全文获取类型
收费全文 | 3245篇 |
免费 | 85篇 |
国内免费 | 21篇 |
专业分类
化学 | 1921篇 |
晶体学 | 28篇 |
力学 | 86篇 |
数学 | 473篇 |
物理学 | 501篇 |
无线电 | 342篇 |
出版年
2023年 | 23篇 |
2021年 | 35篇 |
2020年 | 43篇 |
2019年 | 35篇 |
2018年 | 28篇 |
2017年 | 27篇 |
2016年 | 54篇 |
2015年 | 52篇 |
2014年 | 55篇 |
2013年 | 142篇 |
2012年 | 151篇 |
2011年 | 158篇 |
2010年 | 90篇 |
2009年 | 79篇 |
2008年 | 172篇 |
2007年 | 150篇 |
2006年 | 175篇 |
2005年 | 149篇 |
2004年 | 116篇 |
2003年 | 100篇 |
2002年 | 112篇 |
2001年 | 45篇 |
2000年 | 39篇 |
1999年 | 44篇 |
1998年 | 49篇 |
1997年 | 39篇 |
1996年 | 32篇 |
1995年 | 36篇 |
1994年 | 37篇 |
1993年 | 40篇 |
1992年 | 33篇 |
1991年 | 36篇 |
1990年 | 31篇 |
1989年 | 52篇 |
1988年 | 38篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 55篇 |
1984年 | 54篇 |
1983年 | 43篇 |
1982年 | 52篇 |
1981年 | 59篇 |
1980年 | 37篇 |
1979年 | 27篇 |
1978年 | 45篇 |
1977年 | 36篇 |
1976年 | 51篇 |
1975年 | 39篇 |
1974年 | 37篇 |
1973年 | 33篇 |
排序方式: 共有3351条查询结果,搜索用时 687 毫秒
51.
There is a need to develop broadly applicable, highly sensitive detection methods for microchip CE that do not require analyte derivatization. LIF is highly sensitive but typically requires analyte derivatization. Electrochemistry provides an alternative method for direct analyte detection; however, in its most common form, direct current (DC) amperometry, it is limited to a small number of easily oxidizable or reducible analytes. Pulsed amperometric detection (PAD) is an alternative waveform that can increase the number of electrochemically detectable analytes. Increasing sensitivity for electrochemical detection (EC) and PAD requires the isolation of detection current (nA) from the separation current (muA) in a process generally referred to as current decoupling. Here, we present the development of a simple integrated decoupler to improve sensitivity and its coupling with PAD. A Pd microwire is used as the cathode for decoupling and a second Au or Pt wire is used as the working electrode for either EC or PAD. The electrode system is easy to make, requiring no clean-room facilities or specialized metallization systems. Sensitive detection of a wide range of analytes is shown to be possible using this system. Using this system we were able to achieve detection limits as low as 5 nM for dopamine, 74 nM for glutathione, and 100 nM for glucose. 相似文献
52.
Ann M. Schmiedekamp Igor A. Topol Stanley K. Burt Holy Razafinjanahary Henry Chermette Timothy Pfaltzgraff Christopher J. Michejda 《Journal of computational chemistry》1994,15(8):875-892
The consistency of three density functional computational implementations (DMol, DGauss, and deMon) are compared with high-level Hartree–Fock and Møller–Plesset (MP) calculations for triazene (HN?NNH2) and formyl triazene (HN?NNHCOH). Proton affinities on all electronegative sites are investigated as well as the geometries of the neutral and protonated species. Density functional calculations employing the nonlocal gradient corrections show agreement with MP calculations for both proton affinities and geometries of neutral and protonated triazenes. Local spin density approximation DMol calculations using numerical basis sets must employ an extended basis to agree with other density functional codes using analytic Gaussian basis sets. The lowest energy conformation of triazene was found to be nonplanar; however, the degree of nonplanarity, as well as some bond lengths, is dependent on the basis set, electron correlation treatment, and methods used for the calculation. © 1994 by John Wiley & Sons, Inc. 1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America. 相似文献
53.
54.
