全文获取类型
收费全文 | 4615篇 |
免费 | 406篇 |
国内免费 | 1492篇 |
专业分类
化学 | 3868篇 |
晶体学 | 104篇 |
力学 | 187篇 |
综合类 | 74篇 |
数学 | 1437篇 |
物理学 | 843篇 |
出版年
2024年 | 2篇 |
2023年 | 36篇 |
2022年 | 64篇 |
2021年 | 95篇 |
2020年 | 104篇 |
2019年 | 126篇 |
2018年 | 109篇 |
2017年 | 151篇 |
2016年 | 157篇 |
2015年 | 153篇 |
2014年 | 228篇 |
2013年 | 426篇 |
2012年 | 323篇 |
2011年 | 283篇 |
2010年 | 241篇 |
2009年 | 272篇 |
2008年 | 339篇 |
2007年 | 388篇 |
2006年 | 354篇 |
2005年 | 283篇 |
2004年 | 260篇 |
2003年 | 248篇 |
2002年 | 222篇 |
2001年 | 168篇 |
2000年 | 168篇 |
1999年 | 171篇 |
1998年 | 133篇 |
1997年 | 139篇 |
1996年 | 121篇 |
1995年 | 103篇 |
1994年 | 96篇 |
1993年 | 65篇 |
1992年 | 90篇 |
1991年 | 60篇 |
1990年 | 59篇 |
1989年 | 67篇 |
1988年 | 42篇 |
1987年 | 24篇 |
1986年 | 23篇 |
1985年 | 31篇 |
1984年 | 15篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有6513条查询结果,搜索用时 234 毫秒
31.
《Comptes Rendus Chimie》2017,20(4):435-439
A novel method for the oxidation of alcohols to the corresponding carbonyl compounds has been successfully developed using tert-butyl hydrogenperoxide (TBHP) in the presence of a catalytic amount of recyclable magnetic nanoparticle-supported oxo-vanadium ephedrine complex (VO(ephedrine)2@MNPs) in PEG as a green solvent at 80 °C. The catalyst can be magnetically recycled and successfully reused in six subsequent reaction cycles with only slight decreases of its catalytic activity. 相似文献
32.
The physical properties, namely structural, mechanical, and thermodynamic properties, of Pd2Al intermetallic compound were explored through first-principles calculations within the framework of density functional theory. The calculated lattice constants were consistent with the available experimental data. The calculated elastic constants revealed that Pd2Al was mechanically stable. By the predicted elastic constants, several related properties, namely Cauchy pressures, shear anisotropy factors, directional Young's modulus, bulk, shear and Young's moduli, the ratio of K/G, Vickers hardness, sound velocity, and minimum thermal conductivity for Pd2Al were evaluated. According to the calculated results, it was found that Pd2Al possesses a highly anisotropic feature and behaves in a ductile manner with low stiffness. Finally, temperature-dependence of thermodynamic properties, namely Debye temperature and heat capacity, were also evaluated through the quasi-harmonic Debye model. 相似文献
33.
In this paper, in terms of the Fréchet normal cone, we establish exact separation results for finitely many disjoint closed sets in an Asplund space, which supplement the extremal principle and some fuzzy separation theorems. As an application, we provide a new optimality condition for a constraint optimization problem in terms of Fréchet subdifferential and Fréchet normal cone. 相似文献
34.
35.
利用Banach空间中的锥理论和不动点定理讨论了非线性算子方程变号解的存在性,给出了E_u_0空间下非线性算子方程变号解至少有一个变号解、一个正解和一个负解的条件,并讨论了仅通过一个上解条件得出非线性算子方程变号解的存在性定理. 相似文献
36.
讨论了一种食饵增长为Gilpin-Ayala型的比率依赖的食饵捕食者模型,利用第二加性复合矩阵原理证明线性化系统正轨道解的稳定性,结合系统在凸集中存在唯一的局部正平衡点,证明了正平衡点的全局渐近稳定性.结合数值模拟验证了所得结论的合理性,同时指出定理结论仅为充分条件,丰富完善了模型的动力学性质. 相似文献
37.
We study the convex hull of a set arising as a relaxation of difficult convex mixed integer quadratic programs (MIQP). We characterize the extreme points of the convex hull of the set and the extreme points of its continuous relaxation. We derive four quadratic cutting surfaces that improve the strength of the continuous relaxation. Each of the cutting surfaces is second-order-cone representable. Via a shooting experiment, we provide empirical evidence as to the importance of each inequality type in improving the relaxation. Computational results that employ the new cutting surfaces to strengthen the relaxation for MIQPs arising from portfolio optimization applications are promising. 相似文献
38.
We study the convex hull of the intersection of a disjunctive set defined by parallel hyperplanes and the feasible set of a mixed integer second order cone optimization (MISOCO) problem. We extend our prior work on disjunctive conic cuts (DCCs), which has thus far been restricted to the case in which the intersection of the hyperplanes and the feasible set is bounded. Using a similar technique, we show that one can extend our previous results to the case in which that intersection is unbounded. We provide a complete characterization in closed form of the conic inequalities required to describe the convex hull when the hyperplanes defining the disjunction are parallel. 相似文献
39.
Dr. Anoop Kumar Kushwaha Sushri Soumya Jena Dr. Mihir Ranjan Sahoo Dr. Debashish Das Prof. Saroj Kumar Nayak 《Chemphyschem》2023,24(18):e202300032
High-voltage alkali metal-ion batteries (AMIBs) require a non-hazardous, low-cost, and highly stable electrolyte with a large operating potential and rapid ion conductivity. Here, we have reported a halogen-free high-voltage electrolyte based on SiB11(BO)12−. Because of the weak π-orbital interaction of −BO as well as the mixed covalent and ionic interaction between SiB11-cage and −BO ligand, SiB11(BO)12− has colossal stability. SiB11(BO)12− possesses extremely high vertical detachment energy (9.95 eV), anodic voltage limit (∼10.05 V), and electrochemical stability window (∼9.95 V). Furthermore, SiB11(BO)12− is thermodynamically stable at high temperatures, and its large size allows for faster cation movement. The alkali salts MSiB11(BO)12 (M=Li, Na, and K) are easily dissociated into ionic components. Electrolytes based on SiB11(BO)12− greatly outperform commercial electrolytes. In short, SiB11(BO)12−-based compound is demonstrated to be a high-voltage electrolyte for AMIBs. 相似文献
40.
首先, 在碱性条件下, 不使用表面活性剂, 采用St?ber小球法以正硅酸四乙酯(TEOS)和正硅酸四丙酯(TPOS)为硅源, 生成初级氧化硅球形颗粒; 然后, 使酚醛树脂(间苯二酚和甲醛)与球形氧化硅的羟基共缩合形成酚醛树脂-氧化硅复合材料; 最后, 经高温碳化和酸蚀获得了空心碳纳米球(HCNSs). 通过调节TEOS/TPOS的摩尔比获得了一系列具有良好的单分散性且粒径、 壁厚可调节的HCNSs, 其粒径和壁厚分别在280~430 nm和15~63 nm的范围内. 仅以TPOS为硅源时合成的HCNS-0/4具有较大的粒径(426 nm)和壁厚(63 nm)、 较高的比表面积(1216 m2/g)和孔容(0.508 cm3/g), 并且具有较大的挥发性有机化合物(VOCs)吸附性能, 其正己烷、 甲苯和油气的静态吸附容量分别为2.02, 1.42和0.926 g/g, 正己烷和甲苯的动态吸附容量分别为2.01 g/g和1.37 g/g, 均远高于商业化活性炭. 相似文献