全文获取类型
收费全文 | 516篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 350篇 |
晶体学 | 4篇 |
力学 | 7篇 |
数学 | 80篇 |
物理学 | 85篇 |
出版年
2023年 | 1篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 38篇 |
2012年 | 22篇 |
2011年 | 35篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 33篇 |
2007年 | 30篇 |
2006年 | 28篇 |
2005年 | 41篇 |
2004年 | 39篇 |
2003年 | 21篇 |
2002年 | 26篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有526条查询结果,搜索用时 15 毫秒
81.
Ohyama K Oyamada K Kishikawa N Ohba Y Wada M Maki T Nakashima K Kuroda N 《Journal of chromatography. A》2008,1208(1-2):242-245
Three new chiral stationary phases with different lengths of l-phenylalanine peptide were prepared by solid-phase synthesis with tert-butoxycarbonyl (Boc)-l-phenylalanine on silica. The effect of phenylalanine peptide length on enantioselectivity was studied. The best separation of R/S-warfarin was achieved by the chiral stationary phase with intermediate peptide length. These stationary phases were found to exist mainly in alpha-helical conformation by using FT-IR spectra. The end-capping reagents for the N-terminus of the peptide were also evaluated. 相似文献
82.
Nakamura S Yonehara M Uchiyama M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(4):1068-1078
Silylmetalation of alkenes is challenging due to the low reactivity of the substrates. In contrast, carbometalation of alkenes has been realized through several innovative methods, including activation of the reagent and the substrate. A similar approach could be applicable to silylmetalation of alkenes, and we have recently developed a bimetal activation method using zincate complexes for this purpose. Here, we describe how the silylzincation of alkenes was achieved. First, the strategies for carbometalation of alkenes will be summarized. Secondly, the history and development of silylzincation chemistry are briefly described. Then the details of our findings related to two types of silylzincation of alkenes, as well as recent progress in mechanistic studies, are discussed. The key point in the silylzincation of alkenes proved to be the bimetal activation of the substrate. One metal (copper or titanium) strongly coordinates and activates the alkene moiety, and the other metal (zinc) acts as the electron acceptor from the silyl group by way of the alkene moiety. This dual activation concept is expected to be applicable to other combinations of metals, as well as to new types of reactions. 相似文献
83.
Choshi T Uchida Y Kubota Y Nobuhiro J Takeshita M Hatano T Hibino S 《Chemical & pharmaceutical bulletin》2007,55(7):1060-1064
An asymmetric synthesis of the core carbazole structure, 6-desprenyl-carquinostatin 3 and 6-descycloavandulyl-lavanduquinocin 3, toward a total synthesis of carquinostatin A (1) and lavanduquinocin (2), has been established. Lipase QLM (Meito) catalyzed enantioselective acetylation of the racemic alcohol 6 gave the (-)-acetate 7 and the (+)-alcohol 6 with high enantioselectivity. The absolute stereochemistry of the (-)- and (+)-alcohol 6 have been determined to be R- and S-configurations, respectively, by the advanced Mosher method. In the same manner, the (-)-acetate 13 and the (+)-alcohol 12 have been obtained from the racemic alcohol 12. The (R)-(-)-acetate 13, derived from the (R)-(-)-acetate 7, was the same as the (-)-acetate 13, which has been determined to be (R)-configuration. Oxidation of the (R)-(-)-acetate 13 followed by hydrolysis afforded (R)-(-)-6-desprenyl-carquinostatin [and (R)-(-)-6-descycloavandulyl-lavanduquinocin] 3. In addition, oxidation of the (S)-(+)-alcohol 12 provided (S)-(+)-3, which is the enantiomer of 6-desprenyl-carquinostatin A (R)-(-)-3. 相似文献
84.
