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   202篇
  免费   14篇
  2022年   3篇
  2021年   2篇
  2020年   3篇
  2019年   5篇
  2018年   1篇
  2017年   16篇
  2016年   1篇
  2015年   7篇
  2014年   12篇
  2013年   18篇
  2012年   8篇
  2011年   9篇
  2010年   5篇
  2009年   3篇
  2008年   11篇
  2007年   11篇
  2006年   12篇
  2005年   6篇
  2004年   5篇
  2003年   11篇
  2002年   13篇
  2001年   9篇
  2000年   4篇
  1999年   4篇
  1998年   2篇
  1997年   2篇
  1996年   8篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   2篇
  1990年   3篇
  1989年   5篇
  1988年   2篇
  1987年   2篇
  1986年   1篇
  1978年   1篇
  1970年   1篇
  1965年   1篇
排序方式: 共有216条查询结果,搜索用时 289 毫秒
81.
82.
It is well known that parasitoids are attracted to volatiles emitted by host‐damaged plants; however, this tritrophic interaction may change if plants are attacked by more than one herbivore species. The larval parasitoid Cotesia flavipesCameron (Hymenoptera: Braconidae) has been used intensively in Brazil to control the sugarcane borer, Diatraea saccharalisFabricius (Lepidoptera: Pyralidae) in sugarcane crops, where Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), a non‐stemborer lepidopteran, is also a pest. Here, we investigated the ability of C. flavipes to discriminate between an unsuitable host (S. frugiperda) and a suitable host (D. saccharalis) based on herbivore‐induced plant volatiles (HIPVs) emitted by sugarcane, and whether multiple herbivory (D. saccharalis feeding on stalk + S. frugiperda feeding on leaves) in sugarcane affected the attractiveness of HIPVs to C. flavipes. Olfactometer assays indicated that volatiles of host and non‐host‐damaged plants were attractive to C. flavipes. Even though host‐ and non‐host‐damaged plants emitted considerably different volatile blends, neither naïve nor experienced wasps discriminated suitable and unsuitable hosts by means of HIPVs emitted by sugarcane. With regard to multiple herbivory, wasps innately preferred the odor blend emitted by sugarcane upon non‐host + host herbivory over host‐only damaged plants. Multiple herbivory caused a suppression of some volatiles relative to non‐host‐damaged sugarcane that may have resulted from the unaltered levels of jasmonic acid in host‐damaged plants, or from reduced palatability of host‐damaged plants to S. frugiperda. In conclusion, our study showed that C. flavipes responds to a wide range of plant volatile blends, and does not discriminate host from non‐host and non‐stemborer caterpillars based on HIPVs emitted from sugarcane. Moreover, we showed that multiple herbivory by the sugarcane borer and fall armyworm increases the attractiveness of sugarcane plants to the parasitoids.  相似文献   
83.
The aim of the ecospat package is to make available novel tools and methods to support spatial analyses and modeling of species niches and distributions in a coherent workflow. The package is written in the R language (R Development Core Team) and contains several features, unique in their implementation, that are complementary to other existing R packages. Pre‐modeling analyses include species niche quantifications and comparisons between distinct ranges or time periods, measures of phylogenetic diversity, and other data exploration functionalities (e.g. extrapolation detection, ExDet). Core modeling brings together the new approach of ensemble of small models (ESM) and various implementations of the spatially‐explicit modeling of species assemblages (SESAM) framework. Post‐modeling analyses include evaluation of species predictions based on presence‐only data (Boyce index) and of community predictions, phylogenetic diversity and environmentally‐constrained species co‐occurrences analyses. The ecospat package also provides some functions to supplement the ‘biomod2’ package (e.g. data preparation, permutation tests and cross‐validation of model predictive power). With this novel package, we intend to stimulate the use of comprehensive approaches in spatial modelling of species and community distributions.  相似文献   
84.
85.
The toxic effects of metals on the aquatic environment are documented and well known. Metals are able to unbalance the intracellular redox potential and, therefore, induce the oxidative stress in living organisms. In this study, the responses of glutathione [reduced (GSH) and oxidized (GSSG)] and the structurally GSH-related peptides phytochelatins 3 and 4 (PC3 and PC4) were examined in the marine dinoflagellate Lingulodinium polyedrum exposed to cadmium (Cd). A novel method for PC3 and PC4 synthesis is described here based on a Boc strategy, yielding peptides with purities higher than 97 %. Analytical detection of GSH, GSSG, PC3, and PC4 applying liquid chromatography-tandem mass spectrometry (LC-MS/MS) method had been developed and described as robust and accurate with a detection limit of nmol g?1 dry weight (DW) for PC3 and PC4. The intracellular levels of GSH and GSSG decreased dramatically over 24 and 48-h exposure to 18 μmol L?1 Cd. These decreases were followed by the enhancement of intracellular PC3 and PC4 levels, in which syntheses started to be detected after 2 and 8-h exposure, respectively. Moreover, the PC4/PC3 ratio reached its maximum over 24-h exposure, being 8 to 75-fold higher than the one observed for other microalgae. This seems to be an efficient strategy of L. polyedrum to be protected against Cd environment contamination, since PC4 has more chelating sites and is structurally more stable than PC2 and PC3, the most abundant for other microalgae.  相似文献   
86.
