全文获取类型
收费全文 | 5976篇 |
免费 | 346篇 |
国内免费 | 1628篇 |
专业分类
化学 | 5016篇 |
晶体学 | 115篇 |
力学 | 208篇 |
综合类 | 47篇 |
数学 | 854篇 |
物理学 | 1710篇 |
出版年
2024年 | 8篇 |
2023年 | 82篇 |
2022年 | 126篇 |
2021年 | 107篇 |
2020年 | 120篇 |
2019年 | 136篇 |
2018年 | 113篇 |
2017年 | 150篇 |
2016年 | 167篇 |
2015年 | 174篇 |
2014年 | 287篇 |
2013年 | 538篇 |
2012年 | 461篇 |
2011年 | 404篇 |
2010年 | 323篇 |
2009年 | 382篇 |
2008年 | 433篇 |
2007年 | 535篇 |
2006年 | 360篇 |
2005年 | 303篇 |
2004年 | 295篇 |
2003年 | 260篇 |
2002年 | 229篇 |
2001年 | 165篇 |
2000年 | 194篇 |
1999年 | 197篇 |
1998年 | 157篇 |
1997年 | 148篇 |
1996年 | 159篇 |
1995年 | 133篇 |
1994年 | 118篇 |
1993年 | 107篇 |
1992年 | 106篇 |
1991年 | 79篇 |
1990年 | 69篇 |
1989年 | 92篇 |
1988年 | 60篇 |
1987年 | 31篇 |
1986年 | 25篇 |
1985年 | 34篇 |
1984年 | 16篇 |
1983年 | 23篇 |
1982年 | 15篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有7950条查询结果,搜索用时 15 毫秒
11.
Shanshan Wang Xianbo Kong Zhangjing Chen Guopin Wang Juan Zhang Jing Wang 《Molecules (Basel, Switzerland)》2022,27(13)
Alzheimer’s disease (AD) is a progressive neurological condition. The rising prevalence of AD necessitates the rapid development of efficient therapy options. Despite substantial study, only a few medications are capable of delaying the disease. Several substances with pharmacological activity, derived from plants, have been shown to have positive benefits for the treatment of AD by targeting various enzymes, such as acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), β-secretase, γ-secretase, and monoamine oxidases (MAOs), which are discussed as potential targets. Medicinal plants have already contributed a number of lead molecules to medicine development, with many of them currently undergoing clinical trials. A variety of medicinal plants have been shown to diminish the degenerative symptoms associated with AD, either in their raw form or as isolated compounds. The aim of this review was to provide a brief summary of AD and its current therapies, followed by a discussion of the natural compounds examined as therapeutic agents and the processes underlying the positive effects, particularly the management of AD. 相似文献
12.
Patareeya Lasunon Nutchanat Phonkerd Somprasong Pariwat Nipaporn Sengkhamparn 《Molecules (Basel, Switzerland)》2022,27(11)
The quick-cooking rice product is an interesting product for the market which is easy to cook, with good sensorial qualities and health benefits. This work aimed to study the effect of the soaking conditions, namely baking powder concentration (0.1, 0.2, or 0.3%), soaking temperature (room temperature, 50 or 60 °C), and soaking time (10, 20, or 30 min), in order to improve the physical properties and also the sensory characteristics, with high bioactive compound content, of Quick-Cooking Black Jasmine Rice (QBJR). The physical properties of the final product, namely the rehydration capacity, morphology, and texture, were observed. Moreover, the total phenolic, total flavonoid, and total anthocyanin were determined. The results showed that the samples with a high baking powder concentrations soaked at high temperatures for longer time affect the low rehydration capacity with a high hardness value and a decreased bioactive compound content. In addition, the sensory score including softener, flavor, and overall acceptance were lower score. Moreover, to determine the best soaking condition with complex data, the Fuzzy Analytical Method (FAM) was performed by an online FAM program. The results showed that soaking at room temperature for 30 min in 0.1% of baking powder showed the highest overall performance index of 6.52. 相似文献
13.
