全文获取类型
收费全文 | 4687篇 |
免费 | 120篇 |
国内免费 | 14篇 |
专业分类
化学 | 3526篇 |
晶体学 | 34篇 |
力学 | 76篇 |
数学 | 226篇 |
物理学 | 959篇 |
出版年
2023年 | 31篇 |
2021年 | 47篇 |
2020年 | 47篇 |
2019年 | 64篇 |
2018年 | 38篇 |
2017年 | 43篇 |
2016年 | 70篇 |
2015年 | 88篇 |
2014年 | 86篇 |
2013年 | 211篇 |
2012年 | 208篇 |
2011年 | 241篇 |
2010年 | 117篇 |
2009年 | 131篇 |
2008年 | 220篇 |
2007年 | 216篇 |
2006年 | 267篇 |
2005年 | 263篇 |
2004年 | 262篇 |
2003年 | 207篇 |
2002年 | 240篇 |
2001年 | 144篇 |
2000年 | 107篇 |
1999年 | 77篇 |
1998年 | 54篇 |
1997年 | 47篇 |
1996年 | 70篇 |
1995年 | 56篇 |
1994年 | 63篇 |
1993年 | 56篇 |
1992年 | 72篇 |
1991年 | 65篇 |
1990年 | 54篇 |
1989年 | 49篇 |
1988年 | 45篇 |
1987年 | 39篇 |
1986年 | 47篇 |
1985年 | 78篇 |
1984年 | 66篇 |
1983年 | 24篇 |
1982年 | 59篇 |
1981年 | 35篇 |
1980年 | 35篇 |
1979年 | 49篇 |
1978年 | 40篇 |
1977年 | 49篇 |
1976年 | 32篇 |
1975年 | 30篇 |
1974年 | 30篇 |
1973年 | 34篇 |
排序方式: 共有4821条查询结果,搜索用时 318 毫秒
51.
Kohji Chihara Takeshi Takemura Tsuguo Yamaoka N. Yamamoto Arnold Schaffer Ralph S. Becker 《Photochemistry and photobiology》1979,29(5):1001-1008
Abstract— The absorption and emission spectra, lifetimes and quantum yields of all-trans retinol have been examined as a function of solvent and temperature. In addition, the spectroscopy of retinyl ether and 2 other polyene alcohols have been determined. Based on the results obtained, we conclude that the singlet excited state of retinol and retinyl cther is of a forbidden character and of the type loosely called 1 A- g . Retinol forms a dimer in an alkane solvent when cooling from 298 to 77 K. A general structure for the dimer is proposed. 相似文献
52.
Chang-Kyu Kim A. Takaku M. Yamamoto H. Kawamura K. Shiraishi Y. Igarashi S. Igarashi H. Takayama N. Ikeda 《Journal of Radioanalytical and Nuclear Chemistry》1989,131(1):131-137
Ammonium uranates (AU) obtained by the addition of aqueous NH4 OH to a solution of UO2 (NO3)2 or the equilibrium reaction of UO3 · 2H2 O with the vapour over concentrated NH4 OH have been studied by X-ray diffraction (XRD) analysis, diffuse reflectance Fourier transform infrared spectrometry (DR-FTIR) and chemical analysis. Ammonia can be present as either NH3 or NH
4
+
. For precipitates obtained at a pH of 3.7, ammonia in the form of NH3 is predominant. For ammonium uranate obtained by reaction over concentrated NH4OH, most of the ammonia is bonded as NH
4
+
. The reaction mechanism and structures of the products are also discussed. 相似文献
53.
Mamiko Odoko Kyouta Yamamoto Nobuo Okabe 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):m469-m470
In the title compound, [Ca(C6H5O4)2(C6H6O4)2]·4H2O, which is a kojic acid–Ca2+ complex, the Ca atom is on a twofold axis and is octacoordinated by O atoms from four pyrone ligand molecules. The hydroxyl and ketone O atoms of each ligand form a five‐membered chelate ring with the Ca atom. The crystal structure is stabilized by partial stacking and O—H?O hydrogen bonds. 相似文献
54.
Kenichi Oyaizu Junya Katoh Fumiaki Suzuki Mitsutoshi Jikei Kimihisa Yamamoto Hiroyuki Nishide Eishun Tsuchida 《先进技术聚合物》1991,2(3):155-159
Oligo(phenylene sulfide) (OPS) containing one disulfide bond at the end of the chain, which was obtained by the oxidative polymerization of diphenyl disulfide, had a relatively low Td10%(temperature for 10% weight loss) of 412 °C because of degradation of the disulfide bond. But this thermal cleavage of the disulfide bond promoted the curing reaction through thiophenoxy radical formation. OPS was allowed to react with diiodobenzene at 220 °C. The thermal stability of OPS was improved through the consumption of the disulfide bond and the coupling of the chain. 相似文献
55.
Yamamoto A Akiba N Kodama S Matsunaga A Kato K Nakazawa H 《Journal of chromatography. A》2001,928(2):139-144
A multi-beam circular dichroism (CD) detector which is easily constructed by inserting inexpensive optics into a conventional photo-diode array detector has an advantage of simultaneous detection of the absorbance and CD. The enantiomeric purity determination of malic acid in beverages was performed by this detection system. Malic acid when complexed with Cu(II) was found to have an absorbance maximum at around 750 nm. The L-malic acid-Cu(II) complex showed a positive Cotton effect in its absorbance band and its anisotropy factor (delta epsilon/epsilon) was relatively large at about 1/170. This complex was retained on a reversed-phase column with the addition of racemic 2-hydroxy-3-methylbutyric acid to the mobile phase as the ligand. A plot of the relative peak areas between the CD and the absorption (delta abs/abs) versus optical purity showed good linearity with a correlation coefficient of 0.999, and the precision expressed as the relative standard deviation of the errors from the regression line was +/-2.7% (2sigma). The accuracy of the proposed method was assessed by capillary electrophoresis. Eight commercially available juice products were analyzed using this method. Five of them were thought to be adulterated with synthetic malic acid. 相似文献
56.
57.
58.
59.
Naoya Inazumi Shunzo Yamamoto Yoshimi Sueishi 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(1-2):33-39
The inclusion complexation of p-sulfonatocalix[6]arene (Calix-S6) with three kinds of phenothiazine dyes was studied spectrophotometrically in a mixture
of a room-temperature ionic liquid [bmim]BF4 (1-butyl-3-methylimidazolium tetrafluoroborate) and ethanol. We have determined the association constants of Calix-S6 with
phenothiazine dyes under external static pressure up to 767 bar in the [bmim]BF4-ethanol and alcohol-water mixtures. With increasing external pressure, the inclusion equilibrium in the alcohol-water mixtures
was shifted to the dissociation side. Conversely, the inclusion equilibrium of methylene blue (MB) and azure A (AA) in the
ionic liquid mixture was shifted to the association side. From the analysis of the pressure effects, the reaction volumes
ΔV for inclusion complexation were estimated as −7 to 9 cm3 mol−1 in the [bmim]BF4-ethanol mixture and 20–32 cm3 mol−1 in the alcohol-water mixtures. Based on the results, we have suggested that there is a competing complexation between the
included dye and [bmim]BF4 molecules in the ionic liquid. 相似文献
60.