全文获取类型
收费全文 | 10835篇 |
免费 | 896篇 |
国内免费 | 215篇 |
专业分类
11946篇 |
出版年
2023年 | 246篇 |
2022年 | 307篇 |
2021年 | 446篇 |
2020年 | 430篇 |
2019年 | 584篇 |
2018年 | 544篇 |
2017年 | 415篇 |
2016年 | 409篇 |
2015年 | 414篇 |
2014年 | 875篇 |
2013年 | 1144篇 |
2012年 | 618篇 |
2011年 | 720篇 |
2010年 | 528篇 |
2009年 | 448篇 |
2008年 | 522篇 |
2007年 | 479篇 |
2006年 | 367篇 |
2005年 | 318篇 |
2004年 | 244篇 |
2003年 | 167篇 |
2002年 | 125篇 |
2001年 | 76篇 |
2000年 | 58篇 |
1999年 | 80篇 |
1998年 | 87篇 |
1997年 | 69篇 |
1996年 | 47篇 |
1995年 | 50篇 |
1994年 | 45篇 |
1993年 | 49篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 31篇 |
1989年 | 24篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1985年 | 130篇 |
1984年 | 118篇 |
1983年 | 74篇 |
1982年 | 82篇 |
1981年 | 74篇 |
1980年 | 68篇 |
1979年 | 55篇 |
1978年 | 46篇 |
1977年 | 38篇 |
1976年 | 26篇 |
1975年 | 23篇 |
1974年 | 35篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Sara Bindoli Alessandro Giollo Paola Galozzi Andrea Doria Paolo Sfriso 《Experimental biology and medicine (Maywood, N.J.)》2022,247(4):338
The current SARS-CoV-2 pandemic diffused worldwide has encouraged the rapid development of vaccines to counter the spread of the virus. At present in Italy, 75.01% of the population completed the vaccination course (AIFA.gov.it) and very few adverse events have been recorded by now. Side-effects related to a theoretical over-reaction of the immune system in response to vaccines administration have been described, and the possibility that an autoimmune or a hyperinflammatory condition may occur was recently observed. Herein, we report four cases of hyperinflammatory syndrome with features indicative of Adult-onset Still’s disease (AOSD) and macrophage activation syndrome (MAS), occurred after anti-SARS-CoV-2 vaccine injection and seen at our Unit between March and May 2021. Since interleukin (IL)-1 is one of the pivotal cytokines involved in AOSD pathogenesis, the inhibition of IL-1 is crucial in ameliorating the clinical symptoms of those patients. Moreover, it has been highlighted the central role of IL-1 as a hallmark of the hyperinflammatory status elicited by SARS-CoV-2 infection. In this case series, we successfully employed the IL-1 receptor antagonist anakinra to curb the cytokine release likely unleashed by the vaccine stimulation in potentially predisposed subjects. We also made a literature search to detect other patients with hyperinflammation temporally related to vaccines injection who benefited from IL-1 inhibition, while other AOSD/MAS-like described syndromes improved with other immunomodulatory strategies. 相似文献
992.
Chunyue Wang Shanshan Chen Hangyu Guo Hongbo Jiang Honghan Liu Haoran Fu Di Wang 《International journal of biological sciences》2022,18(5):2075
Ferroptosis and neuroinflammation play crucial roles in Alzheimer''s disease (AD) pathophysiology. Forsythoside A (FA), the main constituent of Forsythia suspensa (Thunb.) Vahl., possesses anti-inflammatory, antibacterial, antioxidant, and neuroprotective properties. The present study aimed to investigate the potential role of FA in AD neuropathology using male APP/PS1 double transgenic AD mice, Aβ1-42-exposed N2a cells, erastin-stimulated HT22 cells, and LPS-induced BV2 cells. FA treatment significantly improved mitochondrial function and inhibited lipid peroxidation in Aβ1-42-exposed N2a cells. In LPS-stimulated BV2 cells, FA treatment decreased the formation of the pro-inflammatory factors IL-6, IL-1β, and NO. In male APP/PS1 mice, FA treatment ameliorated memory and cognitive impairments and suppressed Aβ deposition and p-tau levels in the brain. Analyses using proteomics, immunohistochemistry, ELISA, and western blot revealed that FA treatment significantly augmented dopaminergic signaling, inhibited iron deposition and lipid peroxidation, prevented the activation of IKK/IκB/NF-κB signaling, reduced the secretion of pro-inflammatory factors, and promoted the production of anti-inflammatory factors in the brain. FA treatment exerted anti-ferroptosis and anti-neuroinflammatory effects in erastin-stimulated HT22 cells, and the Nrf2/GPX4 axis played a key role in these effects. Collectively, these results demonstrate the protective effects of FA and highlight its therapeutic potential as a drug component for AD treatment. 相似文献
993.
