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   508篇
  免费   45篇
  2023年   5篇
  2022年   6篇
  2021年   15篇
  2020年   10篇
  2019年   12篇
  2018年   23篇
  2017年   14篇
  2016年   15篇
  2015年   23篇
  2014年   31篇
  2013年   28篇
  2012年   41篇
  2011年   34篇
  2010年   28篇
  2009年   22篇
  2008年   27篇
  2007年   35篇
  2006年   29篇
  2005年   11篇
  2004年   21篇
  2003年   18篇
  2002年   18篇
  2001年   6篇
  2000年   5篇
  1999年   7篇
  1998年   5篇
  1997年   4篇
  1995年   4篇
  1994年   3篇
  1993年   4篇
  1992年   7篇
  1991年   2篇
  1990年   2篇
  1989年   1篇
  1987年   2篇
  1984年   2篇
  1983年   3篇
  1981年   1篇
  1980年   6篇
  1979年   6篇
  1978年   2篇
  1977年   2篇
  1976年   3篇
  1975年   1篇
  1973年   1篇
  1969年   1篇
  1968年   1篇
  1966年   2篇
  1965年   2篇
  1963年   1篇
排序方式: 共有553条查询结果,搜索用时 15 毫秒
71.
72.
The present study investigated the role of sugar beet extract (SBE) as a bio-stimulant to ameliorate the adverse effects of drought on seed germination and growth of wheat (Triticum aestivum L.). Different concentrations of SBE (0, 10, 20, 30, 40 and 50%) were used for priming the wheat seeds. The experiment was conducted in laboratory (PEG-8000 was used to create water stress) as well as under natural environmental conditions (using soil with 100 and 60% field capacity). Significant ameliorating effects of seed priming with SBE were recorded on different germination attributes, i.e., time to 50% emergence (E50), germination index (GI), mean emergence time (MET), germination percentage (G%), coefficient of uniformity of emergence (CUE) and germination energy (GE) under water stress. Without priming, the plants exhibited symptoms of water stress like decreased biomass, reduction in photosynthetic pigments, e.g., chlorophyll, carotenoids. Seed pre-conditioning with SBE improved the plant growth, photosynthetic pigments, antioxidants’ activities and nutrient homeostasis of plants facing water deficit and grown under well-watered conditions. The maximum increase in biomass, content of chlorophyll, carotenoids and activities of superoxide dismutase (SOD) and peroxidase (POD) was 13.4, 8.5, 11.9, 7.6, 13.6, 42.0, 19.8%, respectively, with SBE seed priming under water stress. In conclusion, SBE seed priming effectively reduced the negativities of water stress on seed germination which resulted in better plant growth in terms of enhanced biomass, photosynthetic pigments, antioxidant defense mechanism and better nutrient homeostasis. Overall, the findings suggest that seed pre-conditioning with SBE as a bio-stimulant will be helpful for better crop stand establishment under low field capacity, especially in semi-arid and arid agricultural fields.  相似文献   
73.
Proteomes of pathogenic Leptospira interrogans and L. borgpetersenii and the saprophytic L. biflexa were filtered through computational tools to identify Outer Membrane Proteins (OMPs) that satisfy the required biophysical parameters for their presence on the outer membrane. A total of 133, 130, and 144 OMPs were identified in L. interrogans, L. borgpetersenii, and L. biflexa, respectively, which forms approximately 4% of proteomes. A holistic analysis of transporting and pathogenic characteristics of OMPs together with Clusters of Orthologous Groups (COGs) among the OMPs and their distribution across 3 species was made and put forward a set of 21 candidate OMPs specific to pathogenic leptospires. It is also found that proteins homologous to the candidate OMPs were also present in other pathogenic species of leptospires. Six OMPs from L. interrogans and 2 from L. borgpetersenii observed to have similar COGs while those were not found in any intermediate or saprophytic forms. These OMPs appears to have role in infection and pathogenesis and useful for anti‐leptospiral strategies.  相似文献   
74.
