全文获取类型
收费全文 | 25410篇 |
免费 | 3346篇 |
国内免费 | 1196篇 |
专业分类
电工技术 | 818篇 |
综合类 | 1466篇 |
化学工业 | 5612篇 |
金属工艺 | 4603篇 |
机械仪表 | 1748篇 |
建筑科学 | 878篇 |
矿业工程 | 1018篇 |
能源动力 | 943篇 |
轻工业 | 1147篇 |
水利工程 | 280篇 |
石油天然气 | 744篇 |
武器工业 | 184篇 |
无线电 | 2255篇 |
一般工业技术 | 4854篇 |
冶金工业 | 2669篇 |
原子能技术 | 293篇 |
自动化技术 | 440篇 |
出版年
2024年 | 138篇 |
2023年 | 820篇 |
2022年 | 764篇 |
2021年 | 1050篇 |
2020年 | 1170篇 |
2019年 | 1125篇 |
2018年 | 886篇 |
2017年 | 1034篇 |
2016年 | 931篇 |
2015年 | 937篇 |
2014年 | 1339篇 |
2013年 | 1536篇 |
2012年 | 1587篇 |
2011年 | 1596篇 |
2010年 | 1157篇 |
2009年 | 1250篇 |
2008年 | 1121篇 |
2007年 | 1467篇 |
2006年 | 1438篇 |
2005年 | 1339篇 |
2004年 | 1052篇 |
2003年 | 1123篇 |
2002年 | 890篇 |
2001年 | 733篇 |
2000年 | 695篇 |
1999年 | 536篇 |
1998年 | 453篇 |
1997年 | 329篇 |
1996年 | 304篇 |
1995年 | 233篇 |
1994年 | 203篇 |
1993年 | 159篇 |
1992年 | 123篇 |
1991年 | 98篇 |
1990年 | 85篇 |
1989年 | 74篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
圆锥形零件极限变形程度可用极限拉深系数[mzd]=[d2/D0]来表示。根据圆锥形零件与圆筒形零件的内在联系,经力学分析得出了便于实用的圆锥形零件极限拉深系数[mzd]的计算表达式,并由此给出了用[mzd]所表示的成形极限曲线和第一次拉深时的极限拉深系数。经实验验证表明所确定的成形极限是准确和可靠的。 相似文献
103.
104.
Chan-Yeol Seo Seung-Jun Choi Jeon Choi Choong-Nyeon Park Paul. S. Lee Jai-Young Lee 《Journal of Alloys and Compounds》2003,350(1-2):324-331
AB5-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi3.6Al0.4Co0.7Mn0.3 with a hexagonal CaCu5 structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi3.6Al0.4Co0.7Mn0.3Tiy, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi3.6Al0.4Co0.7Mn0.3Tiy (y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (P–C–T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test. 相似文献
105.
106.
Unidirectionally reinforced graphite/copper composites have been fabricated using a pressure infiltration casting procedure.
T300 and T650 graphite fibers have been used to reinforce copper and copperchromium alloys. The effects of the chromium level
in the copper matrix on the tensile strength, stiffness, and thermal expansion behavior of the composites have been evaluated
through tensile and three-point bend testing, and thermal cycling. At the 0.5 wt% alloying level, chromium increases the stiffness
and optimizes the thermal expansion behavior of graphite/copper composites. The longitudinal tensile strengths of these composites
are above 1606 MPa, whereas the transverse tensile strengths are lower than 40 MPa due to incomplete infiltration during processing.
Scanning electron microscopy analyses reveal that the unalloyed copper matrix composites experienced extensive fiber/matrix
debonding under tensile loading. The addition of chromium to the copper increases the level of matrix bonding to the graphite
fibers, as evidenced by observations of fractured tensile specimens. Auger electron spectroscopy analyses indicate that a
chromium carbide phase present at the interface is responsible for the improved bonding. 相似文献
107.
Ewa Talik Marie-Emilie Lucas Wojciech Suski R. Tro 《Journal of Alloys and Compounds》2003,350(1-2):72-76
The XPS electronic structures of the AFe4Al8 (A=Sc, Y, U, Th) single crystals were measured. The valence band of UFe4Al8 exhibits domination of the U 5f states at the Fermi level, while for the other AFe4Al8 compounds the valence states are shifted by 0.5 eV toward higher binding energy. The multiplet structure of the U 4f and Th 4f states was analyzed in comparison with the U 4f states of U3Ge5 and UNiSb2. 相似文献
108.
挤压铸造制备了Al2O3短纤维/Al 4 5%Cu合金复合材料,研究了关键工艺参数对基体合金凝固方式与组织的影响。结果表明:Al2O3短纤维表面不能作为基体α初晶非自发形核衬底;随凝固冷却速度ε的增大,复合材料基体组织将细化,基体中有更多完整的晶界出现,偏析第二相主要分布于晶界上,其量随ε的增大而明显增多;纤维体积分数Vf的增大将细化基体晶粒尺寸至纤维间隙大小,同时随Vf的增大,主要分布于纤维/基体界面的偏析第二相的量将有所降低;模具、预制块预热温度及合金液浇注温度对复合材料凝固过程的影响归结到对凝固冷却速度的影响上来;外加压力的提高使复合材料基体组织细化。 相似文献
109.
110.
D. Banerjee G. K. Lai G. S. Upadhyaya 《Journal of Materials Engineering and Performance》1995,4(5):563-572
For production of fine-grained and corrosion-resistant tungsten carbide (WC) based cemented carbides, addition of chromium
carbide (Cr33C2) in small amounts is standard practice. No systematic study, however, has been made of the effects of large additions (maximum
6 wt % ) of Cr3C2 as a substitute for tungsten carbide. This study focuses on the effect of hard-phase substitution by C3C2 in WC-1OCo cemented carbide. An attempt is also made to modify the binder metal cobalt by partial or complete substitution
of nickel. Specimens were prepared using the standard liquid-phase sintering process and were tested for sintered porosity,
mechanical properties, corrosion resistance, and microstructural parameters. Results confirm the findings of earlier workers
regarding grain refinement and improvement of mechanical properties upon the addition of small amounts (<2 wt%) of Cr3C2. Modification of the binder phase improves indentation fracture toughness and corrosion resistance. Addition of Cr3C2 independent of the binder type improves corrosion resistance. 相似文献