全文获取类型
收费全文 | 4495篇 |
免费 | 724篇 |
国内免费 | 419篇 |
专业分类
化学 | 3158篇 |
晶体学 | 42篇 |
力学 | 271篇 |
综合类 | 46篇 |
数学 | 424篇 |
物理学 | 1697篇 |
出版年
2024年 | 14篇 |
2023年 | 125篇 |
2022年 | 171篇 |
2021年 | 184篇 |
2020年 | 211篇 |
2019年 | 162篇 |
2018年 | 145篇 |
2017年 | 126篇 |
2016年 | 207篇 |
2015年 | 180篇 |
2014年 | 253篇 |
2013年 | 279篇 |
2012年 | 394篇 |
2011年 | 359篇 |
2010年 | 267篇 |
2009年 | 266篇 |
2008年 | 282篇 |
2007年 | 273篇 |
2006年 | 270篇 |
2005年 | 182篇 |
2004年 | 127篇 |
2003年 | 111篇 |
2002年 | 99篇 |
2001年 | 88篇 |
2000年 | 86篇 |
1999年 | 99篇 |
1998年 | 90篇 |
1997年 | 89篇 |
1996年 | 65篇 |
1995年 | 91篇 |
1994年 | 74篇 |
1993年 | 44篇 |
1992年 | 59篇 |
1991年 | 45篇 |
1990年 | 40篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有5638条查询结果,搜索用时 15 毫秒
81.
Zhang B Li JF Zhong QL Ren B Tian ZQ Zou SZ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7449-7455
Core-shell Au-Pt nanoparticles were synthesized by using a seed growth method and characterized by transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopy. Au(core)-Pt(shell)/GC electrodes were prepared by drop-coating the nanoparticles on clean glassy carbon (GC) surfaces, and their electrochemical behavior in 0.5 M H2SO4 revealed that coating of the Au core by the Pt shell is complete. The electrooxidation of carbon monoxide and methanol on the Au(core)-Pt(shell)/GC was also examined, and the results are similar to those obtained on a bulk Pt electrode. High quality surface-enhanced Raman scattering (SERS) spectra of both adsorbed CO and thiocyanate were observed on the Au(core)-Pt(shell)/GC electrodes. The potential-dependent SERS features resemble those obtained on electrochemically roughened bulk Pt or Pt thin films deposited on roughened Au electrodes. For thiocyanate, the C-N stretching frequency increases with the applied potential, yielding two distinctly different dnu(CN)/dE. From -0.8 to -0.2 V, the dnu(CN)/dE is ca. 50 cm(-1)/V, whereas it is 90 cm(-1)/V above 0 V. The bandwidth along with the band intensity increases sharply above 0 V. At the low-frequency region, Pt-NCS stretching mode at 350 cm(-1) was observed at the potentials from -0.8 to 0 V, whereas the Pt-SCN mode at 280 cm(-1) was largely absent until around 0 V and became dominant at more positive potentials. These potential-dependent spectral transitions were attributed to the adsorption orientation switch from N-bound dominant at the negative potential region to S-bound at more positive potentials. The origin of the SERS activity of the particles is briefly discussed. The study demonstrates a new method of obtaining high quality SERS on Pt-group transition metals, with the possibility of tuning SERS activity by varying the core size and the shell thickness. 相似文献
82.
Xu X Zhao Z Song P Zhou G Xu J Deng P Bourdet G Chanteloup JC Zou JP Fulop A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2444-2447
Infrared (1.2-1.6 microm) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05at.%) ions, was investigated under CW laser diode pumping (lambda=940 nm). The Cr4+ emission band was observed with its peak at 1.34 microm and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda=1.03 microm). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the 3B2(3T2)-3B1(3A2) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 microm) output. 相似文献
83.
Zou Jianzhong Hu Xiaodong Duan Chenying Xu Zheng You Xiaozeng Mak Thomas C. W. 《Transition Metal Chemistry》1998,23(4):477-480
Reaction of either K3[Fe(CN)6] or K4[Fe(CN)6] with a macrocyclic CuII complex, [Cu(teta)](ClO4)2 (teta = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacylotetradecane), in aqueous solution gave the same product as shown by spectroscopic and physicochemical characterisation. The crystal structure of the complex shows that it is a one-dimensional linear chain type heterobinuclear FeIII–CuII polymer. The unit is composed of a [Cu(teta)(H2O)2]2+ cationic complex, a FeIII–CuII alternate linear chain unit, a ClO
4
–
ion and four water molecules. The Cu atom is coordinated in a distorted octahedral arrangement by four nitrogen atoms from one teta ligand and two nitrogen atoms of the bridging cyanide groups. The Cu—N bond distances involving the cyanide bridges, 2.522(7) and 2.608(7)Å, respectively, indicate weak antiferromagnetic interactions between the FeIII and CuII atoms. 相似文献
84.
