全文获取类型
收费全文 | 2904篇 |
免费 | 161篇 |
国内免费 | 11篇 |
专业分类
化学 | 2293篇 |
晶体学 | 26篇 |
力学 | 43篇 |
数学 | 197篇 |
物理学 | 517篇 |
出版年
2023年 | 12篇 |
2022年 | 46篇 |
2021年 | 94篇 |
2020年 | 68篇 |
2019年 | 79篇 |
2018年 | 42篇 |
2017年 | 46篇 |
2016年 | 97篇 |
2015年 | 103篇 |
2014年 | 105篇 |
2013年 | 205篇 |
2012年 | 251篇 |
2011年 | 283篇 |
2010年 | 161篇 |
2009年 | 136篇 |
2008年 | 203篇 |
2007年 | 170篇 |
2006年 | 166篇 |
2005年 | 143篇 |
2004年 | 121篇 |
2003年 | 91篇 |
2002年 | 107篇 |
2001年 | 56篇 |
2000年 | 36篇 |
1999年 | 40篇 |
1998年 | 23篇 |
1997年 | 18篇 |
1996年 | 27篇 |
1995年 | 16篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1969年 | 1篇 |
排序方式: 共有3076条查询结果,搜索用时 843 毫秒
101.
Yongho Shin Tae Yeon Kong Jae Cheol Cheong Jin Young Kim Jae Il Lee Hye Suk Lee 《Biomedical chromatography : BMC》2019,33(9)
A liquid chromatography–tandem mass spectrometric method for the simultaneous determination of 75 abuse drugs and metabolites, including 19 benzodiazepines, 19 amphetamines, two opiates, eight opioids, cocaine, lysergic acid diethylamide, zolpidem, three piperazines and 21 metabolites in human hair samples, was developed and validated. Ten‐milligram hair samples were decontaminated, pulverized using a ball mill, extracted with 1 mL of methanol spiked with 28 deuterated internal standards in an ultrasonic bath for 60 min at 50°C, and purified with Q‐sep dispersive solid‐phase extraction tubes. The purified extracts were evaporated to dryness and the residue was dissolved in 0.1 mL of 10% methanol. The 75 analytes were analyzed on an Acquity HSS T3 column using gradient elution of methanol and 0.1% formic acid and quantified in multiple reaction monitoring mode with positive electrospray ionization. Calibration curves were linear (r ≥ 0.9951) from the lower limit of quantitation (2–200 pg/mg depending on the drug) to 2000 pg/mg. The coefficients of variation and accuracy for intra‐ and inter‐assay analysis at three QC levels were 4.3–12.9% and 89.2–109.1%, respectively. The overall mean recovery ranged from 87.1 to 105.3%. This method was successfully applied to the analysis of 11 forensic hair samples obtained from drug abusers. 相似文献
102.
Yu Na Lim Soo Kyung Chae Woongbin Yim Ji‐Yong Park Woojin Yoon Hoseop Yun Eunha Kim Seung Uk Son Hye‐Young Jang 《应用有机金属化学》2019,33(3)
The reaction of [(domppp) Pd (OAc)2] [domppp = 1,3‐bis (di‐o‐methoxyphenylphosphino)propane] and imidazolium‐functionalized carboxylic acids containing various anions (Br?, PF6?, SbF6? and BF4?) resulted in the formation of nano‐sized Pd (II) aggregates under template‐free conditions. The rate of formation of aggregates can be modulated by changing the anion, affecting the rate of polymerization of CO and olefins without fouling. Herein, we describe the analysis of Pd (II) catalysts by dynamic light scattering, atomic force microscopy, X‐ray photoelectron spectroscopy and X‐ray crystallography, and co‐ and terpolymerization results including the catalytic activity, and bulk density and molecular weight of polymers. 相似文献
103.
104.
