全文获取类型
收费全文 | 2967篇 |
免费 | 124篇 |
国内免费 | 1篇 |
出版年
2022年 | 8篇 |
2021年 | 13篇 |
2019年 | 12篇 |
2018年 | 34篇 |
2017年 | 21篇 |
2016年 | 31篇 |
2015年 | 65篇 |
2014年 | 65篇 |
2013年 | 301篇 |
2012年 | 146篇 |
2011年 | 121篇 |
2010年 | 100篇 |
2009年 | 88篇 |
2008年 | 154篇 |
2007年 | 171篇 |
2006年 | 186篇 |
2005年 | 166篇 |
2004年 | 195篇 |
2003年 | 202篇 |
2002年 | 182篇 |
2001年 | 25篇 |
2000年 | 21篇 |
1999年 | 33篇 |
1998年 | 49篇 |
1997年 | 38篇 |
1996年 | 28篇 |
1995年 | 39篇 |
1994年 | 43篇 |
1993年 | 54篇 |
1992年 | 37篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 38篇 |
1983年 | 25篇 |
1982年 | 36篇 |
1981年 | 27篇 |
1980年 | 21篇 |
1979年 | 9篇 |
1978年 | 19篇 |
1977年 | 22篇 |
1976年 | 10篇 |
1975年 | 17篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 9篇 |
排序方式: 共有3092条查询结果,搜索用时 31 毫秒
991.
Nienke van der Werf Stephen A. Redpath Miyuki Azuma Hideo Yagita Matthew D. Taylor 《PLoS pathogens》2013,9(3)
The suppression of protective Type 2 immunity is a principal factor driving the chronicity of helminth infections, and has been attributed to a range of Th2 cell-extrinsic immune-regulators. However, the intrinsic fate of parasite-specific Th2 cells within a chronic immune down-regulatory environment, and the resultant impact such fate changes may have on host resistance is unknown. We used IL-4gfp reporter mice to demonstrate that during chronic helminth infection with the filarial nematode Litomosoides sigmodontis, CD4+ Th2 cells are conditioned towards an intrinsically hypo-responsive phenotype, characterised by a loss of functional ability to proliferate and produce the cytokines IL-4, IL-5 and IL-2. Th2 cell hypo-responsiveness was a key element determining susceptibility to L. sigmodontis infection, and could be reversed in vivo by blockade of PD-1 resulting in long-term recovery of Th2 cell functional quality and enhanced resistance. Contrasting with T cell dysfunction in Type 1 settings, the control of Th2 cell hypo-responsiveness by PD-1 was mediated through PD-L2, and not PD-L1. Thus, intrinsic changes in Th2 cell quality leading to a functionally hypo-responsive phenotype play a key role in determining susceptibility to filarial infection, and the therapeutic manipulation of Th2 cell-intrinsic quality provides a potential avenue for promoting resistance to helminths. 相似文献
992.
Mayumi Yamato Takeshi Shiba Ken-Ichi Yamada Toshiaki Watanabe Hideo Utsumi 《Free radical research》2013,47(9):844-851
Free radicals are believed to be key factors that promote ischemia reperfusion injury in the brain. This study used the characteristic spectrum of methoxycarbonyl-PROXYL to detect free radical reactions in hydrophilic and lipophilic compartments in a transient middle cerebral artery occlusion (MCAO) mouse model. Methoxycarbonyl-PROXYL, which has a high water/octanol partition coefficient, allows the detection of nitroxyl radical in both compartments simultaneously. Free radicals generation was analysed from the enhanced ESR signal decay rate of methoxycarbonyl-PROXYL. The signal decay rate in the lipidic compartment was significantly enhanced 1 h after reperfusion following MCAO. The enhanced signal decay rate was significantly suppressed by Trolox. The accumulation of lipid peroxidation products increased by 6 h post-reperfusion and was suppressed by methoxycarbonyl-PROXYL or Trolox. These results demonstrate that information pertaining to different sites of free radical generation in vivo can be obtained simultaneously and that lipid-derived radicals are generated in transient MCAO mice. 相似文献
993.
George Imataka Hideo Yamanouchi Junko Hirato Mitsuoki Eguchi Masaru Kojima Koichi Honma Osamu Arisaka 《Cell biochemistry and biophysics》2013,67(2):813-817
We present here a long survival case of a patient with the mosaic form of trisomy 13 who died of aspiration pneumonia at the age of 7 years and 4 months. The autopsy revealed olfactory aplasia and fenestration of the septum pellucidum, and dilated lateral ventricles and atrophic hippocampus. Furthermore, there were numerous “torpedos” (i.e., swollen fusiform Purkinje cell axons), mostly in the granular layer underneath the Purkinje cell layer, and, occasionally, in the granular layer. Similar neuropathological findings have been reported in elderly cases of essential tremor, Parkinson’s disease, or Alzheimer’s disease. Precise mechanism for this axonal change is still unclear. These pathological changes have never previously been reported in the literature on trisomy 13, and the present patient is one of the oldest autopsied individuals with the mosaic trisomy 13. 相似文献
994.
Wei Zhang Hideo Tsurushima Ayako Oyane Yushin Yazaki Yu Sogo Atsuo Ito Akira Matsumura 《Journal of biomedical science》2011,18(1):62
Background
Safe and efficient gene transfer systems are needed for tissue engineering. We have developed an apatite composite layer including the bone morphogenetic protein-2 (BMP-2) gene and fibronectin (FB), and we evaluated its ability to induce bone formation. 相似文献995.
Interferon (IFN)-α was reported to be effective in longterm intrathecal treatment of subacute sclerosing panencephalitis (SSPE).
