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排序方式: 共有180条查询结果,搜索用时 15 毫秒
1.
L C Stephens D M Cromeens V W Robbins P C Stromberg J H Jardine 《Laboratory animal science》1987,37(3):341-344
Significant morbidity and mortality of South African clawed frogs, Xenopus laevis, can be caused by parasitism of the epidermis by a capillarid nematode. These worms produce an erosive dermatitis that is complicated by infection with gram-negative microorganisms. The nematode apparently has a direct life cycle that can be completed within the epidermis of the frog. These characteristics are suggested by the lack of an intermediate host and failure to detect visceral migration. Another unique feature of the parasite was the presence of larvated eggs, in utero. Some have named the parasite Capillaria xenopodis, whereas others called it Pseudocapillaroides xenopi to distinguish it form the typical members of the genus Capillaria. 相似文献
2.
Caitilyn Allen Verlyn K. Stromberg Franzine D. Smith George H. Lacy Mark S. Mount 《Molecular & general genetics : MGG》1986,202(2):276-279
Summary We report the complementation of a genetic lesion in the genome of Erwinia carotovora subsp. carotovora (Ecc), a pathogenic bacterium that incites soft rot of plants. A Sau3AI genomic library of Ecc was constructed using the conjugal cosmid pLAFR-3 as a vector. Sixteen cosmid clones encoding various plant tissue-degrading enzymes were identified, including a proteolytic clone, five cellulolytic clones, and ten pectolytic clones. We detected a mutant of Ecc with no proteolytic activity following transposon mutagenesis with an unstable Tn5-carrying plasmid. Conjugal transfer of the protease-encoding cosmid to this mutant restored near-wildtype extracellular protease production. Further manipulation and study of genes encoding pathogenic determinants in Ecc will be possible using this system. 相似文献
3.
4.
G R Johnson T Saeki N Auersperg A W Gordon M Shoyab D S Salomon K Stromberg 《Biochemical and biophysical research communications》1991,180(2):481-488
Amphiregulin (AR) is a polypeptide growth regulator which has sequence homology to the epidermal growth factor-related family of ligands and contains putative nuclear targeting sequences. Human ovarian carcinoma cell lines and their normal counterparts, ovarian surface epithelial cells (OSEs), were assessed for their ability to respond to and express AR. Addition of exogenous AR (8-200 pM) inhibited the growth of 2 of 3 OSE specimens and 3 of the 6 carcinoma cell lines indicating that AR has the potential to inhibit the growth of normal cells, in addition to carcinoma cells. In contrast, concentrations of AR ranging from 1-5 nM stimulated the growth of all 3 of the OSEs and 4 of the 6 carcinoma cell lines. Immunocytochemical staining of the cells using antipeptide antibodies directed against residues 8-26 of AR indicated that all cells expressed AR and that the staining was localized to the nucleus. The nuclear staining of AR was concentrated in the nucleolus of the carcinoma cells, whereas the staining was diffuse in the nucleus of the OSEs. These results suggest that AR may play a growth regulatory role in the nucleus of cells and this role may be different in normal and malignant epithelial cells. 相似文献
5.
Rat ventral prostate and liver were investigated for the binding in vitro to particulate fractions and for the metabolism of 5 alpha-androstane-3 beta, 17 beta-diol. Comparative investigations were carried out on the metabolism of 5 alpha-androstane-3 alpha, 17 beta-diol. Preparations of the liver were investigated in order to establish the organ specificity of the method. In the prostate, the bulk of the metabolites of 5 alpha-androstane-3 beta, 17 beta-diol was present as steroids of high polarity. Of the less polar metabolites, 17 beta-hydroxy-5 alpha-androstan-3-one, 3 beta-hydroxy-5 alpha-androstan, 17-one and 5 alpha-androstane-3 alpha, 17 beta-diol were detectable. The binding of a 5 alpha-androstane-3 beta, 17 beta-diol to mitochondria and microsomes was unspecific. In the liver, among the less polar metabolites, 3 beta-hydroxy-5 alpha-androstan-17-one was the main metabolite, and the binding was unspecific. The main metabolite in the prostate homogenate of 5 alpha-androstane-3 alpha, 17 beta-diol was 17 beta-hydroxy-5 alpha-androstan-3-one. The portion of highly polar steroids was very low. The portion of unmetabolized hormone was distributed almost equally among the different cell preparations except the nuclei, in which 17 beta-hydroxy-5 alpha-androstan-3-one was higher and 5 alpha-androstane-3 alpha, 17 beta-diol was lower than in the remaining cell fractions. 相似文献
6.
Culture conditions for maintaining first trimester human placenta in organ culture, which enhance the secretion of human chorionic gonadotropin (hCG), are described. Nutrient medium, oxygen tension and Gelfoam support matrix influence the synthesis of hCG by these cultures. Placental tissue remained viable for the duration of experiments (12 days) as judged by the incorporation of tritiated thymidine into DNA and the lack of release of incorporated [125I]iododeoxyuridine. Optimal conditions for hCG synthesis in placental organ culture included an atmosphere of 95% air and 5% Co2 (approximately 20% O2), CMRL 1066 medium containing fetal human or bovine serum, insulin, hydrocortisone and retinal acetate. Multiple pieces of placenta could be cultured in the same dish with an additive effect on hCG secretion. The functional responsiveness of these placental cultures was demonstrated by modulation of hCG synthesis with theophylline and 3'5' dibutyryl cyclic AMP. 相似文献
7.
