全文获取类型
收费全文 | 7528篇 |
免费 | 558篇 |
国内免费 | 1篇 |
出版年
2023年 | 52篇 |
2022年 | 93篇 |
2021年 | 151篇 |
2020年 | 151篇 |
2019年 | 152篇 |
2018年 | 196篇 |
2017年 | 193篇 |
2016年 | 273篇 |
2015年 | 429篇 |
2014年 | 407篇 |
2013年 | 525篇 |
2012年 | 593篇 |
2011年 | 573篇 |
2010年 | 414篇 |
2009年 | 364篇 |
2008年 | 434篇 |
2007年 | 432篇 |
2006年 | 442篇 |
2005年 | 371篇 |
2004年 | 356篇 |
2003年 | 307篇 |
2002年 | 283篇 |
2001年 | 67篇 |
2000年 | 64篇 |
1999年 | 77篇 |
1998年 | 68篇 |
1997年 | 58篇 |
1996年 | 41篇 |
1995年 | 49篇 |
1994年 | 33篇 |
1993年 | 39篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 29篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 22篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1977年 | 16篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有8087条查询结果,搜索用时 15 毫秒
981.
Kadar E Checa AG Damasceno-Oliveira A Oliveira AN Machado JP 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(1):131-130
This study describes the micro-morphological features of the shell nacre in the vent mytilid Bathymodiolus azoricus collected along a bathymetric gradient of deep-sea hydrothermal vents of the mid-Atlantic ridge (MAR). Pressure-dependent
crystallisation patterns were detected in animals subjected to post-capture hydrostatic simulations. We provide evidence for
the following: (1) shell micro morphology in B. azoricus is similar to that of several vent and cold-seep species, but the prismatic shell layers may vary among bathymodiolids; (2)
nacre micro-morphology of mussels from three vent sites of the MAR did not differ significantly; minor differences do not
appear to be related to hydrostatic pressure, but rather to calcium ion availability; (3) decompression stress may cause drop
off in pH of the pallial fluid that damages nascent crystals, and in a more advanced phase, the aragonite tablets as well
as the continuous layer of mature nacre; and (4) adverse effects of decompression on calcium salt deposition in shells was
diminished by re-pressurisation of specimens. The implications of the putative influence of hydrostatic pressure on biomineralisation
processes in molluscs are discussed.
An erratum to this article can be found at 相似文献
982.
Quillaguamán J Doan-Van T Guzmán H Guzmán D Martín J Everest A Hatti-Kaul R 《Applied microbiology and biotechnology》2008,78(2):227-232
High poly(3-hydroxybutyrate) (PHB) content and volumetric productivity were achieved by fed-batch culture of Halomonas boliviensis using a defined medium. Initial shake flask cultivations in a minimal medium revealed that the growth of H. boliviensis was supported only when the medium was supplemented with aspartic acid, glycine, or glutamine. Addition of 0.1% (w/v) glutamine in the medium resulted in the highest cell dry weight (CDW; 3.9 g l−1). Glutamine was replaced by the less expensive monosodium glutamate (MSG) in the medium without any notable change in the
final cell density. Effect of initial concentrations of NH4Cl and K2HPO4 on cell growth and PHB accumulation by H. boliviensis was then analyzed using a fed-batch fermentation system. The best conditions for PHB production by H. boliviensis were attained using 0.4% (w/v) NH4Cl and 0.22% (w/v) K2HPO4 and adding MSG intermittently to the fermentor. Poly(3-hydroxybutyrate) content and CDW reached 90 wt.% and 23 g l−1, respectively, after 18 h of cultivation. In order to increase CDW and PHB content, MSG, NH4Cl, and K2HPO4 were initially fed to the fermentor to maintain their concentrations at 2%, 0.4%, and 0.22% (w/v), respectively, and subsequently their feed was suppressed. This resulted in a CDW of 44 g l−1, PHB content of 81 wt.%, and PHB volumetric productivity of 1.1 g l−1 h−1. 相似文献
983.
Physiological behaviour of loquat and anger rootstocks in relation to salinity and calcium addition 总被引:1,自引:0,他引:1
García-Legaz MF López-Gómez E Mataix Beneyto J Navarro A Sánchez-Blanco MJ 《Journal of plant physiology》2008,165(10):1049-1060
The salinity tolerance of two commercial rootstocks used for loquat plants (Eribotrya japonica Lindl.), loquat and anger, was studied in a pot experiment. The plants were irrigated using solutions containing 5 and 50mM NaCl and 5 and 25mM calcium acetate for 4 months. The growth, tissue mineral content, water status, and leaf gas exchange responses to salt treatment with and without additional calcium were examined. Plant growth was not modified by salinity in anger (50mM), but was reduced in loquat; leaf biomass and stem diameter were particularly affected. However, Cl(-) levels leaf increased with salinity to a greater extent in anger, while the Na(+) content increased to the same extent in both species, indicating that ion transport from root to leaves was not inhibited in either species. Additional calcium (25mM) reduced Na(+) and Cl(-) concentrations in both species, but did not minimise the effects of salinity on the growth of salt-treated loquat plants. The decrease in K(+) concentrations had no effect on growth, as anger was the most tolerant rootstock and had lowest leaf K(+) content. Salinity reduced the Ca(2+) concentration in the roots of both species. However, when calcium was added, the concentration of Ca(2+) increased in the roots of salinised plants. Leaf water potential at pre-dawn decreased significantly in both species under saline conditions. Leaf gas exchange, stomatal conductance and, in particular, net CO(2) assimilation, decreased with salinity only in loquat, indicating that photosynthesis could be the growth-limiting factor in this species. 相似文献
984.
