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   170篇
  免费   18篇
  188篇
  2022年   1篇
  2021年   5篇
  2020年   2篇
  2019年   3篇
  2018年   6篇
  2017年   3篇
  2016年   8篇
  2015年   4篇
  2014年   4篇
  2013年   9篇
  2012年   8篇
  2011年   7篇
  2010年   10篇
  2009年   8篇
  2008年   8篇
  2007年   6篇
  2006年   11篇
  2005年   14篇
  2004年   8篇
  2003年   8篇
  2002年   7篇
  2001年   5篇
  2000年   3篇
  1999年   13篇
  1998年   2篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1994年   3篇
  1993年   3篇
  1992年   2篇
  1991年   3篇
  1990年   2篇
  1988年   1篇
  1969年   1篇
  1966年   1篇
排序方式: 共有188条查询结果,搜索用时 9 毫秒
81.
K Jarni  B De Cuyper  R Brus 《PloS one》2012,7(7):e41231
Microsatellite markers were used to describe the genetic variability of four seed stands of wild cherry (Prunus avium L.). One hundred and thirty one individuals were genotyped at ten nuclear microsatellite loci. Total genetic diversity was high (H E = 0.704), while differences between stands were small but significant (F ST = 0.053, G′ ST = 0.234). There was a significant amount of clonal reproduction in one stand, with only 11 genotypes identified among 36 trees. One stand showed a significant excess (F IS = −0.044) of heterozygosity, and one showed a deficit (F IS = 0.044). Our results demonstrate the importance of taking into account the biological and genetic characteristics of species in forest management, especially when determining a new seed stand. The small genetic differences found between seed stands indicate that a large number of stands are not required. However, they should be carefully selected and should possess adequate genetic variability to ensure low relatedness between seed trees.  相似文献   
82.
83.
Green microalgae have recently drawn attention as promising organisms for biofuel production; however, the question is whether they can grow sufficient biomass relative to limiting input factors to be economically feasible. We have explored this question by determining how much biomass the green microalga Chlorella vulgaris can produce in photobioreactors based on highly efficient light-emitting diodes (LEDs). First, growth results were improved under the less expensive light of 660nm LEDs, developing them in the laboratory to meet the performance levels of the traditional but more expensive 680nm LEDs by adaptive laboratory evolution (ALE). We then optimized several other key parameters, including input superficial gas velocity, CO(2) concentration, light distribution, and growth media in reference to nutrient stoichiometry. Biomass density thereby rose to approximately 20g dry-cell-weight (gDCW) per liter (L). Since the light supply was recognized as a limiting factor, illumination was augmented by optimization at systematic level, providing for a biomass productivity of up to 2.11gDCW/L/day, with a light yield of 0.81 gDCW/Einstein. These figures, which represent the best results ever reported, point to new dimensions in the photoautotrophic performance of microalgal cultures.  相似文献   
84.
Synthesis of a series of tetrahydrocarbazole amides with potent activity against human papillomaviruses is described. Synthetic approaches allowing for variation of the substitution pattern of the tetrahydrocarbazole and the amide are outlined and resulting changes in antiviral activity and certain developability parameters are highlighted. Several compounds with in vitro antiviral activity (W12 antiviral assay) in the single digit nanomolar range were identified and N-[(1R)-6-chloro-2,3,4,9-tetrahydro-1H-carbazol-1-yl]-2-pyridinecarboxamide was selected for further evaluation.  相似文献   
85.
Movement uses resources that may otherwise be allocated to somatic maintenance or reproduction. How does increased energy expenditure affect resource allocation? Using the butterfly Speyeria mormonia, we tested whether experimentally increased flight affects fecundity, lifespan or flight capacity. We measured body mass (storage), resting metabolic rate and lifespan (repair and maintenance), flight metabolic rate (flight capacity), egg number and composition (reproduction), and food intake across the adult lifespan. The flight treatment did not affect body mass or lifespan. Food intake increased sufficiently to offset the increased energy expenditure. Total egg number did not change, but flown females had higher early-life fecundity and higher egg dry mass than control females. Egg dry mass decreased with age in both treatments. Egg protein, triglyceride or glycogen content did not change with flight or age, but some components tracked egg dry mass. Flight elevated resting metabolic rate, indicating increased maintenance costs. Flight metabolism decreased with age, with a steeper slope for flown females. This may reflect accelerated metabolic senescence from detrimental effects of flight. These effects of a drawdown of nutrients via flight contrast with studies restricting adult nutrient input. There, fecundity was reduced, but flight capacity and lifespan were unchanged. The current study showed that when food resources were abundant, wing-monomorphic butterflies living in a continuous meadow landscape resisted flight-induced stress, exhibiting no evidence of a flight-fecundity or flight-longevity trade-off. Instead, flight changed the dynamics of energy use and reproduction as butterflies adopted a faster lifestyle in early life. High investment in early reproduction may have positive fitness effects in the wild, as long as food is available. Our results help to predict the effect of stressful conditions on the life history of insects living in a changing world.  相似文献   
86.
Daily patterns of body mass gain in four species of small wintering birds   总被引:1,自引:0,他引:1  
Theoretically, the trajectories describing the daily accumulation of body reserves are expected to differ between bird species in relation to whether or not they hoard food. To carry reserves on the body may be costly and hoarding species can be expected to hoard food early in the day when light and retrieve it in the afternoon, with a concomitant rapid increase in body mass. Also, the increased food predictability resulting from being able to consume hoarded food late in the day should lead to a relatively faster gain in body reserves in the afternoon in hoarding species compared to non-hoarders. Non-hoarders may have to hedge against possible afternoon losses of foraging opportunities by accumulating more reserves early in the day.
In this study the daily patterns of body mass gain in four small bird species resident during winter in Scandinavia are described. Individually known birds were trained to come to a permanent feeder and their body masses were recorded every hour throughout the day with a remote-controlled balance. The hoarding willow tit Parus montanus , marsh tit P. palustris and European nuthatch Sitta europaea all displayed the most rapid gain in body mass in the early hours of the day. After the initial burst in the morning, reserves were accumulated at a roughly constant rate for the remainder of the day. In contrast, the non-hoarding great tit P. major apparently gained body reserves at a more even rate. The daily pattern of body mass gain found in the hoarding species differs from prevailing theoretical predictions, whereas the pattern in the non-hoarding great tit is in a better agreement with theory, from which this pattern has been predicted repeatedly.  相似文献   
87.
Synthesis of several novel imidazopyridine-5,6,7,8-tetrahydro-8-quinolinamine derivatives with potent activity against HIV are described. Synthetic approaches allowing for variation of the substitution pattern are outlined and resulting changes in antiviral activity and pharmacokinetics are highlighted. Several compounds with low nanomolar anti-HIV activity and oral bioavailability are described.  相似文献   
88.
Isabel Ferreira  Sara Croca  Maria Gabriella Raimondo  Manjit Matharu  Sarah Miller  Ian Giles  David Isenberg  Yiannis Ioannou  John G. Hanly  Murray B. Urowitz  Nicole Anderson  Cynthia Aranow  Anca Askanase  Sang-Cheol Bae  Sasha Bernatsky  Ian N. Bruce  Jill Buyon  Ann E. Clarke  Mary Anne Dooley  Paul Fortin  Ellen Ginzler  Dafna Gladman  Caroline Gordon  Murat Inanc  Søren Jacobsen  Kenneth Kalunian  Diane Kamen  Munther Khamashta  Sam Lim  Susan Manzi  Joan Merrill  Ola Nived  Christine Peschken  Michelle Petri  Rosalind Ramsey-Goldman  Guillermo Ruiz-Irastorza  Jorge Sanchez-Guerrero  Kristjan Steinson  Gunnar K. Sturfelt  Ronald van Vollenhoven  Daniel J. Wallace  Asad Zoma  Anisur Rahman 《Arthritis research & therapy》2017,19(1):287

