全文获取类型
收费全文 | 1699篇 |
免费 | 142篇 |
国内免费 | 1篇 |
出版年
2023年 | 6篇 |
2022年 | 23篇 |
2021年 | 33篇 |
2020年 | 35篇 |
2019年 | 33篇 |
2018年 | 47篇 |
2017年 | 30篇 |
2016年 | 45篇 |
2015年 | 73篇 |
2014年 | 76篇 |
2013年 | 107篇 |
2012年 | 153篇 |
2011年 | 124篇 |
2010年 | 81篇 |
2009年 | 74篇 |
2008年 | 91篇 |
2007年 | 92篇 |
2006年 | 70篇 |
2005年 | 65篇 |
2004年 | 72篇 |
2003年 | 60篇 |
2002年 | 52篇 |
2001年 | 31篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1996年 | 6篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 5篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 20篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1972年 | 13篇 |
1968年 | 5篇 |
排序方式: 共有1842条查询结果,搜索用时 31 毫秒
941.
Ribonucleocapsid formation of severe acute respiratory syndrome coronavirus through molecular action of the N-terminal domain of N protein
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Saikatendu KS Joseph JS Subramanian V Neuman BW Buchmeier MJ Stevens RC Kuhn P 《Journal of virology》2007,81(8):3913-3921
Conserved among all coronaviruses are four structural proteins: the matrix (M), small envelope (E), and spike (S) proteins that are embedded in the viral membrane and the nucleocapsid phosphoprotein (N), which exists in a ribonucleoprotein complex in the lumen. The N-terminal domain of coronaviral N proteins (N-NTD) provides a scaffold for RNA binding, while the C-terminal domain (N-CTD) mainly acts as oligomerization modules during assembly. The C terminus of the N protein anchors it to the viral membrane by associating with M protein. We characterized the structures of N-NTD from severe acute respiratory syndrome coronavirus (SARS-CoV) in two crystal forms, at 1.17 A (monoclinic) and at 1.85 A (cubic), respectively, resolved by molecular replacement using the homologous avian infectious bronchitis virus (IBV) structure. Flexible loops in the solution structure of SARS-CoV N-NTD are now shown to be well ordered around the beta-sheet core. The functionally important positively charged beta-hairpin protrudes out of the core, is oriented similarly to that in the IBV N-NTD, and is involved in crystal packing in the monoclinic form. In the cubic form, the monomers form trimeric units that stack in a helical array. Comparison of crystal packing of SARS-CoV and IBV N-NTDs suggests a common mode of RNA recognition, but they probably associate differently in vivo during the formation of the ribonucleoprotein complex. Electrostatic potential distribution on the surface of homology models of related coronaviral N-NTDs suggests that they use different modes of both RNA recognition and oligomeric assembly, perhaps explaining why their nucleocapsids have different morphologies. 相似文献
942.
Udayakumar Sekaran Cameron McCoy Sandeep Kumar Senthil Subramanian 《Global Change Biology Bioenergy》2019,11(7):836-851
Switchgrass (Panicum virgatum L.) is usually grown on marginal land for biofuel system, in which nitrogen (N) is an essential management practice, and landscape position is a key topographical factor in impacting the production. However, limited information is available regarding how the N application and landscape positions affect soil microbial communities and enzyme activities under switchgrass. Thus, the specific objective of this study was to evaluate the responses of N rate (high, 112 kg N/ha; medium, 56 kg N/ha; and low, 0 kg N/ha) and landscape positions (shoulder and footslope) on soil biological health under switchgrass field. Data showed that N addition significantly influenced carbon and N fractions. The hot water‐soluble organic carbon (HWC) and nitrogen (HWN) fractions were significantly higher at footslope position than the shoulder position. The amount of total phospholipid fatty acid (PLFA), total bacterial, actinomycetes, gram‐negative and gram‐positive bacteria, total fungi, arbuscular mycorrhizal (AM) fungi, and saprophytes PLFAs were highest with medium and high N rates and footslope position. The N addition increased total PLFAs in N fertilizer treatments, viz. medium (5,946 ng PLFA‐C/g soil) and high N rates (5,871 ng PLFA‐C/g soil). Microbial biomass carbon and nitrogen and enzyme activities (urease, β‐glucosidase, acid phosphatase and arylsulfatase) were significantly enhanced by N fertilization (medium and high N rates) compared to control (low N rates) under footslope position. The urease activity under medium (36.3 µmol N‐NH4+ g?1 soil hr?1) and high N rates (31.4 µmol N‐NH4+ g?1 soil hr?1) was 42.9% and 23.6% higher than low N rates, respectively. This study suggests that the application of medium N rate in footslope position to switchgrass can enhance the soil biological properties and hence can protect the environment from the excessive use of N fertilizer. 相似文献
943.
