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   173篇
  免费   8篇
  国内免费   1篇
化学工业   52篇
机械仪表   4篇
建筑科学   5篇
能源动力   26篇
轻工业   35篇
水利工程   4篇
石油天然气   1篇
无线电   4篇
一般工业技术   19篇
冶金工业   14篇
自动化技术   18篇
  2023年   1篇
  2022年   9篇
  2021年   21篇
  2020年   11篇
  2019年   5篇
  2018年   11篇
  2017年   5篇
  2016年   6篇
  2015年   5篇
  2014年   1篇
  2013年   12篇
  2012年   23篇
  2011年   13篇
  2010年   5篇
  2009年   10篇
  2008年   7篇
  2007年   6篇
  2006年   6篇
  2004年   6篇
  2003年   2篇
  2002年   1篇
  2001年   1篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1996年   1篇
  1993年   1篇
  1990年   1篇
  1989年   1篇
  1986年   2篇
  1984年   1篇
  1982年   2篇
  1981年   1篇
  1980年   2篇
排序方式: 共有182条查询结果,搜索用时 14 毫秒
21.
The stereoselective synthesis of chiral 1,3‐diols with the aid of biocatalysts is an attractive tool in organic chemistry. Besides the reduction of diketones, an alternative approach consists of the stereoselective reduction of β‐hydroxy ketones (aldols). Thus, we screened for an alcohol dehydrogenase (ADH) that would selectively reduce a β‐hydroxy‐β‐trifluoromethyl ketone. One potential starting material for this process is readily available by aldol addition of acetone to 2,2,2‐trifluoroacetophenone. Over 200 strains were screened, and only a few yeast strains showed stereoselective reduction activities. The enzyme responsible for the reduction of the β‐hydroxy‐β‐trifluoromethyl ketone was identified after purification and subsequent MALDI‐TOF mass spectrometric analysis. As a result, a new NADP+‐dependent ADH from Pichia pastoris (PPADH) was identified and confirmed to be capable of stereospecific and diastereoselective reduction of the β‐hydroxy‐β‐trifluoromethyl ketone to its corresponding 1,3‐diol. The gene encoding PPADH was cloned and heterologously expressed in Escherichia coli BL21(DE3). To determine the influence of an N‐ or C‐terminal His‐tag fusion, three different recombinant plasmids were constructed. Interestingly, the variant with the N‐terminal His‐tag showed the highest activity; consequently, this variant was purified and characterized. Kinetic parameters and the dependency of activity on pH and temperature were determined. PPADH shows a substrate preference for the reduction of linear and branched aliphatic aldehydes. Surprisingly, the enzyme shows no comparable activity towards ketones other than the β‐hydroxy‐β‐trifluoromethyl ketone.  相似文献   
22.
B-cell chronic lymphocytic leukemia (CLL) results from intrinsic genetic defects and complex microenvironment stimuli that fuel CLL cell growth through an array of survival signaling pathways. Novel small-molecule agents targeting the B-cell receptor pathway and anti-apoptotic proteins alone or in combination have revolutionized the management of CLL, yet combination therapy carries significant toxicity and CLL remains incurable due to residual disease and relapse. Single-molecule inhibitors that can target multiple disease-driving factors are thus an attractive approach to combat both drug resistance and combination-therapy-related toxicities. We demonstrate that SRX3305, a novel small-molecule BTK/PI3K/BRD4 inhibitor that targets three distinctive facets of CLL biology, attenuates CLL cell proliferation and promotes apoptosis in a dose-dependent fashion. SRX3305 also inhibits the activation-induced proliferation of primary CLL cells in vitro and effectively blocks microenvironment-mediated survival signals, including stromal cell contact. Furthermore, SRX3305 blocks CLL cell migration toward CXCL-12 and CXCL-13, which are major chemokines involved in CLL cell homing and retention in microenvironment niches. Importantly, SRX3305 maintains its anti-tumor effects in ibrutinib-resistant CLL cells. Collectively, this study establishes the preclinical efficacy of SRX3305 in CLL, providing significant rationale for its development as a therapeutic agent for CLL and related disorders.  相似文献   
23.
The article deals with the issues related to the implementation of EU greenhouse gas (GHG) emission trading scheme in Baltic States. The main objectives of the article are to analyse the main features and requirements of EU emission trading scheme and to assess the results of the first trading GHG trading period based on verified GHG emissions in Baltic States. The main aim of the article is to compare GHG emission trading results among Baltic States and provide with some insights for the next GHG trading period and assess possible implications on energy sector of Lithuania, Latvia and Estonia.  相似文献   
24.
