全文获取类型
收费全文 | 209137篇 |
免费 | 24442篇 |
国内免费 | 24576篇 |
专业分类
电工技术 | 19181篇 |
技术理论 | 8篇 |
综合类 | 14089篇 |
化学工业 | 42232篇 |
金属工艺 | 8599篇 |
机械仪表 | 13729篇 |
建筑科学 | 9735篇 |
矿业工程 | 2427篇 |
能源动力 | 6885篇 |
轻工业 | 14875篇 |
水利工程 | 2672篇 |
石油天然气 | 4568篇 |
武器工业 | 2038篇 |
无线电 | 31782篇 |
一般工业技术 | 22828篇 |
冶金工业 | 4613篇 |
原子能技术 | 3408篇 |
自动化技术 | 54486篇 |
出版年
2024年 | 1079篇 |
2023年 | 3710篇 |
2022年 | 6606篇 |
2021年 | 7679篇 |
2020年 | 7289篇 |
2019年 | 6645篇 |
2018年 | 6236篇 |
2017年 | 8455篇 |
2016年 | 9164篇 |
2015年 | 10307篇 |
2014年 | 10419篇 |
2013年 | 13667篇 |
2012年 | 15295篇 |
2011年 | 17741篇 |
2010年 | 12559篇 |
2009年 | 12416篇 |
2008年 | 13721篇 |
2007年 | 15207篇 |
2006年 | 14451篇 |
2005年 | 12379篇 |
2004年 | 10527篇 |
2003年 | 8469篇 |
2002年 | 6431篇 |
2001年 | 4873篇 |
2000年 | 4065篇 |
1999年 | 3455篇 |
1998年 | 2897篇 |
1997年 | 2338篇 |
1996年 | 1841篇 |
1995年 | 1558篇 |
1994年 | 1353篇 |
1993年 | 989篇 |
1992年 | 819篇 |
1991年 | 653篇 |
1990年 | 546篇 |
1989年 | 413篇 |
1988年 | 310篇 |
1987年 | 187篇 |
1986年 | 188篇 |
1985年 | 249篇 |
1984年 | 208篇 |
1983年 | 156篇 |
1982年 | 213篇 |
1981年 | 102篇 |
1980年 | 103篇 |
1979年 | 27篇 |
1978年 | 20篇 |
1977年 | 24篇 |
1976年 | 17篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The effect of shear‐controlled orientation injection molding (SCORIM) was investigated for polybutene‐1/polypropylene blends. This article reports on the methods and processing conditions used for blending and injection molding. The properties of SCORIM moldings are compared with those of conventional moldings. SCORIM is based on the application of specific macroscopic shears to a solidifying melt. The multiple shear action enhances molecular alignment. The moldings were investigated with mechanical tests, differential scanning calorimetry studies, and polarized light microscopy. The application of SCORIM improved Young's modulus and the ultimate tensile strength. The gain in stiffness was greater for higher polybutene‐1 content blends. A drastic decrease in the strain at break and toughness was observed in SCORIM moldings. The enhanced molecular orientation of SCORIM moldings resulted in a featureless appearance of the morphology. Interfacial features due to segregation were visible in the micrographs of SCORIM moldings. Both conventional and SCORIM moldings exhibited form I′ in polybutene‐1. This article explains the relationship between the mechanical properties and micromorphologies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 806–813, 2003 相似文献
992.
针对中文组合范畴语法(CCG)分析困难的特点,研究如何将两种彼此相互独立的技术共同应用在中文CCG句法分析上。首先使用预标注算法,使用对数线性模型通过去除那些概率较低的词汇范畴来对句子的潜在分析空间进行剪枝。然后应用启发式搜索算法进一步加速分析过程。最后从时间效率和分析精度两个维度对所使用的方法进行验证。实验表明,基于启发式搜索与预标注的句法分析算法可以显著地提高分析效率与分析精度。 相似文献
993.
