全文获取类型
收费全文 | 1645篇 |
免费 | 65篇 |
国内免费 | 3篇 |
专业分类
化学 | 1364篇 |
晶体学 | 15篇 |
力学 | 20篇 |
数学 | 120篇 |
物理学 | 194篇 |
出版年
2023年 | 6篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 21篇 |
2018年 | 21篇 |
2017年 | 9篇 |
2016年 | 42篇 |
2015年 | 39篇 |
2014年 | 44篇 |
2013年 | 81篇 |
2012年 | 72篇 |
2011年 | 94篇 |
2010年 | 65篇 |
2009年 | 35篇 |
2008年 | 88篇 |
2007年 | 68篇 |
2006年 | 84篇 |
2005年 | 72篇 |
2004年 | 79篇 |
2003年 | 94篇 |
2002年 | 77篇 |
2001年 | 25篇 |
2000年 | 54篇 |
1999年 | 25篇 |
1998年 | 18篇 |
1997年 | 25篇 |
1996年 | 26篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 6篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 22篇 |
1984年 | 23篇 |
1983年 | 11篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 29篇 |
1979年 | 29篇 |
1978年 | 23篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1968年 | 5篇 |
排序方式: 共有1713条查询结果,搜索用时 15 毫秒
131.
132.
Shigeru Ohba Makoto Eishima 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):e557-e558
In the title compound, trans‐[CoCl(NO2)(C2H8N2)2]NO3, a distorted octahedral CoIII complex shows an orientational disorder such that the positions of the nitro and chloro ligands are exchanged. The occupation factors of the major and minor orientations are 84 and 16%, respectively. The O atoms of the nitrate ion are disordered over two sites. 相似文献
133.
Nabajyoti Saikia Shigeru Kato Toshinori Kojima 《Journal of Thermal Analysis and Calorimetry》2012,109(1):273-286
Tricalcium aluminate (Ca3Al2O6, C3A) containing 0?C5% of Sn was synthesized by solid-state method, and the products were characterized by XRD technique. Differential thermo-analytical technique (DTA) along with X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were applied to study the hydration behaviour of different C3A samples with and without the presence of gypsum. Results indicate that C3A can accommodate small amount of Sn in its structure and remaining amount forms SnO2. Hydration studies of the synthesized C3A shows that the additions of 0.5 and 1% Sn increase and 2% Sn decrease the reactivity of C3A at the initial period (<3?h) of hydration. Increasing additions of Sn also increase the amounts of amorphous phases and hexagonal calcium aluminate hydrates in the cement pastes. The stabilities of these hydration products also increase with increasing content of Sn in C3A at the experimental conditions. The presence of Sn significantly changes the hydration of C3A and gypsum solid mixture at the initial period of hydration by enhancing the formation of more amounts of AFt and AFm phases. However, at the later stage of hydration (on or after 3?days), the hydration products in C3A and gypsum pastes with and without the presence of Sn are almost similar. 相似文献
134.
We consider a convex polygonal heat conductor whose inscribed circle touches every side of the conductor. Initially, the conductor
has constant temperature and, at every time, the temperature of its boundary is kept at zero. The hot spot is the point at
which temperature attains its maximum at each given time. It is proved that, if the hot spot is stationary, then the conductor
must satisfy two geometric conditions. In particular, we prove that these geometric conditions yield some symmetries provided
the conductor is either pentagonal or hexagonal.
This research was partially supported by Grants-in-Aid for Scientific Research (B) (# 12440042) and (B) (# 15340047) of Japan
Society for the Promotion of Science, and by a Grant of the Italian MURST. 相似文献
135.
136.
Background
BIR family proteins are evolutionarily conserved anti-apoptotic molecules. One member of Xenopus BIR family proteins, xEIAP/XLX, is a weak apoptosis inhibitor and rapidly degraded in a cell-free apoptotic execution system derived from interphase egg extracts. However, unfertilized eggs are naturally arrested at the metaphase of meiosis II by the concerted activities of Mos-MEK-p42MAPK-p90Rsk kinase cascade (cytostatic factor pathway) and many mitotic kinases. Previous studies suggest that cytostatic factor-arrested egg extracts are more resistant to spontaneous apoptosis than interphase egg extracts in a p42MAPK-dependent manner. We tested whether xEIAP/XLX might be phosphorylated in cytostatic factor-arrested egg extracts, and also examined whether xEIAP/XLX could be functionally regulated by phosphorylation. 相似文献137.
The toxic properties of arsenic are well known. Honey has been widely used for monitoring this element. The present work reports a novel method for the determination of arsenic in honey, bees, pollen, and propolis, based on the coupling of microwave digestion and hydride generation. Method development included the quantitative reduction of arsenic(V) to arsenic(III), the acid used for dilution, and the complete removal of the gases following digestion. The method performance was satisfactory with recoveries between 83% and 111% and corresponding relative standard deviations between 3.1% and 24%. Among the 32 samples of honey, propolis, pollen, and honey bees analyzed, arsenic was detected in four out of six propolis samples at the method limit of detection (0.4?µg?g?1). The results indicate that propolis may be an efficient indicator for arsenic. 相似文献
138.
