全文获取类型
收费全文 | 17439篇 |
免费 | 2311篇 |
国内免费 | 847篇 |
专业分类
化学 | 19798篇 |
晶体学 | 59篇 |
力学 | 28篇 |
综合类 | 14篇 |
数学 | 19篇 |
物理学 | 679篇 |
出版年
2024年 | 32篇 |
2023年 | 248篇 |
2022年 | 612篇 |
2021年 | 665篇 |
2020年 | 1239篇 |
2019年 | 941篇 |
2018年 | 759篇 |
2017年 | 622篇 |
2016年 | 1218篇 |
2015年 | 1065篇 |
2014年 | 1065篇 |
2013年 | 1242篇 |
2012年 | 948篇 |
2011年 | 1023篇 |
2010年 | 879篇 |
2009年 | 912篇 |
2008年 | 866篇 |
2007年 | 786篇 |
2006年 | 735篇 |
2005年 | 662篇 |
2004年 | 676篇 |
2003年 | 541篇 |
2002年 | 1204篇 |
2001年 | 248篇 |
2000年 | 157篇 |
1999年 | 198篇 |
1998年 | 221篇 |
1997年 | 156篇 |
1996年 | 106篇 |
1995年 | 112篇 |
1994年 | 56篇 |
1993年 | 37篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1990年 | 32篇 |
1989年 | 20篇 |
1988年 | 27篇 |
1987年 | 21篇 |
1986年 | 67篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 11篇 |
1970年 | 7篇 |
1966年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Brad M. Rosen Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4950-4964
Atom transfer radical polymerization (ATRP) and single electron‐transfer living radical polymerization (SET‐LRP) both utilize copper complexes of various oxidation states with N‐ligands to perform their respective activation and deactivation steps. Herein, we utilize DFT (B3YLP) methods to determine the preferred ligand‐binding geometries for Cu/N‐ligand complexes related to ATRP and SET‐LRP. We find that those ligands capable of achieving tetrahedral complexes with CuI and trigonal bipyramidal with axial halide complexes with [CuIIX]+ have higher energies of stabilization. We were able to correlate calculated preferential stabilization of [CuIIX]+ with those ligands that perform best in SET‐LRP. A crude calculation of energy of disproportionation revealed that the same preferential binding of [CuIIX]+ results in increased propensity for disproportionation. Finally, by examining the relative energies of the basic steps of ATRP and SET‐LRP, we were able to rationalize the transition from the ATRP mechanism to the SET‐LRP mechanism as we transition from typical nonpolar ATRP solvents to polar SET‐LRP solvents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4950–4964, 2007 相似文献
53.
54.
硅酸盐中桥联键的机制及其性质的CNDO/2法研究 总被引:2,自引:0,他引:2
法计算模型,分析了桥联键的成键机制,解释了硅酸盐的通常性质。以体系总能量随桥角变化关系,解释了硅酸盐矿物及沸石分子筛中桥角Si-O-T出现的范围和几率。 由计算结果还发现,桥氧上具有较高的非键p-电子电荷Q_o~n,并随桥氧的第三配原子性质和距离R(M-O~(br))而变化,使桥氧具有授受电子的双重性质。在此基础上,探讨了沸石分子筛的碳离子催化活性机理,提出了锁与匙匹配原子对的催化活性中心的新观点。 相似文献
55.
Two greener procedures for flow-injection spectrophotometric determination of nitrite in natural waters were developed and critically compared. Replacement of toxic reagents, waste minimization and treatment were exploited to attend the standards of clean chemistry. The flow system was designed with solenoid micro-pumps in order to minimize reagent consumption and waste generation. The first procedure is based on the Griess diazo-coupling reaction with sulfanilamide and N-(1-naphthyl)ethylenediamine (NED) yielding an azo dye, followed by photodegradation of the low amount of waste generated based on the photo-Fenton reaction. The second procedure is based on the formation of iodine from nitrite and iodide in acid medium in order to avoid the use of toxic reagents. For Griess method, linear response was achieved up to 1.0 mg L− 1, described by the equation A = − 0.007 + 0.460C (mg L− 1), r = 0.999. The detection limit was estimated as 8 μg L− 1 at the 99.7% confidence level and the coefficient of variation was 0.8% (n = 20). The sampling rate was estimated as 108 determinations per hour. The consumption of the most toxic reagent (NED) is reduced 55-fold and 20-fold in comparison to batch method and flow injection with continuous reagent addition, respectively. A colorless residue was obtained by in-line photodegradation with reduction of 87% of the total organic carbon content. The results obtained for natural water samples were in agreement with those achieved by the reference method at the 95% confidence level. For the nitrite–iodide method, linear response was observed up to 2.0 mg L− 1, described by the equation A = − 0.024 + 0.148C (mg L− 1), r = 0.999. The detection limit was estimated as 25 μg L− 1 at the 99.7% confidence level and the coefficient of variation was 0.6% (n = 20). The sampling rate was estimated as 44 determinations per hour. Despite avoiding the use of toxic reagents, the nitrite–iodide method presented worst performance in terms of selectivity and sensitivity. 相似文献
56.
集化学家与化学教育家于一身的一代化学大师李比希--纪念李比希诞辰200周年 总被引:1,自引:0,他引:1
在德国著名化学家李比希诞辰200周年之际,对这位集化学家与化学教育家于一身的一代化学大师对科学和科学教育以及人类社会作出的贡献进行了评述。 相似文献
57.
58.
59.
Summary The novel theoretical scheme IMOMM, integrating ab initio and molecular mechanics contributions in a single geometry optimization process, is applied to the structural determination of different [OsO4(NR3)] (NR3 = bulky chiral alkaloid derivative) species closely related to active catalysts for the asymmetric dihydroxylation of olefins. Computed values compare in a satisfactory way with available X-ray data, the relationship between the Os-N distance and the nature of the NR3, ligand being properly reproduced. The computational scheme allows the separate quantification of electronic and steric effects, as well as the identification of the specific steric repulsions responsible for the difference. 相似文献
60.
Highly ordered mesoporous bioactive glasses with superior in vitro bone-forming bioactivities 总被引:3,自引:0,他引:3