全文获取类型
收费全文 | 1239篇 |
免费 | 29篇 |
国内免费 | 6篇 |
专业分类
化学 | 1044篇 |
晶体学 | 13篇 |
力学 | 8篇 |
数学 | 48篇 |
物理学 | 161篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 15篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 22篇 |
2015年 | 22篇 |
2014年 | 39篇 |
2013年 | 35篇 |
2012年 | 64篇 |
2011年 | 89篇 |
2010年 | 43篇 |
2009年 | 44篇 |
2008年 | 82篇 |
2007年 | 88篇 |
2006年 | 89篇 |
2005年 | 76篇 |
2004年 | 83篇 |
2003年 | 59篇 |
2002年 | 73篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 15篇 |
1996年 | 18篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1968年 | 3篇 |
排序方式: 共有1274条查询结果,搜索用时 171 毫秒
141.
Highly enantioselective gem-chlorofluorination of active methylene compounds was carried out by using a copper(II) complex of a chiral spiro pyridyl monooxazoline ligand. This reaction yielded α-chloro-α-fluoro-β-keto esters and α-chloro-α-fluoro-β-keto phosphonates with up to 92% ee. The resulting dihalo β-keto ester was converted into various α-fluoro-α-heteroatom-substituted carbonyl compounds via nucleophilic substitution without loss of optical purity. A fully protected β-amino acid with a gem-chlorofluoromethylene function was also synthesized. 相似文献
142.
Miyagawa T Nagai K Yamada A Sugihara Y Fukuda T Fukuda T Uchida R Tomoda H Omura S Nagamitsu T 《Organic letters》2011,13(5):1158-1161
The first total synthesis of citridone A has been achieved through regioselective intramolecular iodocyclization and regio- and stereoselective Pd(0)-catalyzed coupling as key reactions. 相似文献
143.
Sakamoto K Takashima Y Hamada N Ichida H Yamaguchi H Yamamoto H Harada A 《Organic letters》2011,13(4):672-675
An energy transfer process was investigated using cyclodextrin-oligothiophene rotaxanes (2T-[2]rotaxane). The excited energy of 2T-[2]rotaxane is transferred to the sexithiophene derivative which is included in the cavity of β-CD stoppers of 2T-[2]rotaxane. 相似文献
144.
Uchiyama K Kondo M Yokochi R Takeuchi Y Yamamoto A Inoue Y 《Journal of separation science》2011,34(13):1525-1530
A simple, selective and rapid analytical method for determination of trimethoprim (TMP) in honey samples was developed and validated. This method is based on a SPE technique followed by HPLC with photodiode array detection. After dilution and filtration, aliquots of 500 μL honey samples were directly injected to an on-line SPE HPLC system. TMP was extracted on an RP SPE column, and separated on a hydrophilic interaction chromatography column during HPLC analysis. At the first detection step, the noise level of the photodiode array data was reduced with two-dimensional equalizer filtering, and then the smoothed data were subjected to derivative spectrum chromatography. On the second-derivative chromatogram at 254 nm, the limit of detection and the limit of quantification of TMP in a honey sample were 5 and 10 ng/g, respectively. The proposed method showed high accuracy (60-103%) with adequate sensitivity for TMP monitoring in honey samples. 相似文献
145.
Tachi T Hase T Okamoto Y Kaji N Arima T Matsumoto H Kondo M Tokeshi M Hasegawa Y Baba Y 《Analytical and bioanalytical chemistry》2011,401(7):2301-2305
Microchip analysis is a promising method for therapeutic drug monitoring. This led us to evaluate a microchip-based fluorescence
polarization immunoassay (FPIA) system for point-of-care testing on patients being treated with theophylline. The sera were
collected from 20 patients being treated with theophylline. Fluorescence polarization was measured on the microchip and theophylline
concentrations in serum were obtained. Regression analysis of the correlations was done between the results given by the microchip-based
FPIA and the conventional cloned enzyme donor immunoassay (CEDIA), and between the results given by the microchip-based FPIA
and the conventional particle-enhanced turbidimetric inhibition immunoassay (PETINIA). We successfully carried out a quantitative
analysis of theophylline in serum at values near its therapeutic range in 65 s. The results obtained by the microchip-based
FPIA correlated well with CEDIA and PETINIA results; the correlation coefficients (R
2) were 0.986 and 0.989, respectively. The FPIA system is a simple and rapid method for point-of-care testing of drugs in serum,
and its accuracy is the same as the conventional CEDIA and PETINIA. It is essential to use real samples from patients and
to confirm good correlations with conventional methods for a study on the realization of microchip. 相似文献
146.
