全文获取类型
收费全文 | 40168篇 |
免费 | 9642篇 |
国内免费 | 1434篇 |
专业分类
化学 | 44143篇 |
晶体学 | 349篇 |
力学 | 590篇 |
综合类 | 1篇 |
数学 | 3169篇 |
物理学 | 2992篇 |
出版年
2022年 | 60篇 |
2021年 | 209篇 |
2020年 | 1267篇 |
2019年 | 2634篇 |
2018年 | 1038篇 |
2017年 | 690篇 |
2016年 | 3420篇 |
2015年 | 3580篇 |
2014年 | 3492篇 |
2013年 | 4262篇 |
2012年 | 3062篇 |
2011年 | 2367篇 |
2010年 | 2965篇 |
2009年 | 2915篇 |
2008年 | 2566篇 |
2007年 | 1911篇 |
2006年 | 1637篇 |
2005年 | 1794篇 |
2004年 | 1656篇 |
2003年 | 1496篇 |
2002年 | 2168篇 |
2001年 | 1390篇 |
2000年 | 1334篇 |
1999年 | 413篇 |
1998年 | 108篇 |
1997年 | 120篇 |
1996年 | 136篇 |
1995年 | 76篇 |
1994年 | 105篇 |
1993年 | 94篇 |
1992年 | 96篇 |
1991年 | 64篇 |
1990年 | 73篇 |
1989年 | 71篇 |
1988年 | 61篇 |
1987年 | 64篇 |
1986年 | 57篇 |
1985年 | 87篇 |
1984年 | 103篇 |
1983年 | 88篇 |
1982年 | 102篇 |
1981年 | 103篇 |
1980年 | 108篇 |
1979年 | 108篇 |
1978年 | 112篇 |
1977年 | 116篇 |
1976年 | 98篇 |
1975年 | 103篇 |
1974年 | 110篇 |
1973年 | 80篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Klai Nadia Berredjem Malika Khettache Nawel Belghit Med Yazid Rgaïnia Zine Nour‐Eddine Aouf 《Journal of heterocyclic chemistry》2004,41(1):57-60
Dedicated to the memory of Pr. Ladjama Daif A series of chiral cyclosulfamides have been synthesized by alkaline cyclisation starting from N‐benzoylamino acids (Ala, Val, Leu, Phe) derivatives and chlorosulfonyl isocyanate. A simplified and regioselective deprotection of the cyclic compounds (cyclosulfamides) containing the tert‐butyloxycarbonyl group (Boc) has been achieved in good yield by fusion under reduced pressure. 相似文献
162.
Andrew Bach Xinglong Jiang Joseph Mckenna Kapa Prasad Oljan Repic Wen‐Chung Shieh 《Journal of heterocyclic chemistry》2004,41(4):637-640
An efficient approach has been developed for the synthesis of an isofervenulin analogue 1 employing a one‐pot condensation‐substitution reaction of a chlorocarboethoxytriazine (electrophile) with a urea (nucleophile). The resulting cyclization reaction resulted in the synthesis of a pyrimido‐heterocycle in good yield in either acidic or basic media. The former was assisted by utilizing trimethylsilyl chloride. 相似文献
163.
Crystal Structure of the Zinc Amide Zn[N(SiMe3)2]2 X‐ray quality crystals of Zn[N(SiMe3)2]2 (monoclinic, P21/c) are obtained by sublimation of the zinc amide Zn[N(SiMe3)2]2 at —30 °C in vacuo (300 torr). According to the result of the X‐ray structural analysis, Zn[N(SiMe3)2]2 contains an almost linear N‐Zn‐N unit with two short N‐Zn bonds. 相似文献
164.
We prove that there is no functorial universal finite type invariant for braids in Σ×I if the genus of Σ is positive. To cite this article: P. Bellingeri, L. Funar, C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
165.
Louis Marchildon 《Foundations of Physics》2004,34(1):59-73
In a recently proposed interpretation of quantum mechanics, U. Mohrhoff advocates original and thought-provoking views on space and time, the definition of macroscopic objects, and the meaning of probability statements. The interpretation also addresses a number of questions about factual events and the nature of reality. The purpose of this note is to examine several issues raised by Mohrhoff's interpretation, and to assess whether it helps providing solutions to the long-standing problems of quantum mechanics. 相似文献
166.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
167.
The structure of the title adduct comprises a phenanthroline derivative 2-phenyl-imidazo[4,5-f]1,10-phenanthroline and a methanol.The composition of the crystalline adduct was characterized as C19H12N4.CH3OH.It belongs to orthorhombic system,space group Pna21 with a=1.3693(4)nm,b=2.2988(7)nm,c=0.51338(15)nm,V=1.6160(8)nm^3.Z=4,and final R1=0.0423.wR2=0.1012 .Crystal structure shows that all the 19 carbon atoms and 4 nitrogen atoms are coplanar.The bond length data indicated that a very extensive conjugation system was formed.This conjugation makes the compound being a potentially excellent energy transformer used for luminescent materials. 相似文献
168.
Hong‐Qing Wang Zhao‐Jie Liu Li‐Min Yang Ming‐Wu Ding 《Journal of heterocyclic chemistry》2004,41(3):393-397
A series of new 1H‐pyrazolo[3,4‐d]pyrimidin‐4(5H)‐one Derivatives 5 has been designed and regio‐selectively synthesized via a tandem aza‐Wittig reaction. The structures of all compounds prepared have been confirmed by 1H NMR, IR, EI‐MS spectroscopy and elemental analyses. The results of preliminary bioassay indicate that most compounds 5 possess an inhibition effect against Botrytis cinereapers and Pyricularia oryzae at the concentration of 50 mg/L. 相似文献
169.
170.