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排序方式: 共有491条查询结果,搜索用时 31 毫秒
41.
Dapsens PY Hakim SH Su BL Shanks BH 《Chemical communications (Cambridge, England)》2010,46(47):8980-8982
The current work presents an unprecedented direct observation of macropore formation in the spontaneous self-assembly process to obtain hierarchical meso/macroporous metal oxides made possible with the help of an unusual titanium alkoxide. 相似文献
42.
Paul J. Saines Dr. Brent C. Melot Ram Seshadri Prof. Anthony K. Cheetham Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(25):7579-7585
An anhydrous manganese succinate, Mn(C4H4O4), has been synthesised hydrothermally and studied by single‐crystal X‐ray diffraction. It adopts a succinate pillared structure in which layers of corner‐sharing MnO6 octahedra alternate with sheets that contain chains of edge‐sharing octahedra. This unique 3D framework structure contains highly distorted MnO6 octahedra, which are made possible by the lack of ligand field stabilisation energy for the high‐spin Mn2+ ion. Attempts to dope the structure with other divalent transition‐metal ions were accordingly unsuccessful. Magnetic susceptibility and heat capacity measurements indicate that Mn(C4H4O4) undergoes antiferromagnetic ordering below 12 K, with a second antiferromagnetic transition at approximately 6 K. These two antiferromagnetic phases undergo further transitions in applied fields, underlining the subtle magnetic behaviour that is possible in inorganic–organic frameworks of this structural complexity. 相似文献
43.
We consider associated production of squarks and gluinos with the lightest supersymmetric particle (LSP), or states nearly degenerate in mass with it. Though sub-dominant to pair production of color SU(3)-charged superpartners, these processes are directly sensitive to the wavefunction composition of the lightest neutralinos. Exploiting event-shape variables - including some introduced here for the first time - we are able to identify the composition of the LSP by selecting events involving a single high-pT jet recoiling against missing transverse energy. We illustrate the proposed technique on a set of benchmark cases and propose methods for applying these results in more realistic experimental environments. 相似文献
44.
Christian P. Marocco Erik V. Davis Julie E. Finnell Phung-Hoang Nguyen Scott C. Mateer Ion Ghiviriga Clifford W. Padgett Brent D. Feske 《Tetrahedron: Asymmetry》2011,22(18-19):1784-1789
Fosfomycin is a gram positive and gram negative antibiotic that contains an asymmetric epoxide. An enzyme library was screened for its ability to reduce dimethyl(1-chloro-2-oxopropyl)phosphonate to the corresponding asymmetric chlorohydrin. Homology models were built in MOE, which were shown to accurately model the enzyme–substrate complex displaying the stereoselectivity that we observed. Two enzymes, YDR368w and YHR104w, were chosen for the scale up and synthesis of fosfomycin and its trans-(1S,2S)-diastereomer. 相似文献
45.
A procedure for predicting thermodynamic, dynamic, and rheological properties of polymerically stabilized colloidal dispersions
in good solvents by mapping onto an effective hard sphere dispersion is investigated and evaluated for its range of applicability.
Configurational pressures and energies, calculted by Monte Carlo simulations, are used to assess the model's accuracy for
predicting thermodynamic data. Similarly, long-time self-diffusivities, calculated by equilibrium Brownian Dynamic simulations,
are used to assess the model's feasibility for predicting dynamic properties. Finally, zero shear viscosities are calculated
by the method of hydrodynamic preaveraging and compared to rheological measurements. The various testing methods demonstrate
the effectiveness of the procedure and suggest the model's range of applicability.
Received: 13 March 2000 Accepted: 28 June 2000 相似文献
46.
Thomas R. Cundari Smitha S. Janardan Olayinka Olatunji‐Ojo Brent R. Wilson 《International journal of quantum chemistry》2011,111(15):4303-4308
A computational study of diatomic NiAl is reported. Molecular properties evaluated include the equilibrium bond length (re), equilibrium stretching frequency (ωe), doublet‐quartet energy splitting, and nickel‐aluminum bond strength. Several interesting conclusions have resulted from this research. First, convergence in calculated properties is smoother with recently reported correlation consistent basis sets than earlier basis sets for Ni and Al. Second, with the exception of bond strength, basis set limit properties extrapolated using correlation basis sets are in agreement with reported data. Third, this research suggests that caution may be needed with regard to the use of DFT for developing interatomic potentials for larger scale simulations. For example, B97‐1 showed better agreement with reported re for 2NiAl than B3LYP. However, the situation was reversed for the calculation of ωe. With respect to bond strength, the situation is unclear due to the scatter among experiment and calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
47.
