全文获取类型
收费全文 | 3500篇 |
免费 | 460篇 |
国内免费 | 379篇 |
专业分类
电工技术 | 128篇 |
综合类 | 346篇 |
化学工业 | 639篇 |
金属工艺 | 132篇 |
机械仪表 | 217篇 |
建筑科学 | 275篇 |
矿业工程 | 55篇 |
能源动力 | 40篇 |
轻工业 | 60篇 |
水利工程 | 33篇 |
石油天然气 | 130篇 |
武器工业 | 31篇 |
无线电 | 441篇 |
一般工业技术 | 584篇 |
冶金工业 | 44篇 |
原子能技术 | 13篇 |
自动化技术 | 1171篇 |
出版年
2024年 | 10篇 |
2023年 | 52篇 |
2022年 | 74篇 |
2021年 | 70篇 |
2020年 | 95篇 |
2019年 | 98篇 |
2018年 | 100篇 |
2017年 | 113篇 |
2016年 | 118篇 |
2015年 | 164篇 |
2014年 | 320篇 |
2013年 | 231篇 |
2012年 | 342篇 |
2011年 | 324篇 |
2010年 | 301篇 |
2009年 | 300篇 |
2008年 | 287篇 |
2007年 | 326篇 |
2006年 | 257篇 |
2005年 | 228篇 |
2004年 | 117篇 |
2003年 | 89篇 |
2002年 | 88篇 |
2001年 | 63篇 |
2000年 | 59篇 |
1999年 | 34篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有4339条查询结果,搜索用时 10 毫秒
11.
12.
A novel iron phosphate templated with ethylenediammonium cation, [H3N(CH2)2NH3]2 Fe4 O(PO4)4H2O, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction, thermo-gravimetric analysis, magnetic susceptibility and Mossbauer spectroscopy. The compound crystallizes in the mono-clinic space group C2 with a= 30.3801(5),b= 10.1204(5),c= 10.0977(5) Å, = 107.712(1)°, V = 2957.5(4) Å3 and Z = 6. The structure contains 5 and 6-coordinated Fe atoms bridged by 4-oxygen and PO4 groups to form two types of mixed-valence Fe4P4 cubane-like clusters, which are connected via Fe- O- P bonds to give rise to intersecting channels that house the ethylenediammonium cations and water molecules. Room-temperature Mossbauer data confirm the presence of FeII and FeIII. 相似文献
13.
This paper addresses the problem of reinforcing the ability of the k-NN classification of handwritten characters via distortion-tolerant template matching techniques with a limited quantity of data. We compare three kinds of matching techniques: the conventional simple correlation, the tangent distance, and the global affine transformation (GAT) correlation. Although the k-NN classification method is straightforward and powerful, it consumes a lot of time. Therefore, to reduce the computational cost of matching in k-NN classification, we propose accelerating the GAT correlation method by reformulating its computational model and adopting efficient lookup tables. Recognition experiments performed on the IPTP CDROM1B handwritten numerical database show that the matching techniques of the simple correlation, the tangent distance, and the accelerated GAT correlation achieved recognition rates of 97.07%, 97.50%, and 98.70%, respectively. The computation time ratios of the tangent distance and the accelerated GAT correlation to the simple correlation are 26.3 and 36.5 to 1.0, respectively. 相似文献
14.
15.
Three-dimensionally ordered long-range macroporous carbon structures were prepared using commercially available phenolic resin
by utilizing sacrificial colloidal silica crystalline arrays as templates that were subsequently removed by HF etching after
pyrolysis in an argon atmosphere. SEM, TEM, and BET were employed to characterize the morphology and the surface area of the
porous carbon structures. The pore size (150–1000 nm) and BET surface area, which reflect pore volume (298.6 m2/g (1.32 cm3/g) ∼ 93.7 m2/g (0.12 cm3/g)), of the macroporous carbon structures produced were approximately proportional to the size (150–1000 nm) of the sacrificial
silica sphere templates used (annealing temp. 550°C). The achieved 550 nm porous carbon structures were examined to function
as potential catalyst carriers and were successfully impregnated with Ag or Pt-Ru on their inner walls after borohydride reduction
at room temperature. In addition, porous carbon patterns were fabricated using the ‘micromolding in capillary’ technique,
which has potential applications in the microreaction technology. 相似文献
16.
