全文获取类型
收费全文 | 4631篇 |
免费 | 138篇 |
国内免费 | 16篇 |
专业分类
化学 | 3556篇 |
晶体学 | 39篇 |
力学 | 73篇 |
综合类 | 1篇 |
数学 | 174篇 |
物理学 | 942篇 |
出版年
2022年 | 29篇 |
2021年 | 42篇 |
2020年 | 50篇 |
2019年 | 52篇 |
2018年 | 39篇 |
2017年 | 42篇 |
2016年 | 71篇 |
2015年 | 83篇 |
2014年 | 88篇 |
2013年 | 210篇 |
2012年 | 196篇 |
2011年 | 211篇 |
2010年 | 116篇 |
2009年 | 117篇 |
2008年 | 210篇 |
2007年 | 207篇 |
2006年 | 251篇 |
2005年 | 268篇 |
2004年 | 245篇 |
2003年 | 202篇 |
2002年 | 238篇 |
2001年 | 139篇 |
2000年 | 114篇 |
1999年 | 80篇 |
1998年 | 58篇 |
1997年 | 51篇 |
1996年 | 68篇 |
1995年 | 63篇 |
1994年 | 68篇 |
1993年 | 65篇 |
1992年 | 87篇 |
1991年 | 71篇 |
1990年 | 61篇 |
1989年 | 60篇 |
1988年 | 49篇 |
1987年 | 47篇 |
1986年 | 61篇 |
1985年 | 85篇 |
1984年 | 67篇 |
1983年 | 26篇 |
1982年 | 52篇 |
1981年 | 30篇 |
1980年 | 31篇 |
1979年 | 48篇 |
1978年 | 39篇 |
1977年 | 43篇 |
1976年 | 32篇 |
1975年 | 32篇 |
1974年 | 34篇 |
1973年 | 41篇 |
排序方式: 共有4785条查询结果,搜索用时 93 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.
The enantiodifferentiating [4+4] photocyclodimerization of anthracenecarboxylic acid (AC) mediated by native, mono- and di-3,6-anhydro-γ-cyclodextrins was investigated in both aqueous solution and solid-state. The solid-state photolyses gave inherently disfavored head-to-head photodimers in much higher chemical and optical yields than in the aqueous solution. 相似文献
55.
56.
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
57.
58.
The solubility of glycine,
-alanine,
-valine,
-leucine, and
-isoleucine in water was measured at 298.15 K and pressures up to 400 MPa. The standard deviation of the logarithm of the solubility is 0.001–0.003, equal to or better than the accuracy of atmospheric pressure measurement in the literature (0.001–0.05). A variety of solubility phenomena were observed. The solubility of glycine decreased with increasing pressure, whereas that of
-alanine increased. The
-valine and
-isoleucine have a solubility maximum at around 100 MPa, and
-leucine seems to exhibit a solid-phase phase transition at around 200 MPa. Pressure coefficient of the solubilities at 0.10 MPa is compared with that thermodynamically estimated in reference to aqueous density measurements of glycine and
-alanine at 298.15 K and 0.10 MPa, supporting a reliability of our high-pressure measurements. 相似文献
59.
60.
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