全文获取类型
收费全文 | 69338篇 |
免费 | 5347篇 |
国内免费 | 2760篇 |
专业分类
电工技术 | 3429篇 |
技术理论 | 10篇 |
综合类 | 4075篇 |
化学工业 | 12065篇 |
金属工艺 | 3765篇 |
机械仪表 | 4328篇 |
建筑科学 | 5919篇 |
矿业工程 | 2006篇 |
能源动力 | 2061篇 |
轻工业 | 4229篇 |
水利工程 | 1098篇 |
石油天然气 | 4330篇 |
武器工业 | 535篇 |
无线电 | 8177篇 |
一般工业技术 | 8889篇 |
冶金工业 | 3482篇 |
原子能技术 | 783篇 |
自动化技术 | 8264篇 |
出版年
2024年 | 186篇 |
2023年 | 1066篇 |
2022年 | 1697篇 |
2021年 | 2473篇 |
2020年 | 1970篇 |
2019年 | 1735篇 |
2018年 | 1895篇 |
2017年 | 2185篇 |
2016年 | 1970篇 |
2015年 | 2625篇 |
2014年 | 3251篇 |
2013年 | 3892篇 |
2012年 | 4292篇 |
2011年 | 4536篇 |
2010年 | 3953篇 |
2009年 | 3731篇 |
2008年 | 3662篇 |
2007年 | 3648篇 |
2006年 | 3851篇 |
2005年 | 3331篇 |
2004年 | 2301篇 |
2003年 | 2002篇 |
2002年 | 1930篇 |
2001年 | 1755篇 |
2000年 | 1759篇 |
1999年 | 2013篇 |
1998年 | 1808篇 |
1997年 | 1477篇 |
1996年 | 1407篇 |
1995年 | 1078篇 |
1994年 | 1023篇 |
1993年 | 710篇 |
1992年 | 543篇 |
1991年 | 432篇 |
1990年 | 322篇 |
1989年 | 259篇 |
1988年 | 230篇 |
1987年 | 135篇 |
1986年 | 97篇 |
1985年 | 70篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 39篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
以不同软化点的乙烯裂解焦油调制的各向同性沥青为原料。通过热失重和差热分析,得到不同沥青的DTA和TG曲线,并通过计算机拟合逼近处理,求出沥青样品的氧化活化能和反应级数等数据。不同软化点调制的沥青,其氧化级数均为一级反应,而软化点与氧化反应活化能间没有明显规律性关系,但升温速率对氧化反应的影响有明显规律。说明通过热分析可以预测不同沥青的预氧化碳化处理性能。 相似文献
952.
分析了国外石油石化公司资产管理类型,介绍了国外国有石油石化公司的资产经营管理体制,并以巴西石油公司、意大利埃尼集团、沙特阿拉伯国家石油公司和法国道达尔菲纳埃尔夫公司为例介绍了国外石油石化公司资产经营管理模式。 相似文献
953.
Zhu Zhan-Yang; ali Andrej; Blundell Tom L. 《Protein engineering, design & selection : PEDS》1992,5(1):43-51
We have developed a variable gap penalty function for use inthe comparison program COMPARER which aligns protein sequenceson the basis of their 3-D structures. For deletions and insertions,components are a function of structural features of individualamino acid residues (e.g. secondary structure and accessibility).We have also obtained relative weights for different featuresused in the comparison by examining the equivalent residuesin weight matrices and in alignments for pairs of 3-D structureswhere the equivalences are relatively unambiguous. We have usedthe new parameters and the varible gap penalty function in COMPARERto align protein structures in the Brookhaven Data Bank. Thevariable gap penalty function is useful especially in avoidinggaps in secondary structure elements and the new feature weightsgive improved alignments. The alignments for both azurins andplastocyanins and N- and C-terminal lobes for aspartic proteinasesare discussed 相似文献
954.
955.
956.
957.
Hydrolysis of olive oil, soybean oil, mink fat, lard, palm oil, coconut oil, and a hydrogenated, hardened oil with lipase
from anAspergillus sp. has been studied. The lipase had high specific activity (60,000 U/g) and did not show any positional specificity. The
lipase proved to be a more effective catalyst than Lipolase fromA. oryzae, with an optimal activity at 37°C and pH 6.5–7.0. It was activated by Ca2+ but inactivated by organic solvents such as isopropanol and propanone. All substrates examined could be hydrolyzed to corresponding
fatty acids with this enzyme at concentrations of 5–30 U/meq with yields of 90–99% in 2–24 h. The degree of hydrolysis was
almost logarithmically linear with reaction time and occurred in two stages. The lipase was stable and could be repeatedly
recycled for hydrolysis. 相似文献
958.
本文用沉积-沉淀法制备了新型纳米载体低碳醇合成催化剂,并与共沉淀法所制备的催化剂进行了对比,结果表明,纳米载体催化剂活性高、耐热性能好、醇收率高纳米载体对纳米载体催化剂活性大小的影响顺序为:纳米Al2O3>纳米ZnO-ZnAl2O4>纳米MgAl2O4>纳米MgO.工艺参数对反应性能的影响结果表明,反应温度低,甲醇选择性高;但温度太高(>320℃)CO2。选择性升高,且整个反应为动力学控制;压力升高可提高活性和C1-C2OH选择性,但C4OH选择性下降;结合空速对产物分布的影响,反应可能按Smith和Anderson的缩聚机理进行. 相似文献
959.
960.
Shape‐memory polyurethane/multiwalled carbon nanotube (SMP–MWNT) composites with various multiwalled carbon nanotube (MWNT) contents were synthesized, and the corresponding SMP–MWNT fibers were prepared by melt spinning. The influence of the MWNT content on the spinnability, fracture morphology, thermal and mechanical properties, and shape‐memory behavior of the shape‐memory polymer was studied. The spinning ability of SMP–MWNTs decreased significantly with increasing MWNT content. When the MWNT content reached 8.0 wt %, the fibers could not be produced because of the poor rheological properties of the composites. The melt‐blending, extrusion, and melt‐spinning processes for the shape‐memory fiber (SMF), particularly at low MWNT contents, caused the nanotubes to distribute homogeneously and preferentially align along the drawing direction of the SMF. The crystallization in the SMF was promoted at low MWNT contents because it acted as a nucleation agent. At high MWNT contents, however, the crystallization was hindered because the movement of the polyurethane chains was restricted. The homogeneously distributed and aligned MWNTs preserved the SMF with high tenacity and initial modulus. The recovery ratio and recovery force were also improved because the MWNTs helped to store the internal elastic energy during stretching and fixing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献