全文获取类型
收费全文 | 2534篇 |
免费 | 116篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 20篇 |
2020年 | 7篇 |
2019年 | 33篇 |
2018年 | 29篇 |
2017年 | 30篇 |
2016年 | 38篇 |
2015年 | 56篇 |
2014年 | 72篇 |
2013年 | 256篇 |
2012年 | 125篇 |
2011年 | 125篇 |
2010年 | 69篇 |
2009年 | 78篇 |
2008年 | 142篇 |
2007年 | 163篇 |
2006年 | 161篇 |
2005年 | 147篇 |
2004年 | 161篇 |
2003年 | 152篇 |
2002年 | 151篇 |
2001年 | 36篇 |
2000年 | 37篇 |
1999年 | 58篇 |
1998年 | 41篇 |
1997年 | 37篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 24篇 |
1992年 | 31篇 |
1991年 | 26篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1976年 | 9篇 |
1975年 | 13篇 |
1971年 | 7篇 |
1967年 | 10篇 |
1966年 | 7篇 |
排序方式: 共有2650条查询结果,搜索用时 34 毫秒
991.
992.
Ohtsuki H Yokoyama J Ohba N Ohmiya Y Kawata M 《Archives of insect biochemistry and physiology》2008,69(4):176-188
Species-specific flash patterns in firefly species are important for the investigation of the evolution of Lampyridae. Since nitric oxide synthase (NOS) is one of the key enzymes controlling flash patterns, we determined the cDNA sequences of NOS in the Japanese fireflies Luciola lateralis and L. cruciata. The identity of the NOS sequences was very high between these 2 species. Firefly NOS also exhibited a high identity with those of other insect species, and the cofactor-binding domains were particularly well conserved. Many negatively selected sites were detected throughout the NOS sequences; however, no positive selection was detected. The phylogenetic relationship of insect NOS was different from that of the general classification system, although the lineages corresponded to the major recognized taxonomic groups. 相似文献
993.
Both α-lipoic acid (LA) and ascorbic acid (vitamin C) have been shown to improve endothelial dysfunction, a precursor of atherosclerosis.
Since oxidant stress can cause endothelial dysfunction, we tested the interaction and efficacy of these antioxidants in preventing
oxidant damage to lipids due to both intra- and extracellular oxidant stresses in EA.hy926 endothelial cells. LA spared intracellular
ascorbate in culture and in response to an intracellular oxidant stress induced by the redox cycling agent menadione. Extracellular
oxidant stress generated by incubating cells for 2 h in with 0.2 mg/ml LDL and 5 μM Cu2+ caused a time-dependent increase of the lipid peroxidation product malondialdehyde in both cells and LDL, preceded by rapid
disappearance of` α-tocopherol in LDL. α-Lipoic acid at concentrations of 40–80 μM blunted these effects. Similarly, intracellular
ascorbate concentrations of 1–2 mM also prevented Cu2+-induced lipid peroxidation in LDL and cells. Cu2+-dependent oxidation of LDL in the presence of ascorbate-loaded cells decreased intracellular ascorbate by 20%, but this decrease
was not reversed by LA. Both LA and ascorbate protect endothelial cells and LDL from either intra- or extracellular oxidant
stress, but that LA does not spare ascorbate in oxidatively stressed cells. 相似文献
994.
995.
Mizuta I Tsunoda T Satake W Nakabayashi Y Watanabe M Takeda A Hasegawa K Nakashima K Yamamoto M Hattori N Murata M Toda T 《Human genetics》2008,124(1):89-94
Parkinson’s disease (PD), one of the most common human neurodegenerative disorders, is characterized by the loss of dopaminergic
neurons in the substantia nigra of the midbrain. Our recent case-control association study of 268 SNPs in 121 candidate genes
identified α-synuclein (SNCA) as a susceptibility gene for sporadic PD (P = 1.7 × 10−11). We also replicated the association of fibroblast growth factor 20 (FGF20) with PD (P = 0.0089). To find other susceptibility genes, we added 34 SNPs to the previous screen. Of 302 SNPs in a total 137 genes,
but excluding SNCA, SNPs in NDUFV2, FGF2, CALB1 and B2M showed significant association (P < 0.01; 882 cases and 938 control subjects). We replicated the association analysis for these SNPs in a second independent
sample set (521 cases and 1,003 control subjects). One SNP, rs1805874 in calbindin 1 (CALB1), showed significance in both analyses (P = 7.1 × 10−5; recessive model). When the analysis was stratified relative to the SNCA genotype, the odds ratio of CALB1 tended to increase according to the number of protective alleles in SNCA. In contrast, FGF20 was significant only in the subgroup of SNCA homozygote of risk allele. CALB1 is a calcium-binding protein that widely is expressed in neurons. A relative sparing of
CALB1-positive dopaminergic neurons is observed in PD brains, compared with CALB1-negative neurons. Our genetic analysis suggests
that CALB1 is associated with PD independently of SNCA, and that FGF20 is associated with PD synergistically with SNCA.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
996.
