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   916篇
  免费   13篇
电工技术   14篇
化学工业   197篇
金属工艺   24篇
机械仪表   18篇
建筑科学   32篇
能源动力   37篇
轻工业   49篇
水利工程   5篇
石油天然气   6篇
无线电   119篇
一般工业技术   164篇
冶金工业   117篇
原子能技术   9篇
自动化技术   138篇
  2024年   9篇
  2023年   13篇
  2022年   20篇
  2021年   31篇
  2020年   18篇
  2019年   17篇
  2018年   20篇
  2017年   14篇
  2016年   34篇
  2015年   28篇
  2014年   45篇
  2013年   56篇
  2012年   38篇
  2011年   60篇
  2010年   44篇
  2009年   36篇
  2008年   48篇
  2007年   41篇
  2006年   39篇
  2005年   26篇
  2004年   32篇
  2003年   30篇
  2002年   16篇
  2001年   9篇
  2000年   8篇
  1999年   8篇
  1998年   25篇
  1997年   28篇
  1996年   13篇
  1995年   11篇
  1994年   5篇
  1993年   13篇
  1992年   4篇
  1991年   4篇
  1990年   8篇
  1989年   5篇
  1988年   9篇
  1987年   5篇
  1986年   5篇
  1985年   5篇
  1984年   4篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1980年   6篇
  1979年   3篇
  1977年   5篇
  1976年   15篇
  1975年   3篇
  1972年   2篇
排序方式: 共有929条查询结果,搜索用时 15 毫秒
51.
The aim of this study was to evaluate suicides with a history of problem gambling (PG) and others with no such history (NPG) and to compare the two on mental health problems and service utilization. Data on a sample of 49 PG suicides and 73 NPG suicides were obtained from informants and hospital records. Psychopathology was prevalent in both groups, but problem gamblers were twice as likely to have a personality disorder. Moreover, PG suicides were less in contact with mental health services in their last month, their last year, and their lifetime. NPG suicides consulted specialized services from 3 (last month and last year) to 13 times (lifetime) as often as their PG counterparts. Lower service utilization associated with PG suicides argues in favor of stepping up detection, engagement in care and treatment with respect to problem gambling, especially when comorbidity is present. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
52.
This paper presents results of measurements and calculations of physics parameters in the first gas-cooled fast breeder reactor (GCFR) critical assemblies in the US, a program of experiments conducted on the ZPR-9 facility at Argonne National Laboratory. Through a progressive three-phase series of assemblies, the major features unique to GCFR physics due to the gaseous coolant, and the resulting hard neutron spectrum and greater leakage, were investigated. Phases I and II were simple-geometry, uniform-core assemblies providing tests of nuclear data and GCFR design methods for fast reactors with large void fractions. The Phase III core simulates a GCFR design with three enrichment zones. This report primarily concerns the results obtained in Phase II.In addition to the usual central indices, reaction rate mappings, etc. these initial studies have provided the first experimental data on reactivity coefficients relevant to GCFR safety, such as worths of fuel, control, and cladding materials, Doppler effect, and coolant (helium) depressurization worth. Effects of steam ingress into coolant channels (due to a hypothesized steam generator leak) were simulated using polyethylene. The physics information obtained is providing a valuable base for verification of GCFR design and safety analyses.  相似文献   
53.
A novel, unobtrusive and wearable, multiparameter ambulatory physiologic monitoring system for space and terrestrial applications, termed LifeGuard, is presented. The core element is a wearable monitor, the crew physiologic observation device (CPOD), that provides the capability to continuously record two standard electrocardiogram leads, respiration rate via impedance plethysmography, heart rate, hemoglobin oxygen saturation, ambient or body temperature, three axes of acceleration, and blood pressure. These parameters can be digitally recorded with high fidelity over a 9-h period with precise time stamps and user-defined event markers. Data can be continuously streamed to a base station using a built-in Bluetooth RF link or stored in 32 MB of on-board flash memory and downloaded to a personal computer using a serial port. The device is powered by two AAA batteries. The design, laboratory, and field testing of the wearable monitors are described.  相似文献   
54.
