全文获取类型
收费全文 | 367篇 |
免费 | 28篇 |
出版年
2021年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 11篇 |
2012年 | 14篇 |
2011年 | 17篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 19篇 |
2007年 | 12篇 |
2006年 | 19篇 |
2005年 | 10篇 |
2004年 | 19篇 |
2003年 | 7篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 13篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1987年 | 3篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1964年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有395条查询结果,搜索用时 265 毫秒
51.
Activation of the purinergic receptor P2X7 leads to the cellular permeability of low molecular weight cations. To determine which domains of P2X7 are necessary for this permeability, we exchanged either the C-terminus or portions of the second transmembrane domain (TM2) with those in P2X1 or P2X4. Replacement of the C-terminus of P2X7 with either P2X1 or P2X4 prevented surface expression of the chimeric receptor. Similarly, chimeric P2X7 containing TM2 from P2X1 or P2X4 had reduced surface expression and no permeability to cationic dyes. Exchanging the N-terminal 10 residues or C-terminal 14 residues of the P2X7 TM2 with the corresponding region of P2X1 TM2 partially restored surface expression and limited pore permeability. To further probe TM2 structure, we replaced single residues in P2X7 TM2 with those in P2X1 or P2X4. We identified multiple substitutions that drastically changed pore permeability without altering surface expression. Three substitutions (Q332P, Y336T, and Y343L) individually reduced pore formation as indicated by decreased dye uptake and also reduced membrane blebbing in response to ATP exposure. Three others substitutions, V335T, S342G, and S342A each enhanced dye uptake, membrane blebbing and cell death. Our results demonstrate a critical role for the TM2 domain of P2X7 in receptor function, and provide a structural basis for differences between purinergic receptors. 相似文献
52.
53.
54.
Amiloride does not alter NaCl avoidance in Fischer-344 rats 总被引:2,自引:2,他引:0
Fischer-344 (F-344) rats differ from other common rat strains in that they
fail to show any preference for NaCl at any concentration in two- bottle
preference tests. Because 100 microM amiloride partially blocks the
NaCl-evoked chorda tympani (CT) response in electrophysiological studies,
we tested NaCl preference (0.068-0.273 M) in F-344 rats with and without
100 microM amiloride solution as the solvent. A third group was tested with
unadulterated NaCl solutions following CT transection. Amiloride had no
significant effect on the NaCl preference-aversion function, whereas CT
transection significantly reduced NaCl avoidance. These results suggest
that the amiloride-sensitive component of the NaCl response is not
necessary for F-344 rats to display avoidance of NaCl, but the entire CT
input is.
相似文献
55.
Feedback regulation of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthetase from a marine bacterium, Vibrio MB22 下载免费PDF全文
A marine bacterium, Vibrio MB22, has been studied to determine the pattern of feedback regulation of the first enzyme unique to the biosynthesis of the aromatic amino acids, 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthetase. The crude extract was used to study response of the enzyme to various salts as well as possible feedback inhibitors. Ethylenediaminetetraacetic acid was found to be inhibitory to enzyme activity, and only CoCl(2), of the salts tested, allowed full recovery as well as apparent stimulation of the DAHP synthetase activity. The DAHP synthetase activity was inhibited solely by the aromatic amino acids, tyrosine, tryptophan, and phenylalanine, of the possible effectors tested. Further work demonstrated the existence of three isozymes of DAHP synthetase, each primarily inhibited by one of the aromatic amino acids. 相似文献
56.
The effect of pyridoxine deficiency on the metabolism of the aromatic amino acids by isolated rat liver cells 总被引:1,自引:0,他引:1
J C Stanley M Salter M J Fisher C I Pogson 《Archives of biochemistry and biophysics》1985,240(2):792-800
The total activity of three key enzymes and the flux through eight steps of aromatic amino acid metabolism have been determined in liver cells isolated from rats fed either control or pyridoxine-free diet for 5-6 weeks. The pyridoxine-free diet caused a decrease in the catabolism of tyrosine and phenylalanine because of a drop in the flux through tyrosine aminotransferase. This decrease of expressed cellular tyrosine aminotransferase activity can be fully explained in terms of loss of cofactor. Larger decreases in the catabolism of tryptophan were seen after pyridoxine deprivation. The decreased extent of tryptophan catabolism can be solely attributed to loss of cofactor or increased degradation of kynureninase. Inhibition of tryptophan 2,3-dioxygenase was seen in pyridoxine deficiency, probably because of the buildup of the kynurenine metabolites. The control strength of kynureninase, for flux through kynureninase, was calculated to be less than or equal to 0.004, but 0.41 after pyridoxine deprivation. The sensitivity of the three pathways to pyridoxine deprivation is interpreted and discussed in terms of the different affinities for pyridoxal phosphate and the control strengths of the pyridoxal phosphate-dependent enzymes, tyrosine aminotransferase and kynureninase. 相似文献
57.
