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排序方式: 共有260条查询结果,搜索用时 15 毫秒
201.
202.
Grogan Gideon Roberts Stanley Wan Peter Willetts Andrew 《Biotechnology letters》1994,16(11):1173-1178
Summary Conditions have been devised to enable partially purified enzyme preparations from camphor-grownPseudomonas putida NCIMB 10007 to undertake oxidative and reductive biotransformations of 5-hexylcyclopent-2-enone. 相似文献
203.
204.
Maristerra R. Lemes Dario Grattapaglia James Grogan John Proctor Rogério Gribel 《Plant Ecology》2007,192(2):169-179
Microsatellites were used to evaluate the mating system of the remaining trees in a logged population of Swietenia macrophylla, a highly valuable and threatened hardwood species, in the Brazilian Amazon. A total of 25 open pollinated progeny arrays
of 16 individuals, with their mother trees, were genotyped using eight highly polymorphic microsatellite loci. Genotypic data
analysis from the progeny arrays showed that 373 out of the 400 seedlings (93.25%) were unambiguously the result of outcrossed
matings and that the remaining 6.75% had genotypes consistent with self-fertilisation. Apomixis could be ruled out, since
none of the 400 seedlings analysed had a multi-locus genotype identical to its mother tree. The high estimate of the multi-locus
outcrossing rate (t
m
= 0.938 ± 0.009) using the mixed mating model also indicated that the population in this remnant stand of S. macrophylla was predominantly allogamous. The relatively large difference between the multi-locus and single-locus outcrossing estimates
(t
m
−t
s
= 0.117 ± 0.011) provides evidence that, in spite of the high outcrossing rate, a considerable degree of biparental inbreeding
has contributed to the genetic structure of this population. Levels of outcrossing were not evenly distributed among maternal
trees (t
m
ranging from 0.39 to 1.00), suggesting the occurrence of a variable degree of self-incompatibility and/or dichogamy among
individual trees of this monoecious species. Due to its generalist pollination system and some level of tolerance for selfing,
S. macrophylla seems to be resilient to environmental disturbances such as those caused by logging, since it sets fruits with predominantly
outcrossed seeds even at low stand densities. Therefore, the remaining individuals in logged areas or in relict fragments
may be very important for long-term population recovery and genetic conservation programmes. 相似文献
205.
Arnaud Bataille Scott D. Cashins Laura Grogan Lee F. Skerratt David Hunter Michael McFadden Benjamin Scheele Laura A. Brannelly Amy Macris Peter S. Harlow Sara Bell Lee Berger Bruce Waldman 《Proceedings. Biological sciences / The Royal Society》2015,282(1805)
The pathogenic chytrid fungus Batrachochytrium dendrobatidis
(Bd) can cause precipitous population declines in its amphibian hosts. Responses
of individuals to infection vary greatly with the capacity of their immune
system to respond to the pathogen. We used a combination of comparative and
experimental approaches to identify major histocompatibility complex class II
(MHC-II) alleles encoding molecules that foster the survival of Bd-infected
amphibians. We found that Bd-resistant amphibians across four continents share
common amino acids in three binding pockets of the MHC-II antigen-binding
groove. Moreover, strong signals of selection acting on these specific sites
were evident among all species co-existing with the pathogen. In the laboratory,
we experimentally inoculated Australian tree frogs with Bd to test how each
binding pocket conformation influences disease resistance. Only the conformation
of MHC-II pocket 9 of surviving subjects matched those of Bd-resistant species.
This MHC-II conformation thus may determine amphibian resistance to Bd, although
other MHC-II binding pockets also may contribute to resistance. Rescuing
amphibian biodiversity will depend on our understanding of amphibian immune
defence mechanisms against Bd. The identification of adaptive genetic markers
for Bd resistance represents an important step forward towards that goal. 相似文献
206.
Piero Pasta Giacomo Carrea Nicoletta Gaggero Gideon Grogan Andrew Willetts 《Biotechnology letters》1996,18(10):1123-1128
Summary Several sulfides and bicyclo[3.2.0]hept-2-en-6-one were enantioselectively oxidized to the corresponding sulfoxides and oxa lactones by a crude preparation of the two diketocamphane monooxygenases from Pseudomonas putida. The reactions were carried out in a membrane reactor with the use of poly(ethylene glycol)-N6-(2-aminoethyl)-NAD and coenzyme regeneration by the formate/formate dehydrogenase system. 相似文献
207.
Characterization of Escherichia coli mutants completely defective in synthesis of cyclopropane fatty acids. 总被引:7,自引:2,他引:5
The synthesis of cyclopropane fatty acids (CFA) in bacteria represents a biochemically and physiologically unique membrane modification whose importance for the cell remains unknown, despite extensive study of a Cfa- mutant of Escherichia coli and of the cloned cfa gene. Recently we reported the isolation of new Cfa- mutants (D. W. Grogan and J. E. Cronan, Jr., Mol. Gen. Genet. 196:367-372, 1984). Molecular-genetic and biochemical analysis indicated that these were null mutants of the E. coli cfa locus which were formed by inversions of a chromosomal segment. Isogenic Cfa+ and Cfa- strains were constructed from one such mutant and subjected to various stress conditions. In nearly all cases, both strains responded equally, but certain treatments, such as repeated freezing and thawing, favored the survival of Cfa+ strains over Cfa- strains. Though not essential, CFA thus appeared to play some beneficial role (or roles) in the bacterial cell. 相似文献
208.