Sánchez-Sampedro MA Fernández-Tárrago J Corchete P 《Journal of plant physiology》2008,165(14):1466-1473
A variety of pharmacological effectors of signal transduction pathways were used to investigate the elicitor-activated sequence of cellular responses by which yeast extract (YE) or methyljasmonate (MeJA) enhanced production of silymarin in cell cultures of Silybum marianum. As we recently showed that inhibition of external and internal calcium fluxes significantly increased flavonolignan production in S. marianum cultures, we examined whether calcium mediates signaling events leading to enhancement of silymarin production upon YE or MeJA elicitation. Pre-treatment of cultures with calcium chelators, calcium blockers or intracellular antagonists enhanced the elicitor effect of YE or MeJA. The increase of intracellular-free Ca(2+) level also promoted the elicitor effect, suggesting that an external source of calcium or alterations in internal calcium fluxes were not required for the elicitation to occur. Activation of phosphorylation/dephosphorylation cascades did not appear to mediate the elicitation mechanism; the increase in silymarin induced by elicitation was not suppressed by inhibitors of protein phosphatases or by protein kinase inhibitors. No H(2)O(2) generation was detected at any time after elicitation. Also, diphenyleneiodonium, a potent inhibitor of NAD(P)H-oxidase, did not block silymarin production in elicited cultures. From these results, we conclude that S. marianum cell cultures do not appear to employ conserved signaling components in the transduction of the elicitor signal to downstream responses such as silymarin production. 相似文献
985.
Gevorkian G Gonzalez-Noriega A Acero G Ordoñez J Michalak C Munguia ME Govezensky T Cribbs DH Manoutcharian K 《Neurochemistry international》2008,52(6):1030-1036
Extracellular and intraneuronal formation of amyloid-beta aggregates have been demonstrated to be involved in the pathogenesis of Alzheimer's disease. However, the precise mechanism of amyloid-beta neurotoxicity is not completely understood. Previous studies suggest that binding of amyloid-beta to a number of targets have deleterious effects on cellular functions. In the present study we have shown for the first time that amyloid-beta 1-42 bound to a peptide comprising the microtubule binding domain of the heavy chain of microtubule-associated protein 1B by the screening of a human brain cDNA library expressed on M13 phage. This interaction may explain, in part, the loss of neuronal cytoskeletal integrity, impairment of microtubule-dependent transport and synaptic dysfunction observed previously in Alzheimer's disease. 相似文献
986.
Eniko Kadar Antonio G. Checa Alfredo N. D. P. Oliveira Jorge P. Machado 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(1):123-130
This study describes the micro-morphological features of the shell nacre in the vent mytilid Bathymodiolus azoricus collected along a bathymetric gradient of deep-sea hydrothermal vents of the mid-Atlantic ridge (MAR). Pressure-dependent crystallisation patterns were detected in animals subjected to post-capture hydrostatic simulations. We provide evidence for the following: (1) shell micro morphology in B. azoricus is similar to that of several vent and cold-seep species, but the prismatic shell layers may vary among bathymodiolids; (2) nacre micro-morphology of mussels from three vent sites of the MAR did not differ significantly; minor differences do not appear to be related to hydrostatic pressure, but rather to calcium ion availability; (3) decompression stress may cause drop off in pH of the pallial fluid that damages nascent crystals, and in a more advanced phase, the aragonite tablets as well as the continuous layer of mature nacre; and (4) adverse effects of decompression on calcium salt deposition in shells was diminished by re-pressurisation of specimens. The implications of the putative influence of hydrostatic pressure on biomineralisation processes in molluscs are discussed. 相似文献
987.
Lopes-Lima M Bleher R Forg T Hafner M Machado J 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(1):17-25
Early studies on the outer mantle epithelium (OME) cells of the freshwater bivalve Anodonta cygnea (Linnaeus, 1758) revealed high ionic calcium concentrations by electrophysiological methods and subsequently a high tendency
to reach an intracellular toxic condition. This toxicity could be neutralized by specific mechanisms in the cytosol of OME
cells of A. cygnea. The present immunocytochemistry studies of OME cells by light and transmission electron microscopy (TEM) clearly showed
a positive reaction of an antibody directed against the human plasma membrane Ca2+-ATPase 1 (PMCA-1) in the cytoplasm of OME cells. Also, western blot analysis of different fractions of OME cells with anti
human PMCA-1 and C28R2 antibodies confirmed the presence of a PMCA-like protein with an unusual topographical localization
and a molecular weight of only 70–80 kDa. These results lead us to speculate that this PMCA-like protein is distributed either
in the plasma membrane or in the entire cytosol, where it eventually regulates intracellular calcium levels. Interestingly,
the antibody reactions showed seasonal variations, being highest in OME samples prepared during summer when A. cygnea live under natural acidosis and absent in samples taken in winter conditions, which is in accordance with the seasonal variation
of shell calcification rates. During winter, PMCA-1 antibody reaction was also detected in OME cells of animals kept only
under experimentally induced acidosis conditions. Therefore, we assume that a functional role for this PMCA-like protein in
the intracellular calcium regulation of OME cells during the mineralization of the shells of A. cygnea can be speculated. 相似文献
988.