We describe real time background suppression of autofluorescence from biological samples during frequency domain or phase modulation measurements of intensity decays. For these measurements the samples were excited with a train of light pulses with widths below 1 ps. The detector was gated off for a short time period of 10 to 40 ns during and shortly after the excitation pulse. The reference signal needed for the frequency domain measurement was provided by a long-lifetime reference fluorophore which continues to emit following the off-gating pulse. Both the sample and the reference were measured under identical optical and electronic conditions avoiding the need for correction of the photomultiplier tube signal for the gating sequence. We demonstrate frequency domain background suppression using a mixture of short- and long-lifetime probes and for a long-lifetime probe in human plasma with significant autofluorescence. 相似文献
994.
Cytochrome oxidase from Pseudomonas aeruginosa has been crystallized from 2 m-ammonium sulfate. The crystals occur principally as thin diamond-shaped plates of space group P21212 with unit cell dimensions of 92 Å × 115 Å × 76 Å. Determination of the density of glutaraldehyde-fixed, water-equilibrated crystals (1.167 g/cm3), coupled with the unit cell volume (804,000 Å3), indicates that there is one subunit (~63,000 Mr) per asymmetric unit. X-ray diffraction data which were limited to 12 Å resolution due to small crystal size were obtained for the hk0 and 0kl zones using precession photography. Amplitude and phase data for the hk0, 0kl, and h0l zones were obtained from computer-based Fourier analysis of appropriate micrographs recorded from negatively stained microplates and thin sections of larger crystals using minimal beam electron microscopy. For crystals embedded in the presence of tannic acid it was possible to achieve 20 Å resolution which is comparable to the resolution achieved with negative staining of thin crystalline arrays. In addition, unstained electron diffraction on glutaraldehyde-fixed, glucose-stabilized plates was recorded to a resolution of 9 Å. The three-dimensional packing of the cytochrome oxidase dimer in the unit cell has been deduced from computer reconstructed images of the three principal projections along the crystallographic axes. The cytochrome oxidase dimer is located in the unit cell with the dimer axis coincident with a crystallographic 2-fold axis; thus within the resolution of the present data in projection (9 Å) the two subunits are identical, in agreement with biochemical evidence. The crystals have been prepared with the enzyme in the fully oxidized state and upon reduction a progressive cracking of the crystals is observed, possibly due to a conformational change dependent on the oxidation state of the heme iron. 相似文献
995.
996.
Mercury(II) bridge complexes of the type [Nuc-Hg-Nuc] (Nuc = thymidine or guanosine), and methylmercury(II) complexes of thymidine and guanosine of the type [CH3Hg(Nuc)], have been prepared under appropriate conditions of pH and reactant's stochiometry in acqueous soluton. The various complexes have been characterized by 1H and 13C NMR and used as probes, in competition and exchange studies, to establish the relative affinities of Hg(II) and CH3Hg(II) towards the nucleosides guanosine and thymidine. These studies have confirmed that Hg(II) and CH3Hg(II) bind to N3 of thymidine in preference to N1 of guanosine. The studies further show that reactions of mercury(II) with the nucleosides are thermodynamically controlled; the preperential binding reflects the relative stabilities of the respective complexes. 相似文献
997.
Manuel Boizumault Mohssine El Graoui Susan Searight-Martinet Claude Ney Max Schvoerer 《Comptes Rendus Palevol》2010,9(8):505-511
Within the framework of the European Commission's program “Patine du Desert” (DG Research; INCO-CT-FP6-2004-509100), partially concerning the preservation of Saharan engraved rock art, the approach led to the study of the sandstone patina from the rock art site of Oum La Leg (Anti-Atlas, Morocco). The rock and its Tazina school engravings are sometimes covered with a thin brown-ochre coating which only shows a dark patina, the desert patina. This film corresponds to a weathering cortex whose formation is contemporary with wet events from the Holocene period. On the surface, the patinas’ diversity is linked to the heterogeneous distribution of manganese oxides (birnessite and todorokite) due to a reorganisation which led to the incorporation of aeolian silts. Some dating suggestions are made to establish an ante quem age for the engraved lines. 相似文献
998.
