全文获取类型
收费全文 | 402篇 |
免费 | 40篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 20篇 |
2012年 | 30篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 12篇 |
2008年 | 8篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 17篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1969年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有442条查询结果,搜索用时 15 毫秒
71.
E. Albano Pérez J.A. Coetzee T. Ruiz Téllez M.P. Hill 《South African Journal of Botany》2011,77(3):795-800
We investigated water hyacinth seed banks in several aquatic systems in South Africa. Fifteen sites, mainly in the Eastern and Western Cape provinces, were surveyed from August to October 2009. Soil seed density varied between 0 and 2534 seeds/m2 but did not differ significantly between the type of waterbody (impoundment vs. river) or the history of control carried out at a site. Average germination was 54.17% with very fast velocities (Vigour Index = 36.66) and maximum germination around three days. Although we demonstrated the existence of an important reservoir of seeds, results from this study indicated that a combination of factors such as water fluctuation, eutrophication and seed decomposition might have had a great influence on dispersal and persistence of seeds. 相似文献
72.
A broad review is presented of recent developments in the commercialization of southern Africa indigenous flora for the cut flower trade, including potted flowers and foliages (“greens”). The botany, horticultural traits and potential for commercialization of several indigenous plants have been reported in several publications. The contribution of species indigenous and/or endemic to southern Africa in the development of cut flower crop plants is widely acknowledged. These include what is known in the trade as gladiolus, freesia, gerbera, ornithogalum, clivia, agapanthus, strelitzia, plumbago and protea. Despite the wealth of South African flower bulb species, relatively few have become commercially important in the international bulb industry. Trade figures on the international markets also reflect the importance of a few species of southern African origin. The development of new research tools are contributing to the commercialization of South African plants, although propagation, cultivation and post-harvest handling need to be improved. A list of commercially relevant southern African cut flowers (including those used for fresh flowers, dried flowers, foliage and potted flowers) is presented, together with a subjective evaluation of several genera and species with perceived potential for the development of new crops for the florist trade. It is concluded that research should be focused on potential markets rather than on preconceived product concepts. A special national effort is required to maximize the opportunities presented by the rich diversity of the flora and to develop an internationally competitive cut flower industry. 相似文献
73.
ATP-sensitive K(+) (K(ATP)) channels are composed of pore-forming subunits, typically Kir6.2 in neurons, and regulatory sulfonylurea receptor subunits. In dorsal striatum, activity-dependent H(2)O(2) produced from glutamate receptor activation inhibits dopamine release via K(ATP) channels. Sources of modulatory H(2)O(2) include striatal medium spiny neurons, but not dopaminergic axons. Using fast-scan cyclic voltammetry in guinea-pig striatal slices and immunohistochemistry, we determined the time window for H(2)O(2)/K(ATP)-channel-mediated inhibition and assessed whether modulatory K(ATP) channels are on dopaminergic axons. Comparison of paired-pulse suppression of dopamine release in the absence and presence of glibenclamide, a K(ATP)-channel blocker, or mercaptosuccinate, a glutathione peroxidase inhibitor that enhances endogenous H(2)O(2) levels, revealed a time window for inhibition of 500-1000 ms after stimulation. Immunohistochemistry demonstrated localization of Kir6.2 K(ATP)-channel subunits on dopaminergic axons. Consistent with the presence of functional K(ATP) channels on dopaminergic axons, K(ATP)-channel openers, diazoxide and cromakalim, suppressed single-pulse evoked dopamine release. Although cholinergic interneurons that tonically regulate dopamine release also express K(ATP) channels, diazoxide did not induce the enhanced frequency responsiveness of dopamine release seen with nicotinic-receptor blockade. Together, these studies reveal subsecond regulation of striatal dopamine release by endogenous H(2)O(2) acting at K(ATP) channels on dopaminergic axons, including a role in paired-pulse suppression. 相似文献
74.
