全文获取类型
收费全文 | 2163篇 |
免费 | 167篇 |
国内免费 | 106篇 |
专业分类
化学 | 1004篇 |
晶体学 | 4篇 |
力学 | 2篇 |
综合类 | 6篇 |
数学 | 2篇 |
物理学 | 809篇 |
综合类 | 609篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 30篇 |
2021年 | 42篇 |
2020年 | 51篇 |
2019年 | 52篇 |
2018年 | 76篇 |
2017年 | 86篇 |
2016年 | 83篇 |
2015年 | 67篇 |
2014年 | 89篇 |
2013年 | 485篇 |
2012年 | 92篇 |
2011年 | 89篇 |
2010年 | 75篇 |
2009年 | 88篇 |
2008年 | 89篇 |
2007年 | 113篇 |
2006年 | 77篇 |
2005年 | 62篇 |
2004年 | 83篇 |
2003年 | 60篇 |
2002年 | 72篇 |
2001年 | 55篇 |
2000年 | 46篇 |
1999年 | 48篇 |
1998年 | 34篇 |
1997年 | 38篇 |
1996年 | 20篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 21篇 |
1991年 | 24篇 |
1990年 | 21篇 |
1989年 | 27篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有2436条查询结果,搜索用时 672 毫秒
21.
The apparent molar volumes V of KCl, BaCl2, K2SO4, LaCl3, Co(en)3Cl3 [Tris(ethylenediamine)cobalt(III) chloride], K3Co(CN)6, K3Fe(CN)6, K4Fe(CN)6, and Ba3[Co(CN)6]2 have been determined at 25°C in both light and heavy water. The V values in D2O are systematically lower and increase more rapidly with salt concentration than the V in H2O. The volume of transfer from H2O to D2O as well as the partial molar volume at infinite dilution in both solvents have also been calculated. These results together with literature values for other electrolytes were used to estimate both of these quantities for D2O solutions of individual ions. The predictions of ion hydration models and ion-ion interactions are compared with experimental observations. 相似文献
22.
E. V. Ivanov E. Yu. Lebedeva V. K. Abrosimov N. G. Ivanova 《Russian Chemical Bulletin》2004,53(4):751-757
Densities of Bun
4NBr solutions in MeOH, MeOD, and CD3OH were measured at salt concentrations of up to 1.5 solvomolality units (nearly 2.63·10–2 mole fraction) at 278.15, 288.15, 298.15, 308.15, and 318.15 K. The limiting partial molar volumes of Bun
4NBr dissolved in these alcohols were calculated. The isotope effects in the volume characteristics of the stoichiometric mixture of ions, [Bun
4N+ + Br–], are mainly due to the vibrational changes in the solvent structure upon deuteration of different molecular fragments. Structural transformations in infinitely dilute solution of Bun
4NBr in methanol are governed by non-specific solvation of the symmetrical Bun
4N+ cation. 相似文献
23.
24.
The evolution of methane carbon isotope with depth has been discussed based on diagenetic reaction kinetics and isotopic Rayleigh
fractionational theory. A mathematical model to describe data of methane carbon isotope for the Liaohe oil field has been
established. 相似文献
25.
An oxygen isotope temperature record from 381 to 166 kaB. P. (230Th/234U dating and tuned ages) has been obtained by combining data on the isotopic composition of calcites with that of fluid inclusions
trapped in a stalagmite from a limestone cave in which a fossil cranium deposited. Several laminae in microsequence of the
stalagmite represent climatic events or shifts. The Nanjing man fossil was older than 381 kaB. P. 相似文献
26.
Osmium isotope determination on mantle-derived peridotite xenoliths from Panshishan with N-TIMS 总被引:2,自引:0,他引:2
Weidong Sun Zicheng Peng Xiachen Zhi Daogong Chen Zhaorong Wang Xinhua Zhou 《科学通报(英文版)》1998,43(7):573-573
The187Os/188Os ratios of spinel lherzolite xenoliths from Panshishan determined with N-TIMS are lower than that of the primitive mantle,
which shows depleted mantle characteristics. Their positive correlation with Al2O3/MgO suggests that the geochemical behavior of trace elements Re and Os is similar to that of Al2O3 and MgO respectively during the magmatic evolution and Re-Os isotopic system is largely immune to mantle metasomatism. A
model age of 2.8–3.4 Ga obtained by187Os/188Os-Al2O3/ MgO correlation might represent the homogeneous age of the mantle lithosphere beneath the area. 相似文献
27.
The plagioclase amphibolites from Kuokesu area, Kuruktag, Xinjiang occur as enclaves embedded in the granodioritic gneiss. In the light of major elements and REE data, the parent rocks of the plagioclase amphibolites belong to weak_alkaline basalts. Their Nd model ages mainly range from 2 832 to 3 075 Ma. The seven plagioclase amphibolites yield a reasonable good isochron age of (828±86) Ma(2σ) with I Nd =0.510 981±82, ε Nd ( t )=-11.5±1.6. Such a case shows the existence of great proportion of the Archaean mafic crustal basement on the Kuokesu area. The strong tectonic_thermal event at about 820 Ma made the Sm_Nd isotope of the metamorphic rocks homogenization. This event would be associated with the Tarim Movement. 相似文献
28.
《科学通报(英文版)》1998,43(16):1362-1362
Isotopic geochemical characteristics of helium in garnet and omphacite of eclogite in the Dabie Mountains are discussed. Concentrations of 3He and 4He in garnet and omphacite are 3.9×10 -14- 24.0×10 -14 and 0.48×10 -7-9.42×10 -7cm+3·g -1, respectively. Values of 3He/ 4He have a range of (1.19-4.63)×10 -7. Helium in the eclogite is derived from both mantle and crust. Isotopic geochemical data of helium indicate that eclogite in the Dabie Mountains might be formed in depleted mantle and the age of the cologite would be Indo-China epoch. 相似文献
29.
A potentiometric method using a glass electrode has been applied to determination of ionization constants for deuterium oxide (D2O) in binary mixtures of D2O with dioxane, tetrahydrofuran, acetone, dimethylsulfoxide, CH3CH2OD, and CH3OD at 25°C. The results are compared with values of ionization constants for H2O obtained previously in the corresponding H2O-organic mixtures, and the isotope effect is shown to be small. Further calculations with the D2O results show that the first five solvents mentioned above are neither appreciably acidic nor basic in D2O solution, but that CH3OD shows slightly acidic behavior (pKa=16.0±0.3). 相似文献
30.
19F and 1H NMR spectra of halocarbons 总被引:1,自引:0,他引:1
Foris A 《Magnetic resonance in chemistry : MRC》2004,42(6):534-555
19F NMR chemical shifts and coupling constants are reported for 215 compounds. For 77 of these compounds, 1H NMR spectral data are also given. Long-range couplings, including 8J(F,F) and 5J(F,H), are reported. The complexity of halocarbon spectra owing to the presence of rotational isomers, asymmetric centers, long-range couplings, and chlorine isotope effects are illustrated, and the methods used for analyzing such complex spectra are briefly discussed. 相似文献