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   1628篇
  免费   107篇
  国内免费   2篇
电工技术   6篇
化学工业   522篇
金属工艺   21篇
机械仪表   31篇
建筑科学   51篇
能源动力   49篇
轻工业   351篇
水利工程   13篇
石油天然气   4篇
无线电   73篇
一般工业技术   205篇
冶金工业   186篇
原子能技术   17篇
自动化技术   208篇
  2024年   4篇
  2023年   17篇
  2022年   92篇
  2021年   110篇
  2020年   42篇
  2019年   46篇
  2018年   42篇
  2017年   44篇
  2016年   57篇
  2015年   55篇
  2014年   56篇
  2013年   117篇
  2012年   86篇
  2011年   110篇
  2010年   98篇
  2009年   101篇
  2008年   79篇
  2007年   63篇
  2006年   47篇
  2005年   33篇
  2004年   42篇
  2003年   29篇
  2002年   23篇
  2001年   25篇
  2000年   20篇
  1999年   20篇
  1998年   52篇
  1997年   32篇
  1996年   18篇
  1995年   16篇
  1994年   13篇
  1993年   20篇
  1992年   14篇
  1991年   12篇
  1990年   11篇
  1989年   6篇
  1988年   5篇
  1987年   8篇
  1986年   8篇
  1985年   5篇
  1984年   4篇
  1983年   7篇
  1982年   7篇
  1981年   12篇
  1980年   6篇
  1979年   4篇
  1977年   6篇
  1976年   3篇
  1975年   4篇
  1973年   2篇
排序方式: 共有1737条查询结果,搜索用时 15 毫秒
51.
Normal alkanes show very complicated phase transition kinetics and macroscopic phase equilibrium behavior. This paper focuses on the phase stability and equilibrium of complicated mixtures like n-alkanes and on the enabling global optimization technologies needed to gather problem knowledge. The new ideas contained in this paper include:
(1) novel level set methods for gathering encoded knowledge;
(2) the differential geometry for uncovering pathways to more subtle knowledge;
(3) all supporting non-linearly constrained optimization techniques;
(4) all data handling needed to unravel complex solution structure.
These new ideas are incorporated within the integral path methodology or terrain methods recently developed by Lucia, A., & Yang, F. (2003) [Lucia, A., & Yang F. (2003). Multivariable terrain methods. AIChE Journal 49, 2553] and Lucia, DiMaggio, and Depa (2004) [Lucia, A., DiMaggio, P.A., & Depa, P. (2004). A geometric terrain methodology for global optimization. Journal of Global Optimization 29, 297]. This framework provides global knowledge for understanding solution structure, like the complex solution structure of n-alkanes. In particular, it is shown that knowledge of the Newton and tangent vector fields, Gauss curvature, integral path bifurcation points, and non-differentiable manifolds provides a deterministic way of finding additional solutions, saddle points, and other information that might otherwise go undetected.It is shown that the optimization tools developed in this work provide all knowledge of interest on the appropriate hypothetical single-phase or composite surface (i.e., minima, saddle points, singular points, and integral paths) in phase stability applications. This knowledge can be obtained by solving the phase stability problem exactly once, in a pre-processing step, and used to reliably initialize any multi-phase equilibrium calculation for any feed. This removes the need to repeatedly solve the phase stability problem as the feed composition changes and greatly increases computational efficiency. Numerical examples and geometric illustrations are used to elucidate key ideas and to show how the proposed approach can be used to unravel the complicated phase behavior of n-alkane mixtures.  相似文献   
52.
Line positions, strengths, and absolute energies are calculated for the pure rotational spectrum of water in the region between 0 cm?1 and 877 cm?1. These calculations are done in the context of a reduced centrifugal distortion Hamiltonian, and are based on microwave measurements of this spectrum to 1 THz, and Far Infrared measurements between 32 cm?1 and 715 cm?1.  相似文献   
53.
Constructing code analyzers may be costly and error prone if inadequate technologies and tools are used. If they are written in a conventional programming language, for instance, several thousand lines of code may be required even for relatively simple analyses. One way of facilitating the development of code analyzers is to define a very high-level domain-oriented language and implement an application generator that creates the analyzers from the specification of the analyses they are intended to perform. This paper presents a system for developing code analyzers that uses a database to store both a no-loss fine-grained intermediate representation and the results of the analyses. The system uses an algebraic representation, called F(p), as the user-visible intermediate representation. Analyzers are specified in a declarative language, called F(p)-l, which enables an analysis to be specified in the form of a traversal of an algebraic expression, with access to, and storage of, the database information the algebraic expression indices. A foreign language interface allows the analyzers to be embedded in C programs. This is useful for implementing the user interface of an analyzer, for example, or to facilitate interoperation of the generated analyzers with pre-existing tools. The paper evaluates the strengths and limitations of the proposed system, and compares it to other related approaches  相似文献   
54.
