全文获取类型
收费全文 | 4576篇 |
免费 | 651篇 |
国内免费 | 676篇 |
专业分类
化学 | 3473篇 |
晶体学 | 42篇 |
力学 | 380篇 |
综合类 | 28篇 |
数学 | 480篇 |
物理学 | 1500篇 |
出版年
2023年 | 77篇 |
2022年 | 107篇 |
2021年 | 163篇 |
2020年 | 197篇 |
2019年 | 178篇 |
2018年 | 150篇 |
2017年 | 158篇 |
2016年 | 185篇 |
2015年 | 184篇 |
2014年 | 221篇 |
2013年 | 327篇 |
2012年 | 386篇 |
2011年 | 415篇 |
2010年 | 281篇 |
2009年 | 242篇 |
2008年 | 300篇 |
2007年 | 239篇 |
2006年 | 238篇 |
2005年 | 221篇 |
2004年 | 173篇 |
2003年 | 173篇 |
2002年 | 157篇 |
2001年 | 138篇 |
2000年 | 112篇 |
1999年 | 119篇 |
1998年 | 85篇 |
1997年 | 78篇 |
1996年 | 77篇 |
1995年 | 71篇 |
1994年 | 50篇 |
1993年 | 61篇 |
1992年 | 46篇 |
1991年 | 48篇 |
1990年 | 39篇 |
1989年 | 35篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1970年 | 4篇 |
排序方式: 共有5903条查询结果,搜索用时 62 毫秒
991.
Nanoengineered multifunctional capsules with tailored structures and properties are of particular interest due to their multifunctions and potential applications as new colloidal structures in diverse fields. Among the available fabrication methods, the layer-by-layer (LbL) assembly of multilayer films onto colloidal particles followed by selective template removal has attracted extensive attention due to its advantages of precise control over the size, shape, composition, wall thickness and functions of the obtained capsules. The past decade has witnessed a rapid increase of research concerning the new fabrication strategies, functionalization and applications of this kind of capsules, particularly in the biomedical fields such as drug delivery, biosensors and bioreactors. In this critical review, the very recent progress of the multilayer capsules is summarized. First, the advances in assembly of capsules by the LbL technique are introduced with focus on tailoring the properties of hydrogen-bonded multilayer capsules by cross-linking, and fabrication of capsules based on covalent bonding and bio-specific interactions. Then the fabrication strategies which can speed up capsule fabrication are reviewed. In the following sections, the multi-compartmental capsules and the capsules that can transform their shape under stimulus are presented. Finally, the biomedical applications of multilayer capsules with particular emphasis on drug carriers, biosensors and bioreactors are described (306 references). 相似文献
992.
Advanced multi-compartmental concanavalin A (Con A)/glycogen complex microcapsules incorporated with polymeric micelles were
successfully fabricated by a facile, one-step controlled precipitation method. Dropwise addition of Con A solution into glycogen
solution results in Con A/glycogen complex precipitates, which are captured by polyethyleneimine-modified CaCO3 microparticles, forming a continuous shell structure. Removal of the carbonate cores yields hollow capsules of Con A/glycogen
complex, which have variable sizes and wall thicknesses under different precipitation conditions. The capsules show molecular-recognizable
response to glucose and dextran (M
w, 20 and 40 kDa), leading to breakdown of the capsule structure and release of the incorporated substances such as poly(styrene-b-acrylic acid) micelles. 相似文献
993.
Li‐Hua Tian Dr. Yan‐Xia Zhao Xiao‐Nan Wu Dr. Xun‐Lei Ding Prof. Dr. Sheng‐Gui He Dr. Tong‐Mei Ma 《Chemphyschem》2012,13(5):1282-1288
Oxygen‐rich scandium cluster anions ScO3–5? are prepared by laser ablation and allowed to react with n‐butane in a fast‐flow reactor. A time‐of‐flight mass spectrometer is used to detect the cluster distribution before and after the reactions. The ScO3? and ScO4? clusters can react with n‐butane to produce ScO3H?, ScO3H2?, and ScO4H?, while the more oxygen‐rich cluster ScO5? is inert. The experiment suggests that unreactive cluster isomers of ScO3? and ScO4? are also present in the cluster source. Density functional theory and ab initio methods are used to calculate the structures and reaction mechanisms of the clusters. The theoretical results indicate that the unreactive and reactive cluster isomers of ScO3,4? contain peroxides (O22?) and oxygen‐centered radicals (O.?), respectively. The mechanisms and energetics for conversion of unreactive O22? to reactive O.? species are also theoretically studied. 相似文献
994.