Ming‐Jen Chang Jen‐Yun Tsai Chia‐Wei Chang Hwai‐Ming Chang George J. Jiang 《应用聚合物科学杂志》2007,103(6):3680-3687
Well‐defined polymer‐Mg(OH)2 nanocomposites were prepared by atom transfer radical polymerization (ATRP). The ATRP initiators were covalently attached to the Mg(OH)2 by esterification of 2‐chloropropionyl chloride with hydroxyl group. The amount of polymer grafted from Mg(OH)2 can be controlled using a different catalyst system and adding a small amount of polar solvent. The well‐defined diblock copolymer, consisting of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) were synthesized. The products were characterized by nuclear magnetic resonance, Fourier transform infrared, differential scanning calorimetry, and thermal gravimetric analysis. The morphologies of PS/PMMA and PS/PMMA/Mg(OH)2‐g‐PS‐b‐PMMA blends are compared by using a scanning electron microscope. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3680–3687, 2007 相似文献
994.
4-甲氧基苯乙腈的又一种合成法 总被引:1,自引:0,他引:1
以4-羟基苯乙酰胺为原料,经甲基化和脱水两步反应合成了4-甲氧基苯乙腈,总收率76.5%。 相似文献
995.
We review our X-ray absorption spectroscopy studies of adsorbate geometries on the O-terminated (000
) and Zn-terminated (0001) basel faces, as well as the non-polar (10
0) prism face of ZnO. Studies employing near-edge X-ray absorption fine-structure (NEXAFS) and surface X-ray absorption fine-structure (SEXAFS) are included. 相似文献
996.
The effects of an organic phosphorus nucleating agent on the crystallization behavior and mechanical properties of poly(propylene) were investigated. As the concentration of nucleating agent increased from 0 to 0.8%, the tensile and flexural strengths of the nucleated poly(propylene) resin increased by 15%, the flexural modulus increased by 35%, the crystallization peak temperature increased by 10°C, and the nucleation density (calculated with the nonlinear Voltrra integral equation) increased by 106 times. Mechanical properties increased with nucleation density. Linear equations between the mechanical properties and the logarithmic nucleation density were revealed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 297–301, 2003 相似文献
997.
998.
TiB2的SHS合成过程理论分析 总被引:10,自引:4,他引:10
在TiB2陶瓷材料的自蔓延高温合成(简称SHS)过程中,通过改变原料的起始温度,稀释剂的含量和原始颗粒的尺寸等都可以调节合成过程的绝热温度,产物中熔融相的含量,以及燃烧波蔓延的速度,人而最终影响合成产物的结构和性质。本文对上述各种关系进行了理论计算和分析,其结果对实际合成与制备过程将有着重要的指导作用。 相似文献
999.
在并行测试的研究中对于任务的测试次序一直是个研究重点及难题。用时间Petri网建立关于并行测试系统的模型,并首次用元胞遗传算法(CAGA)对模型中的变迁序列进行搜索,快速得到最好的测试序列。通过仿真结果表明,该算法展示了很好的收敛效果,并且与已有的研究成果相比更具优势。 相似文献
1000.
Removal of chromium (VI) from dilute aqueous solutions by activated carbon developed from Terminalia arjuna nuts activated with zinc chloride 总被引:1,自引:0,他引:1
Different structured activated carbons were prepared from Terminalia arjuna nuts, an agricultural waste, by chemical activation with zinc chloride for the adsorption of Cr(VI) from dilute aqueous solutions. The most important parameter in chemical activation was found to be the chemical ratio (activating agent/precursor, g/g). Carbonization temperature and time are the other two important variables, which had significant effect on the pore structure of carbon. A high surface area of was obtained at a chemical ratio of 300%, carbonization time and temperature of 1 h and 500 °C, respectively. The activated carbon developed shows substantial capability to adsorb Cr(VI) from dilute aqueous solutions. The parameters studied include pH, adsorbent dosage, contact time, and initial concentrations. The kinetic data were best fitted to the Lagergren pseudo-first-order model. The isotherm equilibrium data were well fitted by the Langmuir and Freundlich models. The maximum removal of chromium was obtained at pH 1.0 (about 99% for adsorbent dose of 2 g/l and 10 mg/l initial concentration). 相似文献