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981.
Takuma Fujita Shunsuke Kuwahara Atsufumi Nakahashi John Decatur 《Tetrahedron letters》2007,48(24):4219-4222
Enantiopure (R)-(+)-[VCD(+)945]-4-ethyl-4-methyloctane, the simplest chiral saturated hydrocarbon with a quaternary stereogenic center, was synthesized by the use of MαNP acid method, and its absolute configuration was first unambiguously determined by the 1H NMR anisotropy, X-ray crystallography, and VCD methods. 相似文献
982.
983.
A structural study of saturated aqueous solutions of some alkali halides by X-ray diffraction 总被引:2,自引:0,他引:2
The structure of nearly saturated or supersaturated aqueous solutions of NaCI [6.18 mol (kg H2O)–1], KCI [4.56 mol (kg H2O)–1], KF [16.15 mol (kg H2O)–1] and CsF [31.96 mol (kg H2O)–1] has been investigated by means of solution X-ray diffraction at 25°C. In the NaCI and KCI solutions about 30% and 60%, respectively, of the ions form ion pairs and the Na+–Cl– and K+–Cl– distances have been determined to be 282 and 315 pm, respectively. The average hydration numbers of Na+ and Cl– ions are 4.6 and 5.3, respectively, in the NaCI solution and those of K+ and Cl– ions in the KCI solution are both 5.8. In the KF solution, clusters containing some cations and anions, besides 1:1 (K+–F–) ion pairs, are formed. The K+–F– interatomic distance has been determined to be 269 pm, and nonbonding K+...K+ and F–...F– distances in the clusters are 388 and 432 pm, respectively, and the average coordination numbers n
KF
, n
KK
and n
FF
have been estimated to be 2.3, 1.9, and 1.6, respectively. In the highly supersaturated CsF solution an appreciable amount of clusters containing several caesium and fluoride ions are formed. The Cs+–F– distance in the cluster has been determined to be 312 pm, while the nonbonding Cs+...Cs+ and F–...F– distances are estimated to be 442 and 548 pm, respectively, the distances being about
and
times the Cs+–F– distance, respectively. The coordination numbers n
CsF
, n
CsCs
, and n
FF
in the first coordination sphere of each ion are 3.3, 2.3 and 5.3, respectively, and the result shows the formation of clusters of higher order than 1:1 and 2:2 ion pairs. These ion pairs and clusters may be regarded as embryos for the formation of nuclei of crystals and the results obtained in the present diffraction study support observations for the nucleation of the alkali halide crystals studied by molecular dynamics simulations previously examined. 相似文献
984.
Thermally stimulated depolarization currents and differential scanning calorimetry are performed on thermoplastic polyesters
to characterize both a and b relaxations. The influence on the different relaxations phenomena of the chemical structure (size
of the naphthalene groups, presence of cyclohexane, length of the aliphatic group, ...) as well as the influence of the crystallinity
are discussed. The three phases model with a crystalline part, a rigid amorphous part unable to relax and an amorphous phase
able to relax at various temperatures depending on the distribution of the relaxation times is used to explain the evolution
of the main α relaxation while the standard two-phases model is sufficient to explain the variations of the β relaxation mode.
Elementary analysis of both α and β relaxations show that the β relaxation characterized by a continuous variation of activation
energies as a function of temperature follows the activated state equation with a zero activation entropy while the cooperative
a relaxation exhibits a prominent maximum of the activation energies at the glass transition temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
985.
D. Lőrinczy G. Regdon Jr. B. Keller S. Szakály B. Schäffer 《Journal of Thermal Analysis and Calorimetry》2007,88(2):351-354
Nutritional-physiological
research of near past decades had established the real nutritional value of
fats and oils. In the former theory the nutritional value of fats and oils
is influenced mainly by the rate of saturated/unsaturated fats. It was ruled
out, and positive, inert or risk physiological effect of every single fatty
acid had been established. The health-care effect of omega-3 fatty acid mainly
by the favourable (<3:1) rate of omega-6/omega-3 was established, as inert
was concerned the saturated C16 fatty acid and the
maximal amount of trans-fatty acids carrying health risk in fats was legally
regulated in some countries. These nutritional-physiological requirements
were mainly fulfilled by margarine producers and the elementary fats were
selected in such a way that they should meet these requirements.
