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   2262篇
  免费   171篇
  国内免费   1篇
电工技术   7篇
化学工业   969篇
金属工艺   21篇
机械仪表   41篇
建筑科学   77篇
矿业工程   5篇
能源动力   41篇
轻工业   565篇
水利工程   15篇
石油天然气   7篇
无线电   80篇
一般工业技术   293篇
冶金工业   71篇
原子能技术   6篇
自动化技术   236篇
  2024年   5篇
  2023年   30篇
  2022年   208篇
  2021年   306篇
  2020年   84篇
  2019年   70篇
  2018年   88篇
  2017年   84篇
  2016年   98篇
  2015年   75篇
  2014年   95篇
  2013年   157篇
  2012年   137篇
  2011年   163篇
  2010年   109篇
  2009年   117篇
  2008年   92篇
  2007年   92篇
  2006年   76篇
  2005年   62篇
  2004年   54篇
  2003年   42篇
  2002年   29篇
  2001年   22篇
  2000年   14篇
  1999年   6篇
  1998年   19篇
  1997年   13篇
  1996年   15篇
  1995年   13篇
  1994年   5篇
  1993年   8篇
  1992年   5篇
  1991年   3篇
  1990年   5篇
  1989年   6篇
  1985年   2篇
  1983年   2篇
  1980年   1篇
  1977年   4篇
  1976年   1篇
  1973年   4篇
  1972年   1篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1965年   1篇
  1934年   1篇
  1933年   1篇
  1932年   2篇
排序方式: 共有2434条查询结果,搜索用时 62 毫秒
231.
Due to the incompleteness of animal genome sequencing, the analysis and characterization of serum proteomes of most farm animals are still in their infancy, compared to the already well-documented human serum proteome. This review focuses on the implications of the farm animal serum proteomics in order to identify novel biomarkers for animal welfare, early diagnosis, prognosis and monitoring of infectious disease treatment, and develop new vaccines, aiming at determining the reciprocal benefits for humans and animals.  相似文献   
232.
The building industry is noted for its repeated building defects causing cost increases and time delays during construction. In Spain, despite the Ley de Ordenación de la Edificación (Building Regulation Act), which establishes a general framework to promote overall building quality, construction defects in residential buildings remain a pervasive problem. An analysis of 3647 construction defects is presented which identified the location within the building, subcontractors and building element in 68 residential building developments undertaken by two large Spanish contractors. The research reveals that the most common defects that arise during construction are related to the stability of the structure and inappropriate installation of roofs and facades. These technical faults are caused by poor workmanship rather than by the quality of the materials or products used. By comparing these results with a previous study on defects after handover, it can be concluded that while the nature of defects during construction is basically technical, at handover it is aesthetic or technical.  相似文献   
233.
In this work, we present the Raman peak positions of the quaternary pure selenide compound Cu \(_2\) ZnSnSe \(_4\) (CZTSe) and related secondary phases that were grown and studied under the same conditions. A vast discussion about the position of the X-ray diffraction (XRD) reflections of these compounds is presented. It is known that by using XRD only, CZTSe can be identified but nothing can be said about the presence of some secondary phases. Thin films of CZTSe, Cu \(_2\) SnSe \(_3\) , ZnSe, SnSe, SnSe \(_2\) , MoSe \(_2\) and a-Se were grown, which allowed their investigation by Raman spectroscopy (RS). Here we present all the Raman spectra of these phases and discuss the similarities with the spectra of CZTSe. The effective analysis depth for the common back-scattering geometry commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated for different wavelength values. The observed asymmetric PL band on a CZTSe film is compatible with the presence of CZTSe single-phase and is discussed in the scope of the fluctuating potentials' model. The estimated bandgap energy is close to the values obtained from absorption measurements. In general, the phase identification of CZTSe benefits from the contributions of RS and PL along with the XRD discussion.  相似文献   
234.
Dental ceramic implants have shown superior esthetic behavior and the absence of induced allergic disorders when compared to titanium implants. Zirconia may become a potential candidate to be used as an alternative to titanium dental implants if surface modifications are introduced. In this work, bioactive micropatterned silica coatings were produced on zirconia substrates, using a combined methodology of sol–gel processing and soft lithography. The aim of the work was to compare the in vitro behavior of human gingival fibroblasts (HGFs) and human dermal microvascular endothelial cells (HDMECs) on three types of silica-coated zirconia surfaces: flat and micropatterned (with pillars and with parallel grooves). Our results showed that cells had a higher metabolic activity (HGF, HDMEC) and increased gene expression levels of fibroblast-specific protein-1 (FSP-1) and collagen type I (COL I) on surfaces with pillars. Nevertheless, parallel grooved surfaces were able to guide cell growth. Even capillary tube-like networks of HDMEC were oriented according to the surface geometry. Zirconia and silica with different topographies have shown to be blood compatible and silica coating reduced bacteria adhesion. All together, the results indicated that microstructured bioactive coating seems to be an efficient strategy to improve soft tissue integration on zirconia implants, protecting implants from peri-implant inflammation and improving long-term implant stabilization. This new approach of micropatterned silica coating on zirconia substrates can generate promising novel dental implants, with surfaces that provide physical cues to guide cells and enhance their behavior.  相似文献   
235.