Maki Suzuki Tadashi Miyashita Hajime Kabaya Keiji Ochiai Masahiko Asada Takeshi Tange 《Ecological Research》2008,23(1):151-158
Deer overabundance reduces forest ground-layer vegetation and can cause cascading impacts on a forest ecosystem. To predict
these effects, we must elucidate the relationship between deer density and the status of ground-layer vegetation. This relationship
was studied in the Boso Peninsula, where the deer population density exhibits a clear geographical gradient. We examined species
richness and cover of ground-layer vegetation at several cedar plantations and hardwood forests in the Boso Peninsula. We
also examined whether deer impacts were altered by light condition, soil water content and forest type (cedar and hardwood).
Species richness of ground-layer vegetation was maximized at an intermediate level of deer density, suggesting an intermediate
disturbance effect. This phenomenon was compatible with the observation that evergreen species, which were competitive dominants,
decreased with increasing deer density, whereas less competitive deciduous species increased until herbivory was intermediate.
As deer density increased, cover of ground-layer vegetation gradually decreased, but species unpalatable to deer increased
in abundance, suggesting indirect positive effects of deer for unpalatable species. Cedar plantations tended to have greater
species richness and ground-layer cover than hardwood forests with similar deer levels. Canopy openness, an indicator of light
conditions, increased species richness of hardwood forests and ground-layer cover of cedar plantations, even under deer herbivory.
Topographic wetness index, an indicator of soil water content, significantly increased the ground-layer cover of cedar plantations
under deer herbivory. These results emphasize the importance of environmental productivity and forest type in the management
of ground-layer vegetation experiencing deer overabundance. 相似文献
997.
Kawauchi K Tobiume K Iwashita K Inagaki H Morikawa T Shibukawa Y Moriyama Y Hirata H Kamata H 《Bioscience, biotechnology, and biochemistry》2008,72(6):1564-1570
Cycloprodigiosin hydrochloride (cPrG-HCl), a member of the prodigiosin family of compounds, has been reported to act as an H(+)/Cl(-) symporter. This compound induces apoptosis in several cancer cells and acts as an antitumor drug in animal models. In this study, we found a novel function of cPrG-HCl; to suppress cell death in PC12 cells, which is caused by protein synthesis inhibitors cycloheximide and actinomycin D. cPrG-HCl activated Akt and suppressed apoptosis, and this was accompanied by inhibition of caspase-3 activity and DNA fragmentation independently of its H(+)/Cl(-) symporter activity. Wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, and dominant-negative Ras attenuated the anti-apoptotic activity of cPrG-HCl, which indicates that cPrG-HCl activated the Ras-PI3K-Akt pathway suppressing apoptosis. On the other hand, serum-deprivation-induced apoptosis was not suppressed by cPrG-HCl. 相似文献
998.
999.
When a cell dies in vivo, the event does not go unnoticed. The host has evolved mechanisms to detect the death of cells and rapidly investigate the nature of their demise. If cell death is a result of natural causes - that is, it is part of normal physiological processes - then there is little threat to the organism. In this situation, little else is done other than to remove the corpse. However, if cells have died as the consequence of some violence or disease, then both defence and repair mechanisms are mobilized in the host. The importance of these processes to host defence and disease pathogenesis has only been appreciated relatively recently. This article reviews our current knowledge of these processes. 相似文献
1000.
In the silkmoth Bombyx mori, the germ cells first appear from the posterior ventral side of the egg (from within the mesodermal primordium) after blastoderm formation. This is in contrast to Drosophila, where germ cells appear at the posterior pole before cellular blastoderm formation. To date, germ plasm has not been found in B. mori. In this study, we describe the identification and expression pattern of nanos from B. mori, in which we recovered four nanos orthologues. One orthologue showed strong expression in embryonic germ cells, which was traced back to periplasmic granules dispersed on the ventral midline of the egg from the posterior-ventral focus of preblastoderm embryos. This suggests that, in B. mori, as in dipterans, germ cell formation depends on a localized determinant in the egg. The expression of another orthologue was observed in the posterior of the germ band. We speculate that nanos has dual functions; one in germ cell formation and the other in posterior body patterning, which is conferred by one nanos gene in Drosophila, but is assigned to different genes in B. mori. 相似文献