全文获取类型
收费全文 | 32677篇 |
免费 | 4617篇 |
国内免费 | 2767篇 |
专业分类
电工技术 | 2088篇 |
综合类 | 2473篇 |
化学工业 | 10972篇 |
金属工艺 | 1707篇 |
机械仪表 | 1434篇 |
建筑科学 | 1014篇 |
矿业工程 | 932篇 |
能源动力 | 1499篇 |
轻工业 | 1178篇 |
水利工程 | 601篇 |
石油天然气 | 3935篇 |
武器工业 | 402篇 |
无线电 | 2080篇 |
一般工业技术 | 3721篇 |
冶金工业 | 1235篇 |
原子能技术 | 518篇 |
自动化技术 | 4272篇 |
出版年
2024年 | 156篇 |
2023年 | 627篇 |
2022年 | 1015篇 |
2021年 | 1203篇 |
2020年 | 1411篇 |
2019年 | 1281篇 |
2018年 | 1198篇 |
2017年 | 1416篇 |
2016年 | 1554篇 |
2015年 | 1604篇 |
2014年 | 2024篇 |
2013年 | 2307篇 |
2012年 | 2574篇 |
2011年 | 2639篇 |
2010年 | 2037篇 |
2009年 | 2073篇 |
2008年 | 1879篇 |
2007年 | 2055篇 |
2006年 | 1792篇 |
2005年 | 1465篇 |
2004年 | 1275篇 |
2003年 | 1123篇 |
2002年 | 880篇 |
2001年 | 844篇 |
2000年 | 713篇 |
1999年 | 617篇 |
1998年 | 494篇 |
1997年 | 375篇 |
1996年 | 320篇 |
1995年 | 229篇 |
1994年 | 163篇 |
1993年 | 167篇 |
1992年 | 145篇 |
1991年 | 68篇 |
1990年 | 74篇 |
1989年 | 59篇 |
1988年 | 32篇 |
1987年 | 30篇 |
1986年 | 12篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1959年 | 9篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
利用催化加氢热解技术提取沉积 有机质中生物标志化合物 总被引:6,自引:2,他引:4
利用催化加氢热解技术提取了高演化沉积有机质中共价键结合的生物标志化合物,探讨了干酪根催化加氢热解反应机理,并考察了反应产物分布和影响反应的关键变量.实验表明,程序升温固定床催化加氢热解反应条件:温度上限为520℃,升温速率为5℃/min,氢压大于10MPa,氢气流量为5L/min,分散型催化剂为MoS2(Mo的质量分数为1%).实验结果表明,催化加氢热解对提取高产率、结构重排少的干酪根中共价键结合的生物标志化合物有独特作用,该方法可以应用于有机地球化学领域. 相似文献
82.
本文采用粒子追踪理论对水平管中粒子流动状态进行了数值模拟.文中提出了一种新的粒子碰撞模型,并忽略粒子的旋转和扬力,仅考虑气流阻力和重力对粒子的影响,在输送量为9.13×10~3kg/s,混合比约0.3的条件下,通过数值计算得知:由于粒子间的碰撞,使得异径粒子的速度趋向平均化;粒子间的碰撞是粒子悬浮的原因之一;粒子的浓度沿管轴向是随时间而发生变化的. 相似文献
83.
84.
A general variance predictor for Cavalieri slices 总被引:1,自引:0,他引:1
L. M. CRUZ-ORIVE 《Journal of microscopy》2006,222(3):158-165
A general variance predictor is presented for a Cavalieri design with slices of an arbitrary thickness t ≥ 0. So far, prediction formulae have been available either for measurement functions with smoothness constant q = 0, 1, … , and t ≥ 0, or for fractional q ∈ [0, 1] with t = 0. Because the possibility of using a fractional q adds flexibility to the variance prediction, we have extended the latter for any q ∈ [0, 1] and t ≥ 0. Empirical checks with previously published human brain data suggest an improved performance of the new prediction formula with respect to the hitherto available ones. 相似文献
85.
Makoto Kohga 《含能材料》2006,14(6):471-474
1 IntroductionThe ammonium perchlorate ( AP)-based compositepropellant is currently the most widely used one becausethis propellant has good burning characteristics and me-chanical properties. One of the few serious drawbacks ofthe AP-based propellant is that its products of combus-tion, which include HCl, chlorine, and chlorine oxides,cause atmospheric pollution. Increasing concern for aclean atmosphere in recent years has resulted in a com-pelling need for developing a chlorine-free,enviro… 相似文献
86.
87.
大庆蜡油在酸性催化剂上反应机理的研究 总被引:11,自引:5,他引:6
以大庆蜡油为原料,采用两种不同类型的催化剂,在流化床反应器实验装鬣上进行催化裂化反应。结果表明,大庆蜡油在酸性催化剂上反应所产生的干气组成与高烯烃催化裂化汽油相同,干气的产生主要是单分子裂化反应所造成的。从干气产率、组成以及液化气组成可以看出,大庆蜡油在不同类型的催化剂上明显地表现出裂化反应类型的差异。 相似文献
88.
If a low weight percentage of crude fine fillers can improve properties of polymer materials directly without complicated chemical treatment process involved, it will be significant for many industrial applications. Our previous study indicated that a kind of Cancun natural sand could be an effective filler material for polymer composites. In this current work, the epoxy composites reinforced by this kind of natural sand particles were prepared and thermal and mechanical properties of the composites containing up to 5 wt % of the sand particles were characterized. Results showed that the highest flexural strength appears in the epoxy composite containing 1 wt % sand particles. A damage model was used to interpret the flexural properties, which showed an acceptable agreement with the experimental results. The glass transition temperature, high temperature storage modulus, and dimensional stability of the sand/epoxy composites monotonically increased with the addition of the sand particles. The sand particle/epoxy composites also displayed a noticeable enhancement in thermal conductivity. Theoretical analysis showed that in addition to conduction, other heat transport mechanisms played roles in the improved heat transmission through the composites. As a natural porous micron-scale material, Cancun sand has the potential for applications in cost-effective composites with enhanced mechanical and thermal properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
89.
Hsu‐Wei Fang Hsien‐Chieh Wang Teh‐Hua Tsai Wei‐Bor Tsai Shao‐Yi Hou Hsuan‐Liang Liu Wun‐Hsing Lee Yung‐Chang Lu Chun‐Hsiung Huang 《应用聚合物科学杂志》2008,108(4):2428-2437
Wear of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and wear‐particle‐induced osteolysis and bone resorption are the major factors causing the failure of total joint replacements. It is feasible to improve the lubrication and reduce the wear of artificial joints. We need further understanding of the lubrication mechanism of the synovial fluid. The objective of this study is to evaluate the lubricating ability of three major components in the synovial fluid: albumin, globulin, and phospholipids. An accelerated wear testing procedure in which UHMWPE is rubbed against a microfabricated surface with controlled asperities has been developed to evaluate the lubrication behavior. An analysis of the wear particle dimensions and wear amount of the tests has provided insights for comparing their lubrication performance. It is concluded that the presence of biomolecules at the articulating interface may reduce friction. A higher concentration of a biological lubricant leads to a decrease in the wear particle width. In addition, in combination with the wear results and mechanical analysis, the roles of individual biomolecules contributing to friction and wear at the articulating interface are discussed. These results can help us to identify the role of the biomolecules in the boundary lubrication of artificial joints, and further development of lubricating additives for artificial joints may be feasible. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
90.