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911.
912.
A facile, mild and efficient procedure for the synthesis of fully substituted pyrazolo[3,4-b]pyridin-5-amines is reported. A mixture of an α-azidochalcone, a 5-aminopyrazole and t-BuOK was stirred in DMF at ambient temperature for 5?min to afford the corresponding pyrazolo[3,4-b]pyridin-5-amines in good to excellent yields. 相似文献
913.
A mild, general and efficient copper-catalyzed system for C-S bond formation is developed. With CuI as catalyst and l-Proline as ligand, the S-arylation of nitroalkane-CS2 adducts with aryl iodides were performed under mild conditions to give the corresponding products in good to excellent yields. 相似文献
914.
Tadesse Bekele Tafesse Fatemeh Zamani Mazdeh Anita Chalipour Mehdi Tavakoli Mannan Hajimahmoodi Mohsen Amini 《Chromatographia》2018,81(3):501-508
A gas chromatography–mass spectrometry method for the determination of pregabalin in human plasma is described. The procedure involves precipitation of protein, liquid–liquid extraction with ethylene glycol monomethyl ether, and derivatization with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide in the presence of N-hydroxysuccinimide as additive. Separation was attained on HP column (30 m × 0. 25 mm ID, 0.25 μm) coupled with mass spectrometric detector using electron impact selected ion monitoring. The assay showed an excellent linearity in the concentration range of 0.36–10 μg mL?1 with correlation coefficient (r2) values of 0.999. The intra- and inter-day assay variations for three different concentration levels were less than 10%. The limit of quantification was detected at 0.36 μg mL?1. The method is highly specific, precise, accurate, and reproducible and could also be applied for the determination of pregabalin in human plasma. 相似文献
915.
Modified clay/polyethersulfone (PES) mixed matrix membranes (MMMs) were prepared by acid activated montmorillonite (AA-MMT) with different concentrations and used to eliminate dyes and remove heavy metals from aqueous solution.The morphology and physiochemical properties of prepared clay nanoparticles and MMMs were characterized using X-ray diffraction (XRD),Fourier transform infrared (FTIR) spectroscopy,scanning electron microscopy (SEM),enegy dispersive X-ray (EDX) spectroscopy,Brunauer-Emmett-Teller (BET) analysis,atomic force microscopy (AFM),contact angle measurement and fouling studies.The filtration study showed that removal of dyes and heavy metals was strongly dependent on pH so that dyes with positive and negative charges showed different separation efficiency in acidic and alkaline conditions.The modified membranes possessed better heavy metal removal in acidic and alkaline pHs.When the rejection of heavy metals was measured in an alkaline environment,it was observed that the rejection had a great increase compared to the neutral values for Zn2+ and Ni2+ ions,while rejection of Cu2+ and Cd2+ did not undergo significant changes.So it can be concluded that modified membranes show good selectivity for elimination of Zn2+ and Ni2+ ions with respect to other cations. 相似文献
916.
Mohammadreza Shokouhimehr Mehdi Shahedi Asl Babak Mazinani 《Research on Chemical Intermediates》2018,44(3):1617-1626
In this study, mesoporous silica materials with tuned pores and surface areas were successfully synthesized by adjusting the amount of applied hexane and controlling the hydrothermal temperature. The synthesized silica materials were then functionalized by an amine group to produce solid base catalysts and be applicable as efficient heterogeneous base catalysts for the Henry reaction. The mesoporous silica catalysts possessing large-pores and surface area expose their active catalytic sites and thereby improve contacts with reactants fulfilling the reactions expeditiously in comparison with solid base catalysts possessing small-pores and surface area. The results indicated that the yield of the products is significantly dependent on the structure of the applied solid base catalysts. The modulated large-pore solid base catalysts presented high catalytic activity in Henry reactions and could be reused for five consecutive cycles. 相似文献
917.
Mathematical Programming - We study the geometry of convex optimization problems given in a Domain-Driven form and categorize possible statuses of these problems using duality theory. Our duality... 相似文献
918.
Designs, Codes and Cryptography - In this paper, we analyze the security of subset-resilient hash function families, which is first proposed as a requirement of a hash-based signature scheme called... 相似文献
919.
Izadikhah Mohammad Azadi Elnaz Azadi Majid Farzipoor Saen Reza Toloo Mehdi 《Annals of Operations Research》2022,316(2):1319-1347
Annals of Operations Research - Owing to the increasing importance of sustainable supply chain management (SSCM), it has received much attention from both corporate and academic over the past... 相似文献
920.
Issa Yavari Hassan Kabiri-Fard Shahram Moradi Behrooz Adib Mitra Matlobi 《Monatshefte für Chemie / Chemical Monthly》2003,134(1):23-35
Summary. The structures and relative energies of fundamental conformations of cyclopenta-1,2,3-triene, cyclohexa-1,2,3-triene, cylohepta-1,2,3-triene,
cycloocta-1,2,3-triene, and cyclonona-1,2,3-triene were calculated by the HF/6-31G* and MP2/6-31G*//HF/6-31G* methods. Only a C
2v symmetric planar conformation is available to cyclopenta-1,2,3-triene and cyclohexa-1,2,3-triene. The calculated energy barrier
for ring inversion of the C
S symmetric puckerd conformation of cyclohepta-1,2,3-triene via the planar geometry is 62.2 kJ·mol−1. The C
2 symmetric twist conformation of cycloocta-1,2,3-triene was calculated to be the most stable one. Conformational racemization
of the twist form takes place via the C
S symmetric half-chair geometry, which is by 60.8 kJ·mol−1 less stable than the twist conformer. The C
S symmetric chair and unsymmetrical twist-boat conformations of cyclonona-1,2,3-triene were calculated to have similar energies;
their interconversion takes place via an unsymmetrical low-energy (18.4 kJ·mol−1) transition state. The twist (C
2) and boat (C
S) geometries of cyclonona-1,2,3-triene are higher in energy by 13.2 and 33.9 kJ·mol−1, respectively. Ring inversion in chair and twist-boat conformations takes place via a twist form as intermediate and requires 33.6 kJ·mol−1.
Corresponding author. E-mail: isayavar@yahoo.com
Received March 25, 2002; accepted April 4, 2002 相似文献