Jorge N. S. Freitas Charbel N. El-Hani & Pedro L. B. da Rocha 《Ethology : formerly Zeitschrift fur Tierpsychologie》2008,114(4):389-397
In this work we explored the evolution of sociality in cursorial echimyids by comparing affiliation among three species of Trinomys and one species of Thrichomys. We captured specimens of Trinomys yonenagae, Trinomys albispinus minor, and Thrichomys apereoides in areas of the Brazilian semiarid Caatinga, and Trinomys iheringi denigratus in one area of Atlantic Forest. For each species, we recorded 12 intra‐sexual dyadic encounters in a neutral arena (six between males and six between females) in order to test the hypothesis that species and sex influence level of affiliation. This response variable was assessed based on an affiliation index, calculated as the proportion of the total number of affiliative behaviors to the total number of social behaviors exhibited by the dyad during each encounter. Hypothesis test was performed by means of a parametric two‐way anova . The test was able to detect significant differences only among species, not among sexes. Trinomys yonenagae was the most affiliative species, while T. apereoides and T. albispinus minor were the most agonistic ones. Trinomys iheringi denigratus showed an intermediate pattern. We suggest, based on out‐group comparison, that affiliation in Trinomys increased in the lineage containing T. iheringi denigratus and T. yonenagae and that higher affiliation in the last species can be adaptive to the life in the desert‐like habitat where it lives. 相似文献
989.
Anxiolytic-like effects of intra-lateral septal nuclei (LSN) infusions of the neuropeptide Y (NPY) alone or combined with estradiol benzoate were assessed in ovariectomized Wistar rats in two animal models of anxiety-like behavior. In a conflict test, immediately punished responses were assessed: 17-beta-estradiol (50.0microg/rat, P<0.05) plus vehicle (intra-LSN) or intra-LSN infusions of NPY (2.5microg/microl, P<0.05; 3.0microg/mul, P<0.05) plus vehicle (systemic route) or the combination of subthreshold doses of 17-beta-estradiol (25.0microg/kg) plus intra-LSN infusions of NPY (2.0microg/mul, P<0.05) increased the amount of immediately punished reinforcers. In the elevated plus-maze test several spatial-temporal variables were evaluated: 17-beta-estradiol (50.0microg/kg, P<0.05) plus vehicle (intra-LSN) or intra-LSN infusions of NPY (2.5microg/mul, P<0.05; 3.0microg/mul, P<0.05) plus vehicle (systemic route) or the combination of subthreshold doses of 17-beta-estradiol (25.0microg/kg) plus intra-LSN infusions of NPY (2.0microg/mul, P<0.05) produced anxiolytic-like actions without affecting locomotion. It is concluded that estradiol or NPY may produce anxiolytic-like actions and that subthreshold doses of estradiol and subthreshold doses of NPY when combined produced anxiolytic-like actions. 相似文献
990.
Adrenomedullin is increased by pulsatile shear stress on the vascular endothelium via periodic acceleration (pGz) 总被引:1,自引:0,他引:1
Periodic acceleration (pGz) is produced by a platform which moves the supine body repetitively in a headward to footward direction. The imparted motion produces pulsatile shear stress on the vascular endothelium. Pulsatile shear stress on the vascular endothelium has been shown to elicit production of a host of cardioprotective, cytoprotective mediators. The purpose of this study was to ascertain if pGz also enhances production of adrenomedullin (AM) in normal healthy swine. Twelve pigs (weight range 20-30 kg) were anesthetized, intubated and placed on conventional mechanical ventilation. All animals were secured to the motion platform. In one group (pGz) (n=7) was activated for 1h, and monitored for an additional 3h. A control group (CONT) (n=5) served as time control. Arterial blood gases, hemodynamic measurements, and serum for AM, interleukin 4, 6 and thromboxane B(2) (TBXB2) were measured at baseline, immediately after pGz, and 3h after pGz had been discontinued. There was no significant change from baseline value in IL-4, IL-6 or TBXB2. Mean arterial blood pressure decreased in pGz-treated animals from 115+/-10 at baseline to 90+/-8 after 60 min of pGz (p<0.01). AM levels increase from 776+/-176 pg/ml baseline to 1160+/-68 pg/ml immediately after pGz, and remained elevated to 1584+/-160 pg/ml, 3h after pGz (p<0.01 vs. BL). This is the first report of AM-enhanced production using a non-invasive method of increasing pulsatile shear stress on the vascular endothelium. pGz increases production of AM in normal healthy swine. These changes are independent of IL-4, IL-6 or TBXB2 production. 相似文献