We report the electro-oxidation of formaldehyde on polyaniline films modified with Pt nanoparticles (PANI-Pt films) in an aqueous sulfuric acid solution. The electrodeposition of Pt particles on the PANI matrix was found to promote a mass loss of the film, with a similar effect occurring after cycling the PANI films in the acidic medium containing formaldehyde. However, despite the electrochemical instability of PANI-Pt films, on films containing larger amounts of incorporated Pt particles, the oxidation of formaldehyde produces adsorbed CO species (COads) at a lower positive potential than on bulk Pt. Our findings also indicate that electro-oxidation of COads on the PANI-Pt film surface depends not only on the thickness of PANI film but also on the amount of Pt particles incorporated into the PANI matrix.  相似文献   
55.
The association between nonalcoholic fatty liver disease (NAFLD) and chronic kidney disease has attracted interest and attention over recent years. However, no data are available in children. We determined whether children with NAFLD show signs of renal functional alterations, as determined by estimated glomerular filtration rate (eGFR) and urinary albumin excretion. We studied 596 children with overweight/obesity, 268 with NAFLD (hepatic fat fraction ≥5% on magnetic resonance imaging) and 328 without NAFLD, and 130 healthy normal-weight controls. Decreased GFR was defined as eGFR < 90 mL/min/1.73 m2. Abnormal albuminuria was defined as urinary excretion of ≥30 mg/24 h of albumin. A greater prevalence of eGFR < 90 mL/min/1.73 m2 was observed in patients with NAFLD compared to those without liver involvement and healthy subjects (17.5% vs. 6.7% vs. 0.77%; p < 0.0001). The proportion of children with abnormal albuminuria was also higher in the NAFLD group compared to those without NAFLD, and controls (9.3% vs. 4.0% vs. 0; p < 0.0001). Multivariate logistic regression analysis revealed that NAFLD was associated with decreased eGFR and/or microalbuminuria (odds ratio, 2.54 (confidence interval, 1.16–5.57); p < 0.05) independently of anthropometric and clinical variables. Children with NAFLD are at risk for early renal dysfunction. Recognition of this abnormality in the young may help to prevent the ongoing development of the disease.  相似文献   
56.
近几十年来,旧工业区转型的项目不断增加,范围日益扩大,内涵不断扩充,被认为是城市改造的主要途径。工业区的转型不仅是自身的需要,而且经常能提供一个现实的机会来设想与城市在功能和关系上的深远变化。因为实施的连续性和话题的扩展性,这种转型要放在社会、技术和国际化变化的语境下,考虑典型的城市改造过程中的周期性活力,作为持续演变的效果来进行分析。这种改善往往受到多方面影响,包括:该地区最初的设计、与城市中断了的互动、新的机遇以及潜在的需求。所以,转型不仅意味着现存物质空间的改变,往往还作为观念工具,提供区域层面的解决之道。  相似文献   
57.
The goal of the study was to obtain spaghetti enriched with pea flour with sensory properties close to conventional pasta. To this aim, the study has been organised in two subsequent trials. In the first, the pea flour amount added to the spaghetti was continuously increased until the overall sensory quality reached its threshold value (pea flour concentration = 15%). In fact, the spaghetti samples supplemented with 15% pea flour (15%S‐P) showed less elasticity, unpleasant colour and higher firmness compared to the control sample (CTRL). The second step was aimed to improve the overall sensory quality of the 15%S‐P spaghetti by means of guar gum (GUAR). The sample with GUAR (15%S‐P/GUAR) showed a pleasant colour, odour and taste. Furthermore, the 15%S‐P/GUAR sample recorded a low starch digestibility value (i.e. 54) and a higher soluble fibre content with respect to the 15%S‐P sample.  相似文献   
58.
59.
Zirconium tin titanate (ZST) is often used as a dielectric resonator for the fabrication of microwave devices. Pure compositions do not sinter easily by solid state sintering; therefore, sintering ZST requires sintering aids capable of creating defects that could improve diffusion processes and/or promote liquid phase sintering. The mechanisms by which the additives influence the microstructure and, consequently, the ZSTs dielectric properties are not very clear. The effects of ZnO, Bi2O3, and La2O3, on the stoichiometry and dielectric properties of ZST sintered at different temperatures were investigated in this study.  相似文献   
60.
In this study, a fortified pancake with all parts of pomegranate as juice and by-products, added in the formulation, was designed. The influence of pomegranate addition on nutritional and sensory quality of pancake, as well as on its shelf-life, was assessed. As one would expect, the enrichment significantly improved the pancake polyphenolic content as compared to the control sample. Surprisingly, pomegranate addition did not affect its sensory quality. In fact, the enriched pancake was greatly appreciated from the sensory point of view. Results also suggested that the addition of pomegranate improved the glycemic index (GI). In fact, while a value of GI equal to 100 was obtained for the control sample, a GI of 71 was measured for the fortified sample. In terms of shelf-life, 30 days were obtained for the enriched pancake, whereas the control sample remained acceptable for about 26 days.  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