全文获取类型
收费全文 | 2619篇 |
免费 | 629篇 |
国内免费 | 347篇 |
专业分类
化学 | 1889篇 |
晶体学 | 27篇 |
力学 | 200篇 |
综合类 | 7篇 |
数学 | 251篇 |
物理学 | 1221篇 |
出版年
2024年 | 1篇 |
2023年 | 68篇 |
2022年 | 78篇 |
2021年 | 96篇 |
2020年 | 120篇 |
2019年 | 119篇 |
2018年 | 116篇 |
2017年 | 100篇 |
2016年 | 145篇 |
2015年 | 130篇 |
2014年 | 148篇 |
2013年 | 206篇 |
2012年 | 306篇 |
2011年 | 324篇 |
2010年 | 205篇 |
2009年 | 165篇 |
2008年 | 193篇 |
2007年 | 174篇 |
2006年 | 154篇 |
2005年 | 98篇 |
2004年 | 76篇 |
2003年 | 86篇 |
2002年 | 47篇 |
2001年 | 29篇 |
2000年 | 41篇 |
1999年 | 34篇 |
1998年 | 36篇 |
1997年 | 47篇 |
1996年 | 36篇 |
1995年 | 26篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 14篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有3595条查询结果,搜索用时 15 毫秒
1.
Fractional-order calculus is about the differentiation and integration of non-integer orders. Fractional calculus (FC) is based on fractional-order thinking (FOT) and has been shown to help us to understand complex systems better, improve the processing of complex signals, enhance the control of complex systems, increase the performance of optimization, and even extend the enabling of the potential for creativity. In this article, the authors discuss the fractional dynamics, FOT and rich fractional stochastic models. First, the use of fractional dynamics in big data analytics for quantifying big data variability stemming from the generation of complex systems is justified. Second, we show why fractional dynamics is needed in machine learning and optimal randomness when asking: “is there a more optimal way to optimize?”. Third, an optimal randomness case study for a stochastic configuration network (SCN) machine-learning method with heavy-tailed distributions is discussed. Finally, views on big data and (physics-informed) machine learning with fractional dynamics for future research are presented with concluding remarks. 相似文献
2.
3.
Hua-zhou Niu Chun-ming Liu Wan-chao Hou Sai-nan Li Yu-chi Zhang Zhen Liu Hao-cheng Yun 《Journal of separation science》2022,45(2):492-506
Black bean, in which isoflavones are the main active constituent, also contains saponins and monoterpenes. Soybean isoflavone is a secondary metabolite that is formed during the growth of soybean; it exhibits antioxidant and cardiovascular activities and traces estrogen-like effects. In this study, black bean isoflavones were extracted with n-butanol, and ultrafiltration–liquid chromatography–mass spectrometry was used to screen their activity. Subsequently, the inhibitors were isolated and purified using semipreparative liquid chromatography and stepwise flow rate countercurrent chromatography. Thereafter, five active compounds were identified using mass spectrometry and nuclear magnetic resonance experiments. Finally, the inhibition types of the xanthine oxidase inhibitors were determined using enzymatic kinetic studies. The IC50 values of daidzin, glycitein-7-O-glucoside, genistin, daidzein, and genistein were determined to be 35.08, 56.22, 30.76, 68.79, and 95.37 μg/mL, respectively. Daidzin, genistin, and daidzein exhibited reversible inhibition, whereas glycitein-7-O-glucoside and genistein presented irreversible inhibition. This novel approach, which was based on ultrafiltration–liquid chromatography–mass spectrometry and stepwise flow rate countercurrent chromatography, is a powerful method for screening and isolating xanthine oxidase inhibitors from complex matrices. The study of enzyme inhibition types is helpful for understanding the underlying inhibition mechanism. Therefore, a beneficial platform was developed for the large-scale production of bioactive and nutraceutical ingredients. 相似文献
4.
Wanchao Hou Chunming Liu Sainan Li Yuchi Zhang Yongri Jin Xuwen Li Zhen Liu Huazhou Niu Jianli Xia 《Journal of separation science》2022,45(6):1170-1184
The extraction of Scutellaria baicalensis Georgi was investigated using the response surface methodology-genetic algorithm mathematical regression model, and the extraction variables were optimized to maximize the flavonoid yield. Furthermore, a simple and efficient ultrafiltration–liquid chromatography–mass spectrometry and molecular docking methods were developed for the rapid screening and identification of acetylcholinesterase inhibitors present in Scutellaria baicalensis Georgi. Subsequently, four major chemical constituents, namely baicalein, norwogonin, wogonin, and oroxylin A, were identified as potent acetylcholinesterase inhibitors. This novel approach, involving the use of ultrafiltration–liquid chromatography–mass spectrometry and molecular docking methods combined with stepwise flow rate counter-current chromatography and semi-preparative high-performance liquid chromatography, could potentially provide a powerful tool for the screening and extraction of acetylcholinesterase inhibitors from complex matrices and be a useful platform for the production of bioactive and nutraceutical ingredients. 相似文献
5.