James R. Brorson Vytautas P. Bindokas Toshi Iwama Charles J. Marcuccilli Jane C. Chisholm Richard J. Miller 《Developmental neurobiology》1995,26(3):325-338
Although a neurotoxic role has been postulated for the β-amyloid protein (βAP), which accumulates in brain tissues in Alzheimer's disease, a precise mechanism underlying this toxicity has not been identified. The peptide fragment consisting of amino acid residues 25 through 35 (βAP25-35), in particular, has been reported to be toxic in cultured neurons. We report that βAP25-35, applied to rat hippocampal neurons in culture, caused reversible and repeatable increases in the intracellular Ca2+ concentration ([Ca2+]i), as measured by fura 2 fluorimetry. Furthermore, βAP25-35 induced bursts of excitatory potentials and action potential firing in individual neurons studied with whole cell current clamp recordings. The βAP25-35–induced [Ca2+]i elevations and electrical activity were enhanced by removal of extracellular Mg2+, and they could be blocked by tetrodotoxin, by non-N-methyl-D -aspartate (NMDA) and NMDA glutamate receptor antagonists, and by the L-type Ca2+ channel antagonist nimodipine. Similar responses of bursts of action potentials and [Ca2+]i increases were evoked by βAP1-40. Responses to βAP25-35 were not prevented by pretreatment with pertussis toxin. Excitatory responses and [Ca2+]i elevations were not observed in cerebellar neuron cultures in which inhibitory synapses predominate. Although the effects of βAP25-35 depended on the activation of glutamatergic synapses, there was no enhancement of kainate- or NMDA-induced currents by βAP25-35 in voltage-clamp studies. We conclude that βAP25-35 enhances excitatory activity in glutamatergic synaptic networks, causing excitatory potentials and Ca2+ influx. This property may explain the toxicity of βAP25–35. © 1995 John Wiley & Sons, Inc. 相似文献
999.
In order to study the salinity tolerance of pistachio (Pistacia vera L.), embryos developed from mature seeds were isolated and cultured in vitro and subjected to different NaCl concentrations (0, 42.8, 85.5, 171.1 and 256.6 mM) for 30 days. The results showed that in vitro germination of embryonic axes was not affected by the salt concentration. However, the germinated embryo survival rates decreased from 100% for the control to 62.9% for the highest salt concentration (256.6 mM).In addition, the plantlet growth (length of aerial and root parts, number of leaf produced per embryo, as well as the production of total fresh and dry matter for both aerial parts and roots) showed significant differences according the various salt concentrations. To cite this article: B. Benmahioul et al., C. R. Biologies 332 (2009). 相似文献
1000.
Lorenz R. Rhomberg 《人类与生态风险评估》2009,15(6):1099-1145
For acute inhalation toxicity assessment, I develop a conceptual framework for expressing combinations of intensity (air concentration) and duration that produce equivalent toxicity by examining how the shape of the body-burden uptake curve during a bout of inhalation interacts with various pharmacodynamic measures of the critical body burden needed to produce toxicity. If toxicity depends on attaining a critical tissue concentration, three existing empirical approaches—Haber's Law, the ten Berge equation, and pure air-concentration-dependence—are but local approximations to different parts of an overarching mathematical relationship. The compound-specific half-life of elimination determines the range of durations for which each applies: durations of one half-life or shorter follow Haber's Law, exposures of 4 or more half-lives follow pure air-concentration-dependence, and intermediate durations can be approximated by the ten Berge equation. Better animal-to-human extrapolation is achieved if exposure durations are expressed as number of species-specific half-lives. I consider several alternative pharmacodynamic criteria, such as the dependence of toxicity on time spent above a critical tissue concentration, or on the area under the tissue concentration curve, on the tissue concentration of a toxic metabolite, or on the imbalance of damage and repair processes. 相似文献