全文获取类型
收费全文 | 525篇 |
免费 | 21篇 |
专业分类
化学 | 389篇 |
晶体学 | 11篇 |
力学 | 12篇 |
数学 | 29篇 |
物理学 | 105篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 33篇 |
2011年 | 25篇 |
2010年 | 23篇 |
2009年 | 19篇 |
2008年 | 32篇 |
2007年 | 40篇 |
2006年 | 27篇 |
2005年 | 24篇 |
2004年 | 31篇 |
2003年 | 31篇 |
2002年 | 25篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1985年 | 6篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有546条查询结果,搜索用时 15 毫秒
101.
102.
A physical mixture of polymer‐protected Ag nanoparticles and Rh, Pd, or Pt nanoparticles spontaneously forms Ag‐core bimetallic nanoparticles. The formed nanoparticles were smaller than the parent Ag nanoparticles. In the initial process of this reaction, the surface plasmon absorption of Ag nanoparticles diminished and then almost ceased within one hour. Within several minutes, the decrease in Ag surface plasmon absorption could be analyzed by second‐order reaction. This reaction was accelerated with an increase of temperature and the energy gap in the Fermi level between Ag and the other metals. The activation energy (Ea) of this reaction could be determined. An electron transfer reaction from Ag to other metal nanoparticles was proposed as the initial interaction between these metal nanoparticles because the Fermi level of Ag is relatively high, and the electron transfer is possible in terms of energy. The Marcus plot between the rate constant and the driving force, roughly estimated from the work function of metals, and the observed Ea values reasonably explained the proposed electron transfer mechanism. 相似文献
103.
Silver‐Catalyzed Efficient Synthesis of Oxindoles and Pyrroloindolines via α‐Aminoalkylation of N‐Arylacrylamides with Amino Acid Derivatives
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
α‐Aminoalkylation of N‐arylacrylamides with amino acid derivatives was achieved by silver‐catalysis in moderate to high yields. The reaction provides an efficient strategy for the synthesis of functionalized oxindoles, and is suitable for a wide range of N‐arylacrylamides and amino acids, both of which are inexpensive and readily available. The oxindoles obtained were readily transformed into densely functionalized pyrroloindolines by deprotection and cyclization in one pot. 相似文献
104.
Chetiyanukornkul T Toriba A Kizu R Makino T Nakazawa H Hayakaw K 《Journal of chromatography. A》2002,961(1):107-112
A high-performance liquid chromatographic method has been developed for the quantification of 1-hydroxypyrene (1-OHP) in human urine using deuterated 1-hydroxypyrene ([2H9]1-OHP) as an internal standard with fluorescence detection. [2H9]1-OHP was prepared enzymatically from deuterated pyrene ([2H10]Pyr) with cytochrome P450 1A1. It eluted immediately prior to non-deuterated 1-OHP on alkylamide-type reversed-phase columns and had nearly the same fluorescence characteristics as non-deuterated 1-OHP. The detection limit was 0.1 microg/L and the calibration range was from 1 to 100 nmol/L. Urine sample treatment involved enzymatic hydrolysis followed by solid-phase extraction using Sep-Pak C18 cartridges. The proposed method was used to determine urinary 1-OHP in smokers and non-smokers. 相似文献
105.
The iron-catalyzed Kirmse reaction was used to generate neopentyl alpha-silyl thioethers that were elaborated to meroterpenes using two complementary routes: one route involved a sila-Pummerer rearrangement, and the other route involved a Peterson olefination. While severe eclipsing interactions undermined the efficiency of the stereospecific sila-Pummerer rearrangement, they made it possible to stereoselectively generate E olefins without isolation or separation of syn- and anti-beta-silyl alkoxides. Addition of a neopentyl alpha-silyl alkyllithium intermediate to an aryl aldehyde generated a mixture of syn- and anti-beta-silyl alkoxides. The syn-beta-silyl alkoxide eliminated stereospecifically at -78 degrees C to give an E olefin, whereas the anti-beta-silyl alkoxide was unreactive. The reaction mixture was then acidified and heated to induce stereospecific elimination of the anti isomer to give the same E olefin via a complementary cationic pathway. This route was used to complete the first synthesis of the meroterpene (+/-)-3-hydroxybakuchiol. In addition, we synthesized another meroterpene corresponding to the natural product corylifolin and offer evidence that the structure of corylifolin was misassigned. 相似文献
106.