Dr. Dennis W. Grogan 《Current microbiology》1986,14(2):107-111
A mutant ofEscherichia coli K-12, originally though to lack the major murein lipoprotein (product of the1pp gene) was found to contain an intact1pp locus and to exhibit multiple physiological defects. These included altered morphology, sensitivity to glycine, sensitivity to high temperature, and absolute requirement for certain vitamin B6 derivatives. The genetic properties of the mutant indicated that a chromosomal inversion had caused inactivation of thepdxH (pyridoxine phosphate oxidase) gene. Behavior of this and other Pdx– mutants indicated that growth in unsupplemented complex medium can lead to pyridoxal phosphate limitation and concomitant impairment of cell wall biosynthesis. 相似文献
209.
Cholesterol ester hydrolase (EC 3.1.1.13) activity from the 104,000 X g supernatant of rat testis was fractionated into 28-kDa, 72-kDa, and 420-kDa molecular mass forms by high performance size exclusion chromatography. The 72-kDa and 420-kDa forms (temperature-labile) were completely inactivated by elevation of temperature from 32 to 37 degrees C. Apparent disaggregation of the 420-kDa form suggested that the 72-kDa and 420-kDa enzymes are monomeric and multimeric forms of the same enzyme. The 28-kDa form was shown to be a different enzyme (temperature-stable) which retained activity at 37 degrees C. In contrast, cholesteryl ester hydrolase activities from 104,000 X g supernatants of liver or adrenal gland were unaffected and increased 4-fold, respectively, by elevation of temperature from 32 to 37 degrees C. Both testicular enzymes exhibited pH optima at about 7.3, and were activated by sodium cholate at concentrations near the critical micellar concentration (0.03-0.07%), but inhibited by higher concentrations. The temperature-labile cholesteryl ester hydrolase exhibited a high specificity for cholesteryl esters of monoenoic fatty acids of 18-24 carbons, especially nervonate (24:1), whereas the temperature-stable cholesteryl ester hydrolase exhibited highest specificity for cholesteryl oleate and arachidonate. Neither enzyme hydrolyzed cholesteryl acetate, myristate, palmitate, linoleate, or docosahexaenoate . Both enzymes reached maximum rates of hydrolysis at 150 microM substrates, with each substrate and at both reaction temperatures. Substrate inhibition was observed at higher concentrations (200 microM). The temperature-labile cholesteryl ester hydrolase was induced 20-fold in hypophysectomized rats by injection of follicle-stimulating hormone (FSH) and was localized in Sertoli cells, the target cells for FSH, but was not induced by luteinizing hormone. The temperature-stable cholesteryl ester hydrolase was induced by both FSH and LH and was found in both Sertoli cells and Leydig cells, the respective target cells for FSH and luteinizing hormone. Neither form of the enzyme was present at detectable levels in the germinal cells. The unique properties, localization, and hormonal regulation of both temperature-labile and temperature-stable cholesterol ester hydrolases suggest important roles for these enzymes in the testis. 相似文献
210.
Degradation of extracellular matrix by mouse trophoblast outgrowths: a model for implantation 总被引:7,自引:6,他引:1
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During implantation the embryo attaches to the endometrial surface and trophoblast traverses the uterine epithelium, anchoring in the uterine connective tissue. To determine whether trophoblast can facilitate invasion of the uterus by degrading components of normal uterine extracellular matrix, mouse blastocysts were cultured on a radio-labeled extracellular matrix that contained glycoproteins, elastin, and collagen. The embryos attached to the matrix, and trophoblast spread over the surface. Starting on day 5 of culture there was a release of labeled peptides into the medium. The radioactive peptides released from the matrix by the embryos had molecular weights ranging from more than 25,000 to more than 200. By day 7 there were areas where individual trophoblast cells had separated from one another, revealing the underlying substratum that was cleared of matrix. When trophoblast cells were lysed with NH(4)OH on day 8, it was apparent that the area underneath the trophoblast outgrowth had been cleared of matrix. Scanning electron microscopy and time-lapse cinemicrography confirmed that the digestion of matrix was highly localized, taking place only underneath the trophoblast, with no evidence of digestion of the matrix beyond the periphery of the trophoblast outgrowth. The sharp boundaries of degredation observed may be due to localized proteinase secretion by trophoblast, to membrane proteinases on the surface of trophoblast, or to endocytosis. Digestion of the matrix was not dependent on plasminogen, thus ruling out a role for plasminogen activator. Digestion was not inhibited by a variety of hormones and inhibitors, including progesterone, 17β-estradiol, leupeptin, EDTA, colchicine, NH(4)Cl, or ε-aminocaproic acid. This system of culturing embryos on extracellular matrix may be useful in determining the processes that regulate trophoblast migration and invasion into the maternal tissues during implantation.0 相似文献