全文获取类型
收费全文 | 7509篇 |
免费 | 956篇 |
国内免费 | 818篇 |
专业分类
化学 | 4322篇 |
晶体学 | 76篇 |
力学 | 262篇 |
综合类 | 77篇 |
数学 | 897篇 |
物理学 | 1472篇 |
无线电 | 2177篇 |
出版年
2024年 | 27篇 |
2023年 | 177篇 |
2022年 | 221篇 |
2021年 | 281篇 |
2020年 | 313篇 |
2019年 | 318篇 |
2018年 | 275篇 |
2017年 | 298篇 |
2016年 | 330篇 |
2015年 | 402篇 |
2014年 | 462篇 |
2013年 | 664篇 |
2012年 | 645篇 |
2011年 | 633篇 |
2010年 | 499篇 |
2009年 | 526篇 |
2008年 | 566篇 |
2007年 | 477篇 |
2006年 | 421篇 |
2005年 | 314篇 |
2004年 | 236篇 |
2003年 | 185篇 |
2002年 | 163篇 |
2001年 | 107篇 |
2000年 | 103篇 |
1999年 | 91篇 |
1998年 | 65篇 |
1997年 | 52篇 |
1996年 | 45篇 |
1995年 | 22篇 |
1994年 | 31篇 |
1993年 | 29篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 19篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 9篇 |
排序方式: 共有9283条查询结果,搜索用时 859 毫秒
911.
912.
采用乙二醇回流法合成了复合氟化物KAlF4和KAlF4:Ce3+纳米粒子,并利用X射线衍射(XRD),透射电子显微镜(TEM),X射线光电子能谱(XPS)等技术对其结构、形貌、粒径大小以及表面含氧量进行了表征.结果表明,采用回流法在适当的反应条件下可制得单一晶相的KAJF4和KAlF4:Ce3+纳米粒子,其平均粒径为32.5nm.KAlF4的O1s的XPS分峰谱图表明,其表面只有一种氧种为化学吸附氧(α氧),且表面氧的含量小于5%.KAlF4:Ce3+的发射光谱中最大发射峰位于330nm处,归属于Ce3+的5d→4f跃迁. 相似文献
913.
Lu W Yuan D Sculley J Zhao D Krishna R Zhou HC 《Journal of the American Chemical Society》2011,133(45):18126-18129
A porous polymer network (PPN) grafted with sulfonic acid (PPN-6-SO(3)H) and its lithium salt (PPN-6-SO(3)Li) exhibit significant increases in isosteric heats of CO(2) adsorption and CO(2)-uptake capacities. IAST calculations using single-component-isotherm data and a 15/85 CO(2)/N(2) ratio at 295 K and 1 bar revealed that the sulfonate-grafted PPN-6 networks show exceptionally high adsorption selectivity for CO(2) over N(2) (155 and 414 for PPN-6-SO(3)H and PPN-6-SO(3)Li, respectively). Since these PPNs also possess ultrahigh physicochemical stability, practical applications in postcombustion capture of CO(2) lie well within the realm of possibility. 相似文献
914.
The ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction (IL-based MADLLME) and derivatization was applied for the pretreatment of six sulfonamides (SAs) prior to the determination by high-performance liquid chromatography (HPLC). By adding methanol (disperser), fluorescamine solution (derivatization reagent) and ionic liquid (extraction solvent) into sample, extraction, derivatization, and preconcentration were continuously performed. Several experimental parameters, such as the type and volume of extraction solvent, the type and volume of disperser, amount of derivatization reagent, microwave power, microwave irradiation time, pH of sample solution, and ionic strength were investigated and optimized. When the microwave power was 240 W, the analytes could be derivatized and extracted simultaneously within 90 s. The proposed method was applied to the analysis of river water, honey, milk, and pig plasma samples, and the recoveries of analytes obtained were in the range of 95.0-110.8, 95.4-106.3, 95.0-108.3, and 95.7-107.7, respectively. The relative standard deviations varied between 1.5% and 7.3% (n=5). The results showed that the proposed method was a rapid, convenient and feasible method for the determination of SAs in liquid samples. 相似文献
915.
Lee Y Liu D Seoung D Liu Z Kao CC Vogt T 《Journal of the American Chemical Society》2011,133(6):1674-1677
When the small-pore zeolite natrolite is compressed at ca. 1.5 GPa and heated to ca. 110 °C in the presence of CO(2), the unit cell volume of natrolite expands by 6.8% and ca. 12 wt % of CO(2) is contained in the expanded elliptical channels. This CO(2) insertion into natrolite is found to be reversible upon pressure release. 相似文献
916.
