全文获取类型
收费全文 | 5742篇 |
免费 | 239篇 |
国内免费 | 43篇 |
专业分类
化学 | 4050篇 |
晶体学 | 35篇 |
力学 | 136篇 |
数学 | 1067篇 |
物理学 | 736篇 |
出版年
2024年 | 10篇 |
2023年 | 44篇 |
2022年 | 132篇 |
2021年 | 162篇 |
2020年 | 105篇 |
2019年 | 128篇 |
2018年 | 106篇 |
2017年 | 82篇 |
2016年 | 194篇 |
2015年 | 175篇 |
2014年 | 203篇 |
2013年 | 348篇 |
2012年 | 398篇 |
2011年 | 442篇 |
2010年 | 285篇 |
2009年 | 288篇 |
2008年 | 355篇 |
2007年 | 371篇 |
2006年 | 341篇 |
2005年 | 329篇 |
2004年 | 241篇 |
2003年 | 178篇 |
2002年 | 181篇 |
2001年 | 83篇 |
2000年 | 66篇 |
1999年 | 55篇 |
1998年 | 42篇 |
1997年 | 46篇 |
1996年 | 71篇 |
1995年 | 40篇 |
1994年 | 38篇 |
1993年 | 37篇 |
1992年 | 45篇 |
1991年 | 33篇 |
1990年 | 20篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 21篇 |
1986年 | 25篇 |
1985年 | 37篇 |
1984年 | 31篇 |
1983年 | 22篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1975年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有6024条查询结果,搜索用时 15 毫秒
271.
272.
K. Esquivel Ma. G. García J. F. J. Rodríguez M. Vega González L. Escobar-Alarcón Luis Ortiz-Frade Luis A. Godínez 《Journal of nanoparticle research》2011,13(8):3313-3325
This study presents the synthesis of TiO2 doped with different amounts of Co and Ni, starting from a simple metallic titanium powder. A successful electrophoretic
deposition of these materials on ITO electrodes was achieved for its potential application as photoanodes. EDX, diffuse reflectance
UV–Vis spectroscopy, and XRD measurements gave information on the chemical composition of the material and the location of
the Ni or Co within the crystal structure of TiO2. Raman spectroscopy suggests that for a higher content of doping metal above a defined percentage, the formation of metal
oxide is promoted. A preliminary study of photoelectrocatalytic orange dye degradation shows higher color removal efficiency
as compared to the commercial TiO2 material. 相似文献
273.
274.
275.
Sanjurjo Emilio Naya Miguel Ángel Blanco-Claraco José Luis Torres-Moreno José Luis Giménez-Fernández Antonio 《Nonlinear dynamics》2017,88(3):1935-1951
Nonlinear Dynamics - Multibody simulations are already used in many industries to speed up the development of new products. However, improvements in multibody formulations and the continuous... 相似文献
276.
Luis H. Mendoza-Huizar Clara H. Rios-Reyes 《Journal of Solid State Electrochemistry》2011,15(4):737-745
An electrochemical study of cobalt electrodeposition onto a polycrystalline platinum electrode from an aqueous solution (10−2 M CoCl2 + 1 M NH4Cl (pH 9.5)) was carried out through cyclic voltammetry and potential step techniques. Analysis of the voltammetric data clearly
showed that a cobalt adlayer is formed during the application of potential in the underpotential deposition (upd) region.
Formation of this cobalt adlayer involved the simultaneous presence of both adsorption and 2D nucleation processes. Cobalt
adlayers obtained by linear voltammetry in upd region were analyzed employing diffuse reflectance spectroscopy (DRS). By using
theoretical quantum studies at PM6//HF/LANL1MB level, it was possible to assign the peaks obtained by DRS at 328 and 337 nm
to the cobalt adsorption on Pt(111) and Pt(100), respectively, while the signals recorded at 355 and 362 nm were related with
the clean platinum surfaces Pt(100) and Pt(111). Also, quantum calculations at the PM6 level indicated that the energy formation
order is Co-Pt(100) > Co-Pt(111) > Co-Pt(110) > Co-Co(surface). 相似文献
277.
In this paper we prove a quantitative form of Landis’ conjecture in the plane. Precisely, let W(z) be a measurable real vector-valued function and V(z) ≥0 be a real measurable scalar function, satisfying ‖W‖ L ∞(R 2) ≤ 1 and ‖V‖ L ∞(R 2) ≤ 1. Let u be a real solution of Δu ? ?(Wu) ? Vu = 0 in R 2. Assume that u(0) = 1 and |u(z)| ≤exp (C 0|z|). Then u satisfies inf |z 0| =R sup |z?z 0| <1|u(z)| ≥exp (?CRlog R), where C depends on C 0. In addition to the case of the whole plane, we also establish a quantitative form of Landis’ conjecture defined in an exterior domain. 相似文献
278.
