全文获取类型
收费全文 | 187篇 |
免费 | 35篇 |
专业分类
222篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 5篇 |
2012年 | 12篇 |
2011年 | 18篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 10篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 14篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 4篇 |
2001年 | 4篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 0 毫秒
131.
132.
Tyler J. Slade Trevor P. Bailey Jann A. Grovogui Xia Hua Xiaomi Zhang Jimmy Jiahong Kuo Ido Hadar G. Jeffrey Snyder Chris Wolverton Vinayak P. Dravid Ctirad Uher Mercouri G. Kanatzidis 《Liver Transplantation》2019,9(30)
PbSe is an attractive thermoelectric material due to its favorable electronic structure, high melting point, and lower cost compared to PbTe. Herein, the hitherto unexplored alloys of PbSe with NaSbSe2 (NaPbmSbSem+2) are described and the most promising p‐type PbSe‐based thermoelectrics are found among them. Surprisingly, it is observed that below 500 K, NaPbmSbSem+2 exhibits unorthodox semiconducting‐like electrical conductivity, despite possessing degenerate carrier densities of ≈1020 cm?3. It is shown that the peculiar behavior derives from carrier scattering by the grain boundaries. It is further demonstrated that the high solubility of NaSbSe2 in PbSe augments both the thermoelectric properties while maintaining a rock salt structure. Namely, density functional theory calculations and photoemission spectroscopy demonstrate that introduction of NaSbSe2 lowers the energy separation between the L‐ and Σ‐valence bands and enhances the power factors under 700 K. The crystallographic disorder of Na+, Pb2+, and Sb3+ moreover provides exceptionally strong point defect phonon scattering yielding low lattice thermal conductivities of 1–0.55 W m‐1 K‐1 between 400 and 873 K without nanostructures. As a consequence, NaPb10SbSe12 achieves maximum ZT ≈1.4 near 900 K when optimally doped. More importantly, NaPb10SbSe12 maintains high ZT across a broad temperature range, giving an estimated record ZTavg of ≈0.64 between 400 and 873 K, a significant improvement over existing p‐type PbSe thermoelectrics. 相似文献
133.
Abstract. Fuel-breaks to impede the spread of fires in Mediterranean woody vegetation are created by clearing of shrubs, followed by very intensive cattle grazing before the fire season. The present research analysed the effects of these two disturbance types on herbaceous community composition at the functional group and the species level, by using canonical discriminant ordination analysis and by categorical modeling methods. Grazing caused an increase in the abundance of small species, geophytes, and species with an early flowering period that ends before the grazing period. The abundance of many different species increased as a result of clearing. However, no association was found between positive or negative response to clearing and any species attribute tested. Several a priori functional groups defined by life form and family showed responses to either grazing or clearing. Links between these responses and individual species attributes are discussed. The results emphasize the different nature of the two disturbances: grazing as a selective agent, and shrub clearing as a generalized one. It also stresses the importance of the plant architecture and the morphological and phenological niche in determining community composition under extremely intensive grazing conditions. 相似文献
134.
Eldad J. Hadar William B. Ershler Regina A. Kreisle Shu-Peng Ho Michael J. Volk Roger G. Klopp 《Cancer immunology, immunotherapy : CII》1988,26(1):31-34
Summary Lymphocyte-induced angiogenesis factor (LIA) is a product of T lymphocytes which has been shown to stimulate new vessel formation. Because immune senescence most profoundly affects T lymphocyte functions, we suspected that LIA production would decline with age. An assay for angiogenesis stimulated by allogeneic reaction was performed by injecting spleen cells from young or old donor mice into the skin of irradiated allogeneic recipient mice. The spleen cells from young mice induced a significantly greater number of vessels than did cells from older mice. In additional experiments, spleen cells from young and old animals were treated with a monoclonal antibody GK1.5) directed at the L3T4 antigen on murine T helper lymphocytes. Such treatment significantly reduced the new vessel formation induced by young lymphocytes but had no effect on that induced by lymphocytes from old animals. Studies employing indirect immunofluorescence demonstrated that the proportion of L3T4+ cells in the mononuclear fraction of splenocytes was nearly identical in both young and old mice. From these investigations we can conclude that (1) L3T4+ lymphocytes are responsible for LIA production, and (2) production, like that of other T lymphokines, declines with age.Supported by NIH grant AG 00332 and VA Merit Award (WBE) 相似文献
135.
Rotem Saar-Ashkenazy Ronel Veksler Jonathan Guez Yael Jacob Ilan Shelef Hadar Shalev Alon Friedman Jonathan E. Cohen 《PloS one》2016,11(2)
Altered brain anatomy in specific gray-matter regions has been shown in patients with posttraumatic stress disorder (PTSD). Recently, white-matter tracts have become a focus of research in PTSD. The corpus callosum (CC) is the principal white-matter fiber bundle, crucial in relaying sensory, motor and cognitive information between hemispheres. Alterations in CC fibers have been reported in PTSD and might be assumed to underlie substantial behavioral and cognitive sequelae; however most diffusion tensor imaging (DTI) studies in adult-onset PTSD failed to address the clinical correlates between imaging and PTSD symptoms severity, behavioral manifestation and cognitive functions. In the current study we examined (a) to what extent microstructural integrity of the CC is associated with memory performance and (b) whether imaging and cognitive parameters are associated with PTSD symptom severity. DTI data were obtained and fractional anisotropy (FA) values were computed for 16 patients and 14 controls. PTSD symptom severity was assessed by employing the clinician administered PTSD scale (CAPS) and memory was tested using a task probing item and associative memory for words and pictures. Significant correlations were found between PTSD symptoms severity, memory accuracy and reaction-time to CC FA values in the PTSD group. This study demonstrates meaningful clinical and cognitive correlates of microstructural connectivity. These results have implications for diagnostic tools and future studies aimed at identifying individuals at risk for PTSD. 相似文献
136.
