全文获取类型
收费全文 | 2148篇 |
免费 | 128篇 |
出版年
2023年 | 14篇 |
2022年 | 30篇 |
2021年 | 39篇 |
2020年 | 34篇 |
2019年 | 28篇 |
2018年 | 66篇 |
2017年 | 38篇 |
2016年 | 59篇 |
2015年 | 101篇 |
2014年 | 99篇 |
2013年 | 142篇 |
2012年 | 174篇 |
2011年 | 130篇 |
2010年 | 75篇 |
2009年 | 74篇 |
2008年 | 97篇 |
2007年 | 115篇 |
2006年 | 104篇 |
2005年 | 88篇 |
2004年 | 79篇 |
2003年 | 59篇 |
2002年 | 58篇 |
2001年 | 50篇 |
2000年 | 40篇 |
1999年 | 26篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 19篇 |
1994年 | 10篇 |
1992年 | 25篇 |
1991年 | 35篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 20篇 |
1987年 | 26篇 |
1986年 | 21篇 |
1985年 | 21篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1979年 | 18篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 17篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1968年 | 7篇 |
排序方式: 共有2276条查询结果,搜索用时 453 毫秒
941.
Glucosides from Curculigo orchioides 总被引:2,自引:0,他引:2
From the rhizomes of Curculigo orchioides two phenolic glucosides named orchiosides A and B were isolated besides four known compounds and their structures were elucidated by the combination of 2D-NMR analysis, mass spectrometry and chemical evidences. 相似文献
942.
Seven hopane-type saponins were isolated from the methanol extract of Glinus lotoides. Six of them were identified as novel compounds and designated as lotoideside A [3-O-beta-D-xylopyranosyl (1-->2)-alpha-L-rhamnopyranosyl-6 alpha-O-beta-D-xylopyranosyl-22-beta-O-beta-D-glucopyranosyl-16 beta-hydroxy hopane (1)], lotoideside B [3-O-beta-D-xylopyranosyl (1-->2)-alpha-L-rhamnopyranosyl-22-beta-O-beta-D-glucopyranosyl-6 alpha,16 beta-dihydroxyhopane (2)], lotoideside C [3-OD-xylopyranosyl-6 alpha-O-beta-D-xylopyranosyl-16 beta-O-beta-D-xylopyranosyl-22 beta-hydroxyhopane (3)], lotoideside D [3-O-beta-D-xylopyranosyl-16 beta-O-alpha-L-arabinopyranosyl-6 alpha,22-beta-dihydroxyhopane (4)], lotoideside E [3-O-beta-D-xylopyranosyl-6 alpha-O-beta-D-xylopyranosyl-16 beta,22-beta-dihydroxyhopane (5)], and lotoideside F [3-O-beta-D-xylopyranosyl-22-beta-O-beta-D-glucopyranosyl-16 beta-hydroxyhopan-6-one (6)]. The known compound succulentoside B (7) was also encountered. Their structures were elucidated on the basis of one-and two-dimensional NMR spectroscopic techniques, ESIMS and chemical evidences. 相似文献
943.
Laboratory experiments were conducted to study the effect of different concentrations in the range of 0-100% textile effluents (untreated and treated) on seed germination (%), delay index (DI), plant shoot length and root length, plant biomass, chlorophyll content and carotenoid of three different cultivars of wheat. The textile effluent did not show any inhibitory effect on seed germination at low concentration (6.25%). The other reported plant parameters also followed the similar trend. Seeds germinated in undiluted effluents did not survive for longer period. Based on the tolerance to textile effluent, the wheat cultivars have been arranged in the following order: PBW-343 < PBW-373 < WH-147. It has also been concluded that effect of the textile effluent is cultivar specific and due care should be taken before using the textile effluent for irrigation purpose. 相似文献
944.
Yadav RC Kumar GS Bhadra K Giri P Sinha R Pal S Maiti M 《Bioorganic & medicinal chemistry》2005,13(1):165-174
The interaction of berberine with single stranded poly(rA) structure was investigated using a combination of spectrophotometric, spectrofluorimetric, circular dichroic, viscometric, and thermodynamic studies. The interaction process was characterized by typical hypochromic and bathochromic effects in the absorption spectrum of berberine, enhancement of fluorescence intensity of berberine, increase of viscosity, and perturbation of circular dichroic spectrum of single stranded poly(rA). Scatchard plot obtained from spectrophotometric analysis showed that berberine bound strongly to single stranded poly(rA) in a non-cooperative manner. In contrast, berberine does not show any significant effect (i) in its absorbance and fluorescence spectra on binding to double stranded poly(rA), (ii) alter the circular dichroic spectrum of double stranded poly(rA), or (iii) increase of viscosity of double stranded poly(rA) indicating that it does not bind at all to double stranded poly(rA) structure. Thermodynamic parameters indicated that the binding of the alkaloid to single stranded poly(rA) is an endothermic process and entropy driven. All these findings, taken together clearly support that berberine binds strongly to single stranded poly(rA) structure by a mechanism of partial intercalation leading to its use in gene regulation in eukaryotic cells. 相似文献
945.
