全文获取类型
收费全文 | 15632篇 |
免费 | 1374篇 |
国内免费 | 827篇 |
专业分类
电工技术 | 680篇 |
技术理论 | 1篇 |
综合类 | 1904篇 |
化学工业 | 2087篇 |
金属工艺 | 1833篇 |
机械仪表 | 1235篇 |
建筑科学 | 2770篇 |
矿业工程 | 670篇 |
能源动力 | 337篇 |
轻工业 | 688篇 |
水利工程 | 655篇 |
石油天然气 | 598篇 |
武器工业 | 144篇 |
无线电 | 504篇 |
一般工业技术 | 2486篇 |
冶金工业 | 561篇 |
原子能技术 | 201篇 |
自动化技术 | 479篇 |
出版年
2024年 | 67篇 |
2023年 | 164篇 |
2022年 | 347篇 |
2021年 | 416篇 |
2020年 | 443篇 |
2019年 | 367篇 |
2018年 | 342篇 |
2017年 | 451篇 |
2016年 | 528篇 |
2015年 | 508篇 |
2014年 | 853篇 |
2013年 | 897篇 |
2012年 | 1015篇 |
2011年 | 1093篇 |
2010年 | 810篇 |
2009年 | 892篇 |
2008年 | 867篇 |
2007年 | 1052篇 |
2006年 | 972篇 |
2005年 | 833篇 |
2004年 | 689篇 |
2003年 | 672篇 |
2002年 | 590篇 |
2001年 | 464篇 |
2000年 | 447篇 |
1999年 | 370篇 |
1998年 | 283篇 |
1997年 | 245篇 |
1996年 | 232篇 |
1995年 | 189篇 |
1994年 | 154篇 |
1993年 | 125篇 |
1992年 | 90篇 |
1991年 | 76篇 |
1990年 | 62篇 |
1989年 | 53篇 |
1988年 | 47篇 |
1987年 | 26篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1959年 | 4篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The X-ray diffractive technology was adopted for tentative study of plastic bonded explosive. The datum of some new diffractive peaks in standard PDF cards were added. The effects of strain to interplanar distance and crystal size of the explosive were studied. The results show that grain size of plastic bonded explosive is decreasing with the increasing of the pressure, and the residual stress of the explosive is draw stress. 相似文献
42.
有限元数值模拟试井技术,可通过描述不同网格的瞬变压力对测试范围内各个小单元进行精细描述.综合运用解析试井、数值试井联带分析方法,将测试动态成果与地质静态成果有机结合、相互补充,可实现对复杂断块油气藏的精细描述,达到一口井搞清一个小型复杂断块油气藏的目的. 相似文献
43.
David Mills 《Granular Matter》2004,6(2-3):173-177
For fine powdered materials, capable of being conveyed in dense phase, a conveying region exists in which instability in flow and pipeline blockage can occur if the pressure gradient available is insufficient to maintain a minimum value of solids loading ratio. A reduction in material flow rate can also lead to pipeline blockage in this region. Conveying trials under-taken with cement are used to illustrate the nature of the problem. 相似文献
44.
指出了为发展ADSL而提高市话音频铜线电缆的传输质量和维护水平的必要性,分析了铜线电缆线对有关指标参数低劣的原因和对传输ADSL的影响,并提出了一些改进的意见。 相似文献
45.
介绍一种用于钢筋混凝土框架二阶弹塑性分析的简化单元模式。它考虑了轴力的二阶效应、横截面的塑化和塑性区长度等非线性因素的影响。利用杆件截面的弯矩—曲率关系,可以直接由弹性杆件的转角—位移方程建立单元的非线性刚度矩阵。经与试验结果比较,说明计算结果是正确的。 相似文献
46.
无间隙原子钢的微观结构特征和塑性应变比 总被引:1,自引:0,他引:1
采用X射线衍射的ODF和LP分析技术,SEM电子通道花样和蚀坑技术观测,研究了超深冲无间隙原子钢板的微观结构特征。结果表明:控制化学成分、保证基体纯净、优选工艺参数,促进强的γ-〈111〉∥N.D纤维织构的形成是获得优异成型性的关键。用CMTP方法,由ODF织构数据从理论计算了塑性应变比(r),表明rm值高达3.18。文中讨论了再结晶织构形成机制。 相似文献
47.
稀疏效应下一类捕食者与食饵系统极限环 总被引:1,自引:0,他引:1
蔡淑云 《吉林化工学院学报》2002,19(4):95-97
研讨了稀疏效应下一类捕食者与食饵系统 :x· =x(x(r-x) -y) ,y· =b0 y(x -m) .讨论了该系统平衡点的性态 ,并证明了该系统极限环的存在性和唯一性 . 相似文献
48.
49.
Influence of Storage Time and Temperature on Absorption of Flavor Compounds from Solutions by Plastic Packaging Materials 总被引:1,自引:0,他引:1
R. Van Willige D. Schoolmeester A. Van Ooij J. Linssen A. Voragen 《Journal of food science》2002,67(6):2023-2031
ABSTRACT: Linear low-density polyethylene (LLDPE), oriented polypropylene (OPP), polycarbonate (PC), polyethylene terephthalate (PET film and PET bottle), and polyethylene naphthalate (PEN) were stored in a model solution containing 10 flavor compounds at 4, 20, and 40 °C and flavor absorption by the plastic materials was followed in time. The absorption rate and/or total amount absorbed increased considerably with temperature from 4 to 40 °C. Depending on storage temperature, total flavor absorption by the polyolefins (LLDPE and OPP) was 3 to 2400 times higher than by the polyesters (PC, PET, and PEN). Therefore, in the factor of flavor absorption, polyesters are preferred over polyolefins as packaging material. 相似文献
50.
Nuclear magnetic resonance (n.m.r.) studies of 19F nuclei in a random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T2 components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T1 appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T1 were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals. 相似文献