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   744篇
  免费   49篇
  国内免费   2篇
电工技术   4篇
化学工业   154篇
金属工艺   8篇
机械仪表   18篇
建筑科学   20篇
矿业工程   1篇
能源动力   22篇
轻工业   103篇
水利工程   5篇
石油天然气   4篇
无线电   154篇
一般工业技术   125篇
冶金工业   46篇
原子能技术   2篇
自动化技术   129篇
  2023年   18篇
  2022年   18篇
  2021年   55篇
  2020年   36篇
  2019年   35篇
  2018年   35篇
  2017年   25篇
  2016年   52篇
  2015年   21篇
  2014年   23篇
  2013年   54篇
  2012年   47篇
  2011年   50篇
  2010年   27篇
  2009年   27篇
  2008年   33篇
  2007年   29篇
  2006年   15篇
  2005年   27篇
  2004年   10篇
  2003年   14篇
  2002年   12篇
  2001年   7篇
  2000年   4篇
  1999年   4篇
  1998年   17篇
  1997年   14篇
  1996年   8篇
  1995年   9篇
  1994年   10篇
  1993年   3篇
  1992年   6篇
  1991年   3篇
  1990年   7篇
  1989年   1篇
  1986年   1篇
  1985年   5篇
  1984年   1篇
  1983年   2篇
  1982年   4篇
  1981年   1篇
  1980年   5篇
  1979年   3篇
  1978年   8篇
  1977年   3篇
  1976年   4篇
  1974年   1篇
  1972年   1篇
排序方式: 共有795条查询结果,搜索用时 218 毫秒
1.
To prevent the adulteration of agricultural resources and provide a solution to enhance the green coffee bean supply chain, authentication using the near-infrared spectroscopy (NIRS) technique was investigated. Partial least square with discrimination analysis (PLS-DA) models combined with various preprocessing methods were built from NIR spectra of 153 Vietnamese green coffee samples. The model combined with the standard normal variate and the first order of derivative yielded excellent performance in predicting coffee species with the error cross-validation of 0.0261. PLS-DA model of mean centre and first-order derivative spectra also yielded good performance in verifying geographical indication of green coffee with the error of 0.0656. By contrast, the predicting abilities of post-harvest methods were poor. The overall results showed a high potential of the NIRS in online authentication practices.  相似文献   
2.
A new strategy for the selective coating of tin sulfide (SnS) on the surface of moth‐eye patterned (MEP) conducting polymer film is studied by considering the optical properties of the antireflective moth‐eye pattern and flexibility of polymer films. The semiconductor SnS is selectively coated on the surface of MEP microdomes of poly(3,4‐ethylenedioxythiophene) poly(styrene‐sulfonate) (PEDOT:PSS) film. The SnS coated MEP film is obtained by using pore selectively SnS thin layer functionalized polystyrene honeycomb‐patterned porous (HCP) film as a template. Aqueous PEDOT:PSS solution is poured on the SnS functionalized HCP films and detached for the fabrication of SnS coated MEP films. The films show a satisfactory photo‐responsive property under solar stimulated light illumination due to the antireflective MEP structure of PEDOT film and homogenous SnS coating on the surface of the conducting polymer.  相似文献   
3.
Structure modification has been found to tune significantly the transparent-conducting performance, especially mobility and conductivity of hydrogenated Ga-doped ZnO (HGZO) films. The strong correlation between film thickness and mobility of the films is revealed. The mobility increases quickly with increasing the thickness from 350 to 900 nm, and then tends to be saturated at further thicknesses. A higher mobility than 50 cm2/Vs can be achieved, which is an extra-high value for polycrystalline ZnO films deposited by using the sputtering technique. The thickness-dependent mobility originates from scatterings on grain boundaries and dislocation-induced defects controlled by thin-film growth. Based on the Volmer-Weber model, an expansion model is built up to describe the thickness-dependent crystal growth of the HGZO films, especially at the thick films. As a result, the 800 nm-thick HGZO film obtains the highest performance with high mobility of 51.5 cm2/Vs, low resistivity of 5.3 × 10?4 Ωcm, and good transmittance of 83.3 %.  相似文献   
4.
This work aims to clarify the photocatalytic degradation mechanism and heat reflectance recovery performance of waterborne acrylic polymer/ZnO nanocomposite coating. To fabricate the nanocomposite coating, ZnO nanoparticles (nano-ZnO) were dispersed into acrylic polymer matrix at the various concentrations from 1 to 6% (by total weight of resin solids). The photocatalytic degradation of nanocomposite coating under ultraviolet (UV) light irradiation has been investigated by monitoring its weight loss and chemical/microstructural/morphological changes. As the topcoat layer, its heat reflectance recovery has been evaluated under UV/condensation exposure by using an artificial dirty mixture of 85 wt% nanoclay, 10 wt% silica particles (1–5 μm), 1 wt% carbon black, and 2 wt% engine oil. After 108-cycle UV/condensation exposure, infrared spectra and weight loss analysis indicated that the maximal degradation for nanocomposite coating is observed at 1 wt% nano-ZnO. On the other hand, after 96 hr of UV light exposure, the nanocomposite coating with1 wt% nano-ZnO could restore effectively the reflective index of solar-heat reflectance coating (from 58.45 to 80.78%). Finally, the photodegradation mechanism of this waterborne acrylic polymer coating has been proposed as the UV-induced formation of CC CO conjugated double bonds. As a result, its self-cleaning phenomenon can be achieved as the recovery of heat reflectance.  相似文献   
5.