However, the side effects related with longterm use of IFN-α/β are unclear. We evaluated the therapeutic effects of IFN-α/β
in a 13-years-old patient with SSPE. The cerebrospinal fluid (CSF) measles antibody titer was 64 × NT/128×HI, IgG-index was
4.5, and the SSPE diagnosis was based on electroencephalography (Jabbour-stage II on admission). With Inosiplex (INP) given
orally, IFN-α (3 × 106 units) was infused intraventricularly twice-a-week for 1-year. Resultantly, CSF cell count was elevated (2502/3), total protein
and glucose levels were normal; however, DIAM occurred repeatedly. Consequently, reduced IFN-α (5 × 105 units) with hydrocorton was administered at 2-months interval for 19 months, during which, DIAM occurred four times. Therefore,
IFN-β (3 × 106 units; twice-a-week) therapy was started and continued for 3 years. Although the symptoms were improved considerably, DIAM
recurred after 15-months therapy and CSF cell counts were also elevated (2121/3). Since SSPE progressed to Jabbour-stage IV,
indicated by irreversible consciousness disorder, IFN therapy was discontinued and INP monotherapy was followed for another
3 years. We, therefore, concluded that the longterm intraventricular IFN-α/β infusion therapy of SSPE involved the potential
risk of DIAM with serious irreversible neurological sequelae and should be monitored carefully. 相似文献
996.
Badets M Whittington I Lalubin F Allienne JF Maspimby JL Bentz S Du Preez LH Barton D Hasegawa H Tandon V Imkongwapang R Imkongwapang R Ohler A Combes C Verneau O 《Systematic biology》2011,60(6):762-781
Investigating patterns and processes of parasite diversification over ancient geological periods should involve comparisons of host and parasite phylogenies in a biogeographic context. It has been shown previously that the geographical distribution of host-specific parasites of sarcopterygians was guided, from Palaeozoic to Cainozoic times, mostly by evolution and diversification of their freshwater hosts. Here, we propose phylogenies of neobatrachian frogs and their specific parasites (Platyhelminthes, Monogenea) to investigate coevolutionary processes and historical biogeography of polystomes and further discuss all the possible assumptions that may account for the early evolution of these parasites. Phylogenetic analyses of concatenated rRNA nuclear genes (18S and partial 28S) supplemented by cophylogenetic and biogeographic vicariance analyses reveal four main parasite lineages that can be ascribed to centers of diversity, namely Australia, India, Africa, and South America. In addition, the relationships among these biogeographical monophyletic groups, substantiated by molecular dating, reflect sequential origins during the breakup of Gondwana. The Australian polystome lineage may have been isolated during the first stages of the breakup, whereas the Indian lineage would have arisen after the complete separation of western and eastern Gondwanan components. Next, polystomes would have codiverged with hyloid sensu stricto and ranoid frog lineages before the completion of South American and African plate separation. Ultimately, they would have undergone an extensive diversification in South America when their ancestral host families diversified. Therefore, the presence of polystome parasites in specific anuran host clades and in discrete geographic areas reveals the importance of biogeographic vicariance in diversification processes and supports the occurrence and radiation of amphibians over ancient and recent geological periods. 相似文献
997.
998.
Emoto M Mito F Yamasaki T Yamada K Sato-Akaba H Hirata H Fujii H 《Free radical research》2011,45(11-12):1325-1332
The loss of paramagnetism of nitroxide radicals due to reductant reactions in biological systems, places a fundamental time constraint on their application as an imaging probe in in vivo EPR imaging studies. However, in vitro studies of the newly synthesized tetraethyl-substituted piperidine nitroxide radical demonstrated high resistivity to paramagnetic reduction when exposed to ascorbic acid, a common reduction agent in biological systems. In this work we investigated the use of these nitroxides as an imaging probe in EPR imaging of small rodents. 2,2,6,6-Tetraethyl-piperidine nitroxide (TEEPONE) is not highly soluble in aqueous media, thus a lipid-based emulsion system of lecithin was used to solubilize TEEPONE. The obtained solution was homogenous and with low viscosity, allowing smooth intravenous injection into mice tail vein. Acquired three dimensional (3D) EPR images of mouse head clearly showed TEEPONE distributed in all tissues including brain tissues, with an average measurable signal half-life of more than 80 min, thus demonstrating high resistivity to reduction due to ascorbic acid in in vivo animal studies, and the potential for use of this compound in in vivo studies of animal model systems. 相似文献
999.
Fire severity affects vegetation and seed bank in a wetland 总被引:3,自引:0,他引:3
Questions: How does the severity of prescribed fires affect vegetation and seed bank in a wetland? Location: A fire‐prone reed swamp in northern Japan (250 ha, 40°49′N, 141°22′E, <10 m a.s.l.). Methods: Vegetation, biomass and seed bank were monitored for the 2 yr after annual prescribed fires were discontinued. Plant communities were placed into three categories based on fire severity: high (H) – fire consumed litter completely; moderate (M) – fire removed standing litter but left wet fallen litter; and low (L) – fire incompletely removed standing litter and did not remove fallen litter. Soil samples were collected in autumn 2007 and early summer 2008, and germinable seed bank was investigated by greenhouse trials. Results: High fire severity increased diversity in the next growing season by the establishment of short herbs in the standing vegetation. The biomass of forbs and grasses was greater in H where Phragmites australis biomass was reduced. The density of seed bank was >30 000 seeds m?2 throughout all the treatments. Perennial plants were dominant in the vegetation, while annuals, biennials and rushes were dominant in the seed bank. Small seeds were more abundant in the soil than in the litter. Qualitative and quantitative similarities between seed bank and the vegetation were low, and tended to be higher in H. Conclusions: Fire contributed to the development of diverse standing vegetation via the positive effects on seed bank dynamics, and can be considered a tool to maintain species‐rich marshes. 相似文献
1000.