全文获取类型
收费全文 | 86873篇 |
免费 | 19649篇 |
国内免费 | 3156篇 |
专业分类
电工技术 | 3859篇 |
技术理论 | 1篇 |
综合类 | 3932篇 |
化学工业 | 24912篇 |
金属工艺 | 3204篇 |
机械仪表 | 4024篇 |
建筑科学 | 5135篇 |
矿业工程 | 1313篇 |
能源动力 | 2038篇 |
轻工业 | 12543篇 |
水利工程 | 1409篇 |
石油天然气 | 2053篇 |
武器工业 | 464篇 |
无线电 | 12501篇 |
一般工业技术 | 16780篇 |
冶金工业 | 2542篇 |
原子能技术 | 623篇 |
自动化技术 | 12345篇 |
出版年
2024年 | 281篇 |
2023年 | 864篇 |
2022年 | 1662篇 |
2021年 | 2344篇 |
2020年 | 2983篇 |
2019年 | 4403篇 |
2018年 | 4551篇 |
2017年 | 4977篇 |
2016年 | 5352篇 |
2015年 | 6017篇 |
2014年 | 6497篇 |
2013年 | 8213篇 |
2012年 | 6495篇 |
2011年 | 6621篇 |
2010年 | 6427篇 |
2009年 | 6219篇 |
2008年 | 5667篇 |
2007年 | 5264篇 |
2006年 | 4761篇 |
2005年 | 3912篇 |
2004年 | 3173篇 |
2003年 | 2723篇 |
2002年 | 2617篇 |
2001年 | 2220篇 |
2000年 | 1920篇 |
1999年 | 1104篇 |
1998年 | 462篇 |
1997年 | 373篇 |
1996年 | 305篇 |
1995年 | 235篇 |
1994年 | 200篇 |
1993年 | 166篇 |
1992年 | 122篇 |
1991年 | 110篇 |
1990年 | 78篇 |
1989年 | 60篇 |
1988年 | 50篇 |
1987年 | 48篇 |
1986年 | 38篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
本文介绍了用一种再结晶技术制造高炖、超细Al_2O_3粉体的新方法。 将硫酸铝铵溶液(AA)滴入碳酸氢铵溶液(AHC),经过反应合成一种新的含铝化合物,碳酸氢铝铵(AACH),然后在高温下煅烧,生成超细Al_2O_3粉体。另外还采用了X射线,红外光谱,DTA,以及TEM等手段,研究了反应温度、浓度、PH值和老化条件等对生成物AACH和Al_2O_3的影响。 相似文献
992.
The equilibrium phase compositions of iron have been calculated for gas compositions that could be encountered during the Fischer–Tropsch synthesis. The gas compositions measured experimentally for CO conversion levels in the 30–90% range show that iron should be present as the carbide phase. However, experimental characterization of iron catalysts show that a significant fraction of the iron is present as Fe3O4 following synthesis for several days. A model that can account for the experimental catalyst phase composition and the gases present in the reactor would have a core of Fe3O4 and an outer layer of iron carbides. 相似文献
993.
UASB-接触氧化处理高浓度有机废水试验研究 总被引:7,自引:0,他引:7
本文主要通过UASB 接触氧化生化处理模型对某化工厂废水的试验研究,探索运用UASB法处理高浓度有机废水的可行性。同时还探讨了废水的CODcr及含盐量对UASB处理效率的影响,以及关键参数的选用。 相似文献
994.
一种灰色模糊油田区块水驱指标评价模型 总被引:1,自引:0,他引:1
针对油田开发中的不确定因素,结合油藏开发因素中的定性化指标,提出了一种基于油田开发水驱指标的模糊综合评价模型.通过灰色关联法定量筛选影响油田开发水驱因素的九项指标,运用层次分析法确定了各指标的权重,结合模糊数学中的判断矩阵实现了油田各区块的模糊综合评价.此方法不仅可以对所有区块进行总体评价,还能对各个具体区块进行精细的评价,为油田开发与管理提供了有效的指导.最后,通过实际例子验证了模型的有效性以及可行性. 相似文献
995.
996.
