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   348篇
  免费   9篇
  国内免费   1篇
  2023年   4篇
  2022年   6篇
  2021年   11篇
  2020年   15篇
  2019年   10篇
  2018年   12篇
  2017年   6篇
  2016年   11篇
  2015年   12篇
  2014年   22篇
  2013年   13篇
  2012年   24篇
  2011年   33篇
  2010年   21篇
  2009年   12篇
  2008年   14篇
  2007年   9篇
  2006年   25篇
  2005年   11篇
  2004年   17篇
  2003年   19篇
  2002年   9篇
  2001年   9篇
  2000年   9篇
  1999年   6篇
  1998年   1篇
  1992年   1篇
  1991年   1篇
  1989年   1篇
  1988年   1篇
  1983年   1篇
  1982年   1篇
  1980年   1篇
  1977年   2篇
  1975年   1篇
  1973年   2篇
  1972年   1篇
  1970年   1篇
  1969年   1篇
  1968年   2篇
排序方式: 共有358条查询结果,搜索用时 78 毫秒
91.
The effect of gonadotropin pretreatment of hypophysectomized male rats on LH stimulated serum testosterone concentrations was studied. A 5 day pretreatment period began 2 days after hypophysectomy at 21 or 24 days of age. On the day following the pretreatment period the animals received an intraperitoneal injection of saline or LH 60 min before blood collection. Animals pretreated with NIH-FSH-B1, or with doses of LH approximating the amount present in the NIH-FSH, had increased testosterone concentrations after LH stimulation compared to similarly stimulated saline pretreated animals. Pretreatment with more highly purified FSH Ex 199C at a lower dose than the minimum effective dose of NIH-FSH was also effective. There was no synergistic or additive effect when FSH Ex 199C and LH pretreatments were combined. FSH Ex 199C is more potent and contains appreciably less LH contamination than NIH-FSH-B1. The results obtained using FSH Ex 199C indicate that FSH, independent of LH contamination, can increase testes response to LH stimulation.  相似文献   
92.
Stroke is known to induce massive cell death in the ischemic brain. Either necrotic or apoptotic types of cell death program were observed in neurons in zone of ischemia. We suggest that spatial heterogeneity of glucose and oxygen distribution plays a crucial role in this phenomenon. In order to elucidate the role of glucose and oxygen in ischemic neurons choice of cell death pathway, conditions corresponding to different areas of insult were reproduced in vitro in the model of surviving brain cortex tissue slices. Three zones were modeled in vitro by varying glucose and oxygen concentration in surviving slices incubation media. Modeled ischemic area I (MIA I) was corresponded to the center of suggested ischemic zone where the levels of glucose and oxygen were considered to be extremely low. MIA II was assigned as intermediate area where oxygen concentration was still very low but glucose was present (this area was also divided into two sub-areas MIA IIa and MIA IIb with physiologically low (5 mM) and normal (10 mM) level of glucose respectively). MIA III was considered as a periphery area where glucose concentration was close to physiological level and high level of ROS production had been induced by reoxygenation after anoxia. Analysis of molecular mechanisms of cell death in MIA I, IIa, IIb and III was carried out. Cell death in MIA I was found to proceed by necrotic manner. Apoptosis characterized by cyt c release, caspase 3 activation and internucleosomal DNA fragmentation was observed in MIA III. Cell death in MIA II was accompanied by several (not all) hallmarks of apoptosis. Mechanisms of cell death in MIA IIa and MIA IIb were found to be different. Internucleosomal DNA fragmentation in MIA IIa but not in MIA IIb was sensitive to glycine (5 mM), inhibitor of NMDA receptor MK-801 (10 μM) and PTP inhibitor cyclosporine A (10 μM). Activation of caspase 3 was detected in MIA IIb but not in MIA IIa. However cytochrome c release was observed neither in MIA IIa nor in MIA IIb. In MIAs II–III apoptosis was accompanied by uncoupling of oxidative phosphorylation, which was induced by rise of intracellular Ca2+ and intensive ROS production. Results obtained in present study allow us to propose existence of at least four molecular pathways of cell death development in brain ischemic zone. The choice of cell death pathway is determined by oxygen and glucose concentration in the particular area of the ischemic zone.  相似文献   
93.
