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   401篇
  免费   20篇
  2023年   2篇
  2022年   5篇
  2021年   9篇
  2020年   9篇
  2019年   4篇
  2018年   3篇
  2017年   7篇
  2016年   15篇
  2015年   13篇
  2014年   13篇
  2013年   19篇
  2012年   23篇
  2011年   14篇
  2010年   10篇
  2009年   14篇
  2008年   22篇
  2007年   15篇
  2006年   16篇
  2005年   20篇
  2004年   25篇
  2003年   19篇
  2002年   11篇
  2001年   3篇
  2000年   3篇
  1999年   8篇
  1998年   10篇
  1997年   12篇
  1996年   7篇
  1995年   2篇
  1994年   6篇
  1993年   6篇
  1992年   9篇
  1991年   6篇
  1990年   8篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1984年   3篇
  1983年   2篇
  1982年   5篇
  1980年   3篇
  1977年   6篇
  1975年   1篇
  1974年   3篇
  1973年   2篇
  1972年   4篇
  1971年   1篇
  1970年   2篇
  1968年   3篇
  1967年   2篇
排序方式: 共有421条查询结果,搜索用时 31 毫秒
91.
Oögenesis and the physiological activity of the corpora allata were studied in adult females of the Egyptian locust (Anacridium aegyptium), in ovarian diapause, after electrical stimulation in vivo of the pars intercerebralis. This stimulation provokes (1) a decrease in the quantity of fuchsinophilic material present in the median neurosecretory cell bodies and in the internal cardiac tract, (2) an increase in the physiological activity of the corpora allata (measured by its chromatropic effect on larvae of Locusta), and (3) rupture of the ovarian diapause (advance of maturation of the oöcytes and oviposition by 5 months, and initiation of the ovarian cycle).In the control animals, the same electrical stimulations of various regions of the central nervous system (tritocerebrum, first ganglion of the abdominal cord) have no effect on these phenomena.In allatectomized females, electrical stimulations of the pars intercerebralis are followed by a slight growth of oöcytes, without a deposit of yellow vitellus. The diapause is not broken. Section of the allatocardiac nerves or rupture of the allatocardiac and allato-suboesophageal nervous connexions do not change the physiological state of the corpora allata. In the case of females in which the corpora allata have been disconnected, electrical stimulations of the pars intercerebralis succeed in activating the corpora allata and breaking the ovarian diapause. The aggregate of these results confirms that in locusts the control of the brain over the physiological activity of the corpora allata is above all neuroendocrine.  相似文献   
92.
Localization of the rat immunoglobulin heavy chain locus to chromosome 6   总被引:1,自引:0,他引:1  
We have previously used rat/mouse somatic cell hybrids to localize the rat c-myc gene to chromosome 7 (Sümegi et al. 1983) and the rat immunoglobulin kappa locus to chromosome 4 (Perlmann et al. 1985). We now report that by utilizing rat/mouse somatic cell hybrids, we have localized the rat immunoglobulin heavy chain locus to chromosome 6.  相似文献   
93.
94.
95.
Exogenous farnesol or farnesoic acid (FA) stimulates juvenile hormone III (JH III) biosynthesis by isolated corpora allata from Locusta migratoria in a dose-dependent manner. Farnesol and FA also stimulate a dose-dependent accumulation of substantial amounts of methyl farnesoate (MF), identified by gas chromatography-mass spectroscopy (GCMS) analysis, in the corpora allata. Lower quantities of MF were found in the incubation medium. Corpora allata, denervated 2 days prior to assay, showed low spontaneous rates of JH biosynthesis which were stimulated by farnesol and FA. The dose-response curves for control and denervated corpora allata were similar. During oocyte maturation the rate of farnesol and FA stimulation of JH biosynthesis increased gradually. However, after transection of nervus corporis allati 1 (NCA-1), the rate of stimulated JH synthesis was maintained at preoperative levels. Although the spontaneous rate of JH biosynthesis decreased rapidly after NCA-1 transection, denervated glands could still be stimulated by farnesol or FA to produce large amounts of JH. These results suggest that the low spontaneous rate of JH biosynthesis in denervated corpora allata is not caused by inhibition of the final steps of JH biosynthesis.  相似文献   
96.
We retrospectively investigated outcome data for vagus nerve stimulation (VNS) in children less than 12 years of age with intractable seizures and mitochondrial disease. Five children with a mitochondrial disease, due to electron transport chain deficiency, were studied. Information was collected from clinic visits prior to, and subsequent to, VNS implantation. Data were collected by type and frequency of seizures, encephalogram and neuroimaging findings, and medication history. Four of the children had predominantly myoclonic seizures, while the other child had focal seizures with secondary generalization and myoclonic seizures. All five children did not have significant reduction in seizure frequency with VNS. VNS may not be an effective method to control myoclonic seizures in children with electron transport chain disorders.  相似文献   
97.
