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   325篇
  免费   9篇
电工技术   9篇
化学工业   65篇
金属工艺   2篇
机械仪表   5篇
建筑科学   14篇
矿业工程   1篇
能源动力   9篇
轻工业   33篇
水利工程   6篇
石油天然气   1篇
无线电   72篇
一般工业技术   45篇
冶金工业   26篇
原子能技术   4篇
自动化技术   42篇
  2024年   6篇
  2023年   10篇
  2022年   10篇
  2021年   14篇
  2020年   11篇
  2019年   29篇
  2018年   20篇
  2017年   9篇
  2016年   10篇
  2015年   8篇
  2014年   5篇
  2013年   27篇
  2012年   12篇
  2011年   13篇
  2010年   10篇
  2009年   10篇
  2008年   18篇
  2007年   13篇
  2006年   2篇
  2005年   11篇
  2004年   13篇
  2003年   2篇
  2002年   8篇
  2001年   5篇
  2000年   5篇
  1999年   2篇
  1998年   14篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1994年   1篇
  1993年   5篇
  1990年   1篇
  1989年   1篇
  1987年   1篇
  1986年   1篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1976年   3篇
  1975年   3篇
  1974年   2篇
  1973年   2篇
  1969年   1篇
  1956年   1篇
  1932年   1篇
排序方式: 共有334条查询结果,搜索用时 15 毫秒
61.
OBJECTIVES: Post-radical prostatectomy stress incontinence occurs in up to 20% of patients. Postprostatectomy incontinence is initially treated with undergarments, pads, or drip collectors. Patients with persistent leakage are often treated with a transurethral bulking agent (Contigen) or placement of an artificial genitourinary sphincter (AGUS). We have compared the direct costs of each treatment at our institution over 10 years. METHODS: The Mayo Clinic estimating office provided the Medicare and non-Medicare charges for patients receiving both collagen injection (outpatient) and AGUS placement (2-day hospitalization) during August 1995. The Mayo Store provided the current price of all undergarments, pads, and drip collectors carried. Two local grocery stores provided the cost of Depends undergarments. RESULTS: The following items were the least expensive carried at the Mayo Clinic Store: Entrust undergarments, Active Style pads, and Conveen drip collectors at $0.99, $0.52, $1.05 each, respectively. The average cost of Depends undergarments was $0.52 each. The cost of wearing 5 of the least expensive undergarments or pads per day for 10 years is $9497. The average estimated Medicare and non-Medicare cost for outpatient (general anesthesia) collagen injection is $4300 and $5625, respectively. The average Medicare and non-Medicare cost for AGUS placement is $15,400 and $20,300, respectively. Factoring in our current 22.4% reoperation rate, the average per patient Medicare and non-Medicare cost for AGUS placement is $18,850 and $24,847, respectively. CONCLUSIONS: The cost of the AGUS placement compares favorably with the cost of transurethral collagen injection (under general anesthesia) in patients requiring several (more than three) collagen injection treatments or requiring the continued use of undergarments after collagen injection. Whereas the cost of transurethral collagen injection, when effective, compares favorably with conservative treatment, AGUS placement is significantly more expensive than conservative management for almost all patients except the exceedingly rare patient wearing more than 9 undergarments or pads per day. When the psychosocial benefit of urinary continence is considered, however, transurethral injection of collagen or AGUS placement often becomes the preferred treatment.  相似文献   
62.
We have investigated the structure and shape of GaN-based nanowires grown on (001) Si substrates for optoelectronic device applications. The nanowire heterostructures contained InN disks and In0.4Ga0.6N barrier layers in the active region. The resulting nanowire array comprised two differently shaped nanowires: shorter pencil-like nanowires and longer bead-like nanowires. The two different nanowire shapes evolve due to a variation in the In incorporation rate, which was faster for the bead-like nanowires. Both types of nanowires exhibited evidence of significant migration of both Ga and In during growth. Ga tended to diffuse away and down along the sidewalls, resulting in a Ga-rich shell for all nanowires. Despite the complex structure and great variability in the In composition, the optical properties of the nanowire arrays were very good, with strong luminescence peaking at ~ 1.63 μm.  相似文献   
63.
A new nonlinear optimal and explicit guidance law is presented in this paper for launch vehicles propelled by solid motors. It can ensure very high terminal precision despite not having the exact knowledge of the thrust–time curve apriori. This was motivated from using it for a carrier launch vehicle in a hypersonic mission, which demands an extremely narrow terminal accuracy window for the launch vehicle for successful initiation of operation of the hypersonic vehicle. The proposed explicit guidance scheme, which computes the optimal guidance command online, ensures the required stringent final conditions with high precision at the injection point. A key feature of the proposed guidance law is an innovative extension of the recently developed model predictive static programming guidance with flexible final time. A penalty function approach is also followed to meet the input and output inequality constraints throughout the vehicle trajectory. In this paper, the guidance law has been successfully validated from nonlinear six degree-of-freedom simulation studies by designing an inner-loop autopilot as well, which enhances confidence of its usefulness significantly. In addition to excellent nominal results, the proposed guidance has been found to have good robustness for perturbed cases as well.  相似文献   
64.
