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   3934篇
  免费   286篇
  国内免费   1篇
  2023年   7篇
  2022年   29篇
  2021年   65篇
  2020年   38篇
  2019年   51篇
  2018年   82篇
  2017年   59篇
  2016年   120篇
  2015年   209篇
  2014年   216篇
  2013年   283篇
  2012年   374篇
  2011年   368篇
  2010年   186篇
  2009年   165篇
  2008年   262篇
  2007年   266篇
  2006年   223篇
  2005年   235篇
  2004年   200篇
  2003年   181篇
  2002年   180篇
  2001年   31篇
  2000年   23篇
  1999年   39篇
  1998年   39篇
  1997年   45篇
  1996年   37篇
  1995年   24篇
  1994年   25篇
  1993年   17篇
  1992年   19篇
  1991年   16篇
  1990年   14篇
  1989年   11篇
  1988年   12篇
  1987年   10篇
  1986年   17篇
  1985年   7篇
  1984年   9篇
  1983年   7篇
  1982年   4篇
  1981年   4篇
  1980年   2篇
  1978年   4篇
  1976年   1篇
  1968年   1篇
  1967年   1篇
  1966年   1篇
  1965年   1篇
排序方式: 共有4221条查询结果,搜索用时 31 毫秒
891.
892.
Social impacts of novel technology can, parallel to environmental and economic consequences, influence its sustainability. By analyzing the case of hydrogen production by advanced alkaline water electrolysis (AEL) from a life cycle perspective, this paper illustrates the social implications of the manufacturing of the electrolyzer and hydrogen production when installed in Germany, Austria, and Spain. This paper complements previous environmental and economic assessments, which selected this set of countries based on their different structures in electricity production. The paper uses a mixed method design to analyze the social impact for the workers along the process chain. Appropriate indicators related to working conditions are selected on the basis of the UN Agenda 2030 Sustainable Development Goals. The focus on workers is chosen as a first example to test the relatively new Product Social Impact Life Cycle Assessment (PSILCA) database version 2.0. The results of the quantitative assessment are then complemented and compared through an investigation of the underlying raw data and a qualitative literature analysis. Overall, advanced AEL is found to have least social impact along the German process chain, followed by the Spanish and the Austrian. All three process chains show impacts on global upstream processes. In order to reduce social impact and ultimately contribute to Sustainable Development, policymakers and industry need to work together to further improve certain aspects of working conditions in different locations, particularly within global upstream processes.  相似文献   
893.
The preservation of lactic acid starter cultures by alternative drying processes has attracted increasing attention due to the high costs and energy consumption of freezing and freeze drying. This review thus aims to provide a survey regarding the state of knowledge of starter culture production at high levels of viability. The results from numerous studies on various drying processes and lactic acid bacteria are summarized. The alternative drying processes considered, such as spray drying, fluidized bed drying, and vacuum drying, are mainly of industrial interest. The features, advantages, and disadvantages of these drying processes are described. In conclusion, the important factors that need to be considered, standardized, or optimized to achieve high levels of viability include intrinsic tolerance of cultures, growth media and conditions, stress induction, cell harvesting conditions, protective agents, rehydration conditions, enumeration of cells, and storage conditions.  相似文献   
894.
The occurrence of multiple strains of prions may reflect conformational variability of PrP(Sc), a disease-associated, aggregated variant of the cellular prion protein, PrP(C). Here we used luminescent conjugated polymers (LCPs), which emit conformation-dependent fluorescence spectra, for characterizing prion strains. LCP reactivity and emission spectra of brain sections discriminated among four immunohistochemically indistinguishable, serially mouse-passaged prion strains derived from sheep scrapie, chronic wasting disease (CWD), bovine spongiform encephalopathy (BSE), and mouse-adapted Rocky Mountain Laboratory scrapie prions. Furthermore, using LCPs we differentiated between field isolates of BSE and bovine amyloidotic spongiform encephalopathy, and identified noncongophilic deposits in prion-infected deer and sheep. We found that fibrils with distinct morphologies generated from chemically identical recombinant PrP yielded unique LCP spectra, suggesting that spectral characteristic differences resulted from distinct supramolecular PrP structures. LCPs may help to detect structural differences among discrete protein aggregates and to link protein conformational features with disease phenotypes.  相似文献   
895.
896.