Therapeutic drug monitoring of anti-inflammatory drugs is necessary for the identification of the agents that cause toxic events and for the decision on the treatment for intoxication. Recently, capillary electrophoresis (CE) has been developed for the simple and rapid analyses of a variety of chemical agents. Micellar electrokinetic chromatography (MEKC) can separate acidic, neutral and basic anti-inflammatory drugs in serum. Furthermore, serum samples are directly applied to the CE system without any pretreatments, and some anti-inflammatory drugs can be separated from serum albumin in the MEKC analysis. On the other hand, capillary zone electrophoresis (CZE) enables us to determine a few microg/mL levels of acidic anti-inflammatory drugs with simple running buffer and stacking technique. A rapid and simultaneous determination of several analgesic anti-inflammatory agents, including ibuprofen, acetaminophen, indomethacin, and salicylic acid in human serum has been developed by using CZE. Therefore, the CZE and MEKC analysis may become a potentially useful alternative to high-performance liquid chromatography (HPLC) and fluorescence polarization immunoassay (FPIA) for therapeutic drug monitoring, particularly in serum of patients suffering from intoxication by overdosage of nonsteroidal anti-inflammatory agents. 相似文献
107.
Katsufumi Tanaka Hyota Nakahori Kazutaka Katayama Ryuichi Akiyama 《Colloid and polymer science》2007,285(11):1201-1211
The linear viscoelastic properties of a suspension composed of titanium dioxide nanoparticles were measured under the direct
current (dc) electric field with narrow gap distances between the electrodes. The yielding behavior under no external electric
fields was also discussed. The wall slip at the interface between the parallel plates and the nano-suspension was briefly
discussed. Under the dc electric field, a fine chain-like microstructure was optically found within a narrow gap of 50 μm
between the electrodes in the quiescent state. The nano-suspension confined to a narrow gap of 65 μm between the parallel
plates was rather viscoelastic even at the highest strength of the electric field of 16 kV·mm−1. Furthermore, fast and slow relaxations of the dynamic moduli were found after removal of the electric field. It was pointed
out that the linear viscoelasticity was an appropriate measure of the microstructure before yielding. 相似文献
108.
Kimiko Makino Junya Tabata Tatsuya Yoshioka Minoru Fukuda Masahiko Ikekita Hiroyuki Ohshima Hiroshi Terada 《Colloids and surfaces. B, Biointerfaces》2003,29(4):277-284
The purpose of this work is to know the effect of surface properties of liposomes on their phagocytic uptake by macrophages. For this, liposomes were prepared by the Bangham technique from the mixture of phosphatidylcholine (PC) and cholesterol (Chol) incorporated either with phosphatidylserine (PS), phosphatidylethanolamine (PE) or phosphatidic acid (PA). The liposomes thus prepared had diameters in the range between 150 and 260 nm. Electric surface properties of the liposomes and the macrophages differentiated from HL-60RG cells were determined by measuring their electrophoretic mobilities. The phagocytic uptake of liposomes with different contents of PS, PE and PA by macrophage-like HL-60RG cells was investigated by measuring oxygen consumption associated with phagocytic uptake. The phagocytic activity was found to be the highest with the PC–Chol liposomes containing 7 mol% PS, but no significant effects were observed with PA- and PE-containing PC–Chol liposomes. As the uptake was independent of the electric surface property of liposomes, PS was concluded to be specifically important for phagocytic activity of macrophages. 相似文献
109.
A HPLC method is described in order to separate and identify 4 phenolic compounds including lithospermic acid B, 3,4-dihydroxyphenyllactic acid (danshensu), rosmarinic acid, and protocatechuic aldehyde as well as 3 lipophilic ones (tanshinone I, tanshinone II(A) and cryptotanshinone) from the roots of Salvia miltiorrihiza or the herbal product containing S. miltiorrihiza available in Chinese or Japanese market. The influence of extractive conditions, such as method, solvents and time, on the 4 phenolic marker components in S. miltiorrihiza is well discussed. In order to investigate the stability of lithospermic acid B, the preparation samples of an injection and a granule were analyzed after being stored at 4 degrees C, 20 degrees C and 40 degrees C for up to six months. 相似文献
110.
Yoshimatsu K Kiuchi F Shimomura K Makino Y 《Chemical & pharmaceutical bulletin》2005,53(11):1446-1450
A rapid and reliable solid-phase extraction method for HPLC analysis of opium alkaloids from Papaver plants was established. Fifty mg of dried and powdered plant sample was extracted with 5 ml of 5% acetic acid for 30 min under sonication. After centrifugation, 3 ml of the supernatant was loaded on a reversed-phase cation-exchange solid-phase extraction cartridge. After seriate washings with 0.1 M hydrochloric acid and methanol, alkaloids were eluted with a mixture of 28% ammonia and methanol (1:19). The eluate was concentrated under nitrogen stream at 40 degrees C and the residue was dissolved in 50% aqueous methanol for high performance liquid chromatographic analysis. With this solid-phase extraction method, the recovery of morphine, codeine, oripavine, thebaine, papaverine, noscapine and sanguinarine was from 99.94 to 112.18% when the standard alkaloids were added to the plant samples. Opium alkaloids of a variety of genus Papaver plants cultivated in a field and phytotron were analyzed by this method. 相似文献