全文获取类型
收费全文 | 4296篇 |
免费 | 1060篇 |
国内免费 | 382篇 |
专业分类
化学 | 1079篇 |
晶体学 | 57篇 |
力学 | 273篇 |
综合类 | 36篇 |
数学 | 158篇 |
物理学 | 4135篇 |
出版年
2024年 | 7篇 |
2023年 | 37篇 |
2022年 | 65篇 |
2021年 | 99篇 |
2020年 | 115篇 |
2019年 | 74篇 |
2018年 | 102篇 |
2017年 | 120篇 |
2016年 | 150篇 |
2015年 | 94篇 |
2014年 | 177篇 |
2013年 | 691篇 |
2012年 | 222篇 |
2011年 | 302篇 |
2010年 | 233篇 |
2009年 | 305篇 |
2008年 | 308篇 |
2007年 | 287篇 |
2006年 | 273篇 |
2005年 | 258篇 |
2004年 | 215篇 |
2003年 | 190篇 |
2002年 | 220篇 |
2001年 | 140篇 |
2000年 | 144篇 |
1999年 | 110篇 |
1998年 | 135篇 |
1997年 | 94篇 |
1996年 | 77篇 |
1995年 | 64篇 |
1994年 | 62篇 |
1993年 | 81篇 |
1992年 | 64篇 |
1991年 | 44篇 |
1990年 | 36篇 |
1989年 | 26篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 15篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1973年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有5738条查询结果,搜索用时 46 毫秒
131.
有机硅化合物是半导体工业中产生硅元件的基本原料和有机合成中的重要试剂,是多年来大家研究较多的分子体系之一.本文报导了用同步辐射加速器产生的真空紫外光,电离St(CH3hCI。分子.在50-120n-m波长范围内,测量了各种离子产物与真空紫外光波长的关系,推算得它的绝热电离电势和离子中几个化学键的键能.1实验装置和方法本工作在国家同步辐射实验室光化学实验站进行.进行分子真空紫外光电离研究的实验系统已在文献山中详细描述.同步辐射加速器产生的真空紫外光波长用Ne气的电离势标定,其误差<士0-Inln.单色仪的分辨率为河凸… 相似文献
132.
A series of superabsorbent hydrogels were prepared from carrageenan and partially neutralized acrylic acid by gamma irradiation at room temperature. The gel fraction, swelling kinetics and the equilibrium degree of swelling (EDS) of the hydrogels were studied. It was found that the incorporation of even 1% carrageenan (sodium salt) increases the EDS of the hydrogels from 320 to 800 g/g. Thermal analysis were carried out to determine the amount of free water and bound water in the hydrogels. Under optimum conditions, poly(acrylic acid)–carrageenan hydrogels with high gel fraction (80%) and very high EDS (800 g/g) were prepared gamma radiolytically from aqueous solution containing 15% partially neutralized acrylic acid and 1–5% carrageenan. The hydrogels were also found to be sensitive to the pH and the ionic strength of the medium. 相似文献
133.
Araceli Vernica Flores Carlos Alberto Prez Marco Aurlio Zezzi Arruda 《Analytica chimica acta》2005,530(2):619-305
In the present work, scandium was determined in sediment slurry samples (from three different rivers) by electrothermal atomic absorption spectrometry (ETAAS). Slurries were prepared by weighting 100 mg of dry sediment samples (≤53 μm particle sizes) and adding 6 ml of HCl:HNO3:HF (3:1:2, v/v). Accurate results were only possible due to the synergetic effect between Rh as permanent chemical modifier and acetylacetone (Acac) as complexing agent. The same platform was used for 400 heating cycles. The performance of the chemical modification was evaluated by using scanning electron microscopy (SEM), synchrotron radiation X-ray fluorescence (SRXRF) and some figures of merit (precision and detectability). The best analytical conditions were attained using 1500 and 2550 °C as pyrolysis and atomization temperatures. The scandium content in the liquid phase of the slurries ranged from 61 to 73%, thus indicating, in this study, that both liquid and solid phases play an important role in slurry analyses. An amount of 5.0–20.0 μg l−1 Sc linear range as well as LOD and LOQ of 0.19 and 0.62 μg l−1, respectively, were obtained under these conditions. The accuracy was checked by using microwave-assisted decomposition, and the results compared to those obtained with the proposed methodology (slurry analysis). By checking both sets of the results, there is no statistical difference at the 95% confidence levels. 相似文献
134.
135.
The locality of underground water, contaminated with cyanides, has been successfully cleaned by using the hydraulic barrier method (assembly of pumped wells) since 1986. The average cyanide concentrations in the outflow exceeded 35 m per litre. Contamination had to be eliminated before the discharge into the sewer system. The radiation approach “in situ” i.e. decomposition of cyanides by barrier, was applied and is still being used today. The cyanide concentration was lowered more than one order of magnitude. This process was approved by the Czechoslovak radiation security authorities and further applications of “in Situ” regeneration of underground water contamination is anticipated. 相似文献
136.
