全文获取类型
收费全文 | 1686篇 |
免费 | 64篇 |
国内免费 | 106篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 28篇 |
2018年 | 41篇 |
2017年 | 26篇 |
2016年 | 71篇 |
2015年 | 242篇 |
2014年 | 122篇 |
2013年 | 87篇 |
2012年 | 66篇 |
2011年 | 57篇 |
2010年 | 45篇 |
2009年 | 55篇 |
2008年 | 58篇 |
2007年 | 74篇 |
2006年 | 85篇 |
2005年 | 62篇 |
2004年 | 44篇 |
2003年 | 51篇 |
2002年 | 57篇 |
2001年 | 39篇 |
2000年 | 44篇 |
1999年 | 41篇 |
1998年 | 43篇 |
1997年 | 54篇 |
1996年 | 37篇 |
1995年 | 44篇 |
1994年 | 37篇 |
1993年 | 24篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 30篇 |
1989年 | 22篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1856条查询结果,搜索用时 31 毫秒
21.
The development of plants depends on the photoperiod length, light intensity, temperature, and length of light day integral. The reaction of a plant to the day length or daily light integral can depend on both the range of studied light intensities and photoperiod. Based on the data concerning the effects of light and thermal integrals on the developmental rate of plants of different photoperiodic groups, a photothermal model of plant development was proposed. The model was used to calculate the lengths of optimal photoperiods and ranges of daily temperature gradients ensuring the highest developmental rate of some plants, such as soybean, wheat, cucumber, and barley. 相似文献
22.
Sherwin S. Desser 《New Zealand journal of zoology.》2013,40(1):77-78
Abstract Quantitative and biochemical observations were made on the peripheral blood of a hibernating female tuatara. The packed red cell volume (haematocrit) was 30%. There were about 260 000 erythrocytes and 5000 leucocytes per mm3 blood. Lymphocytes and neutrophils were the predominant leucocytes, followed by monocytes, eosinophils, and basophils. Haemoglobin, plasma protein, glucose, sodium, potassium, cholesterol, and triglyceride levels were determined. These haematological data are compared with data from the same animal obtained during the active summer period. 相似文献
23.
Muwaffaq Ramadan Karajeh 《Archives Of Phytopathology And Plant Protection》2013,46(20):2492-2500
Saccharomyces cerevisiae is a promising plant growth-promoting yeast for different crops. Applicability of S. cerevisiae as a biocontrol agent of the root-knot nematode (Meloidogyne javanica) was investigated on cucumber under growth-room and field conditions. The yeast S. cerevisiae similar to the nematicide, Ethoprophos, when applied as a rhizospheric soil drench treatment led to an obvious reduction of root galling caused by M. javanica and resulted in reducing the nematode reproduction ability on cucumber under growth room and field conditions. The yeast was more effective at 10 than at 5?g/l. Furthermore, the application of S. cerevisiae resulted in improving cucumber plant growth and increasing its fruit yield. High content of total phenolics in cucumber roots of S. cerevisiae-treated plants and hydrogen peroxide-treated plants gives a clue on the ability of the yeast to induced plant resistance in a similar way to exogenous hydrogen peroxide. 相似文献
24.
Olusola O. Odedara Emily I. Ayo-John Moyosore M. Gbuyiro Felicia O. Falade Sunday E. Agbebi 《Archives Of Phytopathology And Plant Protection》2013,46(7):840-845
A field survey was conducted in eight local government areas (LGA) of Ogun state, Nigeria to assess the incidence of viral diseases of yams in the areas. Leaf samples were collected from 90 yam plants which were either symptomatic or asymptomatic. These were bulked into 45 during serological tests and the viruses indexed include yam mosaic virus (YMV); Dioscorea alata bacilliform virus (DaBV) and cucumber mosaic virus (CMV). DaBV was the most prevalent virus on the field with incidence of 48.9% (22/45) followed by YMV which occurred in 42.2% (19/45). CMV had the lowest percentage of incidence; 2.2% (1/45). Of all the LGAs visited, Abeokuta north and Abeokuta south had the highest incidence of YMV and DaBV, respectively. Mixed virus infections were also detected. 相似文献
25.
