全文获取类型
收费全文 | 3337篇 |
免费 | 70篇 |
国内免费 | 6篇 |
专业分类
化学 | 2189篇 |
晶体学 | 18篇 |
力学 | 79篇 |
数学 | 351篇 |
物理学 | 776篇 |
出版年
2023年 | 29篇 |
2022年 | 123篇 |
2021年 | 120篇 |
2020年 | 83篇 |
2019年 | 105篇 |
2018年 | 85篇 |
2017年 | 87篇 |
2016年 | 140篇 |
2015年 | 81篇 |
2014年 | 127篇 |
2013年 | 198篇 |
2012年 | 240篇 |
2011年 | 263篇 |
2010年 | 155篇 |
2009年 | 160篇 |
2008年 | 206篇 |
2007年 | 175篇 |
2006年 | 152篇 |
2005年 | 131篇 |
2004年 | 93篇 |
2003年 | 92篇 |
2002年 | 76篇 |
2001年 | 60篇 |
2000年 | 42篇 |
1999年 | 41篇 |
1998年 | 30篇 |
1997年 | 21篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1971年 | 5篇 |
排序方式: 共有3413条查询结果,搜索用时 15 毫秒
101.
102.
103.
Irradiated A-type carbonated apatites with carbonate content ranging from 1.45% to 4.84% are studied by using electron paramagnetic resonance (EPR). The EPR spectra are mainly constituted of lines associated to axial CO2− species (g=2.0028 and g=1.9973) and orthorhombic CO3− species (g1=2.0170, g2=2.0090 and g3=2.0041). The production of CO2− species on gamma irradiation depends on the carbonate concentration and the hydroxyapatite stoichiometry. The lowest dose detection limit was achieved with stoichiometric samples and carbonate concentration of 3.7%. 相似文献
104.
A study was carried out on the direct determination of Cr and Mn in urine using simultaneous atomic absorption spectrometry (SIMAAS). The heating program conditions, the absorbance signal profiles, the influence of different chemical modifiers, and the urine sample volume delivery into the tube were optimized to perform the calibration with aqueous solutions. Among several chemical modifiers tested, the best recovery and repeatability results were obtained for 3 microg Mg(NO3)2. On using this modifier, the pyrolysis and atomization temperatures for simultaneous determination of Cr and Mn were 1,300 degrees C and 2,500 degrees C, respectively. Urine samples were diluted (1+1) with 2.0% (v/v) HNO3 + 0.05% (w/v) Triton X-100 prepared in high purity water. A 20-microL aliquot of analytical solution and 10 microL of chemical modifier solution were delivered to the graphite tube. The characteristic masses were 7.8 pg for Cr (RSD=4.0%) and 4.6 pg for Mn (RSD=2.6%). The limits of detection were 0.08 microg L(-1) (n=20, 3s) for Cr and 0.16 microg L(-1) (n=20, 3s) for Mn. Recovery studies for 1.0 or 2.5 microg L(-1) of Cr and Mn added to different urine samples showed acceptable results for Cr (100%, RSD=14%) and Mn (88%, RSD=5.6%). 相似文献
105.
Domingues P Domingues MR Amado FM Ferrer-Correia AJ 《Rapid communications in mass spectrometry : RCM》2001,15(10):799-804
Fast atom bombardment mass spectrometry in the positive mode was used for the characterization of sodiated glycerol phosphatidylcholines. The relative abundance (RA) of the protonated species is similar to the RA of the sodiated molecular species. The sodiated fragment ion, [M + Na - 59](+), corresponding to the loss of trimethylamine, and other sodiated fragment ions, were also observed. The decomposition of the sodiated molecule is very similar for all the studied glycerol phosphatidylcholines, in which the most abundant ion corresponds to a neutral loss of 59 Da. Upon collision-induced dissociation (CID) of the [M + Na](+) ion informative ions are formed by the losses of the fatty acids in the sn-1 and sn-2 positions. Other major fragment ions of the sodiated molecule result from loss of non-sodiated and sodiated choline phosphate, [M + Na - 183](+), [M + Na - 184](+.) and [M + Na - 205](+), respectively. The main CID fragmentation pathway of the [M + Na - 59](+) ion yields the [M + Na - 183](+) ion, also observed in the CID spectra of the [M + Na](+) molecular ion. Other major fragment ions are [M + Na - 205](+) and the fragment ion at m/z 147. Collisional activation of [M + Na - 205](+) results in charge site remote fragmentation of both fatty acid alkyl chains. The terminal ions of these series of charge remote fragmentations result from loss of part of the R(1) or R(2) alkyl chain. Other major informative ions correspond to acylium ions. 相似文献
106.
