全文获取类型
收费全文 | 1966篇 |
免费 | 136篇 |
出版年
2023年 | 15篇 |
2022年 | 35篇 |
2021年 | 57篇 |
2020年 | 16篇 |
2019年 | 37篇 |
2018年 | 46篇 |
2017年 | 49篇 |
2016年 | 61篇 |
2015年 | 80篇 |
2014年 | 109篇 |
2013年 | 134篇 |
2012年 | 125篇 |
2011年 | 139篇 |
2010年 | 91篇 |
2009年 | 70篇 |
2008年 | 77篇 |
2007年 | 76篇 |
2006年 | 88篇 |
2005年 | 69篇 |
2004年 | 59篇 |
2003年 | 48篇 |
2002年 | 40篇 |
2001年 | 59篇 |
2000年 | 29篇 |
1999年 | 38篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 8篇 |
1993年 | 15篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1977年 | 11篇 |
1975年 | 11篇 |
1974年 | 10篇 |
1973年 | 13篇 |
1967年 | 8篇 |
排序方式: 共有2102条查询结果,搜索用时 15 毫秒
991.
Shikha Mehta Prashant Kumar Rai Nilesh Kumar Rai A. K. Rai Dane Bicanic Geeta Watal 《Food biophysics》2011,6(4):497-502
This paper reports, the Laser Induced Breakdown Spectroscopy (LIBS) studies and structure elucidation of compounds isolated
from the fruit extract of Moringa oleifera and also deals with their possible effects on some bacterial strains viz. Staphylococcus aureus, Klebsiella pneumonia, Escherichia coli and Pseudomonas aeruginosa. The extract was found to be active against all four microorganisms used. Extent of inhibitory effect of extract was assessed
at different concentrations of 25, 50, 75 mg/ml by measuring diameter of inhibition zone (DIZ). Our results clearly showed
that the 75 mg/ml concentration of the extract had 14, 12 and 18 mm of the DIZ against Staphylococcus aureus, Klebsiella pneumonia and Pseudomonas aeruginosa and 14 mm with 50 mg/ml concentration against Escherichia coli. The results were compared with the standard antibiotic ‘ampicillin’ of 1 mg/ml concentration. LIBS was recorded with high
power pulsed laser beam from Nd: YAG Laser (Continuum Surelite III-10), focused on the surface of the material, which was
in liquid form, to generate plasma on the surface of the sample. LIBS data clearly demonstrate the presence of trace elements,
magnesium and iron, in high concentration in the extract. Whereas, from the phytochemical profile reveals the presence of
two new compounds, S-ethyl-N-{4-[(α-L-rhamnosyloxy) benzyl]} thiocarbamate and 2-acetoxy {4-[(2′,3′,4′-tri-O-acetyl-α-L-rhamnosyloxy)
benzyl]} acetonitrile as the major constituents. This study is the first report on synergetic effect of the phytoconstituents
and certain set of elements present in their defined role in bacterial management against different bacterial strains. 相似文献
992.
993.
994.
Kanaly CW Ding D Mehta AI Waller AF Crocker I Desjardins A Reardon DA Friedman AH Bigner DD Sampson JH 《PloS one》2011,6(1):e16031
Current radiographic response criteria for brain tumors have difficulty describing changes surrounding postoperative resection cavities. Volumetric techniques may offer improved assessment, however usually are time-consuming, subjective and require expert opinion and specialized magnetic resonance imaging (MRI) sequences. We describe the application of a novel volumetric software algorithm that is nearly fully automated and uses standard T1 pre- and post-contrast MRI sequences. T1-weighted pre- and post-contrast images are automatically fused and normalized. The tumor region of interest is grossly outlined by the user. An atlas of the nasal mucosa is automatically detected and used to normalize levels of enhancement. The volume of enhancing tumor is then automatically calculated. We tested the ability of our method to calculate enhancing tumor volume with resection cavity collapse and when the enhancing tumor is obscured by subacute blood in a resection cavity. To determine variability in results, we compared narrowly-defined tumor regions with tumor regions that include adjacent meningeal enhancement and also compared different contrast enhancement threshold levels used for the automatic calculation of enhancing tumor volume. Our method quantified enhancing tumor volume despite resection cavity collapse. It detected tumor volume increase in the midst of blood products that incorrectly caused decreased measurements by other techniques. Similar trends in volume changes across scans were seen with inclusion or exclusion of meningeal enhancement and despite different automated thresholds for tissue enhancement. Our approach appears to overcome many of the challenges with response assessment of enhancing brain tumors and warrants further examination and validation. 相似文献
995.
Earl AM Desjardins CA Fitzgerald MG Arachchi HM Zeng Q Mehta T Griggs A Birren BW Toney NC Carr J Posey J Butler WR 《Standards in genomic sciences》2011,5(3):389-397
Segniliparus rugosus represents one of two species in the genus Segniliparus, the sole genus in the family Segniliparaceae. A unique and interesting feature of this family is the presence of extremely long carbon-chain length mycolic acids bound in the cell wall. S. rugosus is also a medically important species because it is an opportunistic pathogen associated with mammalian lung disease. This report represents the second species in the genus to have its genome sequenced. The 3,567,567 bp long genome with 3,516 protein-coding and 49 RNA genes is part of the NIH Roadmap for Medical Research, Human Microbiome Project. 相似文献
996.
