全文获取类型
收费全文 | 28584篇 |
免费 | 2715篇 |
国内免费 | 1490篇 |
专业分类
电工技术 | 312篇 |
技术理论 | 1篇 |
综合类 | 1686篇 |
化学工业 | 14241篇 |
金属工艺 | 1375篇 |
机械仪表 | 773篇 |
建筑科学 | 1724篇 |
矿业工程 | 304篇 |
能源动力 | 363篇 |
轻工业 | 2519篇 |
水利工程 | 60篇 |
石油天然气 | 1535篇 |
武器工业 | 198篇 |
无线电 | 1877篇 |
一般工业技术 | 4294篇 |
冶金工业 | 518篇 |
原子能技术 | 299篇 |
自动化技术 | 710篇 |
出版年
2024年 | 174篇 |
2023年 | 622篇 |
2022年 | 1267篇 |
2021年 | 1386篇 |
2020年 | 988篇 |
2019年 | 953篇 |
2018年 | 895篇 |
2017年 | 1030篇 |
2016年 | 988篇 |
2015年 | 1045篇 |
2014年 | 1436篇 |
2013年 | 1722篇 |
2012年 | 1845篇 |
2011年 | 1855篇 |
2010年 | 1369篇 |
2009年 | 1494篇 |
2008年 | 1272篇 |
2007年 | 1588篇 |
2006年 | 1530篇 |
2005年 | 1329篇 |
2004年 | 1062篇 |
2003年 | 903篇 |
2002年 | 807篇 |
2001年 | 779篇 |
2000年 | 670篇 |
1999年 | 572篇 |
1998年 | 478篇 |
1997年 | 422篇 |
1996年 | 359篇 |
1995年 | 299篇 |
1994年 | 252篇 |
1993年 | 215篇 |
1992年 | 245篇 |
1991年 | 224篇 |
1990年 | 190篇 |
1989年 | 140篇 |
1988年 | 51篇 |
1987年 | 47篇 |
1986年 | 38篇 |
1985年 | 58篇 |
1984年 | 55篇 |
1983年 | 36篇 |
1982年 | 52篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
《Journal of the European Ceramic Society》2020,40(1):103-107
Tunable and ultrabroadband mid-infrared (MIR) emissions in the range of 2.5–4.5 μm are firstly reported from Co2+-doped nano-chalcogenide (ChG) glass composites. The composites embedded with a variety of binary (ZnS, CdS, ZnSe) and ternary (ZnCdS, ZnSSe) ChG nanocrystals (NCs) can be readily obtained by a simple one-step thermal annealing method. They are highly transparent in the near- and mid-infrared wavelength region. Low-cost and commercially available Er3+-doped fiber lasers can be used as the excitation source. By crystal-field engineering of the embedded NCs through cation- or anion-substitution, the emission properties of Co2+ including its emission peak wavelength and bandwidth can be tailored in a broad spectral range. The phenomena can be accounted for by crystal-field theory. Such nano-ChG composites, perfectly filling the 3–4 μm spectral gap between the oscillations of Cr2+ and Fe2+ doped IIVI ChG crystals, may find important MIR photonic applications (e.g., gas sensing), or can be used directly as an efficient pump source for Fe2+: IIVI crystals which are suffering from lack of pump sources. 相似文献
2.
聚α-烯烃是一种性能优良的润滑油基础油,其相对分子质量及分布直接影响宏观性能。本研究建立了一种用于表征1-癸烯齐聚物相对分子质量及分布的方法。采用带示差折光检测器的凝胶渗透色谱系统,综合考虑分离效果和测试可操作性,优化了流动相流速和凝胶色谱柱的组合方式。以四氢呋喃为流动相,流速为0.8 mL/min,色谱柱组合方式为Styragel HR 0.5,Styragel HR 1,PLGEL 3μm MIXED-E三柱串联,以聚苯乙烯作为标准样品,采用普适校正方法处理色谱流出曲线。此方法测得样品的质均相对分子质量与凝胶渗透色谱-光散射法所测定结果相比较,相对误差相对偏差在3%以内。 相似文献
3.
