首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1045篇
  免费   185篇
  国内免费   100篇
化学   711篇
晶体学   5篇
力学   85篇
综合类   2篇
数学   81篇
物理学   446篇
  2024年   2篇
  2023年   21篇
  2022年   25篇
  2021年   27篇
  2020年   37篇
  2019年   52篇
  2018年   30篇
  2017年   24篇
  2016年   48篇
  2015年   40篇
  2014年   37篇
  2013年   66篇
  2012年   108篇
  2011年   114篇
  2010年   76篇
  2009年   64篇
  2008年   67篇
  2007年   49篇
  2006年   49篇
  2005年   40篇
  2004年   48篇
  2003年   24篇
  2002年   25篇
  2001年   20篇
  2000年   29篇
  1999年   31篇
  1998年   23篇
  1997年   16篇
  1996年   26篇
  1995年   21篇
  1994年   13篇
  1993年   15篇
  1992年   10篇
  1991年   12篇
  1990年   12篇
  1989年   6篇
  1988年   1篇
  1987年   7篇
  1986年   2篇
  1985年   2篇
  1984年   1篇
  1981年   2篇
  1980年   1篇
  1978年   2篇
  1976年   1篇
  1973年   2篇
  1972年   1篇
  1971年   1篇
排序方式: 共有1330条查询结果,搜索用时 15 毫秒
951.
Summary.  A series of 6-naphthylmethyl substituted HEPT analogues bearing a β-carbonyl and a terminal phenyl ring or ester groups on the N-1 side chain of uracil were synthesized, and the in vitro anti-HIV activity was evaluated. Most of these HEPTs were considerably less potent and selective or inactive, only a few compounds showed moderate or high activity against HIV-1. The results demonstrated that the anti-HIV-1 activity of 6-naphthylmethyl substituted HEPT analogues was diminished or eliminated when the β-oxygen of N-1 side chain was replaced by a carbonyl group.  相似文献   
952.
The η2‐thio‐indium complexes [In(η2‐thio)3] (thio = S2CNC5H10, 2 ; SNC4H4, (pyridine‐2‐thionate, pyS, 3 ) and [In(η2‐pyS)22‐acac)], 4 , (acac: acetylacetonate) are prepared by reacting the tris(η2‐acac)indium complex [In(η2‐acac)3], 1 with HS2CNC5H10, pySH, and pySH with ratios of 1:3, 1:3, and 1:2 in dichloromethane at room temperature, respectively. All of these complexes are identified by spectroscopic methods and complexes 2 and 3 are determined by single‐crystal X‐ray diffraction. Crystal data for 2 : space group, C2/c with a = 13.5489(8) Å, b = 12.1821(7) Å, c = 16.0893(10) Å, β = 101.654(1)°, V = 2600.9(3) Å3, and Z = 4. The structure was refined to R = 0.033 and Rw = 0.086; Crystal data for 3 : space group, P21 with a = 8.8064 (6) Å, b = 11.7047 (8) Å, c = 9.4046 (7) Å, β = 114.78 (1)°, V = 880.13(11) Å3, and Z = 2. The structure was refined to R = 0.030 and Rw = 0.061. The geometry around the metal atom of the two complexes is a trigonal prismatic coordination. The piperidinyldithiocarbamate and pyridine‐2‐thionate ligands, respectively, coordinate to the indium metal center through the two sulfur atoms and one sulfur and one nitrogen atoms, respectively. The short C‐N bond length in the range of 1.322(4)–1.381(6) Å in 2 and C‐S bond length in the range of 1.715(2)–1.753(6) Å in 2 and 3 , respectively, indicate considerable partial double bond character.  相似文献   
953.
Cd(Ⅱ)—SAF—DDMBA显色反应的研究及应用   总被引:3,自引:0,他引:3  
研究了Cd(Ⅱ)与水杨基荧光酮(SAF)-溴化十二烷基二甲基苄铵(DDMBA)显色反应的条件,在表面活性剂DDMBA存在下,pH 10的硼砂-氢氧化钠缓冲介质中,Cd(Ⅱ)与SAF形成1:4紫红色配合物,配合物于570nm有最大吸收,表观摩尔吸光系数9.26×10~4,镉含量在0~6μg/25ml符合比耳定律,方法简便、灵敏,精密度高,准确度好,应用于铅渣中镉的测定,结果满意。  相似文献   
954.