This paper proposes a methodology to simulate temperature dependent timing in standard cell designs. Temperature dependent timing characteristics are derived from standard delay format (SDF) files that are created by synthesis tools automatically based on SPICE characterizations. In addition, a fast calculation of temperatures using the equivalent Foster RC network is presented. A case study is also presented in this paper where the temperature dependent frequency variation of a ring oscillator is simulated demonstrating the necessity of temperature dependent timing simulations. An adaptively refineable partitioning method for simulating standard cell designs logi-thermally is proposed as well. This paper also introduces recent enhancements in the CellTherm logi-thermal simulator developed in the Department of Electron Devices, BME, Hungary. Finally, the simulation results are compared and verified with the SPICE compatible ELDO analog simulator from Mentor Graphics.  相似文献   
236.
Studies using massive, passively collected data from communication technologies have revealed many ubiquitous aspects of social networks, helping us understand and model social media, information diffusion and organizational dynamics. More recently, these data have come tagged with geographical information, enabling studies of human mobility patterns and the science of cities. We combine these two pursuits and uncover reproducible mobility patterns among social contacts. First, we introduce measures of mobility similarity and predictability and measure them for populations of users in three large urban areas. We find individuals'' visitations patterns are far more similar to and predictable by social contacts than strangers and that these measures are positively correlated with tie strength. Unsupervised clustering of hourly variations in mobility similarity identifies three categories of social ties and suggests geography is an important feature to contextualize social relationships. We find that the composition of a user''s ego network in terms of the type of contacts they keep is correlated with mobility behaviour. Finally, we extend a popular mobility model to include movement choices based on social contacts and compare its ability to reproduce empirical measurements with two additional models of mobility.  相似文献   
237.
Efficiently harvesting solar energy for photocatalysis remains very challenging. Rational design of architectures by combining nanocomponents of radically different properties, for example, plasmonic, upconversion, and photocatalytic properties, offers a promising route to improve solar energy utilization. Herein, the synthesis of novel, plasmonic Au nanoparticle decorated NaYF4:Yb3+, Er3+, Tm3+‐core@porous‐TiO2‐shell microspheres is reported. They exhibit high surface area, good stability, broadband absorption from ultraviolet to near infrared, and excellent photocatalytic activity, significantly better than the benchmark P25 TiO2. The enhanced activity is attributed to synergistic effects from nanocomponents arranged into the nanostructured architecture in such a way that favors the efficient charge/energy transfer among nanocomponents and largely reduced charge recombination. Optical and energy‐transfer properties are modeled theoretically to support our interpretations of catalytic mechanisms. In addition to yielding novel materials and interesting properties, the current work provides physical insights that can contribute to the future development of plasmon‐enhanced broadband catalysts.  相似文献   
238.
This paper deals with the identification of a single open crack in a straight pipe containing fluid under pressure by frequency measurements. The crack is assumed to be a transverse partial cut of the pipe wall thickness with straight front and it is simulated by an equivalent elastic spring. It is shown that the measurement of the damage-induced shifts in a pair of natural frequencies of the bending vibration can be used to formulate and solve the diagnostic problem. In particular, it is shown that the change in the first two frequencies in a simply supported uniform pipe is sufficient to localize a small crack, except for a symmetrical position, and to determine the damage severity. Closed-form expressions are provided for damage location and severity. An extension of the method to simply supported uniform pipe with two cracks of equal severity is also presented. The analysis is based on an explicit expression of the frequency sensitivity to damage and allows to consider pipes under general set of boundary conditions. Analytical results agree well with the numerical tests.  相似文献   
239.
Extensive radon surveys have been carried out in many countries only in dwellings, whereas surveys in workplaces are rather sparse and generally restricted to specific workplaces/activities, e.g. schools, spas and caves. Moreover, radon-prone areas are generally defined on the basis of radon surveys in dwellings, while radon regulations use this concept to introduce specific requirements in workplaces in such areas. This approach does not take into account that work activities and workplace characteristics can significantly affect radon concentration. Therefore, an extensive survey on radon in different workplaces have been carried out in a large region of Italy (Tuscany), in order to evaluate radon distribution in workplaces over the whole territory and to identify activities and workplace characteristics affecting radon concentration. The results of this extensive survey are compared with the results of the survey carried out in dwellings in the same period. The workplaces monitored were randomly selected among the main work activities in the region, including both public and industrial buildings. The survey monitored over 3500 rooms in more than 1200 buildings for two consecutive periods of ~6 months. Radon concentration was measured by means of passive nuclear track detectors.  相似文献   
240.
The winery industry generates vast amounts of organic waste during the various stages of wine production. Among the possible methodological alternatives available for its treatment, vermicomposting is one of the best-known processes for the biological stabilization of solid organic wastes by transforming them into safer and more stabilized materials suitable for application to soil. In this study we carried out a mesocosm experiment to evaluate the effectiveness of the active phase of vermicomposting for the stabilization of grape marc, an enriched lignocellulosic by-product obtained after the grape crushing and pressing stages in wine production. For this we analysed the chemical, biochemical and microbiological properties of the product resulting from this phase, in comparison with those in a control treatment. Earthworm activity reduced the abundance of both bacterial and fungal PLFA biomarkers. Decreases in microbial activity and in protease and cellulase activities were also attributed to the presence of earthworms. The differences in microbial communities were accompanied by a reduction in the labile C pool and the cellulose content. These results indicate that earthworms played a key role in the stabilization of the grape marc in the short-term, via its effects on organic matter decomposition and microbial biomass and activity.  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