We reported a graphene-based immunosensor for electrochemical quantification of phosphorylated p53 on serine 15 (phospho-p5315), a potential biomarker of gamma-radiation exposure. The principle is based on sandwich immunoassay and the resulting immunocomplex is formed among phospho-p53 capture antibody, phospho-p5315 antigen, biotinylated phospho-p5315 detection antibody and horseradish peroxidase (HRP)-labeled streptavidin. The introduced HRP results in an electrocatalytic response to reduction of hydrogen peroxide in the presence of thionine. Graphene served as sensor platform not only promotes electron transfer, but also increases the surface area to introduce a large amount of capture antibody, thus increasing the detection sensitivity. The experimental conditions including blocking agent, immunoreaction time and substrate concentration have been optimized. Under the optimum conditions, the increase of response current is proportional to the phospho-p5315 concentration in the range of 0.2–10 ng mL−1, with the detection limit of 0.1 ng mL−1. The developed immunosensor exhibits acceptable stability and reproducibility and the assay results for phospho-p5315 are in good correlation with the known values. This easily fabricated immunosensor provides a new promising tool for analysis of phospho-p5315 and other phosphorylated proteins. 相似文献
917.
We present the first gauge-origin independent formulation of Jones birefringence at the Hartree-Fock level of theory. Gauge-origin independence is achieved through the use of London atomic orbitals. The implementation is based on a recently proposed atomic orbital-based response theory formulation that allows for the use of both time- and perturbation-dependent basis sets [Thorvaldsen, Ruud, Kristensen, Jo?rgensen, and Coriani, J. Chem. Phys. 129, 214108 (2008)]. We present the detailed expressions for the response functions entering the Jones birefringence when London atomic orbitals are used. The implementation is tested on a set of polar and dipolar molecules at the Hartree-Fock level of theory. It is demonstrated that London orbitals lead to much improved basis-set convergence, and that the use of small, conventional basis sets may lead to the wrong sign for the calculated birefringence. For large basis sets, London orbitals and conventional basis sets converge to the same results. 相似文献
918.
919.
Su R Wang X Xu X Wang Z Li D Zhao X Li X Zhang H Yu A 《Journal of chromatography. A》2011,1218(31):5047-5054
The multiwall carbon nanotubes (MWCNTs)-based matrix solid phase dispersion (MSPD) was applied for the extraction of hormones, including 17-α-ethinylestradiol, 17-α-estradiol, estriol, 17-β-estradiol, estrone, medroxyprogesterone, progesterone and norethisterone acetate in butter samples. The method includes MSPD extraction of the target analytes from butter samples, derivatization of hormones with heptafluorobutyric acid anhydride-acetonitrile mixture, and determination by gas chromatography-mass spectrometry. The mixture containing 0.30 g graphitized MWCNTs and 0.10 g MWCNTs was selected as absorbent. Ethyl acetate was used as elution solvent. The elution solvent volume and flow rate were 12 mL and 0.9 mL min(-1), respectively. The recoveries of hormones obtained by analyzing the five spiked butter samples were from 84.5 to 111.2% and relative standard deviations from 1.9 to 8.9%. Limits of detection and quantification for determining the analytes were in the range of 0.2-1.3 and 0.8-4.5 μg kg(-1), respectively. Compared with other traditional methods, the proposed method is simpler in the operation and shorter in the sample pretreatment time. 相似文献
920.
A novel hydrated cobalt tetraborate complex NH4[Co(NH3)5(H2O)][B4O5(OH)4]2·6H2O, was synthesized by the reaction of NH4‐borate aqueous with CoCl2 and its structure was determined by single crystal X‐ray diffraction. The crystal system of this complex is orthorhombic, the space group is Pnma, and the unit cell parameters are a=1.2901(2) nm, b=1.6817(3) nm, c=1.1368(2) nm, α=β=γ=90°, V=2.4742(8) nm3, and Z=4. This compound contains infinite borate layers constructed from [B4O5(OH)4]2? units via hydrogen bonds. The adjacent polyborate anion layers are further linked together with the octahedral [Co(NH3)5(H2O)]3+ groups through hydrogen bonds to form 3D framework. The groups and guest water molecules are deposited in the empty space of this framework and interact with the layers by extensive hydrogen bonds. Infrared and Raman spectra (4000–400 cm?1) of NH4[Co(NH3)5(H2O)][B4O5(OH)4]2·6H2O were recorded at room temperature and analyzed. Fundamental vibrational modes were identified and band assignments were made. The middle band observed at 575 cm?1 in Raman spectrum is the pulse vibration of [B4O5(OH)4]2?. 相似文献