全文获取类型
收费全文 | 26786篇 |
免费 | 2796篇 |
国内免费 | 1931篇 |
专业分类
电工技术 | 2025篇 |
综合类 | 2074篇 |
化学工业 | 3955篇 |
金属工艺 | 1761篇 |
机械仪表 | 1785篇 |
建筑科学 | 2133篇 |
矿业工程 | 800篇 |
能源动力 | 748篇 |
轻工业 | 2439篇 |
水利工程 | 595篇 |
石油天然气 | 1275篇 |
武器工业 | 341篇 |
无线电 | 3385篇 |
一般工业技术 | 2763篇 |
冶金工业 | 993篇 |
原子能技术 | 359篇 |
自动化技术 | 4082篇 |
出版年
2024年 | 151篇 |
2023年 | 508篇 |
2022年 | 1026篇 |
2021年 | 1383篇 |
2020年 | 1013篇 |
2019年 | 783篇 |
2018年 | 843篇 |
2017年 | 921篇 |
2016年 | 834篇 |
2015年 | 1242篇 |
2014年 | 1504篇 |
2013年 | 1653篇 |
2012年 | 2122篇 |
2011年 | 2172篇 |
2010年 | 2026篇 |
2009年 | 1894篇 |
2008年 | 1771篇 |
2007年 | 1753篇 |
2006年 | 1573篇 |
2005年 | 1284篇 |
2004年 | 904篇 |
2003年 | 677篇 |
2002年 | 648篇 |
2001年 | 544篇 |
2000年 | 529篇 |
1999年 | 429篇 |
1998年 | 241篇 |
1997年 | 256篇 |
1996年 | 187篇 |
1995年 | 151篇 |
1994年 | 123篇 |
1993年 | 81篇 |
1992年 | 67篇 |
1991年 | 41篇 |
1990年 | 45篇 |
1989年 | 42篇 |
1988年 | 23篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1959年 | 8篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
色谱纯甲醇的制备研究 总被引:3,自引:0,他引:3
随着液相色谱的广泛应用,作为反向液相色谱流动相的色谱纯甲醇的需求量与日俱增,产品供不应求。但色谱纯甲醇要求纯度很高,且在紫外波段(220~280nm)内需很高的透光率。这给色谱纯甲醇的制备增添了很大困难。因而,色谱纯甲醇价格较高,目前东北三省尚无生产厂家,主要依靠外省或国外进口。如何由工业级甲醇制备色谱纯甲醇是本研究的主要课题,实验原理是通过测定影响透气率的主要因素,再通过2.4-二硝基苯肼除去醛、酮,再用浓碱溶液中和羧酸、皂化酯类,再进行精馏,从而获得满意的结果。 相似文献
113.
Orthogonal frequency division multiplexing (OFDM) has been widely considered as a key technique for next generation mobile communication systems. Meanwhile, relaying technologies can improve users’ quality of service, increase network capacity and enlarge cellular coverage at a low cost. In this paper, we focus on subcarrier allocation and utilization in multi-hop OFDM access (OFDMA) wireless networks, and propose two efficient subcarrier allocation schemes aiming to increase network throughput and subcarrier utilization. The first scheme selects suitable links for data transmission from base stations to terminals at the beginning. Then, interference-free links are included into the same group for network resource reuse. For the purpose of global optimization, we propose a Tabu-based searching algorithm as the second subcarrier allocation scheme. Simulation results demonstrate that our proposed algorithms outperform other schemes in both network throughput and subcarrier utilization. 相似文献
114.
115.
高硅铸铝合金镀前浸锌液 总被引:3,自引:1,他引:3
针对高硅铸铝件在组成,组织与性能上的特点,研究了8种高硅铝合金镀前浸锌液。用扫描电镜(SEM)观察了8种不同的浸锌液配方浸锌的试片的表面浸锌膜的微观形貌,测定了浸锌后镀镍层与试片的结合力,优选了能获得良好结合力的最佳浸锌液配方。并研究了随浸锌时间的增加,锌晶核的析出与成长的过程,结果表明,当氢氧化钠140g/L,氧化锌14~20g/L、氯化镍1.5g/L时,试片镀镍后结合力良好。发现浸锌液能够溶解铝合金部分组织,并在铝表面造成孔洞,这种孔洞对镀层起着锚链作用,铝合金表面孔洞的均匀分散以及细小锌晶粒的高度弥散是得到良好结合力的前提。 相似文献
116.
Analysis of the polyethylene glycol glucosides and FA esters thereof by atmospheric-pressure ionization MS 总被引:1,自引:0,他引:1
Xin?Jin Jinzong?YangEmail author Bingtao?Tang Minggui?Zhu Ning?Yu Yi?Liu 《Journal of the American Oil Chemists' Society》2003,80(6):519-524
Polyethylene glycol (PEG) glucosides (PEGG) and the PEGG esters of lauric acid were analyzed by atmospheric-pressure ionization
MS (API-MS) with electrospray ionization. Straightforward mass characterization of the complex mixtures could be achieved
without prior chromatographic separation. The constituents were identified on the basis of quasi-molecular ions. Individual
components could be observed as protonated molecular ions [M+H]+ and/or as their NH4
+, Na+, or K+ adducts in positive ion mode. The mass spectrometric investigation showed that mixtures of PEGG consisted of monoglucoside,
diglucoside, polyglucoside, and free PEG. The esterification product is a mixture of two types of nonionic surfactants: PEG-laurates
and PEGG-laurates. The reasons for distortion of the quasi-molecular ion intensities and the stabilization of adduct ions
were discussed. The rapid and highly sensitive API-MS analysis technique proposed here is well suited for direct characterization
of complex mixtures and suitable for development as a routine analytical method. 相似文献
117.
接枝淀粉共聚物的合成与应用 总被引:2,自引:0,他引:2
介绍了接枝淀粉共聚物的合成方法及应用领域,回顾了我国近年来在该领域所取得的可喜进展。 相似文献
118.
P3软件是一套体现了现代化项目管理理念的项目管理工具,在建设管理上推广应用P3工程管理软件,可以提高各参建单位的工作效率、加快工程信息交流、数据共享和工程进度管理水平,在管理上尽快与国际接轨,本文就P3软件在电力基建工程中的应用做以简单介绍。 相似文献
119.
The curing behavior of synthesized phenol–urea–formaldehyde (PUF) resol resins with various formaldehyde/urea/phenol ratios was studied with differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The results indicated that the synthesis parameters, including the urea content, formaldehyde/phenol ratio, and pH value, had a combined effect on the curing behavior. The pH value played an important role in affecting the shape of the DSC curing curves, the activation energy, and the reaction rate constant. Depending on the pH value, one or two peaks could appear in the DSC curve. The activation energy was lower when pH was below 11. The reaction rate constant increased with an increase in the pH value at both low and high temperatures. The urea content and formaldehyde/phenol ratio had no significant influence on the activation energy and rate constant. DMA showed that both the gel point and tan δ peak temperature (Ttanδ) had the lowest values in the mid‐pH range for the PUF resins. A different trend was observed for the phenol–formaldehyde resin without the urea component. Instead, the gel point and Ttanδ decreased monotonically with an increase in the pH value. For the PUF resins, a high urea content or a low formaldehyde/phenol ratio resulted in a high gel point. The effect of the urea content on Ttanδ was bigger than that on the gel point because of the reversible reaction associated with the urea component. Too much formaldehyde could lead to more reversible reactions and a higher Ttanδ value. The effects of the synthesis conditions on the rigidity of the cured network were complex for the PUF resins. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1368–1375, 2005 相似文献
120.