全文获取类型
收费全文 | 1487篇 |
免费 | 66篇 |
国内免费 | 4篇 |
专业分类
化学 | 1308篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 106篇 |
物理学 | 130篇 |
出版年
2024年 | 1篇 |
2023年 | 20篇 |
2022年 | 29篇 |
2021年 | 40篇 |
2020年 | 39篇 |
2019年 | 26篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 60篇 |
2014年 | 71篇 |
2013年 | 90篇 |
2012年 | 107篇 |
2011年 | 105篇 |
2010年 | 61篇 |
2009年 | 56篇 |
2008年 | 95篇 |
2007年 | 99篇 |
2006年 | 87篇 |
2005年 | 80篇 |
2004年 | 58篇 |
2003年 | 44篇 |
2002年 | 56篇 |
2001年 | 12篇 |
2000年 | 27篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 18篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有1557条查询结果,搜索用时 31 毫秒
921.
Eva Bittrich Marco Kuntzsch Klaus-Jochen Eichhorn Petra Uhlmann 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):1606-1615
The ability of a mixed polymer brush consisting of poly(N-isopropyl acrylamide) (PNIPAAM) and poly(acrylic acid) (PAA) to modify physicochemical interfacial properties is presented. The answer of the binary brush toward changes of environmental conditions like temperature, salt concentration, and pH value was investigated by in situ spectroscopic VIS-ellipsometry as well as AFM and contact angle mesurements in the dry state and compared with the behavior of the corresponding homopolymer brushes. A coupled swelling of PNIPAAm and PAA could be found, leading to a complex pH-, salt-, and temperature-sensitive swelling behavior of these mixed brushes, also depending on the composition of the brush. The complex interaction of the two polymers resulted in new properties of the mixed system. Although the temperature sensitivity of the mixed system was decreased compared with that of the corresponding PNIPAAM brushes, the sensitivity toward pH and salt concentration was amplified compared with that of pure PAA brushes. Additionally it is shown that in spite of the decreased temperature sensitivity of the mixed brush, a temperature-dependent adsorption of human serum albumin was observed whereas an increased adsorption affinity was found that is not predictable from the adsorption affinity of the corresponding homopolymer brushes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1606–1615, 2010 相似文献
922.
923.
Hana Brozmanová Ilona Peřinová Petra Halvová Milan Grundmann 《Journal of separation science》2010,33(15):2287-2293
A LC‐MS/MS method was developed and validated for the determination of cyclosporine A (CsA) and its three phase 1 metabolites AM1, AM9, and AM4N in whole blood and lymphocytes isolated on the Histopaque gradient. 200 μL of whole blood was precipitated with 10 mol/L zinc sulfate in acetonitrile/methanol (40:60, v/v) and lymphocytes isolated from 1.5 mL blood were extracted with acetonitrile/methanol (40:60, v/v). The analytes and internal standard cyclosporine D were separated on RP column BEH C18, 2.1×50 mm, 1.7 μm using gradient LC‐MS/MS analysis in positive electrospray mode. Time of analysis was 5 min. Linearity in blood was 5–2000 μg/L for CsA, AM1, and AM9; 2–500 μg/L for AM4N; and 2–500 μg/L for all substances in lymphocytes. Coefficient of variations was 1.8–9.8% and recovery was 92.0–110.0%. The method was used in early and chronic renal transplant patients for therapeutic drug monitoring of CsA to compare either its share in lymphocytes as target organ or binding to one lymphocyte. The same parameters were calculated for all metabolites tested. 相似文献
924.
Petra Šulcová Lucie Vitásková Miroslav Trojan 《Journal of Thermal Analysis and Calorimetry》2010,99(2):409-413
Compounds based on CeO2 were synthesized as high-temperature environment-friendly inorganic pigments with interesting hues. The pigments have been
synthesized by using the solid state reaction in the temperature range from 1,300 to 1,600 °C. The host lattice of these pigments
is CeO2 that is doped by terbium ions. The incorporation of doped ions provides interesting orange colours after application into
ceramic glaze. The goal was to develop conditions for the synthesis of these compounds and to determine the influence of calcination
temperature on their colouring effects. The simultaneous TG-DTA measurements were used for determination of the temperature
region of the pigment formation and thermal stability of pigments. The pigments were also evaluated from the standpoint of
their structure and particle sizes. 相似文献
925.
Novel fused azecine ring systems were synthesized via the microwave-assisted thermal isomerization of terphenyl or biphenyl-pyridazine compounds possessing a vinyl and a tert-amino group, through application of a new extension of the tert-amino effect. Substrates for the ring closure were prepared from ortho-dihalobenzene or pyridazinone by consecutive Suzuki couplings with ortho-sec-amino- and formylphenylboronic acids, followed by Knoevenagel condensation of the aldehydes obtained. 相似文献
926.
