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1.
序列的翻转与对换的排序问题因在基因组比较中的应用而受到关注.考虑二元序列的翻转与对换的排序问题,分别给出了二元序列的翻转排序与对换排序的近似算法.  相似文献   

2.
Olson MV 《Nature》2001,409(6822):816-818
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3.
4.
F Baldissera  G Broggi  M Mancia 《Nature》1967,215(5096):62-63
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5.
Procoagulant synthesis by cultured fibroblasts triggered by cell adhesion   总被引:1,自引:0,他引:1  
L R Zacharski  O R McIntyre 《Nature》1971,232(5309):338-339
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6.
Nair DT  Johnson RE  Prakash S  Prakash L  Aggarwal AK 《Nature》2004,430(6997):377-380
Almost all DNA polymerases show a strong preference for incorporating the nucleotide that forms the correct Watson-Crick base pair with the template base. In addition, the catalytic efficiencies with which any given polymerase forms the four possible correct base pairs are roughly the same. Human DNA polymerase-iota (hPoliota), a member of the Y family of DNA polymerases, is an exception to these rules. hPoliota incorporates the correct nucleotide opposite a template adenine with a several hundred to several thousand fold greater efficiency than it incorporates the correct nucleotide opposite a template thymine, whereas its efficiency for correct nucleotide incorporation opposite a template guanine or cytosine is intermediate between these two extremes. Here we present the crystal structure of hPoliota bound to a template primer and an incoming nucleotide. The structure reveals a polymerase that is 'specialized' for Hoogsteen base-pairing, whereby the templating base is driven to the syn conformation. Hoogsteen base-pairing offers a basis for the varied efficiencies and fidelities of hPoliota opposite different template bases, and it provides an elegant mechanism for promoting replication through minor-groove purine adducts that interfere with replication.  相似文献   

7.
Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self powered without using battery, without which most of the sensor network may be impossible. The piezoelectric nanogenerators have the potential to serve as self sufficient power sources for micro/nano systems. For wurtzite structures that have non central symmetry, such as ZnO, GaN and InN, a piezoelectric potential (piezopotential) is created in the crystal by applying a strain. The nanogenerator is invented by using the piezopotential as the driving force for electrons to flow in respond to a dynamic straining of piezoelectric nanowires. A gentle straining can produce an output voltage of up to 20~50 V from an integrated nanogenerator. Furthermore, piezopotential in the wurtzite structure can serve as gate voltage that can effectively tune/control the charge transport across an interface/junction; electronics fabricated based on such a mechanism is coined as piezotronics, with applications in force/pressure triggered/controlled electronic devices, sensors, logic units and memory. By using the piezotronic effect, it is showed that the optoelectronic devices fabricated using wurtzite materials can have superior performance as solar cell, photon detector and light emitting diode. Piezotronic is likely to serve as “mechanosensation” for directly interfacing biomechanical action with silicon based technology and active flexible electronics. The paper gives a brief review about the basis of nanogenertors and piezotronics and their potential applications in smart MEMS (micro electro mechanical systems).  相似文献   

8.
将学习曲线与传统的分段方法结合起来,既克服了分段法中不考虑学习效果的缺陷,又克报了学习曲线中不能灵活调整的缺陷,形成两种方法的优点叠加.用学习曲线测算井段的钻井时间,其前提条件是:各井在该井段的钻头选型基本相同,井段直径相同,所穿过的地层相同,所属的井型相同.对钻井参数(钻压、转速、泵压、排量)、泥浆密度与性能、喷嘴直径与个数等时变性因素,不单独列出,而作为在钻井过程中通过逐步学习加以改善的对象.用塔北某地区1号构造上所钻井的二开井段(444.5mm)实际资料测算,得到的结果明显优于钻井监督的计划时间,测算的最大相对误差11.8%,平均为8.8%,而监督组计划误差为41.9%,平均误差率降低了一半以上.  相似文献   

9.
微乳凝胶固定化酶催化油酸丁酯的合成   总被引:2,自引:0,他引:2  
研究了以AOT(二(2—乙基已基)琥珀酸酯磺酸钠)/正庚烷/水/明胶组成的反向微乳凝胶固定化脂肪酶催化油酸和丁醇的酯化反应,分析了凝胶组成、反应温度、溶剂等因素对酯化反应的影响,得到了一种合适的体系,使油酸丁酯酯化率达90%以上。  相似文献   

