全文获取类型
收费全文 | 2307篇 |
免费 | 56篇 |
国内免费 | 4篇 |
专业分类
化学 | 1654篇 |
晶体学 | 32篇 |
力学 | 38篇 |
数学 | 93篇 |
物理学 | 550篇 |
出版年
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 33篇 |
2018年 | 18篇 |
2017年 | 16篇 |
2016年 | 34篇 |
2015年 | 41篇 |
2014年 | 33篇 |
2013年 | 169篇 |
2012年 | 95篇 |
2011年 | 115篇 |
2010年 | 61篇 |
2009年 | 70篇 |
2008年 | 108篇 |
2007年 | 136篇 |
2006年 | 137篇 |
2005年 | 117篇 |
2004年 | 116篇 |
2003年 | 110篇 |
2002年 | 93篇 |
2001年 | 49篇 |
2000年 | 62篇 |
1999年 | 39篇 |
1998年 | 38篇 |
1997年 | 30篇 |
1996年 | 27篇 |
1995年 | 28篇 |
1994年 | 23篇 |
1993年 | 34篇 |
1992年 | 30篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 35篇 |
1984年 | 36篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 28篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1978年 | 31篇 |
1977年 | 28篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1974年 | 19篇 |
1972年 | 11篇 |
1969年 | 13篇 |
排序方式: 共有2367条查询结果,搜索用时 265 毫秒
101.
3,4-Dhydro-6,7-dimethoxy-4-methyl-3-oxo-quinoxaline-2-carbonyl azide is a highly senstive fluorescence derivatization reagent for primary, secondary and tertiary alcohols for high-performance liquid chromatography. Reaction conditions are optimized with benzyl alcohol, n-hexanol, cyclohexanol and 2-methyl-2-butanol. The reagent reacts with the alcohols in benzene to produce the corresponding fluorescent carbamic acid esters, which can be separated on a reversed-phase column YMC Pack C8 with aqueous methanol as eluent. the detection limits for the alchols are 2–5 fmol per 10-μl njection. The reagent also reacts with hydroxysteroids with primary, secondary and/or tertiary alcoholic group(s) to form fluorescent derivatives. Hydroxycarboxylic acids and phenols do not give any chromatographic peaks. 相似文献
102.
Moriya Y Hasegawa T Hayashi K Maruyama M Nakata S Ogawa N 《Analytical and bioanalytical chemistry》2003,376(3):374-378
Visible reflection spectra of diprotonated meso-tetraphenylporphyrin adsorbates spontaneously formed at a dodecane-aqueous sulfuric acid interface have been measured using a home-made device comprising a prism-cell and variable-angle optics. The tilt angle of the pyrrole ring plane was estimated to be 47 degrees from the interface normal by use of an experimentally evaluated molecular density (1.20x10(-10) mol cm(-2)) of the diprotonated molecule in a monolayer form at the liquid-liquid interface. Positive and negative bands have been observed in the p-polarized partial internal reflection (p-PIR) spectra, whose band locations correspond to those in p-polarized external reflection (p-ER) spectra. Nevertheless, the bands in the p-PIR exhibited reversed sign to those of p-ER spectra. These suggest that the surface selection rule of the p-PIR spectrometry has a reversal rule of p-ER and p-PIR can also be used for the analysis of molecular orientation. 相似文献
103.
