全文获取类型
收费全文 | 196篇 |
免费 | 5篇 |
出版年
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2016年 | 3篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 24篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2000年 | 4篇 |
1999年 | 10篇 |
1998年 | 3篇 |
1996年 | 3篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1964年 | 1篇 |
1957年 | 1篇 |
1949年 | 1篇 |
1945年 | 1篇 |
1939年 | 2篇 |
1938年 | 3篇 |
1937年 | 4篇 |
排序方式: 共有201条查询结果,搜索用时 224 毫秒
1.
2.
Structures using X-ray diffraction data collected to 1.5-A resolution have been determined for the protein ribonuclease-A at nine different temperatures ranging from 98 to 320 K. It is determined that the protein molecule expands slightly (0.4% per 100 K) with increasing temperature and that this expansion is linear. The expansion is due primarily to subtle repacking of the molecule, with exposed and mobile loop regions exhibiting the largest movements. Individual atomic Debye-Waller factors exhibit predominantly biphasic behavior, with a small positive slope at low temperatures and a larger positive slope at higher temperatures. The break in this curve occurs at a characteristic temperature of 180-200 K, perhaps indicative of fundamental changes in the dynamical structure of the surrounding protein solvent. The distribution of protein Debye-Waller factors is observed to broaden as well as shift to higher values as the temperature is increased. 相似文献
3.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
4.
A full-length cDNA encoding a human homolog of the 15-kDa subunit (p15) of RNA polymerase II elongation factor SIII was isolated and sequenced. Comparison of the open reading frames of the human p15 cDNA and the previously characterized rat p15 cDNA [Garrett et al., Proc. Natl. Acad. Sci. USA 91 (1994) 5237-5241] indicates that they encode identical proteins and are 93% conserved in nucleotide sequence. 相似文献
5.
Nucleotide variation at the hypervariable esterase 6 isozyme locus of Drosophila simulans 总被引:2,自引:0,他引:2
Esterase 6 (Est-6/EST6) is polymorphic in both Drosophila melanogaster and
D. simulans for two common allozyme forms, as well as for several other
less common variants. Parallel latitudinal clines in the frequencies of the
common EST6-F and EST6-S allozymes in these species have previously been
interpreted in terms of a shared amino acid polymorphism that distinguishes
the two variants and is subject to selection. Here we compare the sequences
of four D. simulans Est-6 isolates and show that overall estimates of
nucleotide heterozygosity in both coding and 5' flanking regions are more
than threefold higher than those obtained previously for this gene in D.
melanogaster. Nevertheless, the ratio of replacement to exon silent-site
polymorphism in D. simulans is less than the ratio of replacement to silent
divergence between D. simulans and D. melanogaster, which could be the
result of increased efficiency of selection against replacement
polymorphisms in D. simulans or to divergent selection between the two
species. We also find that the amino acid polymorphisms separating EST6- F
and EST6-S in D. simulans are not the same as those that separate these
allozymes in D. melanogaster, implying that the shared clines do not
reflect shared molecular targets for selection. All comparisons within and
between the two species reveal a remarkable paucity of variation in a
stretch of nearly 400 bp immediately 5' of the gene, indicative of strong
selective constraint to retain essential aspects of Est-6 promoter
function.
相似文献
6.
7.
8.
9.
10.
Role of follicular dendritic cells in the early HIV-1 infection: in vitro model without specific antibody 总被引:2,自引:0,他引:2
Taruishi M Terashima K Dewan Z Yamamoto N Ikeda S Kobayashi D Eishi Y Yamazaki M Furusaka T Sugimoto M Ishii M Kitamura K Yamamoto N 《Microbiology and immunology》2004,48(9):693-702
About 90% of HIV-1 RNA in the lymph nodes is reported to localize in follicular dendritic cellsnetwork (FDC-NW) as early as several days after infection and as much as that in the late stage. But the mechanism remains to be fully understood. To elucidate the role of follicular dendritic cells (FDC) in the early stage of HIV-1 infection, FDC-like cell strains (FDCLC) were established and they were characterized in the co-culture system with T cells for their effect on HIV-1 trapping and replication in p24 immunoassay, immunohistochemistry as well as confocal and electronmicroscopy. Established FDCLC were positive for CNA-42, S-100alpha and intercellular desmosome-like junctions. L-SIGN and DC-SIGN were also detected in FDCLC. Alu-HIV-1 PCR analysis showed no HIV-1 integration in FDCLC. FDCLC trapped HIV-1 and transferred them to uninfected MOLT-4 T cells (MOLT-4) efficiently in the absence of specific antibody. FDCLC also accelerated HIV-1 replication in HIV-1-pre-exposed MOLT-4. These unique FDCLC effects were explained, at least partly, by the fact that FDCLC up-regulated CD4 expression in MOLT-4 and helped T cells escape from apoptosis in the co-culture. These data suggest that FDC/FDCLC engage not only in trapping but also in active expansion of HIV-1 in the absence of specific antibody. 相似文献