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   2425篇
  免费   205篇
  国内免费   2篇
  2022年   15篇
  2021年   24篇
  2020年   35篇
  2019年   34篇
  2018年   54篇
  2017年   40篇
  2016年   57篇
  2015年   82篇
  2014年   106篇
  2013年   108篇
  2012年   134篇
  2011年   134篇
  2010年   62篇
  2009年   66篇
  2008年   111篇
  2007年   99篇
  2006年   104篇
  2005年   87篇
  2004年   114篇
  2003年   94篇
  2002年   102篇
  2001年   29篇
  2000年   17篇
  1999年   25篇
  1998年   33篇
  1997年   18篇
  1996年   32篇
  1995年   28篇
  1994年   29篇
  1993年   23篇
  1992年   14篇
  1991年   16篇
  1990年   16篇
  1989年   20篇
  1988年   26篇
  1987年   15篇
  1985年   15篇
  1984年   15篇
  1983年   29篇
  1982年   22篇
  1981年   18篇
  1980年   21篇
  1978年   19篇
  1974年   14篇
  1973年   15篇
  1964年   12篇
  1962年   12篇
  1957年   12篇
  1954年   14篇
  1953年   16篇
排序方式: 共有2632条查询结果,搜索用时 15 毫秒
111.
In this study we investigate conformational changes in Loop V-VI of visual arrestin during binding to light-activated, phosphorylated rhodopsin (Rho*-P) using a combination of site-specific cysteine mutagenesis and intramolecular fluorescence quenching. Introduction of cysteines at positions in the N-domain at residues predicted to be in close proximity to Ile-72 in Loop V-VI of arrestin (i.e. Glu-148 and Lys-298) appear to form an intramolecular disulfide bond with I72C, significantly diminishing the binding of arrestin to Rho*-P. Using a fluorescence approach, we show that the steady-state emission from a monobromobimane fluorophore in Loop V-VI is quenched by tryptophan residues placed at 148 or 298. This quenching is relieved upon binding of arrestin to Rho*-P. These results suggest that arrestin Loop V-VI moves during binding to Rho*-P and that conformational flexibility of this loop is essential for arrestin to adopt a high affinity binding state.  相似文献   
112.
We recently reported the disruption of the inner mitochondrial membrane peptidase 2-like (IMMP2L) gene by a chromosomal breakpoint in a patient with Gilles de la Tourette syndrome (GTS). In the present study we sought to identify genetic variation in IMMP2L, which, through alteration of protein function or level of expression might contribute to the manifestation of GTS. We screened 39 GTS patients, and, due to the localization of IMMP2L in the critical region for the autistic disorder (AD) locus on chromosome 7q (AUTS1), 95 multiplex AD families; however, no coding mutations were found in either GTS or AD patients. In addition, no parental-specific expression of IMMP2L was detected in somatic cell hybrids containing human chromosome 7 and human cell lines carrying a maternal uniparental disomy for chromosome 7 (mUPD7). Despite the fact that no deleterious mutations in IMMPL2 (other than the inverted duplication identified previously) were identified in either GTS or AD, this gene cannot be excluded as a possible rare cause of either disorder.  相似文献   
113.
Thermal stress and coral cover as drivers of coral disease outbreaks   总被引:5,自引:0,他引:5  
Very little is known about how environmental changes such as increasing temperature affect disease dynamics in the ocean, especially at large spatial scales. We asked whether the frequency of warm temperature anomalies is positively related to the frequency of coral disease across 1,500 km of Australia's Great Barrier Reef. We used a new high-resolution satellite dataset of ocean temperature and 6 y of coral disease and coral cover data from annual surveys of 48 reefs to answer this question. We found a highly significant relationship between the frequencies of warm temperature anomalies and of white syndrome, an emergent disease, or potentially, a group of diseases, of Pacific reef-building corals. The effect of temperature was highly dependent on coral cover because white syndrome outbreaks followed warm years, but only on high (>50%) cover reefs, suggesting an important role of host density as a threshold for outbreaks. Our results indicate that the frequency of temperature anomalies, which is predicted to increase in most tropical oceans, can increase the susceptibility of corals to disease, leading to outbreaks where corals are abundant.  相似文献   
114.
