全文获取类型
收费全文 | 25495篇 |
免费 | 2158篇 |
国内免费 | 1070篇 |
出版年
2024年 | 54篇 |
2023年 | 609篇 |
2022年 | 842篇 |
2021年 | 1206篇 |
2020年 | 1055篇 |
2019年 | 1322篇 |
2018年 | 1175篇 |
2017年 | 942篇 |
2016年 | 996篇 |
2015年 | 1126篇 |
2014年 | 1759篇 |
2013年 | 2313篇 |
2012年 | 1281篇 |
2011年 | 1452篇 |
2010年 | 1029篇 |
2009年 | 1154篇 |
2008年 | 1170篇 |
2007年 | 1123篇 |
2006年 | 981篇 |
2005年 | 890篇 |
2004年 | 798篇 |
2003年 | 577篇 |
2002年 | 553篇 |
2001年 | 422篇 |
2000年 | 322篇 |
1999年 | 324篇 |
1998年 | 327篇 |
1997年 | 290篇 |
1996年 | 218篇 |
1995年 | 194篇 |
1994年 | 236篇 |
1993年 | 178篇 |
1992年 | 176篇 |
1991年 | 123篇 |
1990年 | 119篇 |
1989年 | 80篇 |
1988年 | 96篇 |
1987年 | 64篇 |
1986年 | 62篇 |
1985年 | 166篇 |
1984年 | 156篇 |
1983年 | 108篇 |
1982年 | 120篇 |
1981年 | 104篇 |
1980年 | 92篇 |
1979年 | 77篇 |
1978年 | 61篇 |
1977年 | 45篇 |
1976年 | 39篇 |
1974年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
102.
J. L. Luis Hernandez 《BioControl》1988,33(2):163-171
Résumé Cinquante deux souches deB. thuringiensis appartenant à 13 sérovars ont été testées sur des chenilles néonates deSpodoptera frugiperda en contaminant la surface du milieu semi-synthétique d'élevage. Deux souches du sérovarkenyae et une autre du sérovartolworthi provoquent le plus de mortalité, suivies par les souches des sérovarsaizawai etkurstaki. Les souches les moins actives appartiennent aux sérotypesalesti, dendrolimus, sotto etcolmeri. L'action des souches sur le développement larvaire a aussi été abordée. Les souches des sérovarskenyae, aizawai etkurstaki ont ralenti le développement des chenilles, tandis que les souches des sérovarsalesti, sotto etcolmeri n'ont eu aucun effet.
相似文献
103.
J. C. Onillon 《BioControl》1988,33(4):481-494
Les problèmes posés par les ravageurs des Citrus ont pris une importance considérable au cours de ces 3 dernières décennies
et cela pour plusieurs raisons:
Le potentiel de ces ravageurs, pour la plupart plurivoltins, est souvent très important et les conditions climatiques favorables
jointes à la persistance pendant toute l'année de la frondaison assurent des niveaux de populations très élevés. 相似文献
– | - dans un 1er temps, l'on peut invoquer l'introduction accidentelle de ravageurs,Dialeurodes citri Ashm en 1945 (Pussard, 1953),Unaspis yanonensis Kuw. en 1963 (Commeau & Sola, 1964) etAleurothrix floccosus Mask. en 1967 (Onillon, 1969). Ces 3 espèces démunies de leur cortège d'ennemis naturels et trouvant dans leur nouvelle aire de répartition des conditions favorables de développement, ont très rapidement présenté d'importantes pullulations. Ces ravageurs nouveaux sont venus compléter une liste déjà longue d'une dizaine de phytophages majeurs au niveau des plantations d'agrumes du Bassin Méditerranéen; |
– | - un 2ème facteur non négligeable est présenté par un vieillissement des plantations et l'importance du co?t des méthodes culturales d'entretien qui sont comme la taille souvent négligées notamment pour les Citrus d'ornement ou de jardins familiaux. Ces facteurs ont alors pour corollaire le maintien d'arbres à frondaison dense assurant un développement optimum du ravageur; |
– | - enfin le développement d'une lutte chimique d'assurance, génératrice de déséquilibres fauniques particulièrement sensibles au niveau des acariens par élimination d'une partie de l'entomofaune prédatrice ou au niveau des cochenilles telles queAspidiotus nerii Bouché ouParlatoria pergandei Comst. par destruction de l'entomofaune parasitaire utile. |
104.
1. Concentrations of the neurotransmitter amines noradrenaline (NA), dopamine (DA), and 5-hydroxytryptamine (5-HT) and the acid metabolites homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in four regions of postmortem brains of demented patients with or without Alzheimer's disease (AD). 2. NA was deficient in the temporal cortex (BA 21) of AD, but not of non-AD, patients. 3. Caudate, in particular, had an impaired dopaminergic system in AD patients, with low HVA levels. 4. In all regions investigated [amygdala, caudate, putamen, temporal cortex (BA 21)] 5-HT was significantly depleted in AD patients, and 5-HIAA was also depleted in amygdala and caudate. 5. These results indicate that neurotransmitter systems other than cholinergic systems are also widely affected in AD and suggest that these deficits may also play an important role in determining the symptomatology of AD. 相似文献
105.
