全文获取类型
收费全文 | 30159篇 |
免费 | 4059篇 |
国内免费 | 2714篇 |
专业分类
化学 | 20519篇 |
晶体学 | 284篇 |
力学 | 1948篇 |
综合类 | 276篇 |
数学 | 3282篇 |
物理学 | 10623篇 |
出版年
2024年 | 105篇 |
2023年 | 589篇 |
2022年 | 907篇 |
2021年 | 1011篇 |
2020年 | 1112篇 |
2019年 | 1084篇 |
2018年 | 911篇 |
2017年 | 814篇 |
2016年 | 1280篇 |
2015年 | 1269篇 |
2014年 | 1537篇 |
2013年 | 2050篇 |
2012年 | 2631篇 |
2011年 | 2659篇 |
2010年 | 1647篇 |
2009年 | 1632篇 |
2008年 | 1736篇 |
2007年 | 1661篇 |
2006年 | 1490篇 |
2005年 | 1228篇 |
2004年 | 940篇 |
2003年 | 789篇 |
2002年 | 751篇 |
2001年 | 563篇 |
2000年 | 559篇 |
1999年 | 652篇 |
1998年 | 581篇 |
1997年 | 575篇 |
1996年 | 659篇 |
1995年 | 507篇 |
1994年 | 465篇 |
1993年 | 389篇 |
1992年 | 371篇 |
1991年 | 322篇 |
1990年 | 255篇 |
1989年 | 203篇 |
1988年 | 157篇 |
1987年 | 138篇 |
1986年 | 127篇 |
1985年 | 119篇 |
1984年 | 88篇 |
1983年 | 61篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
974.
Gerald G. Miller Kevin Brown Ronald B. Moore Malcolm S. McPhee Zhenjun J. Diwu Jixiang Liu Liren Huang J. William Lown David A. Begg Vera Chlumecky John Tulip 《Photochemistry and photobiology》1995,61(6):632-638
Hypocrellins are naturally occurring compounds with photosensitizing properties in biological systems. We have prepared synthetic derivatives of hypocrellin B, which have promise as photosensitizers in the clinical application of photodynamic therapy. The intracellular localization and uptake kinetics of hypocrellin B and several selected hypocrellin congeners were determined semiquantitatively by fluorescence confocal microscopy in monolayer cultures of EMT6/Ed murine tumor cells. Each compound had unique uptake kinetics. Although no compound tested to date has demonstrated nuclear labeling, most could be detected in lysosomes, Golgi, endoplasmic reticulum and, to a minor extent, in cellular membranes. No two compounds gave identical labeling distributions. The differences are assumed to originate in physicochemical properties characteristic of each compound, which may ultimately impact upon the primary modality of phototoxicity. 相似文献
975.
Cai Jin-Hua Ye Yuan-Jian Huang Jin-Wang Yu Han-Cheng Ji Liang-Nian 《Journal of Sol-Gel Science and Technology》2012,62(3):432-440
Three types of silica gel supported titanium dioxide particles immobilizing Zn(II) carboxylphenyl porphyrins appending p-CH3, p-H and p-Cl phenyl substituents (designated as ZnMP–TiO2–SiO2, ZnPP–TiO2–SiO2 and ZnCP–TiO2–SiO2, respectively) have been synthesized and characterized using SEM, XRD, IR, AFS, DRS, UV–Vis, XPS and TG. The photodegradation
of α-terpinene in aqueous suspension was used to determine the photocatalytic activity of TiO2–SiO2 samples which had been impregnated with Zn(II) porphyrins, as sensitizers. The experimental results confirmed that the photocatalytic
activitys of these composites are much higher than those of the nonmodified TiO2–SiO2 under visible light irradiation and follow the order of ZnMP–TiO2–SiO2 > ZnPP–TiO2–SiO2 > ZnCP–TiO2–SiO2. 相似文献
976.
George Ting-Kuo Fey Hui-Jyuan Tu Kai-Pin Huang Yi-Chuan Lin Hsien-Ming Kao Shih-Hung Chan 《Journal of Solid State Electrochemistry》2012,16(5):1857-1862
Carbon-coated LiFePO4 cathode materials were prepared by a solid-state method incorporating different sizes of polystyrene (PS) spheres as carbon sources. In scanning electron microscope images, small PS spheres appear more effective at preventing aggregation of LiFePO4 particles. From transmission electron microscopy images, it was found that the LiFePO4 particles were completely uniformly coated with 5-nm carbon layer when the carbon source was 0.22 μm PS spheres. When the size of PS sphere was increased to 2.75 μm, a network of carbon was formed and wrapped around the LiFePO4 to create a conductive web. Raman spectroscopy and four-point probe conductivity measurement showed that using larger sizes of PS spheres as carbon sources leads to greater conductivity of LiFePO4/C. The LiFePO4 precursor sintered with 0.22 μm PS spheres delivered an initial discharge capacity of 145 mAh g?1 at a 0.2 C rate, but it only sustained 289 cycles at 80% capacity. When the diameter of PS spheres was increased to 2.75 μm, the discharge capacity of LiFePO4/C decreased, but the cycle life reached 755 cycles, the highest number in this work probably due to the network formation of carbon wrapping around LiFePO4 particles. 相似文献
977.
