全文获取类型
收费全文 | 15460篇 |
免费 | 2566篇 |
国内免费 | 1863篇 |
专业分类
化学 | 11573篇 |
晶体学 | 184篇 |
力学 | 787篇 |
综合类 | 97篇 |
数学 | 1382篇 |
物理学 | 5866篇 |
出版年
2024年 | 53篇 |
2023年 | 276篇 |
2022年 | 518篇 |
2021年 | 570篇 |
2020年 | 653篇 |
2019年 | 646篇 |
2018年 | 572篇 |
2017年 | 477篇 |
2016年 | 768篇 |
2015年 | 721篇 |
2014年 | 865篇 |
2013年 | 1208篇 |
2012年 | 1380篇 |
2011年 | 1350篇 |
2010年 | 931篇 |
2009年 | 935篇 |
2008年 | 1045篇 |
2007年 | 944篇 |
2006年 | 849篇 |
2005年 | 757篇 |
2004年 | 616篇 |
2003年 | 523篇 |
2002年 | 570篇 |
2001年 | 396篇 |
2000年 | 291篇 |
1999年 | 303篇 |
1998年 | 249篇 |
1997年 | 221篇 |
1996年 | 200篇 |
1995年 | 164篇 |
1994年 | 140篇 |
1993年 | 109篇 |
1992年 | 107篇 |
1991年 | 102篇 |
1990年 | 69篇 |
1989年 | 56篇 |
1988年 | 39篇 |
1987年 | 30篇 |
1986年 | 34篇 |
1985年 | 34篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
在pH6.4的磷酸二氢钾-磷酸氢二钾缓冲液和CIMAJB、正丁醇、正庚烷组成的微乳液的介质中,水杨基荧光酮与铜(Ⅱ)、铬(Ⅵ)的显色体系灵敏度都有很大提高,选择了合适的测定波长,利用双波长解方程组法同时测定了底泥中的铜和铬。结果令人满意。 相似文献
73.
Method of molecularly imprinted solid phase extraction (MISPE) of (-)-ephedrine from Chinese Ephedra has been developed in the research. The molecularly imprinted polymer (MIP) with good selectivity and affinity for (-)-ephedrine was synthesized with (-)-ephedrine as the template, methacrylic acid as the functional monomer. The washing and elution conditions in MISPE were selected and optimized for efficient analyte extraction and sample clean-up. A clean analytical HPLC base line of ephedra extract was obtained after MISPE, which indicated that the sample pre-treatment was efficient. Good recovery and precision were obtained in the assessment for the MISPE-HPLC procedure, which demonstrated it is a reliable method and can be used for the determination of (-)-ephedrine in herbal ephedra. 相似文献
74.
Huang M Jin Y Jiang H Sun X Chen H Liu B Wang E Dong S 《The journal of physical chemistry. B》2005,109(32):15264-15271
Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated 0.1 M H(2)SO(4). Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost. 相似文献
75.
The reduction of C = C double bonds is one of the most fundamental synthetic transformations and plays a key role in the manufacturing of a wide variety of bulk and fine chemicals. Hydrogenation of olefinic substrates can be achieved readily with molecular hydrogen in many cases, but transfer hydrogenation methods using suitable donor molecules such as formic acid or alcohols are receiving increasing attention as possible synthetic alternatives because it requires no special equipment and avoids the handling of potentially hazardous gaseous hydrogen. 相似文献
76.
Junfeng Zhou Xiaochen Dong Tao Chen Qiang Yang Qiaohua Tan Jianjun Wang 《European Polymer Journal》2007,43(5):2088-2095
A series of well-defined two-armed polymers containing a crown ether core, poly(stearyl methacrylate)-crown ether-poly(stearyl methacrylate) (PSMA-crown-PSMA), with different molecular weight were synthesized via atom transfer radical polymerization (ATRP). The resultant polymers were characterized by 1H NMR and GPC. The self-assembly behaviors of this kind of polymer in selective solvents were studied by TEM, and it was found that polymers with different molecular weight can directly self-assemble into hollow spheres, solid spheres and a monolayer film with regular pores by varying molecular weight and water content. The possible molecular packing motels for their self-assembly behaviors were proposed. 相似文献
77.
Jin Yan Dong Ye Gao Chen Hong Chuan Song Yan Ping He Lei Li Yong Ping Zhong Yan Hui Zhu Jie Cao Luo Wang Ke Qin Zhang Laboratory for Conservation Utilization of Bioresources Yunnan University Kunming China Department of Chemistry Yunnan Normal University Kunming China Provincial Key Lab of Rural Energy Engineering Yunnan Normal University Kunming China 《中国化学快报》2007,18(2):165-167
Microbial transformation of nigranoic acid by Caryospora carllicarpa YMF1.01026 afforded the new derivative 6β-hydro-xynigranoic acid. Its structure was elucidated by spectroscopic methods. 相似文献
78.
Dynamical response of a passivation model subjected to parametric periodic and stochastic perturbations is studied numerically. In response to weak periodic modulation, the system exhibits a rich variety of resonance behavior and induced dynamics, including periodically induced oscillation, birhythmicity, switching between two bistable states, selection of one of the bistable states, mixed-mode and chaotic oscillations. These phenomena are discussed in terms of the stability of saddle focus and an incomplete homoclinic connection. Our numerical results are relevant for a wide class of electro-chemical oscillatory systems, where the re-injection of unstable trajectory on the neighborhood of a saddle focus is a typical feature in the phase space. 相似文献
79.
80.