The lability of the terminal Re-Cl bond that is cis to the bridging CO ligand in the edge-sharing bioctahedral complexes Re(2)(mu-Cl)(mu-CO)(mu-PP)(2)Cl(3)(L), where PP = Ph(2)PC(=CH(2))PPh(2) (dppE) when L = CO (1) and PP = Ph(2)PCH(2)PPh(2) (dppm) when L = CO (2) or XyINC (3), has been exploited in the preparation of mixed-metal Re(4)Pd(2), Re(2)Ag, Re(2)W, Re(2)Pt, and Re(2)Rh assemblies, in which the dirhenium units are bound to the other metals through NCS or CN bridges. These complexes, which retain the Re=Re bonds of the parent dirhenium complexes, comprise the novel centrosymmetric complex [Re(2)Cl(3)(mu-dppE)(2)(CO)(2)(mu-NCS)](2)Pd(2)(mu-SCN)(mu-NCS)Cl(2) (9), and the trimetallic complexes Re(2)Cl(3)(mu-dppE)(2)(CO)(2)[(mu-NC)Ag(CN)] (10), Re(2)Cl(3)(mu-dppE)(2)(CO)(2)[(mu-NC)W(CO)(5)] (11), [Re(2)Cl(3)(mu-dppE)(2)(CO)(2)[(mu-NC)Pt(CN)(CN-t-Bu)(2)]]PF(6) (12), [Re(2)Cl(3)(mu-dppE)(2)(CO)(2)[(mu-N(CN)(2))Rh(CO)(PPh(3))(2)]]O(3)SCF(3) (13), and Re(2)Cl(3)(mu-dppm)(2)(CO)(2)[(mu-NC)W(CO)(5)] (16). The identities of 9 and 16 have been established by X-ray crystallography, and all complexes characterized by IR and NMR spectroscopy and cyclic voltammetry. The reactions of the dicarbonyl complex 1, and the isomeric pair of complexes Re(2)Cl(4)(mu-dppm)(2)(CO)(CNXyl), which have edge-sharing bioctahedral (ESBO) (3) and open bioctahedral (OBO) (4) geometries, with Na[N(CN)(2)] and K[C(CN)(3)] have been used to prepare complexes in which the uncoordinated CN groups have the potential to coordinate other mono- or dimetal units to form extended arrays. The complexes which have been prepared and characterized are the monosubstituted species Re(2)Cl(3)(X)(mu-dppE)(2)(CO)(2) (X = N(CN)(2) (14) or C(CN)(3) (15)) and Re(2)Cl(3)(X)(mu-dppm)(2)(CO)(CNXyl) (X = N(CN)(2) (17) or C(CN)(3) (18) with ESBO structures; X = N(CN)(2) (19) or C(CN)(3) (20) with OBO structures), of which 15, 18, and 20 have been characterized by single-crystal X-ray structure determinations. The substitutional labilities of the Re-Cl bonds in the complexes Re(2)Cl(4)(mu-dppm)(2)(CO) (5), Re(2)Cl(4)(mu-dppm)(2)(CNXyl) (6), and Re(2)Cl(4)(mu-dppm)(2) (7) toward Na[N(CN)(2)] and K[C(CN)(3)] have also been explored and the complexes Re(2)Cl(3)(X)(mu-dppm)(2)(CO) (X = N(CN)(2) (21) or C(CN)(3) (22)), Re(2)Cl(3)(X)(mu-dppm)(2)(CNXyl) (X = N(CN)(2) (23) or C(CN)(3) (24)), Re(2)Cl(2)(X)(2)(mu-dppm)(2)(CNXyl) (X = N(CN)(2) (25) or C(CN)(3) (26)), Re(2)[N(CN)(2)](4)(mu-dppm)(2) (27), and Re(2)[C(CN)(3)](4)(mu-dppm)(2) (28) isolated in good yield. Single-crystal X-ray structure determinations of 24, 26, and 27 have shown that the Re-Re triple bonds present in the starting materials 5-7 are retained in these products.  相似文献   
955.
Highly dispersed platinum nanoparticles were electrodeposited on graphitic carbon nanofibers (GCNFs) by cyclic voltammetry (CV) in 7.7 mM H2PtCl6+0.5 M HCl aqueous solutions. The graphitic carbon nanofibers (GCNFs) used in this paper were grown directly on a graphite disk by chemical vapor deposition (CVD). The micrographs and element composition of Pt/GCNFs/graphite electrode were characterized by scanning electron microscopy (SEM) and electron diffraction spectroscopy (EDS). The electrocatalytic properties of Pt/GCNFs/graphite electrode for methanol oxidation have been investigated by CV and excellent electrocatalytic activity can be observed even at very low platinum loading (md=8.79 microg cm(-2)). The highest mass activity (MA) for methanol oxidation reaches 323 Ag(-1) when Pt/GCNFs/graphite electrode was cycled at a sweep rate of 50 mVs(-1) by CV in 2 M CH3OH+1 M H2SO4 aqueous solutions. This may be attributed to the small particle size and high dispersion of platinum particles coated on GCNFs and shows good potential application in direct methanol fuel cell (DMFC). Additionally, the long-term cycling stability of platinum catalysts was also investigated.  相似文献   
956.
957.
958.
959.
960.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号