首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2795篇
  免费   164篇
  2023年   19篇
  2022年   57篇
  2021年   110篇
  2020年   57篇
  2019年   73篇
  2018年   91篇
  2017年   89篇
  2016年   121篇
  2015年   177篇
  2014年   200篇
  2013年   228篇
  2012年   218篇
  2011年   202篇
  2010年   145篇
  2009年   107篇
  2008年   136篇
  2007年   107篇
  2006年   108篇
  2005年   90篇
  2004年   104篇
  2003年   76篇
  2002年   84篇
  2001年   61篇
  2000年   39篇
  1999年   37篇
  1998年   20篇
  1997年   13篇
  1996年   9篇
  1995年   5篇
  1994年   5篇
  1993年   7篇
  1992年   17篇
  1991年   13篇
  1990年   11篇
  1989年   11篇
  1988年   8篇
  1987年   10篇
  1986年   8篇
  1985年   5篇
  1984年   6篇
  1983年   8篇
  1980年   6篇
  1979年   5篇
  1976年   3篇
  1975年   3篇
  1971年   3篇
  1970年   4篇
  1969年   9篇
  1968年   5篇
  1965年   4篇
排序方式: 共有2959条查询结果,搜索用时 46 毫秒
981.
As part of an ongoing revision of the family Gonyleptidae, we have identified many species that are synonyms of previously described species or misplaced in this family. This article summarizes these findings, adding previously unavailable information or correcting imprecise observations to justify the presented taxonomic changes. The following new familial or subfamilial assignments are proposed: Nemastygnus Roewer, 1929 and Taulisa Roewer, 1956 are transferred to Agoristenidae, Agoristeninae; Napostygnus Roewer, 1929 to Cranaidae; Ceropachylinus peruvianus Roewer, 1956 and Pirunipygus Roewer, 1936 are transferred to Gonyleptidae, Ampycinae; Gyndesops Roewer, 1943, Haversia Roewer, 1913 and Oxapampeus Roewer, 1963 are transferred to Gonyleptidae, Pachylinae. The following generic synonymies are proposed for the family Gonyleptidae: Acanthogonyleptes Mello-Leitão, 1922 = Centroleptes Roewer, 1943; Acrographinotus Roewer, 1929 = Unduavius Roewer, 1929; Gonyleptes Kirby, 1819 = Collonychium Bertkau, 1880; Mischonyx Bertkau, 1880 = Eugonyleptes Roewer, 1913 and Gonazula Roewer, 1930; Parampheres Roewer, 1913 = Metapachyloides Roewer, 1917; Pseudopucrolia Roewer, 1912 = Meteusarcus Roewer, 1913; Haversia Roewer, 1913 = Hoggellula Roewer, 1930. The following specific synonymies are proposed for the family Gonyleptidae: Acanthogonyleptes singularis (Mello-Leitão, 1935) = Centroleptes flavus Roewer, 1943, syn. n.; Geraeocormobius sylvarum Holmberg, 1887 = Discocyrtus serrifemur Roewer, 1943, syn. n.; Gonyleptellus bimaculatus (Sørensen, 1884) = Gonyleptes cancellatus Roewer,1917, syn. n.; Gonyleptes atrus Mello-Leitão, 1923 = Weyhia brieni Giltay, 1928, syn. n.; Gonyleptes fragilis Mello-Leitão, 1923 = Gonyleptes banana Kury, 2003, syn. n.; Gonyleptes horridus Kirby, 1819 = Collonychium bicuspidatum Bertkau, 1880, syn. n., Gonyleptes borgmeyeri Mello-Leitão, 1932, syn. n., Gonyleptes curvicornis Mello-Leitão, 1932, syn. n., Metagonyleptes hamatus Roewer, 1913, syn. n. and Paragonyleptes simoni Roewer, 1930, syn. n.; Gonyleptes pustulatus Sørensen, 1884 = Gonyleptes guttatus Roewer, 1917, syn. n.; Haversia defensa (Butler, 1876) = Sadocus vallentini Hogg, 1913, syn. n.; Liogonyleptoides minensis (Piza, 1946) = Currala bahiensis Soares, 1972, syn. n.; Megapachylus grandis Roewer, 1913 = Metapachyloides almeidai Soares & Soares, 1946, syn. n.; Mischonyx cuspidatus (Roewer, 1913) = Gonazula gibbosa Roewer, 1930 syn. n.; Mischonyx scaber (Kirby, 1819) = Xundarava holacantha Mello-Leitão, 1927, syn. n.; Parampheres tibialis Roewer, 1917 = Metapachyloides rugosus Roewer, 1917, syn. n.; Parapachyloides uncinatus (Sørensen, 1879) = Goyazella armata Mello-Leitão, 1931, syn. n.; Pseudopucrolia mutica (Perty, 1833) = Meteusarcus armatus Roewer, 1913, syn. n. The following new combinations are proposed: Acrographinotus ornatus (Roewer, 1929), comb. n. (ex Unduavius); Gonyleptellus bimaculatus (Sørensen, 1884),comb. n. (ex Gonyleptes);Gonyleptes perlatus (Mello-Leitão, 1935), comb. n. (exMoojenia);Mischonyx scaber (Kirby, 1819), comb. n. (ex Gonyleptes); and Neopachyloides peruvianus (Roewer, 1956), comb. n. (ex Ceropachylus). The following species of Gonyleptidae, Gonyleptinae are revalidated: Gonyleptes atrus Mello-Leitão, 1923 and Gonyleptes curvicornis (Roewer, 1913).  相似文献   
982.
