全文获取类型
收费全文 | 1198篇 |
免费 | 70篇 |
国内免费 | 138篇 |
专业分类
1406篇 |
出版年
2023年 | 14篇 |
2022年 | 13篇 |
2021年 | 13篇 |
2020年 | 25篇 |
2019年 | 19篇 |
2018年 | 18篇 |
2017年 | 25篇 |
2016年 | 26篇 |
2015年 | 24篇 |
2014年 | 44篇 |
2013年 | 64篇 |
2012年 | 40篇 |
2011年 | 41篇 |
2010年 | 31篇 |
2009年 | 51篇 |
2008年 | 64篇 |
2007年 | 57篇 |
2006年 | 75篇 |
2005年 | 60篇 |
2004年 | 61篇 |
2003年 | 53篇 |
2002年 | 36篇 |
2001年 | 45篇 |
2000年 | 38篇 |
1999年 | 44篇 |
1998年 | 41篇 |
1997年 | 40篇 |
1996年 | 23篇 |
1995年 | 35篇 |
1994年 | 20篇 |
1993年 | 22篇 |
1992年 | 25篇 |
1991年 | 28篇 |
1990年 | 45篇 |
1989年 | 27篇 |
1988年 | 24篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有1406条查询结果,搜索用时 15 毫秒
191.
Minogue PJ Miwa M Rockwood DL Mackowiak CL 《International journal of phytoremediation》2012,14(10):1010-1023
Various progenies of Eucalyptus grandis and E. amplifolia, and clones of Populus deltoides, were evaluated for plant removal of nitrogen (N) and phosphorus (P) for 26 months at a municipal waste spray field in north Florida. Tertiary treated wastewater containing 2.73 mg L(-1) nitrate N and 0.30 mg L(-1) total P was applied using sprinkler irrigation (93.8 m3 ha(-1) d(-1)) to fast growing trees utilized for bioenergy. Eucalyptus amplifolia and E. grandis survived and grew very poorly as the result of severe winter injury in two successive years and were not evaluated for nutrient removal. Survival and growth of P. deltoides demonstrated suitability for phytoremediation, and selected clones were evaluated for biomass and nutrient content. Removals of total N (TN) and total P (TP) were greatest for main stem (36% and 44%, respectively) and foliage (44% and 36%, respectively). Low biomass producing clones generally had higher nutrient concentrations, but high biomass producing clones removed more TN and TP. Approximately 789 kg ha(-1) TN and 103 kg ha(-1) TP were removed by the highest biomass producing P. deltoides clone, representing 215% of N and 615% of P inputs. 相似文献
192.
193.
Jerry Mozoruk Laura E. Hunnicutt Wayne B. Hunter Michael G. Bausher 《Journal of plant physiology》2008,165(5)
We have identified a novel gene designated CsV03-3 from Citrus sinensis (L.) Osbeck that encodes a 50 amino acid polypeptide with a predicted molecular mass of 5.4 kDa and a pI of 3.7. CsV03-3 expression is up-regulated by application of methyl jasmonate, salicylic acid, and abscisic acid as well as by abiotic stress and insect herbivory. CsV03-3 belongs to a small gene family consisting of at least three other closely related members (CsV03-1, CsV03-2, and CsV03-4) whose expression is also responsive to phytohormone application and abiotic stress. Sequence similarity searches of the public databases were unsuccessful in finding sequence homologs to CsV03-3 or any CsV03 family member; however, structural prediction models coupled with model comparison to Protein Data Bank folds indicated that the predicted polypeptide encoded by CsV03-3 has structural similarity to proteins with nucleic acid binding activity. Gel mobility shift assays performed on recombinant CsV03-3 protein demonstrated active binding with dsDNA and, to a lesser extent, ssDNA. Based on the phytohormone-inducible expression patterns, the ability to bind nucleic acids, and the lack of significant sequence homology to public databases, we propose that CsV03-3 and its related homologs defines a new class of nucleic acid binding proteins that are responsive to defense and stress signaling in woody perennials. 相似文献
194.
The work reported in this paper aims at developing an accurate, specific, repeatable and robust HPTLC method for the determination of galanthamine in different Amaryllidaceae plant extracts. 相似文献
195.
Stephen L. Lapointe Wayne B. Hunter Rocco T. Alessandro 《Agricultural and Forest Entomology》2004,6(4):251-257
Abstract 1 External gland openings and associated structures on the elytra of teneral and mature Diaprepes root weevils, Diaprepes abbreviatus (L.), were elucidated by scanning electron microscopy (SEM). 2 There were clear differences between teneral, callow adults and fully mature adults. In the field, teneral adults remain in the pupal chamber in the soil until sclerotization of the cuticle is complete or nearly so. 3 Phenotypic variation of the elytra in this species consists of varying patterns and coloration of scaled intervals between a variable number of raised ridges devoid of scales. In addition to being thinner and lighter in colour than fully mature adults, the elytra of teneral adults were devoid of waxy hydrocarbon secretions. 4 External gland openings at the base of each scale were observed on teneral elytra and mature elytra washed with methylene chloride. 5 SEM evidence to document the production of waxy filaments by these glands and partial characterization of these by gas chromatography and mass spectrometry are presented. 相似文献
196.
Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during acclimatization. Plantlets were transferred to ex vitro conditions to study selected physiological changes and growth performance during acclimatization and post-acclimatization.
The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined
by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM).
