全文获取类型
收费全文 | 340篇 |
免费 | 23篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 22篇 |
2011年 | 30篇 |
2010年 | 22篇 |
2009年 | 18篇 |
2008年 | 20篇 |
2007年 | 11篇 |
2006年 | 19篇 |
2005年 | 14篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有363条查询结果,搜索用时 46 毫秒
11.
12.
Joannes Van Cann Esa Koskela Tapio Mappes Anne‐Mari Mikkonen Mikael Mokkonen Phillip C. Watts 《Journal of evolutionary biology》2019,32(10):1141-1151
Intergenerational fitness effects on offspring due to the early life of the parent are well studied from the standpoint of the maternal environment, but intergenerational effects owing to the paternal early life environment are often overlooked. Nonetheless, recent laboratory studies in mammals and ecologically relevant studies in invertebrates predict that paternal effects can have a major impact on the offspring's phenotype. These nongenetic, environment‐dependent paternal effects provide a mechanism for fathers to transmit environmental information to their offspring and could allow rapid adaptation. We used the bank vole Myodes glareolus, a wild rodent species with no paternal care, to test the hypothesis that a high population density environment in the early life of fathers can affect traits associated with offspring fitness. We show that the protein content in the diet and/or social environment experienced during the father's early life (prenatal and weaning) influence the phenotype and survival of his offspring and may indicate adaptation to density‐dependent costs. Furthermore, we show that experiencing multiple environmental factors during the paternal early life can lead to a different outcome on the offspring phenotype than stimulated by experience of a single environmental factor, highlighting the need to study developmental experiences in tandem rather than independent of each other. 相似文献
13.
To image the possible alterations in brain regional GABAA receptor subtype properties in a genetic animal model of human anxiety, mice heterozygous for the deletion of GABAA receptor gamma2 subunit (gamma2+/-) were studied using ligand autoradiographic assays on brain cryostat sections. The [35S]TBPS binding assay was designed to reveal impaired GABA and channel site coupling shown to be more prominent in recombinant alpha1/6beta3 than in alpha1/2beta3gamma2 or beta2 subunit-containing GABAA receptors expressed in HEK 293 cells. Increased GABA-insensitive [35 S]TBPS binding in the gamma2+/- mouse brains was evident in the cerebral cortex and in subcortical regions, the alterations being regionally similar to the loss of gamma2 subnunit-dependent benzodiazepine (BZ) sites as revealed by [3H]Ro 15-4513 autoradiography. As the gamma2 subunit protein is needed for synaptic clustering of GABAA receptors, these results indicate that the extrasynaptic alphabeta3 receptors can be visualized in vitro as atypical GABA-insensitive [35S]TBPS binding sites. The results suggest that GABAAergic synaptic inhibition is widely decreased in the brains of anxiety-prone gamma2+/- mice, while extrasynaptic GABAA receptors are increased. These autoradiographic imaging findings further demonstrate the need to develop GABAA receptor subtype-selective in vivo ligands to aid in assessing the contributions of various subcellular receptor populations in anxious and other patient groups. 相似文献
14.
Tolerance to Diazepam-Induced Motor Impairment: A Study with GABAA Receptor α6 Subunit Knockout Mice
Development of tolerance to motor-impairing effects of repeated administration of moderate diazepam doses (5.0–7.5 mg/kg; three times daily PO 3 weeks) was compared between mice deficient in the cerebellar granule cell–restricted GABAA receptor 6 subunit and their wild-type controls. The 6–/– mice were more impaired by the initial challenge doses of diazepam (5 or 10 mg/kg) than their controls, but acquired partial tolerance by the second tests with the same doses 4–7 days later. Chronic treatment produced complete tolerance in both mouse lines. Ligand autoradiography revealed a significant reduction in baseline benzodiazepine and chloride channel site-bindings in various regions of the 6–/– brains, but the chronic diazepam treatment did not consistently alter baseline or benzodiazepine site agonist and inverse agonist-modulated binding in the 6–/– and wildtype mice. The results indicate that tolerance to motor-impairing actions of diazepam is independent of the diazepam-insensitive 6 subunit-containing receptors, which rules out the possibility that tolerance emerges as an increase in structurally benzodiazepine-insensitive receptor population. 相似文献
15.
