全文获取类型
收费全文 | 3562篇 |
免费 | 344篇 |
国内免费 | 93篇 |
专业分类
化学 | 3256篇 |
晶体学 | 37篇 |
力学 | 65篇 |
综合类 | 15篇 |
数学 | 11篇 |
物理学 | 615篇 |
出版年
2024年 | 12篇 |
2023年 | 47篇 |
2022年 | 68篇 |
2021年 | 123篇 |
2020年 | 166篇 |
2019年 | 114篇 |
2018年 | 87篇 |
2017年 | 80篇 |
2016年 | 144篇 |
2015年 | 154篇 |
2014年 | 135篇 |
2013年 | 341篇 |
2012年 | 266篇 |
2011年 | 179篇 |
2010年 | 143篇 |
2009年 | 175篇 |
2008年 | 155篇 |
2007年 | 212篇 |
2006年 | 191篇 |
2005年 | 154篇 |
2004年 | 162篇 |
2003年 | 148篇 |
2002年 | 116篇 |
2001年 | 89篇 |
2000年 | 57篇 |
1999年 | 68篇 |
1998年 | 58篇 |
1997年 | 50篇 |
1996年 | 40篇 |
1995年 | 35篇 |
1994年 | 27篇 |
1993年 | 30篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 6篇 |
1966年 | 2篇 |
排序方式: 共有3999条查询结果,搜索用时 28 毫秒
101.
在25℃,I=0.10 mol/L KNO3的实验条件下,用pH电位法测定了吲哚-3-乙酸(IAA)在甲醇-水混合溶剂中的质子化常数,讨论了有机溶剂对质子化常数的影响,结果表明在实验范围内溶剂甲醇含量对质子化常数的影响呈线性关系.确定了二元体系M(Ⅱ)-IAA(M=Fe、Co、Ni、Cu、Zn和Cd)在甲醇含量为50%(V/V)的混合溶剂中主要存在的配合物物种,并测定了配合物的稳定常数.实验数据的处理运用计算机程序Hyperquad、Glee和Hyss完成. 相似文献
102.
Hydrothermal reactions of 1, 2, 4‐benzenetricarboxylic acid, 1, 10‐phenanthroline and transition metal cations including ZnII or CoII, in basified aqueous solution gave rise to two complexes, [Zn3(btrc)2(1, 10‐phen)2(H2O)2]n ( 1 ), and [Co3(btrc)2(1, 10‐phen)2(H2O)2]n ( 2 ) (btrc = 1, 2, 4‐benzenetricarboxylate, and 1, 10‐phen = 1, 10‐phenanthroline). 1 2 crystalize isotypically in the triclinic space group P1¯. The btrc ligand acts as multi‐dentate bridging ligand in both compound 1 and 2 to link up transition metal atoms into lamella networks, which are further attached into three‐dimensional frameworks through complex hydrogen bonding and π‐π interactions. The photoluminescence spectrum for compound 1 has also been studied. The corresponding reaction with Cu2+ follows another pathway. 相似文献
103.
An X-ray fluorescence (XRF) method for the rapid and non-destructive analysis of 30 non-organic elements in plant leaves over five orders of magnitude concentration from several percentage of dry weight to sub-milligram per kilogram, is described. There is a growing need for a simple method of monitoring non-organic trace elements in plant material, especially those which accumulate in soils with application of fertilisers, both inorganic and biosolids. Earlier attempts to use XRF for the analysis of plant material suffered from sensitivity loss due to the high background of organic matrices caused by scattering of the X-ray source. We overcome this by using polarised X-ray sources in a Cartesian geometrical arrangement with sample and energy dispersive detector (EDPXRF), a configuration which can achieve an order of magnitude reduction in background compared with unpolarised sources. Further sensitivity gains are made using a high power tube as a source of primary X-rays and for some analytes employing secondary targets for near-monochromatic excitation. Sample preparation is simple involving only pulverising and briquetting of dried samples. Accuracy is evaluated by comparing data obtained for the suite of NIST plant leaf samples (NIST 1515 apple leaves, NIST 1547 peach leaves, NIST 1570a spinach leaves, NIST 1573a tomato leaves and NIST 1575a pine needles) and tobacco leaf standards CTA-OTL-1 and CTA-VTL-2. The data compare well over the whole concentration range and the method provides a rapid analytical tool for monitoring potentially toxic trace elements in all types of foliage with adequate sensitivity for many purposes. 相似文献
104.