Ishiwata S Tokunaga Y Taguchi Y Tokura Y 《Journal of the American Chemical Society》2011,133(35):13818-13820
Orthorhombic perovskites RMnO(3) are representative of spin-driven ferroelectrics. When the radius of the rare-earth ion R is smaller than that of Dy, for instance in YMnO(3), the orthorhombic phase becomes metastable at ambient pressure, which impedes the crystal growth; thus, the detailed magnetic and multiferroic properties of the metastable phase have not been characterized. In this work, we successfully obtained single crystals of orthorhombic YMnO(3) using quasi-hydrothermal conditions under a high pressure of 5.5 GPa. Magnetic and dielectric measurements under magnetic fields revealed that the magnetic ground state is the commensurate E-type antiferromagnetic, while a cycloidal spin phase likely coexists in the intermediate temperature range, which enhances the magnetoelectric response to external fields. 相似文献
147.
Sano S Okubo Y Handa A Nakao M Kitaike S Nagao Y Kakegawa H 《Chemical & pharmaceutical bulletin》2011,59(7):885-888
Isoliquiritigenin [ILG, (E)-1] was readily prepared via the Horner-Wadsworth-Emmons reactions using β-ketophosphonates 5a, b. An improved protocol for the synthesis of (E)-1 via the Claisen-Schmidt condensation was also presented. 相似文献
148.
Yoshinori Inoue Waka Kamichatani Mitsuru Saito Yasuyuki Kobayashi Atsushi Yamamoto 《Chromatographia》2011,73(9-10):849-855
A novel water-holding adsorbent was synthesized by introducing a zwitter-ionic polymer to a hydrophilic methacrylate base resin. The retention abilities of the hydrophilic compounds on the adsorbents with and without cross-link in the zwitter-ionic functional groups were examined. The amount of held water on the non-cross-linked adsorbent was higher than that of the cross-linked one. The extraction efficiencies of the hydrophilic solutes on the adsorbents were evaluated by the solid phase extraction method. These adsorbents showed high affinity for nucleosides and glycosides, and good recoveries for such hydrophilic compounds in the solid-phase extraction were obtained. Furthermore, the retention properties of the hydrophilic solutes on the adsorbents were also evaluated by LC. The hydrophilic solutes were retained on these adsorbents by a partition mode based on a hydrophilic interaction. The retention factors of the hydrophilic solutes showed good correlation to their log P o/w (logarithm of octanol?Cwater partition coefficient) and good separation based on hydrophilic interaction was obtained for nucleobases and nucleosides. 相似文献
149.
The formation of a cocrystallized coordination compound, [Pd(3)(D-pen)(3)](2)·[M(en)(3)](ClO(4))(3) (D-H(2)pen = D-penicillamine; M = Co(III) or Rh(III)), from [Pd(3)(D-pen)(3)] and [M(en)(3)](ClO(4))(3) is reported. In this compound, only the Δ-configurational [M(en)(3)](3+) cations were incorporated when its racemic (Δ/Λ) isomer was employed. Besides this enantioselective incorporation of complex cations, this compound was found to show the selective incorporation of ClO(4)(-) as the anion species. 相似文献
150.
We have shown from in situ synchrotron x-ray diffraction measurements that there are two thermodynamically stable liquid forms of SnI(4), depending on the pressure. Based on the liquid-liquid critical point scenario, our recent measurements suggest that the second critical point, if it exists, may be located in a region close to the point at which the melting curve of the crystalline phase abruptly breaks. This region is, unlike that of water, experimentally accessible with relative ease. 相似文献