全文获取类型
收费全文 | 579篇 |
免费 | 30篇 |
出版年
2023年 | 4篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 18篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 30篇 |
2012年 | 53篇 |
2011年 | 44篇 |
2010年 | 33篇 |
2009年 | 25篇 |
2008年 | 24篇 |
2007年 | 29篇 |
2006年 | 36篇 |
2005年 | 15篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 17篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1966年 | 5篇 |
1965年 | 3篇 |
排序方式: 共有609条查询结果,搜索用时 312 毫秒
41.
L’ubica Halušková Katarína Valentovičová Jana Huttová Igor Mistrík Ladislav Tamás 《Plant Growth Regulation》2010,62(1):59-64
All of the analyzed heavy metals significantly inhibited root growth, but in addition to Cd exposure an elevated IAA-POD activity
was detected under Co, Cu and Hg treatment, while Ni and Pb inhibited its activity. The Cd-induced IAA-POD activity increased
from the root apex towards to the mature region of root tips. However similar or even more severe root growth inhibition was
observed by exogenously applied IAA, IAA-POD activity was activated only at high IAA concentrations. Elevated Cd-induced H2O2 production was detected both in the absence or in the presence of IAA in the reaction mixture, but in the case of IAA as
a possible substrate for PODs the production of H2O2 increased markedly just in the Cd-treated roots. Exogenously applied H2O2 also activated IAA-POD activity. Our results indicated that in the development of Cd toxicity syndrome the production of
ROS during IAA degradation by elevated IAA-POD activity plays a crucial role, mainly under severe Cd stress. 相似文献
42.
L’ubica Halušková Katarína Valentovičová Jana Huttová Igor Mistrík Ladislav Tamás 《Acta Physiologiae Plantarum》2010,32(1):59-65
In the present work, we investigated the alteration of oxidative and peroxidative activities of peroxidases (PODs) along the longitudinal root axis of barley seedlings during heavy metal (HM; e.g., Cd, Cu, Hg, Ni, Pb) treatment. Analysis of the individual root segments revealed that all of the analyzed HMs caused an increase of guaiacol-POD activity, however to a different extent and spatial distribution. Cd-induced ferulic acid POD activity was observed along the whole root tip (RT), while Cu and Hg caused its increase in the meristematic zone and Ni mainly at the end of the differentiation zone of RT. The activation of coniferyl alcohol POD by HMs was detected along the whole RT. HM-induced hydrogen peroxide-generating POD activity was localized mainly to the elongation zone of RT. Elevated chlorogenic acid POD activity was observed in the meristematic zone and at the end of the differentiation zone of RTs. The activation of several PODs is probably associated with enhanced H2O2 production and lignification as a defense response of roots to several HM, to prevent their uncontrolled flux. On the other hand, this defense response is accompanied by root growth inhibition, due to the enhanced rigidification of cell wall and accelerated differentiation of RTs. 相似文献
43.
Vilmos Soós Endre Sebestyén Angéla Juhász Marnie E Light Ladislav Kohout Gabriella Szalai Júlia Tandori Johannes Van Staden Ervin Balázs 《BMC plant biology》2010,10(1):236
Background
Smoke released from burning vegetation functions as an important environmental signal promoting the germination of many plant species following a fire. It not only promotes the germination of species from fire-prone habitats, but several species from non-fire-prone areas also respond, including some crops. The germination stimulatory activity can largely be attributed to the presence of a highly active butenolide compound, 3-methyl-2H-furo[2,3-c]pyran-2-one (referred to as karrikin 1 or KAR1), that has previously been isolated from plant-derived smoke. Several hypotheses have arisen regarding the molecular background of smoke and KAR1 action. 相似文献44.
Hyaluronic acid: a natural biopolymer with a broad range of biomedical and industrial applications 总被引:2,自引:0,他引:2
Hyaluronic acid (hyaluronan, HA) is a linear polysaccharide formed from disaccharide units containing N-acetyl-d-glucosamine and glucuronic acid. It has a high molecular mass, usually in the order of millions of Daltons, and interesting
viscoelastic properties influenced by its polymeric and polyelectrolyte characteristics. HA is present in almost all biological
fluids and tissues. In clinical medicine, it is used as a diagnostic marker for many diseases including cancer, rheumatoid
arthritis and liver pathologies, as well as for supplementation of impaired synovial fluid in arthritic patients by means
of intra-articular injections. It is also used in certain ophthalmological and otological surgeries and cosmetic regeneration
and reconstruction of soft tissue. Herein we present an overview of the occurrence and physiological properties of HA, as
well as of the recent advances in production biotechnology and preparation of the HA-based materials for medical application. 相似文献
45.
Katarína Ďurčeková Jana Huttová Igor Mistrík Marta Ollé Ladislav Tamás 《Plant and Soil》2007,290(1-2):61-68
The effect of Cd on H2O2 production, peroxidase (POD) activity and root hair formation were analyzed in barley root. Cd causes a strong H2O2 burst in the root region 0–6 mm behind the root tip. POD activity was activated in root tip and raised toward the root base
in Cd treated roots. In situ analyses showed that both elevated H2O2 production and POD activity are localized in the early metaxylem vascular bundles. Cd induces root hair formation in the
region 2 to 4 mm behind the root tip that was not detected in control roots. These results suggest that Cd-induced root growth
inhibition is at least partially the consequence of Cd-stimulated premature root development involving xylogenesis and root
hair formation, which is correlated with shortening of root elongation zone and therefore with root growth reduction. 相似文献
46.
