全文获取类型
收费全文 | 18669篇 |
免费 | 2751篇 |
国内免费 | 936篇 |
专业分类
化学 | 20191篇 |
晶体学 | 60篇 |
力学 | 36篇 |
综合类 | 14篇 |
数学 | 75篇 |
物理学 | 1980篇 |
出版年
2024年 | 22篇 |
2023年 | 293篇 |
2022年 | 571篇 |
2021年 | 673篇 |
2020年 | 1271篇 |
2019年 | 980篇 |
2018年 | 814篇 |
2017年 | 659篇 |
2016年 | 1255篇 |
2015年 | 1105篇 |
2014年 | 1126篇 |
2013年 | 1334篇 |
2012年 | 1056篇 |
2011年 | 1174篇 |
2010年 | 974篇 |
2009年 | 1008篇 |
2008年 | 991篇 |
2007年 | 887篇 |
2006年 | 833篇 |
2005年 | 720篇 |
2004年 | 726篇 |
2003年 | 597篇 |
2002年 | 1267篇 |
2001年 | 293篇 |
2000年 | 222篇 |
1999年 | 249篇 |
1998年 | 263篇 |
1997年 | 173篇 |
1996年 | 121篇 |
1995年 | 127篇 |
1994年 | 75篇 |
1993年 | 48篇 |
1992年 | 41篇 |
1991年 | 41篇 |
1990年 | 39篇 |
1989年 | 33篇 |
1988年 | 34篇 |
1987年 | 29篇 |
1986年 | 72篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1976年 | 8篇 |
1974年 | 8篇 |
1972年 | 12篇 |
1966年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Employing a cleavable carbohydrate–peptide linker, a new strategy for single-bead analysis of multivalent cyclic neoglycopeptides based on Edman degradation is described. Edman degradation of glycopeptides is hampered by the acid lability of the glycosidic bond and potential incompatibilities of phenylthiohydantoin (PTH) derivatives of glycosylated amino acids with PTH derivatives of the proteinogenic amino acids. To overcome this problem, carbohydrates are detached from the cyclopeptide templates before single-bead analysis, allowing for micro sequencing under routine conditions. With this strategy, application of multivalent cyclic neoglycopeptides in split-mix libraries with a subsequent screening process becomes possible for the first time. 相似文献
43.
44.
Using radical chemistry novel highly condensed heterocycles have been synthesized. The mechanism for their formation is discussed. 相似文献
45.
P. Murzyn C. R. Pidgeon P. J. Phillips J. -P. Wells N. T. Gordon T. Ashley J. H. Jefferson T. M. Burke J. Giess M. Merrick B. N. Murdin C. D. Maxey 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):220
We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τs300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τs is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τs in non-degenerate lightly n-type Hg0.78Cd0.22Te of approximately the same band gap as InSb, and find that τs varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τs, imply that the Elliott–Yafet model dominates in these materials. 相似文献
46.
Thorsten Brand Kyle Ratinac Jeffrey V. Castro Robert G. Gilbert 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5706-5713
A method was developed for free‐radical polymerization in the confines of a hollow latex particle. Hollow particles were prepared via the dynamic swelling method from polystyrene seed and divinylbenzene and had hollows of 500–1000 nm. So that these hollow poly(divinylbenzene) particles could function as submicrometer reactors, the particles were filled with a monomer (N‐isopropylacrylamide) via the dispersion of the dried particles in the molten monomer. The monomer that was not contained in the hollows was removed by washing and gentle abrasion. Free‐radical polymerization was then initiated by γ radiolysis in the solid state. Transmission electron microscopy showed that poly(N‐isopropylacrylamide) formed in the hollow interior of the particles, which functioned as submicrometer reactors. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5706–5713, 2004 相似文献
47.
Gottfried Mayer Vitali Vogel Bas G. G. Lohmeijer Jean‐Franois Gohy Jacomina A. Van Den Broek Winfried Haase Ulrich S. Schubert Dieter Schubert 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4458-4465
Micelles prepared from amphiphilic block copolymers in which a poly(styrene) segment is connected to a poly(ethylene oxide) block via a bis‐(2,2′:6′,2″‐terpyridine‐ruthenium) complex have been intensely studied. In most cases, the micelle populations were found to be strongly heterogeneous in size because of massive micelle/micelle aggregation. In the study reported in this article we tried to improve the homogeneity of the micelle population. The variant preparation procedure developed, which is described here, was used to prepare two “protomer”‐type micelles: PS20‐[Ru]‐PEO70 and PS20‐[Ru]‐PEO375. The dropwise addition of water to a solution of the compounds in dimethylformamide was replaced by the controlled addition of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equilibrium analyses in an analytical ultracentrifuge and by transmission electron microscopy of negatively stained samples. Sedimentation analysis showed virtually unimodal size distributions, in contrast to the findings on micelles prepared previously. PS20‐[Ru]‐PEO70 micelles were found to have an average molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle preparation by the standard method) and an average hydrodynamic diameter (dh) of 18 nm. For PS20‐[Ru]‐PEO375 micelles, the corresponding values were M = 603,000 g/mol (31 protomers per micelle) and dh = 34 nm. The latter particles were found to be identical to the “equilibrium” micelles prepared in pure water. Both micelle types had a very narrow molar mass distribution but a much broader distribution of s values and thus of hydrodynamic diameters. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity analysis. The findings from electron microscopy were in disagreement with those from the sedimentation analysis both in average micelle diameter and in the width of the distributions, apparently because of imperfections in the staining procedure. The preparation procedure described also may be useful in micelle formation from other types of protomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4458–4465, 2004 相似文献
48.
Vadim G. Kessler 《Journal of Sol-Gel Science and Technology》2004,32(1-3):11-17
The article describes the principles of the Single Source Precursor approach to inorganic materials and introduces the Geometrical Molecular Structure Design Concept (MSDC) based on the choice of a proper molecular structure type for the desired precursor and completing it with ligands providing both the necessary number of donor atoms and the sterical protection of the chosen core. Application of MSDC is illustrated with examples taken from development of new approaches in the synthesis of oxide and sulfide catalysts and ferroelectric oxide materials. 相似文献
49.
50.