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71.
The concentration sensitivity of a thermal conductivity detector (TCD) depends, among other factors, on the amount of sample mixture in the detector's sensing cell. Since the cell volume has to be appropriately matched with column diameter, it makes the concentration sensitivity of a TCD dependent on column diameter and, therefore, on the speed of gas chromatography. Through reduction of column diameter, higher speed tends to lead to a reduction in the concentration sensitivity of the cell. The factor which the most directly affects the concentration sensitivity of a TCD cell is the heat power conducted through the cell. The higher the power, the greater the sensitivity. The limit of detection of a TCD depends on the concentration-sensitivity of its cell and on the level of statistical errors in the measurement. The errors increase with increasing analysis speed. As the column diameter is reduced, the errors cause additional worsening (on top of the decrease in concentration sensitivity) of the detection limit, dynamic range, and other performance characteristics of the TCD. 相似文献
72.
The dispersion of the quantitative results in the analysis of volatile compounds from multicomponent mixtures by different fractionation techniques (solid-phase microextraction and direct thermal desorption) followed by GC or GC-MS presents nonrandom patterns related to the existence of different factors in the fractionation process or in the chromatographic separation which affect, to a different extent, the recovery of the sample components. Statistical techniques have been used to show the relative importance of these factors. The improvement in data precision achieved by using volatile compound concentration ratios is discussed. 相似文献
73.
神经网络法用于多元混酸同时测定 总被引:1,自引:0,他引:1
利用多层神经网络误差反向传播算法处理酸碱电位滴定数据,求得出多元混合酸各组分的浓度,优化了神经网络的结构和参数,测定了三组分有机酸混合样品,结果良好,平均相对偏差RSD≤4%。 相似文献
74.
提出了控制电位电解和恒电流电解两类电解沉积的压电频移分析法测定的理论公式,用实验结果验证了它的正确性. 相似文献
75.
提出了一种动力学李代数方法来研究取代苯体系的非线性光学性质. 对于给定的PPP模型(Pariser-Parr-Pople)哈密顿量, 生成了一个动力学李代数. 依据这些代数元构造出演化算子作为群参数的函数, 通过求解一组非线性微分方程能够得到这些群参数. 再按照统计力学中的密度算子公式给出取代苯分子体系偶极矩的统计平均值. 于是导出二阶极化率的表达式. 与其他量子力学计算结果比较, 表明这种动力学李代数方法在预言有机共轭分子的非线性光学性质上同样有用. 相似文献
76.
Preparation, Crystal Structure and Normal Coordinate Analysis of Linkage Isomeric Pentachlororhodanoosmates(IV) By treatment of [OsCl5I]2? with (SCN)2 in dichloromethane the linkage isomers [OsCl5(NCS)]2? and [OsCl5(SCN)]2? are formed which have been separated by ion exchange chromatography on diethylaminoethyl cellulose. The X-ray structure determination on single crystals of (Ph4As)2[OsCl5(NCS)] (monoclinic, space group P21/a, a = 18.872(2), b = 11.6024(2), c = 22.786(1), β = 109.057(1)°, Z = 4) and (Ph4As)2[OsCl5(SCN)] (monoclinic, space group P21/a, a = 19.057(2), b = 11.306(2), c = 22.612(1), β = 106.64(2)°, Z = 4) reveals the complete ordering of the complex anions. The thiocyanate group is located above one of the Cl ligands of the equatorial plane with the Os? N? C angle of 166.1° for N bonding and the Os? S? C angle of 109.9° for S bonding. The IR and Raman spectra of both linkage isomers known from literature are assigned by normal coordinate analysis based on the general valence force field using the molecular parameters of the X-ray determination. The valence force constants are fd(OsN) = 1,81 and fd(OsS) = 1,32 mdyn/Å. Taking into account increments of the trans influence a good adjustment between observed and calculated frequencies is achieved. 相似文献
77.
