全文获取类型
收费全文 | 1906篇 |
免费 | 56篇 |
国内免费 | 11篇 |
专业分类
化学 | 1336篇 |
晶体学 | 13篇 |
力学 | 21篇 |
数学 | 231篇 |
物理学 | 372篇 |
出版年
2023年 | 4篇 |
2021年 | 20篇 |
2020年 | 35篇 |
2019年 | 36篇 |
2018年 | 27篇 |
2017年 | 20篇 |
2016年 | 45篇 |
2015年 | 41篇 |
2014年 | 27篇 |
2013年 | 116篇 |
2012年 | 96篇 |
2011年 | 113篇 |
2010年 | 61篇 |
2009年 | 85篇 |
2008年 | 103篇 |
2007年 | 98篇 |
2006年 | 119篇 |
2005年 | 104篇 |
2004年 | 123篇 |
2003年 | 125篇 |
2002年 | 82篇 |
2001年 | 58篇 |
2000年 | 43篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 29篇 |
1996年 | 22篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 25篇 |
1992年 | 25篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 26篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有1973条查询结果,搜索用时 78 毫秒
31.
Tatsuro Ouchi Hirotoshi Fujie Satoshi Jokei Yoshiomi Sakamoto Hidenori Chikashita Takeshi Inoi Otto Vogl 《Journal of polymer science. Part A, Polymer chemistry》1986,24(9):2059-2074
Acryloyl-type polymer fixing 1-β-carbonylethyl-5-fluorouracil residues through D -glucofuranoses via ester bonds was synthesized by means of polymerization of the corresponding monomer and polymer reaction. In order to provide the water-soluble objective polymer, the copolymerization of the acryloyl-type monomer with acrylamide was carried out. The extent of release of 5-FU residues from the copolymer was investigated in the enzyme or nonenzyme system in vitro. Furthermore, the antitumor activities of the water-insoluble homopolymer and water-soluble copolymer obtained were tested in vivo. 相似文献
32.
One of the major techniques used for the method development of ternary and quaternary high performance liquid chromatography (HPLC) systems has been to use mixture designs, often referred to as "Glajch's Triangle". This technique does not allow for the systematic and simultaneous optimization of other factors such as gradient time, pH and temperature that affect the quality of separations. An alternative approach is to use experimental designs. The condition, however, that the composition of all components of the mobile phase must total 100% presents a problem when trying to mathematically represent ranges of each mobile phase constituent of a ternary or quaternary system. A method is described here, based on spherical coordinate representations, that adheres to the constraints of the mobile phase composition and allows experimental designs, such as central composite and factorial designs, to be applied to the simultaneous optimization of the mobile phase composition. Other factors, in particular temperature and gradient time, can then be included in the design. As a result of applying these designs to the HPLC separation of phenols and corticosteroids, it was found necessary to include three-way interactions between experimental factors in the model. The significance of these interactions shows that they need to be considered in HPLC method development. 相似文献
33.
Spirodienones bearing the 1-azaspiro[4.5]decane ring system have been synthesized from N-methoxy-(4-halogenophenyl)amides by the intramolecular ipso attack of a nitrenium ion generated with [hydroxy(tosyloxy)iodo]benzene in trifluoroethanol. 相似文献
34.
Explicit expressions are presented for calculating vibration-to-translation (VT) energy conversion probabilities, essential in molecular laser isotope separation. VT conversions in molecular collisions occur by two mechanisms: (1) high-energy impact transfers prevailing at higher temperatures, and (2) Van der Waals-bonding encounters followed by (pre-)dissociations at lower temperatures. While mechanism (1) has been studied for over fifty years culminating in the Schwartz–Slawsky–Herzberg relation, a useful analytic expression for (2) has so far been lacking. An improved dimer formation theory developed by the author together with molecular pre-dissociation physics now provides a VT conversion relation for mechanism (2), which correctly predicts observations. 相似文献
35.
Paul F. Reigler Jeff Larson Lyle Bowman 《Journal of polymer science. Part A, Polymer chemistry》1981,19(12):3247-3255
The thermal and/or catalytic degradation of chloride-containing polymers causes dehydrohalogenation which produces hydrochloric acid. A nonaqueous method has been developed for the termination of hydrochloric acid. The sample is dissolved in tetrahydrofuran and titrated potentiometrically with a standard tetrabutylammonium hydroxide solution in a 7.5% (V/V) aqueous tetrahydrofuran solution with a combination glass-calomel electrode. The method has a relative precision of ±3.7% at the 95% confidence limit and a sensitivity of 25 ppm HCI. 相似文献
36.
Periodic, self-consistent, density functional theory calculations have been performed to demonstrate that subsurface oxygen (O(sb)) dramatically increases the reactivity of the Ag(111) surface. O(sb) greatly facilitates the dissociation of H2, O2, and NO and enhances the binding of H, C, N, O, O2, CO, NO, C2H2, and C2H4 on the Ag(111) surface. This effect originates from an O(sb)-induced upshift of the d-band center of the Ag surface and becomes more pronounced at higher O(sb) coverage. Our findings point to the important role that near-surface impurities, such as O(sb), can play in determining the thermochemistry and kinetics of elementary steps catalyzed by transition metal surfaces. 相似文献
37.
Shin-ichi Hirano Toshinobu Yogo Wataru Sakamoto Seiji Yamada Tomoyuki Nakamura Tomoe Yamammto Hiroyuki Ukai Kouichi Banno Tomoko Nakafuku Yukari Ando 《Journal of Sol-Gel Science and Technology》2003,26(1-3):35-41
Nano sized crystalline particles/polymer hybrids were synthesized form designed metal-organic precursors. The newly developed method is composed of the synthesis of organic matrix by polymerization and the in situ nucleation and growth of crystalline oxide particles in the organic matrix below 100°C. The design of metal-organic precursor modified with polymerizable ligand and the selection of reaction conditions does influence the size and crystallinity of ceramic particles in organic matrix. The nano-sized magnetic particle/polymer hybrid exhibits the interesting feature of superparamagnetism and quantum size effect. The crystalline particles of BaTiO3/, PbTiO3/, and KNbO3/polymer hybrids behave to be dielectric and show the typical electro-rheological behavior. 相似文献
38.
William J.?KraemerEmail author Jeff S.?Volek Barry A.?Spiering Jakob L.?Vingren 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1383-1390
Summary. Early research investigating the effects of L-carnitine supplementation has examined its role in substrate metabolism and in acute exercise performance. These studies have yielded equivocal findings, partially due to difficulties in increasing muscle carnitine concentrations. However, recent studies have proposed that L-carnitine may play a different role in exercise physiology, and preliminary results have been encouraging. Current investigations have theorized that L-carnitine supplementation facilitates exercise recovery. Proposed mechanism is as follows: 1) increased serum carnitine concentration enhances capillary endothelial function; 2) increased blood flow and reduced hypoxia mitigate the cascade of ensuing, destructive chemical events following exercise; 3) thus allowing reduced structural damage of skeletal muscle mediated by more intact receptors in muscle needed for improved protein signaling. This paradigm explains decreased markers of purine catabolism, free radical formation, and muscle tissue disruption after resistance exercise and the increased repair of muscle proteins following long-term L-carnitine supplementation. 相似文献
39.
40.