Iris Lavi Dana Levinson Irena Peri Yoram Tekoah Yitzhak Hadar Betty Schwartz 《Applied microbiology and biotechnology》2010,85(6):1977-1990
Mushroom polysaccharides are potent substances that exhibit antitumor and immunomodulatory properties. Studies comparing the
chemical composition and antitumor-related activities of polysaccharides released by fungal strains under different growth
conditions are not available. Thus, the present study compared polysaccharides extracts produced by Pleurotus pulmonarius from mycelium grown in liquid culture (ME) or fruiting bodies (FBE). Polysaccharides of both ME and FBE had a relatively
high molecular mass. NMR spectroscopy indicated that ME glucan is an α-glucan whereas FBE glucan is a mixture of both α- and
β-glucans. Glucose and galactose where the most prominent monosaccharide in both glucans. Treatment of several colon cancer
cell lines expressing varying amounts of galectin-3 with the two fungal glucans inhibited their viability and significantly
reduced their ability to adhere to the key component of the extracellular matrix, fibronectin, and to a human umbilical vein
endothelial cell monolayer, in a time- and dose-dependent manner mainly in those cell lines expressing high amounts of galectin-3.
We conclude that ME and FBE glucans may exert a direct antiproliferative effect on cancer cells expressing high galectin-3
concentrations and concomitantly downregulate tumor cell adherence, the latter being directly related to cancer progression
and metastasis. 相似文献
137.
Interaction of c(60)-fullerene and carboxyfullerene with proteins: docking and binding site alignment 总被引:1,自引:0,他引:1
Benyamini H Shulman-Peleg A Wolfson HJ Belgorodsky B Fadeev L Gozin M 《Bioconjugate chemistry》2006,17(2):378-386
The unique properties of fullerenes have raised the interest of using them for biomedical applications. Within this framework, the interactions of fullerenes with proteins have been an exciting research target, yet little is known about how native proteins can bind fullerenes, and what is the nature of these interactions. Moreover, though some proteins have been shown to interact with fullerenes, up to date, no crystal structure of such complexes was obtained. Here we report docking studies aimed at examining the interactions of fullerene in two forms (C60 nonsubstituted fullerene and carboxyfullerene) with four proteins that are known to bind fullerene derivatives: HIV protease, fullerene-specific antibody, human serum albumin, and bovine serum albumin. Our work provides docking models with detailed binding pockets information, which closely match available experimental data. We further compare the predicted binding sites using a novel multiple binding site alignment method. A high similarity between the physicochemical properties and surface geometry was found for fullerene's binding sites of HIV protease and the human and bovine serum albumins. 相似文献
138.
Sharfi H Eldar-Finkelman H 《American journal of physiology. Endocrinology and metabolism》2008,294(2):E307-E315
Serine phosphorylation of insulin receptor substrate (IRS) proteins is a potential inhibitory mechanism in insulin signaling. Here we show that IRS-2 is phosphorylated by glycogen synthase kinase (GSK)-3. Phosphorylation by GSK-3 requires prior phosphorylation of its substrates, prompting us to identify the "priming kinase." It was found that the stress activator anisomycin enhanced the ability of GSK-3 to phosphorylate IRS-2. Use of a selective c-Jun NH(2)-terminal kinase (JNK) inhibitor and cells overexpressing JNK implicated JNK as the priming kinase. This allowed us to narrow down the number of potential GSK-3 phosphorylation sites within IRS-2 to four regions that follow the motif SXXXSP. IRS-2 deletion mutants enabled us to localize the GSK-3 and JNK phosphorylation sites to serines 484 and 488, respectively. Mutation at serine 488 reduced JNK phosphorylation of IRS-2, and mutation of each site separately abolished GSK-3 phosphorylation of IRS-2. Treatment of H4IIE liver cells with anisomycin inhibited insulin-induced tyrosine phosphorylation of IRS-2; inhibition was reversed by pretreatment with the JNK and GSK-3 inhibitors. Moreover, overexpression of JNK and GSK-3 in H4IIE cells reduced insulin-induced tyrosine phosphorylation of IRS-2 and its association with the p85 regulatory subunit of phosphatidylinositol 3-kinase. Finally, both GSK-3 and JNK are abnormally upregulated in the diabetic livers of ob/ob mice. Together, our data indicate that IRS-2 is sequentially phosphorylated by JNK and GSK-3 at serines 484/488 and provide evidence for their inhibitory role in hepatic insulin signaling. 相似文献
139.
Molecular analysis of bacterial community succession during prolonged compost curing 总被引:2,自引:0,他引:2
The compost environment consists of complex organic materials that form a habitat for a rich and diverse microbial community. The aim of this research was to study the dynamics of microbial communities during the compost-curing phase. Three different methods based on 16S rRNA gene sequence were applied to monitor changes in the microbial communities: (1) denaturing gradient gel electrophoresis of PCR-generated rRNA gene fragments; (2) partial rRNA gene clone libraries; and (3) a microarray of oligonucleotide probes targeting rRNA gene sequences. All three methods indicated distinctive community shifts during curing and the dominant species prevailing during the different curing stages were identified. We found a successional transition of different bacterial phylogenetic groups during compost curing. The Proteobacteria were the most abundant phylum in all cases. The Bacteroidetes and the Gammaproteobacteria were ubiquitous. During the midcuring stage, Actinobacteria were dominant. Different members of nitrifying bacteria and cellulose and macromolecule-degrading bacteria were found throughout the curing process. In contrast, pathogens were not detected. In the cured compost, bacterial population shifts were still observed after the compost organic matter and other biochemical properties had seemingly stabilized. 相似文献
140.