全文获取类型
收费全文 | 329篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
354篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 25篇 |
2012年 | 35篇 |
2011年 | 27篇 |
2010年 | 24篇 |
2009年 | 10篇 |
2008年 | 12篇 |
2007年 | 20篇 |
2006年 | 19篇 |
2005年 | 14篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有354条查询结果,搜索用时 15 毫秒
11.
We examined the roles of lithology, topography, vegetation and fire in generating local-scale (<1 km2) soil spatial variability in a seasonally dry tropical forest (SDTF) in southern India. For this, we mapped soil (available nutrients, Al, total C, pH, moisture and texture in the top 10cm), rock outcrops, topography, all native woody plants ≥1 cm diameter at breast height (DBH), and spatial variation in fire frequency (times burnt during the 17 years preceding soil sampling) in a permanent 50-ha plot. Unlike classic catenas, lower elevation soils had lesser moisture, plant-available Ca, Cu, Mn, Mg, Zn, B, clay and total C. The distribution of plant-available Ca, Cu, Mn and Mg appeared to largely be determined by the whole-rock chemical composition differences between amphibolites and hornblende-biotite gneisses. Amphibolites were associated with summit positions, while gneisses dominated lower elevations, an observation that concurs with other studies in the region which suggest that hillslope-scale topography has been shaped by differential weathering of lithologies. Neither NO3−-N nor NH4+-N was explained by the basal area of trees belonging to Fabaceae, a family associated with N-fixing species, and no long-term effects of fire on soil parameters were detected. Local-scale lithological variation is an important first-order control over soil variability at the hillslope scale in this SDTF, by both direct influence on nutrient stocks and indirect influence via control of local relief. 相似文献
12.
13.
Differential recovery of membrane proteins after extraction by aqueous methanol and trifluoroethanol
Zhang H Lin Q Ponnusamy S Kothandaraman N Lim TK Zhao C Kit HS Arijit B Rauff M Hew CL Chung MC Joshi SB Choolani M 《Proteomics》2007,7(10):1654-1663
Cell membrane proteome analysis is limited by inherent membrane hydrophobicity. Conventional membrane protein extraction techniques use detergents, chaotropes and organic acids that require sample clean-up or pH adjustment, and are associated with significant sample loss. We extracted membrane proteins from red blood cells (RBCs) using methanol (MeOH), trifluoroethanol (TFE) and urea, and identified membrane proteins using 2-D LC coupled with MALDI-TOF/TOF-MS. We show that organic solvents MeOH- and TFE-based methods have membrane protein analysis efficiencies comparable to urea, and are complementary for the recovery of both hydrophilic and hydrophobic peptides. The mean grand average of hydropathicity (GRAVY) value of identified peptides from the TFE-based method (-0.107) was significantly higher than that of the MeOH-based method (-0.465) (p<0.001). Sequential and adjunctive use of the organic solvents MeOH and TFE increases the number of proteins identified, and the confidence of their identification. We show that this strategy is effective for shotgun membrane proteome analysis. 相似文献
14.
Bandamaravuri Kishore Babu S. S. Reddy Mukesh K. Yadav M. Sukumar Vijendra Mishra A. K. Saxena Dilip K. Arora 《Indian journal of microbiology》2010,50(2):199-204
Genetic diversity analysis of Macrophomina phaseolina isolates obtained from different host range and diverse geographical locations in India was carried out using RAPD fingerprinting.
Of the thirteen 10-mer random primers used, primer OPB-08 gave the maximum polymorphism and the UPGMA clustering could separate
50 isolates in to ten groups at more than 65% similarity level. The ten clusters correlated well with the geographical locations
with exceptions for isolates obtained from Eastern and Western Ghats. There was a segregation of isolates from these two geographical
locations in to two clusters thus, distributing 10 genotypes in to eight geographical locations. All the isolates M. phaseolina irrespective of their host and geographical origin, exhibited two representative monomorphic bands at 250 bp and 1 kb, presence
of these bands suggests that isolates might have evolved from a common ancestor but due to geographical isolation fallowed
by natural selection and genetic drift might have segregated in to subpopulations. Genetic similarity in the pathogenic population
reflects the dispersal of single lineage in all locations in India. 相似文献
15.
