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991.
Summary HPTLC densitometry and HPLC are considered for the simultaneous determination of the degradation products of piroxicam (2-aminopyridine,
DP-I and DP-II). The substances were separated on silica gel with fluorescence indicator in ethylacetate — toluene — diethylamine
(10∶10∶5) and toluene — absolute ethanol — glacial acetic acid (8∶1.2∶0.5) systems. The measuring absorbance (detection of
reflectance) of the separated substances was carried out “in situ” at 296 nm using 4-level calibration (external standard,
nonlinear regresson function) in the concentration range 600–1200 ng 2-aminopyridine/spot and 300–600 ng DP-I and DP-II/spot.
The HPLC method was carried out using RP-8 stationary phase and methanol + phosphate-citrate buffer, pH 3 mobile phase with
addition of sodium pentanesulfonate (40+60, v/v). 2-aminopyridine wass detected at 300 nm, DP-I at 280 nm and DP-II at 248
nm. The concentration range for 2-aminopyridine is 2–40 μg/ml, for DP-I and DP-II 2–20 μg/ml (for an injection volume of 10
μl). The results were evaluated by linear regression analysis. 相似文献
992.
The extraction of radium into a mixture of 2-thenoyltrifluoroacetone (HTTA) and tributyl phosphate (TBP) or trioctylphosphine oxide (TOPO) in n-hexane or cyclohexane has been investigated with regard to the dependence on pH, and TBP and TOPO concentrations. It has been found that the formation of mixed complexes of the type Ra(TTA)2 (TBP)2 and Ra(TTA)2(TOPO)2 occurs and the overall extraction constants of both complexes were calculated. With the systems described, very high distribution ratios of radium have been attained; these may advantageously be used for the separation and concentration of traces of radium. 相似文献
993.
A complete study of the defects created in the gate oxide and at the gate oxide/substrate interface of metal-oxide-semiconductor transistors with thick gate oxide (tox > 10 nm) during high electric field stress, and the mechanisms responsible for these defects creation have been given. In addition, some results of positive/negative high electric field stress with constant gate voltage of commercial n-channel power metal-oxide-semiconductor transistors with thick gate oxide of 100 nm, have been explained using this study. 相似文献
994.
Virgil Percec Gary Johansson Douglas Schlueter Joan C. Ronda Goran Ungar 《Macromolecular Symposia》1996,101(1):43-60
The principles of self-assembly of tapered exo-receptors constructed from monodendrons containing crown-ether, oligooxyethylenic groups and polymer backbones as endo-receptors into tubular supramolecular architectures are described with selected examples. In the case of polymers with flexible backbones it is suggested that a helical chain conformation is induced during the assembly of its own tapered side groups. This mechanism is supported by the enhanced self-assembling ability of tapered side groups attached to a backbone with rigid helical conformation. 相似文献
995.
C.M. Papadakis K. Almdal K. Mortensen F. Rittig G. Fleischer P. Štěpánek 《The European physical journal. E, Soft matter》2000,1(4):275-283
We have studied the bulk dynamics of a compositionally asymmetric poly(ethylene propylene)-poly(dimethylsiloxane) (PEP-PDMS)
diblock copolymer in a large temperature range both in the ordered and in the disordered state. The volume fraction of the
PEP block is 0.22. Apart from the disordered state, the sample shows three ordered morphologies. Using dynamic light scattering,
we have investigated the dynamics in all four phases and combined these results with those obtained using pulsed field gradient
NMR. In the disordered state, we find--apart from the slow cluster mode--the heterogeneity mode related to the self-diffusion
of single chains. The relaxation time of this mode, reduced by temperature and the zero-shear viscosity , , increases with temperature. In the cubic phase right below the ODT temperature, we observe two diffusive processes, and
we attribute the faster one to the mutual diffusion of micelles and block copolymers not bound to micelles (“free chains”)
through the PDMS matrix. The slower mode may either be due to the mutual diffusion of free chains and chains bound to PEP
micelles or to the cooperative diffusion of micellar aggregates. In the non-cubic ordered state at intermediate temperatures,
an additional weak diffusive mode is observed. The low-temperature ordered state is body-centered cubic, and here, only the
mutual diffusion of micelles and free chains lies in our experimental time window.
Received 19 March 1999 and Received in final form 25 August 1999 相似文献
996.
Peter Švančárek Peter Schwendt Jozef Tatiersky Ivana Smatanová Jaromír Marek 《Monatshefte für Chemie / Chemical Monthly》2000,131(2):145-154
Summary. Oxo peroxo glycolato complexes of vanadium(V) (M
2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=NBu4
+ (1), K+ (2), NH4
+ (3), Cs+ (4), NPr4
+ (5)) as well as (NBu4)2[V2O4(C2H2O3)2]ċ H2O (6) have been prepared and characterized by spectroscopic methods. X-Ray structure analysis of 1 revealed the presence of dinuclear [V2O2(O2)2(C2H2O3)2]2− anions with a (chemical structure) bridging core and six coordinated vanadium(V) atoms in a distorted pentagonal pyramidal
array.
Received July 12, 1999. Accepted (revised) October 28, 1999 相似文献
997.
In our laboratory, the synthesis of new inorganic pigments is followed by thermal analysis using a derivatograph apparatus.
First information about the temperature region of the formation of the pigments investigated is provided by thermal analysis.
The attention was directed to the preparation of the pigments based on zinc oxide in new green hues which can be used as medium
colour pigments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
998.
A zinc oxide pigment with an admixture of bismut oxide has been prepared as new yellow pigment for colouring of plastics and
paints. The effect of the Bi2 O3 in the starting mixture on the colour hue of the pigment has been evaluated. The calcination conditions of the pigment synthesis
have been established. The synthesis of these pigments was followed by thermal analysis using a derivatograph apparatus in
our laboratory. The optimum conditions for the synthesis of pigments and the properties of the products have been estimated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
999.
Urška L. Štangar Boris Orel Neva Grošelj Patrick Judeinstein Franco Decker Panagiotis Lianos 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):103-112
Summary. A hybrid silicon precursor (ICS-PPG) obtained by reaction of 3-isocyanatopropyltriethoxy silane with poly-(propyleneglycol)-bis-(2-aminopropyl ether) was recognized as a potential host for various salts and molecular species. It has been used for electrochromic,
gasochromic, photovoltaic, and fuel cell applications. This focuses on proton conducting gels (PWA/ICS-PPG, SiWA/ICS-PPG, and W-PTA/ICS-PPG) obtained after the incorporation of polyoxometalates in the ICS-PPG host. IR spectroscopic measurements are used to reveal the entrapment, the aggregation, and the interactions of W-PTA, PWA, or SiWA with the sol-gel derived network. The proton conductivity of the composites, measured using impedance spectroscopy, increases
with increasing concentration of the polyoxometalates from 10−6 to 10−3 S/cm.
Received June 23, 2000. Accepted (revised) September 18, 2000 相似文献
1000.
The crystallization process of Li2B4O7 in the glass of stoichiometric composition, characterized by the crystal growth of pre-existing nuclei, was analyzed kinetically
by means of DTA. Because the number of pre-existing nuclei for the subsequent growth varies depending on the cooling rate
of the glass-forming melt and heating rate of the as-prepared glass, a modified Kissinger plot was applied for evaluating
the apparent activation energy to the crystal growth in the glass samples with three different thermal histories, i.e., the
pre-annealed, slowly quenched and quickly quenched glasses. The process was characterized by the three dimensional growth
of pre-existing nuclei with the apparent activation energy of ca 340 kJ mol−1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献