全文获取类型
收费全文 | 11275篇 |
免费 | 1095篇 |
国内免费 | 8篇 |
专业分类
12378篇 |
出版年
2021年 | 105篇 |
2018年 | 107篇 |
2017年 | 92篇 |
2016年 | 178篇 |
2015年 | 268篇 |
2014年 | 314篇 |
2013年 | 446篇 |
2012年 | 535篇 |
2011年 | 567篇 |
2010年 | 395篇 |
2009年 | 349篇 |
2008年 | 516篇 |
2007年 | 574篇 |
2006年 | 554篇 |
2005年 | 563篇 |
2004年 | 576篇 |
2003年 | 507篇 |
2002年 | 551篇 |
2001年 | 121篇 |
2000年 | 99篇 |
1999年 | 162篇 |
1998年 | 164篇 |
1997年 | 119篇 |
1996年 | 135篇 |
1995年 | 116篇 |
1994年 | 161篇 |
1993年 | 127篇 |
1992年 | 110篇 |
1991年 | 109篇 |
1990年 | 112篇 |
1989年 | 114篇 |
1988年 | 106篇 |
1987年 | 101篇 |
1986年 | 94篇 |
1985年 | 129篇 |
1984年 | 141篇 |
1983年 | 120篇 |
1982年 | 173篇 |
1981年 | 194篇 |
1980年 | 182篇 |
1979年 | 114篇 |
1978年 | 150篇 |
1977年 | 134篇 |
1976年 | 118篇 |
1975年 | 100篇 |
1974年 | 128篇 |
1973年 | 129篇 |
1972年 | 84篇 |
1970年 | 86篇 |
1969年 | 80篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Homogenates of specific brain regions of three sensory systems (auditory, olfactory, and visual) were prepared from pigmented Long-Evans Hooded rats and assayed for amino acid concentrations and activities of glutaminase, aspartate aminotransferase (total, cytosolic, and, by difference, mitochondrial), malate dehydrogenase, lactate dehydrogenase, and choline acetyltransferase. Comparing the quantitative distributions among regions revealed significant correlations between AAT and aspartate, between glutaminase and glutamate, between glutamate and glutamine, and between AAT plus glutaminase, or glutaminase alone, and the sum of aspartate, glutamate, and GABA, suggesting a metabolic pathway involving the synthesis of a glutamate pool as precursor to aspartate and GABA. Of the inhibitory transmitter amino acids, GABA concentrations routinely exceeded those of glycine, but glycine concentrations were relatively high in brainstem auditory structures. 相似文献
72.
Ergosterol, a membrane sterol found in fungi but not in plants, was used to estimate live mycelial biomass in ectomycorrhizae. Loblolly pine (Pinus taeda L.) seeds were sown in April 1993 and grown with standard nursery culture practices. Correlations between total seedling ergosterol and visual assessment of mycorrhizal colonization were high during July and August but low as ectomycorrhizal development continued into the growing season. Percentages of mycelial dry weight over lateral roots decreased from 9% in July to 2.5% in November because seedling lateral root dry weight accumulated faster than mycelial dry weight. Total ergosterol per seedling increased from July through February. As lateral root dry weight ceased to increase during winter months, ectomycorrhizal mycelia became the major carbohydrate sink of pine seedlings. No distinctive seasonal pattern of soil ergosterol content was observed. The impact of ectomycorrhizal fungi on plant carbohydrate source-sink dynamics can be quantitatively estimated with ergosterol analysis but not with conventional visual determination. 相似文献
73.
The effects of orally administered prostaglandin E2, 16,16-dimethyl prostaglandin E2 and U-46619, an analogue of the prostaglandin endoperoxide PGH2, on gastric secretory volume, acid and mucus were studied in the rat. All of the compounds significantly increased the volume of gastric secretion, mucus secretion, measured as N-acetylneuraminic acid and mucus synthesis measured as the incorporation of [3H]-glucosamine into mucosal glycoprotein; however, only PGE2 and 16,16-dimethyl PGE2 inhibited acid secretion. U-46619, 1.5 mg/kg provided significant protection against ethanol-induced gastric ulcers, an effect that has been previously shown for the other two compounds. These studies provide additional evidence that prostaglandin induced mucosal protection may by related to an effect on mucus and on stimulation of nonparietal cell gastric secretion. Further study of these parameters may be important in the development of antiulcer drugs for long term clinical use. 相似文献
74.
Grantley W. Lycett Ashton J. Delauney Wenming Zhao John A. Gatehouse Ronald R. D. Croy Donald Boulter 《Plant molecular biology》1984,3(2):91-96
The sequence of two cDNA clones coding for the whole of the -subunit and most of the -subunit of legumin are presented together with a considerable amount of protein sequence data to confirm the predicted amino acid sequence. A unique feature shown by these cDNAs is the presence of three 56 base pair tandem repeats in the region encoding the C terminal of the polypeptide. The tandem repeats are also exhibited in the predicted polypeptide sequence as three 18 amino acid repeats which contain extremely high proportions of polar, mainly acidic, residues. The new sequences are compared to the previously published sequence of some shorter legumin cDNAs (Nature 295: 76–79). In the region where the sequences overlap, the previous cDNAs differ from the new ones by only a few base substitutions but most of the repeated region is not present though the sequences on either side are. The possibility that the absence of the repeats may reflect the difference between two types of legumin gene, rather than an artefact of the cloning of the cDNAs, is discussed. 相似文献
75.
Thomas J. Laughlin Adría L. Herrmann Donald E. Olins 《Molecular and cellular biochemistry》1984,62(2):157-163
Summary The macronuclear chromatin of Oxytrichia nova consists of chromatin fragments which are fully soluble in 0.2 mM EDTA and whose DNA length varies from 500–25 000 bp. The DNA migrates electrophoretically as a series of discrete bands, with specific genes present in only one or a few bands. The chromatin fragments are composed of nucleosomes and migrate electrophoretically in proportion to their DNA length. These results suggest schemes for the fractionation of undigested chromatin in order to enrich for specific genes, facilitating analysis of changes in chromatin structure associated with changes in gene expression. 相似文献
76.
Donald A D Macleod 《BMJ (Clinical research ed.)》1984,288(6410):63-64
77.
78.
Nine known temperature phages ofBacillus subtilis, including four that are newly isolated (ϱ6, ϱ10, ϱ14, and ϱ18), have been compared. Analysis by serology, immunity, host
range, and adsorption site similarity place the phages into four groups: Group I, ϕ105, ϱ6, ϱ10, and ϱ14, which are 80–90%
related; Group II, SPO2; Group III, ϕ3T and ϱ11, 100% related; and Group IV, SP16. The phage ϱ18 is largely uncharacterized,
but is heteroimmune to other groups. 相似文献
79.
Haemoglobin concentrations, haematocrit values, red blood cell counts, red blood cell diameter, erythrocyte sedimentation rate and plasma haemoglobin concentration were measured on the air-breathing mud eel Amphipnous cuchia . 相似文献
80.