全文获取类型
收费全文 | 8121篇 |
免费 | 1280篇 |
国内免费 | 1210篇 |
专业分类
化学 | 6096篇 |
晶体学 | 94篇 |
力学 | 527篇 |
综合类 | 104篇 |
数学 | 990篇 |
物理学 | 2800篇 |
出版年
2024年 | 33篇 |
2023年 | 161篇 |
2022年 | 329篇 |
2021年 | 314篇 |
2020年 | 351篇 |
2019年 | 341篇 |
2018年 | 292篇 |
2017年 | 279篇 |
2016年 | 391篇 |
2015年 | 360篇 |
2014年 | 465篇 |
2013年 | 611篇 |
2012年 | 708篇 |
2011年 | 756篇 |
2010年 | 496篇 |
2009年 | 499篇 |
2008年 | 590篇 |
2007年 | 489篇 |
2006年 | 417篇 |
2005年 | 379篇 |
2004年 | 288篇 |
2003年 | 243篇 |
2002年 | 231篇 |
2001年 | 201篇 |
2000年 | 163篇 |
1999年 | 159篇 |
1998年 | 136篇 |
1997年 | 130篇 |
1996年 | 132篇 |
1995年 | 121篇 |
1994年 | 105篇 |
1993年 | 82篇 |
1992年 | 79篇 |
1991年 | 65篇 |
1990年 | 50篇 |
1989年 | 36篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 14篇 |
1985年 | 22篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
241.
242.
243.
244.
受限条件下水的介电性质因测量极具挑战,其在诸多电化学过程与反应输运过程中如何扮演关键角色从未被定量地澄清.本工作利用平衡态分子动力学模拟和受限体系介电性质计算方法,系统性地探索了0.65 nm限域尺寸、5×108 Pa限域压强、不同温度条件下单分子受限冰和受限水的介电性质.详细比较了恒定偶极矩SPC/E水分子模型和可极化的SWM4-NDP水分子模型在描述受限冰、水结构与介电性质上的优劣势,包括统计分析SWM4-NDP模型模拟的单分子层受限水和受限冰的瞬时分子偶极矩概率密度分布,计算每个模拟体系的静态结构因子、静态偶极空间关联函数、静态介电常数、体系偶极时间关联函数和德拜弛豫时间.首次发现了极化水分子模型描述的低维度受限水和受限冰的奇异分子极性变化,并观察到两种模型描述静态结构性质的效果相当, SWM4-NDP模型对于静态介电常数描述的优势会因受限条件的增强而被大幅削减.但在受限水介电极化弛豫动力学性质描述上SWM4-NDP模型明显优于SPC/E模型.我们推断SWM4-NDP模型在探索受限水结构相变动力学以及受限体系离子输运和溶剂化动力学等过程的模拟研究中是比SPC... 相似文献
245.
二氧化碳(CO2)是一种丰富、廉价、无毒以及可再生的一碳资源,也是一种可用于聚合的绿色单体.基于CO2的聚合是近年来的研究热点之一.目前广泛报道的是CO2和环氧单体的聚合反应,经过几十年的发展已经成功实现工业化生产.最近几年,一些CO2参与的新型聚合反应被陆续报道,这些工作大都通过两种途径实现从CO2到高分子材料的转变.第一个途径是先将CO2转化为可以聚合的单体,例如:内酯、环状碳酸酯和2,5-二呋喃甲酸等,再利用开环或者逐步聚合将单体转化为聚合物;另一个途径是直接以CO2为单体和其他类型单体共聚得到聚合物.这两种途径对于发展CO2参与的新型聚合反应,拓展CO2基聚合物种类都具有重要意义.本综述按照CO2直接还是间接参与聚合反应分类总结了近年来在CO2制备高分子材料方面的进展,并对未来发展方向进行了简单阐述. 相似文献
246.
空间-时间分数阶对流扩散方程的数值解法 总被引:1,自引:0,他引:1
本文考虑一个空间-时间分数阶对流扩散方程.这个方程是将一般的对流扩散方程中的时间一阶导数用α(0<α<1)阶导数代替,空间二阶导数用β(1<β<2)阶导数代替.本文提出了一个隐式差分格式,验证了这个格式是无条件稳定的,并证明了它的收敛性,其收敛阶为O(ι h).最后给出了数值例子. 相似文献
247.