In recent years, novel strategies to control insects have been based on protease inhibitors (PIs). In this regard, molecular docking and molecular dynamics simulations have been extensively used to investigate insect gut proteases and the interactions of PIs for the development of resistance against insects. We, herein, report an in silico study of (disodium 5′-inosinate and petunidin 3-glucoside), (calcium 5′-guanylate and chlorogenic acid), chlorogenic acid alone, (kaempferol-3,7-di-O-glucoside with hyperoside and delphinidin 3-glucoside), and (myricetin 3′-glucoside and hyperoside) as potential inhibitors of acetylcholinesterase receptors, actin, α-tubulin, arginine kinase, and histone receptor III subtypes, respectively. The study demonstrated that the inhibitors are capable of forming stable complexes with the corresponding proteins while also showing great potential for inhibitory activity in the proposed protein-inhibitor combinations.  相似文献   
25.
26.
The EU's new energy and environment policy - agreed by government leaders in their Council meeting in March 2007 - established a political agenda to tackle three core energy objectives: sustainability, economic competitiveness and security of supply. A triad of specific policies addresses these challenges: first, the 20/20/20 targets of the EU; then, the Second Strategic Energy Review of the European Commission; and finally, plans to liberalise energy markets. The European Union's ‘20/20/20′ targets for 2020: reduce greenhouse gas emissions by 20% comparing with 1990 level (to become a 30% reduction if other major global economies join), increase the share of renewables in the final energy consumption to 20% and to achieve 20% improvement in energy efficiency compared to the level in 2020 if existing trends were to continue.The aim of the paper is to analyse the feasibility of EU to implement 20/20/20 targets under the various international GHG trading regimes. GHG trading regimes were addressed by developing 10 energy scenarios until 2020 for EU by applying several energy modelling tools ranging from top down partial equilibrium to detailed technology based bottom up models.  相似文献   
27.
The best wind sites in the United States are often located far from electricity demand centers and lack transmission access. Local sites that have lower quality wind resources but do not require as much power transmission capacity are an alternative to distant wind resources. In this paper, we explore the trade-offs between developing new wind generation at local sites and installing wind farms at remote sites. We first examine the general relationship between the high capital costs required for local wind development and the relatively lower capital costs required to install a wind farm capable of generating the same electrical output at a remote site,with the results representing the maximum amount an investor should be willing to pay for transmission access. We suggest that this analysis can be used as a first step in comparing potential wind resources to meet a state renewable portfolio standard (RPS). To illustrate, we compare the cost of local wind (~50 km from the load) to the cost of distant wind requiring new transmission (~550-750 km from the load) to meet the Illinois RPS. We find that local, lower capacity factor wind sites are the lowest cost option for meeting the Illinois RPS if new long distance transmission is required to access distant, higher capacity factor wind resources. If higher capacity wind sites can be connected to the existing grid at minimal cost, in many cases they will have lower costs.  相似文献   
28.
29.
Electrification of isolated area is commonly ensured by autonomous power installation including renewable energy sources. Many software tools are available to size such installations. These tools refer to the daily energy need and the site global renewable potential which leads to inaccurate and wasteful sizing. This paper presents an alternative tool based on the energy consumption and the daily loads profile to compute the size of a standalone PV/batteries system installed in an isolated chalet in Sfax, Tunisia. Obtained results are compared to those provided by PVsyst sizing tool to confirm the proposed algorithm effectiveness. Referring to obtained results, an assessment is proposed to dispatch energy between connected autonomous installations to cover the need of some houses by energy surplus offered by neighbors. A Continuous Petri Net (CPN) is used to model the energy flow between houses.  相似文献   
30.
Consumer interest in a healthy lifestyle and health-promoting natural products is a major driving force for the increasing global demand for bio-functional and sustainable dairy foods. Supplementation of curd cheese with thermo-coagulated acid whey protein (TAWP) led to 8–10% higher contents of moisture, 23–31% of lactose, 12–13% of unsaturated, 5–6% of monounsaturated, 63% of polyunsaturated, and 3–4% of long-chain fatty acids. Lipid quality indices – TI, AI, h/H, and Omega 6/3 among others, were also significantly better than those of control cheese. The addition of indigenous Lactococcus lactis strain enhanced the flavour of cheese samples, decreased the counts of yeast and mould up to 1 log cfu g−1 after 10 days of storage. The replacement of curd with TAWP resulted in novel cheese with overall sensory perception above 77 points and added nutritional and functional value, however, body and texture parameters of modified cheese samples require an improvement.  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