首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22323篇
  免费   1762篇
  国内免费   874篇
电工技术   1235篇
技术理论   2篇
综合类   1467篇
化学工业   3597篇
金属工艺   1162篇
机械仪表   1435篇
建筑科学   1892篇
矿业工程   648篇
能源动力   614篇
轻工业   1451篇
水利工程   396篇
石油天然气   1320篇
武器工业   188篇
无线电   2495篇
一般工业技术   2690篇
冶金工业   1062篇
原子能技术   202篇
自动化技术   3103篇
  2024年   72篇
  2023年   331篇
  2022年   532篇
  2021年   772篇
  2020年   614篇
  2019年   457篇
  2018年   591篇
  2017年   648篇
  2016年   575篇
  2015年   805篇
  2014年   967篇
  2013年   1254篇
  2012年   1308篇
  2011年   1470篇
  2010年   1272篇
  2009年   1189篇
  2008年   1248篇
  2007年   1110篇
  2006年   1258篇
  2005年   1204篇
  2004年   766篇
  2003年   726篇
  2002年   719篇
  2001年   626篇
  2000年   592篇
  1999年   740篇
  1998年   551篇
  1997年   525篇
  1996年   430篇
  1995年   351篇
  1994年   313篇
  1993年   206篇
  1992年   189篇
  1991年   136篇
  1990年   114篇
  1989年   91篇
  1988年   76篇
  1987年   36篇
  1986年   26篇
  1985年   23篇
  1984年   15篇
  1983年   7篇
  1982年   8篇
  1981年   6篇
  1980年   6篇
  1979年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
隧道爆破振动速度研究   总被引:3,自引:0,他引:3  
在隧道爆破开挖中,频繁反复的爆破冲击动压力对隧道设计轮廓线、施工误差和围岩的稳定性等有很大影响。依据爆炸动力学理论和弹性波动理论,分析了同时起爆和微差起爆所产生的爆炸应力场。根据爆炸波在传播过程中的叠加机理,提出了爆破后隧道围岩质点振动速度解析解。爆破振动速度解析解的提出,为隧道开挖采用合适的爆破掘进方法、减少施工误差及提高围岩的稳定性提供了理论依据。  相似文献   
992.
金川二矿区深部开采稳定性分析和采矿设计优化研究   总被引:9,自引:0,他引:9  
金川二矿区已进入深部开采。在采用下向胶结充填法的条件下,能不能实现无矿柱连续回采,对矿山的产量和效益影响极大。本文使用非线性有限元对预留间隔矿柱和不预留间隔矿柱两种方案的围岩应力、位移和塑性区分布以及采场的稳定性状态进行了系统的分析和比较,论证了二矿区深部实施无矿柱连续回采的合理性和可行性,为二矿区深部采矿设计优化提供了依据。  相似文献   
993.
本文建立了基于弯曲流道的颗粒堆积型多孔介质内流体流动的毛细管束模型,并在低雷诺数、低空隙率范围内对颗粒层多孔介质内的渗透率、阻力特性等进行了研究,结果表明弯曲流道毛细管束模型适合于计算颗粒层多孔介质内流体流动。  相似文献   
994.
为解决当前运载火箭电池充放电设备的自动化程度低、手工作业风险大、缺乏有效故障诊断和处理系统等缺点,将虚拟仪器技术应用到运载火箭锌银蓄电池组充放电设备中,设计新型运载火箭锌银蓄电池组充放电设备。其测控系统由硬件与软件组成,硬件采用NI公司的PXI测控平台,软件由充电、放电和加温等3部分组成。通过出厂测试、发射场补充测试和软件测试,证明该设计能提高设备自动化、智能化程度。  相似文献   
995.