Dan Chen Kaixin Du Xiaochen Niu Hongwei Zhang Xue Zhang Yu Tang Jianchun Zhao 《Biomedical chromatography : BMC》2022,36(3):e5288
Amlexanox, an anti-inflammatory and anti-allergic agent, has been widely used clinically for the treatment of canker sores, asthma, and allergic rhinitis. Recently, amlexanox has received considerable attention in curing nonalcoholic fatty liver diseases and hepatitis virus infection. Herein, we first established a sensitive high-performance liquid chromatography-tandem mass spectrum (LC–MS/MS) method for the determination of amlexanox in rat plasma. Propranolol was used as the internal standard (IS). Using a simple protein precipitation method, the amlexanox and IS were separated with Capcell Pak C18 column (2.0 × 50 mm, 5 μm) and eluted with water and acetonitrile each containing 0.1% formic acid using gradient elution condition at a flow rate of 0.4 mL·min−1. Amlexanox and IS were detected by a triple quadrupole mass in multiple reactive monitoring (MRM) under the transitions of m/z 299.2 → 281.2 and m/z 259.9 → 116.1 with positive electrospray ionization, respectively. The calibration curves of amlexanox were established with the range of 50 to 2000 ng·mL−1 (r2 > 0.99). The validation method consisted of selectivity, accuracy, precision, carryover effect, matrix effect, recovery, dilution effect, and stability. The fully validated method was successfully applied to the pharmacokinetic study of amlexanox in Wistar rats. 相似文献
6.
Crystallography Reports - A di-nuclear uranyl complex with the formula of [(UO2)2(L)4(H2O)2]?4H2O (1) (HL = quinoline-6-carboxylic acid) was synthesized hydrothermally and characterized by... 相似文献
7.
针对冷库运行过程中出现的压缩机排气温度高、系统性能衰减等问题,设计并搭建了基于平行流换热器的低压补气冷藏系统实验台对冷藏系统在低压补气和不补气状态下压缩机转速对冷藏系统综合性能的影响进行了分析.结果 表明:随着压缩机转速的增加,两种工况下压缩机排气温度都会增加,在补气模式下排气温度增加了5%,在不补气模式下增加了7.8%;冷藏系统的制冷量也会随之增大,在补气模式下制冷量增加了43%,在不补气模式下增加了25.9%,低压补气模式下增加的制冷量更大一些;压缩机功率随转速的增加而增大,且两种模式下增幅接近,在补气模式下压缩机功率增加了27.44%,在不补气模式下增加了27.34%;另外随着转速的增大系统COP呈现先增大后减小的趋势,在转速为3500 r/min处趋于稳定. 相似文献
8.
Nonlinear Dynamics - Nonlinear vibration isolation provides with an effective way for vibration reduction with broad band and high efficiency. This investigation focuses on the dynamic effects of a... 相似文献
9.
本文首先通过量子分子动力学方法结合多尺度冲击技术研究固相TNT晶体在冲击波加载下的初始分解反应路径及其产物组分变化.通过综合分析键长变化、电子布居和中间产物的存在寿命三个要素给出了不同冲击波速(3-15 km/s)下2类可能的初始分解路径:在低速冲击下(≤7 km/s),TNT发生部分分解和聚合,分解主要源于C-NO2键的断裂,初始分解产物以NO2为主;在高速冲击下(≥9 km/s)则发生完全分解,分解主要始于六元环的形成,即NO2基团上的O与相邻CH3基团上的H相结合,然后六元环被打破,生成了OH自由基,初始分解产物以CN、CO、C2和OH为主.另外,根据模拟数据我们从理论上给出了TNT(ρ0=1.7 g/cm~3)冲击Hugoniot关系为Us=3.377+1.363 u.随后以分子光谱理论为基础,采用含时密度泛函理论获取这些主要分解产物的紫外可见吸收谱、荧光发射谱及振动分辨的荧光发射谱.此项研究有助于我们深入认识TNT高温高压状... 相似文献
10.
Cao Hongmei Deng Shenzhen Tie Zhiwei Tian Jinlei Liu Lili Niu Zhiqiang 《中国科学:化学(英文版)》2022,65(9):1725-1732
Science China Chemistry - Synchronously reducing/self-assembling strategy on Zn substrate was designed to fabricate large-area cation-doped hydrated V2O5/multi-walled carbon nanotube (D-HVO/MWCNT)... 相似文献