Development of simultaneous analysis of tryptophan metabolites in serum and gastric juice – an investigation towards establishing a biomarker test for gastric cancer diagnosis 下载免费PDF全文
Jong Min Choi Won Sang Park Kyo Young Song Hwa Jeong Lee Byung Hwa Jung 《Biomedical chromatography : BMC》2016,30(12):1963-1974
To evaluate changes in tryptophan metabolism and discover diagnostic biomarkers for gastric cancer, a quantitative method was developed for tryptophan and its seven metabolites (indole‐3‐lactic acid, anthranilic acid, serotonin, nicotinic acid, kynurenic acid, kynurenine and 3‐indoxyl sulfate) in both human serum and gastric juice using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Serum and gastric juice were prepared with a simple protein precipitation using aqueous 0.1% formic acid and acetonitrile. As a result, it was found that the kynurenine pathway of tryptophan metabolism was activated in gastric cancer and that the metabolic ratio of kynurenine/tryptophan, which reflects the enzyme activity of indoleamine‐2,3‐dioxygenase, was associated with the observed metabolic changes. Finally, the investigation of tryptophan metabolites, especially kynurenic acid, in serum and gastric juice might serve as biomarkers for gastric cancer. The findings in this study provide critical information of tryptophan metabolism which can be applied to a serum‐based diagnostic test for gastric cancer. 相似文献
105.
106.
V. Singh V. K. Rai S. Watanabe T. K. Gundu?Rao I. Ledoux-Rak H.-Y. Kwak 《Applied physics. B, Lasers and optics》2010,101(3):631-638
The Er3Al5O12 phosphor powders were prepared using the solution combustion method. Formation and homogeneity of the Er3Al5O12 phosphor powders have been verified by X-ray diffraction and energy-dispersive X-ray analysis respectively. The frequency
up-conversion from Er3Al5O12 phosphor powder corresponding to the 2H9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2 and the infrared emission (IR) due to the 4I13/2 → 4I15/2 transitions lying at ∼410, ∼524, ∼556, 645–680 nm and at ∼1.53 μm respectively upon excitation with a Ti-Sapphire pulsed/CW
laser have been reported. The mechanism responsible for the frequency up-conversion and IR emission is discussed in detail.
Defect centres induced by radiation were studied using the techniques of thermoluminescence and electron spin resonance. A single
glow peak at 430°C is observed and the thermoluminescence results show the presence of a defect center which decays at high
temperature. Electron spin resonance studies indicate a center characterized by a g-factor equal to 2.0056 and it is observed
that this center is not related to the thermoluminescence peak. A negligibly small concentration of cation and anion vacancies
appears to be present in the phosphor in accordance with the earlier theoretical predictions. 相似文献
107.
Black phosphorus saturable absorber for ultrafast mode‐locked pulse laser via evanescent field interaction 下载免费PDF全文
Kichul Park Junsu Lee Young Tack Lee Won‐Kook Choi Ju Han Lee Yong‐Won Song 《Annalen der Physik》2015,527(11-12):770-776
Black phosphorus, or BP, has found a lot of applications in recent years including photonics. The most recent studies have shown that the material has an excellent optical nonlinearity useful in many areas, one of which is in saturable absorption for passive mode‐locking. A direct interaction scheme for mode‐locking, however, has a potential to optically cause permanent damage to the already delicate material. Evanescent field interaction scheme has already been proven to be a useful method to prevent such danger for other 2‐dimensional nanomaterials. In this report, we have utilized the evanescent field interaction to demonstrate that the optical nonlinear characteristics of BP is sufficiently strong to use in such an indirect interaction method. The successful demonstration of the passive mode‐locking operation has generated pulses with the pulse duration, repetition rate, and time bandwidth product of 2.18 ps, 15.59 MHz, and 0.336, respectively. 相似文献
108.
