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991.
H. M. Gomes D. dos Santos Gaspareto F. de Souza Ferreira C. A. K. Thomas 《Experimental Mechanics》2008,48(5):683-692
This work presents the main results of a simple closed-loop active control for an electrodynamic shaker in order to generate
acceleration Power Spectral Densities (PSD) according to prescribed Standards used in environmental vibration tests. The main
idea is to start generating acceleration pseudo-signals obeying the prescribed Power Spectral Density and then to acquire
acceleration data from the electrodynamic shaker’s table behaviour. So the Power Spectral Density of the acquired acceleration
is computed and compared with the required PSD and then the time-varying pseudo-acceleration is updated to reflect this corrected
PSD. It was noticed that for piecewise narrow bands frequencies, the electrodynamic shaker acceleration behaves near linearly,
both in frequency and voltage, for the input signals. A code in AgilentVee 7.5 software to acquire, send and process signals
for the active control in a closed-loop scheme was developed. The used A/D D/A hardware was a single PC sound card with specific
characteristics. The control could be accomplished sending and acquiring at the same time with a range of input/output of
±1.5 V with 16 bits of resolution, at 48 kHz and assistance of an external sound amplifier. 相似文献
992.
A non-linear system with 3rd order non-linearity is fully characterized using symmetry analysis (SA) applied to the excitation, as it is done in 2nd order non-linear systems using the pulse inverted method. Symmetry analysis is performed using irreductible representations and the character table of C3 rotation point group, which leads to the construction of three eigen-excitations allowing extraction of the 3rd order non-linearity parameter without the perturbation of fundamental and 2nd order terms. Validation of this concept is based on excitation symmetry analysis method (ESAM) which was tested on simulated noisy signals and compared with classical spectral analysis. 相似文献
993.
B. de Castro C. Freire M. Teresa Duarte M. F. Minas da Piedade I. C. Santos 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(4):370-372
In the title complex, trans‐{2,2′‐[cyclohexane‐1,2‐diylbis(nitrilomethylidyne)]diphenolato‐κ4O,N,N′,O′}nickel(II)–chloroform (1/1), [Ni(C20H20N2O2)]·CHCl3, the Ni atom has a square‐planar geometry, slightly tetrahedrally distorted. The Ni—N and Ni—O bonding distances are within the expected ranges for Ni–Schiff base derivatives. The diimine bridge has a gauche conformation with the cyclohexyl ring almost coplanar with the NiN2O2 plane. The complex molecules pack in dimers with an Ni?Ni distance of 3.59 (1) Å and form a three‐dimensional structure displaying a herring‐bone configuration. Channels are occupied by solvent molecules, which are involved in C—H?O hydrogen bonds with the ligand O atoms. 相似文献
994.
A. M. Santos Ph. Vindevoghel C. Graillat A. Guyot J. Guillot 《Journal of polymer science. Part A, Polymer chemistry》1996,34(7):1271-1281
Two methods of analysis, potentiometry and capillary electrophoresis, were used to study the decomposition of potassium persulfate (KPS) in aqueous solutions. The experiments were carried out in a glass reactor equipped with continuous control of temperature and pH during the reaction. The effect of the pH on the decomposition of KPS was investigated. The rate of KPS decomposition in the presence of a variety of additives (surfactants, inhibitor, monomer-like molecules, and monomers), which are used in emulsion polymerization recipes, was also studied over the temperature range of interest. The rate of disappearance of the persulfate ion was greatly increased in the presence of hydroquinone, but changed very little in the presence of surfactants. © 1996 John Wiley & Sons, Inc. 相似文献
995.
996.
Human protozoan diseases represent a serious health problem worldwide, affecting mainly people in social and economic vulnerability. These diseases have attracted little investment in drug discovery, which is reflected in the limited available therapeutic arsenal. Authorized drugs present problems such as low efficacy in some stages of the disease or toxicity, which result in undesirable side effects and treatment abandonment. Moreover, the emergence of drug-resistant parasite strains makes necessary an even greater effort to develop safe and effective antiparasitic agents. Among the chemotypes investigated for parasitic diseases, the indole nucleus has emerged as a privileged molecular scaffold for the generation of new drug candidates. In this review, the authors provide an overview of the indole-based compounds developed against important parasitic diseases, namely malaria, trypanosomiasis and leishmaniasis, by focusing on the design, optimization and synthesis of the most relevant synthetic indole scaffolds recently reported. 相似文献
997.
A. Santos 《Crystal Research and Technology》1992,27(2):173-179
Two experimental devices have been used with the aim to optimize the synthesis of single crystals by means of the mixed gel-solution technique. These consist of a gel source-reservoir saturated at T0 and a vessel of aqueous solution saturated at Tf. T0 > Tf. In such devices, the evlution of the supersaturation in the vessel of aqeous solutions allows that the grwoth process to be controlled by such a source-reservoir and the crystal itself. Average growth rates of 3 and 4 mm/day have been found for KDP crystals. 相似文献
998.
Flávio Vinícius Crizóstomo Kock Angel Rubén Higuera-Padilla Maiara da Silva Santos Vigatto Ladislau Martin Neto Luiz Alberto Colnago 《Magnetic resonance in chemistry : MRC》2019,57(7):404-411
Although the Cu2+-sorbitol complex [Cu2+-Sorb] structure in crystalline state has been determined by X rays, it is not known in solution, where most studies of this complex are performed. Therefore, the goal of this work was to obtain information about the structure of this complex in aqueous solution using nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The magnetic resonance results indicate that the complex is formed at approximately pH 12. In this pH the sorbitol 1H relaxation times were so short (broad line) that was not possible to use standard nuclear magnetic resonance parameters (nuclear Overhauser effect and spin–spin coupling constants values) to solve the three-dimensional structure. However, valuable structural information about the complex in solution was obtained. The relaxation results indicate that the Cu2+ ions are buried in the structure and not accessible to solvent; the 1H and 13C spectra shows strong paramagnetic shift effect indicating short distance between these nuclei and Cu2+ in the structure. No electron paramagnetic resonance signal was observed in pH 12 indicating strong Cu2+- Cu2+ dipolar interaction, compatible to Cu2+-Cu2+ distances measured in crystal, from 1.148 to 1.393 Angstroms. The complex self-diffusion coefficient (D) of 1.58 × 10−10 m2/s value, determined by Diffusion-Ordered Spectroscopy, is compatible to a molecular weight of 3–6 KDa. Therefore, these results corroborate that the [Cu2+-Sorb] complex is assembled in solution, at pH 12, with several structural parameters compatible to the toroidal hexadecacuprate supramolecular structure determined in solid state. 相似文献
999.
Nonlinear Dynamics - In general, the mechanisms that maintain the activity of neural systems after a triggering stimulus has been removed are not well understood. Different mechanisms involving at... 相似文献
1000.
Anas Semghouli Dr. Zsanett Benke Dr. Attila M. Remete Tamás T. Novák Prof. Santos Fustero Prof. Loránd Kiss 《化学:亚洲杂志》2021,16(23):3873-3881
Novel functionalized azaheterocycles with multiple chiral centers have been accessed from readily available norbornene β-amino acids or β-lactams across a stereocontrolled synthetic route, based on ring-opening metathesis (ROM) of the staring unsaturated bicyclic amino esters, followed by selective cyclization through ring-closing metathesis (RCM). The RCM transformations have been studied under various experimental conditions to assess the scope of conversion, catalyst, yield, and substrate influence. The structure of the starting norbornene β-amino acids predetermined the structure of the new azaheterocycles, and the developed synthetic route took place with the conservation of the configuration of the chiral centers. 相似文献