Zdenko Gardian Ladislav Bumba Adam Schrofel Jana Nebesarova Frantisek Vacha 《BBA》2007,1767(6):725-731
Structure and organisation of Photosystem I and Photosystem II isolated from red alga Cyanidium caldarium was determined by electron microscopy and single particle image analysis. The overall structure of Photosystem II was found to be similar to that known from cyanobacteria. The location of additional 20 kDa (PsbQ′) extrinsic protein that forms part of the oxygen evolving complex was suggested to be in the vicinity of cytochrome c-550 (PsbV) and the 12 kDa (PsbU) protein. Photosystem I was determined as a monomeric unit consisting of PsaA/B core complex with varying amounts of antenna subunits attached. The number of these subunits was seen to be dependent on the light conditions used during cell cultivation. The role of PsaH and PsaG proteins of Photosystem I in trimerisation and antennae complexes binding is discussed. 相似文献
47.
48.
49.
Increased level of cytokines and matrix metalloproteinases in osteoarthritic subchondral bone 总被引:4,自引:0,他引:4
OBJECTIVE: The aim of this study was to investigate the expression of several cytokines, matrix metalloproteinases (MMPs), and tissue inhibitor of matrix metalloproteinases (TIMP)-1 in osteoarthritis (OA) and control sera and different joint tissues. METHODS: Serum, synovial fluid, cartilage, synovial and subchondral bone tissues were examined in OA and control subjects. The protein level of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1alpha, IL-8, IL-10 and MMP-2, MMP-3, MMP-9, and TIMP-1 were measured by immunoanalysis. RESULTS: Serum levels of TNF-alpha, MMP-3 and -9 were significantly higher in OA patients than in controls. Conversely, serum IL-10 was decreased in OA patients. CRP was elevated when compared to healthy controls and decreased significantly 6 months after the surgery. In contrast to control samples, OA cartilage and synovium revealed significantly higher MMP-2, -3, -9 and IL-10. IL-1alpha was significantly higher in OA cartilage and IL-8 in OA synovium. Interestingly, MMP-3, -9, TIMP-1 and all tested cytokines were up-regulated in OA subchondral bone. DISCUSSION: This study demonstrates pro-inflammatory condition of OA pathology and supports the idea that vascularized subchondral region may increase the synthesis of cytokines and MMPs leading to degradation of adjacent cartilage. 相似文献
50.
Ladislav ?igut Petra Holi?ová Karel Klem Mirka ?prtová Carlo Calfapietra Michal V. Marek Vladimír ?punda Otmar Urban 《Annals of botany》2015,116(6):929-939
Background and Aims Plants growing under elevated atmospheric CO2 concentrations often have reduced stomatal conductance and subsequently increased leaf temperature. This study therefore tested the hypothesis that under long-term elevated CO2 the temperature optima of photosynthetic processes will shift towards higher temperatures and the thermostability of the photosynthetic apparatus will increase.Methods The hypothesis was tested for saplings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for 4–5 years to either ambient (AC; 385 µmol mol−1) or elevated (EC; 700 µmol mol−1) CO2 concentrations. Temperature response curves of photosynthetic processes were determined by gas-exchange and chlorophyll fluorescence techniques.Key Results Initial assumptions of reduced light-saturated stomatal conductance and increased leaf temperatures for EC plants were confirmed. Temperature response curves revealed stimulation of light-saturated rates of CO2 assimilation (Amax) and a decline in photorespiration (RL) as a result of EC within a wide temperature range. However, these effects were negligible or reduced at low and high temperatures. Higher temperature optima (Topt) of Amax, Rubisco carboxylation rates (VCmax) and RL were found for EC saplings compared with AC saplings. However, the shifts in Topt of Amax were instantaneous, and disappeared when measured at identical CO2 concentrations. Higher values of Topt at elevated CO2 were attributed particularly to reduced photorespiration and prevailing limitation of photosynthesis by ribulose-1,5-bisphosphate (RuBP) regeneration. Temperature response curves of fluorescence parameters suggested a negligible effect of EC on enhancement of thermostability of photosystem II photochemistry.Conclusions Elevated CO2 instantaneously increases temperature optima of Amax due to reduced photorespiration and limitation of photosynthesis by RuBP regeneration. However, this increase disappears when plants are exposed to identical CO2 concentrations. In addition, increased heat-stress tolerance of primary photochemistry in plants grown at elevated CO2 is unlikely. The hypothesis that long-term cultivation at elevated CO2 leads to acclimation of photosynthesis to higher temperatures is therefore rejected. Nevertheless, incorporating acclimation mechanisms into models simulating carbon flux between the atmosphere and vegetation is necessary. 相似文献