首页 | 官方网站   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   755篇
  免费   30篇
工业技术   785篇
  2021年   30篇
  2020年   15篇
  2019年   5篇
  2018年   14篇
  2017年   14篇
  2016年   24篇
  2015年   16篇
  2014年   23篇
  2013年   55篇
  2012年   37篇
  2011年   38篇
  2010年   33篇
  2009年   30篇
  2008年   45篇
  2007年   39篇
  2006年   32篇
  2005年   26篇
  2004年   23篇
  2003年   14篇
  2002年   25篇
  2001年   13篇
  2000年   4篇
  1999年   8篇
  1998年   22篇
  1997年   14篇
  1996年   18篇
  1995年   10篇
  1994年   13篇
  1993年   11篇
  1992年   9篇
  1990年   6篇
  1989年   8篇
  1988年   6篇
  1987年   6篇
  1986年   7篇
  1985年   11篇
  1984年   6篇
  1983年   5篇
  1981年   7篇
  1980年   4篇
  1979年   3篇
  1978年   3篇
  1977年   5篇
  1976年   3篇
  1975年   8篇
  1974年   6篇
  1972年   3篇
  1970年   4篇
  1968年   3篇
  1966年   3篇
排序方式: 共有785条查询结果,搜索用时 799 毫秒
121.
During pregnancy, freely floating placental villi are adapted to fluid shear stress due to placental perfusion with maternal plasma and blood. In vitro culture of placental villous explants is widely performed under static conditions, hoping the conditions may represent the in utero environment. However, static placental villous explant culture dramatically differs from the in vivo situation. Thus, we established a flow culture system for placental villous explants and compared commonly used static cultured tissue to flow cultured tissue using transmission and scanning electron microscopy, immunohistochemistry, and lactate dehydrogenase (LDH) and human chorionic gonadotropin (hCG) measurements. The data revealed a better structural and biochemical integrity of flow cultured tissue compared to static cultured tissue. Thus, this new flow system can be used to simulate the blood flow from the mother to the placenta and back in the most native-like in vitro system so far and thus can enable novel study designs.  相似文献   
122.
Agelaia-MPI and protonectin are antimicrobial peptides isolated from the wasp Parachartergus fraternus that show antimicrobial and neuroactive activities. Previously, two analogues of these peptides, neuroVAL and protonectin-F, were designed to reduce nonspecific toxicity and improve potency. Here, the three-dimensional structures of neuroVAL, protonectin and protonectin-F were determined by using circular dichroism and NMR spectroscopy. Antibacterial, antifungal, cytotoxic and hemolytic activities were tested for the parent peptides and analogues. All peptides showed moderate antimicrobial activity against Gram-positive bacteria, with agelaia-MPI being the most active. Protonectin and protonectin-F were found to be toxic to cancerous and noncancerous cell lines. Internalization experiments revealed that these peptides accumulate inside both cell types. By contrast, neuroVAL was nontoxic to all tested cells and was able to enter cells without accumulating. In summary, neuroVAL has potential as a nontoxic cell-penetrating peptide, while protonectin-F needs further modification to realize its potential as an antitumor peptide.  相似文献   
123.
Studies on the extraction and separation of vanadium(V) from mixed hydrochloric acid/ammonium thiocyanate solution with CYANEX 921 and CYANEX 925 in kerosene were carried out. The effects of various factors affecting the extraction process as well as temperature were investigated. Addition of thiocyanate to the chloride solution was found to enhance markedly the extraction of vanadium. HCl solution efficiently stripped V(V). The number of stages required for extraction and stripping of vanadium ions was determined from the McCabe–Thiele diagram. Based on the obtained results, the separation of V(V) from spent catalyst leach indicates the efficiency of the proposed process.  相似文献   
124.