Ali Khumaeni Masahiko Tani Kazuyoshi Kurihara Kiichiro Kagawa Hideaki Niki 《Analytical letters》2017,50(12):1992-1999
A novel method of laser-induced plasma spectroscopy utilizing a pulsed transversely excited atmospheric CO2 laser has been developed for the high-sensitivity determination of heavy metals in soil. A coarse metal powder was used to trap the soil and to assist with plasma generation. When the CO2 laser (10.6?µm, 1.5?J, 200?ns) was irradiated on the metal and soil powder, a high-temperature and long-lifetime luminous plasma was induced. Fine particles of soil were dissociated and were excited in the plasma region. The method was used for the rapid determination of Cr, Pb, and Hg in loam. The limits of detection for Cr, Pb, and Hg were approximately 0.8, 15, and 0.7?mg/kg, respectively. 相似文献
139.
Harada T Ikeda S Hashimoto F Sakata T Ikeue K Torimoto T Matsumura M 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):17720-17725
A core-shell composite consisting of a palladium (Pd) nanoparticle and a hollow carbon shell (Pd@hmC) was employed as a catalyst for aerobic oxidation of various alcohols. The core-shell structure was synthesized by consecutive coatings of Pd nanoparticles with siliceous and carbon layers followed by removal of the intermediate siliceous layer. Structural characterizations using TEM and N(2) adsorption-desorption measurements revealed that Pd@hmC thus-obtained was composed of a Pd nanoparticle core of 3-6 nm in diameter and a hollow carbon shell with well-developed mesopore (ca. 2.5 nm in diameter) and micropore (ca. 0.4-0.8 nm in diameter) systems. When compared to some Pd-supported carbons, Pd@hmC showed a high level of catalytic activity for oxidation of benzyl alcohol into benzaldehyde using atmospheric pressure of O(2) as an oxidant. The Pd@hmC composite also exhibited a high level of catalytic activity for aerobic oxidations of other primary benzylic and allylic alcohols into corresponding aldehydes. The presence of a well-developed pore system in the lateral carbon shell enabled efficient diffusion of both substrates and products to reach the central Pd nanoparticles, leading to such high catalytic activities. This core-shell structure also provided high thermal stability of Pd nanoparticles toward coalescence and/or aggregation due to the physical isolation of each Pd nanoparticle from neighboring particles by the carbon shell: this specific property of Pd@hmC resulted in possible regeneration of catalytic activity for these aerobic oxidations by a high-temperature heat treatment of the sample recovered after catalytic reactions. 相似文献
140.
Hidetaka Tsujimoto Hotaka Asuka Shigeru Ikawa Hiroyuki Nakazumi 《Journal of organometallic chemistry》2010,695(17):1972-10838
In order to develop highly emissive red phosphorescent materials for OLED application, novel bis-cyclometalated iridium(III) complexes were developed using the 1-(dibenzo[b,d]furan-4-yl)isoquinolinato-N,C3′ (dbfiq) cyclometalating ligand. When 1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dionate (bdbp) is employed as an ancillary ligand, Ir(dbfiq)2(bdbp) 1 exhibits red photoluminescence (PL) at 640 nm with a quantum yield (ΦPL) of 0.61 (in toluene, 298 K). Replacement of bdbp to dipivaloylmethanate (dpm) and acetylacetonate (acac) (Ir(dbfiq)2(dpm) 2 and Ir(dbfiq)2(acac) 3, respectively) does not affect the PL spectrum, but reduces ΦPL to 0.55 and 0.49 for 2 and 3, respectively. Similar tendency is also found in the doped poly(methyl methacrylate) (PMMA) film, and 1 is more emissive (ΦPL = 0.17) than 2 and 3 (ΦPL = 0.08 and 0.06, respectively). Using 1 as a phosphorescent dopant, polymer light-emitting diodes (PLEDs) were fabricated, of which structure was ITO/PEDOT:PSS (40 nm)/PVCz:1:PBD (100 nm)/CsF (1 nm)/Al (250 nm). Pure red electroluminescence (EL) is obtained from the fabricated PLEDs, affording a CIE chromaticity coordinate of (0.68, 0.31). When 0.51 mol% of 1 is incorporated in the PVCz-based emitting layer, the PLED shows maximum luminance of 7270 cd m−2 at 16.5 V, power efficiency of 1.4 lm W−1 at 7.5 V, and external quantum efficiency of 6.4% at 9.0 V. PLEDs with the same structure and components were also fabricated using 2 and 3, and their device characteristics were investigated. In proportion to the PL quantum yields, 1 affords better device performance than 2 and 3. Owing to four butoxy groups introduced to the bdbp ligand, 1 exhibits high solubility in organic solvents such as chloroform and toluene, and thus, is an excellent red phosphorescent dopant for solution-processed OLEDs. 相似文献