全文获取类型
收费全文 | 32625篇 |
免费 | 6391篇 |
国内免费 | 8257篇 |
专业分类
化学 | 25105篇 |
晶体学 | 863篇 |
力学 | 2269篇 |
综合类 | 966篇 |
数学 | 4776篇 |
物理学 | 13294篇 |
出版年
2024年 | 70篇 |
2023年 | 358篇 |
2022年 | 997篇 |
2021年 | 977篇 |
2020年 | 1073篇 |
2019年 | 1244篇 |
2018年 | 1089篇 |
2017年 | 1237篇 |
2016年 | 1353篇 |
2015年 | 1800篇 |
2014年 | 1983篇 |
2013年 | 2548篇 |
2012年 | 2752篇 |
2011年 | 2855篇 |
2010年 | 2568篇 |
2009年 | 2632篇 |
2008年 | 2842篇 |
2007年 | 2480篇 |
2006年 | 2327篇 |
2005年 | 2216篇 |
2004年 | 1760篇 |
2003年 | 1345篇 |
2002年 | 1482篇 |
2001年 | 1326篇 |
2000年 | 1247篇 |
1999年 | 831篇 |
1998年 | 553篇 |
1997年 | 436篇 |
1996年 | 368篇 |
1995年 | 347篇 |
1994年 | 303篇 |
1993年 | 269篇 |
1992年 | 251篇 |
1991年 | 206篇 |
1990年 | 172篇 |
1989年 | 142篇 |
1988年 | 149篇 |
1987年 | 121篇 |
1986年 | 89篇 |
1985年 | 60篇 |
1984年 | 81篇 |
1983年 | 77篇 |
1982年 | 46篇 |
1981年 | 52篇 |
1980年 | 52篇 |
1979年 | 29篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1971年 | 8篇 |
1936年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The crystal structures of a pair isomers of [Co(3,3-tri)(amp)Cl][ZnCl4] (here 3,3-tri = N-(3-Aminoprop- yl)-1,3-propanediamine; amp=2-(Aminomethyl)pyridine) have been determined by single crystal X-ray diffrac-tion. They are the epimers with the only difference of the orientation of the Sec-NH proton in 3,3-tri ligand. The crystals with the anti-epimer (m1[ZnCl4]·CH3OH·H2O) are monoclinic, space group C2/c with eight molecules in a unit cell of dimensions a=30.401(5)?,b=8.0469(13)?,c=18.817(3)?,β=93.346(3)°,V=4595.3(12)?3,Dc=1.708g·cm-3,Z=8,F000=2416,R=0.0462,Rw=0.1304. The crystals of the syn-epimer (m2[ZnCl4]·H2O) are triclinic, space group P1 with two molecules in a unit cell of dimensions a=8.9752(12)?,b=9.8855(12)?,c=12.6886(16)?,α=89.228(3)°,β=76.447(2)°,γ=80.428(3)°,V=1078.8(2)nm3,Dc=1.721g·cm-3,Z=2,F000=568,R=0.0313,Rw=0.0929. The crystal parameters, such as bond lengths and angles, are well consistent with the data of an ab initio computational result (RHF/LANL2DZ opti-mised structure). The average error for bond length is about 1.6%, only two of them in the isomer m3 (Co-N2 and Co-N4) are over 3%, (3.09% and 4.28% respectively). The errormax for bond angle is 2.52%, the bond angles with an over 2% error are only 3.6% out of all bond angles. 相似文献
992.
Sheng Hua Liu 《Journal of organometallic chemistry》2003,683(2):331-336
Treatment of [Ru(CHCHCH2PPh3)X(CO)(PPh3)2]+ (X=Cl, Br) with KTp (Tp=hydridotris(pyrazolyl)borate) and NaBPh4 produced [TpRu(CHCHCH2PPh3)(CO)(PPh3)]BPh4. Reaction of RuHCl(CO)(PPh3)3 with HCCCH(OEt)2 produced Ru(CHCHCH(OEt)2)Cl(CO)(PPh3)2, which reacted with KTp to give TpRu(CHCHCHO)(CO)(PPh3). Treatment of [TpRu(CHCHCH2PPh3)(CO)(PPh3)]BPh4 with NaN(SiMe3)2 and benzaldehyde produced TpRu(CHCHCHCHPh)(CO)(PPh3). The later complex was also produced when TpRu(CHCHCHO)(CO)(PPh3) was treated with PhCH2PPh3Cl/NaN(SiMe3)2. The bimetallic complex [TpRu(CO)(PPh3)]2(μ-CHCHCHCHC6H4CHCHCHCH) was obtained from the reaction of [TpRu(CHCHCH2PPh3)(CO)(PPh3)]BPh4 with NaN(SiMe3)2 and terephthaldicarboxaldehyde. 相似文献
993.