Biocatalytic production of lactones, and in particular ϵ-caprolactone (CL), have gained increasing interest as a greener route to polymer building blocks, especially through the use of Baeyer–Villiger monooxygenases (BVMOs). Despite several advances in the field, BVMOs, however, still suffer several practical limitations. Alcohol dehydrogenase (ADH)-mediated lactonization of diols in turn has received far less attention and very few enzymes have been identified for the conversion of diols to lactones, with horse-liver ADH (HLADH) remaining the catalyst of choice. Screening of a diverse panel of ADHs, AaSDR-1, a member of the short-chain dehydrogenase/reductase family, was found to produce ϵ-caprolactone from hexane-1,6-diol. Moreover, cofactor regeneration by an NADH oxidase eliminated the requirement of co-substrates, yielding water as the sole by-product. Despite lower turnover frequencies as compared to HLADH, higher selectivity was found for the production of CL, with HLADH forming significant amounts of 6-hydroxyhexanoic acid and adipic acid through aldehyde dehydrogenation/oxidation of the gem-diol intermediates. Also, CL yield were shown to be dependent on buffer choice, as structural elucidation of a Tris adduct confirmed the buffer amine to react with aliphatic aldehydes forming a Schiff-base intermediate which through further ADH oxidation, forms a tricyclic acetal product.  相似文献   
125.
126.
MicroRNAs control the differentiation and function of B cells, which are considered key elements in the pathogenesis of systemic lupus erythematosus (SLE). However, a common micro(mi)RNA signature has not emerged since published data includes patients of variable ethnic background, type of disease, and organ involvement, as well as heterogeneous cell populations. Here, we aimed at identifying a miRNA signature of purified B cells from renal and non-renal severe SLE patients of Latin American background, a population known to express severe disease. Genome-wide miRNA expression analyses were performed on naive and memory B cells and revealed two categories of miRNA signatures. The first signature represents B cell subset-specific miRNAs deregulated in SLE: 11 and six miRNAs discriminating naive and memory B cells of SLE patients from healthy controls (HC), respectively. Whether the miRNA was up or down-regulated in memory B cells as compared with naive B cells in HC, this difference was abolished in SLE patients, and vice versa. The second signature identifies six miRNAs associated with specific pathologic features affecting renal outcome, providing a further understanding for SLE pathogenesis. Overall, the present work provided promising biomarkers in molecular diagnostics for disease severity as well as potential new targets for therapeutic intervention in SLE.  相似文献   
127.
A model cancer cell line was used to initiate polymerisation of pyrrole to form the conducting material polypyrrole. The polymerisation was shown to occur through the action of cytosolic exudates rather than that of the membrane redox sites that normally control the oxidation state of iron as ferricyanide or ferrocyanide. The data demonstrate for the first time that mammalian cells can be used to initiate synthesis of conducting polymers and suggest a possible route to detection of cell damage and/or transcellular processes through in situ and amplifiable signal generation.  相似文献   
128.
129.
Forming impressions of job candidates is a challenging process, one characterized by ambiguity brought about by the uncertainty associated with making decisions and judgments. To reduce ambiguity, hiring professionals have established policies and procedures to facilitate the sourcing and use of information about a candidate. However, recently, a public source of information is increasingly being used—information from social networking sites (SNSs). While conventional wisdom says more information is better and can help make decisions less ambiguous, this relationship may not be as straightforward as expected when facing assessments of candidates. This paper examines two such aspects, information‐task quality and context collapse, and their collective impact on ambiguity when making an assessment of a job candidate. Using data from an online survey‐based experiment, the findings suggest information from SNSs can be useful, yet can create ambiguity for decision makers because of context collapse made possible by SNS technologies.  相似文献   
130.
Pyridine extracts of coal are excellent models for studies of coal structure and reactions, but the pyridine that is retained is undesirable. A method is described, using supercritical carbon dioxide, for the removal of retained pyridine from pyridine extracts of Illinois No. 6 and Western Kentucky No. 9 coals.  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-23

京公网安备 11010802026262号