Cancer stem cells (CSCs) or tumor initiating cells (TICs) make up only a small fraction of total tumor cell population, but recent evidence suggests that they are responsible for tumor initiation and the maintenance of tumor growth. Whether CSCs/TICs originate from normal stem cells or result from the dedifferentiation of terminally differentiated cells remains unknown. Here we provide evidence that sustained expression of the proinflammatory protein tissue transglutaminase (TG2) confers stem cell like properties in non-transformed and transformed mammary epithelial cells. Sustained expression of TG2 was associated with increase in CD44(high)/CD24(low/-) subpopulation, increased ability of cells to form mammospheres, and acquisition of self-renewal ability. Mammospheres derived from TG2-transfected mammary epithelial cells (MCF10A) differentiated into complex secondary structures when grown in Matrigel cultures. Cells in these secondary structures differentiated into Muc1-positive (luminal marker) and integrin α6-positive (basal marker) cells in response to prolactin treatment. Highly aggressive MDA-231 and drug-resistant MCF-7/RT breast cancer cells, which express high basal levels of TG2, shared many traits with TG2-transfected MCF10A stem cells but unlike MCF10A-derived stem cells they failed to form the secondary structures and to differentiate into Muc1-positive luminal cells when grown in Matrigel culture. Downregulation of TG2 attenuated stem cell properties in both non-transformed and transformed mammary epithelial cells. Taken together, these results suggested a new function for TG2 and revealed a novel mechanism responsible for promoting the stem cell characteristics in adult mammary epithelial cells. 相似文献
997.
Hedges DJ Guettouche T Yang S Bademci G Diaz A Andersen A Hulme WF Linker S Mehta A Edwards YJ Beecham GW Martin ER Pericak-Vance MA Zuchner S Vance JM Gilbert JR 《PloS one》2011,6(4):e18595
Despite the ever-increasing throughput and steadily decreasing cost of next generation sequencing (NGS), whole genome sequencing of humans is still not a viable option for the majority of genetics laboratories. This is particularly true in the case of complex disease studies, where large sample sets are often required to achieve adequate statistical power. To fully leverage the potential of NGS technology on large sample sets, several methods have been developed to selectively enrich for regions of interest. Enrichment reduces both monetary and computational costs compared to whole genome sequencing, while allowing researchers to take advantage of NGS throughput. Several targeted enrichment approaches are currently available, including molecular inversion probe ligation sequencing (MIPS), oligonucleotide hybridization based approaches, and PCR-based strategies. To assess how these methods performed when used in conjunction with the ABI SOLID3+, we investigated three enrichment techniques: Nimblegen oligonucleotide hybridization array-based capture; Agilent SureSelect oligonucleotide hybridization solution-based capture; and Raindance Technologies' multiplexed PCR-based approach. Target regions were selected from exons and evolutionarily conserved areas throughout the human genome. Probe and primer pair design was carried out for all three methods using their respective informatics pipelines. In all, approximately 0.8 Mb of target space was identical for all 3 methods. SOLiD sequencing results were analyzed for several metrics, including consistency of coverage depth across samples, on-target versus off-target efficiency, allelic bias, and genotype concordance with array-based genotyping data. Agilent SureSelect exhibited superior on-target efficiency and correlation of read depths across samples. Nimblegen performance was similar at read depths at 20× and below. Both Raindance and Nimblegen SeqCap exhibited tighter distributions of read depth around the mean, but both suffered from lower on-target efficiency in our experiments. Raindance demonstrated the highest versatility in assay design. 相似文献
998.
Autism spectrum disorders (ASD) are highly disabling developmental disorders with a population prevalence of 1-3%. Despite a strong genetic etiology, there are no current therapeutic options that target the core symptoms of ASD. Emerging evidence suggests that dysfunction of glutamatergic signaling, in particular through metabotropic glutamate receptor 5 (mGluR5) receptors, may contribute to phenotypic deficits and may be appropriate targets for pharmacologic intervention. This study assessed the therapeutic potential of 2-methyl-6-phenylethyl-pyrididine (MPEP), an mGluR5-receptor antagonist, on repetitive and anxiety-like behaviors in the valproic acid (VPA) mouse model of autism. Mice were exposed prenatally on day E13 to VPA and assessed for repetitive self-grooming and marble burying behaviors as adults. Anxiety-like behavior and locomotor activity were measured in an open-field. VPA-exposed mice displayed increased repetitive and anxiety-like behaviors, consistent with previously published results. Across both marble burying and self-grooming assays, MPEP significantly reduced repetitive behaviors in VPA-treated mice, but had no effect on locomotor activity. These results are consistent with emerging preclinical literature that mGluR5-antagonists may have therapeutic efficacy for core symptoms of autism. 相似文献
999.
Zaal KJ Reid E Mousavi K Zhang T Mehta A Bugnard E Sartorelli V Ralston E 《PloS one》2011,6(12):e29057
A wave of structural reorganization involving centrosomes, microtubules, Golgi complex and ER exit sites takes place early during skeletal muscle differentiation and completely remodels the secretory pathway. The mechanism of these changes and their functional implications are still poorly understood, in large part because all changes occur seemingly simultaneously. In an effort to uncouple the reorganizations, we have used taxol, nocodazole, and the specific GSK3-β inhibitor DW12, to disrupt the dynamic microtubule network of differentiating cultures of the mouse skeletal muscle cell line C2. Despite strong effects on microtubules, cell shape and cell fusion, none of the treatments prevented early differentiation. Redistribution of centrosomal proteins, conditional on differentiation, was in fact increased by taxol and nocodazole and normal in DW12. Redistributions of Golgi complex and ER exit sites were incomplete but remained tightly linked under all circumstances, and conditional on centrosomal reorganization. We were therefore able to uncouple microtubule reorganization from the other events and to determine that centrosomal proteins lead the reorganization hierarchy. In addition, we have gained new insight into structural and functional aspects of the reorganization of microtubule nucleation during myogenesis. 相似文献
1000.