全文获取类型
收费全文 | 15916篇 |
免费 | 1392篇 |
国内免费 | 1356篇 |
专业分类
18664篇 |
出版年
2024年 | 47篇 |
2023年 | 238篇 |
2022年 | 483篇 |
2021年 | 768篇 |
2020年 | 638篇 |
2019年 | 718篇 |
2018年 | 714篇 |
2017年 | 515篇 |
2016年 | 691篇 |
2015年 | 1040篇 |
2014年 | 1253篇 |
2013年 | 1274篇 |
2012年 | 1470篇 |
2011年 | 1317篇 |
2010年 | 898篇 |
2009年 | 734篇 |
2008年 | 792篇 |
2007年 | 706篇 |
2006年 | 688篇 |
2005年 | 565篇 |
2004年 | 486篇 |
2003年 | 523篇 |
2002年 | 401篇 |
2001年 | 246篇 |
2000年 | 213篇 |
1999年 | 205篇 |
1998年 | 141篇 |
1997年 | 113篇 |
1996年 | 116篇 |
1995年 | 111篇 |
1994年 | 95篇 |
1993年 | 57篇 |
1992年 | 79篇 |
1991年 | 65篇 |
1990年 | 60篇 |
1989年 | 44篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 34篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1962年 | 2篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
Tang XC Zhang JX Zhang SY Wang P Fan XH Li LF Li G Dong BQ Liu W Cheung CL Xu KM Song WJ Vijaykrishna D Poon LL Peiris JS Smith GJ Chen H Guan Y 《Journal of virology》2006,80(15):7481-7490
Coronaviruses can infect a variety of animals including poultry, livestock, and humans and are currently classified into three groups. The interspecies transmissions of coronaviruses between different hosts form a complex ecosystem of which little is known. The outbreak of severe acute respiratory syndrome (SARS) and the recent identification of new coronaviruses have highlighted the necessity for further investigation of coronavirus ecology, in particular the role of bats and other wild animals. In this study, we sampled bat populations in 15 provinces of China and reveal that approximately 6.5% of the bats, from diverse species distributed throughout the region, harbor coronaviruses. Full genomes of four coronavirues from bats were sequenced and analyzed. Phylogenetic analyses of the spike, envelope, membrane, and nucleoprotein structural proteins and the two conserved replicase domains, putative RNA-dependent RNA polymerase and RNA helicase, revealed that bat coronaviruses cluster in three different groups: group 1, another group that includes all SARS and SARS-like coronaviruses (putative group 4), and an independent bat coronavirus group (putative group 5). Further genetic analyses showed that different species of bats maintain coronaviruses from different groups and that a single bat species from different geographic locations supports similar coronaviruses. Thus, the findings of this study suggest that bats may play an integral role in the ecology and evolution of coronaviruses. 相似文献
995.
L M Dong T Yamamura S Tajima A Yamamoto 《Biochemical and biophysical research communications》1992,187(2):1180-1186
Apo E5(Glu3----Lys) is a naturally occurring apolipoprotein E (apo E) mutant found in patients with hyperlipoproteinemia and atherosclerosis. It has been shown to have a high affinity for low density lipoprotein (LDL) receptors. In this study, mutant apo E5 was produced by Chinese hamster ovary cells by means of an in vitro site-directed mutagenesis technique, and its LDL receptor binding activity was assessed. The apo E5 obtained from gene expression bound more readily to the LDL receptor than did plasma apo E3. The concentrations required for 50% competitive binding of 125I-labeled LDL to the LDL receptors were 58.9 ng/ml for plasma apo E3 and 25.7 ng/ml for the expressed apo E5. The expressed apo E5 displayed 229% normal binding. This result is highly consistent with that obtained with plasma apo E5, which showed 217% normal binding. Although the experimental apo E isoproteins contained more sialic acid than plasma apo E, the extent of sialylation had no effect on the receptor binding of apo E. 相似文献
996.
Xin Jinge Zeng Dong Wang Hesong Sun Ning Zhao Ying Dan Yan Pan Kangcheng Jing Bo Ni Xueqin 《Probiotics and antimicrobial proteins》2020,12(1):184-193
Probiotics and Antimicrobial Proteins - Numerous studies have investigated the beneficial effects of Lactobacillus johnsonii strain BS15 on mice and broilers. This study aimed to understand the... 相似文献
997.
998.
999.
Molecular characterization and mRNA transcript profile of vitellogenin in Chinese shrimp, Fenneropenaeus chinensis 总被引:1,自引:0,他引:1
A full-length cDNA encoding vitellogenin (Vg) was cloned from Chinese shrimp, Fenneropenaeus
chinensis using RACE method. The full-length cDNA consist of 7,942 nucleotides including a 7,761 bp open reading frame, which encodes
2,587 amino acid residues. The deduced amino acid sequence showed high (from 94% to 37%) identity with other known crustacean
Vgs. In addition, a consensus cleavage site (R-X-K/R-R) recognized by an endopeptidase and a member of subtilisin family of
serine protease were identified in the deduced Vg precursor. RT-PCR analysis shown that Vg mRNA can be detected in both ovary
and hepatopancreas of vitellogenic females but not in other experimental tissues including muscle, heart, lymph organ, gill,
haemocytes and intestine. These results suggest that the Vg gene may be expressed exclusively in mature females, and both
ovary and hepatopancreas are the possible tissues for Vg synthesis in F. chinensis. In addition, Vg gene is detected in genomic DNA of both females and males. 相似文献
1000.
In addition to its well-characterized effects in immune system, chemokine CC motif ligand 2 (CCL2, formerly known as monocyte chemoattractant protein-1) is believed to play an important role in brain physiological and pathological processes. It has been shown that CCL2 and its cognate receptor chemokine CC motif receptor 2 are constitutively expressed in several brain regions including the hippocampus, and the expression is up-regulated under pathological conditions. Whereas most investigations have so far focused on its involvement in CNS pathology, few studies have examined the effects of CCL2 on neuronal and synaptic physiology. In this study, we tested the effects of CCL2 on neuronal excitability and excitatory synaptic transmission in the CA1 region of rat hippocampal slices using whole-cell patch clamp techniques. Bath application of CCL2 depolarized membrane potential and increased spike firing in CA1 neuronal cells. Bath application of CCL2 also produced an increase of excitatory post-synaptic currents recorded in Schaffer-collateral fibers to CA1 synapses. Quantal analysis revealed that CCL2 increased the frequency of spontaneous excitatory post-synaptic current occurrence and mean quantal content. Taken together, our data indicate that CCL2 enhances neuronal excitability and synaptic transmission via pre-synaptic mechanisms. These results support the emerging concept that chemokines function as neuromodulators in the CNS. 相似文献