Chile pepper plantlets became acclimatized within 6 days after transplantation. During this period, physiological adjustments
occurred, which were critical for plantlet survival. After initial ex vitro transplanting, plantlets experienced water deficit [leaf wilting and reduced relative water content (RWC)], which corresponded
with reduced stomatal conductance (g
s) and transpiration (E), and an increase in stomatal resistance (r
s). Thus, leaf stomata that developed in vitro were functional ex vitro. Because of this stomatal control, plantlets minimized transplant shock, recovered and survived. Prior to transplanting,
plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, g
s, E, and A were significantly lower two days after transplanting. However, within 6 days after transplanting, plantlets recovered and
became photoautotrophic – attaining high A, g
s, and E. Water use efficiency was initially low during the first days after transplanting, but increased dramatically at the end
of the acclimatization period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization
closely correlated with increased plantlet growth.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
197.
Chongwei Zhang Yanhua Lu Lin Tao Xinyi Tao Xiaochun Su Dongzhi Wei 《Journal of enzyme inhibition and medicinal chemistry》2013,28(1):83-90
The inhibitory effects of nobiletin and hesperidin from citrus peel crude extracts on tyrosinase diphenolase activity are evaluated. IC50 of nobiletin and hesperidin is 1.49 mM and 16.08 mM, respectively and their inhibition mechanism is competitive type with Ki = 2.82 mM and noncompetitive with Ki = 9.16 mM, respectively. Crude extracts from citrus peel (C. unshiu Marc.) were extracted with 95% ethanol and fractionated by petroleum ether (PCPE). The ethanol phase (ECPE) was further desorbed from macroporous adsorption resin (FGRE). Their IC50 values were 8.09 mg/mL, 7.53 mg/mL and 4.80 mg/mL, respectively. Their inhibition on melanogenesis in B16 mouse melanoma cells was also evaluated. FGRE showed a significant inhibition (42.5% at 31.25 μg/mL, p < 0.01) while hesperidin showed almost no inhibition. Nobiletin and PCPE give efficacious antiproliferation effects on B16 mouse melanoma cell with IC50 values 88.6 μM and 62.96 μg/mL, respectively, by the MTT test. Hesperidin and other crude extracts showed very low cytotoxity to the B16 cell. 相似文献
198.
《Bioscience, biotechnology, and biochemistry》2013,77(11):2852-2855
We evaluated the effects of a 50% methanol extract of Citrus unshiu powder (MEC) on cytokines in peripheral blood mononuclear cells (PBMCs) obtained from patients with seasonal allergic rhinitis to cedar pollen. The levels of cytokines, such as TNF-α, IFN-γ, IL-2, IL-4, IL-5, IL-10, IL-12 (p70), IL-13, and GM-CSF, produced by pollen-stimulated PBMC were measured. We found that MEC suppressed pollen-induced TNF-α release and increased IFN-γ release from PBMCs. The results suggest that Citrus unshiu powder has an immunomodulatory effect in vitro and that its use could improve seasonal allergic rhinitis symptoms. 相似文献
199.
Ritchie RJ 《The New phytologist》2006,171(3):643-655
13NO3 was used to determine the intracellular compartmentation of NO3 in barley roots (Hordeum vulgare cv. Klondike), followed by a thermodynamic analysis of nitrate transport.Plants were grown in one-tenth Johnson's medium with 1 mol m3 NO3 (NO3-grown plants) or 1 mol m3 NH4NO3 (NH4NO3-grown plants).The cytoplasmic concentrations of NO3 in roots were only approx. 3-6 mol m3 (half-time for exchange approx. 21 s) in both NO3 and NH4NO3 plants. These pool sizes are consistent with published nitrate microelectrode data, but not with previous compartmental analyses.The electrochemical potential gradient for nitrate across the plasmalemma was +26 +/-1 kJ mol1 in both NO3- and NH4NO3-grown plants, indicating active uptake of nitrate. At an external pH of 6, the plasmalemma electrochemical potential for protons would be approx. -29 +/- 4 kJ mol1. If the cytoplasmic pH was 7.3 +/- 0.2, then 2H+/1NO3 cotransport, or a primary ATP-driven pump (2NO3/1ATP), are both thermodynamically possible. NO3 is also actively transported across the tonoplast (approx. +6 to 7 kJ mol1). 相似文献
200.
NH4 : NO3 nutrition influence on biomass productivity and root respiration of poplar and willow clones 下载免费PDF全文
Nitrogen fertilization often improves the yield of intensively managed, short‐rotation coppices. However, information of N nutrition form on the growth of common species and clones used for biomass production is limited. Thus, this study aims at evaluating N form effects on the growth of two Salicaceae clones. Cuttings of the poplar clone Max 4 (Populus maximovizcii × P. nigra) and the willow clone Inger (Salix triandra × S. viminialis) were fertilized in a pot experiment with four ratios of nitrate (NO3?) to ammonium (50%, 62.5%, 75% and 87.5% NO3? balanced with ammonium (NH4+) to constant total N) for one growing season and under stable soil pH. Plants were harvested for analysis of biomass and morphology of leaves, stem and roots. Respiration of fine and coarse roots (RR) was determined and related to biomass growth. Salix cv. Inger accumulated more total dry matter than Populus cv. Max 4. In both Salicaceae clones, the total biomass was significantly influenced by the nitrate ratio and greatest in plants fertilized with 50% NO3? of the total N supply. Both clones possess a different leaf and root morphology, but no significant influence of the NO3? ratio on the morphology was found. Fine RR rates differed significantly between clones, with significantly greater fine RR in Max 4; 87.5% NO3? fertilization increased the fine RR. Fine RR and total accumulated plant biomass were closely related. Our study is the first to show the tremendous influence of fine root respiration, especially including the carbon‐intensive reduction of NO3? to NH4+, on the aboveground growth of Salicaceae clones. Ways to improve yield in SRC are thus to lower the assimilate consumption by fine roots and to match fertilization regimes to the used clones or vice versa. 相似文献