Melissa M. Cadelis Hugo Gordon Alex Grey Soeren Geese Daniel R. Mulholland Bevan S. Weir Brent R. Copp Siouxsie Wiles 《Molecules (Basel, Switzerland)》2021,26(11)
Fungi have become an invaluable source of bioactive natural products, with more than 5 million species of fungi spanning the globe. Fractionation of crude extract of Neodidymelliopsis sp., led to the isolation of a novel polyketide, (2Z)-cillifuranone (1) and five previously reported natural products, (2E)-cillifuranone (2), taiwapyrone (3), xylariolide D (4), pachybasin (5), and N-(5-hydroxypentyl)acetamide (6). It was discovered that (2Z)-cillifuranone (1) was particularly sensitive to ambient temperature and light resulting in isomerisation to (2E)-cillifuranone (2). Structure elucidation of all the natural products were conducted by NMR spectroscopic techniques. The antimicrobial activity of 2, 3, and 5 were evaluated against a variety of bacterial and fungal pathogens. A sodium [1-13C] acetate labelling study was conducted on Neodidymelliopsis sp. and confirmed that pachybasin is biosynthesised through the acetate polyketide pathway. 相似文献
48.
49.
Craig L. Homrighausen Brent J. Kennedy Erick J. Schutte 《Journal of polymer science. Part A, Polymer chemistry》2005,43(20):4922-4932
This research was focused on the design and execution of new synthetic routes to low‐temperature‐curable poly(silarylene–siloxane)polyimides. The synthesis of individual oligoimide and silarylene–siloxane blocks was followed by hydrosilylation polymerization to produce crosslinked copolymers. The silarylene–siloxane and polyimide blocks were structurally characterized by IR and 1H NMR spectroscopy and size exclusion chromatography. The high‐temperature resistance of the copolymers was evaluated through the measurement of heat distortion temperatures (THD's) via thermomechanical analysis and by the determination of the weight loss at elevated temperatures via thermogravimetric analysis. Glass‐transition temperatures (Tg's) of the silarylene–siloxane segments were measured by differential scanning calorimetry. Hydrosilylation curing was conducted at 60 °C in the presence of chloroplatinic acid (H2PtCl6). The copolymers displayed both high‐temperature resistance and low‐temperature flexibility. We observed Tg of the silarylene–siloxane segment as low as ?77 °C and THD of the polyimide segment as high as 323 °C. The influence of various oligoimide molecular weights on the properties of copolymers containing the same silarylene–siloxane was examined. The effect of various silarylene–siloxane molecular weights on the properties of copolymers containing the same oligoimide was also examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4922–4932, 2005 相似文献
50.
Cheng-Kung Liu John A. Cuculo Brent Smith 《Journal of Polymer Science.Polymer Physics》1990,28(4):449-465
An investigation of the diffusion competition between solvent and nonsolvent in a coagulation bath is presented for the formation of a new cellulosic fiber by wet-spinning. The system consisted of the spinnable cellulose solution with a mixture of liquid ammonia/ammonia thiocynate as the solvent and low-molecular-weight alcohols as the nonsolvents. The diffusion competition between solvent and nonsolvent was quantitatively characterized in terms of their mass transfer rate differences. The measurements of this rate difference were performed on the model filament shaped from gelled cellulose solutions. Results revealed that an increase in molecular size of coagulant, bath temperature, and coagulant concentration in the bath enhanced preferential diffusion of solvent from cellulose solution. Fiber spinning experiments showed that a higher value of the initial modulus of the fiber was attained with a coagulation condition providing a lower value of mass transfer rate difference. The importance of mass transfer rate difference was also shown in the influence of the fiber cross-sectional shapes. 相似文献