全文获取类型
收费全文 | 5371篇 |
免费 | 191篇 |
国内免费 | 14篇 |
专业分类
化学 | 3956篇 |
晶体学 | 73篇 |
力学 | 57篇 |
综合类 | 2篇 |
数学 | 243篇 |
物理学 | 1245篇 |
出版年
2023年 | 35篇 |
2022年 | 32篇 |
2021年 | 45篇 |
2020年 | 76篇 |
2019年 | 92篇 |
2018年 | 63篇 |
2017年 | 35篇 |
2016年 | 113篇 |
2015年 | 126篇 |
2014年 | 100篇 |
2013年 | 269篇 |
2012年 | 254篇 |
2011年 | 274篇 |
2010年 | 168篇 |
2009年 | 192篇 |
2008年 | 279篇 |
2007年 | 301篇 |
2006年 | 283篇 |
2005年 | 295篇 |
2004年 | 233篇 |
2003年 | 210篇 |
2002年 | 206篇 |
2001年 | 124篇 |
2000年 | 121篇 |
1999年 | 80篇 |
1998年 | 61篇 |
1997年 | 43篇 |
1996年 | 84篇 |
1995年 | 62篇 |
1994年 | 52篇 |
1993年 | 71篇 |
1992年 | 69篇 |
1991年 | 72篇 |
1990年 | 57篇 |
1989年 | 55篇 |
1988年 | 60篇 |
1987年 | 63篇 |
1986年 | 52篇 |
1985年 | 92篇 |
1984年 | 83篇 |
1983年 | 47篇 |
1982年 | 65篇 |
1981年 | 59篇 |
1980年 | 58篇 |
1979年 | 59篇 |
1978年 | 50篇 |
1977年 | 36篇 |
1976年 | 39篇 |
1974年 | 29篇 |
1973年 | 30篇 |
排序方式: 共有5576条查询结果,搜索用时 46 毫秒
151.
Double C-C bond cleavage of a cyclopentadienyl ligand proceeded to titanacyclopentadienes when 2 equiv of nitriles were added and the resulting two-carbon unit and three-carbon unit were converted into a benzene derivative and a pyridine derivative, respectively, in one-pot. 相似文献
152.
153.
154.
Three-dimensional particle crystals made of dicarboxylic thiolate (MSA)-stabilized gold nanoparticles were formed at an air/water interface. FTIR spectra of this supracrystal showed that three well-resolved peaks existed from 3400 to 3550 cm-1 just falling in a region of OH stretching vibrational mode. Precise analysis showed that all these peaks originated from the water cluster included in the interstice of a particle crystal. 相似文献
155.
156.
Hisaya Sato Yasuyuki Tanaka 《Journal of polymer science. Part A, Polymer chemistry》1979,17(11):3551-3558
1H-NMR spectra of polyisoprene were assigned using polymers of isoprene-1,1,4,4-d4, isoprene-1,1,5,5,5-d5, and isoprene-4,4-d2 polymerized with various catalysts. The methylene-proton signal at 2.1 ppm in cis-1,4 - and trans-1,4-polyisoprenes was divided into H4- and H1-proton signals; H4 resonated at 2.21 ppm in both cis-1,4 and trans-1,4 units whereas H1 resonated at 2.05, 2.21, and 2.15 ppm. Splitting due to the dyad sequences of 1,4 and 3,4 units was apparent. The methine-proton (H3) in a 3,4 unit showed a broad peak centered around 1.5 ppm in C6D6. The overlapping of this signal with the methyl-proton signals at 1.73 and 1.63 ppm resulted in some uncertainty in the determination of the microstructure of polyisoprene which contained a considerable amount of 3,4 unit. 相似文献
157.
158.
Yamamoto Y Yamamoto A Furuta SY Horie M Kodama M Sato W Akiba KY Tsuzuki S Uchimaru T Hashizume D Iwasaki F 《Journal of the American Chemical Society》2005,127(42):14540-14541
The oxidized octaethyltetraphenylporphyrin (1, OETPP) and the corresponding newly prepared octaisobutyltetraphenylporphyrin (3, OisoBuTPP) could be isolated from the reaction of OETPPLi2 (or OisoBuTPPLi2) with SOCl2. The X-ray analysis and the characteristic UV-vis spectra of 1 and 3 revealed that these are the first examples of 16 pi nonaromatic porphyrins. 相似文献
159.
Ohne Zusammenfassung 相似文献
160.
Effect of molecular orientation distribution and crystallinity on the measurement of the crystal lattice modulus of nylon 6 by x-ray diffraction 总被引:1,自引:0,他引:1
The crystal lattice modulus of nylon 6 (-type) was measured by x-ray diffraction using nylon 6 films drawn up to five times. The measured crystal lattice modulus was 173–175 GPa for all specimens whose crystallinity and the Young's modulus were beyond 46% and 3.75 GPa, respectively. These results indicate that a state of homogenous stress can be achieved. In contrast, the values were scattered for the speciments whose crystallinity and Young's modulus are less than the above values. To study the origin, a numerical calculation of the crystal lattice modulus, as measured by x-ray diffraction, was carried out by considering effects on the orientation factors of molecular chains and crystallinity. In this calculation, a previously introduced model was employed, in which oriented crystalline layers are surrounded by oriented amorphous phases so that the strains of the two phases at the boundary are identical. The theoretical results calculated by the introduced model indicated that the crystal lattice modulus by x-ray diffraction is almost equal to the intrinsic crystal modulus if the morphology of the test specimen can be represented as a series model. In contrast, if a parallel model is more appropriate, the difference between the measured modulus and the intrinsic value can be pronounced. Such morphological dependence was found to be less pronounced with increasing high degree of molecular orientation and crystallinity. 相似文献