全文获取类型
收费全文 | 23961篇 |
免费 | 3807篇 |
国内免费 | 2481篇 |
专业分类
化学 | 13583篇 |
晶体学 | 226篇 |
力学 | 896篇 |
综合类 | 105篇 |
数学 | 1794篇 |
物理学 | 6837篇 |
无线电 | 6808篇 |
出版年
2024年 | 102篇 |
2023年 | 535篇 |
2022年 | 700篇 |
2021年 | 942篇 |
2020年 | 943篇 |
2019年 | 928篇 |
2018年 | 831篇 |
2017年 | 745篇 |
2016年 | 1067篇 |
2015年 | 1144篇 |
2014年 | 1319篇 |
2013年 | 1820篇 |
2012年 | 2034篇 |
2011年 | 1995篇 |
2010年 | 1436篇 |
2009年 | 1471篇 |
2008年 | 1612篇 |
2007年 | 1450篇 |
2006年 | 1280篇 |
2005年 | 1136篇 |
2004年 | 881篇 |
2003年 | 855篇 |
2002年 | 861篇 |
2001年 | 640篇 |
2000年 | 504篇 |
1999年 | 483篇 |
1998年 | 376篇 |
1997年 | 319篇 |
1996年 | 293篇 |
1995年 | 264篇 |
1994年 | 219篇 |
1993年 | 184篇 |
1992年 | 166篇 |
1991年 | 156篇 |
1990年 | 90篇 |
1989年 | 86篇 |
1988年 | 63篇 |
1987年 | 44篇 |
1986年 | 58篇 |
1985年 | 45篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Dr. Hong‐Dong Hao Dr. Sergio Wittlin Prof. Dr. Yikang Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7605-7619
Perhydrolysis of a sterically congested multifunctional epoxide was achieved in ethereal H2O2 with the aid of a recently developed Mo catalyst. The resulting hydroperoxide cyclized to give a 1,2,4‐trioxane, which could be readily elaborated into qinghaosu and a range of novel analogues. Some of the compounds with two such trioxane moieties showed in vitro antimalarial activity comparable to or even better than that of artesunate or chloroquine. 相似文献
992.
Chengzhou Zhu Shaojun Guo Prof. Shaojun Dong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):1104-1111
We have demonstrated a rapid and general strategy to synthesize novel three‐dimensional PdPt bimetallic alloy nanosponges in the absence of a capping agent. Significantly, the as‐prepared PdPt bimetallic alloy nanosponges exhibited greatly enhanced activity and stability towards ethanol/methanol electrooxidation in an alkaline medium, which demonstrates the potential of applying these PdPt bimetallic alloy nanosponges as effective electrocatalysts for direct alcohol fuel cells. In addition, this simple method has also been applied for the synthesis of AuPt, AuPd bimetallic, and AuPtPd trimetallic alloy nanosponges. The as‐synthesized three‐dimensional bimetallic/trimetallic alloy nanosponges, because of their convenient preparation, well‐defined sponge‐like network, large‐scale production, and high electrocatalytic performance for ethanol/methanol electrooxidation, may find promising potential applications in various fields, such as formic acid oxidation or oxygen reduction reactions, electrochemical sensors, and hydrogen‐gas sensors. 相似文献
993.
Dr. Qingsong Dong Prof. Xiao‐Juan Yang Shida Gong Dr. Qiong Luo Prof. Qian‐Shu Li Prof. Ji‐Hu Su Dr. Yanxia Zhao Prof. Biao Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15240-15247
A nickel? nickel‐bonded complex, [{Ni(μ‐L.?)}2] ( 1 ; L=[(2,6‐iPr2C6H3)NC(Me)]2), was synthesized from reduction of the LNiBr2 precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)3] ? [{Ni(μ‐L.?)}2] ( 2 ; DME=1,2‐dimethoxyethane), [Na(Et2O)]Na[(L.?)Ni? NiL2?] ( 3 ), and [Na(Et2O)]2Na[L2?Ni? NiL2?] ( 4 ). Here L represents the neutral ligand, L.? denotes its radical monoanion, and L2? is the dianion. All of the four compounds feature a short Ni? Ni bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular ( 1 and 2 ) and the coaxial ( 3 and 4 ) structure, in which the metal? metal bond axis is perpendicular to or collinear with the axes of the α‐diimine ligands, respectively. The electronic structures, Ni? Ni bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations. 相似文献
994.
