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   1237篇
  免费   23篇
电工技术   112篇
综合类   1篇
化学工业   415篇
金属工艺   16篇
机械仪表   25篇
建筑科学   22篇
能源动力   54篇
轻工业   141篇
水利工程   1篇
无线电   60篇
一般工业技术   200篇
冶金工业   99篇
原子能技术   43篇
自动化技术   71篇
  2022年   9篇
  2021年   25篇
  2020年   12篇
  2019年   16篇
  2018年   12篇
  2017年   12篇
  2016年   18篇
  2015年   10篇
  2014年   28篇
  2013年   54篇
  2012年   53篇
  2011年   57篇
  2010年   57篇
  2009年   56篇
  2008年   63篇
  2007年   61篇
  2006年   46篇
  2005年   35篇
  2004年   28篇
  2003年   43篇
  2002年   37篇
  2001年   26篇
  2000年   22篇
  1999年   24篇
  1998年   54篇
  1997年   41篇
  1996年   44篇
  1995年   19篇
  1994年   16篇
  1993年   22篇
  1992年   15篇
  1991年   11篇
  1990年   11篇
  1989年   20篇
  1988年   18篇
  1987年   13篇
  1986年   9篇
  1985年   15篇
  1984年   9篇
  1983年   22篇
  1982年   13篇
  1981年   13篇
  1980年   11篇
  1979年   15篇
  1978年   5篇
  1977年   15篇
  1976年   18篇
  1975年   4篇
  1974年   6篇
  1973年   7篇
排序方式: 共有1260条查询结果,搜索用时 15 毫秒
111.
The respective influences of calcination, drying methods, and washing conditions on the morphologies, surface properties, and photocatalytic activities of TiO2 powders prepared from acid treatments of BaTiO3 were investigated. Rutile powder was obtained using the treatment under strong acid conditions. It possesses a bundle-like shape and comprises rutile nanorods. After calcination, characteristic voids were observed in the particles. Anatase powder was obtained by adjusting pH values of a BaTiO3 suspension to 2.5-3. Drying at 110 °C engendered the formation of spheroidal anatase, although freeze-dried anatase particles assembled into a flake-like shape. The freeze-dried samples show lower crystallinity. With grafting Cu ions, rutile exhibited better photocatalytic performance for the decomposition of gaseous 2-propanol (IPA) under visible light, although it did not work effectively for anatase.  相似文献   
112.
We have synthesized a single crystal of lithium amide (LiNH2, LiND2) by melting method, and performed neutron diffraction of the single crystal at variable temperature. LiND2 is tetragonal structure and I-4 space group. Lattice parameters and unit cell volume of LiND2 at room temperature, 50 °C, 100 °C, 150 °C and 200 °C were determined. Both of the lattice parameters and the unit cell volume increase with increase of temperature. From these results, we have estimated coefficient of volumetric thermal expansion αV of LiND2 to be 222 × 10−6/K. With increase of temperature, all thermal ellipsoids gradually expand because of thermal vibration.  相似文献   
113.
An unusual case of dislocation of the midfoot through the calcaneocuboid and naviculocuneiform joints is presented. The prognosis is excellent for most midfoot dislocations, as long as they are recognized and treated early.  相似文献   
114.
Preparation and properties of novel poly(urethane-imide)s   总被引:7,自引:0,他引:7  
Min Zuo  Qian Xiang  Tsutomu Takeichi 《Polymer》1998,39(26):6883-6889
A series of poly(urethane-imide)s were prepared by a novel approach. Polyurethane (PU) prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate (2,4-TDI), and then end-capped with phenol. The PU prepolymer was blended with poly(amide acid) or oligo(amide acid) prepared from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and oxydianiline (ODA) at room temperature in various weight ratios. The blend films obtained by casting and then drying were not transparent, suggesting that phase separation occurred between the polyimide (PI) and PU components. The films became transparent, however, after thermal treatment at 100°C and then 200°C for 1 h each, irrespective of the ratio of the two components. The poly(urethane-imide) films showed good solvent-resistance. Dynamic mechanical analysis of the films showed that glass transition temperatures (Tg) shifted depending on the ratio of PI and PU components. This shift of Tg, along with the transparency of the films, suggests that the PU and PI components employed here are miscible to some extent and that domains of each phase by microphase separation are small. Tensile measurement of the blend films from poly(amide acid) showed that the films are plastic or elastic, depending on the ratio of the components. Thermal stability of the PU was found to increase by the incorporation of polyimide component.  相似文献   
115.
The effect of additives on paste rheology was investigated for preparation of porous ceramics with unidirectionally aligned cylindrical pores. Ammonium poly-carboxylic acid (APA) used as a dispersant and it was adsorbed on alumina powder surface. The adsorption isotherm of APA was fitted by Langmuir equation. The saturated monolayer adsorption was 5.9 mg/g. The apparent viscosity became a minimum at 0.8 mass % of APA corresponding to 71.2 mPa⋅s. This APA amount of 5.6 mg/g, is in good agreement with the observed APA amount. Since the nylon 66 fibers (0–35 vol. %) mixed with the alumina powder have a strong interaction with each other, they became twisted and agglomerated. This agglomeration increased with increasing fiber content but decreased by adding oleic acid. The pastes with added oleic acid were capable of being extruded at higher pressure. The obtained porous alumina ceramics showed highly oriented cylindrical pores parallel to the extrusion direction. The pore orientation was higher in the oleic acid added pastes than those without oleic acid. The added nylon 66 fibers are mostly converted to pores while maintaining the original shape after sintering. The pore size distribution of the obtained porous ceramics measured by mercury porosimetry method showed a peak at about 4 μm which is apparently smaller than that observed in the SEM photographs and the obtained result is considered to be corresponding to the necks formed by fiber contacts.  相似文献   
116.
