首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   340篇
  免费   25篇
  365篇
  2024年   2篇
  2023年   4篇
  2022年   3篇
  2021年   12篇
  2020年   6篇
  2019年   5篇
  2018年   11篇
  2017年   5篇
  2016年   10篇
  2015年   15篇
  2014年   22篇
  2013年   19篇
  2012年   20篇
  2011年   23篇
  2010年   19篇
  2009年   16篇
  2008年   9篇
  2007年   13篇
  2006年   11篇
  2005年   11篇
  2004年   16篇
  2003年   11篇
  2002年   9篇
  2001年   10篇
  2000年   11篇
  1999年   5篇
  1998年   3篇
  1997年   3篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   1篇
  1991年   4篇
  1990年   9篇
  1989年   7篇
  1988年   4篇
  1987年   5篇
  1986年   7篇
  1985年   6篇
  1984年   3篇
  1983年   4篇
  1982年   1篇
  1980年   4篇
  1978年   1篇
排序方式: 共有365条查询结果,搜索用时 0 毫秒
31.
A novel hybrid of small core@shell structured CoSx@Cu2MoS4 uniformly hybridizing with a molybdenum dichalcogenide/N,S‐codoped graphene hetero‐network (CoSx@Cu2MoS4‐MoS2/NSG) is prepared by a facile route. It shows excellent performance toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in alkaline medium. The hybrid exhibits rapid kinetics for ORR with high electron transfer number of ≈3.97 and exciting durability superior to commercial Pt/C. It also demonstrates great potential with remarkable stability for HER and OER, requiring low overpotential of 118.1 and 351.4 mV, respectively, to reach a current density of 10 mA cm?2. An electrolyzer based on CoSx@Cu2MoS4‐MoS2/NSG produces low cell voltage of 1.60 V and long‐term stability, surpassing a device of Pt/C + RuO2/C. In addition, a Zn‐air battery using cathodic CoSx@Cu2MoS4‐MoS2/NSG catalyst delivers a high cell voltage of ≈1.44 V and a power density of 40 mW cm?2 at 58 mA cm?2, better than the state‐of‐the‐art Pt/C catalyst. These achievements are due to the rational combination of highly active core@shell CoSx@Cu2MoS4 with large‐area and high‐porosity MoS2/NSG to produce unique physicochemical properties with multi‐integrated active centers and synergistic effects. The outperformances of such catalyst suggest an advanced candidate for multielectrocatalysis applications in metal‐air batteries and hydrogen production.  相似文献   
32.
33.
Enzyme replacement therapy (ERT) for Gaucher disease designed to target glucocerebrosidase (GC) to macrophages via mannose-specific endocytosis is very effective in reversing hepatosplenomegaly, and normalizing hematologic parameters but is less effective in improving bone and lung involvement and ineffective in brain. Recombinant GCs containing an in-frame fusion to the HIV-1 trans-activator protein transduction domain (TAT) were expressed in eukaryotic cells in order to obtain active, normally glycosylated GC fusion proteins for enzyme uptake studies. Despite the absence of mannose-specific endocytic receptors on the plasma membranes of various fibroblasts, the recombinant GCs with C-terminal TAT fusions were readily internalized by these cells. Immunofluorescent confocal microscopy demonstrated the recombinant TAT-fusion proteins with a mixed endosomal and lysosomal localization. Thus, TAT-modified GCs represent a novel strategy for a new generation of therapeutic enzymes for ERT for Gaucher disease.  相似文献   
34.
High conductance gamma-aminobutyric acid type A (GABA(A)) channels (>40 picosiemens (pS)) have been reported in some studies on GABA(A) channels in situ but not in others, whereas recombinant GABA(A) channels do not appear to display conductances above 40 pS. Furthermore, the conductance of some native GABA(A) channels can be increased by diazepam or pentobarbital, which are effects not reported for expressed GABA(A) channels. GABARAP, a protein associated with native GABA(A) channels, has been reported to cause clustering of GABA(A) receptors and changes in channel kinetics. We have recorded single channel currents activated by GABA in L929 cells expressing alpha(1), beta(1), and gamma(2S) subunits of human GABA(A) receptors. Channel conductance was never higher than 40 pS and was not significantly increased by diazepam or pentobarbital, although open probability was increased. In contrast, in cells expressing the same three subunits together with GABARAP, channel conductance could be significantly higher than 40 pS, and channel conductance was increased by diazepam and pentobarbital. GABARAP caused clustering of receptors in L929 cells, and we suggest that there may be interactions between subunits of clustered GABA(A) receptors that make them open co-operatively to give high conductance "channels." Recombinant channels may require the influence of GABARAP and perhaps other intracellular proteins to adopt a fuller repertoire of properties of native channels.  相似文献   
35.
The purpose of this study is to quantify the spatial distribution of acoustic velocities and elastic properties (elastic constants) on Human femoral cortical bone. Four cross sections (average thickness of 2.09+/-0.27 mm) have been cut transversally between 40% and 70% of the total length and between them parallelepiped samples in each quadrant have been cut. Ultrasonic technique in transmission with immersion focused transducers at 5 MHz and contact transducers 2.25 MHz were used on the cross sections and parallelepiped samples, respectively. The first technique allows relative spatial distribution of velocities to be obtained, meanwhile the second technique allows the direct assessment of elastic constants. For both techniques, bulk velocities were found to be lower at the posterior side with an increase along the length (from 40% to 70% total length) (p < 0.05). Densities and elastic constants show equivalent pattern of variation. These variations are mainly due the cortical porosity related to vascularisation environment. The spatial distribution of velocities exhibits significant radial variation from the endosteal to the periosteal region. This is in agreement with variation of the porosity at that location. Same range of velocities was obtained with both techniques. The range of longitudinal velocities values varies from 3548 to 3967 m/s and between 18.5 and 33.1 GPa for the bulk velocities and axial elastic constants, respectively. Our results are within the range with those found in the literature. However, it must be noted that the range of acoustic and elastic properties variation is concerning the same bone. So, our new results show the ability of the technique to quantify accurately local variation of acoustic and elastic properties (within the section and along the length) of human cortical bone. Furthermore, our immersion technique could be used to assess the spatial distribution of the elastic constants with the knowledge of spatial distribution of densities.  相似文献   
36.