Disabled submarine (DISSUB) survivors will achieve inert gas tissue saturation within 24 h. Direct ascent to the surface when saturated carries a high risk of decompression sickness (DCS) and death, yet may be necessary during rescue or escape. O(2) has demonstrated benefits in decreasing morbidity and mortality resulting from DCS by enhancing inert gas elimination. Perfluorocarbons (PFCs) also mitigate the effects of DCS by decreasing bubble formation and increasing O(2) delivery. Our hypothesis is that combining O(2) prebreathing (OPB) and PFC administration will reduce the incidence of DCS and death following saturation in an established 20-kg swine model. Yorkshire swine (20 +/- 6.5 kg) were compressed to 5 atmospheres (ATA) in a dry chamber for 22 h before randomization into one of four groups: 1) air and saline, 2) OPB and saline, 3) OPB with PFC given at depth, 4) OPB with PFC given after surfacing. OPB animals received >90% O(2) for 9 min at depth. All animals were returned to the surface (1 ATA) without decompression stops. The incidence of severe DCS < 2 h after surfacing was 96%, 63%, 82%, and 29% for groups 1, 2, 3, and 4, respectively. The incidence of death was 88%, 41%, 54%, and 5% for groups 1, 2, 3, and 4, respectively. OPB combined with PFC administration after surfacing provided the greatest reduction in DCS morbidity and mortality in a saturation swine model. O(2)-related seizure activity before reaching surface did not negatively affect outcome, but further safety studies are warranted.  相似文献   
115.
116.
117.
118.
Abstract A bacterium capable of growth from 59 to 72° C was isolated from geothermal soil collected from Mount Erebus, Ross Island, Antarctica. The isolate was enriched in medium containing thiosulphate and bicarbonate. Subsequently the organism was found also to be capable of heterotrophic growth and autotrophic growth in the presence of hydrogen and carbon dioxide. In a comparison with Bacillus schlegelii and Bacillus tusciae the isolate most closely resembled B. schlegelii . This conclusion was supported by the finding that B. schlegelii is also capable of autotrophic growth using thiosulphate. The new isolate had a characteristic subunit layer on the cell wall which is typical of B. schlegelii .  相似文献   
119.
Preterm birth is a major contributor to neonatal mortality and morbidity. Infection results in elevation of inflammation‐related cytokines followed by infiltration of immune cells into gestational tissue. CXCL12 levels are elevated in preterm birth indicating it may have a role in preterm labour (PTL); however, the pathophysiological correlations between CXCL12/CXCR4 signalling and premature labour are poorly understood. In this study, PTL was induced using lipopolysaccharide (LPS) in a murine model. LPS induced CXCL12 RNA and protein levels significantly and specifically in myometrium compared with controls (3‐fold and 3.5‐fold respectively). Highest levels were found just before the start of labour. LPS also enhanced the infiltration of neutrophils, macrophages and T cells, and induced macrophage M1 polarization. In vitro studies showed that condition medium from LPS‐treated primary smooth muscle cells (SMC) induced macrophage migration, M1 polarization and upregulated inflammation‐related cytokines such as interleukin (IL)‐1, IL‐6 and tumor necrosis factor alpha (TNF‐α). AMD3100 treatment in pregnant mice led to a significant decrease in the rate of PTL (70%), prolonged pregnancy duration and suppressed macrophage infiltration into gestation tissue by 2.5‐fold. Further, in‐vitro treatment of SMC by AMD3100 suppressed the macrophage migration, decreased polarization and downregulated IL‐1, IL‐6 and TNF‐α expression. LPS treatment in pregnant mice induced PTL by increasing myometrial CXCL12, which recruits immune cells that in turn produce inflammation‐related cytokines. These effects stimulated by LPS were completely reversed by AMD3100 through blocking of CXCL12/CXCR4 signalling. Thus, the CXCL12/CXCR4 axis presents an excellent target for preventing infection and inflammation‐related PTL.  相似文献   
120.
Periphytic biomass in a downriver riffle of the Grand River in Southern Ontario, Canada was measured with concrete-block glass slide samplers from May to December 1971. Average rate of accumulation of periphyton on glass slides was 266.2 mg/m2/day ash-free weight, 120.9 mg/m2/day carbon, 20.4 mg/m2/day nitrogen, or 1.11 mg/m2/day chlorophyll a and on concrete blocks was 590.0 mg/m2/day ash-free weight, 202.9 mg/m2/day carbon, 22.8 mg/m2/day nitrogen, or 2.95 mg/m2/day chlorophyll a. The standing biomass of periphyton on glass slides varied from a maximum of 21.6 g/m2 between May 28 and July 15 to a minimum of 0.7 g/m2 in December with an average of 8.6 g/m2. The biomass on concrete blocks ranged from a high of 132.5 g/m2 in August to a low of 29.9 g/m2 in October with a mean of 66.1 g/m2. The well established periphyton on concrete blocks towards the end of the study period was similar to that from native rocks with respect to biomass, carbon and nitrogen contents, and ratios of biomass to chlorophyll a. This suggests that concrete blocks are a better substrate than glass slides for measuring riverbed periphyton. By comparing biomass of periphyton on slides and on concrete blocks, the average rate of loss of periphyton from concrete blocks was estimated to be 2.9 g/m2/day, representing 63% of the mean total accumulation rate of the periphyton. The magnitude of the estimated total loss and the high standing biomass of the periphyton on concrete blocks manifest the importance of the periphyton as a source of organic matter in the river.  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