We investigate quantum fluctuations of striped and honeycomb domain walls in 2D incommensurate states at T=0 near the commensurate-incommensurate transition point. It is revealed that stripes melt due to quantum fluctuations and become a soliton liquid for a large-wall-spacing region. Zero-point energies of striped and honeycomb phases are calculated using an elastic theory. As a consequence of these results, phase diagrams for soliton-lattice and liquid phases are discussed for various domain-wall masses.  相似文献   
117.
In Japan, the Nuclear Power Engineering Corporation (NUPEC), sponsored by the Ministry of Economy, Trade and Industry (METI), has been conducting a series of seismic reliability proving tests using full-scale or close to full-scale models to simulate actual important equipment that is critical for seismic safety of nuclear power plants. The tests are intended to validate the seismic design and reliability with a sufficient margin even under destructive earthquakes. A series of tests was carried out on a reinforced concrete containment vessel (RCCV) for advanced boiling water reactor (ABWR) from 1992 to 1999. A large-scale high-performance shaking table at Tadotsu Engineering Laboratory, the largest in the world, was used for this test. Part 1 reports the test model and the results of pressure and leak tests. Part 2 describes test procedures, input waves and the results of verification tests such as changes of stiffness, characteristic frequency and damping ratio, the failure of the model and the load deflection. Part 3 shows the seismic safety margin that was evaluated from the energy input during the failure test to a design basis earthquake. Part 4 reports simulation analysis results by a stick model with lumped masses.  相似文献   
118.
Issues related to the reliability of man-machine interfaces (MMIs) are discussed from a multi-faceted point of view. Reliability concerning the human operator, the user of MMIs, is discussed using the stimulator data obtained under abnormal plant conditions. Based on the analysis, requirements for MMI design are derived. Cognitive task analysis is also performed to derive design requirements related to human problem solving.Reliability of software, one of the major components of the MMI, is then discussed from the viewpoint of software diversity. Other issues are also discussed to reduce design and implementation errors in the software development process.An experience in carrying out the evaluation of MMIs, one of the critical issues in developing dependable MMIs, is presented to clarify the methodological issues to be solved in the future.The discussions included in this paper show the necessity for a multi-faceted approach to the reliability of MMI both as an integrated object and as a component in a complex human-machine system.  相似文献   
119.
Oral intake of some lactic acid bacteria can have beneficial effects on the host by activating immune responses and enhancing resistance to infection by pathogens. In this study, effects of Lactobacillus sp. on the development of autoimmune disease were examined in mice with collagen-induced arthritis (CIA). CIA, a model of some types of rheumatoid arthritis (RA), can be induced in DBA/1J mice by immunizing them with bovine type II collagen (bCII). Oral intake of skimmed milk (SM) fermented with Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 (SM/OLL1073R-1) was found to markedly inhibit the development of CIA in these mice, compared with a control group fed the control foodstuff. The inhibitory effect of SM fermented with L. delbrueckii subsp. bulgaricus OLLI 102 (SM/OLL1102) or fresh SM was weaker than that of SM/ OLL1073R-1. A deMan Rogosa Sharpe (MRS) broth culture of OLL1073R-1 without any major components of SM had the same inhibitory effect as SM/OLL1073R-1, suggesting that the inhibitory effect of SM/OLL1073R-1 is attributable not only to SM components but also to OLL1073R-1 cells, their metabolites, or both. We found that SM/OLL1073R-1 and SM caused reduced secretion of the cytokine IFN-gamma by lymph node cells (LNCs) in response to bCII. However, SM/OLL1102 did not affect the secretion of IFN-gamma. A polysaccharide fraction secreted by OLL1073R-1 also exhibited the inhibitory effects on both development of CIA and secretion of IFN-gamma.  相似文献   
120.
This study aimed to determine whether combined examinations of myocardial 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) and stress-redistribution 201Tl single-photon emission computed tomography (Tl SPECT) were useful in clarifying myocardial ischaemia and evaluating the prognosis in patients with idiopathic dilated cardiomyopathy (IDCM). Twenty-two patients with IDCM underwent echocardiography, cardiac catheterization, FDG PET, and Tl SPECT. In scintigraphic analysis, the total defect score (TDS) was semiquantitatively determined as the sum of scores of the 17 left ventricular (LV) segments with a 5-point scale (0 as normal to 4 as absent). Patients were classified according to the scintigraphic findings as follows: eight patients with small defects on Tl and FDG (TDS < or = 20) (group I), eight patients with small defects on FDG (TDS < or = 20) with FDG uptake increased relative to Tl or 'mismatch' (group II), and six patients with large defects on FDG and Tl (TDS >20) (group III). Eleven patients (50%) showed reversible defects on Tl and all showed preserved FDG uptake. The patients in group III had significantly lower LV ejection fraction (LVEF) (P<0.05, respectively) and a poorer prognosis as shown by the Kaplan-Meier event-free curve compared with those in groups I and II (P<0.01, respectively). Although patients in group II had significantly greater TDS on Tl compared with those in group I (P<0.01), no significant differences in LVEF and prognosis were found between patients in groups I and II. In multivariate analysis, a TDS on FDG revealed an independent predictor of subsequent cardiac events. In conclusion, such mismatched areas can be assumed to consist of impaired but viable myocardium, and may be associated with ischaemia of the microvasculature. Impaired myocardial glucose metabolism is a more powerful predictor of future cardiac events than perfusion abnormality in patients with IDCM.  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