全文获取类型
收费全文 | 34545篇 |
免费 | 6982篇 |
国内免费 | 11991篇 |
专业分类
化学 | 25599篇 |
晶体学 | 1251篇 |
力学 | 2738篇 |
综合类 | 1545篇 |
数学 | 5515篇 |
物理学 | 16870篇 |
出版年
2024年 | 94篇 |
2023年 | 389篇 |
2022年 | 1176篇 |
2021年 | 1232篇 |
2020年 | 1261篇 |
2019年 | 1157篇 |
2018年 | 1083篇 |
2017年 | 1540篇 |
2016年 | 1222篇 |
2015年 | 1715篇 |
2014年 | 2062篇 |
2013年 | 2699篇 |
2012年 | 2635篇 |
2011年 | 3007篇 |
2010年 | 2798篇 |
2009年 | 3120篇 |
2008年 | 3231篇 |
2007年 | 2923篇 |
2006年 | 2973篇 |
2005年 | 2609篇 |
2004年 | 2100篇 |
2003年 | 1506篇 |
2002年 | 1506篇 |
2001年 | 1708篇 |
2000年 | 1765篇 |
1999年 | 1067篇 |
1998年 | 557篇 |
1997年 | 460篇 |
1996年 | 441篇 |
1995年 | 350篇 |
1994年 | 392篇 |
1993年 | 376篇 |
1992年 | 302篇 |
1991年 | 244篇 |
1990年 | 249篇 |
1989年 | 254篇 |
1988年 | 209篇 |
1987年 | 169篇 |
1986年 | 160篇 |
1985年 | 101篇 |
1984年 | 117篇 |
1983年 | 112篇 |
1982年 | 82篇 |
1981年 | 85篇 |
1980年 | 67篇 |
1979年 | 48篇 |
1978年 | 30篇 |
1977年 | 14篇 |
1965年 | 21篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
In this study, S-doped g-C_3N_4 nanoparticles were successfully prepared by one-step solid-state microwave synthesis. The detailed characterizations through XRD, FT-IR, SEM and XPS were studied. In addition, the electrochemical properties as supercapacitor of the sample were tested by cyclic voltammetry(CV), galvanostatic charge-discharge(GCD) and electrochemical impedance spectroscopy(EIS) techniques. The results showed a high specific capacitance of 691 F/g at current density of 4 A/g in 2 M KOH + 0.15 M K_3[Fe(CN)_6] electrolyte. This study shows that the microwave synthesis is a promising way to design carbon-based electrodes for supercapacitor. 相似文献
74.
Jie Wang Yuntian Xing Yang Dai Yingnan Li Wenyan Xiang Jianrong Dai Fei Xu 《Molecules (Basel, Switzerland)》2022,27(13)
Pomacea canaliculata, one of the 100 most destructive invasive species in the world, and it is an important intermediate host of Angiostrongylus cantonensis. The molluscicides in current use are an effective method for controlling snails. However, most molluscicides have no slow-release effect and are toxic to nontarget organisms. Thus, these molluscicides cannot be used on a large scale to effectively act on snails. In this study, gelatin, a safe and nontoxic substance, was combined with sustained-release molluscicide and was found to reduce the toxicity of niclosamide to nontarget organisms. We assessed the effects of gelatin and molluscicide in controlling P. canaliculata snails and eggs. The results demonstrated that the niclosamide retention time with 1.0% and 1.5% gelatin sustained-release agents reached 20 days. Additionally, the mortality rate of P. canaliculata and their eggs increased as the concentration of the niclosamide sustained-release agents increased. The adult mortality rate of P. canaliculata reached 50% after the snails were exposed to gelatin with 0.1 mg/L niclosamide for 48 h. The hatching rate of P. canaliculata was only 28.5% of the normal group after the treatment was applied. The sustained-release molluscicide at this concentration was less toxic to zebrafish, which means that this molluscicide can increase the safety of niclosamide to control P. canaliculata in aquatic environments. In this study, we explored the safety of using niclosamide sustained-release agents with gelatin against P. canaliculata. The results suggest that gelatin is an ideal sustained-release agent that can provide a foundation for subsequent improvements in control of P. canaliculata. 相似文献
75.
新型含氮螯合树脂的制备及其吸附性能 总被引:1,自引:0,他引:1
以三甘醇和苯磺酰氯为原料,二乙烯三胺为交联剂合成了新型含氮螯合树脂(5),其结构经IR表征.讨论了Ni2 浓度和pH对5吸附容量的影响.动力学研究表明,5对Ni2 的吸附速率符合鲛岛公式. 相似文献
76.
A general solution of sun tracking for an arbitrarily oriented
heliostat towards an arbitrarily located target on the earth is
published. With the most general form of solar tracking formulae, it is
seen that the used azimuth-elevation, spinning-elevation tracking formulae
etc. are the special cases of it. The possibilities of utilizing the
general solution and its significance in solar energy engineering are
discussed. 相似文献
77.
Starting from a discrete spectral problem, a hierarchy of integrable lattice soliton equations is derived. It is shown that the hierarchy is completely integrable in the Liouville sense and possesses discrete bi-Hamiltonian structure. A new integrable
symplectic map and finite-dimensional integrable systems are given
by nonlinearization method. The binary Bargmann constraint gives
rise to a Bäcklund transformation for the resulting
integrable lattice equations. At last, conservation laws of the
hierarchy are presented. 相似文献
78.
79.
80.
LBO晶体超光滑表面抛光机理 总被引:1,自引:0,他引:1
胶体SiO2抛光LBO晶体获得无损伤的超光滑表面,结合前人对抛光机理的认识,探讨了超光滑表面抛光的材料去除机理,分析了化学机械抛光中的原子级材料去除机理.在此基础上,对胶体SiO2抛光LBO晶体表面材料去除机理和超光滑表面的形成进行了详细的描述,研究抛光液的pH值与材料去除率和表面粗糙度的关系.LBO晶体超光滑表面抛光的材料去除机理是抛光液与晶体表面的活泼原子层发生化学反应形成过渡的软质层,软质层在磨料和抛光盘的作用下很容易被无损伤的去除.酸性条件下,随抛光液pH值的减小抛光材料的去除率增大;抛光液pH值为4时,获得最好的表面粗糙度. 相似文献