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   1637篇
  免费   52篇
  国内免费   4篇
电工技术   82篇
综合类   2篇
化学工业   416篇
金属工艺   45篇
机械仪表   39篇
建筑科学   20篇
矿业工程   1篇
能源动力   72篇
轻工业   139篇
水利工程   4篇
石油天然气   5篇
无线电   113篇
一般工业技术   283篇
冶金工业   275篇
原子能技术   46篇
自动化技术   151篇
  2023年   18篇
  2022年   18篇
  2021年   41篇
  2020年   17篇
  2019年   28篇
  2018年   21篇
  2017年   26篇
  2016年   38篇
  2015年   27篇
  2014年   50篇
  2013年   91篇
  2012年   54篇
  2011年   87篇
  2010年   77篇
  2009年   61篇
  2008年   76篇
  2007年   86篇
  2006年   49篇
  2005年   60篇
  2004年   44篇
  2003年   57篇
  2002年   35篇
  2001年   25篇
  2000年   30篇
  1999年   32篇
  1998年   126篇
  1997年   66篇
  1996年   62篇
  1995年   36篇
  1994年   24篇
  1993年   22篇
  1992年   21篇
  1991年   14篇
  1990年   8篇
  1989年   18篇
  1988年   6篇
  1987年   10篇
  1986年   8篇
  1985年   3篇
  1984年   19篇
  1983年   14篇
  1982年   9篇
  1981年   7篇
  1980年   9篇
  1978年   10篇
  1977年   13篇
  1976年   16篇
  1975年   4篇
  1974年   6篇
  1973年   7篇
排序方式: 共有1693条查询结果,搜索用时 15 毫秒
111.
Volcanic disasters can cause severe loss of human life and damage to property. The main damage is caused during an eruption and from subsequent erosion of deposited materials. Heavy rainfall in volcanic areas erodes volcanic deposits, mainly pyroclastic flows and ash fall deposits, which flow as lahar to the foothill of the mountain and cause drastic damage to economically important areas. This post-eruption disaster becomes complex due to the occurrence of stream captures and watershed breakouts that lead to devastating lahars. Continuous monitoring of such geomorphic and hydrologic changes is necessary to cope with changing hazard conditions. Therefore it is important to update the watershed boundaries in order to study current hazard conditions and develop mitigation plans for future disasters. Changes of geomorphic and watershed boundary have occurred in the Mayon Volcano in the Philippines mainly as a result of a major volcanic eruption of 1993, due to which mitigation structures were constructed and modified in the low lying areas. In this study interferometry was used to develop DEM from SAR data to delineate watershed boundaries. New lava flows, pyroclastic flows and lahar deposits in the watersheds were mapped using elevation changes, coherence and intensity derived from the SAR images. Updating geomorphic features of the watersheds and their boundaries using SAR provides a new weather independent alternative technique for monitoring the effect of volcanic activity.  相似文献   
112.
Let X1, X2... be i.i.d. observations with mean μ and variance σ2, and suppose that given a sample of size n one wishes to estimate μ by Xn, subject to the loss function Ln= A2(Xn-μ)2+n. When σ2 is unknown, the optimal sample size n0 for minimizing the risk Rn = E{Ln} cannotbe found. To resolve this problem, Robbins (1959) proposed a sequential procedure whenXi is normally distributed, and then the asymptotic properties have been extensively studied. In this paper, we apply Hall's three stage procedure to the problem without specifying the distribution of Xi and derive the second order asymptotic expansions of the expected sample size and the risk.  相似文献   
113.
Suppose that {Xn} is a strongly mixing process with unknow marginal density f(x) and that we estimate f(x) by a kernel estimator [fcirc]n(x|hn)and want to achive the MISE no larger than some preassigned postive number w. However,the appropriate sample size n*depends on a functional of the unknow density function. Therefore some sequential procedure is required and we adopt a fully sequential procedure. In this paper we investigate the asymptotic properties of the procedure and show that the producure is asymptotically efficient in a certain sense as w→0. The results are almost the same in the i.i.d. setting. our result extend a class of models to which the methodology can be applied. For example economic variable,experiments on a single subject in which obervation are not indepent, and so on.  相似文献   
114.
