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   479篇
  免费   37篇
  516篇
  2021年   5篇
  2020年   6篇
  2019年   8篇
  2017年   5篇
  2016年   9篇
  2015年   11篇
  2014年   11篇
  2013年   20篇
  2012年   25篇
  2011年   31篇
  2010年   18篇
  2009年   10篇
  2008年   15篇
  2007年   14篇
  2006年   12篇
  2005年   14篇
  2004年   10篇
  2003年   13篇
  2002年   19篇
  2001年   13篇
  2000年   16篇
  1999年   9篇
  1998年   10篇
  1997年   4篇
  1996年   9篇
  1995年   10篇
  1994年   5篇
  1991年   4篇
  1990年   5篇
  1989年   14篇
  1988年   6篇
  1987年   6篇
  1986年   9篇
  1985年   4篇
  1983年   8篇
  1982年   9篇
  1980年   4篇
  1979年   4篇
  1976年   5篇
  1974年   6篇
  1973年   5篇
  1972年   7篇
  1971年   3篇
  1970年   11篇
  1968年   7篇
  1967年   3篇
  1966年   10篇
  1964年   4篇
  1947年   5篇
  1946年   3篇
排序方式: 共有516条查询结果,搜索用时 15 毫秒
31.
A 14-year-old Native American girl from the Iroquois Nation was referred as a potential patient with the syndrome of Apparent Mineralocorticoid Excess. Instead, her evaluation revealed resistance to glucocorticoids, mineralocorticoids, and androgens. She lacked Cushingoid features in spite of significantly high cortisol levels. Menstruation was regular and there was no clinical evidence of masculinization despite high serum androgen levels in the male range. The patient's sister had similar clinical features. Partial resistance to exogenous glucocorticoid and mineralocorticoid administration was well demonstrated in both patients. It is proposed that these patients represent the first cases of partial resistance to multiple steroids, possibly owing to a coactivator defect.  相似文献   
32.
The design of functional materials for genomic and proteomic analyses in microscale systems has begun to mature, from materials designed for capillary-based electrophoresis systems to those tailored for microfluidic-based or 'chip-based' platforms. In particular, recent research has focused on evaluating different polymer chemistries for microchannel surface passivation and improved DNA separation matrix performance. Additionally, novel bioconjugate materials designed specifically for electrophoretic separations in microscale channels are facilitating new separation modalities.  相似文献   
33.
34.
The thermotolerant, ethanol-producing yeast strain Kluyveromyces marxianus IMB3 has been immobilized in calcium alginate gel and poly(vinyl alcohol) cryogel (PVAC) beads. The immobilized preparations were used as biocatalyst in fed-batch reactor systems for prolonged periods. The substrate utilized in each case consisted of sugar cane molasses diluted to yield a sugar load of 140?g/l. During the first cycle the maximum ethanol concentration produced by the alginate system was 57?g/l, representing 80% of the maximum theoretical yield. In the system employing the PVAC-immobilized biocatalyst, ethanol production increased to a maximum of 52–53?g/l, representing 73% of the maximum theoretical yield. In both cases, maximum ethanol concentration was achieved within a 72-hour period. When each system was operated on a fed-batch basis for a prolonged period of time the average ethanol concentrations produced in the alginate- and the PVAC-immobilized systems were 21 and 45?g/l, respectively. The results suggest that the PVAC-based immobilization system may provide a more practical alternative to alginate for the production of ethanol by K. marxianus IMB3 in continuous or semi-continuous fermentation systems.  相似文献   
35.
