself because of the efficient vegetative reproduction. 相似文献
70.