Cassava is infected by numerous geminiviruses in Africa and India that cause devastating losses to poor farmers. We here describe the molecular diversity of seven representative cassava mosaic geminiviruses (CMGs) infecting cassava from multiple locations in Tanzania. We report for the first time the presence of two isolates in East Africa: (EACMCV-[TZ1] and EACMCV-[TZ7]) of the species East African cassava mosaic Cameroon virus, originally described in West Africa. The complete nucleotide sequence of EACMCV-[TZ1] DNA-A and DNA-B components shared a high overall sequence identity to EACMCV-[CM] components (92% and 84%). The EACMCV-[TZ1] and -[TZ7] genomic components have recombinations in the same genome regions reported in EACMCV-[CM], but they also have additional recombinations in both components. Evidence from sequence analysis suggests that the two strains have the same ancient origin and are not recent introductions. EACMCV-[TZ1] occurred widely in the southern part of the country. Four other CMG isolates were identified: two were close to the EACMV-Kenya strain (named EACMV-[KE/TZT] and EACMV-[KE/TZM] with 96% sequence identity); one isolate, TZ10, had 98% homology to EACMV-UG2Svr and was named EACMV-UG2 [TZ10]; and finally one isolate was 95% identical to EACMV-[TZ] and named EACMV-[TZ/YV]. One isolate of African cassava mosaic virus with 97% sequence identity with other isolates of ACMV was named ACMV-[TZ]. It represents the first ACMV isolate from Tanzania to be sequenced. The molecular variability of CMGs was also evaluated using partial B component nucleotide sequences of 13 EACMV isolates from Tanzania. Using the sequences of all CMGs currently available, we have shown the presence of a number of putative recombination fragments that are more prominent in all components of EACMV than in ACMV. This new knowledge about the molecular CMG diversity in East Africa, and in Tanzania in particular, has led us to hypothesize about the probable importance of this part of Africa as a source of diversity and evolutionary change both during the early stages of the relationship between CMGs and cassava and in more recent times. The existence of multiple CMG isolates with high DNA genome diversity in Tanzania and the molecular forces behind this diversity pose a threat to cassava production throughout the African continent. 相似文献
58.
Celine Scornavacca Vincent Berry Vincent Lefort Emmanuel JP Douzery Vincent Ranwez 《BMC bioinformatics》2008,9(1):413
Background
Supertree methods combine phylogenies with overlapping sets of taxa into a larger one. Topological conflicts frequently arise among source trees for methodological or biological reasons, such as long branch attraction, lateral gene transfers, gene duplication/loss or deep gene coalescence. When topological conflicts occur among source trees, liberal methods infer supertrees containing the most frequent alternative, while veto methods infer supertrees not contradicting any source tree, i.e. discard all conflicting resolutions. When the source trees host a significant number of topological conflicts or have a small taxon overlap, supertree methods of both kinds can propose poorly resolved, hence uninformative, supertrees. 相似文献59.
Helen Baines Margaret O Nwagwu Graham R Hastie Roman A Wiles Terry M Mayhew Francis JP Ebling 《Reproductive biology and endocrinology : RB&E》2008,6(1):4
Background
The hypogonadal (hpg) mouse is widely used as an animal model with which to investigate the endocrine regulation of spermatogenesis. Chronic treatment of these GnRH-deficient mice with estradiol is known to induce testicular maturation and restore qualitatively normal spermatogenesis. The aim of the current studies was to investigate whether these effects of estradiol are direct effects in the testis, or indirect actions via paradoxical stimulation of FSH secretion from the pituitary gland. 相似文献60.