Background

In patients with systemic lupus erythematosus (SLE) there is no serological test that will reliably distinguish neuropsychiatric (NP) events due to active SLE from those due to other causes. Previously we showed that serum levels of nitrated nucleosomes (NN) were elevated in a small number of patients with NPSLE. Here we measured serum NN in samples from a larger population of patients with SLE and NP events to see whether elevated serum NN could be a marker for NPSLE.

Methods

We obtained serum samples from patients in the Systemic Lupus International Collaborative Clinics (SLICC) inception cohort. This included 216 patients with NP events and two matched controls with SLE but no NP events for each of these patients. For the NP patients we tested samples taken before, during and after the NP event.

Results

Twenty-six patients had events attributed to SLE according to the most stringent SLICC attribution rule. In these patients there was no association between onset of event and elevated serum NN. In 190 patients in whom events were not attributed to SLE by the SLICC rules, median serum NN was elevated at the onset of event (P?=?0.006). The predominant clinical features in this group of 190 patients were headache, mood disorders and anxiety.

Conclusions

Serum NN levels rise at the time of an NP event in a proportion of patients with SLE. Further studies are needed to determine the value of serum NN as a biomarker for NPSLE.
  相似文献   
89.
ALA and its clinical impact, from bench to bedside.   总被引:10,自引:0,他引:10  
ALA-induced protoporphyrin IX (PpIX) is used for fluorescence diagnosis (ALA-FD) and for fluorescence-guided resection of both (pre)malignant and non-malignant diseases. ALA is also applied in photodynamic therapy (ALA-PDT) of superficial (pre)malignant lesions in dermatology, urology, neurosurgery, otorhinolaryngology, gynecology and gastroenterology. Today, ALA is approved as Levulan for actinic keratoses, the ALA-methyl ester Metvix for actinic keratoses and basal cell carcinoma, the ALA-hexyl ester Hexvix for the diagnosis of bladder cancer and Gliolan for malignant glioma. The use of ALA for PDT and FD was established around 25 years ago, with most of the fundamental knowledge gained at the "bench" and implemented at the "bedside" due to the diligence of a few researchers within the first 10 years of research. After 1993 ALA research was taken up by many groups. For patient treatment, several factors are relevant. Administered mainly in a topical or oral form, ALA penetrates tissue in a sub-optimal way, which is currently improved by special techniques and the use of ALA-esters. PpIX accumulation is elevated in many malignant tissues, several tissue abnormalities, and in mucosa. It is also found at elevated levels in macrophages, dendritic cells and activated lymphocytes. Following sufficient PpIX accumulation in the target cells, irradiation is carried out which may be accompanied by a burning sensation at the treatment site. Due to a saturation process of PpIX formation and rapid photobleaching during irradiation the risk of overtreatment is relatively low. Pharmacokinetical studies have demonstrated a low systemic photosensitivity and excretion of PpIX via natural routes.  相似文献   
90.
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