Serum antioxidant enzyme activity in Parkinson's disease 总被引:2,自引:0,他引:2
Jawahar Kalra Ali H. Rajput Subrahmanyam V. Mantha Kailash Prasad 《Molecular and cellular biochemistry》1992,110(2):165-168
Summary The activities of superoxide dismutase (SOD; EC 1.15.1.1) and glutathione peroxidase (GSHPx; EC 1.11.1.9.), the enzymes that metabolize the superoxide anion and hydrogen peroxide, respectively, were measured in serum
from healthy subjects and patients with Parkinson's disease (PD). The activities of SOD and GSHPx in patients with PD were higher than those in normal healthy individuals. These results suggest that the increased activities
of these enzymes could be due to oxidative stress in the initial stages of this disease. 相似文献
106.
Yoshiaki Sumiyoshi Masahiko Kikuchi Morishige Takeshita Kohiti Ohshima Yuhiti Masuda 《Virchows Archiv. B, Cell pathology including molecular pathology》1992,61(1):201-207
In Japan, histiocytic necrotizing lymphadenitis (Kikuchi’s disease) is a relatively common reactive lesion affecting lymph
nodes, but the histogenesis and pathogenesis of the disease have not been clarified. Alpha-interferon has a role in the body’s
defense against, viral infections. Using a polyclonal antibody to human alpha-interferon, we found numerous cells, mainly
histiocytes, containing alpha-interferon in affected foci in the lymph nodes from 24 patients with Kikuchi’s disease. Tubuloreticular
structures, thought by some authors to be associated with the production of interferon, were detected by electron microscopy
in histiocytes, activated lymphocytes and vascular endothelial cells in the affected foci. These results suggested that the
formation of tubuloreticular structures is a secondary phenomenon following stimulation by alpha-interferon. Further, the
activity of 2′–5′ oligoadenylate synthetase, which is induced by alpha-interferon and enhanced during the early or active
stage of viral infection, showed increased levels of activity in the active stage of Kikuchi’s disease and decreased to normal
levels in the convalescent stage 2 weeks later. These results suggested the possibility of a viral etiology for Kikuchi’s
disease. 相似文献
107.
Summary In order to evaluate the frequency of skin sensitivity to Storage Mites and the role of such sensitization in respiratory allergic disease in workers with occupational exposure to stored items we studied 217 dock workers, 93 farmers and 104 white collars.From the results of skin prick tests the sensitization to sole Storage Mites appears significantly higher among people working in docks or farms, compared with a control group. This confirms the role of the working environment in inducing sensitization to Storage Mites. Rhinitis and asthma however affect nearly always (27/29 cases) people with an associated sensitization to House Dust Mites. Further studies are needed to define the allergenic importance of Storage Mites in working environments. 相似文献
108.
High-level expression of a tobacco chitinase gene in Nicotiana sylvestris. Susceptibility of transgenic plants to Cercospora nicotianae infection 总被引:12,自引:0,他引:12
Jean-Marc Neuhaus Patricia Ahl-Goy Ursula Hinz Susan Flores Frederick Meins Jr. 《Plant molecular biology》1991,16(1):141-151
Endochitinases (E.C. 3.2.14, chitinase) are believed to be important in the biochemical defense of plants against chitin-containing fungal pathogens. We introduced a gene for class I (basic) tobacco chitinase regulated by Cauliflower Mosaic Virus 35S-RNA expression signals into Nicotiana sylvestris. The gene was expressed to give mature, enzymatically active chitinase targeted to the intracellular compartment of leaves. Most transformants accumulated extremely high levels of chitinase-up to 120-fold that of non-transformed plants in comparable tissues. Unexpectedly, some transformants exhibited chitinase levels lower than in non-transformed plants suggesting that the transgene inhibited expression of the homologous host gene. Progeny tests indicate this effect is not permanent. High levels of chitinase in transformants did not substantially increase resistance to the chitin-containing fungus Cercospora nicotiana, which causes Frog Eye disease. Therefore class I chitinase does not appear to be the limiting factor in the defense reaction to this pathogen. 相似文献
109.
Sections of two pollarded parkelms (Ulmus glabra) from Damsgaard, Bergen, west Norway have been studied. Changes in annual ring-width are attributed partly to management, namely pollarding, and partly to pathogenic attacks, probably by Ceratocystis ulmi. The oldest attack on the trees dates back to 1826: so far the oldest known record of Dutch elm disease in Norway. Pollarding may be an important factor in attacks by the pathogen within parkelms. A possible relationship between pollarding, the pathogen and the Neolithic elmfall is suggested. 相似文献
110.
F. Amijee E.J. Allans R.N. Waterhouse L.A. Glover A.M. Paton 《Biocontrol Science and Technology》1992,2(3):203-214
L‐forms of the halo blight pathogen, Pseudomonas syringae phaseolicola, were maintained in a medium which suppressed cell wall synthesis. These L‐forms, unlike revertants (walled forms derived from unstable L‐forms) and cell walled (parent) organisms, did not elicit a hypersensitive response in tobacco leaves. Association of L‐forms with Phaseolus vulgaris was established by seed imbibition in L‐form suspensions compared with appropriate control treatments (5% mannitol or heat‐killed cells). Seedling emergence and plant growth was not affected by L‐form imbibition. The association was detected by agglutination assays using polyclonal antibody. The L‐form association was localized to the lower shoot tissue and was progressively lost with age of plants. Plants with associated L‐forms had vigour and shoot weights equivalent to controls and showed no disease symptoms. The cell walled form could not be isolated from plants showing positive agglutination. On challenge with the pathogen, plants associated with L‐forms showed significantly less disease symptoms than controls. Stem extracts, from associated plants, were inhibitory to in vitro cultures of both L‐forms and parent forms of Ps. syr. phaseolicola. These results indicate that L‐form associations confer induced systemic resistance to bean plants and might be developed as novel biocontrol systems. 相似文献