Marumo A Kumazawa T Lee XP Fujimaki K Kuriki A Hasegawa C Sato K Seno H Suzuki O 《Journal of AOAC International》2005,88(6):1655-1660
Seven phenothiazine derivatives, perazine, perphenazine, prochlorperazine, propericiazine, thioproperazine, trifluoperazine, and flupentixol, have been found to be extractable from human plasma and urine samples using disk solid-phase extraction (SPE) with an Empore C18 cartridge. Human plasma and urine (1 mL each) containing the 7 phenothiazine derivatives were mixed with 2 mL of 0.1M NaOH and 7 mL distilled water and then poured into the disk SPE cartridges. The drugs were eluted with 1 mL chloroform- acetonitrile (8 + 2) and determined by liquid chromatography with ammonium formate/formic acid-acetonitrile gradient elution. The detection was performed by ultraviolet absorption at 250 nm. The separation of the 7 phenothiazine derivatives from each other and from impurities was generally satisfactory using a SymmetryShield RP8 column (150 x 2.1 mm id, 3.5 microm particle size). The recoveries of the 7 phenothiazine derivatives spiked into plasma and urine samples were 64.0-89.9% and 65.1-92.1%, respectively. Regression equations for the 7 phenothiazine derivatives showed excellent linearity, with detection limits of 0.021-0.30 microg/mL for plasma and 0.017-0.30 microg/mL for urine. The within-day and day-to-day coefficients of variation for both samples were commonly below 9.0 and 14.9%, respectively. 相似文献
104.
Satoru Hommura Yasuhiro Kunisa Ichiro Terada Masaru Yoshitake 《Journal of fluorine chemistry》2003,120(2):151-155
Characteristics of fibril reinforced membranes developed by Asahi Glass Company are reviewed. PTFE-fibrils <1 μm in diameter are dispersed in ion-exchange membranes uniformly. Mechanical properties, such as tensile strength, tear strength, creep property and compressive property were examined and compared with non-reinforced membranes. Fibril reinforced membranes, even by the addition of a small amount of PTFE-fibrils (2.7 wt.%), show excellent mechanical strength, especially in creep and tear strength. Cell performance is nearly equal to the one using a non-reinforced membrane and cell voltage stays about the same during the cell operation at 80 °C for 3000 h. 相似文献
105.
Chen A Kamata K Nakagawa M Iyoda T Haiqiao Wang H Li X 《The journal of physical chemistry. B》2005,109(39):18283-18288
We have recently demonstrated a one-step process to fabricate silver-polypyrrole (PPy) coaxial nanocables (Chen, A.; Wang, H.; Li, X. Chem. Commun. 2005, 14, 1863). The formation process of silver-PPy coaxial nanocables is discussed in this article. It was found from the results of TEM and SEM images that large numbers of silver atoms were formed when AgNO3 was added to a pyrrole solution. Then silver atoms transform to silver-PPy nanosheets with regular morphology, which will connect together to be more stable. Silver-PPy nanocables will be able to grow at the expense of the silver-PPy nanosheets. Poly(vinylpyrrolidone) (PVP) plays crucial roles in this process: as a capping agent to form silver nanowires, and as a dispersant of pyrrole monomers, which can influence the site at which pyrrole monomer exists. On the basis of experimental analysis, the possible mechanism was proposed. Because of the effect of PVP, silver ions and pyrrole monomers are apt to be adsorbed at the [111] and [100] facets of silver nanosheets, respectively. Obvious polymerization will take place on the boundary of the [111] and [100] facets. The PPy layer stays stable on the [100] facets. Meanwhile, newly formed silver atoms and silver nanosheets will further ripen and grow on the [111] facets. In a word, the morphology of final products and the formation process are determined by the reaction site between AgNO3 and the pyrrole monomer, which is influenced by PVP. 相似文献
106.
Hidetsura Cho Yoshiko Ohnaka Mariko Hayashimatsu Masaru Ueda Keiyuu Shima 《Tetrahedron letters》1986,27(52):6377-6380
Chlorination of 5,6-dihydropyrimidine-4-(3H)-one derivatives (1) with POCl3 gave 1,4(3,4)-dihydropyrimidines (3), whose alkoxycarbonylation (ClCOOREt3N or NaH) afforded regioselectively novel compounds (4). A new Pummerer
rearrangement of compound (1, X=
---S(O)CH3) with
3, gave compound (5h). 相似文献
107.
108.
109.
110.