全文获取类型
收费全文 | 115112篇 |
免费 | 2911篇 |
国内免费 | 1418篇 |
专业分类
化学 | 50763篇 |
晶体学 | 1087篇 |
力学 | 7646篇 |
综合类 | 110篇 |
数学 | 36536篇 |
物理学 | 23299篇 |
出版年
2023年 | 417篇 |
2022年 | 408篇 |
2021年 | 619篇 |
2020年 | 841篇 |
2019年 | 795篇 |
2018年 | 11020篇 |
2017年 | 10845篇 |
2016年 | 7491篇 |
2015年 | 2165篇 |
2014年 | 1789篇 |
2013年 | 2991篇 |
2012年 | 6684篇 |
2011年 | 13273篇 |
2010年 | 7332篇 |
2009年 | 7403篇 |
2008年 | 8918篇 |
2007年 | 10930篇 |
2006年 | 2328篇 |
2005年 | 3121篇 |
2004年 | 3036篇 |
2003年 | 3178篇 |
2002年 | 2157篇 |
2001年 | 1145篇 |
2000年 | 1000篇 |
1999年 | 763篇 |
1998年 | 616篇 |
1997年 | 465篇 |
1996年 | 653篇 |
1995年 | 431篇 |
1994年 | 385篇 |
1993年 | 444篇 |
1992年 | 366篇 |
1991年 | 296篇 |
1990年 | 237篇 |
1989年 | 235篇 |
1988年 | 220篇 |
1987年 | 213篇 |
1986年 | 217篇 |
1985年 | 264篇 |
1984年 | 208篇 |
1983年 | 176篇 |
1982年 | 170篇 |
1981年 | 153篇 |
1980年 | 135篇 |
1979年 | 149篇 |
1978年 | 135篇 |
1977年 | 107篇 |
1976年 | 110篇 |
1973年 | 119篇 |
1968年 | 103篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Salinas-Nolasco MF Méndez-Vivar J Lara VH Bosch P 《Journal of colloid and interface science》2004,274(1):16-24
Samples of polycrystalline calcite were impregnated with solutions of malonic acid of three concentrations (5 x 10(-2), 5 x 10(-3) , and 5 x 10(-4) M) and different pH values (6.00, 7.00, and 8.00). The impregnation was carried out at room temperature to evaluate the adsorption of malonate ion in the calcite surface to optimize the conditions for possible application on limestone and marble in cultural heritage materials. The affinity of the malonate ion was determined through the potentiometric measurement of the surface charge and the corresponding adsorbed amounts by titration, Raman spectroscopy, and small-angle X-ray scattering (SAXS). The results indicate effective adsorption of the malonate ion on the surface at a pH value close to the point of zero charge (pHpzc approximately 8.20) and changes in some surface morphological properties such as the pore shape and the pore size distribution. The presence of a malonate adsorptive layer on calcite generates an interface interaction potential that may influence the reaction and transport mechanisms within the medium. 相似文献
992.
This paper has extended nonequilibrium Monte Carlo (MC) approach to simulate oscillatory shear flow in a lattice block copolymer system. Phase transition and associated rheological behaviors of multiple self-avoiding chains have been investigated. Stress tensor has been obtained based upon sampled configuration distribution functions. At low temperatures, micellar structures have been observed and the underlying frequency-dependent rheological properties exhibit different initial slopes. The simulation outputs are consistent with the experimental observations in literature. Chain deformation during oscillatory shear flow has also been revealed. Although MC simulation cannot account for hydrodynamic interaction, the highlight of our simulation approach is that it can, at small computing cost, investigate polymer chains simultaneously at different spatial scales, i.e., macroscopic rheological behaviors, mesoscopic self-assembled structures, and microscopic chain configurations. 相似文献
993.
Takayuki Abe Shingo Higashide Mitsuhiro Inoue Satoshi Akamaru 《Plasma Chemistry and Plasma Processing》2007,27(6):799-811
Fine particles were modified with a thin film of SnO2 by using a barrel sputtering system that is a dry process. The conditions for the preparation of SnO2 were studied by reactive sputtering onto a glass plate substrate. The optimal conditions for the preparation of tetragonal
SnO2 were identified as 60% partial oxygen pressure and 1.0 Pa total gas pressure with the substrate at room temperature. Under
the optimized conditions, the surfaces of Al flake particles were modified with a thin film of SnO2. XRD and SEM/EDS analysis of the prepared samples showed that the Al particle surfaces were uniformly modified by a thin
film of SnO2 in all cases. The film thicknesses were 80, 130, and 180 nm at RF outputs of 195, 350, and 490 W. These measured thicknesses
coincided with the values estimated from the interference colors of the samples. 相似文献
994.
Bose D Durgbanshi A Martinavarro-Domínguez A Capella-Peiró ME Carda-Broch S Esteve-Romero JS Gil-Agustí MT 《Journal of chromatographic science》2005,43(6):313-318
Acetaminophen is determined in serum and urine samples by a rapid, sensitive, and precise chromatographic method without any pretreatment step in a C18 column using a pure micellar mobile phase of 0.02M sodium dodecyl sulfate at pH 7. Acetaminophen is eluted in less than 5 min with no interference of the protein band. The use of electrochemical and UV detection is compared. Linearities (r > 0.999), as well as intra- and interday precision, are studied in the validation of the method. Limits of detection (LOD) are also calculated to be 0.56, 0.83, and 0.74 ng/mL in micellar solution, serum, and urine using electrochemical detection. The developed micellar liquid chromatographic method is useful for the quantitation of acetaminophen in serum and urine. Recoveries in the biological matrices are in the 98-107% range and results are compared with those obtained using a reference method. Drug excretion (in urine) and serum distribution are studied in several healthy volunteers, and no interference from metabolites is found. The developed procedure can be applied in routine analyses, toxicology, and therapeutic monitoring. 相似文献
995.
996.
Strategically designed sample composition (SSC) is a new technique that decreases the number of analytical determinations needed in routine screening to as few as the number of original sample specimens while providing information that is specific to them. Although this new technique has been applied to environmental studies, this paper describes its first application to food safety studies. Contamination of milk samples with polychlorinated biphenyls (PCBs) was chosen as a case study to show the usefulness and potential of the SSC technique with a fast analytical procedure that involves saponification of the samples and solid-phase microextraction of the PCBs. A total of 20 sample specimens can be analyzed in 11 determinations with excellent predictions of the positive samples and the concentration levels of the contaminants. The robustness of the strategy was investigated and demonstrated. 相似文献
997.
Based on the classifications of the four nucleic acid bases, we introduce a new 2-D method of DNA representation: TB-curve, which avoids loss of information accompanying alternative 2-D representation in which the curve standing for DNA overlaps and intersects itself. The method is illustrated on the coding sequence of the first exon of human beta-globin gene. 相似文献
998.
999.
María Beatriz de la Calle Guntiñas Michiel Ceulemans Claudia Witte Ryszard Łobiński Freddy C. Adams 《Mikrochimica acta》1995,120(1-4):73-82
A method is presented for the selective determination of the volatile selenium species dimethylselenide and dimethyldiselenide, using a commercially available purge-and-trap injection system coupled to capillary gas chromatography-microwave induced plasma-atomic emission spectrometry. The efficiency of the purging step was evaluated and the parameters affecting the purge and trap processes were optimized. The method was applied to the determination of volatile selenium compounds in lake water. Relative detection limits of 2ng/l for dimethylselenide and dimethyldiselenide, corresponding to an absolute detection limit of 10 pg, were achieved. 相似文献
1000.