We identified a novel cDNA (IG20) that is homologous to cDNAs encoding a protein differentially expressed in normal and neoplastic cells (DENN-SV) and human MADD (MAPK-activating death domain-containing protein). Furthermore, we show that the above variants most likely result from alternative splicing of a single gene. Functional analyses of these variants in permanently transfected HeLa cells revealed that IG20 and DENN-SV render them more susceptible or resistant to tumor necrosis factor alpha (TNF-alpha)-induced apoptosis, respectively. All variants tested could interact with TNF receptor 1 and activate ERK and nuclear factor kappaB. However, relative to control cells, only cells expressing IG20 showed enhanced TNF-alpha-induced activation of caspase-8 and -3, whereas cells expressing DENN-SV showed either reduced or no caspase activation. Transfection of these cells with a cDNA encoding CrmA maximally inhibited apoptosis in HeLa-IG20 cells. Our results show that IG20 can promote TNF-alpha-induced apoptosis and activation of caspase-8 and -3 and suggest that it may play a novel role in the regulation of the pleiotropic effects of TNF-alpha through alternative splicing.  相似文献   
94.
Tosylphenylalanine chloromethyl ketone (TPCK) and tosyllysine chloromethyl ketone (TLCK) are irreversible modifiers of histidine which is located in the catalytic triad of chymotrypsin and trypsin, respectively. The effects of TPCK and TLCK on the histidine in the catalytic triad of the desensitized butyrylcholinesterase (BChE), prepared from human serum by heating at 45°C for 24 h, were investigated in detail. It is found that these reagents do not modify, but reversibly inhibit the desensitized enzyme as a function of time. Just as it is for the native enzyme, TPCK is a hyperbolic mixed-type inhibitor of the desensitized BChE with Ki, a and ß values of 0.017 ± 0.003 mM, 3.942 ± 1.125 and 0.524 ± 0.070, respectively. However, TLCK is the pure competitive inhibitor of the desensitized BChE with a Ki value of 0.008 ± 0.000 mM, while it is hyperbolic mixed-type inhibitor of the native form. These findings show that the conformation of the active site cavity of desensitized BChE is different from that of the native enzyme.  相似文献   
95.
Linear growth rates and age-related changes in shell form are analyzed in the bivalveScapharca broughtoni from several areas of Peter the Great Bay, Sea of Japan. Mollusks grow fast during the first 4 to 5 years of life; at the age of 10–12 years, the annual growth increment in shell size does not usually exceed 1–3 mm. Irrespective of habitat, the shell valve convexity ofS. broughtoni increases with age, but the most significant changes in shell form occur during the first year of life. The peculiarities of growth and age-related changes in shell form ofS. broughtoni are discussed from the standpoint of the functional morphology of burrowing bivalve mollusks, which, at the postlarval stage, change from an attached to a free-living mode of life.  相似文献   
96.
97.
Gastropods Nucella heyseana were collected from 1999 to 2001 from different habitats in Vostok Bay (Sea of Japan). The spatial distribution, the seasonal and interannual dynamics, and the composition of aggregations of this mollusk were analyzed. In Vostok Bay, N. heyseana inhabits biotopes that are typical of this species and other members of the genus and sometimes forms aggregations with an unusually high density and biomass (up to 1690 spec/m2 and 3680 g/m2), thus exceeding 10–40 times the greatest values reported elsewhere for populations of the southern Kuril Islands and Pos'eta Bay (Sea of Japan). N. heyseana is a typical polyphagous predator, and its diet includes numerous species of the associated fauna of bivalve and gastropod mollusks (more than 30 species). The abundance, composition, and stability of local aggregations of N. heyseana are largely dependent on the abundance dynamics of its prey (primarily the most common species, such as Mytilus trossulus, Ruditapes philippinarum, Protothaca euglypta, and Littorina spp.). The opinion on the low density of N. heyseana in southern Primorye (Golikov, Kussakin, 1978) is probably based on a lack of information about the intertidal fauna of this region compared to the South Kuril Islands.  相似文献   
98.
