全文获取类型
收费全文 | 6393篇 |
免费 | 1110篇 |
国内免费 | 809篇 |
专业分类
化学 | 4642篇 |
晶体学 | 105篇 |
力学 | 404篇 |
综合类 | 51篇 |
数学 | 752篇 |
物理学 | 2358篇 |
出版年
2024年 | 23篇 |
2023年 | 136篇 |
2022年 | 251篇 |
2021年 | 259篇 |
2020年 | 346篇 |
2019年 | 303篇 |
2018年 | 280篇 |
2017年 | 286篇 |
2016年 | 363篇 |
2015年 | 401篇 |
2014年 | 377篇 |
2013年 | 522篇 |
2012年 | 586篇 |
2011年 | 562篇 |
2010年 | 409篇 |
2009年 | 388篇 |
2008年 | 412篇 |
2007年 | 340篇 |
2006年 | 319篇 |
2005年 | 272篇 |
2004年 | 229篇 |
2003年 | 170篇 |
2002年 | 177篇 |
2001年 | 121篇 |
2000年 | 111篇 |
1999年 | 111篇 |
1998年 | 42篇 |
1997年 | 49篇 |
1996年 | 47篇 |
1995年 | 39篇 |
1994年 | 18篇 |
1993年 | 39篇 |
1992年 | 37篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 25篇 |
1987年 | 11篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1982年 | 15篇 |
1980年 | 9篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有8312条查询结果,搜索用时 15 毫秒
51.
52.
[structure: see text] Total synthesis of a cyclic depsipeptide with proposed structure of palau'amide is achieved, which features a stereoselective elaboration of its 5,7-dihydroxy-2,6-dimethyldodec-2-en-11-ynoic acid unit. The synthetic compound has potent cytotoxicity against three tumor cell lines but different rotation and NMR data compared to those reported for palau'amide, which implies that its conformation is close to that of palau'amide but that some stereochemistry in palau'amide was misassigned. 相似文献
53.
N-Lithioketimines, generated in situ from 2-substituted benzonitriles and t-BuLi, reacted with carbon monoxide to afford five-, six- or seven-membered cyclic products, involving participation by the ortho substituents. The reactions represent new selective transformations of carbonyllithium intermediate which previously were observed to lead to complicated reactions. 相似文献
54.
The ZnCl2 catalyzed reaction of p-methoxybenzyl chloride with alkenes yields the 1:1 addition products 3, which are converted into the γ-lactones 4 via Ru(VIII) catalyzed oxidative degradation of the aromatic ring. 相似文献
55.
Reaction of α-nitro olefins with secondary amines in the presence of palladium(O) catalyst affords allylic amines. 相似文献
56.
Kai Li Harald D. H. Stver 《Journal of polymer science. Part A, Polymer chemistry》1993,31(10):2473-2479
Narrow disperse microparticles are formed by dispersion polymerization of commercial divinylbenzene in acetonitrile or ethanol solution in the presence of 2,2′-azobis(2-methylpropionitrile) initiator and polyvinylpyrrolidone stabilizer. The particles have average diameters between 1 and 9 μm depending on monomer concentration, solvent, and temperature. While the smaller particles are relatively smooth, surface texture increases with diameter to give popcorn shapes at 9 μm diameter. High crosslinker concentration is shown to be essential for particle formation. © 1993 John Wiley & Sons, Inc. 相似文献
57.
Li Z Chen Z Cui H Hales K Qi K Wooley KL Pochan DJ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7533-7539
Disk and cylindrical micellar assemblies were formed through self-organization of poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) amphiphilic triblock copolymers with organic diamines as counterions in water/ tetrahydrofuran (THF) solvent mixtures. The system was investigated by means of transmission electron microscopy and cryogenic transmission electron microscopy. It was found that the assembled-state morphologies could be modified by alteration of the type and concentration of cationic diamine counterion undergoing interaction with the negatively charged, polyelectrolyte PAA corona block, the relative amount of water in the water/THF mixture, and the hydrophobic block chain length. Multivalency of the organic amine counterion was critical for disk formation. It was further demonstrated that a single block copolymer underwent disc-to-cylindrical micellar transitions reversibly with variation in the relative water/THF ratio. The ability to form disks beginning from either THF-rich or water-rich solutions indicated that the disk morphology was thermodynamically stable and that THF was important in keeping the micellar structure from becoming kinetically frozen. The nanoassemblies were produced having low size dispersities and were stable for at least one month. Intermediate structures between disks and cylinders were also observed, indicating two distinct kinetic pathways between the two micelle structures. 相似文献
58.
59.
Methyl radical complexes H3C…HCN and H3C…HNC have been investigated at the UMP2(full)/aug‐cc‐pVTZ level to elucidate the nature of hydrogen bonds. To better understand the intermolecular H‐bond interactions, topological analysis of electron density at bond critical points (BCP) is executed using Bader's atoms‐in‐molecules (AIM) theory. Natural bond orbital (NBO) analysis has also been performed to study the orbital interactions and change of hybridization. Theoretical calculations show that there is no essential difference between the blue‐shift H‐bond and the conventional one. In H3C…HNC complex, rehybridization is responsible for shortening of the N? H bond. The hyperconjugative interaction between the single electron of the methyl radical and N? H antibonding orbital is up to 7.0 kcal/mol, exceeding 3.0 kcal/mol, the upper limit of hyperconjugative n(Y)→σ*(X–H) interaction to form the blue‐shifted H‐bond according to Alabugin's theory. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
60.
Kunio Miki Yasushi Kai Noritake Yasuoka Nobutami Kasai 《Journal of organometallic chemistry》1979,165(1):79-91
The precise molecular structure of [PdCl(CH2SCH3)(PPh3)2] has been determined from three-dimensional X-ray diffraction data collected at ?160°C. The CH2Cl2 solvated crystal ([PdCl(CH2SCH3)(PPh3)2 · CH2Cl2]) belongs to the monoclinic system, space group P21/n, with four formula units in a cell of dimensions: a 14.973(3), b 15.333(3), c 17.377(3) Å and β 115.77(1)° at ?160°C. The structure was solved by the conventional heavy atom method and refined by the least-squares procedure to R = 0.035 for observed reflections. The geometry around the palladium atom is square-planar. The phosphorus atoms of the two triphenylphosphine ligands are mutually trans. The CH2SCH3 group is bonded to the palladium atom only through the PdC σ-bond and the sulfur atom is not bonded to the metal atom (PdC(1) 2.061(3), SC(1) 1.796(3), SC(2) 1.817(5), Pd?S 2.973(1) Å, PdC(1)S 100.64(14)° and C(1)SC(2) 101.28(18)°). The structure is in contrast to that of [PdCl(CH2SCH3)(PPh3)], in which both the carbon and sulfur atoms of the CH2SCH3 group are bonded to the palladium atom. 相似文献