贵金属同时浮选分离富集行为的研究及ICP-AES的测定 总被引:3,自引:0,他引:3
本文通过对贵金属-碘化钾-孔雀绿显色体系的浮选行为研究,建立了一种同时浮选富集分离铂、钯、铑、铱、金的新方法。实验结果表明,在0.36mol/LHCl0.1mol/LKI和2.4×10 ̄(-4)mol/LMG的溶液中,加入环已烷振荡1min,铂、钯、铑、铱、金可被定量浮选,继而用ICP-AES测定。对含量为5~150μg的贵金属,浮选回收率分别为铂88.6%~95.7%,钯92.3%~99.5%,铑93.7%~101%,铱92%~98.5%,金86.4%~94%。方法应用于铜镍矿、铂网废料等物料中上述贵金属元素的测定,结果满意。 相似文献
105.
The elemental analysis and morphology of individual particles indicate that the dominant suspended particles in river water are kaolin covered with hydrated iron(III) oxide which strongly sorbs humic substances. Suspended particles, about 1 mg, collected from 250 ml of water by centrifugation, are treated with 0.7 ml of 0.1M sodium hydroxide to desorb humic substances. Approximately 60% of copper and 30% of lead on or in suspended particles exist as humic complexes. 相似文献
106.
107.
108.
Michael Dolg 《Theoretical chemistry accounts》2005,114(4-5):297-304
Energy-consistent relativistic pseudopotentials for 3d-transition metals Sc to Ni based on modified valence energies are proposed. The pseudopotentials are adjusted at the finite
difference level within the intermediate coupling scheme with respect to multi-configuration Dirac–Hartree–Fock data based
on the Dirac–Coulomb Hamiltonian with an estimate of the Breit contributions in quasidegenerate perturbation theory. Typically
a few hundred to thousand J levels arising from about 35 to 40 configurations ranging from the anion down to the highly charged
cation are considered as references. It is shown that introducing a small common energetic shift of all valence energies reduces
the errors in the parameter adjustment considerably. Results of highly correlated atomic and molecular test calculations using
large basis sets and basis set extrapolation techniques are presented.
To be submitted to Theoretical Chemistry Accounts (special volume on the occasion of Prof. Dr. H. Stoll's 60th birthday) 相似文献
109.
4-Amino-3-hydroxy-2-(2-chlorobenzene)-azo-1-naphthalene sulfonic acid (AHCANSA) was used as a chelating modifier to improve the reactivity of the silica gel surface in terms of selective binding and extraction of heavy metal ions. The surface coverage values were found to be 0.488 and 0.473mmolg–1 for the newly modified physically adsorbed silica gel phase (I) and chemically immobilized-AHCANSA phase (II), respectively. The modified silica gel phases (I, II) were tested for stability in different acidic buffer solutions (pH 1–6) and found to be highly resistant to hydrolysis and leaching by buffer solutions above pH 2. The application of these two phases as solid extractors for a series of mono-, di-, and tri-valent metal ions from aqueous solutions was also performed with different controlling factors such as the pH value of metal ion solutions and equilibrium shaking time. The mmolg–1 metal capacity values determined by silica gel phases (I, II) were found to confirm high affinity and selectivity characters for binding with heavy metal ions such as Cr3+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ in a range of 0.250–0.483. The tested alkali and alkaline earth metals, Na+, K+, Mg2+ and Ca2+, were found to exhibit little interaction and binding ability with the modified silica gel phases. The selectivity characters incorporated into the modified silica gel phases were further utilized and applied in solid phase extraction and pre-concentration of trace concentration levels (1.0µgmL–1 and 2.00–2.50ngmL–1) from real seawater samples. The percentage recovery values determined for Cr3+, Cu2+, Zn2+, Cd2+ and Pb2+ were found to be in the range of 95.2–98.1±2.0–5.0%, and the pre-concentration recovery values for the same tested heavy metal ions were found to be in the range of 92.5–97.1±3.0–6.0% for the two newly modified silica gel phases with a pre-concentration factor of 500.Received December 20, 2002; accepted May 14, 2003
published online September 1, 2003 相似文献
110.
全谱直读ICP-AES法测定纺织品中重金属总量 总被引:3,自引:0,他引:3
采用干法灰化法处理纺织品样品,以全谱直读ICP-AES法对纺织品中铅、镉、砷、铜、钴、镍、铬、锑等重金属元素进行同时测定。方法的相对标准偏差为1.56%~9.62%,各元素的加标回收率为83.2%~108.4%。该方法准确、可靠,完全可以满足日常检测的需要。 相似文献