全文获取类型
收费全文 | 4254篇 |
免费 | 92篇 |
国内免费 | 6篇 |
专业分类
化学 | 2800篇 |
晶体学 | 43篇 |
力学 | 98篇 |
数学 | 555篇 |
物理学 | 856篇 |
出版年
2023年 | 22篇 |
2022年 | 63篇 |
2021年 | 97篇 |
2020年 | 81篇 |
2019年 | 69篇 |
2018年 | 102篇 |
2017年 | 103篇 |
2016年 | 116篇 |
2015年 | 125篇 |
2014年 | 121篇 |
2013年 | 231篇 |
2012年 | 280篇 |
2011年 | 297篇 |
2010年 | 186篇 |
2009年 | 170篇 |
2008年 | 240篇 |
2007年 | 229篇 |
2006年 | 181篇 |
2005年 | 356篇 |
2004年 | 287篇 |
2003年 | 208篇 |
2002年 | 92篇 |
2001年 | 68篇 |
2000年 | 56篇 |
1999年 | 40篇 |
1998年 | 31篇 |
1997年 | 34篇 |
1996年 | 33篇 |
1995年 | 24篇 |
1994年 | 30篇 |
1993年 | 21篇 |
1992年 | 24篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 12篇 |
1968年 | 6篇 |
1957年 | 6篇 |
1956年 | 26篇 |
1955年 | 18篇 |
排序方式: 共有4352条查询结果,搜索用时 15 毫秒
151.
152.
153.
Sim E 《The journal of physical chemistry. B》2005,109(23):11829-11835
The effect of the energy gap between donor and bridge states in the electron transfer of a double mutant photosynthetic purple bacterial reaction center is thoroughly investigated using a recently introduced modified on-the-fly filtered propagator important path integral formalism. By decomposition of the reduced density matrix of a system coupled to a dissipative environment, partial contributions of incoherent hopping, coherent superexchange, and partially coherent hopping transport to the overall electron or charge transfer are evaluated. Within the tight-binding donor-bridge-acceptor model, the three mechanisms coexist for a wide range of donor-bridge energy gap values, and the governing mechanism changes from incoherent hopping to partially coherent hopping and eventually to coherent superexchange as the donor-bridge energy gap becomes large. 相似文献
154.
The accuracy, precision, and reproducibility of a rapid method for determination of fluoride in wine, using a fluoride selective ion electrode, were established by a collaborative study involving 12 laboratories, 5 in Europe and 7 in the United States. The laboratories assayed 6 Youden pairs of fluoride-fortified, red and white wine samples with fluoride concentrations ranging from 0.2 to 3.0 mg/L. The relative standard deviations of repeatability ranged from 1.94 to 4.88%; relative standard deviations of reproducibility ranged from 4.15 to 18.40%. HORRAT values ranged from 0.30 to 0.97. The average recovery was 99.97%. Based on the statistical results of this collaborative study, the Study Director recommends that this method be adopted First Action. 相似文献
155.
Isolation of teratogenic alkaloids by reversed-phase high-performance liquid chromatography 总被引:1,自引:0,他引:1
Reversed-phase high-performance liquid chromatography was used for both analytical and preparative separations of several steroidal alkaloids which occur in extracts of Veratrum californicum. The inclusion of 0.1% trifluoroacetic acid in the mobile phase improved the efficiency of the chromatography and the solubility of the compounds in aqueous acetonitrile. Nuclear magnetic resonance was used to assist the identification of the isolated steroidal alkaloids. The effect of the interaction of trifluoroacetic acid with the alkaloids could be clearly seen by changes in the chemical shifts in the nuclear magnetic resonance spectra. 相似文献
156.
Doménech-Carbó A Doménech-Carbó MT Saurí-Peris MC Gimeno-Adelantado JV Bosch-Reig F 《Analytical and bioanalytical chemistry》2003,375(8):1169-1175
An electrochemical method for identifying anthraquinone-type dyes in microsamples from works of art, based in the voltammetry of microparticles approach, is reported. Upon attachment onto graphite/polyester composite electrodes, natural pigments aloe, henna, cochineal red, madder lake, kermes, shellac, and alizarin and purpurin taken as reference materials can be identified from their square wave voltammetric profiles in MeCN (0.10 mol L(-1) Bu(4)NPF(6)) and aqueous (0.25 mol L(-1) acetic acid+0.25 mol L(-1) sodium acetate) electrolytes. 相似文献
157.
