全文获取类型
收费全文 | 391篇 |
免费 | 87篇 |
国内免费 | 1篇 |
出版年
2023年 | 2篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 15篇 |
2014年 | 26篇 |
2013年 | 15篇 |
2012年 | 19篇 |
2011年 | 24篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 23篇 |
2007年 | 23篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 9篇 |
1973年 | 5篇 |
1969年 | 2篇 |
1961年 | 1篇 |
排序方式: 共有479条查询结果,搜索用时 46 毫秒
1.
We have studied the immunomodulatory properties of epithelial cells from the small intestine on T cell immune function in vitro. Proliferation of lymph node cells stimulated either with antigen or with mitogen was inhibited by epithelial cells in a dose-dependent fashion. The epithelial cell-mediated suppression of lymphocyte proliferation was blocked by indomethacin, a cyclooxygenase pathway inhibitor, demonstrating that the suppressive effect of epithelial cells was related to prostaglandin secretion. Furthermore, the action of epithelial cell-secreted prostaglandin on lymphocytes was related to its effect on IL-2 as the suppressive effect of epithelial cells was abrogated by the addition of exogenous IL-2. As previously reported, epithelial cells constitutively express MHC class II and we found them able to present antigen in a class II-restricted fashion when their suppressive effects were blocked by indomethacin. Furthermore, epithelial cells activated by LPS secrete an IL-1 like molecule in a fashion analogous to other antigen-presenting cells. These results demonstrate that epithelial cells can both enhance and suppress in vitro T cell immune responses and further characterize the mechanisms by which intestinal epithelial cells may function in gut-associated immune responses. 相似文献
2.
3.
D J Haisenleder S Khoury S M Zmeili S Papavasiliou G A Ortolano C Dee J A Duncan J C Marshall 《Molecular endocrinology (Baltimore, Md.)》1987,1(11):834-838
The influence of GnRH pulse frequency on LH subunit mRNA concentrations was examined in castrate, testosterone-replaced male rats. GnRH pulses (25 ng/pulse) or saline to controls, were given via a carotid cannula at intervals of 7.5-240 min for 48 h. alpha and LH beta mRNA concentrations were 109 +/- 23 and 30 +/- 5 pg cDNA bound/100 micrograms pituitary DNA, respectively, in saline controls. GnRH pulse intervals of 15, 30, and 60 min resulted in elevated alpha and LH beta mRNAs (P less than 0.01) and maximum responses (4-fold, alpha; 3-fold, LH beta) were seen after the 30-min pulses. Acute LH release to the last GnRH pulse was seen after the 15-, 30-, and 60-min pulse intervals. In contrast, LH subunit mRNAs were not increased and acute LH release was markedly impaired after the rapid (7.5 min) or slower (120 and 240 min) pulse intervals. Equalization of total GnRH dose/48 h using the 7.5- and 240-min intervals did not increase LH subunit mRNAs to levels produced by the optimal 30-min interval. These data indicate that the frequency of the pulsatile GnRH stimulus regulates expression of alpha and LH beta mRNAs in male rats. Further, GnRH pulse frequencies that increase subunit mRNA concentrations are associated with continuing LH responsiveness to GnRH. 相似文献
4.
5.
6.
Regulation of insulin mRNA abundance and adenylation: dependence on hormones and matrix substrata. 总被引:13,自引:7,他引:6
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The insulin mRNA levels of rat insulinoma cell lines increased six- to eightfold, and the cells entered a transient state of growth arrest when they were cultured in serum-free, hormonally defined medium and on an extract of extracellular matrix derived from a basement membrane-secreting tumor line, EHS. Insulinoma cultures in growth arrest responded to glucose with a two- to threefold increase in insulin secretion associated with an insulin mRNA that contained a poly(A) tail that was 120 to 140 bases longer than normal. 相似文献
7.
8.
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
9.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
10.