A new subfamily Rudisiricinae Gao, Rasnitsyn, Ren & Shih, n. subfam. and a new genus Rudisiricius Gao, Rasnitsyn, Ren & Shih, n. gen. with three new species R. belli Gao, Rasnitsyn, Ren & Shih n. sp., R. crassinodus Gao, Rasnitsyn, Ren & Shih, n. sp., and R. celsus Gao, Rasnitsyn, Ren & Shih, n. sp. are described and illustrated from the family Praesiricidae. The type specimens were collected from the Late Jurassic to Early Cretaceous Yixian Formation, northeastern China. The new subfamily also includes Aulidontes Rasnitsyn from the Upper Jurassic of Karatau in Kazakhstan. This is the first record of Praesiricidae in China. These well-preserved nearly-complete new fossils reported here provide additional material and structure characters about this family, which helps filling some gap in the evolution of Lower Hymenoptera. 相似文献
26.
Enrique Peñalver 《法国昆虫学会纪事》2013,49(1-2):138-147
During a palaeontological excavation of amber at the site named San Just, in the Utrillas-Escucha area of Teruel Province, northeastern Spain, a rich fauna from the Albian (Early Cretaceous) was discovered. Among it, three specimens of Thysanoptera were found that are here attributed to the new genus Hispanothrips n. gen. in the family Stenurothripidae Bagnall 1923. Phylogenetic analyses were conducted that support the resurrection of the family Stenurothripidae and its replacement for Adiheterothripidae Shumsher 1946. 相似文献
27.
28.
In this paper we present a sampling framework for RNA structures of fixed topological genus. We introduce a novel, linear time, uniform sampling algorithm for RNA structures of fixed topological genus g , for arbitrary g>0. Furthermore we develop a linear time sampling algorithm for RNA structures of fixed topological genus g that are weighted by a simplified, loop-based energy functional. For this process the partition function of the energy functional has to be computed once, which has O(n2) time complexity. 相似文献
29.
Angelo Bolzern Daniel Burckhardt Ambros Hänggi 《Zoological Journal of the Linnean Society》2013,168(4):723-848
The taxonomy and systematics of European house spiders, currently constituting the ill‐defined Tegenaria?Malthonica complex (including Aterigena) in the family Agelenidae, are revised. In Europe four monophyletic genera and 81 species are defined. One genus, Eratigena gen. nov. , and seven species are described as new; at species level 17 new synonyms and 20 new combinations are proposed, and the original combination of 14 species is reinstated. Five species could not be placed (incertae sedis) because of insufficient material and one taxon is regarded as ‘nomen dubium’. On the basis of a detailed morphological assessment, 88 characters were chosen for a cladistic analysis. Phylogenetically informative characters include mostly spination patterns as well as spinneret and genital structures. In addition to morphology, three gene sections [cytochrome c oxidase subunit 1 (CO1), nicotinamide adenine dinucleotide dehydrogenase subunit 1 (NADH1) 28S] were analysed. Morphological and molecular analyses were performed individually and in combination applying maximum parsimony and Bayesian tree search methods. In all resulting trees Malthonica and Tegenaria in their present composition are either polyphyletic or paraphyletic. Consequently, we redefined the two genera and erected a new genus, Eratigena gen. nov. Identification keys are provided for the European agelenid genera as well as for the European species of Tegenaria and Eratigena gen. nov. The genera and most of the constituent species are described and illustrated. The new classification has also been applied to some extra European members of the Tegenaria‐Malthonica complex resulting in additional three new synonyms, seven reversals to the original combination, and four new combinations. © 2013 The Linnean Society of London 相似文献
30.
Ecnomus mennelli sp.n. from Lake Naivasha, Kenya, belongs to the natalensis‐group. E. thomasseti was also found at the lake, and these are the first records of Trichoptera from Naivasha. Adults and larvae of both species were collected, and an analysis of the gut contents of the larvae showed them to be mainly predator y on small invertebrates. The ecological requirements and distribution of the African species of Ecnomus are discussed. 相似文献