Thermal barrier coating materials with proper thermal expansion coefficient (TEC), low thermal conductivity, and good high-temperature stability are of great significance for their applications in next-generation turbine engines. Herein, we report a new class of high-entropy (La0.2Sm0.2Er0.2Yb0.2Y0.2)2CexO3+2x with different Ce4+ contents synthesized by a solid-state reaction method. They exhibit different crystal structures at different Ce4+ content, including a bixbyite single phase without Ce4+ doping (x = 0), bixbyite-fluorite dual-phase in the RE2O3-rich region (0 < x < 2), and fluorite single phase in the stoichiometric (x = 2) and CeO2-rich region (x > 2). The high-entropy (La0.2Sm0.2Er0.2Yb0.2Y0.2)2CexO3+2x exhibit tailorable TECs at a large range of 9.04 × 10–6–13.12 × 10–6 °C–1 and engineered low thermal conductivity of 1.79–2.63 W·m–1·K–1. They also possess good sintering resistance and high-temperature phase stability. These results reveal that the high-entropy (La0.2Sm0.2Er0.2Yb0.2Y0.2)2CexO3+2x are promising candidates for thermal barrier coating materials as well as thermally insulating materials and refractories.  相似文献   
996.
Under the condition of constant thickness, improving the low-frequency sound absorption performance of conventional sound-absorbing materials is a challenging research topic. To address this issue, a new reduced graphene oxide/polyvinyl alcohol (RGO/PVA) porous composite ceramic was fabricated using freeze-drying and optimized by redesigning the internal connecting pores of porous ceramic matrixes with a reticular microstructure using RGO and PVA. The as-prepared porous structure showed significant enhancement in the low-frequency sound absorption band compared with pristine porous ceramics. In addition, the hybrid porous ceramics exhibited low thermal conductivity. These favorable properties indicate that the hybrid sound-absorbing ceramics have potential application prospects for noise reduction in the fields of construction and electrical and mechanical devices.  相似文献   
997.
A type of boron nitride–magnesium aluminum silicate (BN-MAS) composite ceramics was fabricated by hot-press sintering at different sintering temperatures. The relationship between the sintering temperature and microstructure was investigated by analyzing the interaction between hexagonal boron nitride (h-BN) and the MAS phase. The main MAS phase in the composite ceramics is the α-cordierite phase at a sintering temperature of 1300°C. At temperatures above 1400°C, the inhibitory effect of h-BN on the crystallization of the MAS system is significant, and MAS mainly exists in the form of an amorphous phase. The composite sintered at 1700°C exhibited the highest bending strength of 218MPa. h-BN and MAS were co-enhanced. MAS can be used as an effective liquid-phase sintering aid to assist in the sintering of h-BN, whereas h-BN can absorb the fracture energy of the composite ceramics through the pull-out and bridging effect of the particles.  相似文献   
998.
The hierarchical SiOC/SiCnws/CF composites (A/B/C structure) were designed via precursor infiltration and pyrolysis process. The SiOC ceramics served as the wave-transparent characteristic materials to adjust the impedance matching. Herein, the in situ growth of SiCnws not only was used for the absorber but served as the reinforcement of SiOC matrix composites. In detail, the SiOC/SiCnws/CF-1200°C-2 exhibits excellent electromagnetic absorption performance with minimum reflection loss of −46 dB at 14.4 GHz with the thickness of 1.6 mm, and its effective absorption band reaches 4.3 GHz. Its compressive strength reaches 8.69 and 16.41 MPa in z and x/y directions, separately. This contribution has a guidance for the application of carbon fiber/ceramics matrix composites in harsh environment.  相似文献   
999.
Small open reading frames (sORFs) are an important class of genes with less than 100 codons. They were historically annotated as noncoding or even junk sequences. In recent years, accumulating evidence suggests that sORFs could encode a considerable number of polypeptides, many of which play important roles in both physiology and disease pathology. However, it has been technically challenging to directly detect sORF-encoded peptides (SEPs). Here, we discuss the latest advances in methodologies for identifying SEPs with mass spectrometry, as well as the progress on functional studies of SEPs.  相似文献   
1000.
Wu  Xiaowei  Tan  Yi  Liu  Rui  Li  Jiayan  Cai  Min  Li  Pengting 《SILICON》2022,14(15):9489-9498
Silicon - In the production of multicrystalline silicon solar cell, diamond wire sawing method (DWS) is an important technique, which has already completely replaced multiwire slurry sawing (MWSS)...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号