全文获取类型
收费全文 | 123篇 |
免费 | 7篇 |
出版年
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 10篇 |
2012年 | 4篇 |
2011年 | 8篇 |
2010年 | 11篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 10篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有130条查询结果,搜索用时 453 毫秒
91.
Isolated populations of drosophila pseudoobscura, separated from North
American populations by about 2,400 km, were found in Colombia in 1960. We
compared for sequences of the small ribosomal RNA (srRNA) gene on the
mitochondria between North American and Colombian D. pseudoobscura in order
to clarify the age of the Colombian isolates. The North American
populations were not genetically different from each other but were
genetically different from the Colombian populations. The Mexican strains
represent the area from which the Colombian founders might have come. The
estimated net nucleotide divergence between Mexican and Colombian D.
pseudoobscura indicates that the Colombian population is not an ancient
lineage. Phylogenies using both distance and parsimony methodologies
reinforced this conclusion. The Colombian samples group together with both
methods but, according to the bootstrap analysis, not significantly. It
appears that the populations have not been separated long enough for their
DNA sequences to show much divergence.
相似文献
92.
4-O-Acetylated, 7-O-acetylated, and 9-O-acetylated 4-methylumbelliferyl-alpha-N-acetyl-neuraminic acids (Neu4,5Ac2-MU, Neu5,7Ac2-MU, Neu5,9Ac2-MU) were tested as substrates of sialidases of Vibrio cholerae and of Clostridium perfringens. Both sialidases were unable to hydrolyse Neu4,5Ac2-MU. This compound at 1 mM concentration did not inhibit significantly the cleavage of Neu5Ac-MU, the best substrate tested. The 4-O-acetylated sialic acid glycoside is hydrolysed slowly by the sialidase from fowl plague virus. The relative substrate specificity, reflected in V/Km of the Vibrio cholerae sialidase is Neu5Ac-MU much greater than Neu5,7Ac2-MU approximately Neu5,9Ac2-MU and of the clostridial enzyme it is Neu5Ac-MU greater than Neu5,9Ac2-MU greater than Neu5,7Ac2-MU. The affinities of both enzymes for the side-chain O-acetylated sialic acid derivatives are higher than for Neu5Ac-MU. The artificial, well-defined substrates, described here, provide the opportunity to quantify the influence of sialic acid O-acetylation on the hydrolysis of sialoglycoconjugates without the side effects introduced by other parts of more complex glycans. 相似文献
93.
94.
95.
AS Glen D Anderson CJ Veltman PM Garvey M Nichols 《New Zealand journal of zoology.》2016,43(2):127-137
A major challenge in controlling overabundant wildlife is monitoring their populations, particularly as they decline to very low density. Camera traps and wildlife detector dogs are increasingly being used for this purpose. We compared the cost-effectiveness of these two approaches for detecting feral cats (Felis catus) on two pastoral properties in Hawke's Bay, North Island, New Zealand. One property was subject to intensive pest removal, while the other had no recent history of pest control. Camera traps and wildlife detector dogs detected cats at similar rates at both sites. The operating costs of each method were also comparable. We identify a number of advantages and disadvantages of each technique, and suggest priorities for further research. 相似文献
96.
TD Smith KP Bhatnagar CJ Bonar KL Shimp MP Mooney MI Siegel 《American journal of physical anthropology》2003,122(3):301-301
97.
Kleineidam RG Pesole G Breukelman HJ Beintema JJ Kastelein RA 《Journal of molecular evolution》1999,48(3):360-368
Mammalian secretory ribonucleases (RNases 1) form a family of extensively studied homologous proteins that were already used
for phylogenetic analyses at the protein sequence level previously. In this paper we report the determination of six ribonuclease
gene sequences of Artiodactyla and two of Cetacea. These sequences have been used with ruminant homologues in phylogenetic
analyses that supported a group including hippopotamus and toothed whales, a group of ruminant pancreatic and brain-type ribonucleases,
and a group of tylopod sequences containing the Arabian camel pancreatic ribonuclease gene and Arabian and Bactrian camel
and alpaca RNase 1 genes of unknown function. In all analyses the pig was the first diverging artiodactyl. This DNA-based
tree is compatible to published trees derived from a number of other genes. The differences to those trees obtained with ribonuclease
protein sequences can be explained by the influence of convergence of pancreatic RNases from hippopotamus, camel, and ruminants
and by taking into account the information from third codon positions in the DNA-based analyses. The evolution of sequence
features of ribonucleases such as the distribution of positively charged amino acids and of potential glycosylation sites
is described with regard to increased double-stranded RNA cleavage that is observed in several cetacean and artiodactyl RNases
which may have no role in ruminant or ruminant-like digestion.
Received: 2 June 1998 / Accepted: 31 August 1998 相似文献
98.
CJ Cooksey 《Biotechnic & histochemistry》2017,92(5):347-356
Methylene blue was synthesized in 1877 and soon found application in medicine, staining for microscopy and as an industrial dye and pigment. An enormous literature has accumulated since its introduction. Early on, it was known that methylene blue could be degraded easily by demethylation; consequently, the purity of commercial samples often was low. Therefore, demethylation products, such as azures and methylene violet, also are considered here. The names and identity of the components, their varying modes of manufacture, analytical methods and their contribution to biological staining are discussed. 相似文献
99.
A report of the ESF-EMBO Symposium Bacterial Networks (BacNet08), Sant Feliu de Guixols, Spain, 13-18 September 2008. 相似文献
100.
Complement proteins in blood recognize charged particles. The anionic phospholipid (aPL) cardiolipin binds both complement proteins C1q and factor H. C1q is an activator of the complement classical pathway, while factor H is an inhibitor of the alternative pathway. To examine opposing effects of C1q and factor H on complement activation by aPL, we surveyed C1q and factor H binding, and complement activation by aPL, either coated on microtitre plates or in liposomes. Both C1q and factor H bound to all aPL tested, and competed directly with each other for binding. All the aPL activated the complement classical pathway, but negligibly the alternative pathway, consistent with accepted roles of C1q and factor H. However, in this system, factor H, by competing directly with C1q for binding to aPL, acts as a direct regulator of the complement classical pathway. This regulatory mechanism is distinct from its action on the alternative pathway. Regulation of classical pathway activation by factor H was confirmed by measuring C4 activation by aPL in human sera in which the C1q:factor H molar ratio was adjusted over a wide range. Thus factor H, which is regarded as a down-regulator only of the alternative pathway, has a distinct role in downregulating activation of the classical complement pathway by aPL. A factor H homologue, β2-glycoprotein-1, also strongly inhibits C1q binding to cardiolipin. Recombinant globular domains of C1q A, B and C chains bound aPL similarly to native C1q, confirming that C1q binds aPL via its globular heads. 相似文献