Le Guigo P  Rolier A  Le Corff J 《Oecologia》2012,169(3):753-761
A plant's own characteristics, but also those of its neighbors, might have an impact on its probability of being colonized by herbivorous insects. A plant might be less colonized and experience associational resistance when it grows near repellent neighbors. In contrast, it might be more colonized and experience associational susceptibility near attractive neighbors. To date, mechanisms that drive associational defense are not really understood. In order to gain insights into the occurrence of associational resistance versus associational susceptibility under field conditions, we conducted an experiment to determine the influence of neighboring plants on the colonization of a focal plant by aphids. The focal plant was always Brassica oleracea. The neighbors were B. oleracea (control), B. napus, B. nigra, or Solanum lycopersicum, which represent contrasting levels of physical and chemical defenses. The focal plant, B. oleracea, was more colonized by the specialist aphid Brevicoryne brassicae, and experienced associational susceptibility when it was surrounded by B. nigra or B. napus. In contrast, B. oleracea was less colonized by the generalist aphid Myzus persicae, and experienced associational resistance when it was surrounded by S. lycopersicum, B. nigra or B. napus. Neighboring plants had no significant impact on host plant choice by the generalist aphid Macrosiphum euphorbiae. In conclusion, attraction or repulsion of the specialist aphid B. brassicae and the generalist aphid M. persicae by B. nigra, B. napus, and S. lycopersicum resulted in associational susceptibility or associational resistance for B. oleracea.  相似文献   
98.
Optimal investment into life-history traits depends on the environmental conditions that organisms are likely to experience during their life. Evolutionary theory tells us that optimal investment in reproduction versus maintenance is likely to shape the pattern of age-associated decline in performance, also known as aging. The currency that is traded against different vital functions is, however, still debated. Here, we took advantage of a phenotypic manipulation of individual quality in early life to explore (1) long-term consequences on life-history trajectories, and (2) the possible physiological mechanism underlying the life-history adjustments. We manipulated phenotypic quality of a cohort of captive zebra finches (Taeniopygia guttata) by assigning breeding pairs to either an enlarged or a reduced brood. Nestlings raised in enlarged broods were in poorer condition than nestlings raised in reduced broods. Interestingly, the effect of environmental conditions experienced during early life extended to the age at first reproduction. Birds from enlarged broods delayed reproduction. Birds that delayed reproduction produced less offspring but lived longer, although neither fecundity nor longevity were directly affected by the experimental brood size. Using the framework of the life-table response experiment modeling, we also explored the effect of early environmental condition on population growth rate and aging. Birds raised in reduced broods tended to have a higher population growth rate, and a steeper decrease of reproductive value with age than birds reared in enlarged broods. Metabolic resources necessary to fight off the damaging effect of reactive oxygen species (ROS) could be the mechanism underlying the observed results, as (1) birds that engaged in a higher number of breeding events had a weaker red blood cell resistance to oxidative stress, (2) red blood cell resistance to oxidative stress predicted short-term mortality (but not longevity), and (3) was related with a parabolic function to age. Overall, these results highlight that early condition can have long-term effects on life-history trajectories by affecting key life-history traits such as age at first reproduction, and suggest that the trade-off between reproduction and self-maintenance might be mediated by the cumulative deleterious effect of ROS.  相似文献   
99.
In male rats, the dorsal penile nerve (DPN) conveys sensory information from the genitals to the lumbosacral spinal segments of the spinal cord. DPN is the afferent limb of a reflex loop that supports reflexive erections, and that includes a network of spinal interneurons and autonomic and somatic motoneurons to the penis and perineal striated muscles. Autonomic efferent pathways to the penis relay in the major pelvic ganglion (MPG). Glutamate (Glu) is a likely candidate as a neurotransmitter of reflexive erections. Both AMPA and NMDA glutamatergic receptor subunits are present in the lumbosacral spinal cord, and AMPA and NMDA receptor antagonists block reflexive erections. In the present study, we used tract-tracing experiments combined with immunohistochemical and immunocytochemical techniques to ascertain the presence of Glu at two different levels of the network controlling reflexive erections. DPN afferents were localized in the dorsal horn of the lumbosacral cord and displayed the characteristics of either C-fibers or Aδ fibers. DPN terminals (some of them glutamatergic) were mainly distributed in the medial edge of the dorsal horn in the L6 spinal segment. GluR1 subunits were present in some DPN afferents, suggesting that they could be autoreceptors. DPN fibers were also present in the MPG, as were Glu terminals and GluR4 subunits. The results reveal the presence of Glu in DPN fibers and terminals and suggest that both the spinal cord and the MPG use glutamatergic transmission to control reflexive erections. This work was supported by grant no. 5R01MH059811–03 from the NIH and by an institutional grant from the Institut National de la Recherche Agronomique.  相似文献   
100.
The two BRCT domains (BRCT1 and BRCT2) of XRCC1 mediate a network of protein–protein interactions with several key factors of the DNA single-strand breaks (SSBs) and base damage repair pathways. BRCT1 is required for the immediate poly(ADP–ribose)-dependent recruitment of XRCC1 to DNA breaks and is essential for survival after DNA damage. To better understand the biological role of XRCC1 in the processing of DNA ends, a search for the BRCT1 domain-associated proteins was performed by mass spectrometry of GST-BRCT1 pulled-down proteins from HeLa cell extracts. Here, we report that the double-strand break (DSB) repair heterotrimeric complex DNA-PK interacts with the BRCT1 domain of XRCC1 and phosphorylates this domain at serine 371 after ionizing irradiation. This caused XRCC1 dimer dissociation. The XRCC1 R399Q variant allele did not affect this phosphorylation. We also show that XRCC1 strongly stimulates the phosphorylation of p53-Ser15 by DNA-PK. The pseudo phosphorylated S371D mutant was a much weaker stimulator of DNA-PK activity whereas the non-phosphorylable mutant S371L endowed with a DNA-PK stimulating capacity failed to fully rescue the DSB repair defect of XRCC1-deficient EM9 rodent cells. The functional association between XRCC1 and DNA-PK in response to IR provides the first evidence for their involvement in a common DSB repair pathway.  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