首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   331篇
  免费   34篇
  2021年   3篇
  2017年   5篇
  2016年   11篇
  2015年   17篇
  2014年   18篇
  2013年   22篇
  2012年   15篇
  2011年   21篇
  2010年   23篇
  2009年   7篇
  2008年   8篇
  2007年   7篇
  2006年   8篇
  2005年   11篇
  2004年   10篇
  2003年   3篇
  2002年   7篇
  2001年   6篇
  2000年   8篇
  1999年   6篇
  1998年   6篇
  1997年   3篇
  1996年   6篇
  1995年   4篇
  1993年   4篇
  1992年   5篇
  1991年   3篇
  1988年   3篇
  1987年   4篇
  1984年   4篇
  1983年   2篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1979年   5篇
  1978年   5篇
  1977年   8篇
  1976年   4篇
  1975年   5篇
  1974年   8篇
  1973年   4篇
  1972年   8篇
  1971年   10篇
  1970年   2篇
  1969年   5篇
  1968年   2篇
  1967年   5篇
  1965年   2篇
  1964年   2篇
  1882年   2篇
排序方式: 共有365条查询结果,搜索用时 15 毫秒
1.
The phosphorylation patterns of proteins were examined during the cell cycle of Chinese hamster ovary cells. This was accomplished by labeling synchronized cells at various times with [32P]orthophosphate and separating the proteins by both isoelectric focusing and nonequilibrium pH gradient two-dimensional gel electrophoresis. The most dramatic changes occurred during late G2/M when approximately eight proteins (including vimentin, lamin B, and histones 1 and 3) showed increased phosphorylation. Ten other proteins appeared to be uniquely phosphorylated during late G2/M. Of these 10 proteins, seven were no longer phosphorylated shortly after mitosis. There is also at least one protein which showed a relative decrease in phosphorylation during late G2/M.  相似文献   
2.
Human placental protein 14 (PP14) has been purified in high yield from first trimester decidual cytosol. High-performance liquid chromatography on anion exchange, gel filtration and reverse-phase chromatography were used. The protein obtained is approximately 97% pure with an overall recovery of about 50% from the original tissue extract. The first 24 amino acids of the N-terminal were found to be Met-Asp-Ile-Pro-Gln-Thr-Lys-Gln-Asp-Leu-Glu-Leu-Pro-Lys-Leu-Ala-Gly-Thr-Glu-His - Glu-Met-Ala-Met. PP14 has been characterized in this study to be a dimeric glycoprotein of Mr 60,000, with homologous subunits having an Mr of 28,000.  相似文献   
3.
1. 2-Deoxy-2-fluoro-d-galactose, 3-deoxy-3-fluoro-d-galactose, 4-deoxy-4-fluoro-d-galactose, 6-deoxy-6-fluoro-d-galactose and 2-deoxy-d-lyxo-hexose are substrates for yeast galactokinase. 2. The variation in K(m) values for the d-hexose derivatives was not associated with a variation in the value of K(m) for MgATP(2-) indicating that the binding of MgATP(2-) is not modified by the binding of the sugar substrate. 3. Donated H bonds from OH-3, OH-4 and OH-6 and an accepted H bond to OH-2 of the d-hexose are important for the binding of the sugar substrate to galactokinase. 4. Yeast galactokinase exhibits similar kinetics to the galactokinase from Escherichia coli and operates by a similar random sequential mechanism. 5. 4-Deoxy-4-fluoro-d-glucose was neither a substrate for nor an inhibitor of yeast galactokinase.  相似文献   
4.
5.
B. Lofts    R. K. Murton  N. J. Westwood 《Ibis》1967,109(3):338-351
  • 1 The gametogenetic response following photo-stimulation was tested in Woodpigeons under controlled laboratory and aviary conditions. Subjects were wild-caught adult or first-winter birds or were hand-reared from wild-taken nestlings. The natural seasonal gonad cycle is described and experiments were related to this cycle.
  • 2 Gonad recrudescence could be initiated in adults with regressed organs by exposure to summer photoperiods, while the normal vernal recrudescence could be prevented if birds were artificially kept on short (winter) daylengths. Thus Woodpigeons could be stimulated towards reproductive condition at seasons when the gonads of wild-living birds remained inactive, viz. late September to mid-February.
  • 3 Juvenile males were unresponsive to extra photo-stimulation until they were about six months old. This meant that some spermatogonial division could be procured in a few individuals in late February, but juveniles were not very noticeably affected by an extended photoperiod until mid-late March. This is the time when juveniles first begin gametogenetic development in the wild, though spermatogenesis normally accelerates in April after which time the rate of gonad development is constant. First-winter females were judged to resemble males in their photoperiodic responses but the sample examined was small.
