全文获取类型
收费全文 | 30973篇 |
免费 | 4970篇 |
国内免费 | 5046篇 |
专业分类
化学 | 24193篇 |
晶体学 | 567篇 |
力学 | 1426篇 |
综合类 | 419篇 |
数学 | 3209篇 |
物理学 | 11175篇 |
出版年
2024年 | 53篇 |
2023年 | 441篇 |
2022年 | 978篇 |
2021年 | 1072篇 |
2020年 | 1178篇 |
2019年 | 1226篇 |
2018年 | 1015篇 |
2017年 | 983篇 |
2016年 | 1412篇 |
2015年 | 1524篇 |
2014年 | 1871篇 |
2013年 | 2492篇 |
2012年 | 2810篇 |
2011年 | 2902篇 |
2010年 | 2181篇 |
2009年 | 2037篇 |
2008年 | 2413篇 |
2007年 | 2100篇 |
2006年 | 1880篇 |
2005年 | 1523篇 |
2004年 | 1353篇 |
2003年 | 1139篇 |
2002年 | 1182篇 |
2001年 | 952篇 |
2000年 | 746篇 |
1999年 | 608篇 |
1998年 | 396篇 |
1997年 | 373篇 |
1996年 | 343篇 |
1995年 | 278篇 |
1994年 | 256篇 |
1993年 | 234篇 |
1992年 | 202篇 |
1991年 | 160篇 |
1990年 | 134篇 |
1989年 | 118篇 |
1988年 | 68篇 |
1987年 | 66篇 |
1986年 | 68篇 |
1985年 | 54篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Lei Liu 《Journal of Mathematical Analysis and Applications》2007,328(2):1484-1486
In this note, we generalize the inequality about the trace of positive semidefinite matrix trk(AB)?k(trA)k(trB) to Hilbert space, and obtain a relevant inequality about positive trace class operator. 相似文献
152.
153.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
154.
氯代5-氟脲嘧啶卟啉的红外光谱特性的研究 总被引:6,自引:0,他引:6
本文对新合成的对位及间位两类氯代苯基 5 氟脲嘧啶卟啉的红外光谱吸收峰进行了归属和总结 ,讨论了其红外吸收频率随取代基位置变化的规律。指出了苯环上的取代基为电负性强的基团时 ,由于场效应的存在 ,使被测化合物的羰基伸缩振动吸收峰的相对强度发生改变。同时 ,表明了嘧啶环上N原子发生了取代 ,形成单、双取代 5 氟脲嘧啶卟啉化合物的红外光谱特性。 相似文献
155.
A Generalized Optical Logic Element or GOLE is device that performs any of the 16 Boolean logic operations on signals in an optical beam with very fast switching among functions. The advantages of a generalized or universal gate in manufacturing are obvious. Extremely flexible functioning becomes possible if the GOLE functionality is switched in response to earlier computations. Likewise Field Programmable Gate Arrays or FPGAs can be used to fix the GOLE functions, making one of the most powerful and flexible processor units ever designed - called a Field GOLE. Such systems can be made in bulk optics to utilize Spatial Light Modulator or SLM capabilities, but integrated optics on silicon will be the choice for most applications. GOLEs can be generalized in several ways to become Fredkin gates and generalized Fredkin gates. They can also be cascaded similarly to electronic gates. 相似文献
156.
157.
The dendrite growth process of transparent NaBi(WO4)2 with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on
the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was
time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased
in the diffusive-convective region. The growth rate of branch had the same change trends as the arm’s. Based on the EPMA-EDS
data of solidification structure of quenched NaBi(WO4)2 melt, it was found that there were component differences from stoichiometric concentration in the melt near the interface
during the growth process.
Supported by the National Natural Science Foundation of China (Grant No. 50331040) and the Innovation Funds from Shanghai
Institute of Ceramics, Chinese Academy of Sciences (Grant No. SCX0623) 相似文献
158.
159.
160.
对不同组分的掺FeⅢ-Ⅴ族混晶GaAs1-xPx,测量了Fe深受主中心空穴热发射的非指数恒温暗电容瞬态及DLTS谱。用混晶无序使Fe深能级展宽的模型理论拟合实验结果,得到Fe能级Gauss型展宽的半宽和中心能级的热发射率,并确定出基态空穴跃迁的中心能级的焓变与组分的关系:先是减少,而后增大,与由光电容方法得到的Gibbs自由能变量与组分x的关系明显不同。 进一步讨论表明,上述两种测量方法得到的Fe中心的激活能不同,可能反映Fe中心的键合状态和混晶无序诱导的品格弛豫的影响。 相似文献