全文获取类型
收费全文 | 20703篇 |
免费 | 3535篇 |
国内免费 | 3574篇 |
专业分类
化学 | 15772篇 |
晶体学 | 341篇 |
力学 | 1343篇 |
综合类 | 296篇 |
数学 | 2404篇 |
物理学 | 7656篇 |
出版年
2024年 | 69篇 |
2023年 | 407篇 |
2022年 | 693篇 |
2021年 | 856篇 |
2020年 | 875篇 |
2019年 | 877篇 |
2018年 | 710篇 |
2017年 | 774篇 |
2016年 | 1079篇 |
2015年 | 1034篇 |
2014年 | 1282篇 |
2013年 | 1640篇 |
2012年 | 1882篇 |
2011年 | 1830篇 |
2010年 | 1475篇 |
2009年 | 1365篇 |
2008年 | 1489篇 |
2007年 | 1281篇 |
2006年 | 1212篇 |
2005年 | 1047篇 |
2004年 | 834篇 |
2003年 | 706篇 |
2002年 | 729篇 |
2001年 | 648篇 |
2000年 | 464篇 |
1999年 | 438篇 |
1998年 | 359篇 |
1997年 | 289篇 |
1996年 | 281篇 |
1995年 | 223篇 |
1994年 | 199篇 |
1993年 | 155篇 |
1992年 | 115篇 |
1991年 | 114篇 |
1990年 | 83篇 |
1989年 | 60篇 |
1988年 | 54篇 |
1987年 | 29篇 |
1986年 | 45篇 |
1985年 | 31篇 |
1984年 | 12篇 |
1983年 | 20篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1974年 | 2篇 |
1959年 | 2篇 |
1957年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
152.
Cheng Chu Zeng Li Ming Hu Jia Zeng Ru Gang Zhong College of Life Science & Bioengineering Beijing University of Technology Beijing China 《中国化学快报》2007,18(2):130-132
The anodic oxidation of caffeic acid in the presence of acetylacetone or methyl acetoacetate in aqueous solution has been studied by cyclic voltammetry and controlled-potential electrolysis techniques. The result showed that caffeic acid was oxidized to the corresponding o-benzoquinone, which underwent further Michael-addition with acetylacetone or methyl acetoacetate to produce caffeic acid derivative 3,4-dihydroxy-6-(1-acetylacetone)-yl cinnamic acid 4a or 3,4-dihydroxy-6-(1-acetyl-methylacetate)-yl cinnamic acid 4b. 相似文献
153.
许多三唑类化合物具有优良的杀菌和植物生长调节活性 ,如三唑酮、三唑醇、烯效唑、烯唑醇等 ,对常见真菌病害具有很好的防治效果 ,并具有增产、抗倒和生长调节作用 ,已成为重要的杀菌剂类型 [1] .为筛选新型高活性三唑类杀菌剂和探讨其活性与结构间的关系 ,我们利用生物等排体理论以常规三唑类杀菌剂三唑酮为先导物设计合成了 1 6个含芳硫基的新三唑类化合物 ,其合成路线如下 :RCCH2 BrO+HNNNB NRCCH2O NNHAC-Na ACBr2NRCCHOBrNN(1 ) (2 ) (3 )3 +SH R′B NRCCHOS R′NN (4 )RCCH2 CH2 NMe2 .HClO+HNNNH2 O… 相似文献
154.
Reactions in the CsCl? TiCl3? Ti system afford CsTiCl3 (CsNiCl3 type, a = 7.3086(7) Å, c = 6.0670(8) Å) and the new phase CsTi2Cl7, the structure of which was determined by single crystal X-ray diffraction means (P2/c, Z = 2, a = 7.0076(4) Å, b = 6.2256(4) Å, c = 12.000(2) Å, β = 92.175(6)°, R/Rw = 0.026/0.035 for 1403 reflections, 2Θ ≤ 60°, MoKα). The structure can be generated by condensation of TiCl6 groups first through cis edges to form TiCl2Cl4/2 ribbons and then by interconnection of these with one chlorine per titanium to give layers, viz., [Ti(Cl)Cl4/2Cl1/2]?. The remaining, singly bonded chlorine projects into the interlayer region and has a Ti? Cl distance 0.208 Å less than the average for the five, 2.466 Å, reflecting significant pi bonding of the chlorine to titanium. Possible interaction of the d orbitals on adjacent titanium(III) atoms is also considered. 相似文献
155.
