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81.
82.
Pyrocarbon/silica gel adsorbents (carbosils, CS) with mesoporous Si-60 (Merck, granule size 0.2–0.5 mm) modified by pyrolysis of CH2Cl2 at 823 K and reaction time from 0.5 to 6 h and then hydrothermally treated at 473 K for 6 h were studied by means of TEM, adsorption and 1H NMR methods. Changes in the structural and adsorptive characteristics of hybrid adsorbents before and after hydrothermal treatment, which depend on pyrocarbon content (C
C), were analyzed on the basis of TEM micrographs and p-nitrophenol and nitrogen adsorption isotherms treated using a constrained regularization method. Interfacial water layers in aqueous suspension of CS were investigated by means of 1H NMR with freezing-out of bulk water at T < 273 K showing nonlinear changes in the Gibbs free energy of interfacial water with increasing C
C because of nonlinear dependence of the structural characteristics of pyrocarbon deposits and CS as a whole on C
C. 相似文献
83.
Surface diffusion in reversed-phase liquid chromatography (RPLC) using silica gels bonded with C1 and C18 alkyl ligands of different densities was studied from the viewpoints of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, according to the four methods proposed by Krug et al., the values of surface diffusion coefficient (Ds) were analyzed to confirm that an actual EEC resulting from substantial physico-chemical effects takes place for surface diffusion. Then, it was also demonstrated that a LFER is observed between surface diffusion and the retention equilibrium. The establishment of EEC and LFER suggests a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length and the densities of C1 and C18 ligands. Finally, a thermodynamic model for the LFER based on the real EEC was used to estimate Ds values under various RPLC conditions. The Ds values can be estimated with a mean square deviation of about 25–30%. The agreement between the Ds values estimated and those experimentally measured suggests that the total mass flux by surface diffusion consists of the two contributions due to C1 and C18 ligands and that the contribution of each ligand is proportional to the ligand density. 相似文献
84.
Interfacial layers have been widely applied to study the formation and stability of emulsion-based systems. However, the application of isolated interfaces to address digestibility of emulsions is often limited because of the complexity of experimental methods and results. This review summarizes the latest developments in analytical methods and literature data on effects of digestion on interfacial layers. Particular emphasis is given to understand the changes on interfacial magnitudes during oral, gastric, and duodenal digestion, either applied separately or sequentially. Limitations of interfacial aspects and key factors that influence emulsion microstructure in bulk and lipid digestion are identified. Understanding the behavior of interfacial layers upon gastrointestinal digestion promotes an accurate tracking of the physiological fate of emulsions. 相似文献
85.
The physicochemical surface characteristics and interfacial behavior of two strains of Brevibacterium linens (BL-MGE and BL-9174), that may enhance cheese flavor, were assessed. Cell surface hydrophobicity was determined by measuring the contact angle of a variety of polar and non-polar wetting agents on lawns of the bacterial cells. The contact angles obtained were used to calculate the cell surface free energy components γLW, γAB, γ+ and γ−. The Lifshitz van der Waals component and the Lewis acid-base component were approximately 35 mJ m−2 and 22 mJ m−2, respectively, for both strains. Under conditions of physiological pH and low ionic strength, neither strain exhibited affinity for an octyl ligand in hydrophobic interaction chromatography. This occurred despite a favorable free energy of interfacial interaction which was attributable almost entirely to favorable acid-base interactions between cells and octyl-sepharose. The nature of surface functional groups was evaluated using X-ray photoelectron spectroscopy. Excluding H, the mean percentage of atomic fraction for C, O, N and P for BL-MGE was 57.7, 37.8, 3.9 and 0.6%, respectively and 61.0, 31.8, 7.0 and 0.2%, respectively for BL-9174. 相似文献
86.
这篇论文综述了美国加州大学戴维斯分校科学院院士Navrotsky课题组多年来在多孔材料上取得的一系列热化学研究结果。讨论了热化学对微孔、介孔材料的结构稳定性和合成过程的影响。借助多种测热手段对影响骨架结构的热焓、热熵和自由能进行了系统的测量和计算。研究数据表明一系列纯硅分子筛、介孔材料和磷酸铝多孔材料同相应的石英相和块磷铝矿相相比能量上最多只高出15 kJ·mol-1。一系列纯硅分子筛的熵值比石英相高出3.2—4.2 J·K-1·mol-1;在0—12.6 J·K-1·mol-1范围内相对应的自由能几乎没有差别。因此,对不同微孔、介孔材料,其骨架结构在能量上是几乎没有区别的。另外,本文通过介绍一种新型测热方法——原位测热,揭示了分子筛合成过程中的动力学和成核/结晶机理。 相似文献
87.
W. Libuś B. Janaszewski R. Pastewski H. Twardowska 《Journal of solution chemistry》1980,9(10):737-752
Solubility isotherms are reported for the NiCl2·4py, MnCl2·4py, and MnCl2·2py solid pyridinates in a number of pyridine+diluent mixtures at 25°C. Activity coefficients of the solvent components have been derived from the total vapor pressures measured by a static method. The standard free energies of transfer for the NiCl2py4 and MnCl2py4 complexes are the same, within the experimental error, in the pyridine+aprotic diluent mixtures, while marked differences are observed in the pyridine+chloroform mixtures. Marked deviations are observed for chloroform and 1,2-dichloroethane from a correlation between the standard free energy of transfer of the complexes, on one hand, and the Hildebrand's solubility parameter of the solvent, on the other, the latter correlation being roughly valid for aprotic solvents. The deviations are tentatively ascribed to hydrogen bond formation of the type H... between the protic solvents and the coordinated pyridine molecules, enhanced by the d electron delocalization. 相似文献
88.
基于Lagrange原理和假设模态法建立了旋转输液管的动力学模型.通过降阶升维的方法求解系统的特征值问题,并分析了旋转输液管自由振动特性.得到了不同端部集中质量和转速下,系统特征值随流速升高的演变轨迹.揭示了临界流速随系统参数的变化规律.研究发现,内部流体的流动对旋转输液管动力学特性存在显著影响.在某些参数组合下,系统低阶模态能够形成不同形式的内共振关系.预示了旋转输液管模型蕴含丰富的动力学现象. 相似文献
89.
90.
Shutao Zhang & Yazhou Han 《分析论及其应用》2022,38(2):178-203
For conformal Hardy-Littlewood-Sobolev(HLS) inequalities [22] and reversed conformal HLS inequalities [8] on $\mathbb{S}^n,$ a new proof is given for the attainability
of their sharp constants. Classical methods used in [22] and [8] depends on rearrangement inequalities. Here, we use the subcritical approach to construct the extremal
sequence and circumvent the blow-up phenomenon by renormalization method. The
merit of the method is that it does not rely on rearrangement inequalities. 相似文献