de Oliveira Elcio Cruz de Santana Maia Lúcio Abdala da Costa Lívio Garcia Lourenço Túlio Campos 《Accreditation and quality assurance》2018,23(6):365-369
Accreditation and Quality Assurance - In any commercial transaction, the presence of tolerances from specification limits is essential to ensure that the true value of the property of interest is... 相似文献
107.
de Oliveira Cristina Soltovski Bet Camila Delinski Bisinella Radla Zabian Bassetto Waiga Lucas Henrique Colman Tiago André Denck Schnitzler Egon 《Journal of Thermal Analysis and Calorimetry》2018,133(3):1491-1498
Journal of Thermal Analysis and Calorimetry - Samples of potato starch (PS), sweet potato starch (SPS) and their binary mixtures, with moisture levels of 10, 15 and 20% (db), were submitted to... 相似文献
108.
109.
Érica Aparecida de Oliveira Bluma Linkowski Faintuch Daniele Seo Angélica Bueno Barbezan Ana Funari Roselaine Campos Targino Ana Maria Moro 《Applied biochemistry and biotechnology》2018,185(4):863-874
Early and accurate detection of primary or metastatic tumors is of great value in staging, treatment management, and prognosis. Tumor angiogenesis plays an essential role in the growth, invasion, and metastatic spread of solid cancers, and so, is a promising approach for tumor imaging. The GX1 (CGNSNPKSC) peptide was identified by phage display library and has been investigated as a marker for human cancers. This study aims to evaluate the 99mTc-HYNIC-PEG4-c (GX1) as a biomarker for tumor imaging. Our results showed that GX1 specifically binds to tumor cells in vitro. SKMEL28 and MDA-MB231 cells achieved total binding peak at 60 min of incubation. For B16F10 and MKN45 cells, the total and specific binding were similar during all time points, while A549 cell line showed rapid cellular total uptake of the tracer at 30 min of incubation. Biodistribution showed low non-specific uptakes and rapid renal excretion. Melanoma tumors showed enhanced GX1 uptake in animal model at 60 min, and it was significantly blocked by cold peptide. The radiotracer showed tumor specificity, especially in melanomas that are highly vascularized tumors. In this sense, it should be considered in future studies, aiming to evaluate degree of angiogenesis, progression, and invasion of tumors. 相似文献
110.
A. M. A. Melo D. L. Alexandre M. R. F. Oliveira R. F. Furtado M. F. Borges P. R. V. Ribeiro A. Biswas H. N. Cheng C. R. Alves E. A. T. Figueiredo 《Journal of Solid State Electrochemistry》2018,22(5):1321-1330
The performance of biosensors depends directly on the strategies adopted during their development. In this paper, a fast and sensitive biosensor for Salmonella Typhimurium detection was assembled by using optimization studies in separate stages. The pre-treatment assays, biomolecular immobilization (primary antibody and protein A concentrations), and analytical response (hydroquinone and hydrogen peroxide concentrations) were optimized via voltammetric methods. In the biosensor assembly, a gold surface was modified via the self-assembled monolayer technique (SAM) using cysteamine thiol and protein A for immobilization of anti-Salmonella antibody. The analytical response of the biosensor was obtained through the use of a secondary antibody labeled with a peroxidase enzyme, and the signal was evaluated by applying the chronoamperometry technique. The biosensor was characterized by infrared spectroscopy and cyclic voltammetry. Optimization of protein A and primary antibody concentrations enabled higher analytical signals of 7.5 and 75 mg mL?1, respectively, to be achieved. The hydroquinone and H2O2 concentrations selected were 3 and 300 mM, respectively. The biosensor developed attained a very low detection limit of 10 CFU mL?1 and a fast response with a final detection time of 125 min. These results indicate that this biosensor is very promising for the food safety and emergency response applications. 相似文献