全文获取类型
收费全文 | 4420篇 |
免费 | 689篇 |
国内免费 | 590篇 |
专业分类
化学 | 2245篇 |
晶体学 | 33篇 |
力学 | 240篇 |
综合类 | 27篇 |
数学 | 540篇 |
物理学 | 1259篇 |
无线电 | 1355篇 |
出版年
2024年 | 15篇 |
2023年 | 119篇 |
2022年 | 156篇 |
2021年 | 184篇 |
2020年 | 170篇 |
2019年 | 178篇 |
2018年 | 162篇 |
2017年 | 143篇 |
2016年 | 217篇 |
2015年 | 212篇 |
2014年 | 219篇 |
2013年 | 308篇 |
2012年 | 422篇 |
2011年 | 430篇 |
2010年 | 325篇 |
2009年 | 255篇 |
2008年 | 252篇 |
2007年 | 279篇 |
2006年 | 243篇 |
2005年 | 212篇 |
2004年 | 148篇 |
2003年 | 136篇 |
2002年 | 85篇 |
2001年 | 89篇 |
2000年 | 83篇 |
1999年 | 106篇 |
1998年 | 83篇 |
1997年 | 82篇 |
1996年 | 72篇 |
1995年 | 52篇 |
1994年 | 42篇 |
1993年 | 44篇 |
1992年 | 40篇 |
1991年 | 27篇 |
1990年 | 24篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 17篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有5699条查询结果,搜索用时 609 毫秒
101.
POROUS MEMBRANE TEMPLATED SYNTHESIS OF POLYMER PILLARED LAYER 总被引:5,自引:0,他引:5
The anodic porous alumina membranes with a definite pore diameter and aspect ratio were used as templates tosynthesize polymer pillared layer structures. The pillared polymer was produced in the template membrane pores, and thelayer on the template surfaces. Rigid cured epoxy resin, polystyrene and soft hydrogel were chosen to confirm themethodology. The pillars were in the form of either tubes or fibers, which were controlled by the alumina membrane pore surface wettability. The structural features were confirmed by scanning electron microscopy results. 相似文献
102.
Yun Gong Changwen Hu Hui Li Wanlong Pan Xueli Niu Zhifa Pu 《Journal of Molecular Structure》2005,740(1-3):153-158
Two nickel (imidazole) complexes, Ni(im)6Cl2·4H2O (1) and Ni(im)6(NO3)2 (2) (im=imidazole) have been synthesized and characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. 1 crystallizes in the triclinic space group P-1 with a=8.800(6) Å, b=9.081(6) Å, c=10.565(7) Å, =75.058(9)°, β=83.143(8)°, γ=61.722(8)°, V=718.3(8) Å3, Z=1 and R1 (wR2)=0.0469 (0.1497). 2 crystallizes in the trigonal space group R-3 with a=12.370(6) Å, b=12.370(6) Å, c=14.782(14) Å, =90.00°, β=90.00°, γ=120.00°, V=1959(2) Å3, Z=3 and R1 (wR2)=0.0358 (0.0955). 1 and 2 exhibit different supramolecular network due to their different counter anions and different hydrogen bonding connection. In compound 1, [Ni(im)6]2+ cation and counter anions Cl− alternatively array in an ABAB fashion via N–HCl hydrogen bonding. In compound 2, the plane of each NO32− is almost parallel and each NO32− connect three different [Ni(im)6]2+ cations via N–HO hydrogen bonding. 相似文献
103.
Sung-Yong Chung Ronghua Yu Niu Jin Si-Young Park Berger P.R. Thompson P.E. 《Electron Device Letters, IEEE》2006,27(5):364-367
This letter presents the room-temperature high-frequency operation of Si/SiGe-based resonant interband tunnel diodes that were fabricated by low-temperature molecular beam epitaxy. The resulting devices show a resistive cutoff frequency f/sub r0/ of 20.2 GHz with a peak current density of 218 kA/cm/sup 2/, a speed index of 35.9 mV/ps, and a peak-to-valley current ratio of 1.47. A specific contact resistivity of 5.3/spl times/10/sup -7/ /spl Omega//spl middot/cm/sup 2/ extracted from RF measurements was achieved by Ni silicidation through a P /spl delta/-doped quantum well by rapid thermal sintering at 430/spl deg/C for 30 s. The resulting devices are very good candidates for RF high-power mixed-signal applications. The device structures presented here are compatible with a standard complementary metal-oxide-semiconductor or heterojunction bipolar transistor process. 相似文献
104.
105.
106.
107.
A Phosphorescent Platinum(II) Bipyridyl Supramolecular Polymer Based on Quadruple Hydrogen Bonds
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Fang‐Wei Liu Dr. Li‐Ya Niu Prof. Yong Chen Prof. Vaidhyanathan Ramamurthy Prof. Li‐Zhu Wu Prof. Chen‐Ho Tung Prof. Yu‐Zhe Chen Prof. Qing‐Zheng Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18132-18139
A platinum(II) bipyridyl complex bearing bis‐ureidopyrimidinone (Pt‐bisUPy) has been designed and its self‐assembling behavior has been thoroughly investigated by 1H NMR, DOSY NMR, Ubbelohde viscometry analysis, UV/Vis, and emission spectroscopies. Pt‐bisUPy underwent concentration‐dependent ring‐chain polymerization in apolar solvents. Hydrogen‐bonding interactions play an important role during the formation of the supramolecular polymers. Hydrogen‐bonded supramolecular polymers were transformed to nanoparticles in water through the miniemulsion method. These nanoparticles showed strong π–π excimeric emission. Metal‐metal‐to‐ligand charge transfer (MMLCT) from Pt–Pt interactions was not significant in the emission spectrum. The phosphorescence of the nanoparticle persisted even under aerobic conditions. The triplet state of these phosphorescent nanomaterials were long‐lived and possessed moderate emission quantum yields. Furthermore, the low toxicity of these materials promises a place for them in in vitro and in vivo bioimaging. 相似文献
108.
109.
Baozhuang Niu Liming Liu Jun Wang 《The Journal of the Operational Research Society》2016,67(2):325-338
Either a company store or a local retailer can be used to establish a sales channel. For high-value products with an existing competing brand, this choice represents a crucial decision a brand-named manufacturer must make for a new market. Under the burden of high operating costs, a weak local retailer may find it difficult to sustain and using it may hurt the manufacturer’s chance to successfully establish the channel. We consider a chain-to-chain competition model comprising two manufacturers and two retailers, in which one retailer may be unable to continue its operation because of high financing costs. We identify a threshold policy for the manufacturers to select the channel structure. Interestingly, we find that channel integration is not always better. Without the consideration of contract termination risk, the manufacturer will bear the operating expenses when its opportunity cost is low or the retailer’s financing cost is sufficiently high. In equilibrium, the manufacturers will choose either (decentralized, decentralized) or (integrated, integrated) channel structure. However, when the termination risk is considered, the equilibrium channel structure would be more likely (integrated, integrated) or (integrated, decentralized). 相似文献
110.