Identification of a new flavone glycoside from <Emphasis Type="Italic">Codonopsis nervosa</Emphasis>
Xian-li Zhou Qiang Fan Shuai Huang Cui-juan Wang You-song Wang 《Chemistry of Natural Compounds》2012,47(6):888-890
A new flavone glycoside, luteolin 7-O-[(6″′-caffeoyl)-β-D-glucopyranosyl-(1 → 6)]-β-D-glucopyranoside (1), was isolated from Codonopsis nervosa, along with three other known compounds, luteolin 7-O-β-D-glucopyranoside (2), luteolin 7-O-gentiobioside (3), and tangshenoside VI (4). Their structures were determined on the basis of 1D and 2D NMR, IR, and HR-ESI-MS. 相似文献
978.
Synthesis and electrochemical properties of K-doped LiFePO4/C composite as cathode material for lithium-ion batteries 总被引:1,自引:0,他引:1
Xuesong Fang Jing Li Kelong Huang Suqin Liu Chenghuan Huang Shuxin Zhuang Jinbao Zhang 《Journal of Solid State Electrochemistry》2012,16(2):767-773
Li1 − x
K
x
FePO4/C (x = 0, 0.03, 0.05, and 0.07) composites were synthesized at 700 °C in an argon atmosphere by carbon thermal reduction method.
Based on X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis, the composite was
ultrafine sphere-like particles with 100–300 nm size, and the lattice structure of LiFePO4 was not destroyed by K doping, while the lattice volume was enlarged. The electrochemical properties were investigated by
four-point probe conductivity measurements, galvanostatic charge and discharge tests, cyclic voltammetry and electrochemical
impedance spectroscopy. The results indicated that the capacity performance at high rate and cyclic stability were improved
by doping an appropriate amount of K, which might be ascribed to the fact that the doped K ion expands Li ion diffusion pathway.
Among the doped materials, the Li0.97K0.03FePO4/C samples exhibited the best electrochemical activity, with the initial discharge capacity of 153.7 mAh g−1 at 0.1 C and the capacity retention rate of about 92% after 50 cycles at above 1 C, 11% higher than undoped sample. Remarkably,
it still showed good cycle retention at a high current rate of 10 C. 相似文献
979.
Huang Q Xu T Wang GY Huang JF Xia H Yin R Tang A Fu WL 《Analytical and bioanalytical chemistry》2012,402(4):1625-1634
Ever since the emergence of bovine spongiform encephalopathy, the source of pharmaceutical heparin has been restricted to
porcine intestinal mucosa. In this project, two real-time fluorescent PCR methods were developed to assist with quality control
analysis. The first is a qualitative method which relies on SYBR Green I chemistry to confirm the porcine origin of industrial
crude porcine heparin (ICPH), identify any ruminant contaminants, and generally control purity. The second is based on TaqMan
chemistry and is able to quantitatively identify porcine, bovine, caprine, and ovine components and contaminants in ICPH.
By targeting mitochondrial DNA, both PCR systems showed a detection limit of 1 pg DNA and amplification efficiencies ranging
between 96% and 102%. Moreover, quantitative PCR showed a detection limit of 0.02 ppm in samples comprising porcine, bovine,
caprine, and ovine DNA. The results of qualitative PCR over 27 ICPH samples showed that all samples were porcine in origin
and that 17 had ruminant contaminants. The results of quantitative PCR further showed that out of all 17 samples with ruminant
contaminants, seven samples had bovine, ovine, and caprine contaminants, two samples had bovine and ovine contaminants, and
eight samples had only ovine contaminants. In conclusion, the qualitative PCR system was found to be a relatively inexpensive,
rapid, and flexible method of identifying the porcine origin of and ruminant contaminants in ICPH, while the quantitative
PCR was found suitable to accurately analyze the components and contaminants in detail. Both methods are suitable for routine
control assays for the evaluation of ICPH purity and origins of contaminants. 相似文献
980.
Jian Zhang Hui Huang Da-Fu Wei Yong Guan Fu-Zeng Hu Anna Zheng 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):626-632
Sequential anionic copolymerization of styrene and glycidyl methacrylate (GMA) was performed with the protection of argon under normal pressure, where styrene, GMA, toluene, THF, n-butyllithium and a small amount of lithium chloride (LiCl) were used as first monomer, second monomer, solvent, polar reagent, initiator and additive, respectively. Polystyrene-b-poly(glycidyl methacrylate) diblock copolymers (PS-b-PGMA) with well-defined structure and narrow molecular weight distribution were prepared by the copolymerization reaction of poly(styryl)lithium with GMA under certain temperatures. The copolymers were characterized using gel permeation chromatography (GPC), 1H-NMR, 13C-NMR, thin layer chromatography (TLC) and hydrochloric acid-dioxane argentimetric methods. The effects of additives, copolymerization temperature and THF dosage on the copolymerization were studied. No chain transfer reaction of anionic polymerization of styrene in toluene was observed. Slightly broader molecular weight distribution of PS-b-PGMA was observed with the increase the GMA repeat units. Using THF/toluene blend solvent could reduce the polydispersity index (M w /M n ) and dissolve the copolymer better than toluene alone. Lower temperature (< -40°C) and LiCl are required to prepare PS-b-PGMA with narrower molecular weight distribution. 相似文献