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排序方式: 共有7585条查询结果,搜索用时 15 毫秒
71.
Alicja Wawrzynów Adam Liwo Ewa Kaczmarczyk Lech Chmurzyński 《Journal of solution chemistry》1998,27(5):463-472
Cationic heteroconjugation equilibria of more than ninety systems consisting of substituted pyridines, their N-oxides, and trimethylamine N-oxide, i. e., in systems with mixed hydrogen bridges of type OHN+ (NHO+) were studied in propylene carbonate. Both experimental systems without proton transfer, BH+/B1, and those with proton transfer, B1H+/B, were explored. The stability of the mixed hydrogen bridges, OHN+ (NHO+), is compared with that of the OHC+-type bridges. The influence of the difference in basicity of the conjugate base of the proton donor and the proton acceptor on the presence of the proton transfer equilibria, and, consequently, the possibility of determination of the cationic heteroconjugation constant values is discussed. 相似文献
72.
73.
前言卟啉在生物化学、分析化学、药物化学等领域有着广泛研究和重要应用[1~3]。近年来虽然对卟啉类化合物的研究报道很多[4~6],但对卟啉在酸性介质中的研究很少。较早期的研究工作认为卟啉类化合物在酸性介质中仅以其二酸形式存在[7]。本文实验结果显示me... 相似文献
74.
β-Aminopropionohydroxamic acid reacts with aliphatic aldehydes or ketones to give 2-substituted 1-hydroxytetrahydropyrimidin-6-ones,
while its reaction with aromatic carbonyl compounds leads to either the same products or Schiff's bases, which can exist in
tautomeric equilibrium in solution.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 691–694, April, 1998. 相似文献
75.
Laurence E. Strong Thomas G. Copeland Margaret Darragh Carter Van Waes 《Journal of solution chemistry》1980,9(2):109-128
Conductivities of aqueous solutions ofortho-, meta-, andpara-toluic acids have been measured for the concentration range 0.1–2 millimolar and at 5° intervals from 5 to 100°C. At each temperature pK
a(m) andA
0 have been calculated using the paired ion model recently described by Fuoss. Thermodynamic parameters have been calculated for the ionization of each acid, and Walden products for the anions. Results are discussed in terms of contributions to acidity by enthalpy and entropy changes as well as by hydration of the various solute species. 相似文献
76.
G. Wu R. M. Izatt M. L. Bruening W. Jiang H. Azab K. E. Krakowiak J. S. Bradshaw 《Journal of inclusion phenomena and macrocyclic chemistry》1992,13(2):121-127
The aqueous protonation and anion-binding SeO
2
–/4
SO
2–
4
, and NO
–
3
) constants of the macrocyclic polyamine ligand, dipyridino-hexaaza-28-crown-8(L), were measured in 0.1M KCl using a potentiometric titration technique. The protonation sequence of the aza groups of L was studied in D2O from the chemical shifts of the nonlabile protons so as to find the charge distribution geometry as a function of pD. The study indicates that in 0.1M KC1 fully protonated L forms stable l: 1 complexes with SeO
2–
4
(logK=3.68) and SO
2–
4
(logK=3.55), but not with NO
–
3
(logK < l.5). All of the amine pK values were above 6.3, thus allowing the use of the protonated form of this ligand over a wide pH range. 相似文献
77.
The stoichiometric solubility constant of eitelite (NaMg
0.5
CO
3
+2H+ ⇄ Na++0.5Mg
2+
+CO
2
(g)+H
2
O, log*K
pso
I
=14.67±0.03 was determined at I=3 m (mol kg−1) (NaClO
4
) and 25°C. The stability of magnesium (hydrogen-)carbonato complexes in this ionic medium was explicitely taken into account.
Consequently, trace activity coefficients of free ionic species, calculated from the Pitzer model with ion-interaction parameters
from the literature, were sufficient for an evaluation of the thermodynamic solubility constants and Gibbs energies of formation
for eitelite (−1039.88±0.60), magnesite (−1033.60±0.40), hydromagnesite (−1174.30±0.50), nesquehonite (−1724.67±0.40), and
brucite (−835.90±0.80 kJ-mol
−1
). The increasing solubilities of nesquehonite and eitelite at higher sodium carbonate molalities were explained by invoking
a magnesium dicarbonato complex (Mg2++2CO
3
2−
⇄ Mg(CO3)
2
2−
, log βz = 3.90 ± 0.08). A set of ion-interaction parameters was obtained from solubility and dissociation constants for carbonic
acid in 1 to 3.5 m NaClO
4
media
which reproduce these constants to 0.02 units in log K. The following Pitzer parameters are consistent with the previously
studied formation of magnesium (hydrogen-)carbonato complexes in 3m NaClO
4
. The model and Gibbs functions of solid phases derived here reproduce original solubility data (−log [H+], [Mg
2+
]
tot
) measured in perchlorate medium within experimental uncertainty.
Presented at the XXII International Conference on Solution Chemistry, July 14–19, 1991, Linz, Austria. 相似文献
78.
Vapor liquid equilibrium (VLE) is successfully predicted from excess enthalpy HE data for binary ether + n-alkane or cyclohexane mixtures. Parameters for the continuous linear association model (CLAM) and for the UNIQUAC Model for the excess Gibbs energy GE were determined from HE data measured at a low temperature (ambient temperature). These parameters are used to predict VLE data at low and high temperatures. The dependence of the accuracy of predictions on the set of HE data chosen to evaluate the parameters and on the model for GE are discussed. 相似文献
79.
80.
稀碱金属铷、铯资源的成功开发,需以相应的相平衡与相图研究成果为指导,开展稀碱金属盐-混合溶剂体系相平衡的研究,对这些金属盐的提纯开发利用具有重要的意义.本文主要从不同的铷、铯盐-混合溶剂三元及四元体系两个方面,归纳总结了此类体系的相平衡研究进展,探讨了研究中存在的一些问题,为深入研究稀碱金属-混合溶剂体系的相平衡奠定了基础. 相似文献