全文获取类型
收费全文 | 380645篇 |
免费 | 84359篇 |
国内免费 | 46425篇 |
专业分类
电工技术 | 37918篇 |
技术理论 | 25篇 |
综合类 | 32585篇 |
化学工业 | 55618篇 |
金属工艺 | 34442篇 |
机械仪表 | 19145篇 |
建筑科学 | 27486篇 |
矿业工程 | 18949篇 |
能源动力 | 13945篇 |
轻工业 | 31880篇 |
水利工程 | 10488篇 |
石油天然气 | 25969篇 |
武器工业 | 5106篇 |
无线电 | 50789篇 |
一般工业技术 | 53064篇 |
冶金工业 | 17736篇 |
原子能技术 | 3251篇 |
自动化技术 | 73033篇 |
出版年
2024年 | 703篇 |
2023年 | 7232篇 |
2022年 | 8963篇 |
2021年 | 12671篇 |
2020年 | 14473篇 |
2019年 | 22627篇 |
2018年 | 24747篇 |
2017年 | 26510篇 |
2016年 | 25020篇 |
2015年 | 26216篇 |
2014年 | 27210篇 |
2013年 | 28487篇 |
2012年 | 28730篇 |
2011年 | 26458篇 |
2010年 | 23470篇 |
2009年 | 19795篇 |
2008年 | 17743篇 |
2007年 | 16684篇 |
2006年 | 16339篇 |
2005年 | 14603篇 |
2004年 | 13989篇 |
2003年 | 11728篇 |
2002年 | 10718篇 |
2001年 | 9490篇 |
2000年 | 9614篇 |
1999年 | 10197篇 |
1998年 | 8811篇 |
1997年 | 7513篇 |
1996年 | 7130篇 |
1995年 | 6622篇 |
1994年 | 5367篇 |
1993年 | 4381篇 |
1992年 | 3897篇 |
1991年 | 2910篇 |
1990年 | 2284篇 |
1989年 | 2007篇 |
1988年 | 1503篇 |
1987年 | 581篇 |
1986年 | 459篇 |
1985年 | 349篇 |
1984年 | 243篇 |
1983年 | 161篇 |
1982年 | 210篇 |
1981年 | 203篇 |
1980年 | 142篇 |
1976年 | 260篇 |
1975年 | 210篇 |
1972年 | 241篇 |
1971年 | 137篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Li-Xiang Wu Lin-Lin Zhu Yang You Rui-Lin Lin Qing-Qing Liu Wei-Ming Guo Hua-Tay Lin Kevin Paul Plucknett 《Ceramics International》2021,47(1):935-942
Dense pressure-sintered reaction-bonded Si3N4 (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu2O3–MgO–Y2O3 sintering additive. The addition of Eu2O3–MgO–Y2O3 was shown to promote full nitridation of the Si powder. The nitrided Si3N4 particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu2O3–MgO–Y2O3 were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu2O3 doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m?1 K?1, significantly higher than the counterpart without Eu2O3 doping, or with ZrO2 doping by conventional methods. 相似文献
2.
Yong Jiang Zhenbang Wei Wenzhou Sun Limeng Liu Zhenkun Huang 《Ceramics International》2021,47(6):7588-7592
Samples in Si–Al-R-O-N (R = Y, Gd, Yb) systems were prepared by solid-state reactions using R2O3, Al2O3, SiO2 and Si3N4 powders as starting materials. X-ray diffraction was done to investigate RAM-J(R) solid solutions [RAM = R4Al2O9, J(R) = R4Si2N2O7] formation and their equilibrium with RSO (R4Si2O10). Phase relations between RAM, J(R) and RSO at 1700 °C were summarized in a phase diagram. It was determined that a limited solid solution of RAM and RSO could be formed along RAM-RSO tie-line, while RAM and J(R) form a continuous solid solution along RAM-J(R) tie-line. In RAM-J(R)-RSO ternary systems, the RAM-J(R) tie-lines were extended towards the RSO corner to form a continuous solid solution area of JRAMss (R = Y, Gd, Yb). The established phase relations in the Si–Al-R-O-N (R = Y, Gd, Yb) systems may facilitate compositional selections for developing JRAMss as monolithic ceramics or for SiC/Si3N4 based composites using the solid-solutions as a second refractory phase. 相似文献
3.
4.
基于能量法和Archard磨损模型,提出了一种考虑磨损的齿轮啮合刚度数值计算方法。根据展成法原理,建立了精确的齿廓曲线方程。利用能量法计算齿轮单齿啮合刚度,并通过分段1阶傅里叶级数拟合获得齿轮总啮合刚度。以Archard磨损模型为基础,计算得到齿面法向磨损量与啮合点处压力角的关系。计算分析了不同磨损量对齿轮啮合刚度的影响。结果表明,磨损量在齿根、齿顶处较大,在节点处的理论磨损量为0 mm,随着压力角的逐渐增加,磨损量先减小后增大;齿面非均匀磨损会降低齿轮啮合刚度,随着磨损量的逐渐增加,啮合刚度逐渐减小。该方法为考虑磨损的齿轮系统动力学建模提供了理论基础。 相似文献
5.
针对目前串联型打磨机器人在打磨球面时存在刚度不足的问题,提出一种3-RSS同轴驱动布局并联机构工具型打磨机器人.同轴驱动布局是将驱动布置在同一轴线,主体由基柱和3组可以绕基柱旋转的机械臂构成,每个机械臂外接支链杆簇,3组支链杆簇与末端打磨头相连.通过构型分析、结构设计,建立同轴驱动布局打磨机器人模型,并对模型进行运动学分析,通过雅可矩阵分析奇异位置,获得打磨机器人的灵活工作空间;经过运动仿真,对比预设路径与仿真轨迹,进行运动误差分析,验证了驱动方案的可行性.研究结果为并联机构打磨机器人拓展工作空间、提高刚度提供了理论与技术支持. 相似文献
6.
7.
8.
9.
针对煤岩体较为破碎或钻孔壁凹凸不平状态下,锚杆支护施工工艺存在支护时间长、支护效率低下等问题,提供了一种矿用多功能一体化锚杆施工设备.对该设备的结构和工作原理进行了分析,在煤矿进行了现场工艺性试验,结果表明:该设备操作简单、工作效率高、自动化程度高,锚杆钻进与锚固性能可靠,能有效实现破碎围岩巷道的高强度支护. 相似文献
10.
Artificial domestication and improvement of the majority of crops began approximately 10,000 years ago, in different parts of the world, to achieve high productivity, good quality, and widespread adaptability. It was initiated from a phenotype-based selection by local farmers and developed to current biotechnology-based breeding to feed over 7 billion people. For most cereal crops, yield relates to grain production, which could be enhanced by increasing grain number and weight. Grain number is typically determined during inflorescence development. Many mutants and genes for inflorescence development have already been characterized in cereal crops. Therefore, optimization of such genes could fine-tune yield-related traits, such as grain number. With the rapidly advancing genome-editing technologies and understanding of yield-related traits, knowledge-driven breeding by design is becoming a reality. This review introduces knowledge about inflorescence yield-related traits in cereal crops, focusing on rice, maize, and wheat. Next, emerging genome-editing technologies and recent studies that apply this technology to engineer crop yield improvement by targeting inflorescence development are reviewed. These approaches promise to usher in a new era of breeding practice. 相似文献