BackgroundAlcohol consumption has a disinhibiting effect that may make sexual risk behaviors and disease transmission more likely. The characteristics of alcohol-serving outlets (e.g. music, dim lights, lack of condoms) may further encourage risky sexual activity. We hypothesize that frequenting alcohol outlets will be associated with HIV risk.MethodsIn a sample of 2,533 school-attending young women in rural South Africa, we performed a cross-sectional analysis to examine the association between frequency of alcohol outlet visits in the last six months and four outcomes related to HIV risk: number of sex partners in the last three months, unprotected sex acts in the last three months, transactional sex with most recent partner, and HSV-2 infection. We also tested for interaction by alcohol consumption.ResultsVisiting alcohol outlets was associated with having more sex partners [adjusted odds ratio (aOR), one versus zero partners (95% confidence interval (CI)): 1.51 (1.21, 1.88)], more unprotected sex acts [aOR, one versus zero acts (95% CI): 2.28 (1.52, 3.42)], higher levels of transactional sex [aOR (95% CI): 1.63 (1.03, 2.59)], and HSV-2 infection [aOR (95% CI): 1.30 (0.88, 1.91)]. In combination with exposure to alcohol consumption, visits to alcohol outlets were more strongly associated with all four outcomes than with either risk factor alone. Statistical evidence of interaction between alcohol outlet visits and alcohol consumption was observed for all outcomes except transactional sex.ConclusionsFrequenting alcohol outlets was associated with increased sexual risk in rural South African young women, especially when they consumed alcohol. Sexual health interventions targeted at alcohol outlets may effectively reach adolescents at high risk for sexually transmitted infections like HIV and HSV-2.

Trial Registration

HIV Prevention Trials Network HPTN 068  相似文献   
99.
Although whole human genome sequencing can be done with readily available technical and financial resources, the need for detailed analyses of genomes of certain populations still exists. Here we present, for the first time, sequencing and analysis of a Turkish human genome. We have performed 35x coverage using paired-end sequencing, where over 95% of sequencing reads are mapped to the reference genome covering more than 99% of the bases. The assembly of unmapped reads rendered 11,654 contigs, 2,168 of which did not reveal any homology to known sequences, resulting in ∼1 Mbp of unmapped sequence. Single nucleotide polymorphism (SNP) discovery resulted in 3,537,794 SNP calls with 29,184 SNPs identified in coding regions, where 106 were nonsense and 259 were categorized as having a high-impact effect. The homo/hetero zygosity (1,415,123∶2,122,671 or 1∶1.5) and transition/transversion ratios (2,383,204∶1,154,590 or 2.06∶1) were within expected limits. Of the identified SNPs, 480,396 were potentially novel with 2,925 in coding regions, including 48 nonsense and 95 high-impact SNPs. Functional analysis of novel high-impact SNPs revealed various interaction networks, notably involving hereditary and neurological disorders or diseases. Assembly results indicated 713,640 indels (1∶1.09 insertion/deletion ratio), ranging from −52 bp to 34 bp in length and causing about 180 codon insertion/deletions and 246 frame shifts. Using paired-end- and read-depth-based methods, we discovered 9,109 structural variants and compared our variant findings with other populations. Our results suggest that whole genome sequencing is a valuable tool for understanding variations in the human genome across different populations. Detailed analyses of genomes of diverse origins greatly benefits research in genetics and medicine and should be conducted on a larger scale.  相似文献   
100.
Highlights? MS quantifies 1,578 mitochondrial acetyl sites altered during CR and loss of SIRT3 ? SIRT3 functions as a prominent regulator in CR adaptation ? CR and SIRT3 regulate previously unrecognized processes in mitochondria ? We provide an acetylation atlas for understanding mitochondrial regulation in CR  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