全文获取类型
收费全文 | 6023篇 |
免费 | 1001篇 |
国内免费 | 1288篇 |
出版年
2023年 | 215篇 |
2022年 | 270篇 |
2021年 | 312篇 |
2020年 | 292篇 |
2019年 | 324篇 |
2018年 | 302篇 |
2017年 | 309篇 |
2016年 | 370篇 |
2015年 | 342篇 |
2014年 | 457篇 |
2013年 | 503篇 |
2012年 | 379篇 |
2011年 | 378篇 |
2010年 | 259篇 |
2009年 | 324篇 |
2008年 | 302篇 |
2007年 | 363篇 |
2006年 | 312篇 |
2005年 | 279篇 |
2004年 | 220篇 |
2003年 | 194篇 |
2002年 | 195篇 |
2001年 | 134篇 |
2000年 | 144篇 |
1999年 | 107篇 |
1998年 | 102篇 |
1997年 | 162篇 |
1996年 | 78篇 |
1995年 | 77篇 |
1994年 | 57篇 |
1993年 | 66篇 |
1992年 | 50篇 |
1991年 | 37篇 |
1990年 | 43篇 |
1989年 | 45篇 |
1988年 | 29篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 31篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 9篇 |
排序方式: 共有8312条查询结果,搜索用时 15 毫秒
1.
2.
3.
In the current work, the quantification of different poly(ethylene glycol) (PEG)–potassium phosphate/sodium citrate aqueous two-phase system (ATPS) phase-forming components was investigated by using conductivity and refractive index measurements. For this purpose, refractive index and conductivity calibration curves were obtained for ATPS at different pH values in the presence of different bovine serum albumin (BSA) concentrations. Whereas BSA had no effect on the conductivity, it had a considerable effect on the refractive index. Finally, a convenient dilution of the samples prior to the ATPS constituent determination is needed to ensure no significant influence from BSA. 相似文献
4.
5.
This paper introduces the vectorial Kappa (κv) that one can utilize to assess congruence between two vectorial mosaics. The vectorial Kappa extends for vectorial mosaics the approach of the so-called Cohen's Kappa index, commonly used to compare raster mosaics. By comparing both approaches, we aim to demonstrate how efficient and convenient a vector-based congruence may be when working on vectorial mosaics. 相似文献
6.
7.
Massimo Mezzavilla Annamaria Iorio Marco Bobbo Angela D'Eustacchio Marco Merlo Paolo Gasparini Sheila Ulivi Gianfranco Sinagra 《Gene》2014
Background
Recent studies suggested that resting heart rate (RHR) might be an independent predictor of cardiovascular mortality and morbidity. Nonetheless, the interrelation between RHR and cardiovascular diseases is not clear. In order to resolve this puzzle, the importance of genetic determinants of RHR has been recently suggested, but it needs to be further investigated.Objective
The aim of this study was to estimate the contribution of common genetic variations on RHR using Genome Wide Association Study.Methods
We performed a Genome Wide Association Study in an isolated population cohort of 1737 individuals, the Italian Network on Genetic Isolates — Friuli Venezia Giulia (INGI-FVG). Moreover, a haplotype analysis was performed. A regression tree analysis was run to highlight the effect of each haplotype combination on the phenotype.Results
A significant level of association (p < 5 × 10− 8) was detected for Single Nucleotide Polymorphisms (SNPs) in two genes expressed in the heart: MAML1 and CANX. Founding that the three different variants of the haplotype, which encompass both genes, yielded a phenotypic correlation. Indeed, a haplotype in homozygosity is significantly associated with the lower quartile of RHR (RHR ≤ 58 bpm). Moreover no significant association was found between cardiovascular risk factors and the different haplotype combinations.Conclusion
Mastermind-like 1 and Calnexin were found to be associated with RHR. We demonstrated a relation between a haplotype and the lower quartile of RHR in our populations. Our findings highlight that genetic determinants of RHR may be implicated in determining cardiovascular diseases and could allow a better risk stratification. 相似文献8.
3种滨藜属牧草苗期叶片解剖结构及生理特性对干旱的响应 总被引:1,自引:0,他引:1
通过盆栽控水试验,设置5个干旱胁迫水平,分别为最大田间持水量的80%(CK)、60%(轻度胁迫)、45%(中度胁迫)、30%(重度胁迫)、20%(极重度胁迫),并同步设计充足灌水后自然干旱实验,测定干旱胁迫对3种滨藜属牧草叶片形态解剖结构、叶片相对含水量、叶绿素含量、净光合速率、可溶性糖含量、质膜相对透性和丙二醛含量等生理生化指标的影响,以明确3种滨藜属牧草的抗旱特性,并探索其抗旱机理。结果表明:(1)3种滨藜属牧草均具有适应旱生环境的典型叶片结构特征,即在干旱胁迫条件下叶片组织结构形态表现为叶片栅栏组织逐渐变薄,而海绵组织在胁迫早期先变薄后增厚的现象,叶肉组织结构紧密度也出现了先降低后增高的规律。(2)随着干旱胁迫的加剧,叶片的可溶性糖含量增加,而其相对含水量减少,3种滨藜属牧草在土壤含水量很低的情况下叶片仍能保持高于52%的相对含水量。(3)在干旱胁迫下,3种滨藜属牧草叶片的叶绿素含量、净光合速率、气孔导度和蒸腾速率都发生显著变化,细胞膜受到的伤害程度有明显差异。(4)3种滨藜属牧草抗旱能力均较强,在干旱胁迫下其抗旱性综合表现为灰白滨藜变种1灰白滨藜变种2四翅滨藜。 相似文献
9.
K. K. Nkongolo 《Plant Systematics and Evolution》1996,203(1-2):27-40
A detailed karyotype analysis was made on the somatic complement ofPicea rubens andP. glauca. B-chromosomes were observed in someP. glauca populations. The karyotypes are generally asymmetrical with most of the chromosomes having median to median-submedian centromeres.Picea glauca chromosomes 2, 3, 7, and 8 have secondary constriction on their short arm and chromosome 10 has a secondary constriction on the long arm. Chromosome 3 was the most easily identifiable, as it has two secondary constrictions located on the short arm. InP. rubens, all the chromosomes but chromosomes 8 and 9 have one to four distinctive secondary constrictions. In general, the diagrammatic comparisons show a high degree of similarity amongP. mariana, P. rubens, andP. glauca. GenomicP. mariana probe strongly hybridized to dots of genomic DNA fromP. rubens andP. glauca indicating that there is a high sequence homology among these three species. The synchronizing agent, hydroxyurea was used at different concentrations to enhance the mitotic index of cell suspensions derived from embryogenic cultures. Hydroxyurea at 1.25 mM increased significantly the mitotic index. An increase of hydroxyurea from 1.25 mM to 5 mM and 10 mM resulted in a steady decrease of mitotic index. 相似文献
10.
Abstract The gene-protein database was used to obtain the two-dimensional polyacrylamide gel coordinates of proteins phosphorylated in extracts of Escherichia coli including those phosphorylated by eukaryotic-like kinase activities. These suggest that the phosphoproteins correspond to, or co-migrate with, the product of an open reading frame at 1.3 min (Orf80), Enzyme 1 of the phosphoenolpyruvate-dependent phosphotransferase system (Ptsl), the tRNA synthetase for histidine (HisS), and proteins involved in the response to carbon starvation and quinone treatment. 相似文献