Yuan Cao Wanyi Liu Lan Qin Bingqiang Liu Shuai Chen Jing Ye Xianzhao Xia Chao Wang 《Entropy (Basel, Switzerland)》2022,24(11)
Entropy is a measure of uncertainty or randomness. It is the foundation for almost all cryptographic systems. True random number generators (TRNGs) and physical unclonable functions (PUFs) are the silicon primitives to respectively harvest dynamic and static entropy to generate random bit streams. In this survey paper, we present a systematic and comprehensive review of different state-of-the-art methods to harvest entropy from silicon-based devices, including the implementations, applications, and the security of the designs. Furthermore, we conclude the trends of the entropy source design to point out the current spots of entropy harvesting. 相似文献
248.
Wanyu Qin Huihan Xi Aixia Wang Xue Gong Zhiying Chen Yue He Lili Wang Liya Liu Fengzhong Wang Litao Tong 《Molecules (Basel, Switzerland)》2022,27(17)
The structural and functional properties of physical modified rice flour, including ultrasound treated rice flour (US), microwave treated rice flour (MW) and hydrothermal treated rice flour (HT) were investigated with wet-milled rice flour (WF) used as a positive control. The results showed the presence of small dents and pores on the rice flour granules of US and MW while more fragments and cracks were showed in HT. XRD and FTIR revealed that moderate ultrasonic treatment promoted the orderly arrangement of starch while hydrothermal treatment destroyed the crystalline structure of rice flour. In addition, the significant decrease of gelatinization enthalpy and the narrowing gelatinization temperature were observed in US. Compared to that of SF, adding physical modified rice flour led to a batter with higher viscoelasticity and lower tan δ. However, the batter added HT exhibited highest G′ and G″ values and lowest tan δ, which led to a harder texture of bread. Texture analysis demonstrated that physical modified rice flour (except HT) reduced the hardness, cohesion, and gumminess of rice bread. Especially, the specific volume of bread with US increased by 15.6% and the hardness decreased by 17.6%. This study suggested that ultrasound treatment of rice flour could improve texture properties and appearance of rice bread. 相似文献
249.
Xiaoya Zhang Junli Wu Long Qin Guangxi Wang Ping Li Anmin Yu Aizhong Liu Rui Sun 《Molecules (Basel, Switzerland)》2022,27(19)
An effective method for separating and purifying critical saponins (polyphyllin II and polyphyllin VII) from a Paris polyphylla var. yunnanensis extract was developed in this study which was environmentally friendly and economical. Static adsorption kinetics, thermodynamics, and the dynamic adsorption-desorption of macroporous resins were investigated, and then the conditions of purification and separation were optimized by fitting with an adsorption thermodynamics equation and a kinetic equation. Effective NKA-9 resin from seven macroporous resins was screened out to separate and purify the two saponins. The static adsorption and dynamic adsorption were chemical and physical adsorption dual-processes on the NKA-9 resin. Under the optimum parameters, the contents of polyphyllin II and polyphyllin VII in the product were 17.3-fold and 28.6-fold those in plant extracts, respectively. The total yields of the two saponins were 93.16%. This research thus provides a theoretical foundation for the large-scale industrial production of the natural drugs polyphyllin II and polyphyllin VII. 相似文献
250.
Liying Zhang Shihan Qin Sunv Tang Shuai E Kailin Li Jing Li Wei Cai Lei Sun Hui Li 《Molecules (Basel, Switzerland)》2022,27(19)
Tojapride is composed of Caulis Perillae, Rhizoma Cyperi, Radix Glycyrrhizae, Citrus aurantium L., Coptis chinensis Franch, Pericarpium Citri Reticulatae, Reynoutria japonica Houtt, Tetradium ruticarpum, and Cleistocactus sepium. It has the effects of inhibiting gastric acid and relieving pain. It is clinically used for treating gastroesophageal reflux disease. To further study the pharmacodynamic properties of Tojapride, the systematic characterization of the chemical constituents in Tojapride was investigated using ultra-performance liquid chromatography with Q-Exactive Orbitrap mass spectrometry combined with parallel reaction monitoring for the first time. Eventually, a total of 222 compounds, including flavonoids, alkaloids, and glycyrrhizic acid derivatives, were identified based on the chromatographic retention times, MS/MS2 information, and bibliography data; a total of 218 of these were reported for the first time as being present in Tojapride. This newly developed approach provides a powerful tool for extending our understanding of chemical constituents of Tojapride, which can be further extended to other TCMP composition research. 相似文献