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991.
Chao Luo Yujie Zhu Oleg Borodin Tao Gao Xiulin Fan Yunhua Xu Kang Xu Chunsheng Wang 《Advanced functional materials》2016,26(5):745-752
The sulfur‐based cathode materials suffer severely from poor cycling stability and low utilization, incurred by their stepwise reaction mechanism that generates polysulfide intermediates and the subsequent irreversible losses. In this work, those issues are significantly relieved by entrapping sulfur species in carbon host rich in oxygen functionalities. Sulfur species in such C/S composite are highly stabilized by their interaction with oxygen, and can deliver a reversible capacity of 508 mAh/(g of S) for 2000 cycles when coupled with Li, representing the best cycling stability up to date. More interestingly, extra capacity can be accessed by simply prelithiating the oxygen‐stabilized C/S composites down to 0.6 V for a few cycles, which enables a high capacity of 1621 mAh/(g of S) that eventually stabilizes at 820 mAh/(g of S) for 600 cycles. The mechanism for this electrochemical activation process is investigated with both spectroscopic and electrochemical techniques, which reveal that the inactive sulfur bonded to oxygen is liberated in the initial deep lithiation precycles and becomes electrochemically active. The oxygen‐stabilized sulfur can also be coupled with Na anode to form Na/S cell, confirming that the formation of S?O interaction in C/S composite generates promising sulfur‐based cathode materials for Li–S and Na–S batteries. 相似文献
992.
以二叔丁基过氧化物(DTBP)为氧化剂,苯硫酚为硫化试剂,在无金属参与的条件下,于120℃下采用一步法合成了硫代苄醚.这种构筑C(sp~3)—S键的方法具有高原子经济性和高选择性的优点,并以较高的收率获得了一系列目标化合物. 相似文献
993.
The influences on the thermal degradation and crystallization behaviors of poly(p-dioxanone) (PPDO) were initially investigated by adding bis-(2,6-diisopropylphenyl) carbodiimide (labeled as St). It was found that the addition of St could significantly enhance the thermal stability and crystallizability of PPDO. The thermal decomposition temperature of PPDO increased with the increase of the amount of St added. The thermal decomposition activation energies of PPDO increased from 94.2 to 130.8 kJ mol?1 in the case of 5 wt% St. The addition of St did not change the crystal structure of PPDO, while it increased the number of nucleation sites and improved the crystallizability of PPDO. The crystallization activation energies, calculated by the Kissinger method, for PPDO and PPDO/5 wt% St were ?111.4 and ?141.5 kJ mol?1, respectively, confirming the crystallizability of PPDO was enhanced after the addition of St. 相似文献
994.
Star-g-poly (acrylic acid)/organo-zeolite 4A (S-g-PAA/OZ) superabsorbent composite was prepared by grafting partially neutralized acrylic acid onto starch in the presence of organo-zeolite 4A (OZ) as an inorganic component. The morphology was characterized with scanning electron microscopy (SEM). Energy dispersive spectrometer (EDS) analysis revealed the fine distribution of OZ in superabsorbent composite. The swelling kinetics of the composites were characterized by means of a Schott's second-order model. The effect of OZ concentration in the composite on the water absorbency and swelling behavior were tested. The swelling properties of the composites were evaluated in various environments; pH, salinity, temperature, urea solution, and solvent-water mixtures. The activation energy (ΔE) for water during the swelling process was also determined through Arrhenius plots. The results showed that the proper amount of OZ was beneficial for improvement of the water absorbent capacity and the initial swelling rate in distilled water. The optimum prepared composite with 10 wt % OZ, possessed the maximum water absorption (511g/g) in distilled water and (521 g/g) in 0.1 wt % urea solution. The results inferred that S-g-PAA/OZ superabsorbent composite can be exploited for agriculture and medical applications. 相似文献
995.
The influence of three different co-agents, triallyl isocyanurate (TAIC), trimethylol propane trimethacrylate (TMPTMA) and high vinyl poly(butadiene) (HVPBd), on the curing characteristics, including the cure kinetics, of peroxide-cured EPDM compounds and the mechanical properties of the resulting EPDM vulcanizates were studied. The results showed that the addition of each co-agent could improve the cure extent of the EPDM samples; the hardness and modulus of the EPDM vulcanizates were also improved. In particular, the compound containing TAIC obtained the highest cure extent. However, the addition of TMPTMA negatively affected the scorch safety, especially below 165°C. From the cure kinetics of the EPDM compounds, obtained by using the cure data from a moving die rheometer, it was found that the Deng–Isayev, first-order and Hsich models showed better agreement with experimental data compared to the Kamal–Sourour model. The reaction rate constants were gradually increased with the elevated temperature, and TMPTMA could significantly promote the curing reaction rate, TAIC secondly, while HVPBd showed no effect. In addition, the apparent activation energy of all EPDM compounds, calculated by the Deng–Isayev model, was estimated slightly higher than that of the other three kinetic models. However, due to the addition of the three co-agents, the activation energy of the curing reaction decreased, with the EPDM compound with TAIC showing the lowest activation energy. 相似文献
996.