在手性金属钛催化剂存在下 ,研究了α′ 苯磺酰基 α ,β 不饱和酮与开链二烯的不对称催化环加成反应 ,讨论了α′ 苯磺酰基 α ,β 不饱和酮与开链二烯的反应活性和对映选择性 ,以高的收率和光学纯度合成了环己烯衍生物 ,并对部分产物的构型进行了鉴定 相似文献
994.
Three hexakis(imidazole)metallo complexes of Co, Cd and Ni were synthesized and spectroscopically characterized. The crystal and molecular structures have been determined by X-ray crystallography analysis. The metal ions have an octahedral geometry with the MN6 chromophore. The electrochemical experimental results indicate that both [Co(Im)6]C12·2HCl·2H2O (1) and [Ni(Im)6]C12·4H2O (3) [Im=imidazole] could interact with DNA mainly by intercalation. 相似文献
995.
Zhenchuan Wen Xuejian Ma Xiaoyu Yang Pengqing Bi Mengsi Niu Kangning Zhang Lin Feng Xiaotao Hao 《中国化学快报》2019,30(5):995-999
In this work, the donor:acceptor ratio effected photophysical properties of non-fullerene organic solar cells are comparatively investigated. Effective transportation of the photo-generated charge carriers can be obtained with the PDBD-T:ITIC ratio variation. There is no significant energy loss variation exists in the process of changing the D:A ratio. 相似文献
996.
Palladium-benzimidazolium salt catalyst systems have been studied for the Suzuki coupling. A different substitutent effect has been uncovered with respect to nitrogen substituents in the benzimidazolium salts from the palladium-imidazolium salt analogs. A practical and highly active palladium catalyst system, PdCl2/N,N′-dibenzylbenzimidazolium chloride 2, has been identified for the Suzuki coupling of aromatic halides with arylboronic acids. The coupling of a wide array of aromatic halides with arylboronic acids with the PdCl2-2 catalyst system gave good to excellent yields. The effective palladium loading could be as low as 0.0001 mol% and 0.01-0.1 mol% for iodide and bromide substrates, respectively. The coupling of unactivated aromatic chlorides with arylboronic acids also gave good results using Cs2CO3 as base with a 2 mol% palladium loading. The electronic factors from aromatic halides exert a significant influence on the Suzuki coupling catalyzed by the PdCl2-2 system while the electronic effect from the arylboronic counterparts is negligible. The aromatic halides with modest steric hindrance could also couple smoothly with phenylboronic acids using the PdCl2-2 catalyst system. 相似文献
997.
A two-tiered organizing scheme with multiple-length scales for construction of dandelion-like hollow CuO microspheres has been elucidated: (1) mesoscale formation of rhombic building units from smaller nanoribbons via oriented aggregation and (2) macroscopic organization of these units into the CuO microspheres. This self-assembly concept may also be applicable to other metal oxides by creating geometric constraints for constructional units. 相似文献
998.
金复合介孔SBA-15吸附血红蛋白在H2O2电催化反应中的应用 总被引:2,自引:0,他引:2
以P123嵌段共聚物表面活性剂为模板剂制备介孔氧化硅SBA-15,并用沉积-沉淀(DP)法在SBA-15介孔表面负载纳米Au颗粒制备得到金复合介孔SBA-15材料(Au-SBA-15).再以Au-SBA-15材料制备玻碳修饰电极,将血红蛋白固定于修饰电极上用循环伏安法考察其对不同浓度H2O2溶液的电催化反应.在固定了血红蛋白的Hb/Au-SBA-15/GC修饰电极上,H2O2在+0.95
V处出现了氧化峰,且随着H2O2浓度的增大峰电流不断增加,说明金复合介孔氧化硅材料具有良好的生物兼容性,有利于血红蛋白的固定,其修饰电极对H2O2溶液具有一定的电催化作用. 相似文献
999.
有害杂草的微量元素分析 总被引:18,自引:0,他引:18
紫茎泽兰和水葫芦均属有害杂草,大规模防治的有效方法还未找到,本文分析研究了采自昆明郊区的紫茎泽兰和滇池水域的水葫芦中微量元素的含量,为进一步开发利用这两种杂草提供科学依据。 相似文献
1000.