Nikolai V. Tkachenko Petra Kaplas Alexander Efimov Jukka Viheriälä Helge Lemmetyinen 《Applied Surface Science》2010,256(12):3900-1928
Thin organic films were deposited on silicon oxide surfaces with golden interdigitated electrodes (interelectrode gap was 2 μm), and the film resistivities were measured in dark and under white light illumination. The compounds selected for the measurements include molecules widely used in solar cell applications, such as polythiophene (PHT), fullerene (C60), pyrelene tetracarboxylic diimide (PTCDI) and copper phthalocyanine (CuPc), as well as molecules potentially interesting for photovoltaic applications, e.g. porphyrin-fullerene dyads. The films were deposited using thermal evaporation (e.g. for C60 and CuPc films), spin coating for PHT, and Langmuir-Schaeffer for the layer-by-layer deposition of porphyrin-fullerene dyads. The most conducting materials in the series are films of PHT and CuPc with resistivities 1.2 × 103 Ω m and 3 × 104 Ω m, respectively. Under light illumination resistivity of all films decreases, with the strongest light effect observed for PTCDI, for which resistivity decreases by 100 times, from 3.2 × 108 Ω m in dark to 3.1 × 106 Ω m under the light. 相似文献
927.
Petra J. van Houdt Jan C. de Munck Maeike Zijlmans Geertjan Huiskamp Frans S.S. Leijten Paul A.J.M. Boon Pauly P.W. Ossenblok 《Magnetic resonance imaging》2010
The simultaneous recording of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) can be used to localize interictal epileptiform discharges (IEDs). Previous studies have reported varying degrees of concordance of EEG-fMRI with electroclinical findings. The aim of the present study is to evaluate to what extent this variability is determined by the analytical strategy or by the properties of the EEG data. For that purpose, 42 IED sets obtained in 29 patients with epilepsy were reanalyzed using a finite impulse response approach, which estimates the hemodynamic response function (HRF) from the data and allows non-causal effects. Cardiac effects were treated as additional confounders in the model. This approach was compared to the classical approach assuming a fixed HRF for each voxel in the brain. The performance of each method was assessed by comparing the fMRI results to the EEG focus. The flexible model revealed more significantly activated voxels, which resulted in more activated brain regions concordant with the EEG focus (26 vs. 16). Correction for cardiac effects improved the results in 7 out of the 42 data sets. Furthermore, design theory for event-related experiments was applied in order to determine the influence of the number of IEDs and their temporal distribution on the success of an experiment. It appeared that this success is highly dependent upon the number of IEDs present during the recording and less on their temporal spacing. We conclude that the outcome of EEG-fMRI can be improved by using an optimized analytical strategy, but also depends on the number of IEDs occurring during the recording. 相似文献
928.
N. Petra J. Zweck A. A. Kosterev S. E. Minkoff D. Thomazy 《Applied physics. B, Lasers and optics》2009,94(4):673-680
Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors are based on a recent approach to photoacoustic detection which
employs a quartz tuning fork as an acoustic transducer. These sensors enable detection of trace gases for air quality monitoring,
industrial process control, and medical diagnostics. To detect a trace gas, modulated laser radiation is directed between
the tines of a tuning fork. The optical energy absorbed by the gas results in a periodic thermal expansion which gives rise
to a weak acoustic pressure wave. This pressure wave excites a resonant vibration of the tuning fork thereby generating an
electrical signal via the piezoelectric effect. This paper describes a theoretical model of a QEPAS sensor. By deriving analytical
solutions for the partial differential equations in the model, we obtain a formula for the piezoelectric current in terms
of the optical, mechanical, and electrical parameters of the system. We use the model to calculate the optimal position of
the laser beam with respect to the tuning fork and the phase of the piezoelectric current. We also show that a QEPAS transducer
with a particular 32.8 kHz tuning fork is 2–3 times as sensitive as one with a 4.25 kHz tuning fork. These simulation results
closely match experimental data. 相似文献
929.
930.
Noureddine Igbida Karima Sbihi Petra Wittbold 《NoDEA : Nonlinear Differential Equations and Applications》2010,17(1):69-93
We consider a class of nonlinear degenerate problems of Stefan type: $u_t- \Delta w -\nabla F(u,w)= g(\cdot,u), \ w\in \beta(u)$ where β is a maximal monotone graph in ${\mathbb{R}^2,}We consider a class of nonlinear degenerate problems of Stefan type:
ut- Dw -?F(u,w) = g(·,u), w ? b(u)u_t- \Delta w -\nabla F(u,w)= g(\cdot,u), \ w\in \beta(u) 相似文献 |