V. Truong    B.R. Bhandari    T. Howes    B. Adhikari 《Journal of food science》2002,67(8):3011-3018
ABSTRACT: Physical aging of amorphous anhydrous fructose at temperature 5 °C and at 22 °C was studied using differential scanning calorimetry (DSC). The dynamic glass transition temperature, Tg0 for unaged samples was 16 °C and 13.3 °C for heating rate of 10 °C/min and 1 °C/min, respectively. The fictive temperature, Tf0 for unaged samples calculated by Richardson and Savill method was 12 °C, which is close to the dynamic value obtained from the lower DSC heating rate. The fictive temperature Tf of the aged fructose glasses at temperatures both below and above the transition region was fitted well by a non-exponential decay function (Williams-Watts form). Aging above the transition region (22 °C) for 18 d increased both the dynamic glass transition temperature Tg and the fictive temperature Tf. However, aging below the transition region (5 °C) for 1 d increased the dynamic glass transition temperature Tg but decreased the fictive temperature Tf.  相似文献   
6.
In this paper, two algebraic decoders for the (103, 52, 19) and (113, 57, 15) quadratic residue codes, which have lengths greater than 100, are presented. The results have been verified by software simulation that programs in C++ language have been executed to check possible error patterns of both quadratic residue codes.  相似文献   
7.
Analysis of amino acids is complicated by treatment with ampicillin. High voltage electrophoresis, which is convenient for the qualitative assessment of metabolic diseases, yields smears of ampicillin that mask the bands of citrulline, homocitrulline, phenylalanine, cystine, and homocystine. The addition of penicillinase prior to high voltage electrophoresis eliminates ampicillin and other penicillins and reveals these key amino acids.  相似文献   
8.
The interaction of lithium atoms into amorphous tungsten oxide films deposited by thermal evaporation, sputtering and sol-gel synthesis is studied spectroscopically. The mechanism of insertion of lithium into the film depends on the amount and the bonding state of water to the tungsten oxide network. Thermally evaporated tungsten oxide film contains water bonded chemically in the form of a hydrogen tungsten bronze which facilitates the accommodation of a high number of lithium atoms. In the sputtered film, water is physisorbed and the lithiation is incomplete. Tungsten oxide films prepared by sol-gel synthesis have structural water molecules directly involved in the lithiation process. The formation of lithium tungstate independent of the preparation method is demonstrated.  相似文献   
9.
The Kernighan/Lin graph partitioning heuristic, also known as min-cut or group migration, has been extended over several decades very successfully for circuit partitioning. Those extensions customized the heuristic and its associated data structure to rapidly compute the minimum-cut metric central to circuit partitioning; as such, those extensions are not directly applicable to other problems. In this paper, we extend the heuristic for functional partitioning, which in turn can solve the much investigated codesign problem of partitioning a system's coarse-grained functions among hardware and software components. The key extension customizes the heuristic and data structure to rapidly compute execution-time and communication metrics, crucial to hardware and software partitioning, and leads to near-linear time-complexity and excellent resulting quality. Another extension uses a new criteria for terminating the heuristic, eliminating time-consuming and unnecessary fine-tuning of a partition. Our experiments demonstrate extremely fast execution times (just a few seconds) with results matched only by the slower simulated annealing heuristic, meaning that the extended Kernighan/Lin heuristic will likely prove hard to beat for hardware and software functional partitioning.  相似文献   
10.
The potential of the developing zebrafish model for toxicology and drug discovery is limited by inefficient approaches to manipulating and chemically exposing zebrafish embryos-namely, manual placement of embryos into 96- or 384-well plates and exposure of embryos while still in the chorion, a barrier of poorly characterized permeability enclosing the developing embryo. We report the automated dechorionation of 1600 embryos at once at 4 h postfertilization (hpf) and placement of the dechorionated embryos into 96-well plates for exposure by 6 hpf. The process removed ≥95% of the embryos from their chorions with 2% embryo mortality by 24 hpf, and 2% of the embryos malformed at 120 hpf. The robotic embryo placement allocated 6-hpf embryos to 94.7% ± 4.2% of the wells in multiple 96-well trials. The rate of embryo mortality was 2.8% (43 of 1536) from robotic handling, the rate of missed wells was 1.2% (18 of 1536), and the frequency of multipicks was <0.1%. Embryo malformations observed at 24 hpf occurred nearly twice as frequently from robotic handling (16 of 864; 1.9%) as from manual pipetting (9 of 864; 1%). There was no statistical difference between the success of performing the embryo placement robotically or manually.  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