One of the reasons for the lack of nerve regeneration in the CNS is the formation of a glial scar over-expressing multiple inhibitory factors including myelin-associated proteins and members of the Semaphorin family. Innovative therapeutic strategies must stimulate axon extension across the lesion site despite this inhibitory molecular barrier. We recently developed a synthetic neurotrophic compound combining an omega-alkanol with a retinol-like cycle (3-(15-hydroxy-pentadecyl)-2,4,4,-trimethyl-cyclohexen-2-one (tCFA15)). Here, we demonstrate that tCFA15 is able to promote cortical axon outgrowth in vitro even in the presence of the inhibitory Semaphorin 3A and myelin extracts. This growth-promoting effect is selectively observed in axons and requires multiple growth-associated intracellular pathways. Our results illustrate the potential use of synthetic neurotrophic compounds to promote nerve regeneration by counteracting the axonal growth inhibition triggered by glial scar-associated inhibitory factors.  相似文献   
37.
The synthesis of a series of Tocopherol long chain Fatty Alcohols (TFA) and their biological activities on the modulation of microglial activation are described. Specifically, the 2-(12-hydroxy-dodecyl)-2,5,7,8-tetramethyl-chroman-6-ol, the TFA bearing 12 carbon atoms on the side chain (n=12), shows the most potent inhibition of secretion on nitric oxide (NO) and tumour necrosis factor-alpha (TNF-alpha) by lipopolysaccharide (LPS)-activated microglia.  相似文献   
38.
Recently, 3D small intestinal organoids (enteroids) have been developed from cultures of intestinal stem cells which differentiate in vitro to generate all the differentiated epithelial cell types associated with the intestine and mimic the structural properties of the intestine observed in vivo. Small‐molecule drug treatment can skew organoid epithelial cell differentiation toward particular lineages, and these skewed enteroids may provide useful tools to study specific epithelial cell populations, such as goblet and Paneth cells. However, the extent to which differentiated epithelial cell populations in these skewed enteroids represent their in vivo counterparts is not fully understood. This study utilises label‐free quantitative proteomics to determine whether skewing murine enteroid cultures toward the goblet or Paneth cell lineages results in changes in abundance of proteins associated with these cell lineages in vivo. Here, proteomics data confirms that skewed enteroids recapitulate important features of the in vivo gut environment, demonstrating that they can serve as useful models for the investigation of normal and disease processes in the intestine. Furthermore, comparison of mass spectrometry data with histology data contained within the Human Protein Atlas identifies putative novel markers for goblet and Paneth cells.  相似文献   
39.
The Papanicolaou test (or Pap test) has long been used as a screening tool to detect cervical precancerous/cancerous lesions. However, studies on the use of this test to predict both the presence and change in size of genital warts are limited. We examined whether cervical Papanicolaou test results are associated with the size of the largest anal wart over time in HIV-infected women in an on-going cohort study in the US. A sample of 976 HIV-infected women included in a public dataset obtained from the Women’s Interagency HIV Study (WIHS) was selected for analysis. A linear mixed model was performed to determine the relationship between the size of anal warts and cervical Pap test results. About 32% of participants had abnormal cervical Pap test results at baseline. In the adjusted model, a woman with a result of Atypia Squamous Cell Undetermined Significance/Low-grade Squamous Intraepithelial Lesion (ASCUS/LSIL) had an anal wart, on average, 12.81 mm2 larger than a woman with normal cervical cytology. The growth rate of the largest anal wart after each visit in a woman with ASCUS/LSIL was 1.56 mm2 slower than that of a woman with normal cervical results. However, they were not significant (P = 0.54 and P = 0.82, respectively). This is the first study to examine the relationship between cervical Pap test results and anal wart development in HIV-infected women. Even though no association between the size of anal wart and cervical Pap test results was found, a screening program using anal cytology testing in HIV-infected women should be considered. Further studies in cost-effectiveness and efficacy of an anal cytology test screening program are warranted.  相似文献   
40.
The Chinese water pine Glyptostrobus pensilis is the sole surviving species of the genus Glyptostrobus. It is endemic to southern China, central Vietnam, and eastern Laos, and today it is nearly extinct in the wild. Forest community characteristics and population structure of G. pensilis in China have remained un-known up to now. We investigated six swamp forest stands and analyzed their forest community characteristics (i.e. vertical stratification, species composition, and diversity) and population structure, including the frequency distribution of DBH (diameter at breast height) and age-classes as found in Fujian Province, southeastern China. The vertical stratifications of all the forest stands were rather simple. The remaining wild specimens ranged from roughly 15 to some 357 years for an average of ca. 85 years, with only a few individuals less than 20 years old. Compared with the stands and populations of G. pensilis in Vietnam, the taxonomic compositions of the stands in the two regions were different, except for the dominant species-G. pensilis. The Shannon-Wiener index showed the overstory of each stand had much lower diversity (0.26 on average) in Fujian Province than that (1.97 on average) in Vietnam, whereas the diversity indices were about the same (around 2.41) for the understories in the two regions. Furthermore, we discovered 18 G. pensilis seedlings at the study sites in Fujian Province. This discovery demonstrates that G. pensilis regeneration is extremely poor and its populations are declining, although these populations are rela-tively healthier than those in Vietnam.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号