An already well-described method for the determination of nitrofuran metabolites 3-amino-5-methyl-morpholino-2-oxazolidinone (AMOZ), 3-amino-2-oxazolidinone (AOZ), semicarbazide (SEM) and 1-aminohydantoin (AHD) was adapted to the needs of our laboratory and checked for its robustness regarding sample conditions and the processing step. Using the same data, the method was validated and the measurement uncertainty was estimated. All criteria and requirements of Commission Decision 2002/657/EC were fulfilled. The CC(alpha) determined lies between 0.1 and 0.7 microg/kg, the CC(beta) lies between 0.1 and 0.9 microg/kg, the measurement uncertainty was estimated as being between 7 and 17% taking into account matrix, time and sample preparation influences.  相似文献   
897.
Nitric oxide (NO) plays a pivotal role in the modulation of multiple physiological processes. It acts as a messenger molecule within the cardiovascular system. NO is a highly unstable free radical in circulating blood and is oxidized rapidly to nitrite and nitrate. Recent studies suggest that nitrite has the potential to function as a surrogate of NO production under physiological and pathophysiological conditions and could therefore be of high relevance as a biochemical parameter in experimental and clinical studies. Under hypoxic conditions nitrite is reduced to bioactive NO by deoxyhemoglobin. This mechanism may represent a dynamic cycle of NO generation to adapt the demand and supply for the vascular system. Because of these potential biological functions the concentration of nitrite in blood is thought to be of particular importance. The determination of nitrite in biological matrices represents a considerable analytical challenge. Methodological problems often arise from pre-analytical sample preparation, sample contamination due to the ubiquity of nitrite, and from lack of selectivity and sensitivity. These analytical difficulties may be a plausible explanation for reported highly diverging concentrations of nitrite in the human circulation. The aim of this article is to review the methods of quantitative analysis of nitrite in the human circulation, notably in plasma and blood, and to discuss pre-analytical and analytical factors potentially affecting accurate quantification of nitrite in these human fluids.  相似文献   
898.
The symposium High Performance Proteomics was held in Dortmund on May 14-16, 2007, to celebrate the opening of the Zentrum für Angewandte Proteomik as well as the 6(th) anniversary of the German Human Brain Proteome Project. It offered an outstanding opportunity to obtain a broad overview about all fields of proteomics and related fields, combining the expertise of biochemists, physicians, bioinformatics, mathematicians and other researchers in Life Sciences. The main topics were the presentation of state-of-the-art proteomics technologies as well as possible transfer models for industrial applications. An accompanying industrial exhibition, as well as a discussion panel, offered the possibility to get in contact with colleagues and potential industrial partners. A visit to the former colliery Zeche Zollern and the social event at the Harenberg City-Center with an excellent view around Dortmund also left time for further communication between the more than 200 attendees.  相似文献   
899.
Ammodytoxins are neurotoxic secretory phospholipase A(2) molecules, some of the most toxic components of the long-nosed viper (Vipera ammodytes ammodytes) venom. Envenomation by this and by closely related vipers is quite frequent in southern parts of Europe and serotherapy is used in the most severe cases. Because of occasional complications, alternative medical treatment of envenomation is needed. In the present study, ammodytoxin inhibitor was purified from the serum of V. a. ammodytes using two affinity procedures and a gel exclusion chromatography step. The ammodytoxin inhibitor from V. a. ammodytes serum consists of 23- and 25-kDa glycoproteins that form an oligomer, probably a tetramer, of about 100 kDa. N-terminal sequencing and immunological analysis revealed that both types of subunit are very similar to gamma-type secretory phospholipase A(2) inhibitors. The ammodytoxin inhibitor from V. a. ammodytes serum is a potent inhibitor of phospholipase activity and hence probably also the neurotoxicity of ammodytoxins. Discovery of the novel natural inhibitor of these potent secretory phospholipase A(2) toxins opens up prospects for the development of new types of small peptide inhibitors for use in regulating the physiological and pathological activities of secretory phospholipases A(2).  相似文献   
900.
Innovative therapies for severe lung diseases (such as allergic and chronic asthma, chronic obstructive pulmonary disease or any type of lung cancer) require a detailed understanding of the cellular and immune processes in the lung. This protocol details a method to obtain the immune cells of the bronchi as well as the cytokines and mediators produced by these cells for further investigation. The broncho-alveolar lavage fluid (BALF) is taken by injecting physiological solution through the tracheal tube into the murine airways and carefully regained by winding up the connected syringe. After centrifugation, the resulting BALF supernatant can be stored for detection of cytokines or other mediators by enzyme-linked immunosorbent assay or other methods; the resuspended cell pellet can also be used for flow cytometric analyses, to check cell viability and the level of apoptosis, as well as other applications. In addition, CD4+ T cells isolated from wild-type and genetically modified mice alone or along with other immunologically important cells such as T regulatory cells, which can be used to reconstitute immunodeficient mice, may be retrieved from the airways with this method. This protocol can be completed within 35 min.  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