全文获取类型
收费全文 | 60篇 |
免费 | 5篇 |
国内免费 | 1篇 |
出版年
2022年 | 1篇 |
2021年 | 4篇 |
2016年 | 1篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 4篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 2篇 |
2005年 | 1篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1976年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有66条查询结果,搜索用时 15 毫秒
11.
12.
The annual reproductive cycle of the brown bullhead catfish, Ictalurus nebulosus Lesueur, was investigated over a two-year period. In females, GSI increased in the spring as follicles enlarged and the granulosa became hypertrophied, dropped during spawning in August, then rose in the autumn as follicles enlarged slightly. 3β-Hydroxysteroid dehydrogenase (3β-HSD) activity was limited to thecal nests of large, vitellogenic follicles. Plasma testosterone and estradiol-17β levels increased in parallel with GSI. Levels of both steroids dropped prior to the spawning period, although a peak in estradiol-17β was evident during the spawning period. No 11-ketotestosterone was detected in female plasma. In males, GSI increased in the spring as spermatogenesis proceeded, and dropped during spawning. 3β-HSD activity was confined to Leydig cells and was most intense prior to spawning. Plasma testosterone and 11-ketotestosterone peaked during the pre-spawning period, dropped prior to spawning, then rose slowly during the autumn. A peak in estradiol-17β occurred during the spawning period. Significant differences in GSI and plasma steroid levels during the pre-spawning and spawning periods were observed between the two yearly cycles; they may be related to differences in rainfall during these periods. 相似文献
13.
J Pudney 《Journal of reproduction and fertility》1986,77(1):37-49
During spermatogenesis in sexually mature ground squirrels Leydig and Sertoli cells were morphologically well differentiated. For Leydig cells the most prominent organelles were lipid droplets, mitochondria with tubulo-vesicular cristae and abundant agranular reticulum organized as a mass of anastomosing tubules. These morphological criteria suggest that the Leydig cells were steroidogenically active. Sertoli cells exhibited a topographical distribution of certain organelles with basal regions containing stacks of granular reticulum, and large areas of agranular reticulum. The cytoplasm surrounding maturing germ cells contained numerous microtubules, and an adluminal layer of spermatids at a certain stage of spermiogenesis became enveloped by Sertoli cytoplasm containing an enormous proliferation of agranular reticulum. The presence of these organelles in Sertoli cells suggests that during spermatogenesis they are active in the synthesis of proteins and steroids. In particular the mass of agranular reticulum surrounding late stage spermatids indicates that steroids may be required for spermatid maturation and/or spermiation. By contrast Leydig and Sertoli cells observed during testicular regression, when only spermatogonia remain in the seminiferous tubules, had undergone structural changes. Leydig cells were still numerous and large with abundant agranular reticulum that was now organized as a loose assemblage of single unbranched tubules. Sertoli cells were drastically reduced in both cytoplasmic volume and content of organelles. 相似文献
14.
15.
The method of Triton X-100 extraction and critical point drying of whole mounts of cultured chick and human myoblasts was used to study the presence of intracellular bundles of filaments within these cells. Observation by means of transmission and scanning electron microscopy demonstrated a complex system of filament bundles which appeared morphologically and spatially heterogeneous. Most obvious were long dense bundles or cables traversing along the ventral surface of developing myoblasts, presumably the ‘stress fibers’ seen in light microscopy. Other bundle types occurred which were composed of loose aggregates of filaments coursing through the remnant cell body. A prominent accumulation of filaments was also seen at the lateral edges of these myoblasts. These lateral edge cables were thicker and denser than any other type of filament bundle observed in the myoblasts. Reaction of unextracted myoblasts directly to human antiplatelet myosin conjugated to rhodamine demonstrated that the most intense reaction also occurred along the lateral edges of both human and chick myoblasts. During development of chick myoblasts the filament bundles became oriented parallel to the cell axis giving the cell a fusiform morphology. It is possible that the various filament bundle structures and their differing structural and spatial dispositions could be related to functional differences among the diverse population of intracellular bundles of filaments. 相似文献
16.
17.
Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands 总被引:2,自引:2,他引:0
Britten CJ; van den Eijnden DH; McDowell W; Kelly VA; Witham SJ; Edbrooke MR; Bird MI; de Vries T; Smithers N 《Glycobiology》1998,8(4):321-327
The alpha3 fucosyltransferase, FucT-VII, is one of the key
glycosyltransferases involved in the biosynthesis of the sialyl Lewis X
(sLex) antigen on human leukocytes. The sialyl Lewis X antigen
(NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential
component of the recruitment of leukocytes to sites of inflammation,
mediating the primary interaction between circulating leukocytes and
activated endothelium. In order to characterize the enzymatic properties of
the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been
expressed in Trichoplusia ni insect cells. The enzyme is capable of
synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from
3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels
of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies
using fucosylated NeuAcalpha(2-3)-(Galbeta(1- 4)GlcNAc)3-Me acceptors
demonstrate that FucT-VII is able to synthesize both di-fucosylated and
tri-fucosylated structures from mono- fucosylated precursors, but
preferentially fucosylates the distal GlcNAc within a polylactosamine
chain. Furthermore, the rate of fucosylation of the internal GlcNAc
residues is reduced once fucose has been added to the distal GlcNAc. These
results indicate that FucT-VII is capable of generating complex selectin
ligands, in vitro , however the order of fucose addition to the lactosamine
chain affects the rate of selectin ligand synthesis.
相似文献
18.
Cell-mediated immunity (CMI) is key to defense against intracellular pathogens such as Chlamydia trachomatis and viruses that infect the lower female genital tract, but little is known about CMI at this site. Recent studies indicate that there are immunological microenvironments within the female genital tract, and that immune functions are affected by hormones as well as infections and inflammatory processes. To determine the distribution of mediators of CMI within the lower female genital tract, we have enumerated and characterized T-lymphocyte subsets and natural killer and antigen presenting cells (APCs; macrophages and dendritic cells) in the introitus, vagina, ectocervix, endocervix and cervical transformation zone (TZ) from healthy women, and have examined the effects of the menstrual cycle, menopause and inflammation on these parameters. In women without inflammation, T cells and APCs were most prevalent in the cervical TZ and surrounding tissue. Intraepithelial lymphocytes were predominantly CD8+ T cell+; most CD8+ cells in the TZ and endocervix, and a proportion of cells in the ectocervix, expressed T-cell internal antigen-1, a marker of cytotoxic potential. In contrast, the normal vaginal mucosa contained few T cells and APCs. Cervicitis and vaginitis cases had increased numbers of intraepithelial CD8+ and CD4+ lymphocytes and APCs. The menstrual cycle and menopause had no apparent effect on cellular localization or abundance in any of the lower genital tract tissues. These data indicate that the cervix, especially the TZ, is the major inductive and effector site for CMI in the lower female genital tract. Because CD4+ T cells and APCs are primary host cells for human immunodeficiency virus type 1 (HIV-1), these data also provide further evidence that the cervix is a primary infection site of HIV-1, and that inflammation increases the risk of HIV transmission. 相似文献
19.
Isolation of a murine homologue of the Drosophila neuralized gene, a gene required for axonemal integrity in spermatozoa and terminal maturation of the mammary gland 下载免费PDF全文
Vollrath B Pudney J Asa S Leder P Fitzgerald K 《Molecular and cellular biology》2001,21(21):7481-7494
The Drosophila neuralized gene shows genetic interactions with Notch, Enhancer of split, and other neurogenic genes and is thought to be involved in cell fate specification in the central nervous system and the mesoderm. In addition, a human homologue of the Drosophila neuralized gene has been described as a potential tumor suppressor gene in malignant astrocytomas. We have isolated a murine homologue of the Drosophila and human Neuralized genes and, in an effort to understand its physiological function, derived mice with a targeted deletion of this gene. Surprisingly, mice homozygous for the introduced mutation do not show aberrant cell fate specifications in the central nervous system or in the developing mesoderm. This is in contrast to mice with targeted deletions in other vertebrate homologues of neurogenic genes such as Notch, Delta, and Cbf-1. Male Neuralized null mice, however, are sterile due to a defect in axoneme organization in the spermatozoa that leads to highly compromised tail movement and sperm immotility. In addition, female Neuralized null animals are defective in the final stages of mammary gland maturation during pregnancy. 相似文献
20.
Yutao Liu Melanie E. Garrett Michelle F. Dennis Kimberly T. Green VA Mid-Atlantic MIRECC Registry Workgroup Allison E. Ashley-Koch Michael A. Hauser Jean C. Beckham Nathan A. Kimbrel 《PloS one》2015,10(3)