全文获取类型
收费全文 | 2630篇 |
免费 | 119篇 |
国内免费 | 14篇 |
专业分类
化学 | 1911篇 |
晶体学 | 10篇 |
力学 | 48篇 |
数学 | 421篇 |
物理学 | 373篇 |
出版年
2023年 | 15篇 |
2022年 | 15篇 |
2021年 | 35篇 |
2020年 | 60篇 |
2019年 | 50篇 |
2018年 | 34篇 |
2017年 | 27篇 |
2016年 | 90篇 |
2015年 | 73篇 |
2014年 | 83篇 |
2013年 | 111篇 |
2012年 | 117篇 |
2011年 | 119篇 |
2010年 | 107篇 |
2009年 | 84篇 |
2008年 | 115篇 |
2007年 | 116篇 |
2006年 | 123篇 |
2005年 | 110篇 |
2004年 | 100篇 |
2003年 | 81篇 |
2002年 | 95篇 |
2001年 | 46篇 |
2000年 | 50篇 |
1999年 | 52篇 |
1998年 | 46篇 |
1997年 | 54篇 |
1996年 | 56篇 |
1995年 | 54篇 |
1994年 | 51篇 |
1993年 | 38篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 26篇 |
1989年 | 42篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 25篇 |
1985年 | 25篇 |
1984年 | 30篇 |
1983年 | 33篇 |
1981年 | 21篇 |
1980年 | 24篇 |
1979年 | 31篇 |
1978年 | 26篇 |
1977年 | 20篇 |
1976年 | 22篇 |
1975年 | 15篇 |
1973年 | 18篇 |
1971年 | 20篇 |
排序方式: 共有2763条查询结果,搜索用时 15 毫秒
51.
Glow discharge mass spectrometry 总被引:5,自引:0,他引:5
Hoffmann V Kasik M Robinson PK Venzago C 《Analytical and bioanalytical chemistry》2005,381(1):173-188
Over the past twenty years or so, glow discharge mass spectrometry (GDMS) has become the industry standard for the analysis of trace elements in metals and semiconductors. A review of its history is followed by a picture of the present situation and a look to where the future may lie. Applications are summarised, including the ability of GDMS to offer depth-resolved data and non-conductor analysis, and the well-documented quantitative nature of the results is reviewed. The effects resulting from the physical properties of the analyte material are discussed at length. Finally, recent work such as fast flow sources and pulsed glow discharges is reviewed. 相似文献
52.
53.
54.
Investigations carried out in order to determine traces of 25 elements in tungsten in the lower g/g range are reported on. Atomic absorption spectrometry and plasma atomic emission spectrometry as well as solution photometry and activation analysis were the main techniques used. 相似文献
55.
The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions. 相似文献
56.
Robert Martin Nicole Gros Volker Böhmer Hermann Kämmerer 《Monatshefte für Chemie / Chemical Monthly》1979,110(5):1057-1066
TheFries rearrangement of different methoxy benzoates has been investigated. Frompara-methoxy benzoates the corresponding hydroxy-4-methoxy benzophenones could be obtained in good yields by treatment withLewis acids (especially TiCl4) in nitromethane at 20°C (4-hydroxy derivatives) or without solvent at 120°C (2-hydroxy derivatives). Under the same conditions only demethylation occurs withortho-methoxy benzoates leading to the corresponding salicylates. Small amounts of hydroxy-2-methoxy benzophenones were obtained by treatment with polyphosphoric acid. 相似文献
57.
Andreas Stockhammer Klaus-Hermann Dahmen Tobias Gerfin Luigi M. Venanzi Volker Gramlich Walter Fetter 《Helvetica chimica acta》1991,74(5):989-992
The cluster compounds [Pt3(μ-CO)3(PR3)3] act as Lewis bases towards the metal halides of Group XI, MX, Group XII, MX2, and Group XIII, MX3, to form cluster compounds of the composition [{MXn}{Pt3(μ-CO)3(PR3)3}]. The X-ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt3(μ-CO)3(PPh(i-Pr)2)3}]. 相似文献
58.
Fausi?RassoulEmail author Heinz?L?ster Volker?Richter 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1501-1507
Summary. L-Carnitine, L-(−)-β-hydroxy-γ-trimethylaminobutyrate, plays an important role as a factor necessary for the transport of long-chain fatty acids into the mitochondria. In order to investigate the influence of L-carnitine on hyperlipidaemias, the experimental model of the sucrose-induced hypertriglyceridaemia of the rat was used. In these experiments L-carnitine in the dose of 11 mg per day and 100 g body weight (over the period of 1 week) was able to antagonize the sucrose-induced hypertriglyceridaemia and the increase of serum free fatty acid level in female rats of the Wistar strain. Carnitine administration did not change the activities of lipogenic enzymes and fatty acid synthesis in the liver. However, L-carnitine increases the rate of hepatic fatty acid oxidation. Our results indicate a hypotriglyceridemic and free fatty acid lowering effect of L-carnitine, and suggest the use of this compound in the therapy of hyperlipidaemias. 相似文献
59.
Serber Z Straub W Corsini L Nomura AM Shimba N Craik CS Ortiz de Montellano P Dötsch V 《Journal of the American Chemical Society》2004,126(22):7119-7125
Studying protein components of large intracellular complexes by in-cell NMR has so far been impossible because the backbone resonances are unobservable due to their slow tumbling rates. We describe a methodology that overcomes this difficulty through selective labeling of methyl groups, which possess more favorable relaxation behavior. Comparison of different in-cell labeling schemes with three different proteins, calmodulin, NmerA, and FKBP, shows that selective labeling with [(13)C]methyl groups on methionine and alanine provides excellent sensitivity with low background levels at very low costs. 相似文献
60.
The amphiphilic shape-persistent macrocycle 1 containing four phenol-OH groups as polar side groups and four hexyloxy groups as nonpolar side groups in an adaptable arrangement was recrystallized from solvents of different polarity. X-ray crystallography reveals that the conformation of the macrocycle is solvent dependent such that in the pyridine solvate only two of the nonpolar side groups point outward while in the THF solvate all four of them point outward. Moreover, in the latter case the three-dimensional packing leads to the formation of a supramolecular channel structure with a large pore size. 相似文献