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   1918篇
  免费   76篇
  国内免费   4篇
电工技术   23篇
综合类   4篇
化学工业   604篇
金属工艺   74篇
机械仪表   88篇
建筑科学   39篇
矿业工程   6篇
能源动力   67篇
轻工业   147篇
水利工程   14篇
石油天然气   7篇
无线电   149篇
一般工业技术   269篇
冶金工业   180篇
原子能技术   18篇
自动化技术   309篇
  2023年   12篇
  2022年   94篇
  2021年   98篇
  2020年   42篇
  2019年   52篇
  2018年   55篇
  2017年   77篇
  2016年   81篇
  2015年   57篇
  2014年   97篇
  2013年   146篇
  2012年   95篇
  2011年   101篇
  2010年   89篇
  2009年   96篇
  2008年   104篇
  2007年   70篇
  2006年   67篇
  2005年   45篇
  2004年   43篇
  2003年   47篇
  2002年   26篇
  2001年   16篇
  2000年   24篇
  1999年   20篇
  1998年   29篇
  1997年   25篇
  1996年   26篇
  1995年   21篇
  1994年   22篇
  1993年   17篇
  1992年   13篇
  1991年   15篇
  1990年   8篇
  1989年   12篇
  1988年   14篇
  1987年   9篇
  1985年   8篇
  1984年   9篇
  1983年   19篇
  1982年   7篇
  1981年   9篇
  1980年   10篇
  1979年   8篇
  1978年   9篇
  1977年   9篇
  1975年   4篇
  1973年   6篇
  1972年   5篇
  1971年   6篇
排序方式: 共有1998条查询结果,搜索用时 31 毫秒
101.
The determination of pesticide residues in food matrices is a formidable challenge mainly because of the small quantities of analytes and large amounts of interfering substances which can be co-extracted with analytes and, in most cases, adversely affect the results of an analysis. However, safety concerns require that pesticides of the wide range of chemical properties (including acidic, basic and neutral) should be monitored. Because of the wide variety of food matrices, the sample must initially be cleaned up before final analysis. That is why the analytical chemist is faced with the need to devise new methodologies for determining such residues to be determined in a single analytical run. To accomplish the goal, QuEChERS methodology has been developed. It is a streamlined and effective extraction and cleanup approach for the analysis of diverse analyte residues in food matrices. So far, there have been achieved promising results by liquid or gas chromatography analysis, including pesticides, but also acrylamide, pharmaceuticals and veterinary drugs.  相似文献   
102.
Fully bio‐based and biodegradable composites were compression molded from unidirectionally aligned sisal fiber bundles and a polylactide polymer matrix (PLLA). Caustic soda treatment was employed to modify the strength of sisal fibers and to improve fiber to matrix adhesion. Mechanical properties of PLLA/sisal fiber composites improved with caustic soda treatment: the mean flexural strength and modulus increased from 279 MPa and 19.4 GPa respectively to 286 MPa and 22 GPa at a fiber volume fraction of Vf = 0.6. The glass transition temperature decreased with increasing fiber content in composites reinforced with untreated sisal fibers due to interfacial friction. The damping at the caustic soda‐treated fibers‐PLLA interface was reduced due to the presence of transcrystalline morphology at the fiber to matrix interface. It was demonstrated that high strength, high modulus sisal‐PLLA composites can be produced with effective stress transfer at well‐bonded fiber to matrix interfaces. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40999.  相似文献   
103.
With increasingly strict automotive emission regulations the exhaust gas aftertreatment becomes more complex and expensive. Mathematical modelling and simulations play an important role in design of the aftertreatment systems consisting of multiple catalytic devices, reducing the time and cost demands of the system design. In this paper a combined exhaust gas aftertreatment system for diesel engines is studied. It consists of a diesel oxidation catalyst (DOC) for CO and hydrocarbons oxidation, a catalyzed diesel particulate filter (CDPF) for soot filtration, and an NOx storage and reduction catalyst (NSRC, also called lean NOx trap, LNT) for NOx abatement. Effective mathematical models of the individual converters are presented and used first to demonstrate the functionalities of the system, and then to conduct a parametric simulation study. The aim of this study is to map the influence of the individual components on the performance of the entire system in standard test driving cycle. The sizes of the DOC, CDPF, and NSRC converters are varied while the overall volume of the combined system is kept constant. The resulting maps of pressure drop, CO, HC, particulate matter, and NOx conversions show non-linear dependences on the sizes of individual converters. Co-operative and competitive effects occurring in the combined system are discussed. Suitable reactors sizes are found that enable high conversions of all controlled exhaust gas components.  相似文献   
104.
