全文获取类型
收费全文 | 10603篇 |
免费 | 899篇 |
出版年
2023年 | 37篇 |
2022年 | 89篇 |
2021年 | 156篇 |
2020年 | 115篇 |
2019年 | 156篇 |
2018年 | 198篇 |
2017年 | 170篇 |
2016年 | 266篇 |
2015年 | 432篇 |
2014年 | 441篇 |
2013年 | 634篇 |
2012年 | 725篇 |
2011年 | 678篇 |
2010年 | 468篇 |
2009年 | 430篇 |
2008年 | 580篇 |
2007年 | 628篇 |
2006年 | 548篇 |
2005年 | 558篇 |
2004年 | 561篇 |
2003年 | 553篇 |
2002年 | 629篇 |
2001年 | 128篇 |
2000年 | 92篇 |
1999年 | 140篇 |
1998年 | 156篇 |
1997年 | 145篇 |
1996年 | 128篇 |
1995年 | 109篇 |
1994年 | 100篇 |
1993年 | 101篇 |
1992年 | 104篇 |
1991年 | 80篇 |
1990年 | 70篇 |
1989年 | 64篇 |
1988年 | 50篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 53篇 |
1984年 | 67篇 |
1983年 | 59篇 |
1982年 | 95篇 |
1981年 | 84篇 |
1980年 | 63篇 |
1979年 | 55篇 |
1978年 | 52篇 |
1977年 | 51篇 |
1976年 | 51篇 |
1975年 | 35篇 |
1973年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Beaubois E Girard S Lallechere S Davies E Paladian F Bonnet P Ledoigt G Vian A 《Plant, cell & environment》2007,30(7):834-844
992.
Luis J. Lpez Giraldo Mickaël Laguerre Jrme Lecomte Maria-Cruz Figueroa-Espinoza Nathalie Barouh Bruno Bara Pierre Villeneuve 《Enzyme and microbial technology》2007,41(6-7):721-726
Chlorogenic acid (5-caffeoylquinic acid or 5-CQA) is an hydrophilic phenolic compound with antioxidant properties. Because of its high polarity, its antioxidant properties may be altered when formulated in oil based food or cosmetic preparations. Therefore, there is an interest in trying to enhance its hydrophobicity by grafting of an aliphatic chain. Such lipophilization reactions can be generally achieved through enzymatic catalysis. Our study consisted in synthesizing fatty cholorogenate esters in a two steps reaction. Firstly, 5-CQA was chemically esterified by methanol using an Amberlite IR120 H resin to obtain methyl chlorogenate that is more soluble in the fatty alcohols than 5-CQA. Secondly, this chlorogenate intermediate was transesterified with fatty alcohols of various chain lengths (C4, C8, C12, or C16) in the presence of Candida antarctica B lipase. Under optimal reaction conditions (aw = 0.05; 5% (w/w) of biocatalyst), the transesterification rates were until two-fold higher than in the direct lipase-catalyzed esterification of chlorogenic acid by the same alcohols. The two-step reaction overall yield was between 61 and 93% depending on the alcohol chain length, whereas it was 40–60% for the direct esterification with the same alcohols. 相似文献
993.
Gle Corine; Del Amo Yolanda; Bec Beatrice; Sautour Benoit; Froidefond Jean-Marie; Gohin Francis; Maurer Daniele; Plus Martin; Laborde Pierre; Chardy Pierre 《Journal of plankton research》2007,29(11):999-1014
Phytoplankton dynamics were assessed in the macrotidal ecosystemof Arcachon Bay through high-frequency surveys over a 5-yearperiod in order to characterize typology of environmental conditionsat the onset of the productive period. Temporal variations ofhydrological and biological parameters were examined in externaland internal waters of the lagoon, during the winter–springperiods from 1999 to 2003. An additional survey was performedduring winter–spring 2005 in order to study the verticalstructure of the water column. The occurrence of winter phytoplanktonblooms between January and March emerged as a recurrent event.The early onset of the productive period is influenced by thebiological functioning of adjacent Bay of Biscay oceanic waters.It is hypothesized that under a propitious hydrodynamic regime,phytoplankton inocula from the Bay of Biscay enter in the ArcachonBay where cells presumably find favourable conditions for theirfast development. The timing of the onset of those winter bloomsin Arcachon Bay seems to be mainly influenced by the presenceof anticyclonic weather conditions (associated with an increasein incident irradiance) during late winter (i.e. by February),while the water column does not show any particular stabilizationnor stratification liable to facilitate the onset of these blooms.Moreover, these winter blooms dominated by diatoms led to anearly nutrient depletion which could have inevitable consequenceson the structuration of the food web during spring and summer. 相似文献
994.
