全文获取类型
收费全文 | 47275篇 |
免费 | 4503篇 |
国内免费 | 2172篇 |
专业分类
电工技术 | 2898篇 |
技术理论 | 2篇 |
综合类 | 2703篇 |
化学工业 | 8150篇 |
金属工艺 | 2863篇 |
机械仪表 | 3155篇 |
建筑科学 | 3556篇 |
矿业工程 | 1377篇 |
能源动力 | 1380篇 |
轻工业 | 3018篇 |
水利工程 | 745篇 |
石油天然气 | 2665篇 |
武器工业 | 380篇 |
无线电 | 5717篇 |
一般工业技术 | 6299篇 |
冶金工业 | 2551篇 |
原子能技术 | 612篇 |
自动化技术 | 5879篇 |
出版年
2024年 | 182篇 |
2023年 | 900篇 |
2022年 | 1413篇 |
2021年 | 2349篇 |
2020年 | 1710篇 |
2019年 | 1547篇 |
2018年 | 1637篇 |
2017年 | 1675篇 |
2016年 | 1551篇 |
2015年 | 2059篇 |
2014年 | 2445篇 |
2013年 | 2963篇 |
2012年 | 3054篇 |
2011年 | 3475篇 |
2010年 | 2739篇 |
2009年 | 2665篇 |
2008年 | 2669篇 |
2007年 | 2379篇 |
2006年 | 2495篇 |
2005年 | 1987篇 |
2004年 | 1459篇 |
2003年 | 1298篇 |
2002年 | 1197篇 |
2001年 | 1057篇 |
2000年 | 1032篇 |
1999年 | 1078篇 |
1998年 | 879篇 |
1997年 | 771篇 |
1996年 | 663篇 |
1995年 | 545篇 |
1994年 | 433篇 |
1993年 | 292篇 |
1992年 | 246篇 |
1991年 | 209篇 |
1990年 | 179篇 |
1989年 | 158篇 |
1988年 | 101篇 |
1987年 | 86篇 |
1986年 | 56篇 |
1985年 | 50篇 |
1984年 | 34篇 |
1983年 | 38篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 30篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
51.
The molecular design of short peptides to achieve a tailor-made functional architecture has attracted attention during the past decade but remains challenging as a result of insufficient understanding of the relationship between peptide sequence and assembled supramolecular structures. We report a hybrid-resolution model to computationally explore the sequence–structure relationship of self-assembly for tripeptides containing only phenylalanine and isoleucine. We found that all these tripeptides have a tendency to assemble into nanofibers composed of laterally associated filaments. Molecular arrangements within the assemblies are diverse and vary depending on the sequences. This structural diversity originates from (1) distinct conformations of peptide building blocks that lead to different surface geometries of the filaments and (2) unique sidechain arrangements at the filament interfaces for each sequence. Many conformations are available for tripeptides in solution, but only an extended β-strand and another resembling a right-handed turn are observed in assemblies. It was found that the sequence dependence of these conformations and the packing of resulting filaments are determined by multiple competing noncovalent forces, with hydrophobic interactions involving Phe being particularly important. The sequence pattern for each type of assembly conformation and packing has been identified. These results highlight the importance of the interplay between conformation, molecular packing, and sequences for determining detailed nanostructures of peptides and provide a detailed insight to support a more precise design of peptide-based nanomaterials. 相似文献
52.
Wenyun Yang Qiwei Hu Guanyi Qiao Liang Zha Shunquan Liu Jingzhi Han Honglin Du Yan Zhang Yingchang Yang Changsheng Wang 《中国稀土学报(英文版)》2019,37(10):1102-1107
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites. 相似文献
53.
Mohammad Reza Gaeeni Morteza Sasani Ghamsari Abbas Majd Abadi Mohammad Hossein Majles Ara Wooje Han Hyung‐Ho Park 《Journal of the American Ceramic Society》2015,98(6):1818-1822
A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before. 相似文献
54.
55.
介绍了如何配置与优化水电厂的自动化元件,其配置选型应以可靠实用、结构简单、便于维护为原则,同时还应结合电厂的各种介质特点、设备运行方式、控制方式等因素综合考虑. 相似文献
56.
57.
Flotation is a water treatment alternative to sedimentation, and uses small bubbles to remove low-density particles from potable water and wastewater. The effect of zeta potential, bubble size and particle size on removal efficiency of the electro-flotation process was investigated because previous model-simulations indicated that these attributes are critical for high collision efficiency between micro-bubbles and particles. Solutions containing Al3+ as the metal ion were subjected to various conditions. The zeta potentials of bubbles and particles were similar under identical conditions, and their charges were influenced by metal ion concentration and pH. Maximum removal efficiency was 98 and 12% in the presence and absence of flocculation, respectively. Removal efficiency was higher when particle size was similar to bubble size. These results agree with modelling simulations and indicate that collision efficiency is greater when the zeta potential of one is negative and that of the other is positive and when their sizes are similar. 相似文献
58.
59.
汽油烃类族组成测试方法对比 总被引:1,自引:0,他引:1
介绍了使用荧光指示剂吸附色谱法、多维气相色谱法的测定影响因素和近红外光谱快速法的分析特点以及三种方法在汽油族组成测定中的应用,并就三种方法对同一试样的测定结果进行了对比,找出各种测定方法容易产生误差的原因及分析对策。 相似文献
60.
以马来酸酐和2-丁基辛醇为原料,经酯化得到相应的双酯,以乙醇作混相促进剂,使双酯与亚硫酸氢钠进行磺化反应,合成了磺基琥珀酸双2-丁基辛酯钠盐。采用正交试验对酯化反应条件进行了优化。合成产物的临界胶束浓度(cmc)值为3.58×10-6mol/L,表面张力(γcmc)为27.568mN/m。 相似文献