We define a novel notion of quasi-adaptive non-interactive zero-knowledge (NIZK) proofs for probability distributions on parameterized languages. It is quasi-adaptive in the sense that the common reference string (CRS) generator can generate the CRS depending on the language parameters. However, the simulation is required to be uniform, i.e., a single efficient simulator should work for the whole class of parameterized languages. For distributions on languages that are linear subspaces of vector spaces over bilinear groups, we give computationally sound quasi-adaptive NIZKs that are shorter and more efficient than Groth–Sahai NIZKs. For many cryptographic applications quasi-adaptive NIZKs suffice and our constructions can lead to significant efficiency improvements in the standard model. Our construction can be based on any k-linear assumption, and in particular under the eXternal Diffie Hellman (XDH) assumption our proofs are even competitive with Random Oracle-based \(\Sigma \)-protocol NIZK proofs. We also show that our system can be extended to include integer tags in the defining linear equations, where the tags are provided adaptively by the adversary. This leads to applicability of our system to many applications that use tags, e.g., applications using Cramer–Shoup projective hash proofs. Our techniques also lead to the shortest known (ciphertext) fully secure identity-based encryption scheme under standard static assumptions. Further, we also get a short publicly verifiable CCA2-secure IBE scheme.  相似文献   
65.
The analysis of the effects of mass transport and chemical reaction on pollutant removal from a gas-phase in a three-phase slurry adsorber-reactor is presented. A mathematical model, consisting of four coupled differential equations, was developed to describe the process and solved numerically. The modeling assumptions included: perfect mixing in the three-phase slurry, Henry's law, a linear adsorption isotherm and a second order, irreversible chemical reaction. The model was found to adequately represent limited existing experimental data and to qualitatively predict the effects of the various transport coefficients on the pollutant removal efficiency of the process. The model was also used for design analysis. Although the model-process achieved significant pollutant removal for representative operating conditions, the percent removal was ultimately limited by mass transport from the gas bubbles to the liquid slurry.  相似文献   
66.
Abstract An efficient method for the preparation of 1,3-dithiolanes of aliphatic and both activated and deactivated aromatic carbonyl compounds with 1,2-ethanedithiol in the presence of a catalytic amount of inexpensive, easily recyclable, monodispersed, chemoselective Ni-nanoparticles having high TON and TOF is reported. An efficient method for the chemoselective thioacetalization of ketones in the presence of aldehydes using Ni-nanoparticles is also reported in this article. Our reaction is kinetically controlled and the method is relatively expedient, avoids the use of cost-prohibitive reagents, high temperatures and leads to excellent yield. Graphical Abstract Selective Protection of Carbonyl Compounds Over Nano-sized Nickel Catalysts Ajeet Kumar,a Santosh Kumar,a Amit Saxena,a Arnab De,b Subho Mozumdara* aDepartment of Chemistry, University of Delhi, Delhi, 110007, India; b Department of Chemistry, Indiana University, Bloomington, USA; subhoscom@yahoo.co.in An efficient method for the preparation of 1,3-dithiolanes of aliphatic and both activated and deactivated aromatic carbonyl compounds with 1,2-ethanedithiol in the presence of a catalytic amount of inexpensive, easily recyclable, monodispersed, chemoselective Ni-nanoparticles having high TON and TOF is reported. We report an efficient method for the chemoselective thioacetalization of ketones in the presence of aldehydes using Ni-nanoparticles. Our reaction is kinetically controlled and the method is relatively expedient, avoids the use of cost-prohibitive reagents, high temperatures and leads to excellent yield.   相似文献   
67.
68.
Motion databases have a strong potential to guide progress in the field of machine recognition and motion-based animation. Existing databases either have a very loose structure that does not sample the domain according to any controlled methodology or too few action samples which limit their potential to quantitatively evaluate the performance of motion-based techniques. The controlled sampling of the motor domain in the database may lead investigators to identify the fundamental difficulties of motion cognition problems and allow the addressing of these issues in a more objective way. In this paper, we describe the construction of our Human Motion Database using controlled sampling methods (parametric and cognitive sampling) to obtain the structure necessary for the quantitative evaluation of several motion-based research problems. The Human Motion Database is organized into several components: the praxicon dataset, the cross-validation dataset, the generalization dataset, the compositionality dataset, and the interaction dataset. The main contributions of this paper include (1) a survey of human motion databases describing data sources related to motion synthesis and analysis problems, (2) a sampling methodology that takes advantage of a systematic controlled capture, denoted as cognitive sampling and parametric sampling, and (3) a novel structured motion database organized into several datasets addressing a number of aspects in the motion domain.  相似文献   
69.
We describe a new approach to speech recognition, in which all Hidden Markov Model (HMM) states share the same Gaussian Mixture Model (GMM) structure with the same number of Gaussians in each state. The model is defined by vectors associated with each state with a dimension of, say, 50, together with a global mapping from this vector space to the space of parameters of the GMM. This model appears to give better results than a conventional model, and the extra structure offers many new opportunities for modeling innovations while maintaining compatibility with most standard techniques.  相似文献   
70.
The fractionator is illustrated by means of a biomedical example involving the estimation of the number of lymphatic valves in lungs of infants who had died from sudden infant death syndrome (SIDS) and other known causes. The method is unbiased irrespective of tissue deformations and it does not require external information such as section thickness. An upper bound of the coefficient of error of the estimate of the number of valves within one lung was 6.5%, despite the fact that the number of valves counted per lung at the last stage ranged between 11 and 37 only. The upper bound includes the biological variation of the number of valves among infant lungs. Some theoretical remarks are also made on the efficiency of the fractionator. It is suggested, for instance, that the initial sampling stages cause more impact on the precision of the final estimator than the subsequent stages, and that an optimal arrangement of fragments submitted to systematic sampling should have the smallest fragments at the ends, with fragment contents increasing smoothly toward the middle of the series.  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