This study reports for the first time the extraction and quantification of sterols in six species of brown macroalgae from Antarctica: Adenocystis utricularis, Ascoseira mirabilis, Cystosphaera jacquinotii, Desmarestia anceps, Desmarestia antarctica, and Himantothallus grandifolius. Ultrasound irradiation was used as a promotor to extract sterols from algal biomass. The extracts were analyzed by high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for sterol quantization (ergosterol, brassicasterol, fucosterol, β-sitosterol, campesterol, cholesterol, and stigmasterol). In general, fucosterol was the most abundant (6.60 to 48.13 mg kg?1), followed by β-sitosterol (5.29 to 16.49 mg kg?1), stigmasterol (2.69 to 14.84 mg kg?1) in five of the six examined algae. The sterol campesterol was found in lower concentrations (0.07 to 0.15 mg kg?1) in all studied samples.  相似文献   
87.
A spirocyclic class of ROMK inhibitors was developed containing a structurally diverse heterocyclic sulfone moiety and spirocyclic core starting from lead 1. These compounds not only displayed exquisite ROMK potency but significantly improved selectivity over hERG. The lead compounds were found to have favorable pharmacokinetic properties and displayed robust diuretic, natriuretic and blood pressure lowering effects in spontaneously hypertensive rats.  相似文献   
88.
Popillia japonica Newman (Coleoptera: Scarabaeidae) is a highly polyphagous invasive beetle originating from Japan. This insect is highly resilient and able to rapidly adapt to new vegetation. Insect-associated microorganisms can play important roles in insect physiology, helping their hosts to adapt to changing conditions and potentially contributing to an insect's invasive potential. Such symbiotic bacteria can be part of a core microbiota that is stably transmitted throughout the host's life cycle or selectively recruited from the environment at each developmental stage. The aim of this study was to investigate the origin, stability and turnover of the bacterial communities associated with an invasive population of P. japonica from Italy. Our results demonstrate that soil microbes represent an important source of gut bacteria for P. japonica larvae, but as the insect develops, its gut microbiota richness and diversity decreased substantially, paralleled by changes in community composition. Notably, only 16.75% of the soil bacteria present in larvae are maintained until the adult stage. We further identified the micro-environments of different gut sections as an important factor shaping microbiota composition in this species, likely due to differences in pH, oxygen availability and redox potential. In addition, P. japonica also harboured a stable bacterial community across all developmental stages, consisting of taxa well known for the degradation of plant material, namely the families Ruminococcacae, Christensenellaceae and Lachnospiraceae. Interestingly, the family Christensenallaceae had so far been observed exclusively in humans. However, the Christensenellaceae operational taxonomic units found in P. japonica belong to different taxonomic clades within this family.  相似文献   
89.
From April of 2000 to May of 2003, 28 consecutive patients with chronic osteomyelitis of the lower extremity underwent surgical debridement and reconstruction with anterolateral thigh perforator flaps (six cases were combined with vastus lateralis muscle flaps). All wounds were open for a minimum period of 6 weeks (average, 24.7 months; range, 6 weeks to 52 months). The average patient age was 42.8 years (range, 18 to 71 years), there were 21 male and seven female patients, and the average follow-up period was 18.2 months (range, 5 to 41 months). The cause of injury was an open fracture in 10 cases, secondary wound complications after reduction in eight cases, and diabetic foot in 10 cases. The surface defects ranged from 50 to 153 cm. The wounds were debrided an average of 2.5 times and then reconstructed with flap and treated with antibiotics for 6 weeks. Antibiotic beads were used in six cases and secondary bone graft procedures were performed in seven cases 3 months after the flap coverage. All 28 flaps were successful without any signs of recurrences or persistent osteomyelitis, but partial wound dehiscence was observed during early rehabilitation in two cases suspected of delayed healing caused by diabetes. These wounds healed spontaneously. All patients achieved acceptable gait function after rehabilitation. No debulking procedure was necessary in any case. Although the muscle flap is known to provide superior vascular supply, the type of flap used for coverage seems to be less critical in the final outcome, provided that total debridement and obliteration of dead spaces are achieved. A well-vascularized anterolateral thigh perforator flap was successfully used to combat infection and bring stability to wounds with chronic osteomyelitis.  相似文献   
90.
Fibronectin is a large cell adhesion molecule that is composed of several functional domains. The cell-binding domain that binds to cell surface integrins consists of repeated homologous type III modules. In this study, recombinant fragments from the cell-binding domain of human fibronectin that participate in a newly characterized fibronectin-fibronectin interaction with FNIII1 were crystallized. In each case, the crystals had more than one fibronectin fragment in the asymmetric unit. Crystals of FNIII10-11 grew in the space group C2 with a = 117.1 A, b = 38.6 A, c = 80.6 A, beta = 97.2 degrees, and two molecules in the asymmetric unit. These crystals diffracted to 2.5 A resolution. Fragment FNIII8-11 and a shorter fragment, FNIII8-10, crystallized in hexagonal space groups with large unit cells and two to four molecules per asymmetric unit. Even very large crystals of these fragments did not diffract beyond 4 A. The crystal packing for this collection of fibronectin fragments suggests conformational flexibility between linked type III modules. The functional relevance of this flexibility for elongated versus compact models of the cell-binding domain of fibronectin is discussed.  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