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   918篇
  免费   6篇
  国内免费   9篇
系统科学   19篇
丛书文集   3篇
教育与普及   105篇
理论与方法论   4篇
现状及发展   26篇
研究方法   2篇
综合类   774篇
  2019年   1篇
  2018年   1篇
  2017年   8篇
  2016年   4篇
  2015年   7篇
  2014年   2篇
  2013年   3篇
  2012年   9篇
  2011年   247篇
  2010年   70篇
  2009年   144篇
  2008年   16篇
  2007年   10篇
  2006年   27篇
  2005年   24篇
  2004年   84篇
  2003年   61篇
  2002年   33篇
  2001年   19篇
  2000年   7篇
  1999年   20篇
  1998年   29篇
  1997年   18篇
  1996年   4篇
  1995年   4篇
  1994年   6篇
  1993年   12篇
  1992年   21篇
  1991年   25篇
  1990年   2篇
  1989年   3篇
  1988年   1篇
  1987年   2篇
  1985年   4篇
  1984年   2篇
  1976年   3篇
排序方式: 共有933条查询结果,搜索用时 15 毫秒
121.
随着计算机技术的迅速发展和普及,传统模式的教学方法逐渐被多媒体教学所取代.从课程特点出发,介绍了多媒体教学在精细化学品化学和天然产物化学课程教学中的优势,结合多媒体技术在精细化学品化学和天然产物化学教学中的应用,阐述了多媒体技术在相应教学中的作用.  相似文献   
122.
探讨Tropic1808基因重组蛋白对损伤坐骨神经的新生大鼠脊髓细胞凋亡影响,将新生SD大鼠一侧坐骨神经切断后,用无菌止血海绵包裹断离的神经近侧端,海绵内加入Tropic1808基因重组蛋白,阳性用神经生长因子、阴性用生理盐水作为对照;术后3、6、12h经TUNEL法染色,在光镜、电镜和图像分析系统下,了解L4-L5段脊髓细胞凋亡情况。得到生理盐水组的脊髓出现大量绸亡细胞;Tropic1808基因重组蛋白组凋亡细胞数量较生理盐水组显减少;Tropic1808基因重组蛋白组与神经生长因子组之间凋亡细胞数量的差别无显性意义。说明Tropic1808基因重组蛋白有保护受损神经组织,减少细胞凋亡的作用。  相似文献   
123.
KM小鼠与BALB/c小鼠五项免疫学指标的初步观察   总被引:3,自引:0,他引:3  
采用五种免疫功能测定法对832只健康KM小鼠和83只BALB/c小鼠进行免疫学功能指标的测定,结果表明ConA诱导小鼠脾淋巴细胞转化能力OD值分别为0.0148-0.0192和0.01201~0.0206,二硝基氟苯诱导小鼠迟发型变态反应(耳肿胀法)小鼠耳重差分别为10.39~12.17mg和11.468~16.234mg;血清溶血素抗体积数分别为78.98~91.30和106.73~116.07  相似文献   
124.
Improved MFCC-Based Feature for Robust Speaker Identification   总被引:2,自引:0,他引:2  
The Mel-frequency cepstral coefficient (MFCC) is the most widely used feature in speech and speaker recognition. However, MFCC is very sensitive to noise interference, which tends to drastically degrade the performance of recognition systems because of the mismatches between training and testing. In this paper, the logarithmic transformation in the standard MFCC analysis is replaced by a combined function to improve the noisy sensitivity. The proposed feature extraction process is also combined with speech enhancement methods, such as spectral subtraction and median-filter to further suppress the noise. Experiments show that the proposed robust MFCC-based feature significantly reduces the recognition error rate over a wide signal-to-noise ratio range.  相似文献   
125.
提出了一种新型的鼓泡式光生物制氢反应器,并将Rhodopseudomonas palustris CQK-01光合产氢菌在光生物制氢反应器中进行序批式培养,以葡萄糖为碳源底物,以590nm单波长光为光源,研究了不同鼓泡条件下光合细菌的生长、产氢及底物降解特性.实验结果表明,在光生物制氢反应器中适当鼓入氩气气泡可以有效降低反应器内液相氢浓度,减少产物反馈抑制作用,促进产氢性能的提高,并且不同鼓泡频率对光合细菌的生长和产氢有较大影响.实验中间隔3h鼓泡时光合细菌产氢性能最佳,反应器最大产氢量33.25mmol,光能转化效率为18.46%,产氢得率为1.79mol(H2)/mol(glucose),平均底物消耗速率为0.28mmolL-1h-1和平均产氢速率为0.50mmolL-1h-1.  相似文献   
126.
Carboxymethyl starch with lower degree of substitution was blended with acrylate copolymer for revealing the relation between mechanical properties and chemical structure of blending film.Effects of carboxymethylation of starch,acrylate constituent units of acrylate copolymers,and copolymer content of the film on the properties were investigated.The mechanical properties were evaluated in terms of tensile strength,breaking elongation,abrasion resistance,and flex-fatigue resistance.Film morphology was examined with X-ray diffraction (XRD),scanning electron microscopy (SEM),and atomic force microscope (AFM).It was found that the properties depended on the degree of substitution of carboxymethyl starch,chemical structure of acrylate units,and content of acrylate copolymer.Phase-separation of the two ingredients occurred within film matrix and the separation was decreased after starch carboxymethylation.Breaking elongation and flex-fatigue resistance of the film reached maximums when acrylate copolymer content was 50%.Excessively increasing the content of acrylate copolymer reduced the film properties.  相似文献   
127.
pH值对猪粪废水微生物燃料电池产电性能的影响   总被引:1,自引:0,他引:1  
构建了以布阴极组为空气阴极的单室微生物燃料电池,并将其应用于猪粪废水的处理与产电.重点考察了阳极液pH值对猪粪废水处理和产电性能的影响.结果表明,阳极液pH=10时MFC的产电和废水处理性能最佳,输出功率密度达到2.10W/m3,与阳极液pH=6和pH=8时的电池相比,输出功率分别提高约2.7倍和1.9倍.同时,阳极液pH=10时,COD去除率和氨氮去除率也分别达到86.7%和92.8%,比阳极液pH=6和pH=8时MFC的COD去除率提高了约13.8%和6.7%;氨氮去除率提高了约5.3%和3.5%.本研究表明,调控阳极液pH值能够有效强化猪粪废水处理和产电,为猪粪废水资源化处理提供了一条新途径.  相似文献   
128.
Previous studies have indicated that data compression in wireless sensor networks is not always beneficial to energy conservation due to the additional computational energy costs. This work gives an energy-efficient arbitration mechanism that enhances the performance of compression algorithms by avoiding unnecessary energy losses. The adaptive compression arbitration system uses a new prediction modeling and adaptation. Tests show that the modeling method gives better predictions with the adaptive mechanism...  相似文献   
129.
Accurate geometrical calibration is critical to obtaining high resolution and artifact free reconstructed images for modern animal single photon emission computed tomography(SPECT) systems.Although there have been many published works on the calibration of various SPECT systems,few studies have been done to evaluate the efficacy of the proposed calibration methods in a quantitative manner.This paper presents a numerical method to assess both the uniqueness and the quantitative accuracy of SPECT calibration,...  相似文献   
130.
The iterative reconstruction algorithms for X-ray CT image reconstruction suffer from their high computational cost.Recently Nvidia releases common unified device architecture(CUDA),allowing developers to access to the processing power of Nvidia graphical processing units(GPUs),in order to perform general purpose computations.The use of the GPU,as an alternative computation platform,allows decreasing processing times,for parallel algorithms.This paper aims to demonstrate the feasibility of such an implement...  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