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   1397篇
  免费   134篇
  2024年   1篇
  2023年   12篇
  2022年   28篇
  2021年   52篇
  2020年   23篇
  2019年   30篇
  2018年   42篇
  2017年   42篇
  2016年   64篇
  2015年   91篇
  2014年   122篇
  2013年   115篇
  2012年   132篇
  2011年   111篇
  2010年   83篇
  2009年   70篇
  2008年   87篇
  2007年   77篇
  2006年   85篇
  2005年   60篇
  2004年   54篇
  2003年   56篇
  2002年   41篇
  2001年   3篇
  2000年   5篇
  1999年   8篇
  1998年   5篇
  1997年   2篇
  1996年   6篇
  1995年   1篇
  1994年   6篇
  1993年   2篇
  1992年   3篇
  1989年   4篇
  1988年   3篇
  1984年   1篇
  1983年   1篇
  1980年   1篇
  1978年   1篇
  1975年   1篇
排序方式: 共有1531条查询结果,搜索用时 15 毫秒
201.
Organic rechargeable batteries gain huge scientific interest owing to the design flexibility and resource renewability of the active materials. However, the low reduction potentials still remain a challenge to compete with the inorganic cathodes. This study demonstrates a simple and efficient approach to tune the redox properties of perylene diimides (PDIs) as high voltage cathodes for organic‐based sodium‐ion batteries (SIBs). With appropriate electron‐withdrawing groups as substituents on perylene diimides, this study shows a remarkable tunability in the discharge potential from 2.1 to 2.6 V versus Na+/Na with a sodium intake of ≈1.6 ions per molecule. Further, this study explores tuning the shape of the voltage profiles by systematically tuning the dihedral angle in the perylene ring and demonstrates a single plateau discharge profile for tetrabromo‐substituted perylene diimide (dihedral angles θ1 & θ2 = 38°). Detailed structural analysis and electrochemical studies on substituted PDIs unveil the correlation between molecular structure and voltage profile. The results are promising and offer new avenues to tailor the redox properties of organic electrodes, a step closer toward the realization of greener and sustainable electrochemical storage devices.  相似文献   
202.
The urgent need for optimizing the available energy through smart grids and efficient large‐scale energy storage systems is pushing the construction and deployment of Li‐ion batteries in the MW range which, in the long term, are expected to hit the GW dimension while demanding over 1000 ton of positive active material per system. This amount of Li‐based material is equivalent to almost 1% of current Li consumption and can strongly influence the evolution of the lithium supply and cost. Given this uncertainty, it becomes mandatory to develop an energy storage technology that depends on almost infinite and widespread resources: Na‐ion batteries are the best technology for large‐scale applications. With small working cells in the market that cannot compete in cost ($/W h) with commercial Li‐ion batteries, the consolidation of Na‐ion batteries mainly depends on increasing their energy density and stability, the negative electrodes being at the heart of these two requirements. Promising Na‐based negative electrodes for large‐scale battery applications are reviewed, along with the study of the solid electrolyte interphase formed in the anode surface, which is at the origin of most of the stability problems.  相似文献   
203.
204.
Transects that traverse substantial climate gradients are important tools for climate change research and allow questions on the extent to which phenotypic variation associates with climate, the link between climate and species distributions, and variation in sensitivity to climate change among biomes to be addressed. However, the potential limitations of individual transect studies have recently been highlighted. Here, we argue that replicating and networking transects, along with the introduction of experimental treatments, addresses these concerns. Transect networks provide cost‐effective and robust insights into ecological and evolutionary adaptation and improve forecasting of ecosystem change. We draw on the experience and research facilitated by the Australian Transect Network to demonstrate our case, with examples, to clarify how population‐ and community‐level studies can be integrated with observations from multiple transects, manipulative experiments, genomics, and ecological modeling to gain novel insights into how species and systems respond to climate change. This integration can provide a spatiotemporal understanding of past and future climate‐induced changes, which will inform effective management actions for promoting biodiversity resilience.  相似文献   
205.