10.
研究了Fenton反应产生的羟基自由基对Ⅰ型胶原蛋白的降解作用。单独的过氧化氢(H2O2),Fe2+以及超氧阴离子自由基(O2-·)均对胶原蛋白无降解作用。但是,在经过氧化氢和Fe2+构成的Fenton反应产生羟基自由基后,胶原蛋白发生了降解。胶原蛋白的降解作用随着羟基自由基的增加(H2O2+Fe2+浓度增加)而加强。但羟基自由基的生成是瞬间完成的,其对胶原蛋白的降解作用随着H2O2和Fe2+反应时间的延长而降低。  相似文献   

11.
Inhibition by arousal of epilepsy induced by chlorambucil in rats   总被引:5,自引:0,他引:5  
J P Pinel  S L Chorover 《Nature》1972,236(5344):232-234
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12.
13.
激光晶化多晶硅的制备与XRD谱   总被引:12,自引:0,他引:12  
对氢化非晶硅(a-Si∶H)进行了脱氢和不同能量密 度的准分子激光晶化多晶硅的实验, 对所得样品用X射线衍射表征. 针对多晶硅(111)面特征峰的强度、 晶面间距和宽化信息, 分析了激光功率密度对晶化多晶硅结晶度和应力的影响, 根据谢乐公式(Scherrer)估算了晶粒的大小, 得到用准分子激光晶化多晶硅的较佳工艺参数, 并且验证了激光辐射对薄膜材料作用的3种情况.  相似文献   

14.
S Alemany  J M Mato  P Str?lfors 《Nature》1987,330(6143):77-79
The mechanism of insulin action is only partly understood. At one end of the signalling chain, the structure of the insulin receptor is known in detail, and at the other end, insulin controls cellular metabolism by regulating the phosphorylation of serine and threonine residues in key target enzymes. The molecular events linking the occupied receptor to changes in target enzyme phosphorylation have remained obscure. Recently, insulin was shown to promote the hydrolysis of a phosphatidylinositol glycan with release of its polar head-group. The head group was reported to activate a high-affinity cyclic AMP-phosphodiesterase and pyruvate dehydrogenase, to inhibit catecholamine-stimulated lipolysis, and also to inhibit phospholipid methyltransferase and adenylate cyclase. We report here that in intact adipocytes this head-group faithfully copies the insulin-directed effects on the phosphorylation and dephosphorylation of target proteins of the hormone.  相似文献   

15.
微波法制备固体碱催化肉桂醛合成反应   总被引:1,自引:0,他引:1  
用微波法制备了固体碱催化剂KF/γ-Al2O3,MgO/γ-Al2O3、KF/NaY和MgO/NaY,并以苯甲醛与乙醛合成肉桂醛为目标反应测试催化性能,同时考察了负载化,反应时间以及催化剂制备方法对反应的影响,结果表明上述催化剂中以KF/γ-Al2O3的活性最好,该催化剂的最佳负载比为25%(质量比);与浸渍法和焙烧法相比,微波法制备的KF/γ-Al2O3催化性能要好得多。  相似文献   

16.
紊流消能与泥沙制紊分析   总被引:2,自引:0,他引:2  
在一次洪水过程中,各时点含沙量随水流紊动及摩阻比降而正变,紊流消能规律占主导;而对于一个洪水过程整体,间歇性的泥沙与水流的滑脱影响积累起来,显示出泥沙制紊作用。在河流多次洪水记录中,取洪水期平均流量大致相等的几次洪水相比较,可看出泥沙制紊作用并与试验室水槽多次稳定流实验结果一致:洪水期平均含沙量较大的洪水,其加权平均流速较大,而加权平均摩阻比降较小。反之亦然。文中用大量实际资料对紊流消能和泥沙制紊进行了论证。  相似文献   

17.
Immunosuppression by L-asparaginase   总被引:3,自引:0,他引:3  
R S Schwartz 《Nature》1969,224(5216):275-276
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18.
Structures by numbers   总被引:4,自引:0,他引:4  
Abbott A 《Nature》2000,408(6809):130-132
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19.
Dogged by doubts     
Cyranoski D 《Nature》2005,438(7071):1059
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20.
《Nature》1970,228(5271):490-491
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