全文获取类型
收费全文 | 8343篇 |
免费 | 1198篇 |
国内免费 | 1699篇 |
专业分类
化学 | 6243篇 |
晶体学 | 161篇 |
力学 | 491篇 |
综合类 | 162篇 |
数学 | 1337篇 |
物理学 | 2846篇 |
出版年
2024年 | 20篇 |
2023年 | 140篇 |
2022年 | 286篇 |
2021年 | 294篇 |
2020年 | 341篇 |
2019年 | 352篇 |
2018年 | 304篇 |
2017年 | 353篇 |
2016年 | 360篇 |
2015年 | 439篇 |
2014年 | 563篇 |
2013年 | 737篇 |
2012年 | 712篇 |
2011年 | 727篇 |
2010年 | 619篇 |
2009年 | 599篇 |
2008年 | 694篇 |
2007年 | 590篇 |
2006年 | 583篇 |
2005年 | 444篇 |
2004年 | 333篇 |
2003年 | 222篇 |
2002年 | 230篇 |
2001年 | 184篇 |
2000年 | 208篇 |
1999年 | 141篇 |
1998年 | 79篇 |
1997年 | 69篇 |
1996年 | 48篇 |
1995年 | 25篇 |
1994年 | 45篇 |
1993年 | 39篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 37篇 |
1989年 | 33篇 |
1988年 | 35篇 |
1987年 | 27篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 19篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
In the discrete-time Sparre Andersen risk model with investments and dividend payments, the company controls the dividend payments and the proportions of venture investments in order to maximize the cumulative expected discounted dividends prior to ruin. The paper gets the algorithm of the optimal dividend strategy by analyzing a Hamilton-Jacobi-Bellman equation and transforming the value function. Furthermore, the existence of the optimal solution of the transformation function is proved by using compression mapping and fixed point principle. In order to make the calculation easier, this paper also proposes an
innovative random simulation method for the optimal strategy, and proves that the simulation result is the consistent estimate of the real value. Finally, the random simulation method in the Matlab is used for numerical analysis in an example, which shows the innovative simulation method is a very good and helpful method for making dividend payment and investment decisions. 相似文献
42.
DongJunWANG QunLUO DanDanJIA XiaoDongLI XinQiouWANG YongHuang ZhenZHEN XinHouLIU 《中国化学快报》2003,14(12):1306-1308
The hydrolysis of tetraethoxysilane (TEOS) occurred on the surface of poly(methyl methacrylate) (PMMA) microshperes immediately after these microshperes were prepared in TEOS. Micron-sized hollow SiO2 spheres were obtained by calcination of the coated PMMA microshperes. It was found that the final hollow spheres were constituted by small SiO2 particles. 相似文献
43.
44.
45.
46.
Angelica pubescens and Angelica sinensis belong to the Umbelliferae family and both are used as traditional Chinese medicines. In the present study, headspace solid-phase microextraction (HS-SPME) with gas chromatography-mass spectrometry (GC-MS) was used for the analysis of the volatile constituents present in their roots. Eighty-seven compounds in Angelica pubescens and thirty-six compounds in Angelica sinensis were identified by GC-MS. Their relative contents were calculated by the peak area ratio. HS-SPME was compared to steam distillation (SD) by analyzing the volatile constituents of Angelica sinensis root. A good agreement between results obtained with both techniques was found. As a conclusion, HS-SPME is a powerful tool for determining the volatile constituents present in the TCMs. 相似文献
47.
Heat capacities of Pr(NCS)3·7H2O and Nd(NCS)3· 7H2O haw been measured from 13 to 300 K by using a fully automated adiabatic calorimeter. Schottky anomaly was observed for Pr(NCS)3·7H2O below 50 K. The polynomial equations for calculating the heat capacity values of the two compounds in the range of 13-300 K were obtained by the least-squares fitting based on the experimental Cp data. The Cp values below 13 K were estimated by using the Debye-Einstein and Schottky heat capacity functions. The standard molar thermodynamic functions were computed from 0 to 300 K. The standard entropies and Gibbs energies of formation of the two compounds were also calculated. 相似文献
48.
Two layered amine-templated cobalt squarates, [C6N2H14]2[Co2(C4O4)3(H2O)4], I, and [C3N2H5]2[Co2(C4O4)3(H2O)4], II, have been prepared under hydrothermal conditions. Both I and II contain chains formed by dimers comprising two cobalt atoms bound to the squarate units, the chains being connected through hydrogen bond interactions. An amine-templated cobalt squarate of the formula [C4N2H12][Co(C4O4)2(H2O)4][H2O]2, III, as well as its Ni, Zn and Cd analogues have been prepared by room temperature reactions. III has a layered architecture wherein the cobalt-squarate monomers are linked by the amine molecules. Co and Zn analogues of [Ni(C4O4)(H2O)2(C3N2H4)] with ligating imidazole units have also been prepared and characterized. 相似文献
49.
0 IntroductionMetallosupramolecular oligomers and polymerscan result from the interaction of metal ions with ap-propriate multidentate ligands designed for multinucle-ar binding[1,2], and there are considerable interests in thedesign of species containing known numbers of metalions in defined spatial arrangements. The electronic andphotophysical properties of oligopyridine complexes oftransition-metal ions make their incorporation particu-larlyattractive and the possibilityofinter-metallic ele… 相似文献
50.
In the degassing process of transformer oil with ultrasonic waves ,decompostition of the oil was observed.Light hydrocarbons,including methane,ethane,ethylene ,aceylene,propane etc,were found to be released continuously from the oil into headspace within a closed vial placed in an ultrasonic field ,The gases came from decomposition of hydrocarbon molecules under cavitation effect. 相似文献