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81.
Regulation of amino acid utilization in Neurospora crassa: effect of nmr-1 and ms-5 mutations. 总被引:7,自引:2,他引:5 下载免费PDF全文
The effect of the nmr-1 and ms-5 mutations, which lead to insensitivity to glutamine-mediated nitrogen metabolite repression, was examined with respect to extracellular deaminase production by Neurospora crassa. Deaminase production normally requires nitrogen limitation, but these mutations eliminated this requirement and allowed production of deaminase activity under nitrogen metabolite repressing conditions. Demonstration of normal glutamine transport by both strains eliminated the possibility that these mutations exerted their effects through repressor exclusion. We have proposed a new working model for nitrogen regulation in Neurospora based on the findings that these mutations affected a nitrogen-regulated activity in addition to those activities originally reported and that the mutations are genetically very closely linked and likely allelic. 相似文献
82.
The production of an extracellular deaminase activity involved with the utilization of amino acids as sole sources of nitrogen is under the control of the nit-2 locus of Neurospora crassa. This locus is the sole major nitrogen regulatory locus described for N. crassa and is believed to encode a positive effector required for induction of activities involved with the utilization of alternate nitrogen sources. Production of deaminase activity requires the lifting of nitrogen metabolite repression, the presence of a functional nit-2 gene product, and specific induction by amino acids. Additional parameters of enzyme production are described. 相似文献
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Demonstration of a novel ecto-enzyme on human erythrocytes, capable of degrading ADP and of inhibiting ADP-induced platelet aggregation 总被引:2,自引:0,他引:2
The role of ADP as an important inducer of platelet aggregation is generally accepted. Therefore it has been postulated by many authors that the enzymatic removal of extracellular ADP from the circulation is essential to avoid platelet aggregation and thrombus formation. Here we show that erythrocytes essentially contribute to the clearance of ADP. The removal of ADP from suspensions of washed human erythrocytes was due to at least two different activities. One activity, which had already been observed by earlier workers, was identified as adenylate kinase, on the basis of the reaction products and the inhibition by adenosine(5')pentaphospho(5')adenosine (Ap5A). This enzyme was not associated with the cells and was always detectable in cell-free supernatants, indicating that the enzyme had leaked from the cells into the extracellular medium. In contrast, the second activity, which is described here for the first time, was tightly bound to the cells. The activity was not inhibited by Ap5A. The main product of the reaction was AMP, and enzyme activity depended on the presence of divalent cations. The Michaelis constant was about 28 mumol/l. This activity seemed to be an ecto-ADPase. Studies with various inhibitors revealed that degradation of ADP was not due to a non-specific phosphatase. Besides the well known ADPase on the endothelium, the ecto-activity on erythrocytes may play an important part in destroying pro-aggregatory ADP. 相似文献
85.
In vitro total-gas, CH4, H2, volatile fatty acid, and lactate kinetics studies on luminal contents from the small intestine, cecum, and colon of the pig. 总被引:2,自引:2,他引:0 下载免费PDF全文
Two experiments were conducted to assess differences in fermentative activities of digesta obtained from various regions of the pig gastrointestinal tract. In experiment 1, the contents of small intestines, ceca, and colons of 110-kg pigs were collected, diluted twofold, and incubated for 2 h at 37 degrees C. In experiment 2, colonic samples from 16,100-kg pigs were similarly treated, except that the incubation period was 5 h. Total gas (gas pressure), CH4, H2, lactate, formate, acetate, propionate, butyrate, valerate, and isovalerate were measured in experiment 1. Only the gas variables were measured in experiment 2. Statistically significant differences (P greater than 0.05) were not observed among the gas production rate estimates across the small-intestinal, cecal, and colonic regions in experiment 1. Furthermore, all the small-intestinal samples and half the cecal samples assayed in experiment 1 were nonmethanogenic. The mean methanogenic and total-gas production rate estimates for the colonic samples in experiment 1 were 0.052 ml g of wet contents-1 h-1 and 1.7 ml of total gas g of wet contents-1 h-1, respectively. No differences in the methanogenic rate estimates were detected between the proximal, middle, and distal thirds of the pig colons (P greater than 0.05). The volatile fatty acid and lactate molar percentages measured in experiment 1 were consistent with previously published observations. Hydrogen accumulated to the greatest extent (7 microM on average) in the in vitro incubations of small-intestinal contents, whereas the H2 concentrations ranged from 0.5 to 1 microM for the incubated cecal and colonic samples in experiment 1.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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During the last 60 years, the inversion polymorphism on the third
chromosome of Drosophila pseudoobscura has become a case study of the
evolution of linked blocks of genes, isolated from each other by the
suppression of recombination in heterozygotes for different inversions. Due
to its location within inverted regions in most gene arrangements, the
amylase (Amy) gene region can be used to elucidate the molecular pattern of
evolution in these inversions. We studied this region in the Tree Line
phylad of gene arrangements, with regard to both restriction site
polymorphisms (RSP) and nucleotide sequences. The analysis of restriction
maps, encompassing 26 kb, corroborates the cytogenetic phylogeny
established on the basis of inversion breakpoints. However, we found that
the 2.7 kb of nucleotide sequences of the AmyI gene are identical in both
Estes Park and Hidalgo arrangements, despite the fact that these inversions
arose independently from Tree Line. These contrasting results suggest that
a homogenizing force, most likely gene conversion, is able to bring about
localized exchanges between otherwise isolated gene arrangements.
相似文献
88.
S. A. Forbes A. A. J. Pannett J. H. D. Bassett B. Harding C. Wooding R. V. Thakker R. Butler D. Ogilvie R. Anand P. Gaudray G. Weber C. Larsson C. X. Zhang A. Calender J. W. M. Höppener C. J. M. Lips K. Kas 《Human genetics》1997,100(3-4):481-485
The multiple endocrine neoplasia type 1 (MEN1) locus has been previously localised to 11q13 by combined tumour deletion mapping
and recombination studies, and a 0.5-Mb region, flanked by PYGM and D11S449, has been defined. In the course of constructing
a contig, we have identified the location of the gene encoding the B56β subunit of protein phosphatase 2A (PP2A), which is
involved in cell signal transduction pathways and thus represents a candidate gene for MEN1. We have searched for mutations
in the PP2A-B56β coding region, together with the 5′ and 3′ untranslated regions in six MEN1 patients. DNA sequence abnormalities
were not identified and thus the PP2A-B56β gene is excluded as the candidate gene for MEN1. However, our precise localisation
of PP2A-B56β to this region of 11q13 may help in elucidating the basis for other disease genes mapping to this gene-rich region.
Received: 17 April 1997 / Accepted: 22 April 1997 相似文献
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