4.
石墨炉原子吸收光谱(GFAAS)法测定石英玻璃中硼的研究 总被引:2,自引:0,他引:2
试样经氢氟酸分解,通过加入化学改进剂和多次注射浓缩样品及低温、长时间灰化的方法,在硝酸介质中用石墨炉原子吸收光谱法(GFAAS)测定石英玻璃中硼的含量。该方法解决了GFAAS法分析石英玻璃中硼灵敏度低和准确度低的问题。 相似文献
5.
6.
通过密度测定和DSC热分析,观测了超高分子量聚乙烯的辐射效应。实验结果表明:在吸收剂量0—1.13MGy范围内,密度随吸收剂量的增加而增大,熔化热和熔点也有所增加,特别是在低剂量范围内增加十分明显。以上结果都说明,超高分子量聚乙烯在辐照过程中,结晶在完善或有新的结晶形成 相似文献
7.
把瞬态记录仪Biomation8l00与微型计算机IBM─pC/XT联接建成了一个高速数据采集系统,本文介绍了系统的硬件接口设计及软件设计。在超声分子束条件下,把它应用于环氧乙烷(C_2H_4O)的多光子电离与离解飞行时间(MPID─TOF)质谱的实验研究中,并给出了实验结果;本系统在微观基元化学反应动力学实验研究中广泛适用于对时间分辨微弱信号的探测。 相似文献
8.
D. Porter 《Advanced Performance Materials》1996,3(3-4):309-324
The use of molecular-level materials modelling techniques in the development of advanced performance polymers is discussed, with particular emphasis upon bridging the large difference in the scales of dimensions between atomic structure and fabricated parts. The advantages and disadvantages of bulk quantitative structure-property relations and atomistic modelling are assessed, and the method of group interaction modelling is suggested as a means of bridging the dimensional scales.After a brief introduction to the concept of group interaction modelling, examples of modelling the engineering properties of polymers are presented which are difficult to model quantitatively by any other means. The important phase transitions from the crystal and glassy states of matter to those of rubber- and liquidlike states are shown quantitatively to be due to the same isoenergetic condition. The viscoelastic properties of a polymer are critical for many applications and expressions are derived for the loss and storage components of the complex modulus, with reference to failure initiation conditions. The effect of crosslinking in thermosets upon the glass transition temperature and viscoelastic properties is outlined. Finally, the scaling of time from atomic vibrations to the years involved in creep and ageing effects are discussed. 相似文献
9.
A quantum chemical study of the binding of Li+ cation to polyalkyloxides has been carried out. The lithium cation interaction with three polyalkyloxides (polyethylene oxide (PEO), polytrimethylene oxide (PTMO), and polypropylene oxide (PPO)) has been investigated using ab initio molecular orbital theory at the HF/6-31G* level with molecular models for the polymers. Coordination by one to six oxygens was considered. In addition, higher level calculations were carried out using G3(MP2) theory for coordination of Li+ by one oxygen. For coordination of lithium by one oxygen, the binding energy ordering is PTMO>PPO>PEO, with PTMO having the largest lithium cation affinity. The same ordering is found for larger coordination numbers with the exception of coordination by six oxygens, where the ordering changes due to the steric interactions. 相似文献
10.
Banded textures produced in a thermotropic liquid crystal polymer by shearing between glass slides are examined by using both transmission electron and polarized light microscopy. The periodic variation in director orientation about the shear axis, as measured by light microscopy, is shown to be distinctly different from that indicated by electron diffraction. Measurements of birefringence and observation of Zernicke phase contrast indicate periodic variations in optical properties of the polymer, in step with the bands. Such effects are accounted for in terms of a synchronous rotation of the planar aromatic groups about the molecular chain axes. Evidence for an out-of-plane component of molecular orientation is also presented. 相似文献