Eun‐Ju Ha Bong‐Soo Kim Eun‐Kyoung Park Ki‐Won Song Sun‐Gu Lee Seong Soo A. An Hyun‐jong Paik 《先进技术聚合物》2013,24(1):75-80
Ni2+‐complexed poly(2‐acetamidoacrylic acid) (PAAA) hydrogel beads were developed for the site‐specific reversible immobilization and purification of the histidine‐tagged green fluorescent protein (His‐tagged GFP). PAAA hydrogel beads were prepared by photopolymerization, and significantly improved mechanical properties of PAAA hydrogel beads were observed in comparison with PAAA hydrogel from our previous study. Confocal laser scanning microscopy was used to determine the binding of His‐tagged GFP to the hydrogel beads in three‐dimensional space. Photoluminescence spectroscopy revealed 89% of binding efficiency of His‐tagged GFP to the Ni2+‐PAAA hydrogel beads, 51% of yielding recovery. The maximum binding capacity of His‐tagged GFP was estimated to be 0.45 µg/mg of Ni2+‐PAAA hydrogel beads. The recombinant His‐tagged GFP from the soluble fraction of E. coli BL21(DE3) cell lysates was purified with Ni2+‐PAAA hydrogel beads. The major advantage of the Ni2+‐PAAA hydrogel beads system was simple preparation procedures of producing the matrix, because PAAA hydrogel beads had relatively enhanced mechanical strength than soft hydrogels. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
109.
Characterization of Nitro-Substituted Polybenzimidazole Synthesized by the Reaction with Nitric Acid
Abstract Nitro-substituted poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole]s (PBIs) were synthesized by the reaction of PBI with nitric acid in sulfuric acid under various conditions. The number of nitro groups substituted on the aromatic ring of PBI per polymeric unit varied from 1.44 to 3.55 according to the reaction conditions. An increase in reaction temperature and concentration of the nitric acid increased the degree of substitution. The inherent viscosity of the substituted polymer increased as the reaction temperature decreased. When the reaction temperature was 30°C, the inherent viscosity of the polymer increased as the concentration of nitric acid increased. The nitro-substituted PBI exhibited polyelectrolyte behavior in formic acid. The nitro groups substituted on PBI were dissociated when the polymer was heated to 450°C, displaying exothermic behavior, and the decomposition of polymer was proportional to its nitro group content. All nitro-substituted PBIs showed better solubilities in polar aprotic and acidic solvents, such as dimethylacetamide, dimethylsulfoxide, dimethylformamide, N-methylpyrrolidone, formic acid, sulfuric acid, and trifluoromethanesulfonic acid. 相似文献
110.
Sang Gyo Seo Ji Hyun Yeo JI Hye Kim Ji-Beom Kim Tae-Joon Cho Dong Yeon Lee 《Experimental & molecular medicine》2013,45(11):e62
Non healing chronic wounds are difficult to treat in patients with diabetes and can result in severe medical problems for these patients and for society. Negative-pressure wound therapy (NPWT) has been adopted to treat intractable chronic wounds and has been reported to be effective. However, the mechanisms underlying the effects of this treatment have not been elucidated. To assess the vasculogenic effect of NPWT, we evaluated the systemic mobilization of endothelial progenitor cells (EPCs) during NPWT. Twenty-two of 29 consecutive patients who presented at the clinic of Seoul National Universty Hospital between December 2009 and November 2010 who underwent NPWT for diabetic foot infections or skin ulcers were included in this study. Peripheral blood samples were taken before NPWT (pre-NPWT) and 7–14 days after the initiation of NPWT (during-NPWT). Fluorescence-activated cell sorting (FACS) analysis showed that the number of cells in EPC-enriched fractions increased after NPWT, and the numbers of EPC colony forming units (CFUs) significantly increased during NPWT. We believe that NPWT is useful for treating patients with diabetic foot infections and skin ulcers, especially when these conditions are accompanied by peripheral arterial insufficiency. The systemic mobilization of EPCs during NPWT may be a mechanism for healing intractable wounds in diabetic patients with foot infections or skin defects via the formation of increased granulation tissue with numerous small blood vessels. 相似文献