85.
Ying Lv Bofeng Zhang Guobing Zou Xiaodong Yue Zhikang Xu Haiyan Li 《Entropy (Basel, Switzerland)》2022,24(7)
Domain adaptation aims to learn a classifier for a target domain task by using related labeled data from the source domain. Because source domain data and target domain task may be mismatched, there is an uncertainty of source domain data with respect to the target domain task. Ignoring the uncertainty may lead to models with unreliable and suboptimal classification results for the target domain task. However, most previous works focus on reducing the gap in data distribution between the source and target domains. They do not consider the uncertainty of source domain data about the target domain task and cannot apply the uncertainty to learn an adaptive classifier. Aimed at this problem, we revisit the domain adaptation from source domain data uncertainty based on evidence theory and thereby devise an adaptive classifier with the uncertainty measure. Based on evidence theory, we first design an evidence net to estimate the uncertainty of source domain data about the target domain task. Second, we design a general loss function with the uncertainty measure for the adaptive classifier and extend the loss function to support vector machine. Finally, numerical experiments on simulation datasets and real-world applications are given to comprehensively demonstrate the effectiveness of the adaptive classifier with the uncertainty measure. 相似文献
86.
87.
Yang Ye Xiang Qi Bing Xu Ying Lin Huan Xiang Liang Zou Xiang-Yang Ye Tian Xie 《Chemical science》2022,13(23):6959
Herein, we present a facile and efficient allylation method via Ni-catalyzed cross-electrophile coupling of readily available allylic acetates with a variety of substituted alkenyl bromides using zinc as the terminal reductant. This Ni-catalyzed modular approach displays excellent functional group tolerance and a broad substrate scope, which the creation of a series of 1,4-dienes including several structurally complex natural products and pharmaceutical motifs. Moreover, the coupling strategy has the potential to realize enantiomeric control. The practicality of this transformation is demonstrated through the potent modification of the naturally antitumor active molecule β-elemene.Herein, we present a facile and efficient allylation method via Ni-catalyzed cross-electrophile coupling of readily available allylic acetates with a variety of substituted alkenyl bromides using zinc as the terminal reductant. 相似文献
88.
In recent years, research on applications of three-way decision (e.g., TWD) has attracted the attention of many scholars. In this paper, we combine TWD with multi-attribute decision-making (MADM). First, we utilize the essential idea of TOPSIS in MADM theory to propose a pair of new ideal relation models based on TWD, namely, the three-way ideal superiority model and the three-way ideal inferiority model. Second, in order to reduce errors caused by the subjectivity of decision-makers, we develop two new methods to calculate the state sets for the two proposed ideal relation models. Third, we employ aggregate relative loss functions to calculate the thresholds of each object, divide all objects into three different territories and sort all objects. Then, we use a concrete example of building appearance selection to verify the rationality and feasibility of our proposed models. Furthermore, we apply comparative analysis, Spearman’s rank correlation analysis and experiment analysis to illustrate the consistency and superiority of our methods. 相似文献
89.
Deep submicron n-channel metal-oxide-semiconductor field-effect transistors (NMOSFETs) with shallow trench isolation (STI) are exposed to ionizing dose radiation under different bias conditions.The total ionizing dose radiation induced subthreshold leakage current increase and the hump effect under four different irradiation bias conditions including the worst case (ON bias) for the transistors are discussed.The high electric fields at the corners are partly responsible for the subthreshold hump effect.Charge trapped in the isolation oxide,particularly at the Si/SiO 2 interface along the sidewalls of the trench oxide creates a leakage path,which becomes a dominant contributor to the offstate drain-to-source leakage current in the NMOSFET.Non-uniform charge distribution is introduced into a threedimensional (3D) simulation.Good agreement between experimental and simulation results is demonstrated.We find that the electric field distribution along with the STI sidewall is important for the radiation effect under different bias conditions. 相似文献
90.
Load optimal design for a primary test stand facility based on a zero-dimensional load model 下载免费PDF全文
In order to couple the numerical simulation of a primary test stand driver with an optimal load design, a zero-dimensional wire array load model is designed based on the Saturn load model using PSPICE, which is an upgraded version of the Simulation Program with Integrated Circuit Emphasis (SPICE) designed by the ORCAD Corporation to perform circuit simulations. This paper calculates different load parameters and discusses factors influencing the driving current curve. With appropriate driving current curves chosen, further magneto-hydrodynamic calculations are carried out and discussed to provide the best results for experiments. The suggested optimal load parameters play an important role in experimental load design. 相似文献