全文获取类型
收费全文 | 2346篇 |
免费 | 27篇 |
国内免费 | 49篇 |
专业分类
化学 | 1999篇 |
力学 | 13篇 |
综合类 | 8篇 |
数学 | 45篇 |
物理学 | 357篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 43篇 |
2018年 | 54篇 |
2017年 | 164篇 |
2016年 | 164篇 |
2015年 | 105篇 |
2014年 | 32篇 |
2013年 | 38篇 |
2012年 | 227篇 |
2011年 | 292篇 |
2010年 | 48篇 |
2009年 | 6篇 |
2008年 | 160篇 |
2007年 | 148篇 |
2006年 | 163篇 |
2005年 | 143篇 |
2004年 | 88篇 |
2003年 | 151篇 |
2002年 | 55篇 |
2001年 | 87篇 |
2000年 | 74篇 |
1999年 | 46篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有2422条查询结果,搜索用时 15 毫秒
11.
A Tosflex-mercury film electrode (TMFE) was prepared by spin-coating a solution of the perfluorinated anion exchange polymer Tosflex onto a glassy carbon electrode surface followed by electrodeposition of mercury film on this electrode. This electrode was used for the determination of trace bismuth(III) which was preconcentrated onto the TMFE as anionic bismuth(III) complexes with chloride in a chloride medium. The preconcentration was carried out at a potential of-0.2 V, and the preconcentration of the bismuth(III) was enhanced significantly by the anion-exchange feature of Tosflex. The accumulated bismuth(III) was then determined by anodic square-wave stripping voltammetry (SWSV). Various parameters influencing the determination of bismuth(III) were examined in detail. With 2 min accumulation, the analytical signal versus concentration dependence was linear up to 50 ppb, and the detection limit was 0.58 ppb. This modified electrode showed good resistance to the interferences from surface-active compounds and common ions. 相似文献
12.
A tandem free radical cyclization-rearrangement sequence was designed and executed to produce tricyclo[4.3.2.0(1,5)]undecane 7 from cyclopentene 6A in a single operation. The total synthesis of suberosenone was accomplished from 7. 相似文献
13.
Tsibakhashvili NY Asatiani NV Abuladze MK Birkaya BG Sapojnikova NA Mosulishvili LM Holman HY 《Biomedical chromatography : BMC》2002,16(5):327-331
Rapid and effective separation of bacteria Arthrobacter oxydans was performed using capillary electrophoresis. For optimal separation of bacteria the influence of buffer concentration, pH and applied voltage were studied. It was found that the most appropriate conditions for electrophoretic mobility measurements are as follows: applied voltage 6-14 kV; buffer concentration 5-10 mM pH 6-8. At the stationary phase of growth there are always two main heterogeneous peaks. They are connected with the morphology of bacteria as well as with cell aggregation. The heterogeneity of samples may be explained by surface modifications of bacterial cells. 相似文献
14.
A procedure for the Raman spectra calculation of vitreous and molten silicates was presented in this paper. It includes molecular dynamics MD simulation for the generation of equilibrium configurations, Wilson's GF matrix method for the calculations of eigenfrequencies and corresponding vectors, electro-optical parameters method (EOPM) for the Raman intensity calculations, and the bond polarizability model (BPM) for the determination of polarizability and polarizability derivative. One of the most important characteristics of this procedure is the achievement of the partial Raman spectra of five tetrahedral units, as well as the total spectral envelope. In this paper, the calculation was carried out for the vitreous and molten calcium silicates with different compositions and at various temperatures. It is worthwhile to note that the calculation is based on statistical configurations distribution in the space and so it is not needed to artificially adjust the full width at half maximum (FWHM) of spectra. It was also tested through the good agreement of the calculated spectra with the experimental, including some regularity of spectral properties. According to the calculation, the symmetrical stretching of whole tetrahedral units, to which the stretching of Si-O(nb) bond gives the main contribution to intensity, is proven to be the dominance in the high-frequency range (800-1200 cm(-1)) and the symmetrical bending of Si-O(b)-Si, to which the stretching of Si-O(b) bond exhibits the main contribution, is the dominance in the medium-frequency range (400-700 cm(-1)). As the first theoretical results, the Raman scattering coefficient of each Q(i) was found little change along with the variation of composition and temperature. 相似文献
15.