The neural crest (NC) corresponds to a collection of multipotent and oligopotent progenitors endowed with both neural and mesenchymal potentials. The derivatives of the NC at trunk level include neurons and glial cells of the peripheral nervous system in addition to melanocytes, smooth muscle cells and some endocrine cells. Environmental factors control the fate decisions of NC cells. Despite the well-known influence of flavonoids on the central nervous system, the issue of whether they also influence NC cells has not been yet addressed. Flavonoids are polyphenolic compounds that are integral components of the human diet. The biological activities of these compounds cover a very broad spectrum, from anticancer and antibacterial activities to inhibition of bone reabsorption and modulation of inflammatory response. In the present work, we have investigated the actions of the flavonoids hesperidin, rutin and quercetin on NC cells of quail, in vitro. We show for the first time, that hesperidin and rutin increase the viability of trunk NC cells in culture, without affecting cell differentiation and proliferation. The molecular mechanism of this action is dependent on ERK2 and PI3K pathways. Quercetin had no effect on NC progenitors. Taken together, these results suggest that flavonoids hesperidin and rutin increase NC cell survival, which may be useful against the toxicity of some chemicals during embryonic development.  相似文献   
983.
The present study described clinical and epidemiological aspects of three cases of feline histoplasmosis and compared them to previously described cases. A detailed mycological identification and antifungal susceptibility profile of each isolate are presented. Secondarily, a serological survey for anti-Histoplasma antibodies was performed with domestic and wild cats. Diseased animals presented nodular to ulcerated skin lesions and respiratory disorders as main clinical signs. H. capsulatum var. capsulatum was isolated and the strains showed to be susceptible to antifungal drugs. Considering that feline histoplasmosis is uncommonly observed in veterinary clinics, diagnosis, and clinical management in endemic areas should be improved.  相似文献   
984.
Cold restraint stress (CRS) model exerts similar effect as physiological stress because it combines emotional stress (escape reaction) and physical stress (muscle work). It is well established that various responses to stress are regulated by sympathoadrenal system, brain monoaminergic systems and oxidative processes. Nardostachys jatamansi (NJE) is known to possess soothing and sedative action on the central nervous system. The present investigation was performed to explore the anti-stress activity of NJE on CRS model, through its effect on biochemical and neurochemical alterations. The rats were restrained in metallic chambers for 3?h at 4?°C was followed by sacrifice and assessment of stress related alterations. Hydro-ethanolic (30:70) extract of NJE was administrated orally at the doses of 200 and 500?mg/kg for 14?days and compared with vehicle control and Panax ginseng (100?mg/kg). Effects of NJE on CRS induced oxidative stress including reduced glutathione, glutathione peroxidase, glutathione reductase, glutathione-s-transferase were estimated. Dopamine, norepinephrine, serotonin and 5-hydroxy indole acetic acid were measured in the cerebral cortex, hippocampus and hypothalamus by HPLC electrochemical detector. NJE at both doses significantly inhibited CRS induced oxidative stress. It significantly mitigated CRS induced altered level of neurotransmitters in different brain regions. The study implied that NJE has the ability to provide protection against CRS induced oxidative stress and neurochemical alterations. Findings indicated that NJE revealed potent anti-stress effect implicating its therapeutic importance in stress-related disorders.  相似文献   
985.
Diabetes mellitus is a disease associated with several changes in the central nervous system, including oxidative stress and abnormal glutamatergic neurotransmission, and the astrocytes play an essential role in these alterations. In vitro studies of astroglial function have been performed using cultures of primary astrocytes or C6 glioma cells. Herein, we investigated glutamate uptake, glutamine synthetase and S100B secretion in C6 glioma cells cultured in a high-glucose environment, as well as some parameters of oxidative stress and damage. C6 glioma cells, cultured in 12 mM glucose medium, exhibited signals of oxidative and nitrosative stress similar to those found in diabetes mellitus and other models of diabetic disease (decrease in glutathione, elevated NO, DNA damage). Interestingly, we found an increase in glutamate uptake and S100B secretion, and a decrease in glutamine synthetase, which might be linked to the altered glutamatergic communication in diabetes mellitus. Moreover, glutamate uptake in C6 glioma cells, like primary astrocytes, was stimulated by extracellular S100B. Aminoguanidine partially prevented the glial alterations induced by the 12 mM glucose medium. Together, these data emphasize the relevance of astroglia in diabetes mellitus, as well as the importance of glial parameters in the evaluation of diabetic disease progression and treatment.  相似文献   
986.