Silvia G. Motti Manuel Kober-Czerny Marcello Righetto Philippe Holzhey Joel Smith Hans Kraus Henry J. Snaith Michael B. Johnston Laura M. Herz 《Advanced functional materials》2023,33(32):2300363
Metal halide perovskite (MHP) semiconductors have driven a revolution in optoelectronic technologies over the last decade, in particular for high-efficiency photovoltaic applications. Low-dimensional MHPs presenting electronic confinement have promising additional prospects in light emission and quantum technologies. However, the optimisation of such applications requires a comprehensive understanding of the nature of charge carriers and their transport mechanisms. This study employs a combination of ultrafast optical and terahertz spectroscopy to investigate phonon energies, charge-carrier mobilities, and exciton formation in 2D (PEA)2PbI4 and (BA)2PbI4 (where PEA is phenylethylammonium and BA is butylammonium). Temperature-dependent measurements of free charge-carrier mobilities reveal band transport in these strongly confined semiconductors, with surprisingly high in-plane mobilities. Enhanced charge-phonon coupling is shown to reduce charge-carrier mobilities in (BA)2PbI4 with respect to (PEA)2PbI4. Exciton and free charge-carrier dynamics are disentangled by simultaneous monitoring of transient absorption and THz photoconductivity. A sustained free charge-carrier population is observed, surpassing the Saha equation predictions even at low temperature. These findings provide new insights into the temperature-dependent interplay of exciton and free-carrier populations in 2D MHPs. Furthermore, such sustained free charge-carrier population and high mobilities demonstrate the potential of these semiconductors for applications such as solar cells, transistors, and electrically driven light sources. 相似文献
55.
Faisal Ahmed Carlos Rodríguez-Fernández Henry A. Fernandez Yi Zhang Abde Mayeen Shafi Md Gius Uddin Xiaoqi Cui Hoon Hahn Yoon Naveed Mehmood Andreas C. Liapis Lide Yao Humeyra Caglayan Zhipei Sun Harri Lipsanen 《Advanced functional materials》2023,33(33):2302051
Developing selective and coherent polymorphic crystals at the nanoscale offers a novel strategy for designing integrated architectures for photonic and optoelectronic applications such as metasurfaces, optical gratings, photodetectors, and image sensors. Here, a direct optical writing approach is demonstrated to deterministically create polymorphic 2D materials by locally inducing metallic 1T′-MoTe2 on the semiconducting 2H-MoTe2 host layer. In the polymorphic-engineered MoTe2, 2H- and 1T′- crystalline phases exhibit strong optical contrast from near-infrared to telecom-band ranges (1–1.5 µm), due to the change in the band structure and increase in surface roughness. Sevenfold enhancement of third harmonic generation intensity is realized with conversion efficiency (susceptibility) of ≈1.7 × 10−7 (1.1 × 10−19 m2 V−2) and ≈1.7 × 10−8 (0.3 × 10−19 m2 V−2) for 1T′ and 2H-MoTe2, respectively at telecom-band ultrafast pump laser. Lastly, based on polymorphic engineering on MoTe2, a Schottky photodiode with a high photoresponsivity of 90 AW−1 is demonstrated. This study proposes facile polymorphic engineered structures that will greatly benefit realizing integrated photonics and optoelectronic circuits. 相似文献
56.
57.
58.
59.
Using recently developed theoretical techniques it has been possible to achieve an exact variational solution of the Schrödinger equation within a modest basis set or one-eleltron functions. The full configuration interaction for this system included a total of 256473 1A1 spin-and space-adapted configurations. Comparison with many-body perturbation theory proves to be quite interesting. 相似文献
60.
Cyrille Ceugniet Ltitia Lepetit Nancy Lauth De Viguerie Henry Jammes Nicole Peyrot Monique Rivire 《Journal of chromatography. A》1998,810(1-2):237-240
A high-performance liquid chromatographic (HPLC) procedure was developed to allow the rapid separation, in a single run, of a mixture of the main retinal isomers (all-trans, 13-cis, 9-cis), all-trans-retinol, and of the two major photooxygenated photoproducts (5,8-peroxyretinal and 5,6-epoxyretinal). The mixture was separated by HPLC on an octadecyl (ODS) column with 16% (v/v) diethyl ether in hexane as mobile phase and anthracene as the internal standard. A commercial type cosmetic formulation containing 0.05% all-trans-retinal was analyzed successfully for this analyte. 相似文献