Our
method helps to the producers to quickly determine the amount of the liquid
and solid fat at certain temperature and/or to adjust the technological temperature
parameters. The main steps of our method are: a./ determination of cooling
rate (K min–1) of the crystallizer device;
b./ determination of the rate of liquid/solid fat at 10°C temperature.
This value is used for the determination of the rate of fats and oils as a
function of technology and required consistency firmness (spread ability);
c./ determination of the temperature from the cooling curve where the crystallization
of most part of the fat has finished. This value is used for the determination
of outlet temperature parameter of product coming out from the crystallizer
device for margarines or mixed-fat spreads with water-in-oil system. 相似文献
986.
987.
由X-射线光电子谱测定的原子内层电子的电离能(也称结合能)能反映分子内部不同区域的原子特性,常用于估计分子内不同部位的化学活性、分子中的电子结构变化以及取代基效应[1]。还用于研究价电子性质[2-4]和化合物的气相酸碱性[5]。目前,对原子内层电子电离能的研究有实验测定和 相似文献
988.
H. Kleeberg 《Journal of solution chemistry》1986,15(2):169-176
The concentration dependence of the H2O spectra in solutions of tetrabutylammonium bromide Bu4NBr in methylene chloride was investigated by IR-spectroscopy. At low salt and H2O concentrations the equilibrium: Br
f
–
+HOHfBr–HOH dominates where f indicates free or not hydrogen-bonded Br– and H2O. With increasing salt content, Br–H–O–HBr– complexes are present in addition. At high salt and H2O content, including the saturated aqueous Bu4NBr solution, H-bonded cyclic dimers seem to be important.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples. December 4–7, 1984. 相似文献
989.
Let
be a saturated formation containing the class of supersolvable groups and let G be a finite group. The following theorems are presented: (1) G ∈
if and only if there is a normal subgroup H such that G/H ∈
and every maximal subgroup of all Sylow subgroups of H is either c-normal or S-quasinormally embedded in G. (2) G ∈
if and only if there is a normal subgroup H such that G/H ∈
and every maximal subgroup of all Sylow subgroups of F*(H), the generalized Fitting subgroup of H, is either c-normal or S-quasinormally embedded in G. (3) G ∈
if and only if there is a normal subgroup H such that G/H ∈
and every cyclic subgroup of F*(H) of prime order or order 4 is either c-normal or S-quasinormally embedded in G.
Supported by the Natural Science Foundation of China and the Natural Science Foundation of Guangxi Autonomous Region (No.
0249001).
Corresponding author. Supported in part by the Natural Science Foundation of China (10571181), NSF of Guangdong Province (06023728)
and ARF(GDEI). 相似文献
990.
应用缓蚀剂控制混凝土中钢筋的腐蚀具有高效、廉价和易操作等优点,越来越受腐蚀研究者的关注。近年来,对环保型缓蚀剂的需求日益增加。因此,本工作发展了由癸二酸二异辛酯、D-葡萄糖酸钠和硫酸锌组成的环保型复合缓蚀剂并应用电化学测试技术和表面分析方法研究其对钢筋的缓蚀作用。结果表明,Q235钢筋在pH为11.00,含0.5 mol∙L-1 NaCl的模拟污染的混凝土孔隙液中处于活化状态并发生局部腐蚀。含有59 mmol∙L-1癸二酸二异辛酯,0.5 mmol∙L-1 D-葡萄糖酸钠和1.5 mmol∙L-1硫酸锌组成的复合缓蚀剂对钢筋具有良好的协同缓蚀效应,在模拟污染混凝土孔隙液中和水泥砂浆试样中对钢筋的缓蚀效率分别达到96.8%和90.0%。该复合缓蚀剂是一种混合型缓蚀剂,对钢筋腐蚀的阴极反应和阳极反应均有抑制作用。 相似文献