The distribution and abundance of the nematode Camallanus oxycephalus infecting white bass, Morone chrysops, in western Lake Erie was studied for over 2 years. Infection was generally more frequent and of higher intensity in large fish. The frequency distributions of nematode abundance in all segments of the fish population followed the negative binomial distribution. The data show seasonal cycles in population structure, site selection, intensity of infection, maturation, and reproduction. Infection occurs during July and August with a resulting peak in population density; during late summer and autumn, mortality, probably density-dependent, reduces the population by 30 to 60%; surviving worms are eliminated at 1 year of age. Growth and development of female worms is arrested from November to April, then proceeds at a rapid rate until the worms release their larvae and die. This growth pattern is probably related to temperature but may also involve host hormone cycles. The dispersal period of the nematode coincides with the annual maximum density of the intermediate host, a cyclopoid copepod,and is interpreted as an adaptation which increases the probability of successful transmission. Because the number of larvae produced by each female worm is a function of body volume, natural selection has favored rapid spring growth and attainment of large body size relative to the male worm. Both seasonal timing in the life cycle and the number of larvae produced are important factors in determining the abundance of this and perhaps other parasites. Evidence is presented suggesting that fluctuations of environmental parameters may disrupt the timing of transmission and alter the distribution and abundance of the parasite. It is hypothesized that the magnitude of such changes in parasite abundance may be related to the complexity of the host-parasite system. 相似文献
8.
R van Reis A S Lubiniecki R A Olson R R Stromberg J A Madsen L I Friedman 《Journal of immunology (Baltimore, Md. : 1950)》1984,133(2):758-763
The production of human gamma-interferon (HuIFN-gamma) in unfractionated and nylon wool column-fractionated leukocyte cell cultures stimulated with PMA and PHA was investigated. Production was studied with normal and reduced autologous serum protein levels in 96-hr spinner cultures. A 10- to 15-fold enhancement of production and a 50-fold increase in specific activity of crude HuIFN-gamma was demonstrated in nylon column-fractionated/reduced serum cell cultures. Kinetic analysis revealed a production rate maximum within 6 hr of induction in unprocessed cell cultures, whereas production occurred at an essentially constant rate for 48 hr in fractionated cell cultures. 相似文献
9.
Epidemiology of ruminant helminths is the foundation on which strategic parasite control programmes are designed. Without this information one is not able to use anthelmintics to provide the optimal benefits for controlling both the adult worm and the pasture larval populations. The absence of strategic programmes generally results in using anthelmintics at the convenience of the producer, which may have little if any impact on parasite populations. The design of a strategic parasite control programme requires a knowledge of the dynamics of egg shedding from the host and the resulting pasture larval populations. It is important to know if larvae are available when animals are turned out onto pasture, when larval populations reach their maximal numbers and when they are induced to become hypobiotic. The goal is to keep pasture larval populations as low as possible. The use of pasture rotation adds another dimension to control programmes. The longer a pasture is allowed to remain fallow, the lower the pasture larval burden will be when it is grazed next. However, when we use intensive rotational grazing, animals may return to the pasture about 28 days later, when the larvae resulting from the eggs shed in the previous grazing are infective. This practice forces cattle to eat all of the forage available, including the grass closest to the faecal pat, where most of the infective larvae are available. If we treated cattle before turning them onto a clean rotationally grazed pasture, we should be able to control parasitism. Using a long-acting anthelmintic should enhance helminth control in rotationally grazed pastures and actually help to clean the pastures. Another grazing management practice is to alternately graze different species. This programme with the strategic use of anthelmintics should reduce parasitism in both host species. 相似文献
10.
Processing of viral envelope glycoprotein by the endomannosidase pathway: evaluation of host cell specificity 总被引:4,自引:2,他引:2
Endo-alpha-D-mannosidase is an enzyme involved in N-linked oligosaccharide
processing which through its capacity to cleave the internal linkage
between the glucose-substituted mannose and the remainder of the
polymannose carbohydrate unit can provide an alternate pathway for
achieving deglucosylation and thereby make possible the continued formation
of complex oligosaccharides during a glucosidase blockade. In view of the
important role which has been attributed to glucose on nascent
glycoproteins as a regulator of a number of biological events, we chose to
further define the in vivo action of endomannosidase by focusing on the
well characterized VSV envelope glycoprotein (G protein) which can be
formed by the large array of cell lines susceptible to infection by this
pathogen. Through an assessment of the extent to which the G protein was
converted to an endo-beta-N- acetylglucosaminidase (endo H)-resistant form
during a castanospermine imposed glucosidase blockade, we found that
utilization of the endomannosidase-mediated deglucosylation route was
clearly host cell specific, ranging from greater than 90% in HepG2 and PtK1
cells to complete absence in CHO, MDCK, and MDBK cells, with intermediate
values in BHK, BW5147.3, LLC-PK1, BRL, and NRK cell lines. In some of the
latter group the electrophoretic pattern after endo H treatment suggested
that only one of the two N-linked oligosaccharides of the G protein was
processed by endomannosidase. In the presence of the specific
endomannosidase inhibitor, Glcalpha1-->3(1- deoxy)mannojirimycin, the
conversion of the G protein into an endo H- resistant form was completely
arrested. While the lack of G protein processing by CHO cells was
consistent with the absence of in vitro measured endomannosidase activity
in this cell line, the failure of MDBK and MDCK cells to convert the G
protein into an endo H-resistant form was surprising since these cell lines
have substantial levels of the enzyme. Similarly, we observed that
influenza virus hemagglutinin was not processed in castanospermine-treated
MDCK cells. Our findings suggest that studies which rely on glucosidase
inhibition to explore the function of glucose in controlling such critical
biological phenomena as intracellular movement or quality control should be
carried out in cell lines in which the glycoprotein under study is not a
substrate for endomannosidase action.
相似文献