全文获取类型
收费全文 | 6410篇 |
免费 | 1064篇 |
国内免费 | 799篇 |
专业分类
化学 | 4691篇 |
晶体学 | 102篇 |
力学 | 388篇 |
综合类 | 44篇 |
数学 | 697篇 |
物理学 | 2351篇 |
出版年
2024年 | 23篇 |
2023年 | 139篇 |
2022年 | 246篇 |
2021年 | 261篇 |
2020年 | 348篇 |
2019年 | 306篇 |
2018年 | 275篇 |
2017年 | 285篇 |
2016年 | 360篇 |
2015年 | 395篇 |
2014年 | 361篇 |
2013年 | 517篇 |
2012年 | 571篇 |
2011年 | 553篇 |
2010年 | 400篇 |
2009年 | 381篇 |
2008年 | 404篇 |
2007年 | 331篇 |
2006年 | 315篇 |
2005年 | 276篇 |
2004年 | 226篇 |
2003年 | 157篇 |
2002年 | 164篇 |
2001年 | 114篇 |
2000年 | 105篇 |
1999年 | 102篇 |
1998年 | 43篇 |
1997年 | 50篇 |
1996年 | 44篇 |
1995年 | 37篇 |
1994年 | 22篇 |
1993年 | 36篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 20篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 18篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 17篇 |
1975年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有8273条查询结果,搜索用时 15 毫秒
51.
[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
52.
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
53.
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
54.
Reaction of α-nitro olefins with secondary amines in the presence of palladium(O) catalyst affords allylic amines. 相似文献
55.
John T. Stock 《Trends in analytical chemistry : TRAC》1983,2(11):261-262
The automatic control of certain physical phenomena, such as temperature and speed of rotation, has long been commonplace. However, the means by which this form of control can be applied to a chemical process are not so obvious. A sensing system must be found to monitor the status of the particular chemical system. 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.
A new procedure for the preparation of high aspect ratio Au nanowires utilizing gold electroless reduction in the hexagonally ordered, thiol-modified nanosized channels of the SBA-15 material is reported. Two different Au precursors were adsorbed onto pedant thiol groups, covalently bonded to the mesoporous silica surface, and used as seeds to grow extended Au nanostructures by treatment in Au electroless reduction bath. It is shown that the dimensions and the assembly of the Au seeds are important parameters for the subsequent electroless reduction process. The [AuCl4]- ions complexed to the TOAB molecules assembled on the thiol-modified mesoporous surface of the SBA-15 material are suitable precursors for the subsequent gold electroless reduction. The resulting structures are several micrometer long Au nanowires with uniform diameters of about 5 nm, having large single-crystalline domains. The TEM results clearly show that the growth of the Au nanowires is templated by the channel structure of the SBA-15 material. 相似文献
58.
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
59.
60.
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