全文获取类型
收费全文 | 12893篇 |
免费 | 431篇 |
国内免费 | 31篇 |
专业分类
化学 | 9536篇 |
晶体学 | 108篇 |
力学 | 234篇 |
数学 | 1471篇 |
物理学 | 2006篇 |
出版年
2023年 | 96篇 |
2022年 | 168篇 |
2021年 | 215篇 |
2020年 | 229篇 |
2019年 | 210篇 |
2018年 | 222篇 |
2017年 | 199篇 |
2016年 | 454篇 |
2015年 | 380篇 |
2014年 | 402篇 |
2013年 | 822篇 |
2012年 | 797篇 |
2011年 | 892篇 |
2010年 | 480篇 |
2009年 | 433篇 |
2008年 | 860篇 |
2007年 | 813篇 |
2006年 | 706篇 |
2005年 | 672篇 |
2004年 | 506篇 |
2003年 | 475篇 |
2002年 | 462篇 |
2001年 | 270篇 |
2000年 | 245篇 |
1999年 | 189篇 |
1998年 | 136篇 |
1997年 | 137篇 |
1996年 | 179篇 |
1995年 | 141篇 |
1994年 | 125篇 |
1993年 | 136篇 |
1992年 | 116篇 |
1991年 | 81篇 |
1990年 | 60篇 |
1989年 | 59篇 |
1988年 | 53篇 |
1987年 | 47篇 |
1986年 | 42篇 |
1985年 | 90篇 |
1984年 | 87篇 |
1983年 | 55篇 |
1982年 | 74篇 |
1981年 | 58篇 |
1980年 | 57篇 |
1979年 | 34篇 |
1978年 | 42篇 |
1977年 | 38篇 |
1975年 | 34篇 |
1955年 | 37篇 |
1954年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Corona-Avendaño S Rojas-Hernández A Romero-Romo MA Pardavé MP Ramírez-Silva MT 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(13-14):3139-3144
Noradrenaline is a catecholamine which has been largely recognised to play a very important role in biological systems. In view of the neurotransmitter's alleged importance, this work aimed at showing the influence of time on its spectral behaviour using different analytical methods and determining its acidity constants through spectrophotometric titration and by the so-called point-by-point analysis, where the samples are freshly prepared for each pH value investigated at the instant required. Because the catecholamines are light-sensitive and likely to react with the oxygen in the surrounding air, both methods used preclude its incidence onto the samples being analysed under the presence of a nitrogen atmosphere maintained over the solutions. The constants obtained through point-by-point analysis were log beta1 = 30.71+/-0.16, log beta2 = 22.00+/-0.15 and log beta3 = 11.69+/-0.16. 相似文献
42.
Applied Biochemistry and Biotechnology - Biological systems can convert renewable resources, including lignocellulosic biomass, starch crops, and carbon dioxide, into fuels, chemicals, and... 相似文献
43.
A simple technique is described for the routine simultaneous capillary electrophoretic determination of 6 cations in wine. Separation was achieved on a fused silica capillary column with a UV-Cat-1, alpha-hydroxysobutyric acid and 18-crown-6-ether buffer at pH 4.5 and indirect UV detection at 214 nm. The content of magnesium, sodium, potassium, calcium, manganese, and lithium was determined. The method is quantitative, with recoveries in the 92-102% range, and linear over more than one order of magnitude. The precision is better than 2.5-3.4%. The method is sensible, with detection limits between 0.01 and 0.06 mg/L. Twenty-five red wines with a Certified Brand of Origin from Galicia (north-western Spain) were analyzed by the proposed method. Various wines showed very similar electrophoretic profiles, but significant quantitative differences were observed. 相似文献
44.
A new graphite-epoxy composite electrode (GECE) containing Bi(NO(3))(3) as a built-in bismuth precursor for simultaneous and individual anodic stripping analysis of heavy trace metals like lead and cadmium is reported. The developed Bi(NO(3))(3)-GECE is compatible with bismuth film electrodes reported previously including the composite electrodes (Bi-GECE) recently reported by our group. Bi(NO(3))(3)-GECE displays the ability for the detection of both individual and simultaneous determination of heavy trace metals and exhibits well defined, reproducible and sharp stripping signals. The sensitive response is combined with the minimal toxicity of Bi(NO(3))(3). This novel sensor would be an appropriate alternative tool to sensors using bismuth in solution during their utilization in environmental quality monitoring as well as other applications. 相似文献
45.
