全文获取类型
收费全文 | 76322篇 |
免费 | 14797篇 |
国内免费 | 23894篇 |
专业分类
化学 | 56525篇 |
晶体学 | 2815篇 |
力学 | 5506篇 |
综合类 | 2480篇 |
数学 | 11646篇 |
物理学 | 36041篇 |
出版年
2024年 | 228篇 |
2023年 | 937篇 |
2022年 | 2703篇 |
2021年 | 2740篇 |
2020年 | 2758篇 |
2019年 | 2743篇 |
2018年 | 2513篇 |
2017年 | 3385篇 |
2016年 | 2937篇 |
2015年 | 3965篇 |
2014年 | 4854篇 |
2013年 | 6231篇 |
2012年 | 6613篇 |
2011年 | 7082篇 |
2010年 | 6599篇 |
2009年 | 6677篇 |
2008年 | 7318篇 |
2007年 | 6672篇 |
2006年 | 6454篇 |
2005年 | 5301篇 |
2004年 | 4098篇 |
2003年 | 3105篇 |
2002年 | 3052篇 |
2001年 | 3016篇 |
2000年 | 2924篇 |
1999年 | 1880篇 |
1998年 | 1026篇 |
1997年 | 807篇 |
1996年 | 736篇 |
1995年 | 673篇 |
1994年 | 663篇 |
1993年 | 620篇 |
1992年 | 595篇 |
1991年 | 395篇 |
1990年 | 360篇 |
1989年 | 377篇 |
1988年 | 333篇 |
1987年 | 285篇 |
1986年 | 255篇 |
1985年 | 177篇 |
1984年 | 162篇 |
1983年 | 150篇 |
1982年 | 111篇 |
1981年 | 91篇 |
1980年 | 81篇 |
1979年 | 90篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1965年 | 36篇 |
1959年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
Jian Ping LI* Ping LIU Yu Lu WANG College of Chemistry & Environmental Science Henan Normal University Xinxiang Key Laboratory of Environmental Science Technology of High Education of Henan Province Xinxiang 《中国化学快报》2003,14(7)
Azo compounds are widely utilized as analytic reagents and dyes1, they can also be used in material of non-linear optics, material of optics information storing in laser disks, and dyes with oil solubility in photochromy in modern technology2. Recently, many noteworthy studies have shown that some azo compounds possess excellent optical memory and photoelectric properties3,4. For example, polymer scaffolds bearing azobenzene-potential are useful for optical information storage, azo-dye doped… 相似文献
95.
Propargylic alcohols are versatile precursors to many organic molecules including natural products and pharmaceutical compounds.[1] In our continuing interest in the development of practical methods for synthesis of ferrocene derivatives, we decided to investigate the efficiencies of ferrocenylacetylene addition to aromatic aldehydes under t-BuOKcatalyzed condition.[2] Interestingly, we found that the usually reliable coupling reaction between terminal alkyne of type 1 and aromatic aldehydes of type 2 does not furnish the expected propargylic alcohols, but that the isomeric aryl enones 3are found in high yield and very short reaction time (10~20 min). This provided a promising protocol for preparation of ferrocenyl chalcones in a practical, economical and mild sense compared with the traditional method. To the best of our knowledge, this unusual reaction was first observed for the addition of ferrocenylacetylene to aldehyde in a base-catalyzed manner (Eq. 1). 相似文献
96.
MEN Xiu-Qin WANG Jin-Xian SHI Xiao-Ning WANG Ke-Hu 《有机化学》2003,23(Z1):307-307
Carbon-carbon double bond-forming reactions have always been great importance in organic synthesis. Manymethods have been described for C =C bond formation. We[1] have reported the new method of C =C bond formation of nickel catalyzed organozinc with aromatic aldehydes in the presence of Me3SiC1. 相似文献
97.
Effects of simultaneously doped and deposited Ag on the photocatalytic activity and surface states of TiO2 总被引:8,自引:0,他引:8
Ag-TiO2 catalysts with different Ag contents were prepared via a sol-gel method in the absence of light. Based on the characterizations of XRD, photoluminescence (PL), surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and XPS as well as the evaluation of the photocatalytic activity for degrading rhodamine B(RhB) solutions, it was found that the Ag dopant promoted the phase transformation as well as had an inhibition effect on the growth of anatase crystallite. The PL and SPS intensities were decreased with increasing Ag content, indicating that the Ag dopant could effectively inhibit the recombination of the photoinduced electrons and holes. However, the active sites capturing the photoinduced electrons reduced, while the Ag content exceeded 5 mol %. At rather low Ag dopant concentrations, the migration and diffusion of Ag+ ions were predominant, while at rather high Ag dopant concentrations, the migration, diffusion, and reduction of Ag ions simultaneously occurred. The Ag-TiO2 photocatalysts with appropriate content of Ag (Ag species concentration is from about 3 to 5 mol %) possessed abundant electron traps so as to be favorable for the separation of the photoinduced electron-hole pairs, which could greatly enhance the activity of the photocatalysts. From the results of FISPS measurements, it could be found that the impurity bands and abundant surface states were introduced into the interfacial layer of TiO2 because of Ag simultaneously doping and depositing, which could improve the absorption capability for visible light of the photocatalysts. 相似文献
98.
Alan R. Katritzky Subbu Perumal Wojciech Kuzmierkiewicz Ping Lue John V. Greenhill 《Helvetica chimica acta》1991,74(8):1924-1930
tert- Alkyl sulfides are conveniently prepared from α-(1H-benzotriazol-1-yl)alkyl sulfides by displacement of the 1H-benzotriazol-1-yl group with Grignard reagents. The 1-[α-(alkylthio)alkyl]- and 1-[α-(arylthio)alkyl]-1H-benzotriazole intermediates are easily available by several routes: (i) displacement of the halogen from appropriate halides by sodium salts of thiols, (ii) condensation of 1H-benzotriazole and thiols with carbonyl compounds, or (iii) lithiation of N-substituted 1H-benzotriazoles and subsequent treatment with electrophiles. 相似文献
99.
100.