995.
通过添加对映体拆分剂,合成了4种含膦手性的丙炔胺磷酸酯单体[HC帒CC H2NH(PO)R1R2].单体1,R1=OPh,R2=NC4H7COOCH3;单体2,R1=OPh,R2=NC4H7COOCH2CH3;单体3,R1=OPh,R2=NC4H7-COOC(CH3)3;单体4,R1=Ph,R2=NC4H7COOC(CH3)3].1H-NMR和31P-NMR表征可知对映体(单体1)不能被拆分剂拆分,而单体2、单体3、单体4通过拆分剂可以制得单一手性的磷化合物.以(nbd)Rh+[η6-C6H5B--(C6H5)3]为催化剂,以三氯甲烷为溶剂成功得到聚合物分子量范围在0.4×10-4~0.7×10-4,分子量分布在1.26~1.98范围的3种含手性膦侧基的丙炔胺类聚合物.比旋光度([α]D)、圆二色谱(CD)对聚合物的不同侧基及温度对光学活性的影响表明,聚合物具有良好的光学活性且能够形成单一方向的螺旋构象,说明膦手性在构建螺旋聚合物具有重要作用. 相似文献
996.
利用氢氧化钾对苯乙烯-马来酸酐交替共聚物(SMA)进行水解,所得中等皂化程度的SMA水解产物(SMAA)在水溶液中具有刚性棒状直链构型;将此特殊结构的大分子作为分散剂用于苯乙烯悬浮聚合,通过控制搅拌速度和油水比,可得到梭形聚苯乙烯粒子;在优化条件下,粒子平均长度6.8 mm,宽度1.4 mm,厚度0.5 mm,长径比约5.0.其可能的机理为,中等皂化程度的刚棒直链型SMAA在聚合物"软粒子"表面能形成难以"回复"的有效保护层,使由剪切形成的变形聚合物"软粒子"在聚合过程中能保持形状和尺寸的稳定,从而得到梭形聚合物粒子. 相似文献
997.
998.
We consider both divergence and non-divergence parabolic equations on a half space in weighted Sobolev spaces. All the leading coefficients are assumed to be only measurable in the time and one spatial variable except one coefficient, which is assumed to be only measurable either in the time or the spatial variable. As functions of the other variables the coefficients have small bounded mean oscillation (BMO) semi-norms. The lower-order coefficients are allowed to blow up near the boundary with a certain optimal growth condition. As a corollary, we also obtain the corresponding results for elliptic equations. 相似文献
999.
董亚莹 《纯粹数学与应用数学》2015,31(1):18-26
利用与不变子空间方法相关的等价变换和变换v=enu给出了非齐次非线性扩散方程的等价方程,并得到了等价方程的高维不变子空间.最后给出一些例子构造了非齐次非线性扩散方程的广义泛函分离变量解. 相似文献
1000.
Measure of noncompactness and semilinear nonlocal functional differential equations in Banach spaces 下载免费PDF全文
This paper is concerned with the measure of noncompactness in the spaces of continuous functions and semilinear functional differential equations with nonlocal conditions in Banach spaces.The relationship between the Hausdorff measure of noncompactness of intersections and the modulus of equicontinuity is studied for some subsets related to the semigroup of linear operators in Banach spaces.The existence of mild solutions is obtained for a class of nonlocal semilinear functional differential equations without the assumption of compactness or equicontinuity on the associated semigroups of linear operators. 相似文献