T. S. Suryanarayanan T. S. Murali N. Thirunavukkarasu M. B. Govinda Rajulu G. Venkatesan R. Sukumar 《Biodiversity and Conservation》2011,20(5):913-928
Fungal endophytes of tropical trees are expected to be exceptionally species rich as a consequence of high tree diversity
in the tropics and the purported host restriction among the endophytes. Based on this premise, endophytes have been regarded
as a focal group for estimating fungal numbers because their possible hyperdiverse nature would reflect significantly global
fungal diversity. We present our consolidated ten-year work on 75 dicotyledonous tree hosts belonging to 33 families and growing
in three different types of tropical forests of the NBR in the Western Ghats, southern India. We conclude that endophyte diversity
in these forests is limited due to loose host affiliations among endophytes. Some endophytes have a wide host range and colonize
taxonomically disparate hosts suggesting adaptations in them to counter a variety of defense chemicals in their hosts. Furthermore,
such polyphagous endophytes dominate the endophyte assemblages of different tree hosts. Individual leaves may be densely colonized
but only by a few endophyte species. It appears that the environment (the type of forest in this case) has a larger role in
determining the endophyte assemblage of a plant host than the taxonomy of the host plant. Thus, different tropical plant communities
have to be studied for their endophyte diversity to test the generalization that endophytes are hyperdiverse in the tropics,
estimate their true species richness, and use them as a predictor group for more accurate assessment of global fungal diversity. 相似文献
16.
Jeyasekaran G. Raj K. Thirumalai Shakila R. Jeya Thangarani A. Jemila Sukumar D. Jailani V. Abdul Kadhar 《World journal of microbiology & biotechnology》2011,27(4):953-959
A multiplex PCR based assay was developed for the identification of the genus Salmonella. Five sets of primers from different genomic sequences such as fimA, himA,
hns, invA and hto genes were selected for the identification of serogroups of Salmonella
enterica such as S. Typhi, S. ParatyphiA, S. Typhimurium, S. Enteritidis and S. Weltevreden. The selected primers amplified products with the sizes of 85, 123, 152, 275 and 496 bp, respectively, for the
genus Salmonella. This assay was found to be highly sensitive, as it could detect 5 cells of Salmonella and 1,000 fg of genomic DNA. Amplification of DNA extracted from other genera viz. V. cholerae and E. coli yielded negative results. This assay provides specific and reliable results and allows for the cost–effective detection of
Salmonella in one reaction tube in mixed bacterial communities. 相似文献
17.
S.A. Syam Kumar Raghavendra Holla Prabakar Sukumar Sriram Padmanaban Nagarajan Vivekanandan 《Reports of Practical Oncology and Radiotherapy》2013,18(2):87-94
Aim
To compare and evaluate the performance of two different volumetric modulated arc therapy delivery techniques.Background
Volumetric modulated arc therapy is a novel technique that has recently been made available for clinical use. Planning and dosimetric comparison study was done for Elekta VMAT and Varian RapidArc for different treatment sites.Materials and methods
Ten patients were selected for the planning comparison study. This includes 2 head and neck, 2 oesophagus, 1 bladder, 3 cervix and 2 rectum cases. Total dose of 50 Gy was given for all the plans. All plans were done for RapidArc using Eclipse and for Elekta VMAT with Monaco treatment planning system. All plans were generated with 6 MV X-rays for both RapidArc and Elekta VMAT. Plans were evaluated based on the ability to meet the dose volume histogram, dose homogeneity index, radiation conformity index, estimated radiation delivery time, integral dose and monitor units needed to deliver the prescribed dose.Results
RapidArc plans achieved the best conformity (CI95% = 1.08 ± 0.07) while Elekta VMAT plans were slightly inferior (CI95% = 1.10 ± 0.05). The in-homogeneity in the PTV was highest with Elekta VMAT with HI equal to 0.12 ± 0.02 Gy when compared to RapidArc with 0.08 ± 0.03. Significant changes were observed between the RapidArc and Elekta VMAT plans in terms of the healthy tissue mean dose and integral dose. Elekta VMAT plans show a reduction in the healthy tissue mean dose (6.92 ± 2.90) Gy when compared to RapidArc (7.83 ± 3.31) Gy. The integral dose is found to be inferior with Elekta VMAT (11.50 ± 6.49) × 104 Gy cm3 when compared to RapidArc (13.11 ± 7.52) × 104 Gy cm3. Both Varian RapidArc and Elekta VMAT respected the planning objective for all organs at risk. Gamma analysis result for the pre-treatment quality assurance shows good agreement between the planned and delivered fluence for 3 mm DTA, 3% DD for all the evaluated points inside the PTV, for both VMAT and RapidArc techniques.Conclusion
The study concludes that a variable gantry speed with variable dose rate is important for efficient arc therapy delivery. RapidArc presents a slight improvement in the OAR sparing with better target coverage when compared to Elekta VMAT. Trivial differences were noted in all the plans for organ at risk but the two techniques provided satisfactory conformal avoidance and conformation. 相似文献18.