A qualitative discussion on atom-surface elastic scattering taking place in the presence of laser radiation is given. It is suggested that appreciable effects of laser radiation on diffraction patterns may be expected if the laser radiation is capable of inducing electronic transitions in atoms with a large probability.Research sponsored by the Air Force Office of Scientific Research (AFSC), United States Air Force, under Contract No. F49620-78-C-0005, and the National Science Foundation under Grant No. CHE77-27826. The United States Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation hereon.Alfred P. Sloan Research Fellow, 1976–1980; Camille and Henry Dreyfus Teacher-Scholar, 1975–1980. 相似文献
137.
The absorption of millimeter electromagnetic radiation (v=1.4, 1.71, and 5 cm−1) by aqueous solutions of glycine (pH 6.1–6.2) in the concentration range of 0.5–2.5 mol L−1 was measured. It was found that the absorbing ability of the water present in the solutions, is higher than that of pure
water. This phenomenon is explained by the presence of a center of negative hydration in the structure of the glycine zwitterion,
which results in an increase in the rotational mobility of water molecules immobilized in the hydrate shell of the glycine
zwitterion.
For Part 5, see Ref. 1.
Deceased.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1305–1307, July, 1997. 相似文献
138.
Poly(N‐vinyl‐2‐pyrrolidone‐crotonic acid) [P(VP/CrA)] hydrogels were prepared by irradiating the ternary mixture of VP/CrA and crosslinking agent ethylene glycol dimethacrylate (EGDMA) in water by γ rays at ambient temperature. Differential scanning calorimetry and thermogravimetric analysis were performed to evaluate the thermal properties of ionized networks and to establish if they showed thermal differences that could be related to the CrA content in the gel system. The volume swelling ratio of P(VP/CrA) hydrogels were investigated as a function of the pH in the immersing solution. The volume swelling ratio of these hydrogels increased with an increase in pH and a decrease CrA content in the hydrogel. The volume swelling ratio of the hydrogels was also evaluated using an equation, based on the Flory—Huggins thermodynamic theory, the phantom network theory of James–Guth and Donnan theory of swelling of weakly charged ionic gels for determination of the molecular weight between crosslinks and the polymer–solvent interaction parameter (χ). Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
139.
Detailed EPR and ENDOR experiments on the cocrystalline complex of 1-methyluracil:9-Ethyladenine (MUEA) have revealed that the major radiation-induced products observed at 10 K on MU are: MUEA1, a radical formed by net hydrogen abstraction from the N1-CH3 methyl group, MUEA2, the MU radical anion, and MUEA3, the C5 H-addition radical. The following four products were observed on the adenine moiety at 10 K, MUEA4, the N3 protonated adenine anion, MUEA5, the native adenine cation, MUEA6, the amino deprotonated adenine cation, and MUEA7, the C8 H-addition radical formed by net H-addition to C8 of the adenine base. The geometries, energetics, and hyperfine properties of all possible radicals of MU and EA, the native anions and cations, as well as radicals formed via net hydrogen atom abstraction (deprotonated cations) or addition (protonated anions) were investigated theoretically. All systems were optimized using the hybrid Hartree–Fock–density functional theory functional B3LYP, in conjunction with the 6-31G(d,p) basis set of Pople and co-workers. Calculations of the anisotropic hyperfine couplings for all the radicals observed in MUEA are presented and are shown to compare favorably with the experimentally measured hyperfine couplings. The calculated ionizations potentials indicate that EA would be the preferred oxidation site. In MUEA, both the adenine cation and its N4-deprotonated derivative were observed. The calculated electron affinities indicate that MU would be the preferred reduction site. In MUEA radical, MUEA2 is a uracil reduction product, however the protonation state of this radical could not be determined experimentally. Calculations suggest that MUEA2 is actually the C4=O protonated anion. 相似文献
140.
C.L. Duarte M.N. Mori Yasko Kodama H. Oikawa M.H.O. Sampa 《Radiation Physics and Chemistry》2007,76(11-12):1885-1889
The Brazilian agriculture activities have consumed about 288,000 tons of pesticides per year conditioned in about 107,000,000 packing with weight of approximately 23,000 tons. The discharge of empty plastic packing of pesticides can be an environmental concern causing problems to human health, animals, and plants if done without inspection and monitoring. The objective of this work is to study the ionizing radiation effect in the main pesticides used in Brazil for plastic packing decontamination. Among the commercial pesticides, chlorpyrifos has significant importance because of its wide distribution and extensive use and persistence. The radiation-induced degradation of chlorpyrifos in liquid samples and in polyethylene pack was studied by gamma radiolysis. Packing of high-density polyethylene (HDPE) three layer coextruded, named COEX, contaminated with chlorpyrifos, were irradiated using both a multipurpose Co-60 gamma irradiator and a gamma source with 5000 Ci total activity Gamma cell type. The chemical analysis of the chlorpyrifos was made using a gas chromatography associated to the Mass Spectrometry—GCMS from Shimadzu Model QP 5000. Gamma radiation was efficient for removing chlorpyrifos from the plastic packing, in all studied cases. 相似文献