El Abdllaoui A Auger P Kooi BW Bravo de la Parra R Mchich R 《Mathematical biosciences》2007,210(1):335-354
We consider a predator-prey model in a two-patch environment and assume that migration between patches is faster than prey growth, predator mortality and predator-prey interactions. Prey (resp. predator) migration rates are considered to be predator (resp. prey) density-dependent. Prey leave a patch at a migration rate proportional to the local predator density. Predators leave a patch at a migration rate inversely proportional to local prey population density. Taking advantage of the two different time scales, we use aggregation methods to obtain a reduced (aggregated) model governing the total prey and predator densities. First, we show that for a large class of density-dependent migration rules for predators and prey there exists a unique and stable equilibrium for migration. Second, a numerical bifurcation analysis is presented. We show that bifurcation diagrams obtained from the complete and aggregated models are consistent with each other for reasonable values of the ratio between the two time scales, fast for migration and slow for local demography. Our results show that, under some particular conditions, the density dependence of migrations can generate a limit cycle. Also a co-dim two Bautin bifurcation point is observed in some range of migration parameters and this implies that bistability of an equilibrium and limit cycle is possible. 相似文献
995.
996.
997.
A novel family of lectins evolutionarily related to class V chitinases: an example of neofunctionalization in legumes
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A lectin has been identified in black locust (Robinia pseudoacacia) bark that shares approximately 50% sequence identity with plant class V chitinases but is essentially devoid of chitinase activity. Specificity studies indicated that the black locust chitinase-related agglutinin (RobpsCRA) preferentially binds to high-mannose N-glycans comprising the proximal pentasaccharide core structure. Closely related orthologs of RobpsCRA could be identified in the legumes Glycine max, Medicago truncatula, and Lotus japonicus but in no other plant species, suggesting that this novel lectin family most probably evolved in an ancient legume species or possibly an earlier ancestor. This identification of RobpsCRA not only illustrates neofunctionalization in plants, but also provides firm evidence that plants are capable of developing a sugar-binding domain from an existing structural scaffold with a different activity and accordingly sheds new light on the molecular evolution of plant lectins. 相似文献
998.
999.
Julier B Huguet T Chardon F Ayadi R Pierre JB Prosperi JM Barre P Huyghe C 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2007,114(8):1391-1406
In many legume crops, especially in forage legumes, aerial morphogenesis defined as growth and development of plant organs,
is an essential trait as it determines plant and seed biomass as well as forage quality (protein concentration, dry matter
digestibility). Medicago truncatula is a model species for legume crops. A set of 29 accessions of M. truncatula was evaluated for aerial morphogenetic traits. A recombinant inbred lines (RILs) mapping population was used for analysing
quantitative variation in aerial morphogenetic traits and QTL detection. Genes described to be involved in aerial morphogenetic
traits in other species were mapped to analyse co-location between QTLs and genes. A large variation was found for flowering
date, morphology and dynamics of branch elongation among the 29 accessions and within the RILs population. Flowering date
was negatively correlated to main stem and branch length. QTLs were detected for all traits, and each QTL explained from 5.2
to 59.2% of the phenotypic variation. A QTL explaining a large part of genetic variation for flowering date and branch growth
was found on chromosome 7. The other chromosomes were also involved in the variation detected in several traits. Mapping of
candidate genes indicates a co-location between a homologue of Constans gene or a flowering locus T (FT) gene and the QTL
of flowering date on chromosome 7. Other candidate genes for several QTLs are described.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
1000.
Superparasitism refers to a female parasitoid laying an egg in a host already parasitized by a conspecific. In solitary species, only one offspring per host is expected to complete development, hence the game. Hosts are often clumped in patches and several females exploiting such an aggregate of resource make its state change over time, hence the dynamical character of the game. Two coupled questions arise: (i) Is it worth accepting a parasitized host? (ii) When to leave the host patch? Through these decisions (i) the competition for healthy hosts and (ii) the trade-off between leaving in quest of a better patch and staying to make the patch less profitable for other parasitoids (this is a way to lower superparasitism likely to occur after having left the patch) are addressed. The aim of this work is to characterize a strategy that would be evolutionarily relevant in such a situation, as it directly concerns females' reproductive success. Investigating a (synchronous) nonzero-sum two-player differential game allows us to characterize candidate dynamic evolutionarily stable policies in terms of both oviposition and patch-leaving decisions. For that matter, the game is (in the most part of the parameter space) completely solved if the probability that superparasitism succeeds is assumed to be close to one-half, a fair value under direct competition. The strategic equilibrium consists, for each females, in (i) superparasitizing consistently upon arrival on the patch, and (ii) leaving when the loss of fitness due to superparasitism likely to occur after its departure is reduced to zero. The competing females are thus expected to leave the patch as they arrived: synchronously. Superparasitism does not necessarily lead to a war of attrition. 相似文献