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   146篇
  免费   13篇
电工技术   4篇
化学工业   33篇
金属工艺   5篇
机械仪表   2篇
建筑科学   2篇
矿业工程   2篇
轻工业   11篇
水利工程   2篇
无线电   8篇
一般工业技术   20篇
冶金工业   55篇
原子能技术   1篇
自动化技术   14篇
  2022年   2篇
  2020年   2篇
  2018年   5篇
  2017年   2篇
  2016年   3篇
  2015年   10篇
  2014年   6篇
  2013年   11篇
  2012年   5篇
  2011年   3篇
  2010年   2篇
  2008年   5篇
  2007年   3篇
  2006年   1篇
  2005年   5篇
  2004年   1篇
  2003年   4篇
  2002年   3篇
  2001年   2篇
  2000年   2篇
  1999年   4篇
  1998年   20篇
  1997年   10篇
  1996年   10篇
  1995年   4篇
  1994年   6篇
  1993年   4篇
  1992年   2篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1976年   4篇
  1972年   1篇
  1970年   1篇
  1964年   1篇
  1956年   1篇
  1934年   1篇
排序方式: 共有159条查询结果,搜索用时 31 毫秒
51.
52.
We analyze the behavior of an electromagnetic wave which propagates in a left-handed material. Second-order dispersion and cubic–quintic nonlinearities are considered. This behavior of an electromagnetic wave is modeled by a nonlinear Schrödinger equation which is solved by collective coordinates theory in order to characterize the light pulse intensity profile. More so, a specific frequency range has been outlined where electromagnetic wave behavior will be investigated. The perfect combination of second-order dispersion and cubic nonlinearity leads to a robust soliton. When the quintic nonlinearity comes into play, it provokes strong and long internal perturbations which lead to Benjamin–Feir instability. This phenomenon, also called modulational instability, induces appearance of a Kuznetsov–Ma waves train. We numerically verify the validity of Kuznetsov–Ma theory by presenting physical conditions which lead to Kuznetsov–Ma waves train generation. Thereafter, some properties of such waves train are also verified.  相似文献   
53.
The exact boundary controllability of the non-linear Korteweg-de Vries equation on bounded domains is studied. Only the first spatial derivative at the right endpoint is assumed to be controlled. In this case, the exact controllability has been shown by Rosier (1997) when the length L of the domain is not in the set N  相似文献   
54.
We present a statistical analysis of a large set of absorption spectra of phytoplankton, measured in natural samples collected from ocean water, in conjunction with detailed pigment concentrations. We processed the absorption spectra with a sophisticated neural network method suitable for classifying complex phenomena, the so-called self-organizing maps (SOM) proposed by Kohonen [Kohonen, Self Organizing Maps (Springer-Verlag, 1984)]. The aim was to compress the information embedded in the data set into a reduced number of classes characterizing the data set, which facilitates the analysis. By processing the absorption spectra, we were able to retrieve well-known relationships among pigment concentrations and to display them on maps to facilitate their interpretation. We then showed that the SOM enabled us to extract pertinent information about pigment concentrations normalized to chlorophyll a. We were able to propose new relationships between the fucoxanthin/Tchl-a ratio and the derivative of the absorption spectrum at 510 nm and between the Tchl-b/Tchl-a ratio and the derivative at 640 nm. Finally, we demonstrate the possibility of inverting the absorption spectrum to retrieve the pigment concentrations with better accuracy than a regression analysis using the Tchl-a concentration derived from the absorption at 440 nm. We also discuss the data coding used to build the self-organizing map. This methodology is very general and can be used to analyze a large class of complex data.  相似文献   
55.
56.
57.
Oleoyl-CoA elongase catalyzes four successive reactions: condensation of malonyl-CoA to oleoyl-CoA, reduction, dehydration, and another reduction. Evidence supporting this mechanism and the multienzymatic nature of the elongation complex are reported. A particulate membrane fraction from rapeseed is able to elongate intermediates (R,S) 3-hydroxy-20∶0-CoA and (E) 2,3–20∶1-CoA to very long chain fatty acids in the presence of malonyl-CoA. Studies of the 3-ketoacyl-CoA synthase activities showed that maximal activity could be measured by using 15 to 30 μM 18∶1-CoA and 30 μM malonyl-CoA, and that 18∶0-CoA and 18∶1-CoA were the best substrates. Comparison of the condensation and the overall elongation activities indicated that condensation is the rate-limiting step of the elongation process. The 3-hydroxyacyl-CoA dehydratase activity was maximal in the presence of 75 μM Triton X-100 and 25 μg of proteins. Finally, the acyl-CoA elongase complex was solubilized and purified. During the purification process, the 3-hydroxyacyl-CoA dehydratase copurified with the elongase complex, strongly suggesting that this enzyme belongs to the elongase complex. The apparent molecular mass of 700 kDa determined for the elongase complex, and the fact that four different polypeptide bands were detected after sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the purified fraction, further suggest that the acyl-CoA elongase is a multienzymatic complex.  相似文献   
58.
3D interlock woven fabrics are promising materials to replace the 2D structures in the field of ballistic protection. The structural complexity of this material caused many difficulties in numerical modeling. This paper presents a new tool that permits to generate a geometry model of any woven fabric, then, mesh this model in shell or solid elements, and apply the mechanical properties of yarns to them. The tool shows many advantages over existing software. It is very handy in use with an organization of the functions in menu and using a graphic interface. It can describe correctly the geometry of all textile woven fabrics. With this tool, the orientation of the local axes of finite elements following the yarn direction facilitates defining the yarn mechanical properties in a numerical model. This tool can be largely applied because it is compatible with popular finite element codes such as Abaqus, Ansys, Radioss etc. Thanks to this tool, a finite element model was carried out to describe a ballistic impact on a 3D warp interlock Kevlar KM2? fabric. This work focuses on studying the effect of friction onto the ballistic impact behavior of this textile interlock structure. Results showed that the friction among yarns affects considerably on the impact behavior of this fabric. The effect of the friction between projectile and yarn is less important. The friction plays an important role in keeping the fabric structural stability during the impact event. This phenomenon explained why the projectile is easier to penetrate this 3D warp interlock fabric in the no-friction case. This result also indicates that the ballistic performance of the interlock woven fabrics can be improved by using fibers with great friction coefficients.  相似文献   
59.
The observation of an 11-years-old child is presented. He had bilateral congenital palpebral ptosis and multiple facial malformations, like maxillary and mandibular hypoplasia, dental malpositions, ogival palace, anomalies of the external ear, lesions determined by a latero-facial dechyscence (perforation 6, 7, 8). The affection was produced by a embryogenesis disturbance following the existence of two pathological genes. Their actions were overlapped during the 7--8 and 11 weeks of embryonic life, which caused damages in the maxillary and mandibular bones suture, which allow the formation of the inferior and middle stage of the face.  相似文献   
60.
The ectopic pregnancy (EP) could be treated by spontaneous resolution, or medical treatment or laparoscopic treatment. Spontaneous resolution of EP with beta hCG < 1,000 mUl/ml, plasmatic progesterone < 5 ng/ml had 74% success rate. Methotrexate (MTX) injection is the common Medical treatment of EP with beta hCG < or = 5,000 mUl/ml and mean diameter of EP < or = 3 cm: a single dose of 50 mg/m2 or 1 mg/kg intramuscular injection had 93.4% success rate; local injection under sonographic control (1 mg/kg) had 80.2% success rate. The surgical conservative treatment by laparoscopy had 94% success rate.  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