W. H. S. Brandão A. L. Aguiar L. A. Ribeiro D. S. Galvão J. M. De Sousa 《Chemphyschem》2021,22(7):701-707
Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( and ) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( ). Moreover, it was obtained that Young's modulus (YMod) (750–900 GPa) and ultimate strength (σUS) (120–150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. YMod values obtained for PopNTs are not significantly temperature-dependent. While the σUS values for the showed a quasi-linear dependence with the temperature, the exhibited no clear trends. 相似文献
158.
San Vicente B Navarro Villoslada F Moreno-Bondi MC 《Analytical and bioanalytical chemistry》2004,380(1):115-122
A bisphenol A (BPA) molecularly imprinted polymer, the composition of which was optimised using a chemometric approach, has been applied to the selective preconcentration of the template from aqueous samples. The selectivity of the polymer toward BPA and related compounds was evaluated chromatographically. The BPA-imprinted polymer was packed in a column and used for continuous on-column solid-phase extraction (MISPE) of aqueous samples followed by subsequent analysis by HPLC with fluorescence detection of the eluted fractions. The composition of the washing solvent applied in the MISPE procedure was optimised to favour the specific interactions of the MIP with BPA and to remove the non-selectively bound matrix components. The MISPE method has proven to be effective for selective preconcentration of BPA in aqueous samples (recoveries >84% obtained in the eluate for 10–100 mL sample volumes) enabling detection and quantification limits of 1.0 and 3.3 ng mL–1, respectively (based on 25 mL sample size). Analytical recoveries were between 92 and 101% for river water samples spiked with known amounts of BPA (30, 60, and 80 ng mL–1); relative standard deviations (RSD) were lower than 5.0%. 相似文献
159.
Shiro Kubuki Hitomi Masuda Koken Matsuda Kazuhiko Akiyama Ayuko Kitajo Shigeto Okada Péter Zsabka Zoltán Homonnay Ernõ Kuzmann Tetsuaki Nishida 《Hyperfine Interactions》2014,226(1-3):765-770
Charge-discharge capacity and cyclicity of lithium ion battery (LIB) was evaluated in which 15Li2O·10Fe2O3·xSnO2·5P2O5·(70–x)V2O5 glass (x?=?0 and 20 in mol%, abbreviated as xLFSPV) was used as a cathode. A local structure of xLFSPV glass before and after charging was investigated by 57Fe- and 119Sn-Mössbauer spectroscopies. 57Fe-Mössbauer spectrum of xLFSPV glass with ‘x’ of 20 was composed of a doublet with isomer shift (δ) of 0.35±0.02 mm s???1 and quadrupole splitting (Δ) of 0.88±0.03 mm s???1 due to distorted FeIIIO4 tetrahedra. 119Sn-Mössbauer spectrum of this glass consisted of a doublet with δ of 0.08±0.01 and Δ of 0.52±0.01 mms???1 due to distorted SnVIO6 octahedra. After discharging the battery from 4.5 to 1.0 V, larger δ of 0.40±0.03 mm s???1 and Δ of 0.94±0.04 mm s???1 were obtained, indicating that both iconicity of Fe-O bonds and local distortion of FeIIIO4 tetrahedra were increased. On the contrary, identical δ of 0.09±0.01 mm s???1 and Δ of 0.50±0.01 mm s???1 were observed in the 119Sn-Mössbauer spectrum of 20LFSPV glass after the discharge, indicating that chemical environment of SnIVO6 octahedra was not affected after the discharge. Charge-discharge curve of LIB containing 20LFSPV glass as a cathode active material recorded under the current density of 8.3 mA g???1 (0.011 mA cm???2) between 1.0 and 4.5 V showed a large initial charge capacity of 431.1 mAh g???1 and discharge capacity of 382.3 mAh g???1, respectively. These results indicate that 20LFSPV glass could be a new cathode active material for LIB. 相似文献
160.