The effect of different organoclays and mixing methods on the cure kinetics and properties of epoxy nanocomposites based on Epon828 and Epicure3046 was studied. The two kinds of organoclay used in this study, both based on natural montmorillonite but differing in intercalant chemistry, were I.30E (Nanomer I.30E—treated with a long‐chain primary amine intercalant) and C.30B (Cloisite 30B—treated with a quaternary ammonium intercalant, less reactive with epoxy than the primary amine). The two mixing processes used to prepare the nanocomposites were (i) a room‐temperature process, in which the clay and epoxy are mixed at room temperature, and (ii) a high‐temperature process, in which the clay and epoxy are mixed at 120°C for 1 h by means of mechanical mixing. The nanocomposites were cured at room temperature and at high temperature. The quality of dispersion and intercalation/exfoliation were analyzed by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The heat evolution of the epoxy resin formulation and its nanocomposite systems was measured using differential scanning calorimetry at different heating rates of 2.5, 5, 10, 15, and 20°C min?1. The cure kinetics of these systems was modeled by means of different approaches. Kissinger and isoconversional models were used to calculate the kinetics parameters while the Avrami model was utilized to compare the cure behavior of the epoxy systems. The cure kinetics and mechanical properties were found to be influenced by the presence of nanoclay, by the type of intercalant, and by the mixing method. POLYM. ENG. SCI., 47:649–661, 2007. © 2007 Society of Plastics Engineers. 相似文献
997.
根据铅酸蓄电池在放电过程中内部电化学反应导致外部电特性变化的特点,提出一种基于支持向量机原理的电解液密度辨识模型。利用支持向量机理论非线性回归的特性,简化测量电解液密度的过程,在恶劣环境下检测动力电池的电解液密度更显其优越性。预测实验表明,采用改进的交叉验证预测模型具有泛化能力强、稳定性好的特点,并且在小样本的条件下能达到预期的辨识精度。 相似文献
998.
2,7‐Bis(4‐aminophenoxy) naphthalene (BAPN), a naphthalene‐containing diamine, was synthesized and polymerized with a 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) to obtain a polyimide (PI) via thermal imidization. To enhance the thermal and mechanical properties of the polymer, PI–Montmorillonite (MMT) nanocomposites were prepared from a DMAc solution of poly(amic acid) and a DMAc dispersion of MMT, which were organo‐modified with various amounts of n‐dodecylamine (DOA) or cetylpyridium chloride (CPC). FTIR, XRD, and TEM (transmission electron microscopy) were used to verify the incorporation of the modifying agents into the clay structure and the intercalation of the organoclay into the PI matrix. Results demonstrated that the introduction of a small amount of MMT (up to 5%) led to the improvement in thermal stability and mechanical properties of PI. The decomposition temperature of 5% weight loss (Td,5%) in N2 was increased by 46 and 36°C in comparison with pristine PI for the organoclay content of 5% with DOA and CPC, respectively. The nanocomposites were simultaneously strengthened and toughened. The dielectric constant, CTE, and water absorption were decreased. However, at higher organoclay contents (5–10%), these properties were reduced because the organoclay was poorly dispersed and resulted in aggregate formation. The effects of different organo‐modifiers on the properties of PI–MMT nanocomposite were also studied; the results showed that DOA was comparable with CPC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006 相似文献
999.
Steve Lien‐Chung Hsu Keng‐Chuan Chang Yuan‐Pin Huang Shih‐Jung Tsai 《应用聚合物科学杂志》2003,88(10):2388-2391
A poly(imide benzoxazole) was prepared directly from trimellitic anhydride chloride and 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane (BisAPAF) monomers in a two‐step method. In the first step, a poly(hydroxyamide amic acid) precursor was synthesized by the low‐temperature solution polymerization in an organic solvent. Subsequently, thermal cyclodehydration of the poly(hydroxyamide amic acid) precursor at 350°C produced the corresponding poly(imide benzoxazole). The inherent viscosity of the precursor polymer was 0.22 dL/g. The cyclized poly(imide benzoxazole) showed a glass transition temperature (Tg) at 329°C and a 5% weight loss temperature at 530°C in nitrogen and at 525°C in air. The poly(imide benzoxazole) is amorphous as evidenced by the wide‐angle X‐ray diffraction measurement. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance spectroscopy (1H NMR). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2388–2391, 2003 相似文献
1000.
比较是人们常用的评估不同事物优劣、异同的表达方式,利用机器识别比较句并进一步抽取比较要素是语言信息处理领域一项新颖又有实用价值的课题。该文依据比较句与比较要素之间是一种“你中有我,我中有你”的共生关系,将比较句识别与比较要素抽取两个任务合二为一完成;根据词意分类,构建由领域词典、情感词典、标记词典、普通词典构成的词典系统;根据汉语比较句句义分类,构建比较句识别与比较要素抽取规则库。以第四届中文倾向性评测(COAE2012)发布的测试语料为实验对象,该系统取得了较好的实验(评测)结果。 相似文献