Summary A new index of performance of the chromatographic separation between two adjacent peaks, the discrimination factor, d0, is defined. It is normalized between 0 and 1 and is directly and easily determined from the chromatogram. It does not depend
on any assumption regarding peak shape, except that the peak profiles of individual sample components have a single mode.
Its value depends on the relative heights of the two peaks as well as on their separation.
The separation power of a chromatographic system is classically measured by its peak capacity, defined on the basis of constant
resolution between adjacent peaks. A previously developed statistical theory of the composition of mixtures makes it possible
to extend the concept of peak capacity by taking into account the peak height distribution in typical average chromatograms.
A new parameter, the effective peak capacity, is defined for this purpose on the basis of a constant discrimination factor
between adjacent peaks. It allows to take into account the distribution of peak heights in statistical theories of the evaluation
of complex chromatograms and in the measurement of the limit of determination in quantitative analysis.
The characteristics of the two new parameters, the discrimination factor and effective peak capacity, are discussed and compared
with those of their classical homologs, resolution and peak capacity, in the case of gaussian component peaks of equal widths. 相似文献
78.
Olle Nilsson 《Journal of separation science》1982,5(1):38-44
The total length-based second moment contribution from longitudinal sample diffusion in both phases on a column, σD , is derived by adding individual partial differential contributions to a partial differential equation accounting for the longitudinal diffusion processes only. Although each diffusion-dispersed sample part is equilibrated between two phases, the resulting σ,D (= 2D mt m + 2D st s) can be interpreted as the sum of two independent contributions in accordance with the variance addition rule. (D m and D s are the mean diffusion coefficients and t mand t s the mean residence times of the sample in the mobile and stationary phases, respectively.) The same σD expression is derived from the random walk model of Giddings by treating the diffusional process in each phase as statistically independent of the other processes. Under these conditions the broadening contribution from longitudinal diffusion in the mobile phase is shown to be independent of the velocity profile. 相似文献
79.
Herein, we discuss the analyses and quantification of the different components in porphyrin mixtures, prepared from p-anisaldehyde, p-tolualdehyde, and 5-(4-bromophenyl)-dipyrromethane with acid catalysis, using NMR and HPLC. The advantages and disadvantages of these analytical methods are emphasized. Due to the similar size of a bromine atom and a methyl group it was possible to grow crystals suitable for X-ray crystallographic studies from a mixture of porphyrins, where the 4-position of the meso-phenyl rings was either substituted with methyl groups or bromine atoms. We also show that X-ray studies are inferior to NMR analysis for determining the components in a porphyrin mixture. 相似文献
80.
Lenice de Loureno Marques Ernesto Schulz Lang Herton Fenner Eduardo Ernesto Castellano 《无机化学与普通化学杂志》2005,631(4):745-748
[Hg(sulfamethoxazolato)2]·2DMSO ( 1 ) and [Cu2(CH3COO)4(sulfa‐methoxazole)2] ( 2 ) can be obtained by the reaction of sulfamethoxazole with mercury acetate or copper acetate in methanol. The structures of the two complexes were characterized by single crystal X—ray diffractometry. Compound 1 consists of sulfamethoxazolato ligands bridging the metal ions building an unidimensional chain. Two solvent dimethylsulfoxide molecules are involved via N‐H···O hydrogen bridges. The mercury atom shows a linear primary coordination arrangement formed by two trans deprotonated sulfonamidic nitrogen atoms. The overall coordination around the metal atom may be regarded as a strongly distorted octahedron when the interactions of mercury with four sulfonamidic oxygen atoms [bond distances of 2.761(4) Å—2.971(4) Å] are also considered to build an equatorial plane and the N1 and N1′ atoms [bond distance of 2.037(5) Å] occupy the apical positions. Compound 2 is a dinuclear complex in which the copper ions are bridged by four syn‐syn acetate ligands which are related by a symmetry centre located in the centre of the complex. Each copper atom presents a nearly octahedral coordination where the equatorial plane is formed by four oxygen atoms and an isoxazolic nitrogen atom and the second copper atom occupy the apical positions. 相似文献