Cytochemical localization of hydrogen peroxide-generating sites suggests NADPH (nicotinamide adenine dinucleotide 3-phosphate [reduced form]) oxidase expression at the maternal-fetal interface. To explore this possibility, we have characterized the expression and activity of the NADPH oxidase complex in trophoblast cells during the postimplantation period. Implantation sites and ectoplacental cones (EPCs) from 7.5-gestational day embryos from CD1 mice were used as a source for expression analyses of NADPH oxidase catalytic and regulatory subunits. EPCs grown in primary culture were used to investigate the production of superoxide anion through dihydroxyethidium oxidation in confocal microscopy and immunohistochemical assays. NADPH subunits Cybb (gp91phox), Cyba (p22phox), Ncf4 (p40phox), Ncf1 (p47phox), Ncf2 (p67phox), and Rac1 were expressed by trophoblast cells. The fundamental subunits of membrane CYBB and cytosolic NCF2 were markedly upregulated after phorbol-12-myristate-13-acetate (PMA) treatment, as detected by quantitative real-time PCR, Western blotting, and immunohistochemistry. Fluorescence microscopy imaging showed colocalization of cytosolic and plasma membrane NADPH oxidase subunits mainly after PMA treatment, suggesting assembly of the complex after enzyme activation. Cultured EPCs produced superoxide in a NADPH-dependent manner, associating the NADPH oxidase-mediated superoxide production with postimplantation trophoblast physiology. NADPH-oxidase cDNA subunit sequencing showed a high degree of homology between the trophoblast and neutrophil isoforms of the oxidase, emphasizing a putative role for reactive oxygen species production in phagocytic activity and innate immune responses.  相似文献   
987.
Following a screening on EMS-induced Drosophila mutants defective for formation and morphogenesis of epithelial cells, we have identified three lethal mutants defective for the production of embryonic cuticle. The mutants are allelic to the CG12140 gene, the fly homologue of electron transfer flavoprotein:ubiquinone oxidoreductase (ETF:QO). In humans, inherited defects in this inner membrane protein account for multiple acyl-CoA dehydrogenase deficiency (MADD), a metabolic disease of β-oxidation, with a broad range of clinical phenotypes, varying from embryonic lethal to mild forms. The three mutant alleles carried distinct missense mutations in ETF:QO (G65E, A68V and S104F) and maternal mutant embryos for ETF:QO showed lethal morphogenetic defects and a significant induction of apoptosis following germ-band elongation. This phenotype is accompanied by an embryonic accumulation of short- and medium-chain acylcarnitines (C4, C8 and C12) as well as long-chain acylcarnitines (C14 and C16:1), whose elevation is also found in severe MADD forms in humans under intense metabolic decompensation. In agreement the ETF:QO activity in the mutant embryos is markedly decreased in relation to wild type activity. Amino acid sequence analysis and structural mapping into a molecular model of ETF:QO show that all mutations map at FAD interacting residues, two of which at the nucleotide-binding Rossmann fold. This structural domain is composed by a β-strand connected by a short loop to an α-helix, and its perturbation results in impaired cofactor association via structural destabilisation and consequently enzymatic inactivation. This work thus pinpoints the molecular origins of a severe MADD-like phenotype in the fruit fly and establishes the proof of concept concerning the suitability of this organism as a potential model organism for MADD.  相似文献   
988.
989.
Coxiella burnetii is the agent of Q fever , an emergent worldwide zoonosis of wide clinical spectrum. Although C. burnetii infection is typically associated with acute infection, atypical pneumonia and flu-like symptoms, endocarditis, osteoarticular manifestations and severe disease are possible, especially when the patient has a suppressed immune system; however, these severe complications are typically neglected. This study reports the sequencing of the repetitive element IS1111 of the transposase gene of C. burnetii from blood and bronchoalveolar lavage (BAL) samples from a patient with severe pneumonia following methotrexate therapy, resulting in the molecular diagnosis of Q fever in a patient who had been diagnosed with active seronegative polyarthritis two years earlier. To the best of our knowledge, this represents the first documented case of the isolation of C. burnetii DNA from a BAL sample.  相似文献   
990.
Ketoconazole is a clinically safe antifungal agent that also inhibits the growth of Leishmania spp. A study was undertaken to determine whether Leishmania parasites are prone to becoming resistant to ketoconazole by upregulating C14-demethylase after stepwise pharmacological pressure. Leishmania amazonensis promastigotes [inhibitory concentration (IC)?? = 2 μM] were subjected to stepwise selection with ketoconazole and two resistant lines were obtained, La8 (IC?? = 8 μM) and La10 (IC?? = 10 μM). As a result, we found that the resistance level was directly proportional to the C14-demethylase mRNA expression level; we also observed that expression levels were six and 12 times higher in La8 and La10, respectively. This is the first demonstration that L. amazonensis can up-regulate C14-demethylase in response to drug pressure and this report contributes to the understanding of the mechanisms of parasite resistance.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号