全文获取类型
收费全文 | 4601篇 |
免费 | 414篇 |
出版年
2023年 | 41篇 |
2022年 | 64篇 |
2021年 | 205篇 |
2020年 | 85篇 |
2019年 | 120篇 |
2018年 | 134篇 |
2017年 | 126篇 |
2016年 | 199篇 |
2015年 | 351篇 |
2014年 | 369篇 |
2013年 | 387篇 |
2012年 | 504篇 |
2011年 | 467篇 |
2010年 | 266篇 |
2009年 | 192篇 |
2008年 | 268篇 |
2007年 | 242篇 |
2006年 | 199篇 |
2005年 | 180篇 |
2004年 | 128篇 |
2003年 | 146篇 |
2002年 | 129篇 |
2001年 | 16篇 |
2000年 | 13篇 |
1999年 | 21篇 |
1998年 | 20篇 |
1997年 | 18篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1969年 | 3篇 |
1967年 | 4篇 |
1966年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有5015条查询结果,搜索用时 31 毫秒
11.
12.
Fusarium moniliforme grown in a chemically defined medium in submerged culture accumulated amino acids extracellularly. Alanine and glutamic acid were present in greatest amounts, with traces of glycine, lysine, threonine, and valine detectable. Increasing the glucose and urea concentrations of the medium increased yields of alanine. Further increases in alanine production occurred with elevated levels of mineral salts in the medium, whereas the addition of a vitamin mixture proved to be inhibitory. Chemical changes resulting from the growth of F. moniliforme in the final fermentation medium disclosed maximal alanine production, mycelial weight, and glucose consumption after 72 hr of incubation at 28.5 C. Total soluble nitrogen, by contrast, was minimal at the same time period. The pH remained in the alkaline range throughout the fermentation. 相似文献
13.
14.
15.
Prion protein (PrP) with amino-proximal deletions restoring susceptibility of PrP knockout mice to scrapie. 总被引:35,自引:3,他引:32
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M Fischer T Rülicke A Raeber A Sailer M Moser B Oesch S Brandner A Aguzzi C Weissmann 《The EMBO journal》1996,15(6):1255-1264
The 'protein only' hypothesis postulates that the prion, the agent causing transmissible spongiform encephalopathies, is PrP(Sc), an isoform of the host protein PrP(C). Protease treatment of prion preparations cleaves off approximately 60 N-terminal residues of PrP(Sc) but does not abrogate infectivity. Disruption of the PrP gene in the mouse abolishes susceptibility to scrapie and prion replication. We have introduced into PrP knockout mice transgenes encoding wild-type PrP or PrP lacking 26 or 49 amino-proximal amino acids which are protease susceptible in PrP(Sc). Inoculation with prions led to fatal disease, prion propagation and accumulation of PrP(Sc) in mice expressing both wild-type and truncated PrPs. Within the framework of the 'protein only' hypothesis, this means that the amino-proximal segment of PrP(C) is not required either for its susceptibility to conversion into the pathogenic, infectious form of PrP or for the generation of PrP(Sc). 相似文献
16.
Tipton CM Sebastian LA Edwards PK Moran MM 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》1995,2(1):P62-P63
Measurements from mission specialists after space flights or from subjects subjected to head down tilt experiments have demonstrated a decrease in exercise performance. Similar decreases have been reported for rats that have participated in simulated microgravity studies using the head down-tail suspended method of Morey-Holton (HDS). Because it is unclear whether older animal populations would exhibit similar responses, we undertook a HDS study with Fischer 344 male rats. 相似文献
17.
The Rhodobacter sphaeroides cytochrome c2 signal peptide is not necessary for export and heme attachment. 总被引:3,自引:1,他引:2
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rhodobacter sphaeroides cytochrome c2 (cyt c2) is a member of the heme-containing cytochrome c protein family that is found in the periplasmic space of this gram-negative bacterium. This exported polypeptide is made as a higher-molecular-weight precursor with a typical procaryotic signal peptide. Therefore, cyt c2 maturation is normally expected to involve precursor translocation across the cytoplasmic membrane, cleavage of the signal peptide, and covalent heme attachment. Surprisingly, synthesis as a precursor polypeptide is not a prerequisite for cyt c2 maturation because deleting the entire signal peptide does not prevent export, heme attachment, or function. Although cytochrome levels were reduced about threefold in cells containing this mutant protein, steady-state cyt c2 levels were significantly higher than those of other exported bacterial polypeptides which contain analogous signal peptide deletions. Thus, this mutant protein has the unique ability to be translocated across the cytoplasmic membrane in the absence of a signal peptide. The covalent association of heme with this mutant protein also suggests that the signal peptide is not required for ligand attachment to the polypeptide chain. These results have uncovered some novel aspects of bacterial c-type cytochrome biosynthesis. 相似文献
18.
19.
Johann Sebastian Braun Brigitte Kaissling Michel Le Hir Wolfgang Zenker 《Cell and tissue research》1993,273(2):209-217
This report deals with the distribution, morphology and specific topical relationships of bone-marrow-derived cells (free cells) in the spinal meninges and dorsal root ganglia of the normal rat. The morphology of these cells has been studied by transmission and scanning electron microscopy. Cells expressing the major histocompatibility complex (MHC) class II gene product have been recognized by immunofluorescence. At the level of the transmission electron microscope, free cells are found in all layers of the meninges. Many of them display characteristic ultrastructural features of macrophages, whereas others show a highly vacuolated cytoplasm and are endowed with many processes. These elements lack a conspicuous lysosomal system and might represent dendritic cells. Scanning electron microscopy has revealed that free cells contact the cerebrospinal fluid via abundant cytoplasmic processes that cross the cell layers of the pia mater and of the arachnoid. Cells expressing the MHC class II antigen are also found in all layers of the meninges. They are particularly abundant in the layers immediately adjacent to the subarachnoid space, in the neighbourhood of dural vessels, along the spinal roots and in the dural funnels. In addition to the meninges, strong immunoreactivity for MHC class II antigen is observed in the dorsal root ganglia. The ultrastructural and immunohistochemical findings of this study suggest the existence of a well-developed system of immunological surveillance of the subarachnoid space and of the dorsal root ganglia. 相似文献
20.
Max R. Brown Hannes Becher Sebastian Williams Alex D. Twyford 《American journal of botany》2023,110(1):e16100