Pressure-induced reentrant micellization of amphiphilic block copolymers in dilute aqueous solutions
Osaka N Miyazaki S Okabe S Endo H Sasai A Seno K Aoshima S Shibayama M 《The Journal of chemical physics》2007,127(9):094905
The pressure-induced structural changes of a block copolymer, poly(2-ethoxyethoxyethyl vinyl ether)-block-poly(2-hydroxyethyl vinyl ether) (pEOEOVE-b-pHOVE) in aqueous solutions, were studied by means of small-angle neutron scattering (SANS) and dynamic light scattering (DLS) from atmospheric pressure up to 400 MPa. pEOEOVE-b-pHOVE formed a spherical micellar structure above 40 degrees C due to poor solubility of pEOEOVE. Micellization phase diagram was determined by DLS, and a covex-upward pressure-temperature (P-T) phase diagram was obtained having a peak around (P,T)=(150 MPa,48 degrees C). The SANS curves at 50 degrees C were analyzed as a function of P. The micellar core size decreased by pressurizing at low P's (P相似文献
85.
86.
Saito Y Ueta I Ogawa M Abe A Yogo K Shirai S Jinno K 《Analytical and bioanalytical chemistry》2009,393(3):861-869
A miniaturized sample preparation technique that uses a fine-fiber-packed needle as the extraction medium is reviewed, especially
in relation to its application to the analysis of volatile organic compounds by gas chromatography. When the needle was packed
longitudinally with a bundle of fine filaments (12 μm o.d.) which were also surface-coated with polymeric materials, successful
sample preconcentration was obtained. Improved sensitivity was also established by introducing simultaneous derivatization
reactions into the extraction process in the fiber-packed needle. The storage performance of the needle clearly demonstrated
the potential of the technique for typical on-site sampling during environmental analysis. In this short review, the fiber-packed
extraction needle developed by the authors is summarized along with applications that use the fiber-packed needle as a miniaturized
extraction device. 相似文献
87.
Vu Quoc Thang Toshiaki Taniike Masaki Umemori Mitsuhiro Ikeya Yuichi Hiraoka Nguyen Duc Nghia Minoru Terano 《大分子反应工程》2009,3(8):467-472
Preservation of initial polymer/catalyst particle morphology under air, was examined using stopped‐flow Ziegler–Natta polymerization with various quenching conditions and post‐chemical treatments. The exposure of the initial particles to air caused the fast formation of cracks on the surface, finally leading to significant reformation of the particle shape, when polymerizing particles were washed with heptane at ?65 °C under N2 or under CO2. On the other hand, when the particles were washed with heptane containing an appropriate amount of tetrahydrofuran under CO2, the particle morphology under air was almost completely maintained even after 1 h exposure. The present results are useful for various ex situ characterizations of unstable initial polymer/catalyst particles.
88.
Toshio Sumi Mitsuhiro Miyazaki Toshio Sakata 《Linear algebra and its applications》2009,431(10):1858-1868
Tensor type data are becoming important recently in various application fields. We determine the rank of a 3-tensor with 2 slices in comparison with its Kronecker canonical form over the complex and real number field. 相似文献
89.
Keiko Nunokawa Mitsuhiro Ito Tetsu Yonezawa Tomoji Ozeki Seiji Watase 《Journal of organometallic chemistry》2006,691(4):638-642
An SR-modified Au cluster with a sub-nanometer size, Au11(S-4-NC5H4)3(PPh3)7 (1), has been synthesized by NaBH4 reduction of Au(S-py)(PPh3) or by reacting [Au9(PPh3)8](NO3)3 with HS-4-py in good yield. Its molecular structure has been elucidated by single crystal X-ray diffraction, and TEM observation has been achieved for the first time for this size of SR-modified Au clusters. The core structure is best described in terms of an incomplete icosahedron. CV measurements in CH2Cl2 have suggested that the cluster does not coagulate in solution with significant concentration. 相似文献
90.
Fistulosin 1, which was isolated from the root of the Welsh onion, is a novel indole alkaloid that has antifungal activity. The first total synthesis of the reported structure of fistulosin using our cycloisomerization of diene is described. 相似文献