Ding LX Wang AL Li GR Liu ZQ Zhao WX Su CY Tong YX 《Journal of the American Chemical Society》2012,134(13):5730-5733
Porous Pt-Ni-P composite nanotube arrays (NTAs) on a conductive substrate in good solid contact are successfully synthesized via template-assisted electrodeposition and show high electrochemical activity and long-term stability for methanol electrooxidation. Hollow nanotubular structures, porous nanostructures, and synergistic electronic effects of various elements contribute to the high electrocatalytic performance of porous Pt-Ni-P composite NTA electrocatalysts. 相似文献
995.
Tong R Hemmati HD Langer R Kohane DS 《Journal of the American Chemical Society》2012,134(21):8848-8855
We report a novel nanoparticulate drug delivery system that undergoes reversible volume change from 150 to 40 nm upon phototriggering with UV light. The volume change of these monodisperse nanoparticles comprising spiropyran, which undergoes reversible photoisomerization, and PEGylated lipid enables repetitive dosing from a single administration and enhances tissue penetration. The photoswitching allows particles to fluoresce and release drugs inside cells when illuminated with UV light. The mechanism of the light-induced size switching and triggered-release is studied. These particles provide spatiotemporal control of drug release and enhanced tissue penetration, useful properties in many disease states including cancer. 相似文献
996.
Bessel beam propagation in scattering media is simulated using the angular spectrum method combined with slice-by-slice propagation model. Generating Bessel beams with a spatial light modulator, which provides a means to adjust flexibly the parameters of the Bessel beam, allows us to validate the simulation results experimentally. The study reveals that the self-reconstructing length changes oppositely with the axicon angle (i.e., the larger the axieon angle, the shorter the self-reconstructing length). The radius of the incident beam has little influence on the self-reconstruction of the Bessel beam central lobe. 相似文献
997.
An edge emitting laser with two symmetrical near-circular spots located far field (FF) is demonstrated using tapered double-sided Bragg reflection waveguides (BRWs). The BRWs consist of six pairs of top p-type and bottom n-type A10.Ga0.9 As/A10.3 Ga0.7As Bragg reflectors with a period thickness of 850 nm. The device has a 4° tapered angle configuration and exhibits two stable circular beams with a separation angle of 52°. Typical FF angles of 5.87° and 7.8° in the lateral and vertical directions, respectively, are achieved. The lateral FF angle in the ridged section is independent of the injection current (〉0.8 A) beeause of narrow ridge (-10 μm) confinement. By contrast, the FF angle in the tapered section shows an increase rate of 1.2 1.66°/A. The periodic modulation of the lasing wavelength is observed to be sensitive to self-heating effects. 相似文献
998.
Perforated nanocap array: Facile fabrication process and efficient surface enhanced Raman scattering with fluorescence suppression 下载免费PDF全文
Recently, individual reduced-symmetry metal nanostructures and their plasmonic properties have been studied extensively. However, little attention has been paid to the approach to fabricating ordered reduced-symmetry metal nanostructure arrays. In this paper, a novel perforated silver nanocap array with high surface-enhanced Raman scattering (SERS) activity and fluorescence suppression is reported. The array is fabricated by electron beam evaporating Ag onto the perforated barrier layer side of a hard anodization (HA) anodic aluminum oxide (AAO) template. The morphology and optical property of the perforated silver nanocap array are characterized by an atomic force microscope (AFM), a scanning electron microscope (SEM), and absorption spectra. The results of SERS measurements reveal that the perforated silver nanocap array offers high SERS activity and fluorescence suppression compared with an imperforated silver nanocap array. 相似文献
999.
Efficiency and droop improvement in a blue InGaN-based light emitting diode with a p-InGaN layer inserted in the GaN barriers 下载免费PDF全文
The advantages of a blue InGaN-based light-emitting diode with a p-InGaN layer inserted in the GaN barriers is studied. The carrier concentration in the quantum well, radiative recombination rate in the active region, output power, and internal quantum efficiency are investigated. The simulation results show that the InGaN-based light-emitting diode with a p-InGaN layer inserted in the barriers has better performance over its conventional counterpart and the light emitting diode with p-GaN inserted in the barriers. The improvement is due to enhanced Mg acceptor activation and enhanced hole injection into the quantum wells. 相似文献
1000.
As typical one‐dimensional nanostructures for waveguiding tightly confined optical fields beyond the diffraction limit, metal nanowires have been used as versatile nanoscale building blocks for functional plasmonic and photonic structures and devices. Metal nanowires, especially those fabricated by bottom‐up synthesis such as Ag and Au nanowires, usually exhibit excellent diameter uniformity and surface smoothness with diameters down to tens of nanometers, which offers great opportunities for plasmonic waveguiding of optical fields with deep‐subwavelength confinement, coherence maintenance and low scattering losses. Based on nanowire plasmonic waveguides, a variety of applications ranging from plasmonic couplers, interferometers, resonators to photon emitters have been reported in recent years. In this article, significant progresses in these nanowire plasmonic waveguides, circuits and devices are reviewed. Future outlook and challenges are also discussed. 相似文献