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   1606篇
  免费   28篇
电工技术   20篇
化学工业   206篇
金属工艺   23篇
机械仪表   52篇
建筑科学   47篇
矿业工程   3篇
能源动力   34篇
轻工业   147篇
水利工程   20篇
石油天然气   14篇
无线电   140篇
一般工业技术   223篇
冶金工业   575篇
原子能技术   7篇
自动化技术   123篇
  2022年   7篇
  2021年   21篇
  2020年   12篇
  2019年   16篇
  2018年   21篇
  2017年   15篇
  2016年   26篇
  2015年   19篇
  2014年   28篇
  2013年   45篇
  2012年   41篇
  2011年   71篇
  2010年   45篇
  2009年   36篇
  2008年   52篇
  2007年   52篇
  2006年   44篇
  2005年   49篇
  2004年   36篇
  2003年   26篇
  2002年   31篇
  2001年   31篇
  2000年   31篇
  1999年   48篇
  1998年   153篇
  1997年   97篇
  1996年   73篇
  1995年   53篇
  1994年   49篇
  1993年   53篇
  1992年   35篇
  1991年   21篇
  1990年   27篇
  1989年   20篇
  1988年   11篇
  1987年   12篇
  1986年   17篇
  1985年   16篇
  1984年   14篇
  1983年   12篇
  1982年   13篇
  1981年   12篇
  1980年   13篇
  1979年   9篇
  1977年   16篇
  1976年   28篇
  1975年   6篇
  1974年   8篇
  1973年   8篇
  1971年   7篇
排序方式: 共有1634条查询结果,搜索用时 15 毫秒
81.
82.
1. An improved purification was developed for L-lactate oxidase from Mycobacterium smegmatis. 2. The mol.wt. of the native enzyme by a sedimentation-equilibrium analysis was 345 000, and other ultracentrifuge methods gave values in the range 345 000-350 000. 3. An amino acid analysis, determinations of protein and flavin, a sedimentation-velocity analysis and an approach to equilibrium analysis gave values for the subunit mol.wt. in the range 43 500-47 000. 4. It was concluded that L-lactate oxidase contains eight subunits of mol.wt. 43 500. 5. Cross-linking of the subunits with dimethyl suberimidate and electron-microscopy studies were consistent with an octameric structure.  相似文献   
83.
Processing methods have been optimized for the formation of graphitic carbon nanofiber (GCNF)/epoxy nanocomposites containing GCNFs highly dispersed throughout a thermoset epoxy matrix. GCNFs having a herringbone atomic structure are surface-derivatized with bifunctional hexanediamine linker molecules (GCNF-HDA) capable of covalent binding to an epoxy matrix during thermal curing and are cut to smaller dimension using high-power ultrasonication. GCNF-HDA nanofibers are dispersed in epoxy resin at 0.3 wt.% loading using variable levels of ultrasonication processing prior to thermal curing. Effects of sonication power on the quality of the GCNF-HDA/epoxy material obtained after curing have been determined from flexural property measurements, thermomechanical analysis and SEM/TEM imaging. GCNF-HDA/epoxy material of the highest quality is obtained using low-power sonication, although high-power sonication for short periods gives improved flexural properties without lowering the glass transition temperature. Good dispersion and polymer wetting of the GCNF component is evident on the nanoscale.  相似文献   
84.
The minimum revenue requirements method of capital investment analysis is widely used by investor-owned utilities. The present worth method is more familiar to graduates of industrial engineering curricula. This paper considers a particular variant of the minimum revenue requirements method and presents the assumptions that must be adopted to insure exact equivalence between the two methods. A numerical example is provided to illustrate the tabular computation algorithm commonly used by practitioners of both methods. Several models for computing revenue requirements are given, each based on a different view of the cost of capital. The results of these computations are compared to those obtained when the present worth method is used to treat borrowed funds both implicitly and explicitly. Theorems from Oso [13] are used to generalize the results. Additional theorems extend findings regarding the equivalence of the minimum revenue requirements and the present worth methods.  相似文献   
85.
Flexicoker coke derived from Athabasca Oil Sands bitumen contains a number of heavy metals, including vanadium, nickel, iron and titanium, which are susceptible to extraction by hydrometallurgical procedures. The leaching behaviour has been studied as a function of pH, temperature and the presence of salts and redox agents. Greater than 50% extraction of the vanadium, iron and nickel can be achieved by acid leaches, but only about 20% of the titanium can be extracted. Weakly acidic leaches extract about 30% of the nickel content but no significant amounts of the other metals. If cokes derived from Athabasca Oil Sands bitumen by the flexicoking process or the conventional delayed-coker coking process are combusted at temperatures below 500 °C, the vanadium and nickel values in the residual ash are readily susceptible to acid leaching.  相似文献   
86.
Three distinct and different types of teaching improvement are identified and described: Type R (remedial) consists of the detection and elimination of errors in teaching, such as in preparation or evaluation. Type F (facilitative) emphasizes the use of appropriate general principles: use of objectives, frequent testing, knowledge of results to facilitate student learning. Type O (optimizing) requires the use of a research orientation in order to determine the procedures and techniques that produce the highest level of student achievement. (French abstract) (22 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
87.
Metals have been deposited on semiconductors from standard plating solutions, in defined areas which have been lightly damaged by ion bombardment. The contacts are either ohmic or rectifying, depending on bombardment dose and plating conditions. The process has been used to make gallium-arsenide f.e.t.s.  相似文献   
88.
Measurements of the nuclear spin lattice relaxation times of3He adsorbed on porous material for a wide range of temperatures (0.33<T<1.5 K) and applied magnetic fields (3.75<H<25 kG) indicate that the relaxation time of the adsorbed atoms is anomalously short with respect to the minimum allowable value for internuclear dipolar interactions, and the observed temperature and field dependence establishes that paramagnetic impurities on the surface do not play a major role in the relaxation process. Comparison with the relaxation rates of129Xe adsorbed on Vycor glass suggests that the relaxation is intimately related to the mobility of the3He adatoms.  相似文献   
89.
The orientational ordering of ortho-hydrogen molecules on a triangular lattice is calculated as a function of ortho concentration using the method of restricted traces. The calculated temperatures for the transitions from the disordered phase to the long range pinwheel ordered phase show a strong concentration dependence with a critical concentration X c=73% below which the long range ordering is not realized in this model. The results are consistent with recent NMR studies of ortho-para hydrogen mixtures adsorbed as a commensurate × structure on hexagonal boron nitride for which X c=69±4%. The values of the observed transition temperatures can only be understood if there is a large renormalization of the effective quadrupolar interaction constant in 2D.  相似文献   
90.
Fluid mechanics on the microscale is an important subject for researchers who are interested in studying microdevices since physical phenomena change from macroscale to microscale. Channel flow is a fundamental topic for fluid mechanics. By using a molecular sensor known as pressure-sensitive paint (PSP), detailed pressure data can be obtained inside the microchannel and at the channel entrance. The achievable spatial resolution of the acquired pressure map can be as high as 5 mum. PSP measurements are obtained for various pressure ratios from 1.76 to 20, with Knudsen number (K n) varying from 0.003 to 0.4. Compressibility and rarefaction effects can be seen in the pressure data inside the microchannel and at the channel entrance.  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