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排序方式: 共有179条查询结果,搜索用时 25 毫秒
1.
Sex determination: a hypothesis based on steroid ratios 总被引:2,自引:0,他引:2
M H Bogart 《Journal of theoretical biology》1987,128(3):349-357
This paper presents a hypothesis for sex determination based on the ratio of androgen to estrogen in the gonad during sexual differentiation. In vertebrates the ratio of these steroids, and therefore, the sex of an individual is controlled by the quantity of the enzyme aromatase. For animals with a ZZ, ZW sex determining mechanism, such as birds, in which the heterogametic sex is female, an inducer for the aromatase gene is postulated to be on the W chromosome. In animals with an XX, XY system in which the heterogametic sex is male, such as mammals, the Y chromosome is postulated to code for a repressor of the aromatase gene. This hypothesis can account for naturally occurring sex reversal such as seen in some fish and amphibians, experimentally induced sex reversal by administration of steroids in birds, reptiles, fish and amphibians, and temperature-dependent sex determination as in reptiles. For invertebrates the same hypothetical model applies though the specific androgenic and estrogenic steroids differ. Both the X-to-autosome ratio method of sex determination typified by fruit flies and the haplodiploid method of bees as well as hormonal control of sexual differentiation in crustaceans are accounted for by this hypothesis. 相似文献
2.
Partial deletions of the cytoplasmic domain of CD2 result in a partial defect in signal transduction 总被引:8,自引:0,他引:8
B E Bierer R E Bogart S J Burakoff 《Journal of immunology (Baltimore, Md. : 1950)》1990,144(3):785-789
CD2 (T11, the T cell erythrocyte receptor or the SRBC receptor), a nonpolymorphic 47- to 55-kDa glycoprotein, appears to play a role in T lymphocyte adhesion, signal transduction, and differentiation. Pairs of anti-CD2 mAb induce T cell proliferation, suggesting that CD2 may be an Ag-independent pathway of T cell activation. We have expressed the human CD2 and a number of cytoplasmic domain deletion mutants of CD2 in an Ag-reactive murine hybridoma. We have previously shown that a cytoplasmic domain deletion mutant, CD2 delta B, in which the carboxyl-terminal 100 amino acids have been deleted, is no longer capable of signaling through CD2. Here we have expressed a second cytoplasmic domain deletion mutant, CD2 delta S, in which the terminal 41 amino acids have been removed, including the region with greatest conservation between the mouse, rat, and human species. CD2 delta S+ hybridomas were able to respond to Ag and to LFA-3 plus an anti-CD2 mAb. Although the CD2 delta S+ hybridomas responded comparably to the wild-type CD2+ hybridomas to certain pairs of anti-CD2 mAb (e.g., MT110 + 9-1 mAb), these CD2 delta S+ hybridomas were markedly deficient in their ability to respond to other pairs of stimulatory anti-CD2 mAb (e.g., 9.6 + 9-1 mAb). These data suggest that the cytoplasmic domain may have several functional regions, as partial deletions of the cytoplasmic domain appear to result in partial defects in signal transduction. 相似文献
3.
4.
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
5.
6.
The karyotype of Pan paniscus is reexamined by G-banding and examined for the first time by C-banding. In addition, examination of the chromosomes by the use of the fluorochromes adreamycine and 33258 Hoechst is undertaken. C-banding showed a surprising pattern with numerous terminal C-bands, as interstitial C-band, and several chromosomes lacking C-bands. Polymorphic conditions for C-bands are also identified involving several pairs. In a comparison to the chromosomes of man, G-banding revealed two pericentric inversions not previously observed. Only chromosome pairs No. 9,11,12 and the X are similar to man's by all techniques employed. 相似文献
7.
Fritz Herz Alexander Schermer Murray Halwer Lee H. Bogart 《Archives of biochemistry and biophysics》1981,212(2):581-588
HT-29, a cell line derived from a human colon carcinoma, exhibits very low alkaline phosphatase activity. The enzyme is thermolabile and is of the intestinal type. Hyperosmolality and/or sodium butyrate induce increased levels of activity. The increase is most pronounced with HT-29 cells growing in hyperosmolar medium containing sodium butyrate. Under these conditions specific activity rises over 1000-fold. The effect of hyperosmolality is blocked by cycloheximide and that of sodium butyrate by thymidine, cordycepin, and cycloheximide. By contrast to other human cancer cell lines, the enzyme of HT-29 is not influenced by cell density and glucocorticoid hormones. 5-Bromo-2′-deoxyuridine and inhibitors of DNA synthesis cause a slight increase in specific activity. 相似文献
8.
Evidence for a Polymorphism in Gametic Segregation Using a Malate Dehydrogenase Locus in the Tetraploid Treefrog HYLA VERSICOLOR 总被引:1,自引:1,他引:0 下载免费PDF全文
Artificial cross combinations of tetraploid Hyla versicolor were analyzed electrophoretically using a polymorphic malate dehydrogenase locus (MDH-1) to determine the mechanism of chromosome segregation. Models for differentiating between disomic and tetrasomic inheritance are presented and tested. In some crosses progeny genotypes fit a disomic mode of segregation. In other crosses there is only evidence for a tetrasomic mode of segregation. Additional crosses produced genotypic ratios which conformed to either a disomic or tetrasomic mode of segregation. The same type of inheritance was demonstrated for any individual when used in multiple cross combinations. These results suggest that there exists in H. versicolor a polymorphism with respect to segregation of gametes, resulting from differences in chromosome pairings during meiosis I. 相似文献
9.
The karyology was studied in nine species of Antilopinae and evaluated with regard to cytotaxonomic relations within the subfamily. Karyotypes of three of these species were previously undescribed. Chromosomes were examined by conventional staining methods, G-, C-, and T-banding techniques, and by autoradiography. Evolutionary differentiation of karyotypes in this group is characterized by extensive Robertsonian fusions and a particular translocation between the X chromosome and an autosome. With comparison of Giemsa-banding patterns a taxonomy has been constructed which differs most markedly from the classical taxonomy in two aspects: the blackbuck, Antilope cervicapra, shows a strong karyotypic affinity to gazelles of the subgenus Nanger; Thomson's gazelle, Gazella thomsoni, lacks the numerous Robertsonian fusions and the X-autosome translocation common to other members of Gazella studied to date. Cases of intraspecific polymorphism of chromosome morphology and number are presented. 相似文献
10.
Risk Factors for Late-Stage HIV Disease Presentation at Initial HIV Diagnosis in Durban,South Africa
Paul K. Drain Elena Losina Gary Parker Janet Giddy Douglas Ross Jeffrey N. Katz Sharon M. Coleman Laura M. Bogart Kenneth A. Freedberg Rochelle P. Walensky Ingrid V. Bassett 《PloS one》2013,8(1)