Photoinhibition of photosystem II was studied in vivo with bean (Phaseolus vulgaris) plants grown in the presence of 0.3 (control), 4, or 15 microM Cu(2+). Although photoinhibition, measured in the presence of lincomycin to block concurrent recovery, is faster in leaves of Cu(2+)-treated plants than in control leaves, thylakoids isolated from Cu-treated plants did not show high sensitivity to photoinhibition. Direct effects of excess Cu(2+) on chloroplast metabolism are actually unlikely, because the Cu concentration of chloroplasts of Cu-treated plants was lower than that of their leaves. Excess Cu in the growth medium did not cause severe oxidative stress, collapse of antioxidative defenses, or loss of photoprotection. Thus, these hypothetical effects can be eliminated as causes for Cu-enhanced photoinhibition in intact leaves. However, Cu treatment lowered the leaf chlorophyll (Chl) concentration and reduced the thylakoid membrane network. The loss of Chl and sensitivity to photoinhibition could be overcome by adding excess Fe together with excess Cu to the growth medium. The addition of Fe lowered the Cu(2+) concentration of the leaves, suggesting that Cu outcompetes Fe in Fe uptake. We suggest that the reduction of leaf Chl concentration, caused by the Cu-induced iron deficiency, causes the high photosensitivity of photosystem II in Cu(2+)-treated plants. A causal relationship between the susceptibility to photoinhibition and the leaf optical density was established in several plant species. Plant species adapted to high-light habitats apparently benefit from thick leaves because the rate of photoinhibition is directly proportional to light intensity, but photosynthesis becomes saturated by moderate light. 相似文献
16.
Liukkonen-Anttila T Honkanen H Peltokangas P Pelkonen O Hohtola E 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,134(1):69-77
We examined hepatic cytochrome P450 activity in wild and hand-reared grey partridges (Perdix perdix), capercaillies (Tetrao urogallus) and ring-necked pheasants (Phasianus colchicus), as well as the enzyme activity in a variety of tissues of hand-reared Japanese quails (Coturnix coturnix japonica) and pigeons (Columba livia). Post-mortem decrease in hepatic enzyme activity in the grey partridge was measured. Hepatic 7-ethoxyresorufin-O-deethylase activity was similar in wild and hand-reared grey partridges and pheasants, but the activity was significantly lower in wild than in hand-reared capercaillies, probably resulting from their phenolic-rich diet. In the tissues of both quails and pigeons 7-ethoxycoumarin-O-deethylase exhibited the highest and 7-pentoxyresorufin-O-deethylase the lowest activity. Hepatic enzyme activity was significantly higher than that in other tissues. In the small intestine some activity could be found, reflecting some intestinal detoxication capacity. Enzyme activity decreased by 34-69% during the 30-min sampling period, which confirmed the importance of equalising sampling time to obtain comparable data. Because the hand-reared birds in this study were fed the same commercial diets, we assumed that the enzyme activity values detected reflect species differences without any induction by dietary secondary compounds. 相似文献
17.
We measured the light response curve of photosynthetic oxygen evolution by illuminating a leaf disc in an air-tight windowed chamber. Oxygen production was measured by monitoring the quenching of luminescence of an organometallic ruthenium compound. A photodiode based chlorophyll a fluorometer was used to measure the luminescence intensity. Oxygen evolution measurements with a traditional oxygen electrode gave the same numerical values at different light intensities when the same leaf disk was tested. The quality of the measurement signal of the new method was found to be similar to that obtained with the oxygen electrode method. The new luminescence based system is more stable against electrical disturbances than an oxygen electrode, its response to oxygen pressure changes is very rapid, and the new method allows the same basic equipment to be used for chlorophyll fluorescence and oxygen measurements. 相似文献
18.