Gagan Preet Singh Sidhu Aditi Shreeya Bali Harminder Pal Singh Daizy R. Batish Ravinder Kumar Kohli 《International journal of phytoremediation》2018,20(5):483-489
Coronopus didymus was examined in terms of its ability to remediate Pb-contaminated soils. Pot experiments were conducted for 4 and 6 weeks to compare the growth, biomass, photosynthetic efficiency, lead (Pb) uptake, and accumulation by C. didymus plants. The plants grew well having no visible toxic symptoms and 100% survivability, exposed to different Pb-spiked soils 100, 350, 1500, and 2500 mg kg?1, supplied as lead nitrate. After 4 weeks, root and shoot concentrations reached 1652 and 502 mg Pb kg?1 DW, while after 6 weeks they increased up to 3091 and 527 mg Pb kg?1 DW, respectively, at highest Pb concentration. As compared to the 4 week experiments, the plant growth and biomass yield were higher after 6 weeks of Pb exposure. However, the chlorophyll content of leaves decreased but only a slight decline in photosynthetic efficiency was observed on exposure to Pb at both 4 and 6 weeks. The Pb accumulation was higher in roots than in the shoots. The bioconcentration factor of Pb was > 1 in all the plant samples, but the translocation factor was < 1. This suggested C. didymus as a good candidate for phytoremediation of Pb-contaminated soils and can be used for future remediation purposes. 相似文献
946.
Sanjaya Gyawali Shiaoman Chao Shyam Saran Vaish Shiv P. Singh Sajid Rehman Siya Ram Vishwakarma Ramesh Pal Singh Verma 《Molecular breeding : new strategies in plant improvement》2018,38(5):62
Spot blotch (SB) in barley is caused by the fungal pathogen Cochliobolus sativus and considered one of the major constraints to successful barley production. Resistance to C. sativus was evaluated, using a barley collection of 336 genotypes (AM-2014), at the seedling and adult stages. Seedling resistance was evaluated by using a mixture of 19 virulent isolates in Morocco. Virulent isolates prevalent in Uttar Pradesh were used for phenotyping resistance at the adult stage in India. The AM-2014 panel was genotyped with 9-K single-nucleotide polymorphism (SNP) markers using iSelect Illumina Infinium. Genome wide association studies (GWAS) were carried out using SNP markers, infection responses, disease severity, and area under the disease progress curve (AUDPC). The mixed linear model was employed in TASSEL using principal component analysis (PCA) and Kinship matrix (K) as covariates. Higher SB severity, 82.3?±?13.5 (mean?±?SD), was recorded at the Banaras Hindu University (BHU) compared to 47.6?±?15.0 at the Narendra Dev University of Agriculture and Technology (NDUAT). Nine QTL, Rcs-qtl-1H-126.9, Rcs-qtl-2H-148.16, Rcs-qtl-3H-25.27, Rcs-qtl-5H-80.35, Rcs-qtl-6H-58.24, Rcs-qtl-7H-29.62, Rcs-qtl-7H-29.72, Rcs-qtl-7H-32.81, and Rcs-qtl-7H-34.74, were detected for SB resistance at the seedling stage. For SB severity at the adult stage, a QTL, Rcs-qtl-7H-32.81, was detected at BHU while seven QTL, Rcs-qtl-2H-91.09, Rcs-qtl-3H-145.64, Rcs-qtl-4H-14.43, Rcs-qtl-6H-6.49, Rcs-qtl-7H-114.43, Rcs-qtl-7H-151.66, and Rcs-qtl-7H-150.36, were found for SB severity at NDUAT. Three QTL, Rcs-qtl-4H-18.61, Rcs-qtl-4H-67.91, and Rcs-qtl-5H-110.25, were significant for AUDPC of SB at BHU. The QTLs reported in this study are important to advance marker-assisted selection and gene pyramiding of SB resistance in South Asia and North Africa in future. 相似文献
947.
