全文获取类型
收费全文 | 776篇 |
免费 | 19篇 |
国内免费 | 6篇 |
专业分类
化学 | 574篇 |
晶体学 | 6篇 |
力学 | 5篇 |
数学 | 47篇 |
物理学 | 169篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 5篇 |
2016年 | 17篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 40篇 |
2012年 | 34篇 |
2011年 | 34篇 |
2010年 | 20篇 |
2009年 | 41篇 |
2008年 | 41篇 |
2007年 | 35篇 |
2006年 | 40篇 |
2005年 | 46篇 |
2004年 | 45篇 |
2003年 | 30篇 |
2002年 | 28篇 |
2001年 | 17篇 |
2000年 | 8篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1968年 | 2篇 |
排序方式: 共有801条查询结果,搜索用时 15 毫秒
231.
Kazuhisa Hiratani Hirotaka Uzawa Kazuyuki Kasuga Hide Kambayashi 《Tetrahedron letters》1997,38(52):319-8996
A series of crownophanes containing two phenolic moieties within a macrocyclic ring have been successfully synthesized by a one-step thermal reaction from the corresponding macrocyclic polyethers by using a “Tandem Claisen Rearrangement”. 相似文献
232.
Dou?XiaomingEmail author Yuan?Bo Zhao?Haiying Yin?Guangzhong Yukihiro?Ozaki 《中国科学B辑(英文版)》2004,47(3):257-266
Since the theory of generalized two-dimensional (2-D) correlation spectroscopy was proposed, it has been keenly concerned
in scientific research and its analytical method has been widely applied in various analytical fields. The mathematical process
to construct generalized 2-D correlation spectroscopy and the physical meaning of 2-D correlation spectral map are described,
and three examples in the fields of chemical analysis and molecular biology are provided, such as the component analysis of
organic solvent, the analysis of biological molecules in the solvent with different pH values and structural analysis of protein.
The theory and analytical method of generalized 2-D correlation spectroscopy are also detailedly commented. 相似文献
233.
1,3-Butadiene-2-carboxylates were treated with a titanium(II) alkoxide reagent, Ti(O-i-Pr)4/2i-PrMgCl, to generate diene-titanium alkoxide complexes, the presence of which was verified by hydrolysis and deuteriolysis to give the corresponding monoolefins or their bis-deuterated counterpart. These diene complexes underwent successive addition to an aldehyde (as the first electrophile) and iodine (as the second one) in a highly regio- and stereoselective manner to give the corresponding iodo alcohol. Optically active 1,3-butadiene-2-carboxylates afforded the same adducts of high asymmetric induction. Besides these electron-deficient dienes, electron-rich 2-siloxy-1,3-butadienes also participated in the formation of the titanium complex, which led to the preparation of functionalized enol silyl ethers through regio- and stereoselective coupling with carbonyl compounds and hydrolytic workup. 相似文献
234.
The red leaves of Graptophyllum pictum (L.) Griff. (G. pictum) are used in Indonesian folk medicine. The present study was carried out to elucidate the antiinflammatory effect of the ethanol extract obtained from this crude drug. The extract was partitioned between ether and water, and then the water-soluble fraction was extracted with 1-butanol. The 1-butanol-soluble fraction was extracted with chloroform-acetone, hot methanol and water, successively, and the hot methanol-soluble fraction (fr.) was chromatographed (frs. I-III). The antiinflammatory activity of these fractions was investigated on carrageenin-induced edema in rats and acetic acid-induced vascular permeability as well as the writhing symptom in mice. The ethanol extract (p.o.) showed an antiinflammatory activity as well as an analgesic activity and these activities shifted to the water-soluble fraction, 1-butanol-soluble fraction, methanol-soluble fraction and fr. II, successively. It was found that fr. II contained flavonoids. These results suggest that these flavonoids are at least partly responsible for the antiinflammatory effect of the ethanol extract of G. pictum. 相似文献
235.