M. Sc. Markus Warnke Tobias Jung Dr. Juri Dermer Karin Hipp Dr. Nico Jehmlich Prof. Dr. Martin von Bergen Sascha Ferlaino Dr. Alexander Fries Prof. Dr. Michael Müller Prof. Dr. Matthias Boll 《Angewandte Chemie (International ed. in English)》2016,55(5):1881-1884
The hydroxylation of vitamin D3 (VD3, cholecalciferol) side chains to give 25‐hydroxyvitamin D3 (25OHVD3) is a crucial reaction in the formation of the circulating and biologically active forms of VD3. It is usually catalyzed by cytochrome P450 monooxygenases that depend on complex electron donor systems. Cell‐free extracts and a purified Mo enzyme from a bacterium anaerobically grown with cholesterol were employed for the regioselective, ferricyanide‐dependent hydroxylation of VD3 and proVD3 (7‐dehydrocholesterol) into the corresponding tertiary alcohols with greater than 99 % yield. Hydroxylation of VD3 strictly depends on a cyclodextrin‐assisted isomerization of VD3 into preVD3, the actual enzymatic substrate. This facile and robust method developed for 25OHVD3 synthesis is a novel example for the concept of substrate‐engineered catalysis and offers an attractive alternative to chemical or O2 /electron‐donor‐dependent enzymatic procedures. 相似文献
997.
Efficient Room‐Temperature,Au+‐Mediated Coupling of a Carbene Ligand with Methane To Generate C2Hx (x=4, 6) 下载免费PDF全文
Dr. Shaodong Zhou Dr. Jilai Li Dr. Xiao‐Nan Wu Dr. Maria Schlangen Prof. Helmut Schwarz 《Angewandte Chemie (International ed. in English)》2016,55(1):441-444
The thermal reactions of the closed‐shell, “naked” gold–carbene complex [Au(CH2)]+ with methane have been explored by using FTICR mass spectrometry complemented by quantum chemical (QC) calculations at the CCSD(T)//BMK level of theory. Mechanistic aspects for this unprecedentedly efficient carbene insertion in the C? H bond of methane have been addressed and the origin of the counterintuitive high reactivity of [Au(CH2)]+ towards this most inert hydrocarbon is discussed. 相似文献
998.
Exploiting Electrostatics To Generate Unsaturation: Oxidative GeE Bond Formation Using a Non π‐Donor Stabilized [R(L)Ge:]+ Cation 下载免费PDF全文
Dr. Arnab Rit Dr. Rémi Tirfoin Prof.Dr. Simon Aldridge 《Angewandte Chemie (International ed. in English)》2016,55(1):378-382
The two‐coordinate germanium cation [(IDipp){(Me3Si)2CH}Ge:]+ has been synthesized, which lacks π‐donor stabilization of the metal center and consequently has a very small HOMO–LUMO gap (187 kJ mol?1). It undergoes a variety of facile oxidative bond‐forming reactions, most notably allowing access to the first examples of Group 14 metal cations containing M?E multiple bonds (E=C, N). The use of an electrostatic (rather than purely steric) strategy to discourage aggregation means that less bulky systems (for example, containing a primary alkylidene fragment, ?CHR) are accessible. 相似文献
999.
Phenyltrimethylammonium Salts as Methylation Reagents in the Nickel‐Catalyzed Methylation of C−H Bonds 下载免费PDF全文
Takeshi Uemura Mao Yamaguchi Prof. Dr. Naoto Chatani 《Angewandte Chemie (International ed. in English)》2016,55(9):3162-3165
Methylation of C(sp2)?H bonds was achieved through the NiII‐catalyzed reaction of benzamides with phenyltrimethylammonium bromide or iodide as the source of the methyl group. The reaction has a broad scope and shows high functional‐group compatibility. The reaction is also applicable to the methylation of C(sp3)?H bonds in aliphatic amides. 相似文献
1000.
Friedel–Crafts‐Type Intermolecular C−H Silylation of Electron‐Rich Arenes Initiated by Base‐Metal Salts 下载免费PDF全文
Dr. Qin Yin Dr. Hendrik F. T. Klare Prof. Dr. Martin Oestreich 《Angewandte Chemie (International ed. in English)》2016,55(9):3204-3207
An electrophilic aromatic substitution (SEAr) with a catalytically generated silicon electrophile is reported. Essentially any commercially available base‐metal salt acts as an initiator/catalyst when activated with NaBArF4 . The thus‐generated Lewis acid then promotes the SEAr of electron‐rich arenes with hydrosilanes but not halosilanes. This new C?H silylation was optimized for FeCl2 /NaBArF4 , affording good yields at catalyst loadings as low as 0.5 mol %. The procedure is exceedingly straightforward and comes close to typical Friedel–Crafts methods, where no added base is needed to absorb the released protons. 相似文献