全文获取类型
收费全文 | 1584篇 |
免费 | 37篇 |
国内免费 | 5篇 |
专业分类
化学 | 998篇 |
晶体学 | 26篇 |
力学 | 42篇 |
数学 | 136篇 |
物理学 | 424篇 |
出版年
2024年 | 10篇 |
2023年 | 10篇 |
2022年 | 41篇 |
2021年 | 38篇 |
2020年 | 58篇 |
2019年 | 54篇 |
2018年 | 51篇 |
2017年 | 52篇 |
2016年 | 65篇 |
2015年 | 42篇 |
2014年 | 69篇 |
2013年 | 116篇 |
2012年 | 96篇 |
2011年 | 99篇 |
2010年 | 75篇 |
2009年 | 66篇 |
2008年 | 80篇 |
2007年 | 54篇 |
2006年 | 44篇 |
2005年 | 34篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 25篇 |
2001年 | 9篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1987年 | 7篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1976年 | 26篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 13篇 |
1972年 | 7篇 |
1958年 | 7篇 |
排序方式: 共有1626条查询结果,搜索用时 0 毫秒
21.
Background correction has been shown to be an effective and indispensable modification in the spectrophotometric determination of ascorbic acid. The decomposition of ascorbic acid in pharmaceutical samples was carried out by incubation with sodium hydroxide to give products that were insensitive to ultraviolet light. The rapid oxidation in air of ascorbic acid, especially in dilute solutions, was avoided by the use of the flow injection principle for spectrophotometric determination and by employing a carrier stream of an anti-oxidizing nature consisting of 6 micrograms ml(-1) of 2-mercaptoethanol in 0.25% sulphuric acid. The optimized method with a single channel manifold made use of a carrier stream flow rate of 1.1 ml min(-1), an injection volume of 50 microl, a delay coil of 50 cm (0.5 mm i.d.) and detection at 245 nm. The throughput was at least 180 injections h(-1). The proposed flow injection method yielded results for the analysis of 0-20 micrograms ml(-1) of ascorbic acid that were 99-102% (relative standard deviation 0.6% or better) in agreement with those produced by comparable methods involving titration with iodine, chloranil or 2,6-dichlorophenolindophenol [4-(2,6-dichloro-4-hydroxyphenylimino)cyclohexa-2,5-dieno ne], and high-performance liquid chromatography. When the agreement was not good (as low as 14% with respect to the method being compared), this was traced to the presence of substances which are known to interfere in one or other of the methods of comparison. 相似文献
22.
23.
24.
25.
Abstract A biocompatible zinc (II) complex based on a tetradentate N,N,O,O-type salen ligand was synthesized, characterized and used for the solvent-free ring-opening polymerization (ROP) of L-lactide in bulk at 180?°C to prepare high molecular weight poly(L-lactide) (Mn : 82,600?Da; Mw : 140,000?Da; PDI: 1.70). Poly(L-lactide) (PLLA) was characterized using FTIR, 1H NMR, 13C NMR, GPC, TGA, DSC, WAXD, and MALDI-ToF. Kinetic measurement was carried out and first-order behavior to monomer was observed. The k app was found as 6?±?0.001?×?10?4?s?1. The biocompatibility of the PLLA was confirmed by in vitro cytotoxicity against NIH/3T3 fibroblast cell line and can be used in biomedical applications. 相似文献
26.
Nawal K. Z. AlFadhly Nawfal Alhelfi Ammar B. Altemimi Deepak Kumar Verma Francesco Cacciola Arunaksharan Narayanankutty 《Molecules (Basel, Switzerland)》2022,27(17)
Spirulina is a kind of blue-green algae (BGA) that is multicellular, filamentous, and prokaryotic. It is also known as a cyanobacterium. It is classified within the phylum known as blue-green algae. Despite the fact that it includes a high concentration of nutrients, such as proteins, vitamins, minerals, and fatty acids—in particular, the necessary omega-3 fatty acids and omega-6 fatty acids—the percentage of total fat and cholesterol that can be found in these algae is substantially lower when compared to other food sources. This is the case even if the percentage of total fat that can be found in these algae is also significantly lower. In addition to this, spirulina has a high concentration of bioactive compounds, such as phenols, phycocyanin pigment, and polysaccharides, which all take part in a number of biological activities, such as antioxidant and anti-inflammatory activity. As a result of this, spirulina has found its way into the formulation of a great number of medicinal foods, functional foods, and nutritional supplements. Therefore, this article makes an effort to shed light on spirulina, its nutritional value as a result of its chemical composition, and its applications to some food product formulations, such as dairy products, snacks, cookies, and pasta, that are necessary at an industrial level in the food industry all over the world. In addition, this article supports the idea of incorporating it into the food sector, both from a nutritional and health perspective, as it offers numerous advantages. 相似文献
27.
Sirajudheen Anwar Jonaid Ahmad Malik Sakeel Ahmed Verma Abhishek Kameshwar Jowaher Alanazi Abdulwahab Alamri Nafees Ahemad 《Molecules (Basel, Switzerland)》2022,27(22)
Cancer is the leading cause of death and has remained a big challenge for the scientific community. Because of the growing concerns, new therapeutic regimens are highly demanded to decrease the global burden. Despite advancements in chemotherapy, drug resistance is still a major hurdle to successful treatment. The primary challenge should be identifying and developing appropriate therapeutics for cancer patients to improve their survival. Multiple pathways are dysregulated in cancers, including disturbance in cellular metabolism, cell cycle, apoptosis, or epigenetic alterations. Over the last two decades, natural products have been a major research interest due to their therapeutic potential in various ailments. Natural compounds seem to be an alternative option for cancer management. Natural substances derived from plants and marine sources have been shown to have anti-cancer activity in preclinical settings. They might be proved as a sword to kill cancerous cells. The present review attempted to consolidate the available information on natural compounds derived from plants and marine sources and their anti-cancer potential underlying EMT mechanisms. 相似文献
28.
Chen Hui Sharma Sunil K. Sharma Priyanka R. Chi Kai Fung Eric Aubrecht Katherine Keroletswe Ngonye Chigome Samuel Hsiao Benjamin S. 《Cellulose (London, England)》2021,28(13):8611-8628
Cellulose - Mercury contamination in drinking water is a worldwide problem due to its severely harming effects on the human body. A nanostructured natural bioadsorbent, carboxycellulose nanofiber... 相似文献
29.
Improvement on Quantum Teleportation of Three and Four Qubit States Using Multi-Qubit Cluster States
Verma Vikram Singh Nidhi Singh Ravi S. 《International Journal of Theoretical Physics》2021,60(10):3973-3981
International Journal of Theoretical Physics - In 2016, Li et al. [Int. J. Theor. Phys. 55, 1820–1823 (2016)] proposed schemes for quantum teleportation of certain class of three and four... 相似文献
30.
Taurine is a naturally occurring sulfur-containing amino acid that is found abundantly in excitatory tissues, such as the heart, brain, retina and skeletal muscles. Taurine was first isolated in the 1800s, but not much was known about this molecule until the 1990s. In 1985, taurine was first approved as the treatment among heart failure patients in Japan. Accumulating studies have shown that taurine supplementation also protects against pathologies associated with mitochondrial defects, such as aging, mitochondrial diseases, metabolic syndrome, cancer, cardiovascular diseases and neurological disorders. In this review, we will provide a general overview on the mitochondria biology and the consequence of mitochondrial defects in pathologies. Then, we will discuss the antioxidant action of taurine, particularly in relation to the maintenance of mitochondria function. We will also describe several reported studies on the current use of taurine supplementation in several mitochondria-associated pathologies in humans. 相似文献