The mercuration of a series of aryliminomethylferrocenes occurred predominantly in an ortho-position of the substituted ferrocenyl ring to yield 2-mercurated ferrocenylimines. The regiospecificity of this reaction suggests that the mercury is directed into the ortho-position by coordination of the mercury to imino nitrogen with subsequent electrophilic substitution. The chromatographic and spectral properties of the 2-mercurated products show the presence of an intramolecular N → Hg coordination via the five-membered ring in these molecules, which was further confirmed by the single-crystal structure analysis of 2-chloromercuro-1-[(4-methoxyphenylimino)methyl]ferrocene. 相似文献
156.
交联聚异丁烯酸甲酯型负载树脂的孔结构与分离稀土性能的关系 总被引:3,自引:0,他引:3
本文报导异丁烯酸甲酯型负载树脂的交联度、致孔剂组成和含量对负载树脂孔结构的影响.结果指出,良溶剂和劣溶剂按一定比例混合作为致孔剂,可制备不同孔结构的树脂.致孔剂量增加,树脂表观比重减小,而比表面积、孔体积与平均孔径均增加.交联度从10%增加到35%,表观比重和比表面积增加,而孔体积与平均孔径减小.增加致孔剂所含良溶剂的比例,树脂的表观比重、比表面积增加,而孔体积与平均孔径减小.已制备一系列不同孔结构的2-乙己基膦酸单2-乙己基酯(P507)负载树脂,比较了它们分离La、Ce、Pr、Nd的性能.结果表明,适当孔结构的负载树脂用于萃取色层分离稀土元素具有优良的分离性能. 相似文献
157.
Platinum nanoclusters were deposited along the supercoiled DNA strands after incubation of cis-(trans-1R,2R-diaminocyclohexane)(dl-camphorato)platinum(Ⅱ) (Cdp), an analogue of the anti-tumor drug-carboplatin, with DNA and K2PtCl4 for 600 min and then through reduction of dimethylaminoborane (DMAB). The decrease of absorption of DNA at 260 nm indicates the coordination of Cdp and DNA. TEM and AFM were employed to characterize the morphologies and structures of platinum nanoclusters. 相似文献
158.
[reaction: see text] Continuing from the syntheses and the antibacterial studies of a library of pyranmycins, we further probed the proximity around ring III of pyranmycin by introducing an "extended arm" that has hydroxyethyl or aminoethyl groups at the O-2' ', O-3' ', or O-4' ' positions. The results from the antibacterial studies reveal the optimal structural motif is the attachment of an extended arm with a terminal hydroxyl group at the O-3' ' position. 相似文献
159.
A GPI-anchored dipeptide of sperm CD52 antigen was prepared through a convergent synthesis. First, the dipeptide with its C-terminus free and the GPI with its nonreducing end phosphoethanolamine bearing a free amino group were synthesized separately. Then, the two building blocks were coupled with use of EDC/HOBt as the condensation reagent. Finally, the GPI-anchored peptide was deprotected to give the target molecule 1. 相似文献
160.
水合硫酸氢钠催化合成2-乙氧基萘 总被引:2,自引:0,他引:2
以-水合硫酸氢钠为催化剂,β-萘酚和无水乙醇为原料合成了2-乙氧基萘。优化反应条件为:β-萘酚150mmol,无水乙醇900mmol,催化剂2.0g,回流反应时间5h,产率85.5%。 相似文献