Paital AR Mitra T Ray D Wong WT Ribas-Ariño J Novoa JJ Ribas J Aromí G 《Chemical communications (Cambridge, England)》2005,(41):5172-5174
Based on a combined theoretical-experimental study, we propose that substituted m-phenylene ligands (m-N-Phi-N) can act as tuneable strong ferromagnetic couplers connecting Cu(II) ions; a new complex presenting that bridge with J close to +15 cm(-1) has been suggested and synthesized. 相似文献
46.
Burguera JL Quintana IA Salager JL Burguera M Rondón C Carrero P Anton de Salager R Petit de Peña Y 《The Analyst》1999,124(4):593-599
An on-line time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwave-aided oxidation with potassium persulfate has been developed for the determination of the different mercury species in fish-eggs oil samples. A three-phase surfactant-oil-water emulsion produced an advantageous flow when a peristaltic pump was used to introduce the highly viscous sample into the system. The optimum proportion of the oil-water mixture ratio was 2:3 v/v with a Tween 20 surfactant concentration in the emulsion of 0.008% v/v. Inorganic mercury was determined after reduction with sodium borohydride while total mercury was determined after an oxidation step with persulfate prior to the reduction step to elemental mercury with the same reducing agent. The difference between total and inorganic mercury determined the organomercury content in samples. A linear calibration graph was obtained in the range 0.1-20 micrograms l-1 of Hg2+ by injecting 0.7 ml of samples. The detection limits based on 3 sigma of the blank signals were 0.11 and 0.12 microgram l-1 for total and inorganic mercury, respectively. The relative standard deviation of ten independent measurements were 2.8 and 2.2% for 10 micrograms l-1 and 8.8 and 9.0% for 0.1 microgram l-1 amounts of total and inorganic mercury, respectively. The recoveries of 0.3, 0.6 and 8 micrograms l-1 of inorganic and organic mercury added to fish-eggs oil samples ranged from 93.0 to 94.8% and from 100 to 106%, respectively. Good agreement with those values obtained for total mercury content in real samples by electrothermal atomic absorption spectrometry was also obtained, differences between mean values were < 7%. With the proposed procedure, 22 proteropterous catfish-eggs oil samples from the northwestern coast of Venezuela were measured; while the organic mercury lay in the range 2.0 and 3.3 micrograms l-1, inorganic mercury was not detected. 相似文献
47.
Takaaki Tsuchida Gang Zheng Ravindra K. Pandey William R. Potter David A. Bellnier Barbara W. Henderson Harubumi Kato Thomas J. Dougherty 《Photochemistry and photobiology》1997,66(2):224-228
Human serum albumin (HSA) is one of the key components in human blood that may influence drug distribution. As such, it is important to know the affinity of any drug for albumin. Previously, Photofrina mixture of monomeric, dimeric and oligomeric porphyrins, has been subjected to HSA binding studies. However, due to its complex nature, binding studies on Photofrin or other hematoporphyrin derivatives with HSA are inconclusive. In this report, the binding properties of some components (dimers and trimers) of Photofrin® and the relationship between murine photosensitizing efficacy and those binding properties were investigated. The interaction of these porphyrins with HSA was investigated by direct ultrafiltration and fluorescent titration techniques with fluorescent probes such as dansyl-L-proline (DP), which is known to interact selectively with site II on HSA. Porphyrins also were tested for antitumor activity in a mouse model following intravenous administration and exposure to laser light. Together, the results suggest that the photosensitizers that were preferentially bound to site II of HSA were most effective at controlling murine tumor regrowth 相似文献
48.
49.
50.
The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a
coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH3COO)2·2H2O is a two-stage process with Cd(CH3COO)2·H2O as intermediate. The way of Cd(CH3COO)2 decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO2 are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions
in which intermediates, Cd and CdCO3, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending
on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with
oxygen.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献