全文获取类型
收费全文 | 6580篇 |
免费 | 563篇 |
国内免费 | 5篇 |
出版年
2023年 | 37篇 |
2021年 | 99篇 |
2020年 | 81篇 |
2019年 | 115篇 |
2018年 | 114篇 |
2017年 | 88篇 |
2016年 | 156篇 |
2015年 | 290篇 |
2014年 | 302篇 |
2013年 | 344篇 |
2012年 | 477篇 |
2011年 | 448篇 |
2010年 | 294篇 |
2009年 | 295篇 |
2008年 | 397篇 |
2007年 | 380篇 |
2006年 | 355篇 |
2005年 | 319篇 |
2004年 | 323篇 |
2003年 | 331篇 |
2002年 | 242篇 |
2001年 | 82篇 |
2000年 | 61篇 |
1999年 | 91篇 |
1998年 | 102篇 |
1997年 | 67篇 |
1996年 | 57篇 |
1995年 | 72篇 |
1994年 | 55篇 |
1993年 | 53篇 |
1992年 | 54篇 |
1991年 | 56篇 |
1990年 | 56篇 |
1989年 | 45篇 |
1988年 | 48篇 |
1987年 | 35篇 |
1986年 | 45篇 |
1985年 | 40篇 |
1984年 | 43篇 |
1983年 | 32篇 |
1982年 | 46篇 |
1981年 | 43篇 |
1980年 | 32篇 |
1979年 | 40篇 |
1978年 | 26篇 |
1977年 | 33篇 |
1976年 | 22篇 |
1975年 | 24篇 |
1974年 | 40篇 |
1973年 | 23篇 |
排序方式: 共有7148条查询结果,搜索用时 312 毫秒
1.
2.
3.
The 30-Base-Pair Deletion in Chinese Variants of the Epstein-Barr Virus LMP1 Gene Is Not the Major Effector of Functional Differences between Variant LMP1 Genes in Human Lymphocytes 总被引:7,自引:3,他引:4 下载免费PDF全文
Rowena J. Johnson Maria Stack Sheila A. Hazlewood Matthew Jones Colin G. Blackmore Li-Fu Hu Martin Rowe 《Journal of virology》1998,72(5):4038-4048
One group of sequence variants of Epstein-Barr virus is characterized by a 10-amino-acid deletion within the CTAR-2 functional domain of the latent membrane protein, LMP1. A role for this deletion in enhancing the tumorigenicity of the viral oncogene in rodent fibroblasts was recently demonstrated. We examined the effect of this deletion upon LMP1 function in four human lymphoid cell lines by using three natural variants of LMP1: the prototype B95.8 gene and the CAO and AG876 genes, both of which have codons 343 to 352 of the B95.8-LMP1 deleted. These experiments revealed that LMP1-mediated upregulation of CD40 and CD54 was markedly impaired (by 60 to 90%) with CAO-LMP1 compared with B95.8-LMP1. In contrast, the function of AG876-LMP1 was indistinguishable from that of B95.8-LMP1 in two lines and was only slightly impaired in the other two lines. Activation of NF-κB by CAO-LMP1 was not impaired in any of the lines; rather, activation of an NF-κB reporter by CAO-LMP1 was consistently about twofold greater than the activation with B95.8- or AG876-LMP1. Therefore, while the CAO-LMP1 is functionally distinct from the prototype B95.8-LMP1 in human lymphocytes, the 10-amino-acid deletion appears not to be directly responsible. This conclusion was confirmed by using a B95.8-LMP1 mutant with codons 343 to 352 deleted and chimerae of CAO- and B95.8-LMP1 in which the CTAR-2 domains of these genes were exchanged. Sequences outside the CTAR-2 domain were implicated in the distinct functional characteristics of CAO-LMP1 in human lymphoid cells. 相似文献
4.
5.
During the process optimisation of glucoamylase production by Aspergillus awamori, cell morphology was controlled at such a state that spore aggregation was completely prevented. Samples from five fermentations on complex media using either glucose or starch as carbon source were characterised with a Bohlin CS rheometer. The experimental data were conveniently described in terms of the power law model. 相似文献
6.
Colin K.W. Watts Robert L. Sutherland 《Biochemical and biophysical research communications》1984,120(1):109-115
Saturation and competitive binding analyses demonstrated the presence of a high affinity (KD = 0.92 nM), specific antiestrogen binding site (AEBS) in rat liver microsomes and at least 75% of total liver AEBS was recovered in this fraction. When microsomes were further separated into smooth and rough fractions, AEBS was concentrated in the latter. Subsequent dissociation of ribosomes from the rough membranes revealed that AEBS was associated with the membrane and not the ribosomal fraction. Antiestrogen binding activity could not be extracted from membranes with 1 M KCl or 0.5 M acetic acid but could be solubilized with sodium cholate. These data indicate that AEBS is an integral membrane component of the rough microsomal fraction of rat liver. 相似文献
7.
Summary The developing pigment strand of rice (Oryza sativa L.) was studied by conventional electron microscopy and also by use of thick sections post-fixed with zinc iodide and osmium (ZIO).When the rice caryopsis achieves maximum length, a suberised adcrusting wall layer is laid down over the original primary walls of the pigment strand. Concomitant with suberin deposition a proliferation of tubular endoplasmic reticulum occurs in the cytoplasm giving rise to numerous interconnected vesicles which bear ribosomes. The vesicles in the general cytoplasm retain their ribosomes while those close to the wall become smooth and contain an electron-opaque granular material which is eventually deposited to the outside of the plasmalemma. This granular material may be the precursor(s) from which suberin is polymerised. The suberised wall attains about six times the width of the original primary wall and plasmodesmata, which traverse both primary wall and suberised wall layers, become greatly elongated.Lipid bodies increase in both size and frequency during development, eventually coalescing to form a complete plug across the pigment strand and occluding the symplast of this tissue. The significance of these ultrastructural observations is discussed in relation to the previously demonstrated role of the pigment strand as a translocation pathway for water and assimilates during grain filling.Abbreviations ER
endoplasmic reticulum
- ZIO
zinc iodide-osmium fixation 相似文献
8.
Estimation of chitin deposition in the pupal and adult cuticles of adult Drosophila melanogaster during the pupal period is described. The timing of the periods of chitin deposition is compared with that deduced by previous workers using electron microscopy. The hypothesis that lethalcryptocephal mutant homozygotes are unable to evert their cephalic complexes at pupation because of excess chitin deposition is examined. The data obtained show no evidence that the mutation has any effect on chitin deposition. 相似文献
9.
10.
Surmounting barriers in ionic channels 总被引:8,自引:0,他引:8