Soil degradation is a worsening global phenomenon driven by socio‐economic pressures, poor land management practices and climate change. A deterioration of soil structure at timescales ranging from seconds to centuries is implicated in most forms of soil degradation including the depletion of nutrients and organic matter, erosion and compaction. New soil–crop models that could account for soil structure dynamics at decadal to centennial timescales would provide insights into the relative importance of the various underlying physical (e.g. tillage, traffic compaction, swell/shrink and freeze/thaw) and biological (e.g. plant root growth, soil microbial and faunal activity) mechanisms, their impacts on soil hydrological processes and plant growth, as well as the relevant timescales of soil degradation and recovery. However, the development of such a model remains a challenge due to the enormous complexity of the interactions in the soil–plant system. In this paper, we focus on the impacts of biological processes on soil structure dynamics, especially the growth of plant roots and the activity of soil fauna and microorganisms. We first define what we mean by soil structure and then review current understanding of how these biological agents impact soil structure. We then develop a new framework for modelling soil structure dynamics, which is designed to be compatible with soil–crop models that operate at the soil profile scale and for long temporal scales (i.e. decades, centuries). We illustrate the modelling concept with a case study on the role of root growth and earthworm bioturbation in restoring the structure of a severely compacted soil.  相似文献   
36.
Two dimensional NMR spectra of porcine brain natriuretic peptide have been recorded at 400 MHz. Peak assignments have been made and the combined information from chemical shifts, coupling constants, temperature coefficients, exchange studies and nuclear Overhauser effects has been used to determine the conformation of pBNP in aqueous media. Overall the peptide appears to be conformationally averaged with the possibility of some restricted flexibility in localized regions. The conformation of porcine brain natriuretic peptide in water is compared to previous studies in d6-DMSO and to studies of atrial natriuretic peptide and some closely related analogues in H2O and d6-DMSO.  相似文献   
37.
Pasta is popular for its ease of cooking and its low glycaemic index (GI). This interesting nutritional property can be attributed to its specific compact structure generally described as a protein network entrapping starch granules. Despite this low GI, pasta is poor in fibres and lack some essential amino acids. To enhance its nutritional composition, pasta can be fortified with non-traditional ingredients such as legume flours. The objective of this study was to investigate the impact of legume flour addition on pasta structure and the inherent consequences on the in vitro digestibility of starch. The addition of a high level (35%, w/w) of legume flour, especially split pea flour, induced some minor structural changes in pasta. The inclusion of fibres, the dilution of gluten proteins by albumins and globulins, and the larger amount of thin protein films (in split pea pasta) may have favoured higher susceptibility of starch to digestive enzymes. At the opposite, the presence of some partially gelatinised starch granules in the core of fortified pasta may have favoured the decrease in the in vitro starch digestibility. As a consequence, a high level of legume flour addition in pasta did not have any significant impact on its in vitro starch digestibility. A high level of split pea and faba bean flours can thus be added to pasta to increase its nutritional composition while keeping its low glycaemic index.  相似文献   
38.
Octopamine treatment has previously been shown to increase honey bee foraging behaviour. We determined the effects of octopamine on other tasks to learn how octopamine affects division of labour in honey bee colonies. Octopamine treatment did not increase the rate of corpse removal from the hive, suggesting that elevated brain levels of octopamine do not act to increase the performance of all flight-related tasks. Octopamine treatment also did not increase attendance in the queen's retinue, suggesting that elevated brain levels of octopamine do not act to increase responsiveness to all olfactory stimuli. Consistent with these findings, octopamine treatment enhanced the foraging response to brood pheromone but not the cell capping response, a component of brood care. These results demonstrate a relatively specific form of neuromodulation by octopamine in the regulation of division of labour in honey bee colonies.  相似文献   
39.
40.
A series of General Circulation Model experiments are performed to examine the role of paleogeography as an explanation of the Tertiary global cooling trend. Systematic long-term variations in topography and land—sea distribution are potential causes of long-term climate change. However, climate model sensitivity experiments indicate a geographically related cooling during the last 20 million years, but not a long-term Cenozoic trend. Coarse resolution changes in geography throughout the Tertiary may not be the explanation of the Tertiary global cooling trend. Either a series of events, some geographically related, or another forcing factor, most probably atmospheric CO2 concentration, are offered as alternative explanations of the Tertiary global cooling trend.  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