Akhilesh Kumar Mishra Satyendra Kumar Mishra Amar Pal Singh 《Plasmonics (Norwell, Mass.)》2018,13(4):1183-1190
Surface plasmons (SPs), the coherent charge density oscillations of the electrons bound to the metal-dielectric interface, are dominating the research field of optics. One of the ubiquitous applications of SPs is in sensing. In the present work, we have theoretically studied a couple of surface plasmon resonance (SPR)-based fiber-coupled ultra-sensitive refractive index sensors working in the infrared (IR) region. Either of the copper (Cu) and aluminum (Al) is used as surface plasmon exciting layers in these sensing probes. On the top of the metal layer, field-enhancing graphene and silicon layers are considered. The probes are characterized in terms of sensitivity and detection accuracy (DA). The sensitivities of Cu- and Al-based optimized probes are obtained respectively to be 23.50 and 24 μm/refractive index unit (RIU). To ensure the probes’ compatibility with bio-samples, an extra bio-recognition layer of graphene has been considered over the silicon layer which resulted into the respective sensitivities of 20 and 19.50 μm/RIU for Cu- and Al-based probes with appreciably good DAs. 相似文献
948.
Kathryn R. Fixen Nilanjan Pal Chowdhury Marta Martinez‐Perez Saroj Poudel Eric S. Boyd Caroline S. Harwood 《Environmental microbiology》2018,20(7):2500-2508
The phototrophic alpha‐proteobacterium, Rhodopseudomonas palustris, is a model for studies of regulatory and physiological parameters that control the activity of nitrogenase. This enzyme produces the energy‐rich compound H2, in addition to converting N2 gas to NH3. Nitrogenase is an ATP‐requiring enzyme that uses large amounts of reducing power, but the electron transfer pathway to nitrogenase in R. palustris was incompletely known. Here, we show that the ferredoxin, Fer1, is the primary but not sole electron carrier protein encoded by R. palustris that serves as an electron donor to nitrogenase. A flavodoxin, FldA, is also an important electron donor, especially under iron limitation. We present a model where the electron bifurcating complex, FixABCX, can reduce both ferredoxin and flavodoxin to transfer electrons to nitrogenase, and we present bioinformatic evidence that FixABCX and Fer1 form a conserved electron transfer pathway to nitrogenase in nitrogen‐fixing proteobacteria. These results may be useful in the design of strategies to reroute electrons generated during metabolism of organic compounds to nitrogenase to achieve maximal activity. 相似文献
949.
Krishnendu Pramanik Priyanka Pal Tithi Soren Soumik Mitra Pallab Kumar Ghosh Anumita Sarkar Tushar Kanti Maiti 《Journal of plant biochemistry and biotechnology.》2018,27(3):362-372
Phytic acid or phytate (myo-inositol hexakisphosphate) is the principal storage indigestible form of phosphorus in different crops. It is considered as an antinutrient in human as well as animal (including fish, poultry, pig, chicken etc.) diet due to its chelating behavior of certain essential divalent minerals (Fe2+, Mg2+, Zn2+, Ca2+ etc.). The unabsorbed, indigested form of phosphorus also causes phosphate pollution in the soil by animal wastes. Phytate degrading enzymes like phytases (myo-inositol hexakisphosphate phosphohydrolase) in this regard can be very useful and also economically feasible to reduce the risk of phosphate pollution and increase the nutrient value in animal feeds at the same time. The Klebsiella phytases are suitable to use in the food industries of plant origin for their excellent thermal stability and high pH tolerance. From the present in silico investigation, it was found that Klebsiella phytases were 46–47 kDa molecular weight protein of histidine phosphatase superfamily having thermostability and alkalinity nature. This thermostability can be achieved due to possession of higher percentage of α helices and β sheets at the same time; the presence of higher aliphatic indices (range in between 88 and 91) etc. Interestingly, a strong correlation was found to be pertinent from phylogenetic studies of proteins with their cDNA among both species and strain level. Hence, the present study would be beneficial for future researchers (3D model available in Protein Model Database with acc. no.: PM0080562) to meet the demand of agricultural and industrial production of bacterial phytases particularly for agricultural farming. 相似文献
950.
Rituparna Das Nayan Ranjan Saha Arundhati Pal Dipankar Chattopadhyay Amal Kanti Paul 《生物学前沿》2018,13(4):297-308