Preparation of three-dimensional ordered macroporous SiCN ceramic using sacrificing template method 总被引:4,自引:0,他引:4
Hao Wang Shuang-yang Zheng Xiao-dong Li Dong-pyo Kim 《Microporous and mesoporous materials》2005,80(1-3):357-362
Three-dimensional (3D) long range well ordered macroporous SiCN ceramics were prepared by infiltrating sacrificial colloidal silica templates with the low molecular weight preceramic polymer, polysilazane. This was followed by a thermal curing step, pyrolysis at 1250 °C in a N2 atmosphere, and finally the removal of the templates by etching with dilute HF. The produced macroporous SiCN ceramics showed high BET surface areas (pore volume) in the range 455 m2/g (0.31 cm3/g)–250 m2/g (0.16 cm3/g) with the pore sizes of 98–578 nm, which could be tailored by controlling the sizes of the sacrificial silica spheres in the range 112–650 nm. The sphere-inversed macropores were interconnected by 50 ± 30 nm windows and 3–5 nm mesopores embedded in the porous SiCN ceramic frameworks, which resulted in a trimodal pore size distribution. The surface of the achieved porous SiCN ceramic was then modified by Pt–Ru nanoparticle depositing under mild chemical conditions. 相似文献
17.
基于糖尿病性视网膜病变中最早出现的微小动脉瘤病症进行了研究,提出一种有效的微小动脉瘤检测算法。首先在传统模板匹配算法的基础上提出了一种动态多参数模板匹配算法,并且使用相对误差和与相关系数来共同制约匹配度,从而实现了更为精确的匹配提取;其次提出了基于分布特性的计分策略和自适应加权的汇总策略,避免了单纯采用各个特征量作为独立约束指标进行筛选时忽视各个特征量的约束力大小的弊端。实验结果表明,该检测算法能够有效地提高微小动脉瘤的检测真阳性率。 相似文献
18.
Virote Boonamnuayvitaya Chadapa Tayamanon Wiwut Tanthapanichakoon 《Chemical engineering science》2006,61(5):1686-1691
Mesoporous silica materials were synthesized by sol-gel method using tetraethoxysilane (TEOS) as precursors and surfactants i.e., cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyoxyethylene cetyl ether (Brij 56) as templates. Surfactant templates were completely removed by calcination to form mesoporous structure. The effects of type and amount of surfactants on the characteristics of samples were studied. The textural characteristics such as surface area, pore volume, pore size, and pore size distribution were determined by nitrogen sorption isotherms. Fourier transform infrared (FTIR) spectroscopy was employed to qualitatively identify the chemical functionality and to confirm the removal of surfactant template. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to directly observe surface morphology and mesoporous structure, respectively. The adsorption capacity of the synthesized adsorbent for toluene vapor was examined. We found that the pore volume and pore size of mesoporous materials affected the adsorption capacity. The sample prepared with high content of CTAB under basic condition (pH ∼7) yielded large pore volumes and pore sizes and subsequently possessed the high adsorption capacity for toluene vapor. 相似文献
19.
Polystyrene (PS) blocks in poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymers were partially sulfonated and the acid groups converted to Na+SO3− groups to create ionomers. Then, dimethylacetamide was used to selectively swell the ionic PS domains and the swollen films were exposed to sol-gel reactive tetraethylorthosilicate solutions. (EtO)4−xSi(OH)x monomers then permeated films so that sol-gel reactions occurred within/around the ionic PS domains. Environmental scanning electron microscopy/energy dispersive X-ray spectroscopy investigations showed that silicate structures can be incorporated within the interior of the ionomer films. Differential scanning calorimetry studies indicated that there is no variance in the PIB block Tg with respect to ionomer formation, or with respect to silicate loading of the ionomer at low levels, which suggests that the silicate component does not reside in the PIB phase. 23Na solid state NMR spectroscopy detected isolated Na+SO3− groups as well as aggregated SO3−Na+ ion pairs for ‘as cast’ and ‘dry’ non-silicate containing ionomer samples. In a hydrated sample, almost all Na+ ions were solvent-separated. AFM analysis showed that phase separation exists, but that the degree of order is significantly less than that for hybrids based on the corresponding benzyltrimethylammonium ionomer. This frustrated morphology was also seen in the results of small angle X-ray scattering experiments. Given the scale of organic/inorganic heterogeneity, these hybrids are properly classified as nanocomposites. 相似文献
20.
针对传统Excel表中散乱而不规范的业务数据,本文采用模板技术,提出了一种散乱Excel数据规范化处理新方法。并以某公司的数据为例进行实验分析,实验结果表明,该方法能够将分散的Excel表格中的信息进行提取,将源表中的数据进行规范化处理并写入标准模板,而且在对Excel表格信息提取并导入标准模板时,无需中间文件转换。该方法具有自动生成表格、自动填写表格的功能,并在实际应用中取得了良好的效果。该研究使用户查看与导出数据更加方便快捷。 相似文献