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   3505篇
  免费   47篇
  国内免费   2篇
电工技术   15篇
化学工业   447篇
金属工艺   43篇
机械仪表   45篇
建筑科学   92篇
矿业工程   6篇
能源动力   54篇
轻工业   157篇
水利工程   29篇
石油天然气   6篇
无线电   192篇
一般工业技术   361篇
冶金工业   1829篇
原子能技术   11篇
自动化技术   267篇
  2021年   24篇
  2019年   16篇
  2018年   22篇
  2017年   20篇
  2016年   33篇
  2015年   27篇
  2014年   33篇
  2013年   111篇
  2012年   50篇
  2011年   70篇
  2010年   58篇
  2009年   60篇
  2008年   83篇
  2007年   58篇
  2006年   76篇
  2005年   51篇
  2004年   55篇
  2003年   62篇
  2002年   53篇
  2001年   45篇
  2000年   35篇
  1999年   107篇
  1998年   550篇
  1997年   337篇
  1996年   212篇
  1995年   145篇
  1994年   146篇
  1993年   130篇
  1992年   41篇
  1991年   41篇
  1990年   41篇
  1989年   47篇
  1988年   35篇
  1987年   40篇
  1986年   40篇
  1985年   40篇
  1984年   37篇
  1983年   30篇
  1982年   25篇
  1981年   38篇
  1980年   38篇
  1979年   24篇
  1978年   29篇
  1977年   62篇
  1976年   107篇
  1975年   25篇
  1974年   23篇
  1973年   18篇
  1971年   14篇
  1966年   10篇
排序方式: 共有3554条查询结果,搜索用时 0 毫秒
71.
Preoperative radiotherapy for adenocarcinoma of the rectosigmoid   总被引:2,自引:0,他引:2  
Ninety-seven patients with adenocarcinoma of the rectosigmoid have been treated with high dose (5000-6000 rad) preoperative irradiation from 1960 through 1972 at the University of Oregon Health Sciences Center. Fifty-seven were initially clinically resectable and 40 were initially inoperable. Forty of the 57 initially clinically resectable patients had "curative" resections and are at risk for more than 5 years. An increase in 5-year survival (from 38% to 53%) and an absence of pelvic recurrence have occurred in those patients receiving preoperative irradiation and "curative" resection. Four of the 40 initially inoperable patients are alive without tumor. Three of the four survivors had irradiation and surgery; one had irradiation only. An additional four patients had no evidence of tumor at death. Tumor was totally sterilized by irradiation and nine patients and reduced to microfocal extent in an additional three of the 97 patients. Incidence of complications was no greater than has been reported in a surgical series from the same institution.  相似文献   
72.
We report on the electrochromic behavior of a dinuclear ruthenium complex, which provides high environmental stability together with an intense absorption maximum at 1237 nm in solution in its +3 oxidation state. To verify its optoelectronic properties, we used this complex as the photoactive material in a planar photodetector prototype for near-infrared light pulses, succeeding in the detection of a train of light pulses at a wavelength of 1280 nm.  相似文献   
73.
Few studies have examined African American clients' subjective experiences in counseling from their perspective. This study used a constructivist paradigm, grounded theory methodology, and dimensional analysis to develop a model of clients' subjective experiences in counseling. Derived from clients' perspectives, the model suggests that the African American participants in this study engaged in an ongoing assessing process. Initially, they assessed client-therapist match, which was influenced by 3 factors: salience of Black identity, court involvement, and ideology similarity between client and therapist. These clients then assessed their safety in therapy and their counselor's effectiveness simultaneously. Clients in turn used information obtained from their assessing process to monitor and manage their degree of self-disclosing along a continuum. The model has important implications for future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
74.
Static tests and ultrasonic measurements (2.25 MHz) have been carried out on a series of composite laminates of glass fibres in a polypropylene matrix. A range of angle ply laminates were prepared for this study, with laminate angles θ of ±0, 10, 20, 30 and 40^∘. The high frequency measurements were made using the ultrasonic immersion technique, which allows the determination of a complete set of the elastic constants of a material. The relationship between the ultrasonically determined elastic constants of the angle ply laminates was found to be in excellent agreement with theoretical predictions, as previously validated for carbon fibre/epoxy angle ply laminates. A comparison between the ultrasonic and statically measured values was made for two of the angle ply laminates (θ = 0 and 20^∘). It was found that the static values were lower than those measured at ultrasonic frequency, particularly those constants that were more matrix dominated (for example the transverse moduli of the laminates). Measurements on a pure polypropylene sample at both testing frequencies confirmed that the change in matrix properties with frequency was the cause of this difference. The change in properties with test frequency is likely to be much larger in this system than in other composite materials because the glass transition temperature of polypropylene is close to ambient temperature. Dynamic mechanical tests (1 Hz) were carried out on a sample of pure polypropylene to assess this effect. We also give an appropriate method of estimating the dependence of glass transition temperature on frequency. The results for polypropylene are compared with those for other commonly used polymer matrix materials: epoxy resin, nylon and polyetheretherketone (PEEK): DMTA measurements were also made on these samples. The effect of test frequency on matrix properties, for the glass/PP laminates, was further investigated by examining the relationship of the Poisson's ratios with laminate angle using a mixture of ultrasonic experiments and theoretical predictions. Previously we have shown that the degree of anisotropy between the reinforcing fibre and the matrix phase is paramount in determining whether the material will show a negative Poisson's ratio at a critical laminate angle. The ultrasonic measurements carried out in this study on the glass/PP laminates showed a minimum in one of the Poisson's ratio at a laminate angle of 32°, but the value did not become negative. However, theoretical predictions showed that for a static frequency measurement (1 Hz), where the matrix is softer and hence the anisotropy of each laminate ply is higher, the laminate will show a negative Poisson's ratio with a minimum at a laminate angle of around 28°.  相似文献   
75.