Near-infrared spectroscopy for liquids of microliter volume using capillaries with wall transmission
In the present study we propose a capillary tube method for measuring near-infrared (NIR) spectra of microliter liquid and solution samples. This method enables one to measure NIR spectra of liquids and solutions of only 2.5 microl. As an example of the capillary tube method, Fourier-transform NIR spectra of benzene were measured using a capillary tube with a diameter of 1 mm. Positions and intensities of the NIR bands in the spectra obtained by the capillary tube were almost identical to those measured using a quartz cuvette cell. Moreover, capillary NIR spectra of human blood serum obtained from a patient with backbone neoplasm were also measured. Subtraction of the NIR spectrum of water from those of human blood serum develops unambiguously some NIR bands due to blood components such as proteins and glucose. Our results suggest that capillary NIR spectroscopy will open new areas of NIR applications for small amounts of liquid and solution samples. 相似文献
236.
237.
The transesterification of molten ethylene-vinylacetate (EVA) copolymers by octanol with sodium methoxide as catalyst in an extruder has been monitored by on-line near infrared (NIR) spectroscopy. A total of 60 NIR spectra were acquired for 37 min with the last spectrum recorded 31 min after the addition of octanol and catalyst was stopped. The experimental spectra show strong baseline fluctuations which are corrected for by multiplicative scatter correction (MSC). The chemometric methods of the orthogonal projection approach (OPA) and multivariate curve resolution (MCR) were used to resolve the spectra and to derive concentration profiles of the species. The detailed analysis reveals the absence of completely pure variables which leads to small errors in the calculation of pure spectra. The initial estimation of a concentration that is necessary as an input parameter for MCR also presents a non-trivial task. We obtained results that were not ideal but applicable for practical concentration control. They enable a fast monitoring of the process in real-time and resolve the spectra of the EVA copolymer and the ethylene-vinyl alcohol (EVAL) copolymer to be very close to the reference spectra. The chemometric methods used and the decomposed spectra are discussed in detail. 相似文献
238.
Amounts of crystalline phases of airborne particulates collected on a silicon wafer (10 x 10 mm) using a high-volume air sampler were analyzed by grazing incidence X-ray diffractometry (GIXD). Airborne particulates were classified into five size ranges (1.09-10.5 microm) with a cascade impactor attached on the sampling ports of the high-volume air sampler. GIXD was used throughout this analysis to obtain better sensitivity for small amounts of airborne particulates on the silicon wafer. Calibration standards on the silicon wafer for the diffractometric determination were prepared by the suspension droplet method of the crystalline standards dispersed in cyclohexane. Analytical lines were (020) for gypsum, (101) for quartz, (104) for calcite, (200) for halite, and (110) for sal ammoniac. The sample and the calibrating standards were heated at 350 degrees C for 2 h to avoid mutual interference with gypsum (041 and 221) when calcite and halite were determined. The GIXD method enables us to determine 0.23-13.2 microg of gypsum, quartz, calcite, halite and sal ammoniac in 0.110-0.233 mg of airborne particulates on the silicon wafer. 相似文献
239.
Structural changes in the local conformation of poly(N-isopropylacrylamide) (PNiPA) during the thermally and solvent-induced coil-globule transitions in an aqueous solution were studied by using attenuated total reflection / infrared (ATR/IR) spectroscopy combined with density functional theory (DFT) calculation. DFT calculation makes it possible to connect the spectral changes observed during the transitions with the structural changes of the local conformation of polymer chains. The results suggest that some of the intramolecular C=O···H-N hydrogen bonds of amide groups are broken, and the changes in local conformations occur during the coil-globule transitions of PNiPA. In this paper, an overview of our recent studies on the coil-globule transitions of PNiPA is given for introducing a new idea that may explain the stimulus sensitivities of PNiPA in solutions; the solubility of segments concerning with the local conformation of repeating monomer units is changed by an external perturbation, and then the polymer system shows the coil-globule transition. 相似文献
240.