This paper presents novel opportunities for management of fly ash by synthesizing the material into cordierite ceramics and using it as a reinforcing phase for light metal alloys. Metal matrix composites (based on magnesium alloy and aluminum alloy) were produced by squeeze casting. The magnesium matrix composites with a suitably selected reinforcing phase content (2 wt.%) exhibited much better strength properties than the unmodified alloy (AM60). It was also demonstrated that the wettability (or the lack thereof) in the metal-ceramic system is critical to successful production of the composites based on the AK7 alloy with cordierite. Light alloy matrix composites reinforced with cordierite ceramics particles are innovative materials that combine high strength with low weight, which may be a key factor of merit for numerous applications of the composite in various branches of industries.  相似文献   
105.
Decommissioning of nuclear facilities becomes an important issue in all areas of nuclear technology, mainly in their energetic applications. Decommissioning process has to be planned in the safe, ecological and economic manner. It determines the requirements on appropriate evaluation of needed technologies, media, amount of solid materials released into the environment, radioactivity of effluents, amount of radioactive waste for disposal, number and exposure of personnel and finally the financial demands. A detailed evaluation of these parameters may be done by analytical calculation approach. This approach models a real process of decommissioning with its individual basic activities. The methodology of integrated material flow and radioactivity distribution within this calculation evaluation tool is applied and implemented to describe the real decommissioning activities and their mutual relations to obtain more accurate outputs.  相似文献   
106.
In this paper, we investigated the effects of neonatal exposure to methoxychlor (MXC), a synthetic organochlorine used as an insecticide with estrogenic, antiestrogenic, and antiandrogenic activities on ovarian follicles of adult pigs. Piglets were injected with MXC (20 μg/kg body weight) or corn oil (controls) from postnatal Day 1 to Day 10 (n = 5 per group). Then, mRNA expression, protein abundance and immunolocalization of growth and differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), anti-Müllerian hormone (AMH) and cognate receptors (ACVR1, BMPR1A, BMPR1B, TGFBR1, BMPR2, and AMHR2), as well as FSH receptor (FSHR) were examined in preantral and small antral ovarian follicles of sexually mature gilts. The plasma AMH and FSH levels were also assessed. In preantral follicles, neonatal exposure to MXC increased GDF9, BMPR1B, TGFBR1, and BMPR2 mRNAs, while the levels of AMH and BMP15 mRNAs decreased. In addition, MXC also decreased BMP15 and BMPR1B protein abundance. Regarding small antral follicles, neonatal exposure to MXC upregulated mRNAs for BMPR1B, BMPR2, and AMHR2 and downregulated mRNAs for AMH, BMPR1A, and FSHR. MXC decreased the protein abundance of AMH, and all examined receptors in small antral follicles. GDF9 and BMP15 were immunolocalized in oocytes and granulosa cells of preantral follicles of control and treated ovaries. All analyzed receptors were detected in the oocytes and granulosa cells of preantral follicles, and in the granulosa and theca cells of small antral follicles. The exception, however, was FSHR, which was detected only in the granulosa cells of small antral follicles. In addition, MXC decreased the plasma AMH and FSH concentrations. In conclusion, the present study may indicate long-term effects of neonatal MXC exposure on GDF9, BMP15, AMH, and FSH signaling in ovaries of adult pigs. However, the MXC effects varied at different stages of follicular development. It seems that neonatal MXC exposure may result in accelerated initial recruitment of ovarian follicles and impaired cyclic recruitment of antral follicles.  相似文献   
107.
The frequency dependences of the coefficients of reflection from a lattice of double split rings excited by an RF magnetic field and from an RF-absorbent composite based on resistive films or fibers are analyzed. It is shown that partial reflections from the surface of the composite and the closely spaced lattice can compensate each other and, thus, the reflection from the composite can be significantly reduced. It is experimentally confirmed that the reflection can be decreased by more than 15 dB as compared to the reflection from the composite in the absence of the lattice.  相似文献   
108.
Bandpass frequency-selective surfaces (FSSs) controlled by varactors and representing biperiodic lattices formed from slotted squares in a thin metallic screen are considered. Main factors affecting the FSS tuning range with different circuits for connection of control varactors are experimentally evaluated. Experimental results obtained by the waveguide method of measuring the transmission coefficient through samples of both individual FSS elements loaded with varactors of various types and lattices consisting of these elements at microwave frequencies are presented. Based on the measured data, attainable values of the relative tuning of the FSS resonance frequency are evaluated: f max/f min = 1.4 for control circuits with two MA46N120 low-capacitance varactors in each FSS element and f max/f min = 1.5 for control circuits with one VV857 medium-capacitance varactor.  相似文献   
109.
The present state of the development and production of Russian and foreign radio-measuring instruments in the frequency range up to 178.4 GHz (and higher) and the proposed glossary of the new generation of Russian instruments are considered.  相似文献   
110.
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