Targeted comparative RNA interference analysis reveals differential requirement of genes essential for cell proliferation 下载免费PDF全文
Machida YJ Chen Y Machida Y Malhotra A Sarkar S Dutta A 《Molecular biology of the cell》2006,17(11):4837-4845
Differences in the genetic and epigenetic make up of cell lines have been very useful for dissecting the roles of specific genes in the biology of a cell. Targeted comparative RNAi (TARCOR) analysis uses high throughput RNA interference (RNAi) against a targeted gene set and rigorous quantitation of the phenotype to identify genes with a differential requirement for proliferation between cell lines of different genetic backgrounds. To demonstrate the utility of such an analysis, we examined 257 growth-regulated genes in parallel in a breast epithelial cell line, MCF10A, and a prostate cancer cell line, PC3. Depletion of an unexpectedly high number of genes (25%) differentially affected proliferation of the two cell lines. Knockdown of many genes that spare PC3 (p53-) but inhibit MCF10A (p53+) proliferation induces p53 in MCF10A cells. EBNA1BP2, involved in ribosome biogenesis, is an example of such a gene, with its depletion arresting MCF10A at G1/S in a p53-dependent manner. TARCOR is thus useful for identifying cell type-specific genes and pathways involved in proliferation and also for exploring the heterogeneity of cell lines. In particular, our data emphasize the importance of considering the genetic status, when performing siRNA screens in mammalian cells. 相似文献
19.
The structure of an active mutant of (S)-mandelate dehydrogenase (MDH-GOX2) from Pseudomonas putida has been determined at 2.15 A resolution. The membrane-associated flavoenzyme (S)-mandelate dehydrogenase (MDH) catalyzes the oxidation of (S)-mandelate to give a flavin hydroquinone intermediate which is subsequently reoxidized by an organic oxidant residing in the membrane. The enzyme was rendered soluble by replacing its 39-residue membrane-binding peptide segment with a corresponding 20-residue segment from its soluble homologue, glycolate oxidase (GOX). Because of their amphipathic nature and peculiar solubilization properties, membrane proteins are notoriously difficult to crystallize, yet represent a large fraction of the proteins encoded by genomes currently being deciphered. Here we present the first report of such a structure in which an internal membrane-binding segment has been replaced, leading to successful crystallization of the fully active enzyme in the absence of detergents. This approach may have general application to other membrane-bound proteins. The overall fold of the molecule is that of a TIM barrel, and it forms a tight tetramer within the crystal lattice that has circular 4-fold symmetry. The structure of MDH-GOX2 reveals how this molecule can interact with a membrane, although it is limited by the absence of a membrane-binding segment. MDH-GOX2 and GOX adopt similar conformations, yet they retain features characteristic of membrane and globular proteins, respectively. MDH-GOX2 has a distinctly electropositive surface capable of interacting with the membrane, while the opposite surface is largely electronegative. GOX shows no such pattern. MDH appears to form a new class of monotopic integral membrane protein that interacts with the membrane through coplanar electrostatic binding surfaces and hydrophobic interactions, thus combining features of both the prostaglandin synthase/squaline-hopine cyclase and the C-2 coagulation factor domain classes of membrane proteins. 相似文献
20.
NF-kappaB promotes breast cancer cell migration and metastasis by inducing the expression of the chemokine receptor CXCR4 总被引:34,自引:0,他引:34
Helbig G Christopherson KW Bhat-Nakshatri P Kumar S Kishimoto H Miller KD Broxmeyer HE Nakshatri H 《The Journal of biological chemistry》2003,278(24):21631-21638