Qualitative and Quantitative Analysis of Potentilla fulgens Roots by NMR,Matrix‐assisted Laser Desorption/Ionisation with Time‐of‐Flight MS,Electrospray Ionisation MS/MS and HPLC/UV
下载免费PDF全文
![点击此处可从《Phytochemical analysis : PCA》网站下载免费的PDF全文](/ch/ext_images/free.gif)
944.
Komivi Senyo Akutse Jane Wanjiru Kimemia Sunday Ekesi Fathiya Mbarak Khamis Odhiambo Levi Ombura Sevgan Subramanian 《Journal of Applied Entomology》2019,143(6):626-634
Maize is a major staple food for over 300 million people in sub‐Saharan Africa. Sustainable productivity of this primary crop has been recently threatened by Fall armyworm (FAW), Spodoptera frugiperda invasion. Due to lack of environmentally safe management strategies, immediate responses by growers and governments to tackle FAW are based on rampant use of pesticides. Looking for efficient biopesticides, twenty entomopathogenic fungal isolates (14 Metarhizium anisopliae and 6 Beauveria bassiana) were screened for their efficacy against eggs and second instar larvae of FAW. A single discriminating concentration of 1 × 108 conidia ml?1 and four replicates per treatment were used in all experiments. Isolates were assessed for their ability to cause mortality of FAW second instar larvae, eggs and the neonate larvae that emerged from treated eggs. Among the isolates tested, only B. bassiana ICIPE 676 caused moderate mortality of 30% to second instar larvae. Metarhizium anisopliae ICIPE 78, ICIPE 40 and ICIPE 20 caused egg mortalities of 87.0%, 83.0% and 79.5%, respectively, and M. anisopliae ICIPE 41 and ICIPE 7 outperformed all the others by causing 96.5% and 93.7% mortality to the neonate larvae, respectively. The cumulated mortality of eggs and neonates was highest with M. anisopliae ICIPE 41 (97.5%), followed by M. anisopliae ICIPE 7, 655, 40, 20 and 78 with total mortality of 96.0%, 95.0%, 93.5%, 93.0% and 92.0%, respectively. These isolates with high cumulated mortality (≥92%), especially ICIPE 78 and 7, which are already commercialized for spider mites and ticks control respectively, would be good candidates for development as biopesticides for management of FAW in Africa if further evidence of their efficacy is obtained in the field. 相似文献
945.
Govindan Subramanian Scott J. Bowen Yaqi Zhu Nicole Roush Theresa Zachary Christopher Javens Tracey Williams Ann Janssen Andrea Gonzales 《Bioorganic & medicinal chemistry letters》2019,29(19):126624
In silico virtual screening using the ligand-based ROCS approach and the commercially purchasable compound collection from the ZINC database resulted in the identification of distinctly different and novel acetamide core frameworks with series representatives 1a and 2a exhibiting nanomolar affinity in the kinase domain only hTrkA HTRF biochemical assay. Additional experimental validation using the Caliper technology with either the active or inactive kinase conditions demonstrated the leads, 1a and 2a, to preferentially bind the kinase inactive state. X-ray structural analysis of the kinase domain of hTrkA…1a/2a complexes confirmed the kinase, bind the inhibitor leads in the inactive state and to exhibit a type 2 binding mode with the DFG-out and αC-helix out conformation. The leads also demonstrated sub-micromolar activity in the full length hTrkA cell-based assay and selectivity against the closely related hTrkB isoform. However, the poor microsomal stability and permeability of the leads is suggestive of a multiparametric lead optimization effort requirement for further progression. 相似文献
946.
Lala NL Ramaseshan R Bojun L Sundarrajan S Barhate RS Ying-Jun L Ramakrishna S 《Biotechnology and bioengineering》2007,97(6):1357-1365
A comparative study of antimicrobial activity is done using three different electrospun nanofibers namely-CA, PAN, and PVC used as control and with various amounts of AgNO(3) being treated with UV-irradiation leading to the enhancement of silver nanoparticles. DMF is used as the common solvent which helps to undergo spontaneous slow reduction at room temperature to form silver nanoparticles followed by UV-irradiation using a 400 W source. The time required for the formation of silver nanoparticles is short and they are more or less well dispersed with few such aggregates. The presence of silver nanoparticles is confirmed using various characterization techniques. The antimicrobial activity is studied using nanofibers with fabricated functionality. 相似文献
947.
