全文获取类型
收费全文 | 27051篇 |
免费 | 3494篇 |
国内免费 | 3203篇 |
专业分类
化学 | 11829篇 |
晶体学 | 327篇 |
力学 | 828篇 |
综合类 | 189篇 |
数学 | 1446篇 |
物理学 | 6371篇 |
综合类 | 12758篇 |
出版年
2024年 | 97篇 |
2023年 | 492篇 |
2022年 | 878篇 |
2021年 | 1048篇 |
2020年 | 1058篇 |
2019年 | 937篇 |
2018年 | 829篇 |
2017年 | 868篇 |
2016年 | 1113篇 |
2015年 | 1322篇 |
2014年 | 1802篇 |
2013年 | 2046篇 |
2012年 | 2313篇 |
2011年 | 2437篇 |
2010年 | 1949篇 |
2009年 | 1909篇 |
2008年 | 2028篇 |
2007年 | 1803篇 |
2006年 | 1552篇 |
2005年 | 1191篇 |
2004年 | 928篇 |
2003年 | 638篇 |
2002年 | 589篇 |
2001年 | 483篇 |
2000年 | 437篇 |
1999年 | 482篇 |
1998年 | 340篇 |
1997年 | 295篇 |
1996年 | 307篇 |
1995年 | 242篇 |
1994年 | 237篇 |
1993年 | 228篇 |
1992年 | 179篇 |
1991年 | 154篇 |
1990年 | 128篇 |
1989年 | 103篇 |
1988年 | 87篇 |
1987年 | 64篇 |
1986年 | 57篇 |
1985年 | 39篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1957年 | 5篇 |
1955年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
141.
简述了正交法在钻井液配方优化中的原理和方法,并证明了采用正交法进行钻井液处理剂的配方优选时,不仅能考虑多种因素、找出各因素对指标的影响,而且可充分考虑到各因素之间的交互作用,从而优选配置出最佳的钻井液。此方法简单、可靠,可带来较好的经济效益。 相似文献
142.
143.
144.
MA Yunsheng ZHU Junfa Zhuang Shuxian JIANG Zhiquan ZHOU Weiping ZHAI Runsheng Bao Xinhe 《科学通报(英文版)》2002,47(14)
The preparation of SmOx/Rh(100) and CO adsorption on this model surface have been investigated with Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption spectroscopy (TDS). The oxygen adsorption on the SmRh alloy surface leads to the aggregation of Sm on the surface. The thermal treatment of this oxidized surface induces the further agglomeration of SmOx on the Rh(100) surface. Compared with CO TDS on the clean Rh(100) surface, three additional CO desorption peaks can be observed at 176, 331 and 600 K on the SmOx/Rh(100) surface. The CO desorption peak at 176 K may originate from CO adsorbed on SmOx islands, while the appearance of the CO adsorption peaks at 331 and 600 K, depending on the oxidation state of Sm, is attributed to CO species located at the interface of SmOx/Rh(100). 相似文献
145.
本文把扩展电阻法应用于陶瓷微区电导性能研究.建立了微区的定位标识系统,可精确、方便地对选定的微区进行电导性能及组分的重复测定.该方法在研究Ba(Sn_(1-x)Sb_x)O_3、ZnO及BaTiO_3半导体瓷应用中得到有意义的结果. 相似文献
146.
147.
We reported controllable synthesis of ZnS nanocrystal-polymer transparent hybrids by using polymethylmethacrylate (PMMA) as
a polymer matrix. In a typical run, the appropriate amounts of zinc chloride (ZnCl2) and sodium sulfide (Na2S) in the presence of 2-mercaptoethanol (ME) as the organic ligand were well dispersed in H2O/dimethylformamide solution without any aggregation. In addition, the Mn-doped ZnS nanocrystals (NCs) were synthesized with
similar method. Then, ZnS-PMMA hybrids were obtained via free radical polymerization in situ by using ZnS NCs functionalized
with methacryloxypropyltrimethoxysilane (MPS). FT-IR characterization indicates the formation of robust bonding between ZnS
NCs and the organic ligand. The TEM images show that ZnS NCs are well dispersed in PMMA matrix, and particle size of as-prepared
ZnS NCs is about 2.6 nm, in agreement with the computing results of Brus’s model and Debye–Scherrer formula. The photoluminescence
measurements present that ZnS NCs, Mn-doped ZnS NCs, and ZnS/PMMA hybrid show good optical properties. 相似文献
148.
Three novel zinc complexes [Zn(dbsf)(H2O)2] ( 1 ), [Zn(dbsf)(2,2′‐bpy)(H2O)]·(i‐C3H7OH) ( 2 ) and [Zn(dbsf)(DMF)] ( 3 ) (H2dbsf = 4,4′‐dicarboxybiphenyl sulfone, 2,2′‐bpy = 2,2′‐bipyridine, i‐C3H7OH = iso‐propanol, DMF = N,N‐dimethylformamide) were first obtained and characterized by single crystal X‐ray crystallography. Although the results show that all the complexes 1–3 have one‐dimensional chains formed via coordination bonds, unique three‐dimensional supramolecular structures are formed due to different coordination modes and configuration of the dbsf2? ligand, hydrogen bonds and π–π interactions. Iso‐propanol molecules are in open channels of 2 while larger empty channels are formed in 3 . As compared with emission band of the free H2dbsf ligand, emission peaks of the complexes 1–3 are red‐shifted, and they show blue emission, which originates from enlarging conjugation upon coordination. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
149.
150.
Suoyuan Lian Lei Gao Zhenhui Kang Di Wu Yang Lan Lin Xu 《Solid State Communications》2004,132(6):375-378
Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe3O4. A mechanism for nanowire growth is proposed. 相似文献