全文获取类型
收费全文 | 7437篇 |
免费 | 876篇 |
国内免费 | 2018篇 |
出版年
2024年 | 53篇 |
2023年 | 260篇 |
2022年 | 250篇 |
2021年 | 346篇 |
2020年 | 381篇 |
2019年 | 440篇 |
2018年 | 349篇 |
2017年 | 347篇 |
2016年 | 397篇 |
2015年 | 393篇 |
2014年 | 455篇 |
2013年 | 557篇 |
2012年 | 444篇 |
2011年 | 422篇 |
2010年 | 339篇 |
2009年 | 403篇 |
2008年 | 408篇 |
2007年 | 452篇 |
2006年 | 383篇 |
2005年 | 317篇 |
2004年 | 300篇 |
2003年 | 242篇 |
2002年 | 246篇 |
2001年 | 206篇 |
2000年 | 169篇 |
1999年 | 178篇 |
1998年 | 160篇 |
1997年 | 119篇 |
1996年 | 129篇 |
1995年 | 103篇 |
1994年 | 103篇 |
1993年 | 119篇 |
1992年 | 96篇 |
1991年 | 89篇 |
1990年 | 91篇 |
1989年 | 64篇 |
1988年 | 66篇 |
1987年 | 47篇 |
1986年 | 62篇 |
1985年 | 69篇 |
1984年 | 53篇 |
1983年 | 27篇 |
1982年 | 42篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1976年 | 15篇 |
1975年 | 14篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
71.
72.
73.
A. K. Watson 《Journal of nematology》1986,18(2):149-153
The knapweed nematode, Subanguina picridis, forms galls on the leaves, stems, and root collar of Russian knapweed, Acroptilon repens. After being revived from a dormant, cryptobiotic state, second-stage juveniles required at least 1 month in a free-living state before becoming infective. Galls were induced on relatively slow-growing host plants that retained their apical meristems at or near the soil surface for 2-5 weeks. Galls developed extensive areas of nutritive tissue. The nematode was introduced from the Soviet Union and released in Canada for the biological control of Russian knapweed. 相似文献
74.
The chlorellavorous bacterium . "Vampirovibrio chlorellavorus" Gromov et Mamkaeva, grows only by killing and consuming the cell contents of species of the green alga Chlorella Beijerinck. Of the 76 algal strains examined in this study, the bacterium attacks all 31 strains of the species C. vulgaris. C. sorokiniana, and C. kessleri, but attacks only two of 39 strains of nine other Chlorella species. Neither of two Prototheca strains was susceptible to attack. This narrow host specificity may be related to cell surface properties . 相似文献
75.
Sensitivity and host efficiency of susceptible (''Lee 68'', ''Coker 156'') and resistant (''Bragg'', ''Centennial'', ''Forrest'', ''Lee 74'') soybean (Glycine max (L.) Merr.) cultivars for races of Meloidogyne incognita (Mi) were determined in greenhouse experiments. Eight Mi populations collected from the southeastern United States were utilized. All Mi races reproduced readily on Lee 68 and Lee 74 and moderately on Forrest and Bragg. Coker 156 exhibited resistance to races 1 and 2, and some race 3 populations, but was very susceptible to certain race 3 and 4 populations. Reproduction of all races was lowest on Centennial. Forrest and Centennial shoot growth was not significantly suppressed by any race. There were no distinct differences in virulence between races except for a race 3 population which reproduced readily on all cultivars, stunting their growth. Considerable variation in reproduction existed within races 1 and 3. 相似文献
76.
Brant J. Bassam Barry G. Rolfe Michael A. Djordjevic 《Molecular & general genetics : MGG》1986,203(1):49-57
Summary A 6.7 kb HindIII fragment from the Sym-plasmid of strain NGR234 was found to code a nodD-like gene flanked by two loci which were required for siratro host range. Transfer of the 6.7 kb fragment from NGR234 to R. trifolii strain ANU843 conferred extended host range ability to this strain on siratro plants but not to other plants normally nodulated by strain NGR234. Tn5 mutagenesis of the 6.7 kb fragment showed that insertions located into loci flanking the nodD-like gene abolished the extended host range phenotype. A hybridization probe spanning one of the host specificity loci was shown to hybridize to three specific bands in the NGR234 genome. Complementation and DNA hybridization data showed that the nodD-like gene of strain NGR234 was functionally similar to that in R. trifolii. The introduction to R. trifolii of the 6.7 kb HindIII fragment containing Tn5 insertions located in the nodD-like gene did not abolish the ability to extend the host range of R. trifolii to siratro plants. However, transfer of the 6.7 kb HindIII to R. trifolii derivatives containing Tn5 insertions into either nodA, B or C or other R. trifolii nod genes failed to confer siratro nodulation to these recipients. Reconstruction experiments showed that the 6.7 kb fragment from strain NGR234 and the 14 kb nodulation region of R. trifolii could induce the nodulation of siratro plants when introduced together into Sym-plasmid-cured Rhizobium strains. 相似文献
77.
78.
The parasitoidEphedrus cerasicola Starý oviposited in all 4 nymphal instars and in newly moulted adults ofMyzus persicae (Sulzer). The different host categories were offered with no choice. The duration of an oviposition increased with the age of nymphs, being about 13, 18, 21, 22, and 17 s from 1 st instars to adults, respectively. Observations of number of stabbing attacks prior to oviposition, percent of the encounters not resulting in oviposition, time from first encounter to oviposition, handling time and aphid defensive behaviour also indicated that 1 st instarM. persicae are most easily parasitized. The behaviour ofE. cerasicola in encounters with unparasitized and parasitized hosts, suggested that the parasitoid could discriminate. In encounters with parasitized 1 st to 4th instar aphids,E. cerasicola used only the antennae in 80% of the encounters that resulted in discrimination. 相似文献
79.
80.
DAVID HOLLIS 《Zoological Journal of the Linnean Society》1985,83(4):325-342
The genus Parapsylla (Homoptera: Psylloidea) is redescribed and placed in the Diaphorininae of the Family Aphalaridae. Its relationships within this subfamily are discussed. The genus Agmapsylla syn. nov. is placed into the synonymy of Parapsylla , and Pennavena syn. nov. and Eudiaphorina syn. nov. are placed into the synonymy of Diaphorina. The eight known species of Parapsylla are distributed in southern Africa and upland areas of East Africa. Host plant relationships are not clearly established but the genus appears to be associated with species of Maytenus (Celastraceae), Olinia (Oliniaceae) and possibly Olea (Oleaceae) and Syzygium (Myrtaceae). Parapsylla relicta syn. nov, and A. aureus syn. nov. are placed into the synonymy of Arytaina capensis. Parapsylla capensis comb. nov. is transferred from Arytaina, Parapsylla valens comb. nov. is transferred from Diaphorina , and the following new species are described: P. angolensis sp. nov., P. eafra sp. nov., P. huila sp. nov., P. marginipennis sp. nov., P. rufa sp. nov. and P. theroni sp. nov. 相似文献