  • 4 The results confirm that the natural gonad cycle in the Woodpigeon is controlled (via gonadotrophic hormones) by seasonal changes in daylength. More important is the finding that the species appears to possess no post-nuptial refractory period. Thus, at the end of the breeding season in September birds kept on summer daylengths were maintained in full reproductive condition until December. The testes of controls placed on winter daylengths regressed within one month, but they were immediately responsive to a summer daylength which stimulated spermatogenesis within a month.
  • 5 The discussion argues that the avian refractory period is not a necessary period for gonad rehabihtation and reorganization and that it has not evolved as a fixed period serving to time the breeding season; views which until now have been current. Instead, it functions only as a safety mechanism, preventing unseasonal reproduction in those species for which natural selection favours seasonal breeding. In such species the evolution of sensitivity to a particular daylength could result in breeding taking place at the wrong time, for example spring responding species might also respond in the autumn. Because natural selection permits Woodpigeons to remain in breeding condition from March until September, without disadvantage, a direct response to natural daylength can regulate the cycle, and there is no need for a period of pituitary refractoriness. It is not known if some pigeons have lost the refractory period or whether they never possessed one.
  相似文献   
6.
Many recent studies have suggested that heat and other inducers of the heat shock (stress) response in eukaryotic cells might result in the generation of abnormal proteins which would result in the overloading of protein degradation systems and the stabilization of proteins involved in positively regulating heat shock (hs) gene expression. In this study we have examined the effects different heat treatments and other hs inducers have on protein degradation in Chinese hamster ovary (CHO) and Drosophila Kc and Schneider cells. We have found that intermediate temperatures which induced the hs response (42 degrees C in CHO and 34 degrees C in Kc cells) did increase protein degradation rates whereas, higher temperatures which also induced the hs response (45 degrees C in CHO and 37 degrees C in Kc cells) initially increased but then decreased protein degradation rates. While these results are consistent with a model in which the protein degradation system is being overloaded and/or components of it are being depleted, we have found several conditions which induce hs proteins which rule out this mechanism. Exposure of either cell type to amino acid analogs (5 mM canavanine or 5 mM S-aminoethyl cysteine) resulted in the rapid degradation of those proteins which had incorporated the analogs in both CHO and Drosophila cells. However, the addition of analogs had little or no effect on the degradation of preexisting proteins, indicating that the introduction of abnormal proteins probably didn't overload the protein degradation system(s). The addition of 100 microM cadmium sulfate or 100 microM sodium arsenite had little or no effect on protein degradation rates in CHO cells even though both were good inducers of the hs proteins. Thus, exposure to inducers of the hs response does not universally increase protein degradation rates nor does it stabilize preexisting proteins. Therefore, the degradation of abnormal proteins is probably not involved in inducing the hs genes.  相似文献   
7.
An Ustilago maydis ergosterol biosynthesis mutant (A14) which is partially blocked in sterol 14alpha-demethylase (P45014DM) activity is described. This mutant accumulated the abnormal 14alpha-methyl sterols, eburicol, 14alpha-methylfecosterol, and obtusifoliol, along with significant amounts of ergosterol. Although the A14 mutant grew nearly as well as the wild type, it was impaired in cell extension growth, which indicated a dysfunction in apical cell wall synthesis. The mutant was also found to be hypersensitive to the azole fungicides penconazole and tebuconazole.  相似文献   
8.
The P light chain of myosin is partially phosphorylated in resting slow and fast twitch skeletal muscles of the rabbit in vivo. The extent of P light-chain phosphorylation increases in both muscles on stimulation. Rabbit slow-twitch muscles contain two forms of the P light chain that migrate with the same electrophoretic mobilities as the two forms of P light chain in rabbit ventricular muscle. The rate of phosphorylation of the P light chain in slow-twitch muscle is slower than its rate of phosphorylation in fast-twitch muscles during tetanus. The rate of P light-chain dephosphorylation is slow after tetanic contraction of fast-twitch muscles in vivo. The time course of dephosphorylation does not correlate with the decline of post-tetanic potentiation of peak twitch tension in rabbit fast-twitch muscles. The frequency of stimulation is an important factor in determining the extent of P light-chain phosphorylation in fast- and slow-twitch muscles.  相似文献   
9.
10.
Reliable estimates of the frequency of Gaucher disease-producing mutations are not available. The high frequency of Gaucher disease in the Ashkenazi Jewish population is due to the occurrence of a mutation at nucleotide (nt) 1226. We have screened 593 DNA samples from normal Ashkenazi Jews, as well as 62 DNA samples from all our Ashkenazi Jewish patients with Gaucher disease, for the presence of the 1226 mutation. In the 593 presumed normal Ashkenazi Jewish individuals the 1226 mutation was identified in the heterozygous state in 37 and in the homozygous state in two, giving a gene frequency of .035 for the mutation. This 1226 mutation represented 73% of the 124 Gaucher disease alleles in Jewish Gaucher disease patients. Accordingly we estimate that the gene frequency for Gaucher disease among the Ashkenazi Jewish population is .047, which is equivalent to a carrier frequency of 8.9% and a birth incidence of 1:450.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号