Tyrosyl radicals are involved in many biologically important processes. The development of model compounds to mimic radical enzyme active sites, such as galactose oxidase (GO), has widely contributed to an enhanced understanding of their spectral properties, structural attributes and even reactivity. An emerging approach towards the synthesis of such active site mimetics is the use of peptidic ligands. The potential of cyclodecapeptides to bear phenoxyl radicals has been evaluated through three compounds. LH(4) (2+) is a cyclodecapetide containing two histidine residues (mimicking His(496) and His(581) of GO) and two tyrosine residues (mimicking Tyr(495) and the Tyr(272)* radical of GO). L(tBu)H(4) (2+) and L(OMe)H(4) (2+) incorporate 2,4,6-protected phenols in place of each tyrosine in LH(4) (2+). The deprotonation constants of each peptide determined by potentiometric titrations showed that there are some interactions between the acido-basic residues. Cyclic voltammetric studies revealed that only the peptides incorporating 2,4,6-protected phenolates exhibit reversible redox couples and are thus precursors of radicals stable enough to persist in solution. These studies also showed L(OMe2-) to possess the lower oxidation potential, indicating that this peptide, in its radical form, is the most stabilized. The electrochemically generated radical species have been characterized by EPR spectroscopy.  相似文献   
75.
76.
The demand for cloud computing is increasing dramatically due to the high computational requirements of business, social, web and scientific applications. Nowadays, applications and services are hosted on the cloud in order to reduce the costs of hardware, software and maintenance. To satisfy this high demand, the number of large-scale data centers has increased, which consumes a high volume of electrical power, has a negative impact on the environment, and comes with high operational costs. In this paper, we discuss many ongoing or implemented energy aware resource allocation techniques for cloud environments. We also present a comprehensive review on the different energy aware resource allocation and selection algorithms for virtual machines in the cloud. Finally, we come up with further research issues and challenges for future cloud environments.  相似文献   
77.
Chemical and isotopic changes in plant biochemicals that were transformed into organic geochemicals have been measured in anaerobic, freshwater marsh environments. In two litter bag studies, plant biochemicals decayed extensively in the first year, as recorded by dry weight, C:N ratios, δ15N of bulk tissue and amino acids, and δ13C of individual amino acids. Molecular analyses of Rubisco revealed that the high-molecular-weight enzyme subunit could be recognized antigenically for at least 12 months, but concentrations and amounts declined. Geochemical compounds, advanced glycation endproducts, were not found in fresh plants, but formed gradually with first indications documented at 3 months. The organic remains of plants were reworked or replaced by microbial products from decomposition, as indicated by a shift in the isotopic composition of individual amino acids in total plant protein. In experiments with Rubisco, isotopic changes over time in the individual amino acids in the 50–60 kDa molecular weight range were substantial. These high-molecular-weight substances were no longer pristine molecules. Biochemical and isotopic tools for studying living processes have been demonstrated to be effective and novel approaches to identify and quantify altered geochemical remnants. Received: 1 July 1998 / Accepted: 15 March 1999  相似文献   
78.
Partial 16S nucleotide sequences of Chlamydia psittaci isolates S26/3 (abortion), P94/1 (pigeon) and Chlamydia pecorum isolates W73 (enteric) and E58 (encephalomyelitis) were determined. Analysis of these data indicates very high levels of interspecies sequence conservation, with C. psittaci being more closely related to C. pecorum than to C. pneumoniae or C. trachomatis. Restriction enzyme analysis of nucleotide sequences indicated that BslI can be used to clearly distinguish C. psittaci and C. pecorum isolates. Psittacine and non-psittacine (pigeon) avian isolates of C. psittaci were distinguished using MaeI.  相似文献   
79.
Small molecule drugs have readily been developed against many proteins in the human proteome, but RNA has remained an elusive target for drug discovery. Increasingly, we see that RNA, and to a lesser extent DNA elements, show a persistent tertiary structure responsible for many diverse and complex cellular functions. In this digest, we have summarized recent advances in screening approaches for RNA targets and outlined the discovery of novel, drug-like small molecules against RNA targets from various classes and therapeutic areas. The link of structure, function, and small-molecule Druggability validates now for the first time that RNA can be the targets of therapeutic agents.  相似文献   
80.
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