The socio-economic impacts of the free-floating aquatic plant water hyacinth, Eichhornia crassipes (Pontederiaceae), on aquatic systems are well documented, yet the impacts on aquatic biodiversity, particularly invertebrate biodiversity, are less well understood. This study aimed to determine whether the presence of water hyacinth altered the diversity and assemblage structure of benthic macroinvertebrates in a conservation area. The benthic macroinvertebrate assemblage was sampled over 1 year at five sites under water hyacinth mats and at five sites without water hyacinth at Lake Nsezi—Nseleni River in the vicinity of Richards Bay, KwaZulu-Natal, South Africa. Artificial substrates were placed beneath water hyacinth mats or in the open water to allow for colonization by freshwater macroinvertebrates, and left for a period of 6 weeks, repeated on seven occasions. Twenty nine families comprising 18,797 individuals were collected, 817 (13 families) individuals were from under water hyacinth mat sites compared to 17,980 (27 families) individuals from open water sites. Ninety-eight percent of individuals collected were, however, the invasive snail, Tarebia granifera. Open water samples were separated from samples beneath the water hyacinth mat by non-metric Multidimensional Scaling, indicating reduced biodiversity associated with the presence of water hyacinth. Exclusion of the dominant Thiaridae from the analysis did not alter the groupings. Family richness(s) and abundance (N) were significantly higher in open water communities(S: H3 = 21.09; P = 0.0001; N: H3 = 22.58; P = 0.00001), while evenness (J’) was higher under water hyacinth mats (H3 = 20.13; P = 0.0002). The presence of water hyacinth had a significantly negative impact on aquatic macroinvertebrate biodiversity in a conservation area, and therefore the control of this invasive aquatic plant must play a major role in catchment management. 相似文献
75.
Anika I Tsuchida Michiel Beekhuizen Marieke C ‘t Hart Timothy RDJ Radstake Wouter JA Dhert Daniel BF Saris Gerjo JVM van Osch Laura B Creemers 《Arthritis research & therapy》2014,16(5)
Introduction
This study aimed to evaluate whether profiles of several soluble mediators in synovial fluid and cartilage tissue are pathology-dependent and how their production is related to in vitro tissue formation by chondrocytes from diseased and healthy tissue.Methods
Samples were obtained from donors without joint pathology (n = 39), with focal defects (n = 65) and osteoarthritis (n = 61). A multiplex bead assay (Luminex) was performed measuring up to 21 cytokines: Interleukin (IL)-1α, IL-1β, IL-1RA, IL-4, IL-6, IL-6Rα, IL-7, IL-8, IL-10, IL-13, tumor necrosis factor (TNF)α, Interferon (IFN)γ, oncostatin M (OSM), leukemia inhibitory factor (LIF), adiponectin, leptin, monocyte chemotactic factor (MCP)1, RANTES, basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), vascular growth factor (VEGF).Results
In synovial fluid of patients with cartilage pathology, IL-6, IL-13, IFNγ and OSM levels were higher than in donors without joint pathology (P ≤0.001). IL-13, IFNγ and OSM were also different between donors with cartilage defects and OA (P <0.05). In cartilage tissue from debrided defects, VEGF was higher than in non-pathological or osteoarthritic joints (P ≤0.001). IL-1α, IL-6, TNFα and OSM concentrations (in ng/ml) were markedly higher in cartilage tissue than in synovial fluid (P <0.01). Culture of chondrocytes generally led to a massive induction of most cytokines (P <0.001). Although the release of inflammatory cytokines was also here dependent on the pathological condition (P <0.001) the actual profiles were different from tissue or synovial fluid and between non-expanded and expanded chondrocytes. Cartilage formation was lower by healthy unexpanded chondrocytes than by osteoarthritic or defect chondrocytes.Conclusions
Several pro-inflammatory, pro-angiogenic and pro-repair cytokines were elevated in joints with symptomatic cartilage defects and/or osteoarthritis, although different cytokines were elevated in synovial fluid compared to tissue or cells. Hence a clear molecular profile was evident dependent on disease status of the joint, which however changed in composition depending on the biological sample analysed. These alterations did not affect in vitro tissue formation with these chondrocytes, as this was at least as effective or even better compared to healthy chondrocytes. 相似文献76.
Elizabeth du Toit Cari van Schalkwyk Rory Dunbar Karen Jennings Blia Yang David Coetzee Nulda Beyers 《PloS one》2014,9(5)
Background
Few studies have evaluated access to and retention in pre-ART care.Objectives
To evaluate the proportion of People Living With HIV (PLWH) in pre-ART and ART care and factors associated with retention in pre-ART and ART care from a community cohort.Methods
A cross sectional survey was conducted from February – April 2011. Self reported HIV positive, negative or participants of unknown status completed a questionnaire on their HIV testing history, access to pre-ART and retention in pre-ART and ART care.Results
872 randomly selected adults who reported being HIV positive in the ZAMSTAR 2010 prevalence survey were included and revisited. 579 (66%) reconfirmed their positive status and were included in this analysis. 380 (66%) had initiated ART with 357 of these (94%) retained in ART care. 199 (34%) had never initiated ART of whom 186 (93%) accessed pre-ART care, and 86 (43%) were retained in pre-ART care. In a univariable analysis none of the factors analysed were significantly associated with retention in care in the pre-ART group. Due to the high retention in ART care, factors associated with retention in ART care, were not analysed further.Conclusion
Retention in ART care was high; however it was low in pre-ART care. The opportunity exists, if care is better integrated, to engage with clients in primary health care facilities to bring them back to, and retain them in, pre-ART care. 相似文献77.