We studied the occurrence of laying gaps in free-living populations of the pied flycatcher, Ficedula hypoleuca, and the great tit, Parus major, in a pollution gradient of a copper smelter in south-west Finland. Laying gaps were 2.8 times more common in F. hypoleuca than in P. major. The probability of laying gaps was highest in the heavily polluted zone and lowest in the unpolluted zone for both bird
species. Cold weather at the time of laying increased the number of laying gaps in both species, but in P. major this effect was most pronounced in the heavily polluted environment. In the most heavily polluted environment the laying
gaps were more likely to occur near the beginning of the laying sequence in both species. The laying gap probability increased
with increasing laying date in P. major but not in F. hypoleuca. We suggest that the increased number of laying gaps in the polluted environment results from limited Ca availability and
the interference of heavy metals with Ca metabolism in laying females. 相似文献
19.
Taras Antal Heta Mattila Marja Hakala-Yatkin Taina Tyystjärvi Esa Tyystjärvi 《Planta》2010,232(4):887-898
Nitrogen deficiency diminishes consumption of photosynthates in anabolic metabolism. We studied adjustments of the photosynthetic
machinery in nitrogen-deficient bean plants and found four phenomena. First, the number of chloroplasts per cell decreased.
Chloroplasts of nitrogen starved leaves contained less pigments than those of control leaves, but the in vitro activities
of light reactions did not change when measured on chlorophyll basis. Second, nitrogen deficiency induced cyclic electron
transfer. The amounts of Rubisco and ferredoxin-NADP+ reductase decreased in nitrogen starved plants. Low activities of these enzymes are expected to lead to increase in reduction
of oxygen by photosystem I. However, diaminobenzidine staining did not reveal hydrogen peroxide production in nitrogen starved
plants. Measurements of far-red-light-induced redox changes of the primary donor of photosystem I suggested that instead of
producing oxygen radicals, nitrogen starved plants develop a high activity of cyclic electron transport that competes with
oxygen for electrons. Nitrogen starvation led to decrease in photochemical quenching and increase in non-photochemical quenching,
indicating that cyclic electron transport reduces the plastoquinone pool and acidifies the lumen. A third effect is redistribution
of excitation energy between the photosystems in favor of photosystem I. Thus, thylakoids of nitrogen starved plants appeared
to be locked in state 2, which further protects photosystem II by decreasing its absorption cross-section. As a fourth response,
the proportion of non-QB-reducing photosystem II reaction centers increased and the redox potential of the QB/QB− pair decreased by 25 mV in a fraction of photosystem II centers of nitrogen starved plants. 相似文献
20.
Ye L Haider HKh Esa WB Law PK Zhang W Su L Zhang Y Sim EK 《Experimental biology and medicine (Maywood, N.J.)》2007,232(11):1477-1487
Low-level transgene efficiency is one of the main obstacles in ex vivo nonviral vector-mediated gene transfer into primary human skeletal myoblasts (hSkMs). We optimized the cholesterol:N-[1-(2, 3-dioleoyloxy)propyl]-N, N, N-trimethylammonium methylsulfate liposome (CD liposome) and 22-kDa polyethylenimine (PEI22)- and 25-kDa polyethylenimine (PEI25)-mediated transfection of primary hSkMs for angiogenic gene delivery. We found that transfection efficiency and cell viability of three nonviral vectors were cell passage dependent: early cell passages of hSkMs had higher transfection efficiencies with poor cell viabilities, whereas later cell passages of hSkMs had lower transfection efficiencies with better cell viabilities. Trypsinization improved the transfection efficiency by 20% to 60% compared with adherent hSkMs. Optimum gene transfection efficiency was found with passage 6 trypsinized hSkMs: transfection efficiency with CD lipoplexes was 6.99 +/- 0.13%, PEI22 polyplexes was 18.58 +/- 1.57%, and PEI25 polyplexes was 13.32 +/- 0.88%. When pEGFP (a plasmid encoding the enhanced green fluorescent protein) was replaced with a vector containing human vascular endothelial growth factor 165 (phVEGF(165)), the optimized gene transfection conditions resulted in hVEGF(165) expression up to Day 18 with a peak level at Day 2 after transfection. This study demonstrated that therapeutic angiogenic gene transfer through CD or PEI is feasible and safe after optimization. It could be a potential strategy for treatment of ischemic disease for angiomyogenesis. 相似文献