Jin R Jureller JE Kim HY Scherer NF 《Journal of the American Chemical Society》2005,127(36):12482-12483
Femtosecond laser excited second harmonic (SH) activity from single Ag nanoparticles is reported. A correlation of SH single-particle measurements with high-resolution imaging of particle morphology by TEM was achieved by creating position markers on an optical and electron transparent substrate (Si3N4 thin film, approximately 100 nm). We compared the SH activity of single Ag nanoparticles (nanospheres versus nanorods) and cluster structures (composed of two or multiple particles, e.g., dimers and trimers). The direct correlation of single-particle structures and SH activity, spectral and power dependence, strongly suggests one-photon resonant driven nonlinear oscillator response mechanism. 相似文献
16.
Chae SC Song JH Pounsambath P Yuan HY Lee JH Kim JJ Lee YC Chung HT 《Experimental & molecular medicine》2004,36(3):274-278
The family of T-cell immunoglobulin domain and mucin domain (TIM) proteins is identified to be expressed on T cells. A member of Tim family, Tim-3 (T cell immunoglobulin mucin 3) is selectively expressed on the surface of differentiated Th1 cells. Tim-3 might have an important role in the induction of autoimmune diseases by regulating macrophage activation and interacts with Tim-3 ligand to regulate Th1 responses. To determine the variation sites in the coding and promoter region of human Tim-3 gene, we performed variation scanning by direct sequencing using the genomic DNA isolated from the patients with asthma or allergic rhinitis and healthy controls without asthma and allergic rhinitis. We identified four single nucleotide polymorphisms (SNPs) including one novel SNPs (-1541C>T) and two variation sites (-1292_-1289delTAAA and -1282_-1278dupTAAAA) in the coding and promoter region of human Tim-3 gene in both the patients and healthy groups. 相似文献
17.
A copper microparticle-modified carbon fiber microdisk array electrode was fabricated and employed in capillary electrophoresis for the simultaneous determination of the five aminoglycoside antibiotics (AGs) including netilmicin, tobramycin, lincomycin, kanamycin and amikacin. The array electrode exhibited high catalytic activity for AGs, good reproducibility and stability. Under the optimum separation conditions (separation voltage of 6.2 kV, electrophoretic medium of 125 mM NaOH), the five AGs above were baseline separated within 20 min. At a working electrode potential of 0.7 V (versus saturated calomel electrode), the calibration curves were linear over two orders of magnitude of concentration, and the detection limits (SIN=3) were below 2 microM except for lincomycin (6.7 microM). The developed method was successfully employed for the simultaneous determination of the five AGs studied in pharmaceutical injections. The feasibility of this method for the simultaneous determination of lincomycin, kanamycin and amikacin in urine sample was also demonstrated. 相似文献
18.
Use of synchronous first-derivative fluorimetry for determination of gentamycin is described. Gentamycin reacts with acetylacetone and formaldehyde in pH 5.6 HOAc/NaOAc buffer solution to form N-gentamyl-2,6-dimethyl-3,5-diacethyl-1,4-dihydropyridine[I] which is a fluorescent substance. Spectra of [I] and the reagent blank can be separated with synchronous derivative fluorimetry, and gentamycin can be determined directly. The synchronous spectral peaks of [I] and the reagent blank are at 434 and 411 nm, respectively. The first-derivative peak of [I] is at 425 nm. Effects of pH, foreign ions, buffer system, and heating time on the determination of gentamycin have been examined. The linear regression equation of the calibration graph is C=0.0513H-0.0416, with a correlation coefficient of linear regression of 0.9978. C means total potency of gentamycin: U ml(-1); H means peak height in the linear regression equation calibration graph. The linear range for the determination of gentamycin is from 0.00 to 3.00 U ml(-1). Recovery is from 95.06 to 112.0%, R.S.D. of 3.8%. The results determined by the fluorimetric method agreed roughly with those by the microbiological method. The method is simple and has low detection limit. 相似文献
19.
20.