全文获取类型
收费全文 | 68438篇 |
免费 | 6956篇 |
国内免费 | 8124篇 |
专业分类
化学 | 27204篇 |
晶体学 | 778篇 |
力学 | 2000篇 |
综合类 | 566篇 |
数学 | 5015篇 |
物理学 | 14108篇 |
综合类 | 33847篇 |
出版年
2024年 | 162篇 |
2023年 | 746篇 |
2022年 | 1541篇 |
2021年 | 1691篇 |
2020年 | 1750篇 |
2019年 | 1551篇 |
2018年 | 1518篇 |
2017年 | 1689篇 |
2016年 | 1973篇 |
2015年 | 2522篇 |
2014年 | 3406篇 |
2013年 | 4269篇 |
2012年 | 4820篇 |
2011年 | 5288篇 |
2010年 | 4502篇 |
2009年 | 4684篇 |
2008年 | 5141篇 |
2007年 | 4876篇 |
2006年 | 4376篇 |
2005年 | 3768篇 |
2004年 | 2964篇 |
2003年 | 2246篇 |
2002年 | 2397篇 |
2001年 | 2123篇 |
2000年 | 1963篇 |
1999年 | 1559篇 |
1998年 | 1103篇 |
1997年 | 1021篇 |
1996年 | 1032篇 |
1995年 | 909篇 |
1994年 | 856篇 |
1993年 | 740篇 |
1992年 | 667篇 |
1991年 | 606篇 |
1990年 | 533篇 |
1989年 | 456篇 |
1988年 | 410篇 |
1987年 | 297篇 |
1986年 | 238篇 |
1985年 | 221篇 |
1984年 | 134篇 |
1983年 | 95篇 |
1982年 | 93篇 |
1981年 | 74篇 |
1980年 | 68篇 |
1979年 | 70篇 |
1978年 | 49篇 |
1976年 | 39篇 |
1974年 | 43篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
利用初等方法研究了一个包含Smarandache Ceil函数Sk(n)的对偶函数-Sk(n),给出了当k=6时方程-S6(1)+-S6(2)+…+-S6(n)=6Ω(n)的具体正整数解。 相似文献
12.
在40℃恒温水浴下用次氯酸钠对2种煤液化残渣进行氧化,将反应所得混合物用滤膜过滤,滤出液依次用石油醚、二硫化碳、四氯化碳和乙酸乙酯萃取,得到的萃取物用气相色谱/质谱(GC/MS)分析.根据分析结果系统地考察了2种煤液化残渣中所含杂原子化合物的分布,为从煤液化残渣中选择性地脱除这些杂原子化合物及提取高附加值化学品提供了一条路径. 相似文献
13.
Analysis and pharmacokinetic study of polyphyllin H in beagle dog plasma after oral administration of Rhizoma Paridis Extracts by LC‐MS/MS
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
14.
15.
Jie Lu Ju-Kang Wu Yao Jiang Dr. Peng Tan Lin Zhang Yu Lei Prof. Xiao-Qin Liu Prof. Lin-Bing Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(16):6490-6496
Hierarchically porous metal–organic frameworks (HP-MOFs) are promising in various applications. Most reported HP-MOFs are prepared based on the generation of mesopores in microporous frameworks, and the formed mesopores are connected by microporous channels, limiting the accessibility of mesopores for bulky molecules. A hierarchical structure is formed by constructing microporous MOFs in uninterrupted mesoporous tunnels. Using the confined space in as-prepared mesoporous silica, highly dispersed metal precursors for MOFs are coated on the internal surface of mesoporous tunnels. Ligand vapor-induced crystallization is employed to enable quantitative formation of MOFs in situ, in which sublimated ligands diffuse into mesoporous tunnels and react with metal precursors. The obtained hierarchically porous composites exhibit record-high adsorption capacity for the bulky molecule trypsin. The thermal and storage stability of trypsin is improved upon immobilization on the composites. 相似文献
16.
17.
Single Crystal to Single Crystal (SC‐to‐SC) Transformation from a Nonporous to Porous Metal–Organic Framework and Its Application Potential in Gas Adsorption and Suzuki Coupling Reaction through Postmodification
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Rupam Sen Debraj Saha Dr. Subratanath Koner Dr. Paula Brandão Dr. Zhi Lin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5962-5971
A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH2 groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m2 g?1. The material also possesses good CO2 (8 wt %) and H2 (1.87 wt %) adsorption capabilities. 相似文献
18.
在学校组织开展的各项活动特别是体育比赛活动中,难免出现各类突发性事故。对突发事件的应急处理和善后工作,考验着高校各级领导特别是辅导员的工作能力。如何科学、有效地处理突发事件,避免及减少突发事件带来的损失,提升高校辅导员应对突发事件的能力和水平,具有重要的现实意义。 相似文献
19.
20.
A self-propelled object coupled with an enzyme reaction between urease and urea was investigated at the air/aqueous interface. A plastic object that was fixed to a urease-immobilized filter paper was used as a self-propelled object, termed a urease motor, placed on an aqueous urea solution. The driving force of the urease motor is the difference in the surface tension around the object. Oscillatory motion or no motion was triggered depending on the initial pH of the urea solution. Both the frequency and maximum speed of the oscillatory motion varied depending on the initial pH of the water phase. The mechanisms underlying the oscillatory motion and no motion were discussed in relation to the bell-shaped enzyme activity of urease in the enzyme reaction and the surface tension around the urease motor. 相似文献