全文获取类型
收费全文 | 398篇 |
免费 | 34篇 |
国内免费 | 40篇 |
专业分类
化学 | 230篇 |
晶体学 | 3篇 |
力学 | 10篇 |
综合类 | 3篇 |
数学 | 49篇 |
物理学 | 57篇 |
无线电 | 120篇 |
出版年
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 17篇 |
2020年 | 20篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 18篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 31篇 |
2012年 | 28篇 |
2011年 | 23篇 |
2010年 | 13篇 |
2009年 | 20篇 |
2008年 | 21篇 |
2007年 | 22篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 21篇 |
2003年 | 12篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 3篇 |
排序方式: 共有472条查询结果,搜索用时 15 毫秒
41.
Macroporous copolymer of glycidyl methacrylate and ethylene dimethacrylate containing surface epoxy groups was firstly synthesized
with dodecyl alcohol and cyclohexanol as liquid pore-forming agents and nanosize calcium carbonate as solid porogenic agent.
The scanning electron microscopy was used to characterize their surface structure. Under the optimum conditions, β-galactosidase
from Aspergillus oryzae was immobilized on the support obtained above, and the basic property and the kinetic data of the reaction on immobilized
enzyme were determined. These data were compared with those obtained for the enzyme immobilized on the support prepared only
with the liquid solution as pore-forming agent. Satisfactory results were obtained in enzyme activity, immobilization yield,
pH stability, thermal stability, operational stability, and Michaelis constants K
M. The results indicated that the copolymer of glycidyl methacrilate and ethylene dimethacrylate newly prepared was more suitable
to immobilize enzyme than the carrier synthesized with traditional method. 相似文献
42.
43.
Hong Y Liao JY Cao D Zang X Kuang DB Wang L Meier H Su CY 《The Journal of organic chemistry》2011,76(19):8015-8021
A novel efficient metal free sensitizer containing asymmetric double donor-π-acceptor chains (DC) was synthesized for dye-sensitized solar cells (DSSCs). Comparing to 3.80%, 4.40% and 4.64% for the DSSCs based on the dyes with single chain (SC1, SC2) and cosensitizers (SC1 + SC2), the overall conversion efficiency reaches 6.06% for DC-sensitized solar cells as a result of its longer electron lifetime and higher incident monochromatic photon-to-current conversion efficiency. 相似文献
44.
A CMOS variable gain low noise amplifier(LNA) is presented for 4.2-4.8 GHz ultra-wideband application in accordance with Chinese standard.The design method for the wideband input matching is presented and the low noise performance of the LNA is illustrated.A three-bit digital programmable gain control circuit is exploited to achieve variable gain.The design was implemented in 0.13-μm RF CMOS process,and the die occupies an area of 0.9 mm~2 with ESD pads.Totally the circuit draws 18 mA DC current from 1.2 V DC supply,the LNA exhibits minimum noise figure of 2.3 dB,S(1,1) less than -9 dB and S(2,2) less than -10 dB.The maximum and the minimum power gains are 28.5 dB and 16 dB respectively.The tuning step of the gain is about 4 dB with four steps in all.Also the input 1 dB compression point is -10 dBm and input third order intercept point(IIP3) is -2 dBm. 相似文献
45.
46.
介绍了用显微拉曼研究经低强度He-Ne激光照射。并在均匀磁场中处理过的水稻的结果。并与未经处理水稻的拉曼光谱进行了比较。基本依据是激光对生物分子的共振激发作用理论。从实验结果看.其间的谱线有一定差异,表明激光照射和均匀磁场处理,有可能改变水稻的遗传特性。 相似文献
47.
代数微分方程组的亚纯解 总被引:5,自引:4,他引:1
在本文里,利用亚纯函数的Nevanlinna的值分布理论,我们讨论了两类代数微分方程组的亚纯解的存在性问题,得到个更为精确的 结果。 相似文献
48.
49.
All-optical 1 ×4 broadcast and 1 ×3 multicast experiments of a 40-Gb/s return-to-zero on-off keying (RZ- OOK) signal based on a periodically poled lithium niobate (PPLN) waveguide are demonstrated in this letter. Clear opened eye diagrams and error-free performance are achieved for the broadcast signals at 1541.3, 1543.7, 1548.5, and 1550.9 nm. Multicast technology uses cascaded second-harmonic generation and difference-frequency generation in a Ti:PPLN waveguide. An error-free operation with a negligible power penalty is achieved for the three wavelength-division multiplexing multicast signals at 1533, 1537, and 1541 nm. 相似文献
50.