全文获取类型
收费全文 | 4322篇 |
免费 | 173篇 |
国内免费 | 13篇 |
专业分类
化学 | 3318篇 |
晶体学 | 32篇 |
力学 | 70篇 |
数学 | 173篇 |
物理学 | 915篇 |
出版年
2023年 | 34篇 |
2022年 | 26篇 |
2021年 | 52篇 |
2020年 | 52篇 |
2019年 | 68篇 |
2018年 | 47篇 |
2017年 | 50篇 |
2016年 | 87篇 |
2015年 | 97篇 |
2014年 | 105篇 |
2013年 | 204篇 |
2012年 | 209篇 |
2011年 | 220篇 |
2010年 | 116篇 |
2009年 | 117篇 |
2008年 | 215篇 |
2007年 | 191篇 |
2006年 | 217篇 |
2005年 | 235篇 |
2004年 | 211篇 |
2003年 | 171篇 |
2002年 | 210篇 |
2001年 | 136篇 |
2000年 | 103篇 |
1999年 | 73篇 |
1998年 | 49篇 |
1997年 | 40篇 |
1996年 | 52篇 |
1995年 | 52篇 |
1994年 | 55篇 |
1993年 | 51篇 |
1992年 | 71篇 |
1991年 | 62篇 |
1990年 | 55篇 |
1989年 | 49篇 |
1988年 | 44篇 |
1987年 | 35篇 |
1986年 | 44篇 |
1985年 | 69篇 |
1984年 | 60篇 |
1982年 | 48篇 |
1981年 | 29篇 |
1980年 | 31篇 |
1979年 | 46篇 |
1978年 | 39篇 |
1977年 | 43篇 |
1976年 | 30篇 |
1975年 | 29篇 |
1974年 | 30篇 |
1973年 | 35篇 |
排序方式: 共有4508条查询结果,搜索用时 126 毫秒
51.
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
52.
53.
54.
55.
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
56.
57.
58.
The interaction of AlR2(BHT)(OEt2) and AlMe(BHT)2 with methylmethacrylate (MMA) leads to the formation of the Lewis acid-base complexes AlR2(BHT)(MMA) [R = Me (1), Et (2)] and AlMe-(BHT)2(MMA) (3), respectively. The molecular structure of 1 has been determined by X-ray crystallography. The decrease in the C=O and C=C stretching frequencies in the IR spectrum, and downfield shift in the 13C NMR spectrum of the - and γ-carbons of the MMA, when compared to free MMA, is presented with respect to the activator ability of sterically crowded aryloxide compounds of aluminum to aluminum-porphyrin catalyzed (Inoue) polymerization of MMA. 相似文献
59.
Y Nishioka S Kyotani M Okamura M Miyazaki Y Sakamoto M Morita K Okazaki S Ohnishi Y Yamamoto K Ito 《Chemical & pharmaceutical bulletin》1992,40(1):267-268
Hepatic artery of dogs was embolized with cisplatin (CDDP) albumin microspheres containing chitin and chitosan to investigate the in vivo CDDP release kinetics from CDDP albumin microspheres, the CDDP cumulative characteristics in the liver, and the influence of microsphere administration on hepatic tissue. Results showed that changes in blood CDDP content were dependent on CDDP albumin microsphere type and that release kinetics were better sustained when chitin was added to the microspheres or when the microspheres were treated with chitosan. In particular, the administration of CDDP in the chitin-containing CDDP chitosan albumin microspheres showed a blood CDDP content of approximately 0.26 micrograms Pt/ml 14 d after administration. The administration of chitin-containing or chitosan treated CDDP microspheres showed a CDDP content in the hepatic tissue of 0.14 to 0.23 micrograms Pt/g 28 d after administration. They also showed better control of CDDP release than those without chitin or chitosan treatment. No CDDP influence on hepatic tissue was observed. We conclude that, even in vivo, chitin and chitosan are effective embolic materials. 相似文献
60.
Sontaya Limmatvapirat Etsuo Yonemochi Toshio Oguchi Keiji Yamamoto 《Journal of inclusion phenomena and macrocyclic chemistry》1998,31(4):367-379
A complex between deoxycholic acid (DCA) and salicylic acid (SA) was prepared by grinding and coprecipitation methods. The resultant complex was characterized by means of powder X-ray diffractometry, IR spectroscopy and thermal analysis. The stoichiometry (DCA : SA 1 : 1) of the complex obtained by grinding was identical to that obtained by coprecipitation. The powder X-ray diffraction pattern of the DCA–SA complex differed from the typical pattern of DCA–guest complexes such as DCA–camphor and DCA–phenanthrene complexes. IR spectra suggested that a different kind of hydrogen bonding was formed in the crystal of the DCA–SA complex, compared with the other DCA–guest complexes. This was in good agreement with data from the crystal structure. 相似文献