全文获取类型
收费全文 | 11342篇 |
免费 | 524篇 |
国内免费 | 75篇 |
专业分类
化学 | 7998篇 |
晶体学 | 121篇 |
力学 | 324篇 |
综合类 | 1篇 |
数学 | 971篇 |
物理学 | 2526篇 |
出版年
2023年 | 55篇 |
2022年 | 154篇 |
2021年 | 246篇 |
2020年 | 212篇 |
2019年 | 220篇 |
2018年 | 188篇 |
2017年 | 162篇 |
2016年 | 358篇 |
2015年 | 330篇 |
2014年 | 423篇 |
2013年 | 711篇 |
2012年 | 898篇 |
2011年 | 1034篇 |
2010年 | 597篇 |
2009年 | 472篇 |
2008年 | 776篇 |
2007年 | 692篇 |
2006年 | 631篇 |
2005年 | 611篇 |
2004年 | 493篇 |
2003年 | 391篇 |
2002年 | 410篇 |
2001年 | 254篇 |
2000年 | 227篇 |
1999年 | 155篇 |
1998年 | 94篇 |
1997年 | 87篇 |
1996年 | 111篇 |
1995年 | 97篇 |
1994年 | 87篇 |
1993年 | 70篇 |
1992年 | 68篇 |
1991年 | 65篇 |
1990年 | 68篇 |
1989年 | 46篇 |
1988年 | 38篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 38篇 |
1984年 | 26篇 |
1983年 | 25篇 |
1982年 | 26篇 |
1981年 | 27篇 |
1980年 | 16篇 |
1979年 | 22篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1975年 | 15篇 |
1972年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Kim GN Kim EJ Son D Bacala A Imlay R Kirk P McNeil RR Metcalf W Cheng CP Mao ZP Yan Y Xu YT Zhu YC Abashian A Gotow K Kajino F Low E Naito F Piilonen L Childers R Darden C Lusin S Rosenfeld C Wilson S Frautschi M Kagan H Kass R Trahern CG Ko W Lander RL Maeshima K Malchow RL Higashi JR Kurihara Y Maki A Nozaki T Omori T Perez P Sagawa H Sakai Y Sugimoto Y Takaiwa Y Terada S Tsuchiya K Poling R Green J Park IH Sakamoto S Sannes F Schnetzer S Stone R Trentalange S Zimmerman D Miyano K Miyata H 《Physical review letters》1988,61(8):911-914
82.
J. J. Engelen S. J. de Jong M. Poletiek J. A. M. Vermaseren 《Zeitschrift fur Physik C Particles and Fields》1988,41(1):173-177
We present cross sections for heavy flavour production through photon gluon fusion in electron proton collisions at HERA energy. The electron photon vertex is taken into account explicitly, and theQ 2 of the exchanged photon ranges from nearly zero (almost real photon) to the kinematically allowed maximum. In our approach the scale is set by the mass of the produced quarks. Our formalism is also applicable to the production of light quarks as long as the invariant mass of the pair is sufficiently high, so we also give cross sections for \(u\bar u,d\bar d\) and \(s\bar s\) production. 相似文献
83.
84.
William W. Paudler Richard A. Vandahm Young N. Park 《Journal of heterocyclic chemistry》1972,9(1):81-85
The diazaanalog of “cycl[3,2,2]azine”, “1,4-diazacycl[3,2,2]azine” (1,4,7b-triazacyclopent-[cd]indene) and its 2-methyl derivative were prepared. These compounds are subject to facile acid-catalyzed hydrolysis affording substituted imidazo[1,2-a]pyridines. 相似文献
85.
A new class of chiral dienophiles, 5-alkoxy-2(5H)-furanones, has been developed. Both enantiomers of 5-menthyloxy-2(5H)-ftiranone are readily available in enantiomerically pure form, starting from furfural and d- or l-menthol. Excellent diastereoselectivities (d.e. β99%) are obtained in thermal Diels-Alder reactions with several cyclic and acyclic dienes. The use of silyl dienol ethers has resulted in new routes to enantiomerically pure cyclohexanones in a highly regioselective manner. 相似文献
86.
Observation of a quadrupole plasmon mode for a colloidal solution of gold nanoprisms 总被引:3,自引:0,他引:3
Millstone JE Park S Shuford KL Qin L Schatz GC Mirkin CA 《Journal of the American Chemical Society》2005,127(15):5312-5313
The synthesis and optical properties of single crystalline gold nanoprisms have been investigated. A three-step mediated seed growth process in an aqueous solution generated gold nanoprisms with a relatively homogeneous size distribution. The purity of these nanostructures has allowed us to observe a weak quadrupole resonance in addition to a strong dipole resonance associated with these novel structures. The experimental optical spectra agree with discrete dipole approximation calculations that have been modeled from the dimensions of gold nanoprisms produced in this synthesis. 相似文献
87.
88.
89.
90.
Three new Ni(BDC)/2,2'-bipy compounds, Ni2(BDC)(HBDC)2(2,2'-bipy)2 (2), Ni3(BDC)3(2,2'-bipy)2 (3), and Ni(BDC)(2,2-bipy)2.2H2O (5), in addition to the previously reported Ni(BDC)(2,2'-bipy).0.75H2BDC (1) and Ni(BDC)(2,2'-bipy)(H2O) (4) [BDC = 1,4-benzenedicarboxylate; 2,2'-bipy = 2,2'-bipyridine], have been synthesized by hydrothermal reactions. A systematic investigation of the effect of the reaction temperature and pH resulted in a series of compounds with different compositions and dimensionality. The diverse product slate illustrates the marked sensitivity of the structural chemistry of polycarboxylate aromatic ligands to synthesis conditions. Compound 1, which has a channel structure containing guest H2BDC molecules, is formed at the lowest pH. The guest H2BDC molecules are connected by hydrogen bonds and form extended chains. At a slightly higher pH, a dimeric molecular compound 2 is formed with a lower number of protonated carboxylate groups per nickel atom and per BDC ligand. Reactions at higher temperature and the same pH lead to the transformation of 1 and 2 into the two-dimensional, layered trinuclear compound 3. As the pH is increased, a one-dimensional polymer 4 is formed with a water molecule coordinated to Ni2+. Bis-monodentate and bischelating BDC ligands alternate along the chain to give a crankshaft rather than a regular zigzag arrangement. A further increase of the pH leads to the one-dimensional chain compound 5, which has two chelating 2,2'-bipy ligands. Crystal data: 2, triclinic, space group P, a = 7.4896(9) angstroms, b = 9.912(1) angstroms, c = 13.508(2) angstroms, alpha = 86.390(2) degrees , beta = 75.825(2) degrees, gamma = 79.612(2) degrees, Z = 2; 3, orthorhombic, space group Pbca, a = 9.626(2) angstroms, b = 17.980(3) angstroms, c = 25.131(5) angstroms, Z = 4; 5, orthorhombic, space group Pbcn, a = 14.266(2) angstroms, b = 10.692(2) angstroms, c = 17.171(2) angstroms, Z = 8. 相似文献