78.
Zhu Z Burnett CM Maksymov G Stepniak E Sierra A Subbotina E Anderson ME Coetzee WA Hodgson-Zingman DM Zingman LV 《Biochemical and biophysical research communications》2011,(4):637-641
The cardiovascular system operates under demands ranging from conditions of rest to extreme stress. One mechanism of cardiac stress tolerance is action potential duration shortening driven by ATP-sensitive potassium (KATP) channels. KATP channel expression has a significant physiologic impact on action potential duration shortening and myocardial energy consumption in response to physiologic heart rate acceleration. However, the effect of reduced channel expression on action potential duration shortening in response to severe metabolic stress is yet to be established. Here, transgenic mice with myocardium-specific expression of a dominant negative KATP channel subunit were compared with littermate controls. Evaluation of KATP channel whole cell current and channel number/patch was assessed by patch clamp in isolated ventricular cardiomyocytes. Monophasic action potentials were monitored in retrogradely perfused, isolated hearts during the transition to hypoxic perfusate. An 80–85% reduction in cardiac KATP channel current density results in a similar magnitude, but significantly slower rate, of shortening of the ventricular action potential duration in response to severe hypoxia, despite no significant difference in coronary flow. Therefore, the number of functional cardiac sarcolemmal KATP channels is a critical determinant of the rate of adaptation of myocardial membrane excitability, with implications for optimization of cardiac energy consumption and consequent cardioprotection under conditions of severe metabolic stress. 相似文献
79.
Kock JL Venter P Smith DP Van Wyk PW Botes PJ Coetzee DJ Pohl CH Botha A Riedel KH Nigam S 《Antonie van Leeuwenhoek》2000,77(4):401-406
Research on the distribution of oxylipins (3-hydroxy fatty acids) in flocculant strains of the yeast Saccharomyces cerevisiae led to the uncovering of a novel ghosting phenomenon observed during assumed lectin-mediated aggregation. We found that intracellular oxylipin-containing osmiophilic layers migrate through yeast cell walls in a ghostlike fashion without visually affecting the cell wall structure or the layers. This migration resulted in the binding of these layers to cell walls of adjacent cells. Consequently, ghosting seems a prerequisite for flocculation to occur. However, ghosting alone may not be sufficient to ensure flocculation. 相似文献
80.
Oscar K. K. Bedzo Kim Trollope Lalitha D. Gottumukkala Gerhardt Coetzee Johann F. Görgens 《Biotechnology progress》2019,35(3):e2797
The immobilization of β-fructofuranosidase for short-chain fructooligosaccharide (scFOS) synthesis holds the potential for a more efficient use of the biocatalyst. However, the choice of carrier and immobilization technique is a key to achieving that efficiency. In this study, calcium alginate (CA), Amberlite IRA 900 (AI900) and Dowex Marathon MSA (DMM) were tested as supports for immobilizing a novel engineered β-fructofuranosidase from Aspergillus japonicus for scFOS synthesis. Several immobilization parameters were estimated to ascertain the effectiveness of the carriers in immobilizing the enzyme. The performance of the immobilized biocatalysts are compared in terms of the yield of scFOS produced and reusability. The selection of carriers and reagents was motivated by the need to ensure safety of application in the production of food-grade products. The CA and AI900 both recorded impressive immobilization yields of 82 and 62%, respectively, while the DMM recorded 47%. Enzyme immobilizations on CA, AI900 and DMM showed activity recoveries of 23, 27, and 17%, respectively. The CA, AI900 immobilized and the free enzymes recorded their highest scFOS yields of 59, 53, and 61%, respectively. The AI900 immobilized enzyme produced a consistent scFOS yield and composition for 12 batch cycles but for the CA immobilized enzyme, only 6 batch cycles gave a consistent scFOS yield. In its first record of application in scFOS production, the AI900 anion exchange resin exhibited potential as an adequate carrier for industrial application with possible savings on cost of immobilization and reduced technical difficulty. 相似文献