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81.
82.
The conformers of the monohalocyclohexasilanes, Si6H11X (X=F, Cl, Br or I) and the haloundecamethylcyclohexasilanes, Si6Me11X (X=F, Cl, Br or I) are investigated by DFT calculations employing the B3LYP density functional and 6‐31+G* basis sets for elements up to the third row, and SDD basis sets for heavier elements. Five minima are found for Si6H11X—the axial and equatorial chair conformers, with the substituent X either in an axial or equatorial position—and another three twisted structures. The equatorial chair conformer is the global minimum for the X=Cl, Br and I, the axial chair for X=F. The barrier for the ring inversion is ~13 kJ mol?1 for all four compounds. Five minima closely related to those of Si6H11X are found for Si6Me11X. Again, the equatorial chair is the global minimum for X=Cl, Br and I, and the axial chair for X=F. Additionally, two symmetrical boat conformers are found as local minima on the potential energy surfaces for X=F, Cl and Br, but not for X=I. The barrier for the ring inversion is ~14–16 kJ mol?1 for all compounds. The conformational equilibria for Si6Me11X in toluene solution are investigated using temperature dependent Raman spectroscopy. The wavenumber range of the stretching vibrations of the heavy atoms X and Si from 270–370 cm?1 is analyzed. Using the van′t Hoff relationship, the enthalpy differences between axial and equatorial chair conformers (Hax?Heq.) are 1.1 kJ mol?1 for X=F, and 1.8 to 2.8 kJ mol?1 for X=Cl, Br and I. Due to rapid interconversion, only a single Raman band originating from the “averaged” twist and boat conformers could be observed. Generally, reasonable agreement between the calculated relative energies and the experimentally determined values is found. 相似文献
83.
Leaching test for calcined kaolinite and kaolinite/TiO<Subscript>2</Subscript> photoactive composite
Michaela Tokarčíková Kateřina Mamulová Kutláková Jana Seidlerová 《Chemical Papers》2016,70(9):1253-1261
Kaolinite is a suitable material for fixing TiO2 nanoparticles in a composite form. The kaolinite/TiO2 composite has promising photoactive properties which are as important as is the possible impact of the composite on the environment. Accordingly, the stability of the kaolinite/TiO2 composite dried at 105°C (KTI1) and calcined at 600 °C (KTI6) and the stability of the original kaolinite treated at various temperatures (105–800 °C) were studied by the leaching test in accordance with European standard BS EN 12457-2:2002 (British Standards Institution, 2002). The stability was evaluated on the basis of elements leached from the materials to extraction agents. Atomic emission spectrometry with inductively coupled plasma was used for determining the concentration of elements. In order to better understand the process of calcination and the structure changes in the kaolinite/TiO2 composite and calcined kaolinite, the materials were evaluated using X-ray powder diffraction and infrared spectroscopy with Fourier transformation. The processes of kaolinite dehydroxylation and metakaolinite formation were observed. Kaolinite is an appropriate carrier for composite preparation due to its stability even after its treatment at high temperatures. The experiments confirmed the TiO2 nanoparticles to be very strongly bound to the kaolinite surface. On the other hand, the experiments demonstrated that the presence of TiO2 on the kaolinite surface caused the release of Al in high concentrations to the final extracts, especially after kaolinite/TiO2 composite calcination. 相似文献
84.
For many clinical purposes various artificial devices are applied, which contact human tissue and can thus cause adverse reactions between prosthetic surfaces and body components. Of the many materials applied for orthopaedic joint replacements the most common are cobalt-chromium-molybdenum alloys. In these cases considerable amounts of cobalt-chromium-molybdenum wear particles are released from the prostheses which have to be regarded as a cause of long-time problems for the patient.Since these particles are dissolved in body fluids of the surrounding area they are distributed in the whole body via blood. Elevated metal concentrations have been found in blood and urine of persons with endoprostheses. Partly the metals are excreted via urine, but to some extend they accumulate in different organs.Therefore this study dealt with the development of an analytical method for the determination of seven relevant trace elements, namely Al, Co, Cr, Mo, Nb, Ni, and Ti in nine kinds of human tissue (brain, heart, kidney, liver, lung, muscle, lymphatic nodes, spleen, body fat) starting with drawing of the sample, sample work up and finally analysis by means of atomic spectrometry. The optimized method was then applied to determine the metal contents in organs of persons (post mortem) with total hip replacements with metal on metal bearing surfaces. Comparison of the data obtained with those of persons without hip-endoprostheses shows that brain and lung are the main targets for elemental accumulation in persons with hip-endoprostheses. Mo and Nb represent the elements with the highest tendency to be accumulated. 相似文献
85.