Alloys for high temperature applications rely on a protective oxide layer formed by selective oxidation. In Fe20Cr5Al type alloys the useful lifetime is governed by the depletion of aluminium by oxidation down to a critical aluminium content. Following spallation of the oxide scale the bare metal is exposed to air and catastrophic failure due to breakaway oxidation occurs if the aluminium content is too low. In this paper a model for the calculation of the critical aluminium content is presented. Based on Wagner's ideas on selective oxidation in ternary alloys, the critical aluminium content is calculated as that corresponding to the transition between external and internal oxidation. The resulting aluminium contents are temperature dependent and cover the range of values 0 to 3.5 wt.% reported in the literature. In the second part of the paper aluminium depletion profiles in Fe20Cr5Al plates have been calculated assuming a parabolic growth law for the oxidation process. The solution of the differential equation is an extension of the one dimensional solution presented by Whittle and coworkers for chromium depletion in FeCr sheet material, to three dimensions. Because of the increased consumption of aluminium at the corners of the sample, the critical aluminium content is first reached there. Based on the calculation, the reduction in lifetime, due to premature breakaway oxidation at the corners can be estimated.  相似文献   
55.
We study theoretically and experimentally the increase of normal incidence reflectivity generated by addition of a third material in the period of a standard periodic multilayer, for wavelengths in the range 20 to 40 nm. The nature and thickness of the three materials has been optimized to provide the best enhancement of reflectivity. Theoretical reflectivity of an optimized B4C/Mo/Si multilayer reaches 42% at 32 nm. B4C/Mo/Si multilayers have been deposited with a magnetron sputtering system and a reflectivity of 34% at 32 nm has been measured on a synchrotron radiation source.  相似文献   
56.
Journal of Materials Science - In this study coatings of kaolin and talc particles were successfully applied on the surface of polyamide 12 powder intended for laser sintering (LS). Microscopic...  相似文献   
57.

Aquivion membrane displays improved properties as compared to Nafion membrane, partly due to shorter side chains. However, some improvements are still necessary for proton exchange membrane fuel cell to operate at low relative humidity. To overcome this drawback, the addition of clay nanoparticle into the Aquivion matrix can be considered. In this study, different composite membranes have been prepared mixing short-side-chain PFSA (perfluorosulfonic acid) Aquivion and selectively modified halloysite nanotubes for PEMFC low relative humidity operation. Halloysites were grafted with fluorinated groups, sulfonated groups, or perfluoro-sulfonated groups on inner or outer surface of the tubes. The obtained composite membranes showed improved properties, especially higher water uptake associated with reduced swelling and better mechanical strength compared to pristine Aquivion membrane and commercially available Nafion HP used as reference. The best performance in this study was obtained with Aquivion loaded with 5 wt% of pretreated perfluoro-sulfonated halloysite. The composite membrane, referred to as Aq/pHNT-SF5, displayed the largest water uptake and proton conductivity among the panel of membranes tested. The chemical stability was not affected by the presence of halloysite in the Aquivion matrix.

Graphical abstract
  相似文献   
58.
59.
60.
This paper proposes a model of the mechanical behaviour of corroded reinforced concrete members subjected to bending under service load. The model is based on the formulation of a macro-element to be used in FEM analysis, having a length equal to the distance between two consecutive flexural cracks and a cross-section equal to the member cross-section. The mechanical formulation is directly written in generalized variables (bending moment and curvature) and is based on the concept of the transfer length necessary for the transmission of tensile load from re-bar to tensile concrete thanks to the bond. It is thus possible to take into account the effect of reinforcement corrosion on the bond between re-bar and concrete, by increasing the transfer length versus intensity of corrosion. The variation of the transfer length versus corrosion is expressed using a scalar damage parameter. A first experimental validation is performed on a 17-year-old beam kept in a chloride environment under its service load.  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