Nijhout HF Smith WA Schachar I Subramanian S Tobler A Grunert LW 《Developmental biology》2007,302(2):569-576
During the larval feeding period, the growth of the wing imaginal disks of Lepidoptera is dependent on continuous feeding. Feeding and nutrition exert their effect via the secretion of bombyxin, the lepidopteran insulin-like hormone. When larvae stop feeding and enter the wandering stage in preparation for metamorphosis, the control of imaginal disk growth becomes feeding and nutrition-independent. Growth of the wing imaginal disks of non-feeding wandering stage Manduca sexta can be stopped by removal of the brain, indicating that a brain-derived factor is required for continued disk growth. Isolated wing disk growth in vitro requires both 20-hydroxyecdysone (20E) and either brain extract or bombyxin to achieve normal growth. In vitro, brain extracts and synthetic bombyxin have little or no effect in stimulating disk growth, but they greatly enhance the effect of 20E, indicating that 20E and bombyxin act synergistically to modulate growth of the imaginal disk. Brain extract and bombyxin induce a suite of insulin-response events in cultured wing disks, which indicate that bombyxin and 20E act through separate and synergistic pathways. The dose-response to 20E reaches a plateau at about 0.1 microg/ml. Tracheal differentiation of the wing disks can be induced to initiate in vitro by a low concentration of 20E, whereas higher concentrations of 20E only stimulate growth. 相似文献
948.
Subramanian R Solo S Mishra MM Murugan P Siddaraju N Basu D Srinivasan R 《Acta cytologica》2007,51(3):417-420
BACKGROUND: The role offine needle aspiration cytology (FNAC) in diagnosis and differentiation of primary orbital lymphoid lesions is debatable, and little literature exists on cytodiagnosis of orbital lymphoid lesions. CASES: Four patients with orbital lesions underwent routine FNAC. In 3 cases, histopathologic examination was performed with immunohistochemistry (IHC). Cytologic features and diag- noses were correlated with histopathologic diagnoses. Two were cytologically diagnosed with low-grade non-Hodgkin lymphoma (NHL) and 2 with pseudolymphoma and inflammatory pseudotumor, respectively. Of the 2 cases of histologically diagnosed NHL, 1 had concordant diagnosis and the other had a jalse negative diagnosis of pseudolymphoma; both showed significant increase in mast cells, with neoplastie lymphoid cells exhibiting a higher N:C ratio and coarser chromatin texture. The case cytologically interpreted as suspicious for NHL was identified as a psetedolymphoma on histology (false positive). The case of inflammatory pseudotumor, in which hiopiy was not peiformned, responded well to corticosteroids, strengthening the cytologic diagnosis. CONCLUSION: FNAC diagnosis and differentiation of benign vs. malignant primacy orbital lymphoid lesions is often difficult. Careful cytologic interpretation with respect to certain subtle cytologic details is needed in minimizing false positive or false negative diagnoses. In difficult situations, IHC using suitable immunomarkers proves highly useful. 相似文献
949.
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of cognitive function. Existing evidence indicates that abnormal processing and extracellular deposition of the longer form of the amyloid peptide Abeta(1-42), a proteolytic derivative of the amyloid precursor protein (APP), is a key step in the pathogenesis of AD. Active immunization with Abeta(1-42) has been shown to decrease brain beta deposition and improve cognitive performance in mouse models of AD. In the present study, we sought to express the synthetic gene encoding AB in Escherichia coli to enable rapid production of the antigen and its purification. The synthetic gene has been constructed from six oligonucleotides by employing overlapping PCR strategy and expressed in E. coli using the T7 promoter system. The recombinant peptide has been purified to homogeneity by a single step Ni+2 affinity chromatography. Enzyme-linked immunosorbent assay (ELISA) using polyclonal anti-Abeta(1-42) sera confirms that the corresponding linear B-cell epitopic sequences are available for immunorecognition in the recombinant peptide. This methodology enables rapid, continuous production and purification in bulk amounts of human Abeta sequence by employing bacterial expression system 相似文献
950.
Motion detection, noise reduction, texture suppression, and contour enhancement by spatiotemporal Gabor filters with surround inhibition 总被引:2,自引:0,他引:2
We study the orientation and speed tuning properties of spatiotemporal three-dimensional (3D) Gabor and motion energy filters as models of time-dependent receptive fields of simple and complex cells in the primary visual cortex (V1). We augment the motion energy operator with surround suppression to model the inhibitory effect of stimuli outside the classical receptive field. We show that spatiotemporal integration and surround suppression lead to substantial noise reduction. We propose an effective and straightforward motion detection computation that uses the population code of a set of motion energy filters tuned to different velocities. We also show that surround inhibition leads to suppression of texture and thus improves the visibility of object contours and facilitates figure/ground segregation and the detection and recognition of objects. 相似文献