Nonthermal plasma technologies offer an innovative approach to the problem of decomposing various volatile organic compounds (VOCs). The authors focused on DC capillary tube discharge plasma reactors to study the decomposition/destruction efficiency for toluene, EGM, trichloroethane and trichloroethylene at 50-2300 ppm levels in dry air. The effects of gas flow rate, VOC concentration and reactor operating conditions on decomposition and analysis of reactant conversion for each VOC were investigated. The results show that VOC destruction efficiency as high as 90% can be achieved, even under a short residence time (3.8 ms) with a destruction energy efficiency of up to 95 g (VOC)/kWh. Laboratory-scale plasma technology was successfully demonstrated for its potential application for VOC control in the semiconductor clean-room environment  相似文献   
115.
To understand the cause of read/write error due to lube accumulation, a model to simulate the slider’s response to the contact impact, which can occur between a lubricant droplet on the disk and a slider, was developed. The contact impact model is based on the water-hammer pressure model with an additional damping force, where the wave-shock pressure is assumed to function as the contact pressure, and the damping force defines the damping characteristics of the impact which are due to the lubricant’s high viscosity and squeeze between the droplet and slider contact area along the slider local velocity direction. The transient contact impact is dependent on lube droplet density, disk velocity, pitch angle of the slider, and contact area between the droplet and the slider. The measured read/write signal jump due to lube pickup can be explained by the simulation results. This modeling and simulation are helpful to us in understanding the read/write signal loss due to a lube droplet at head disk interface.  相似文献   
116.
117.
A giant danaid butterfly, Idea leuconoe, specializes on apocynaceous plants such as Parsonsia laevigata, which has been reported to contain pyrrolizidine alkaloids. Females of I. leuconoe deposited eggs in response to methanolic extract of P. laevigata, and subsequent bioassay-guided fractionation of the extract revealed that phytochemicals crucial for host recognition by ovipositing females are Parsonsia-specific macrocyclic pyrrolizidine alkaloids including parsonsianine, parsonsianidine, and 17-methylparsonsianidine. Parsonine, another P. laevigata pyrrolizidine component with a keto-dihydropyrrolizine moiety that is closely related in structure to male pheromones of the butterfly, and several nonhost pyrrolizidine alkaloids were entirely inactive. We interpret these data as strong evidence for an ancestral association through herbivory between danaid butterflies and pyrrolizidine alkaloids.  相似文献   
118.
The synergistic effect of methyltrioctylammonium chloride (QCI) on the extraction of Np(V) by 1-phenyl-3-methyl-4-benzoyl-pyrazolone(HP) in benzene is studied over the pH range 2-6. This system extracts Np(V) better than any previously reported. The interaction of the extractants and monomer-dimer equilibria affect the distribution behavior of Np(V) in a complicated manner. Analysis of the results suggests that NpO2 + (M+) is extracted as mixed dimers, (QMP2QCl)o and (QMP2QP)o.  相似文献   
119.
Specific heat of a single crystalline URhSi was measured by a relaxation method in a temperature range 0.3–25 K in magnetic fields up to 8 T applied along the two of the principal axes. The low-temperature specific heat exponentially decays with magnetic field. The decay is much faster in fields applied along the easy magnetization direction (the c-axis) than for the hard axis (the a-axis) case. A strong upturn in cp/T versus T below 0.6 K that disappears with application of magnetic field is observed suggesting possible magnetic or superconducting phase transition at lower temperatures. The electrical resistivity in the vicinity of the ferromagnetic phase temperature is found to be reduced by more than 50% upon application of magnetic field of 8 T applied along the c-axis. URhSi represent an itinerant ferromagnetic system with influence of spin fluctuations.  相似文献   
120.
This paper studies the following variant of the Vehicle Routing Problem that we call the Grasp and Delivery for Moving Objects (GDMO) problem, motivated by robot navigation: The input to the problem consists of n products, each of which moves on a predefined path with a fixed constant speed, and a robot arm of capacity one. In each round, the robot arm grasps one product and then delivers it to the depot. The goal of the problem is to find a collection of tours such that the robot arm grasps and delivers as many products as possible. In this paper we prove the following results: (i) If the products move on broken lines with at least one bend, then the GDMO is MAXSNP-hard, and (ii) it can be approximated with ratio 2. However, (iii) if we impose the “straight line without bend” restriction on the motion of every product, then the GDMO becomes tractable. Y. Asahiro’s research was supported in part by Grant-in-Aid for Young Scientists 15700021, and Research on Priority Areas 16092223. E. Miyano’s research was supported in part by Grant-in-Aid for Research on Priority Areas 16092223. Presently, S. Shimoirisa is with the Software Development Engineering Department, Products Development Center, Retail Information Systems Company, Toshiba TEC Corporation.  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