Nobuyoshi Koga Yuri Goshi Shuto Yamada Luis A. Pérez-Maqueda 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1463-1474
Practical usefulness of the kinetic deconvolution for partially overlapped thermal decomposition processes of solids was examined by applying to the co-precipitated basic zinc carbonate and zinc carbonate. Comparing with the experimental deconvolutions by thermoanalytical techniques and mathematical deconvolutions using different statistical fitting functions, performance of the kinetic deconvolution based on an accumulative kinetic equation for the independent processes overlapped partially was evaluated in views of the peak deconvolution and kinetic evaluation. Two-independent kinetic processes of thermal decompositions of basic zinc carbonate and zinc carbonate were successfully deconvoluted by means of the thermoanalytical measurements in flowing CO2 and by applying sample controlled thermal analysis (SCTA). The deconvolutions by the mathematical curve fittings using different fitting functions and subsequent formal kinetic analysis provide acceptable values of the mass-loss fractions and apparent activation energies of the respective reaction processes, but the estimated kinetic model function changes depending on the fitting functions employed for the peak deconvolution. The mass-loss fractions and apparent kinetic parameters of the respective reaction processes can be optimized simultaneously by the kinetic deconvolution based on the kinetic equation through nonlinear least square analysis, where all the parameters indicated acceptable correspondences to those estimated through the experimental and mathematical deconvolutions. As long as the reaction processes overlapped are independent kinetically, the simple and rapid procedure of kinetic deconvolution is useful as a tool for characterizing the partially overlapped kinetic processes of the thermal decomposition of solids. 相似文献
279.
Rosa Ana Pérez José Luis Tadeo Beatriz Albero Esther Miguel Consuelo Sánchez-Brunete 《Analytical and bioanalytical chemistry》2013,405(1):389-400
Different extraction methods, followed by gas chromatography coupled to triple quadrupole mass spectrometry, were evaluated for simultaneous extraction of seven polychlorinated biphenyls (PCBs) and six polybrominated diphenyl ethers (PBDEs) from common weeds. Pressurized liquid extraction (PLE) with in-cell clean-up, ultrasound-assisted extraction (UAE) with in-column clean-up, and UAE with dispersive solid-phase extraction (dSPE) clean-up were evaluated and compared. In-cell clean-up with 4 g Florisil and 0.5 g graphitized carbon black (GCB) and two extraction cycles of 10 min with n-hexane–ethyl acetate 80:20 (v/v) at 60 °C were used for the PLE procedure. UAE with in-column clean-up was conducted under conditions similar to those reported for the PLE method whereas in UAE with dSPE clean-up purification of the extract was performed after extraction using primary and secondary amine sorbent (PSA) and GCB. Recovery from 82 to 104 % was obtained for all the compounds by PLE whereas, in general, lower extraction efficiency was obtained by UAE with in-column clean-up (especially for BDE-17 and BDE-183, for which recovery was 70 and 41 %, respectively) and by UAE with dSPE clean-up, for which the main drawback is that BDE-183 cannot be extracted. Finally, PLE was used for analysis of PCBs and PBDEs in different plants (Lolium rigidum, Lactuca serriola, Malva sylvestris, and Verbascum thapsus) collected from residential and/or rural areas of Madrid (Spain). Several of the analyzed compounds were detected at low levels in these plants, but only PCB-153 could be quantified. Figure
Analysis of PCBs and PBDEs from plants 相似文献
280.
We present a comparative study on the C-H stretching vibrations at air/DMSO (dimethyl sulfoxide) interface with both the free-induction decay (FID) coherent vibrational dynamics and the sub-wavenumber high resolution sum-frequency generation vibrational spectroscopy measurements. In principle the frequency-domain and time-domain spectroscopic measurements should generate identical information for a given molecular system. However, when the molecular systems are with several coupled or overlapping vibrational modes, obtain- ing detailed spectroscopic and coherent dynamics information is not as straightforward and rather difficult from either the time-domain or the frequency domain measurements. For the case of air/DMSO interface that is with moderately complex vibrational spectra, we show that the frequency-domain measurement with sub-wavenumber high-resolution sum-frequency generation vibrational spectroscopy is probably more advantageous than the time- domain measurement in obtaining quantitative understanding of the structure and coherent dynamics of the molecular interface. 相似文献