本文通过将新型化学气相反应促进剂Zn(NH4)3Cl5引入到热壁外延系统中,以二元素单质Zn和Se为原料,直接在Si(111)衬底上生长了高质量的ZnSe晶体薄膜,薄膜成分接近理想化学计量比。研究了主要工艺参数对薄膜生长形貌和性能的影响。采用SEM、AFM、EDS和PL谱技术研究了生长的ZnSe薄膜的形貌、成分和发光特性。研究结果表明,热壁温度和生长时间是影响ZnSe薄膜形貌的主要因素;气相反应促进剂在薄膜生长和调节成分方面扮演了关键角色,Zn(NH4)3Cl5的存在使得Zn(g)和Se2(g)合成ZnSe晶体的反应转变为气固非一致反应,从而更容易获得近乎理想化学计量比的ZnSe薄膜。ZnSe薄膜在氦镉激光激发下,室温下PL谱由近带边发射和(VZn-ClSe)组合的SA发光组成,而在飞秒激光激发下,仅在481nm处显示出强烈的双光子发射峰。 相似文献
14.
David E. Mery Amanda J. Compadre Paola E. Ordez Edward J. Selvik Vladimir Morocho Jorge Contreras Omar Malagn Darin E. Jones Philip J. Breen Michael J. Balick Flavio G. Gaudio Monica L. Guzman Cesar M. Compadre 《Molecules (Basel, Switzerland)》2022,27(9)
A method to identify anticancer compounds in plants was proposed based on the hypothesis that these compounds are primarily present in plants to provide them with an ecological advantage over neighboring plants and other competitors. According to this view, identifying plants that contain compounds that inhibit or interfere with the development of other plant species may facilitate the discovery of novel anticancer agents. The method was developed and tested using Magnolia grandiflora, Gynoxys verrucosa, Picradeniopsis oppositifolia, and Hedyosmum racemosum, which are plant species known to possess compounds with cytotoxic activities. Plant extracts were screened for growth inhibitory activity, and then a thin-layer chromatography bioautography assay was conducted. This located the major antileukemic compounds 1, 2, 4, and 5 in the extracts. Once the active compounds were located, they were extracted and purified, and their structures were determined. The growth inhibitory activity of the purified compounds showed a significant correlation with their antileukemic activity. The proposed approach is rapid, inexpensive, and can easily be implemented in areas of the world with high biodiversity but with less access to advanced facilities and biological assays. 相似文献
15.
16.
Blue luminescent compounds T1-T4 containing triphenylamine donors,bipyridine acceptors and olefinic linkers were synthesized and characterized by 1H NMR,13C NMR and high resolution mass spectrometry(HR... 相似文献
17.
《Journal of Coordination Chemistry》2012,65(22):3659-3665
Some Schiff-base complexes of UO2(II) ion derived from 2-hydroxyacetophenone and aliphatic diamines under reflux conditions have been synthesized. The resulting ligands and their complexes have been characterized by elemental analyses (C, H, N), infrared, 1H NMR, 13C NMR and mass spectra. In these efficient reactions, Schiff-base complexes with important applications in analytical and organic chemistry are prepared. 相似文献
18.
基于CPLD工作模式可调的线阵CCD驱动电路设计 总被引:3,自引:1,他引:3
针对传统驱动电路一旦做出修改,则需对硬件或程序进行改变的缺点,以型号为TCD1707D的线阵CCD为例,介绍了一种工作模式可调的驱动方法.该方法是利用复杂可编程逻辑器件和控制外端结合,通过分别设置内外触发来实现的.在外触发模式下,利用外触发脉冲,可由用户控制CCD的曝光和信号输出时间;内触发时,可以调节CCD的积分时间和驱动频率.为提高信号输出质量,针对EMC问题给出了线阵CCD的外围驱动电路.实验结果表明,该方法调试方便、电路结构简单、集成度较高、输出信号可靠稳定、受干扰小,可配合多种用户需要,对高速精确测量及线阵推扫模式具有一定参考价值. 相似文献
19.
The paper is devoted to the research of large deviation probabilities in the approximation by compound Poisson law. 相似文献
20.
Luiza Amália Moraes Luis Romero Grados 《Journal of Mathematical Analysis and Applications》2003,281(2):575-586
Let Au(BG) be the Banach algebra of all complex valued functions defined on the closed unit ball BG of a complex Banach space G which are uniformly continuous on BG and holomorphic in the interior of BG, endowed with the sup norm. A characterization of the boundaries for Au(BG) is given in case G belongs to a class of Banach spaces that includes the pre-dual of a Lorentz sequence space studied by Gowers in Israel J. Math. 69 (1990) 129-151. The non-existence of the Shilov boundary for Au(BG) is also proved. 相似文献