86.
Mihly
vri Gbor Murnszky Michaela Zeiner Istvn Virg Ilse Steffan Victor G. Mihucz Enik Tatr Sergio Caroli Gyula Zray 《Microchemical Journal》2007,87(2):159-162
The Platinum Group Elements (PGEs) used in automotive catalytic converters are partly emitted into the air during use and can enter the human respiratory system. Due to the increasing use of automotive catalytic converters, the importance of this problem cannot be overlooked.The goal of this investigation was to determine the concentration of Pt in the urine of individuals occupationally exposed to urban air with heavy traffic. Sector field inductively coupled plasma mass spectrometry (SF–ICP–MS) was used for determination of Pt in the urine of tram drivers. 38 and 34 subjects were investigated in Vienna and Budapest, respectively. Samples were taken from the tram drivers both before and after the shift.The results for Pt were compared to those from a previous study performed by our team. The comparison showed that the concentration medians were 4 times higher than the previous ones. Moreover, the values in Budapest were about twice as high as those from Vienna. A partly significant change could be observed between the two sets of data: before, and after the shift. 相似文献
87.
Rodica Olar Michaela Badea E. Cristurean C. Parnau D. Marinescu 《Journal of Thermal Analysis and Calorimetry》2006,84(1):53-58
The complexes of the type M(HDMBG)2(CH3COO)2·nH2O ((1)
M:Mn, n=1.5; (2)
M:Ni, n=0; (3)
M:Cu, n=2; (4)
M:Zn, n=2; DMBG: N,N-dimethylbiguanide)
present in vitro antimicrobial activity. The thermal analysis has evidenced
the thermal intervals of stability and also the thermodynamics effects that
accompany them. The different nature of the ligands generates a different
thermal behaviour for the complexes. The thermal transformations are complex
processes according to TG and DTG curves including dehydration, oxidative
condensation of –C=N– units as well as thermolysis processes.
The final products of decomposition are the most stable metal oxides. 相似文献
88.
89.
Martín-Matute B Bogár K Edin M Kaynak FB Bäckvall JE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(20):5832-5842
A range of ruthenium cyclopentadienyl (Cp) complexes have been prepared and used for isomerization of allylic alcohols to the corresponding saturated carbonyl compounds. Complexes bearing CO ligands show higher activity than those with PPh3 ligands. The isomerization rate is highly affected by the substituents on the Cp ring. Tetra(phenyl)methyl-substituted catalysts rapidly isomerize allylic alcohols under very mild reaction conditions (ambient temperature) with short reaction times. Substituted allylic alcohols have been isomerized by employing Ru-Cp complexes. A study of the isomerization catalyzed by [Ru(Ph5Cp)(CO)2H] (14) indicates that the isomerization catalyzed by ruthenium hydrides partly follows a different mechanism than that of ruthenium halides activated by KOtBu. Furthermore, the lack of ketone exchange when the isomerization was performed in the presence of an unsaturated ketone (1 equiv), different from that obtained by dehydrogenation of the starting allylic alcohol, supports a mechanism in which the isomerization takes place within the coordination sphere of the ruthenium catalyst. 相似文献
90.
Walter J. Gutjahr Stefan Katzensteiner Peter Reiter Christian Stummer Michaela Denk 《Central European Journal of Operations Research》2008,16(3):281-306
This paper presents a new model for project portfolio selection, paying specific attention to competence development. The
model seeks to maximize a weighted average of economic gains from projects and strategic gains from the increment of desirable
competencies. As a sub-problem, scheduling and staff assignment for a candidate set of selected projects must also be optimized.
We provide a nonlinear mixed-integer program formulation for the overall problem, and then propose heuristic solution techniques
composed of (1) a greedy heuristic for the scheduling and staff assignment part, and (2) two (alternative) metaheuristics
for the project selection part. The paper outlines experimental results on a real-world application provided by the E-Commerce
Competence Center Austria and, for a slightly simplified instance, presents comparisons with the exact solution computed by
CPLEX. 相似文献