MicroRNAs (miRNAs) are endogenous small regulatory RNAs, which control gene expression in eukaryotes. In plants they repress mRNA targets containing a highly complementary site, either by cleavage or translational repression. Studies of individual miRNA/target interactions highlight the involvement of the miRNA-based regulations in a broad range of developmental programs, throughout plant lifecycle. MicroRNAs can have distinct regulatory functions on their targets: some determine their spatial accumulation, some have a buffering role that ensures the robustness of their expression pattern, and finally others establish the temporal expression of targeted genes.  相似文献   
206.
An in silico approach was used to investigate cytochrome c and the cytochrome c gene of Phanerochaete chrysosporium. The cytochrome c gene contains four introns. Omission of the introns reveals a DNA sequence coding for a complete predicted amino acid sequence for P. chrysosporium cytochrome c consistent with those of other cytochromes c. Fungal cytochromes c often have a short N-terminal peptide preceding a Gly that is the N-terminal amino acid in many cytochromes c. Thus a microexon codes for an N-terminal pentapeptide (MetProTyrAlaPro) in P. chrysosporium that is identical to the N-terminal pentapeptide of Schizosaccharomyces pombe, a well studied yeast, the genome of which bears more similarity to higher eukaryotes than to other fungi. The fourth intron, when omitted, reveals the presence of another microexon resulting in a sequence for the C-terminal portion of the protein and the stop codon. Interestingly, two interpretations for the sequence of this intron leads to predictions that the C-terminal sequence ends with either AlaValAsn or AlaTyr. Selected aspects of the molecular architecture of cytochrome c and regulatory control elements of the P. chrysosporium cytochrome c gene were analyzed and compared to those present in other fungi and to those present in genes for lignin peroxidases and cytochromes P-450, two important families of hemeproteins produced by this fungus.  相似文献   
207.
1 The intra‐plot spatial distribution of the green leafhopper Empoasca vitis (Goethe) (Cicadellidae, Empoascini) was assessed over three successive growing seasons in a Bordeaux vineyard. Weekly measurements of adult trappings and nymphal counts were performed in a 1.7‐ha plot on 130 sampling points. 2 Statistical and geostatistical analyses revealed inconsistent spatial distributions of adults and nymphs in spring, but consistent spatial distributions in summer, which were identical every year. 3 Similarities between spatial distributions of the mobile adults and the sedentary and aggregated nymphs strongly suggest that adults disperse inside the plot to areas preferred for egg deposition. 4 The similarity of summer populations among years suggests that this insects distribution is based on (perennial) differences in plot characteristics.  相似文献   
208.
The conformational behavior of a long single-chain double-stranded DNA in solutions of free silver ions and silver nanoparticles generated via the reduction of AgNO3 by NaBH4 was monitored by fluorescence and electron microscopies and UV spectroscopy. The interaction of monovalent silver ions with DNA induces shrinking of a DNA-coiled polymer chain as a result of a decrease in the DNA persistence length through the complexation of Ag+ with DNA bases. In contrast, the reduction of silver ions by NaBH4 in DNA solutions triggers DNA compaction: a DNA transition from elongated coil state into a compact state. This transition is continuous, unlike the all-or-none discrete DNA compaction that is commonly seen with multications. It is suggested that the collapse of DNA is accompanied by growth aggregation of silver nanoparticles generated on the DNA template.  相似文献   
209.
Targeted liquid chromatography-mass spectrometry (LC-MS) technology using size exclusion chromatography and metabolite profiling based on gas chromatography-mass spectrometry (GC-MS) were used to study the nickel-rich latex of the hyperaccumulating tree Sebertia acuminata. More than 120 compounds were detected, 57 of these were subsequently identified. A methylated aldaric acid (2,4,5-trihydroxy-3-methoxy-1,6-hexan-dioic acid) was identified for the first time in biological extracts and its structure was confirmed by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. After citric acid, it appears to be one of the most abundant small organic molecules present in the latex studied. Nickel(II) complexes of stoichiometry NiII:acid=1:2 were detected for these two acids as well as for malic, itaconic, erythronic, galacturonic, tartaric, aconitic and saccharic acids. These results provide further evidence that organic acids may play an important role in the transport and possibly in the storage of metal ions in hyperaccumulating plants.  相似文献   
210.
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