全文获取类型
收费全文 | 69348篇 |
免费 | 6333篇 |
国内免费 | 3690篇 |
专业分类
电工技术 | 5245篇 |
综合类 | 5448篇 |
化学工业 | 11417篇 |
金属工艺 | 7560篇 |
机械仪表 | 4121篇 |
建筑科学 | 6066篇 |
矿业工程 | 1684篇 |
能源动力 | 4331篇 |
轻工业 | 4316篇 |
水利工程 | 1678篇 |
石油天然气 | 3523篇 |
武器工业 | 638篇 |
无线电 | 6143篇 |
一般工业技术 | 7723篇 |
冶金工业 | 4720篇 |
原子能技术 | 1305篇 |
自动化技术 | 3453篇 |
出版年
2024年 | 256篇 |
2023年 | 948篇 |
2022年 | 1835篇 |
2021年 | 2218篇 |
2020年 | 2296篇 |
2019年 | 1861篇 |
2018年 | 1736篇 |
2017年 | 2359篇 |
2016年 | 2528篇 |
2015年 | 2606篇 |
2014年 | 4094篇 |
2013年 | 4281篇 |
2012年 | 5114篇 |
2011年 | 5526篇 |
2010年 | 3841篇 |
2009年 | 4029篇 |
2008年 | 3542篇 |
2007年 | 4563篇 |
2006年 | 4198篇 |
2005年 | 3405篇 |
2004年 | 3016篇 |
2003年 | 2579篇 |
2002年 | 2133篇 |
2001年 | 1900篇 |
2000年 | 1560篇 |
1999年 | 1235篇 |
1998年 | 995篇 |
1997年 | 867篇 |
1996年 | 773篇 |
1995年 | 592篇 |
1994年 | 520篇 |
1993年 | 362篇 |
1992年 | 349篇 |
1991年 | 304篇 |
1990年 | 227篇 |
1989年 | 153篇 |
1988年 | 123篇 |
1987年 | 73篇 |
1986年 | 76篇 |
1985年 | 64篇 |
1984年 | 57篇 |
1983年 | 43篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 24篇 |
1979年 | 17篇 |
1977年 | 8篇 |
1975年 | 4篇 |
1959年 | 13篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk. 相似文献
42.
《Ceramics International》2020,46(15):24204-24212
The effects of in-situ synthesis columnar mullite and pore structure on the hot modulus of rupture (HMOR), thermal shock resistance and corrosion resistance of corundum castables have been investigated in this paper. When 2% nano silica was added, the pore diameters of castables could be decreased to 15 nm (at 110 °C), 1 μm (1100 °C) and 6 μm (1500 °C), respectively. The corresponding reducing magnitude of pore size is 98.5%, 83.3% and 33.3%. The HMOR of castables fired at 1500 °C increased by 110% to 3.64 MPa. Furthermore, after three thermal shock cycles, the residual strength ratio of castables increased from 5.2% to 15.3%. A large amount of cross-distributed columnar mullite was formed between nano silica and α-Al2O3 by the two-dimensional nucleation mechanism, which remarkably enhanced the high temperature properties. The penetration index reduced from 30.86% to 19.88%, suggesting that smaller pore size and higher viscosity had a great influence to the penetration process. 相似文献
43.
摘要:为了研究退火温度对镀锌DP980+Z烘烤硬化值的影响,退火温度控制在760~820℃之间,系统分析退火温度对烘烤硬化值的影响。通过准静态拉伸试验机测量烘烤硬化值及抗拉强度,采用lepara试剂对组织中的马氏体进行着色,利用金相显微镜及图像处理软件测量马氏体的体积分数;采用扫描电镜观察DP980+Z的双相组织特点,并且将组织图片通过CAD转化成有限元图进行网格划分,建立代表性体积单元(RVE),通过有限元分析铁素体、马氏体强度对烘烤硬化值的影响。在同样的变形量情况下,DP980+Z的原始屈服强度越高,烘烤硬化值越高。 相似文献
44.
A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application. 相似文献
45.
Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313. 相似文献
46.
介绍了邢钢180 m^2烧结机投产以来,在提高混合料温度方面所采取的主要措施.该厂通过提高生石灰质量、采用蒸汽预热混合料、在混合机中加热红泥浆等,改善了混合料的透气性,进而提高了烧结矿产、质量. 相似文献
47.
48.
AlSb晶体内二维磁极化子的磁场与温度效应 总被引:1,自引:0,他引:1
在考虑声子之间相互作用的同时,本文应用线性组合算符和微扰法研究了电子自旋对弱耦合二维磁极化子特性的影响。对AlSb晶体所作的数值计算结果表明,随着磁场的加强,磁极化子平均数减少;随着温度的增加,磁极化子平均数也增加;随着温度的增加,电子自旋作用以及声子之间相互作用都加强;随着磁场的加强,电子自旋作用增加而声子之间相互作用基本不变。 相似文献
49.
为了提高注入剖面测井的准确性,研制了一种新型注入剖面组合测井仪。该仪器由流量处理单元、伽马处理单元、井温处理单元、磁性定位处理单元、调制式传输、电源电路六部分组成。一次下井可同时测取流量、伽马、井温、磁性定位四组参数。具有测取资料精度高、单芯电缆传输、流量可单点测量也可连续测量以厦现场监测和维修方便等特点。 相似文献
50.