Numerical transform inversion can be useful to solve stochastic models arising in the performance evaluation of telecommunications and computer systems. We contribute to this technique in this paper by extending our recently developed variant of the Laguerre method for numerically inverting Laplace transforms to multidimensional Laplace transforms. An important application of multidimensional inversion is to calculate time-dependent performance measures of stochastic systems. Key features of our new algorithm are: (1) an efficient FFT-based extension of our previously developed variant of the Fourierseries method to calculate the coefficients of the multidimensional Laguerre generating function, and (2) systematic methods for scaling to accelerate convergence of infinite series, using Wynn's ε-algorithm and exploiting geometric decay rates of Laguerre coefficients. These features greatly speed up the algorithm while controlling errors. We illustrate the effectiveness of our algorithm through numerical examples. For many problems, hundreds of function evaluations can be computed in just a few seconds.  相似文献   
76.
In 3 experiments, the authors investigated the effects of to-be-remembered (TBR) and intervening list length on free recall to determine whether selective rehearsal could explain the previous finding that recall was affected only by TBR list length. In Experiments 1 (covert rehearsal) and 2 (overt rehearsal), participants saw 5- and 20-word lists and had to recall the list prior to that last presented list. In Experiment 3, either 1 or 2 lists were presented, and recall of TBR list was postcued. Recall proportion decreased with increased TBR list length. Moreover, the authors found extended recency effects when recall was replotted by when words were last rehearsed (Experiments 2 and 3) and an effect of intervening list length when rehearsal was reduced (Experiment 3). (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
77.
The paper presents a novel approach for modelling and simulation of the surface generation in the machining process. The approach, by integrating a dynamic cutting force model, regenerative vibration model, machining system response model and tool profile model, models the complex surface generation process. Matlab Simulink is used to interactively perform the simulation in a user-friendly, effective and efficient manner. The effects of machining variables and tooling characteristics on the surface generation are investigated through simulations. CNC turning trials have been carried out to evaluate and validate the approach and simulations presented. The proposed approach contributes to comprehensive and better understanding of the machining system, and is promising for industrial applications with particular reference to the optimisation of the machining process based on the product/component surface functionality requirements.  相似文献   
78.
Shape deformation in continuous map generalization   总被引:2,自引:0,他引:2  
Given a collection of regions on a map, we seek a method of continuously altering the regions as the scale is varied. This is formalized and brought to rigor as well-defined problems in homotopic deformation. We ask the regions to preserve topology, area-ratios, and relative position as they change over time. A solution is presented using differential methods and computational geometric techniques. Most notably, an application of this method is used to provide an algorithm to obtain cartograms.
Rachel WardEmail:

Jeff Danciger   Jeffrey received his undergraduate degree from the College of Creative Studies at UCSB in mathematics and physics. He is currently working on his Ph.D. in mathematics at Stanford University. His research interests include low dimensional topology and geometric analysis. Satyan L. Devadoss   is an Associate Professor of Mathematics at Williams College. His research interests lie in the interplay between topology and geometry, notably in applications to theoretical physics (moduli spaces and string theory) and computer science (cartography and polytopes). John Mugno   received his undergraduate degree from Williams College and is currently continuing his studies in mathematics at the University of Maryland. His areas of interest include combinatorics and topology. Don Sheehy   received his undergraduate degree in Princeton University and is currently pursuing a PhD in Computer Science at Carnegie Mellon University. His research focuses on computational geometry algorithms for meshing. Rachel Ward   received her undergraduate degree at the University of Texas at Austin. She is now a PhD student at Princeton University in the Program in Applied and Computational Mathematics. Her current work is in the area of compressed sensing, combining tools from computational harmonic analysis, probability, and optimization theory.   相似文献   
79.
Simulations based on physiologic modeling have been used for over twenty years to clarify the pharmacokinetics of inhaled anesthetics. We describe ANSIM, an anesthesia simulator for the IBM PC. ANSIM uses established modeling techniques to create a life-like anesthesia simulator. ANSIM is useful as an educational tool for demonstrating classic concepts of uptake and distribution of inhaled anesthetics.  相似文献   
80.
Disturbance of the brain homeostasis, either directly via the formation of abnormal proteins or cerebral hypo-perfusion, or indirectly via peripheral inflammation, will activate microglia to synthesise a variety of pro-inflammatory agents which may lead to inflammation and cell death. The pro-inflammatory cytokines will induce changes in the iron proteins responsible for maintaining iron homeostasis, such that increased amounts of iron will be deposited in cells in the brain. The generation of reactive oxygen and nitrogen species, which is directly involved in the inflammatory process, can significantly affect iron metabolism via their interaction with iron-regulatory proteins (IRPs). This underlies the importance of ensuring that iron is maintained in a form that can be kept under control; hence, the elegant mechanisms which have become increasingly well understood for regulating iron homeostasis. Therapeutic approaches to minimise the toxicity of iron include N-acetyl cysteine, non-steroidal anti-inflammatory compounds and iron chelation.  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