全文获取类型
收费全文 | 3066篇 |
免费 | 71篇 |
国内免费 | 3篇 |
专业分类
化学 | 2246篇 |
晶体学 | 9篇 |
力学 | 37篇 |
数学 | 296篇 |
物理学 | 552篇 |
出版年
2022年 | 66篇 |
2021年 | 56篇 |
2020年 | 33篇 |
2019年 | 47篇 |
2016年 | 67篇 |
2015年 | 60篇 |
2014年 | 51篇 |
2013年 | 142篇 |
2012年 | 122篇 |
2011年 | 129篇 |
2010年 | 89篇 |
2009年 | 81篇 |
2008年 | 116篇 |
2007年 | 110篇 |
2006年 | 120篇 |
2005年 | 104篇 |
2004年 | 82篇 |
2003年 | 65篇 |
2002年 | 63篇 |
2001年 | 55篇 |
2000年 | 65篇 |
1999年 | 32篇 |
1998年 | 32篇 |
1996年 | 47篇 |
1995年 | 59篇 |
1994年 | 36篇 |
1993年 | 49篇 |
1992年 | 43篇 |
1991年 | 31篇 |
1990年 | 43篇 |
1989年 | 38篇 |
1988年 | 29篇 |
1987年 | 29篇 |
1986年 | 30篇 |
1984年 | 33篇 |
1982年 | 37篇 |
1981年 | 43篇 |
1980年 | 30篇 |
1979年 | 38篇 |
1978年 | 27篇 |
1977年 | 32篇 |
1976年 | 31篇 |
1974年 | 41篇 |
1973年 | 31篇 |
1968年 | 30篇 |
1967年 | 35篇 |
1966年 | 42篇 |
1965年 | 28篇 |
1964年 | 40篇 |
1963年 | 36篇 |
排序方式: 共有3140条查询结果,搜索用时 0 毫秒
101.
Molybdenum cofactor (Moco) deficiency (MoCD) is characterized by neonatal-onset myoclonic epileptic encephalopathy and dystonia with cerebral MRI changes similar to hypoxic–ischemic lesions. The molecular cause of the disease is the loss of sulfite oxidase (SOX) activity, one of four Moco-dependent enzymes in men. Accumulating toxic sulfite causes a secondary increase of metabolites such as S-sulfocysteine and thiosulfate as well as a decrease in cysteine and its oxidized form, cystine. Moco is synthesized by a three-step biosynthetic pathway that involves the gene products of MOCS1, MOCS2, MOCS3, and GPHN. Depending on which synthetic step is impaired, MoCD is classified as type A, B, or C. This distinction is relevant for patient management because the metabolic block in MoCD type A can be circumvented by administering cyclic pyranopterin monophosphate (cPMP). Substitution therapy with cPMP is highly effective in reducing sulfite toxicity and restoring biochemical homeostasis, while the clinical outcome critically depends on the degree of brain injury prior to the start of treatment. In the absence of a specific treatment for MoCD type B/C and SOX deficiency, we summarize recent progress in our understanding of the underlying metabolic changes in cysteine homeostasis and propose novel therapeutic interventions to circumvent those pathological changes. 相似文献
102.
Simona Rizzo Tiziana Benincori Francesca Fontana Dario Pasini Roberto Cirilli 《Molecules (Basel, Switzerland)》2022,27(23)
The chiral resolving ability of the commercially available amylose (3,5-dimethylphenylcarbamate)-based chiral stationary phase (CSP) toward four chiral probes representative of four kinds of stereogenicity (central, axial, helical, and planar) was investigated. Besides chirality, the evident structural feature of selectands is an extremely limited conformational freedom. The chiral rigid analytes were analyzed by using pure short alcohols as mobile phases at different column temperatures. The enantioselectivity was found to be suitable for all compounds investigated. This evidence confirms that the use of the amylose-based CSP in HPLC is an effective strategy for obtaining the resolution of chiral compounds containing any kind of stereogenic element. In addition, the experimental retention and enantioselectivity behavior, as well as the established enantiomer elution order of the investigated chiral analytes, may be used as key information to track essential details on the enantiorecognition mechanism of the amylose-based chiral stationary phase. 相似文献
103.
Aleksandra Ilic Jesper Schwarz Catherine Johnson Lisa H. M. de Groot Simon Kaufhold Reiner Lomoth Kenneth Wrnmark 《Chemical science》2022,13(32):9165
Fe–N-heterocyclic carbene (NHC) complexes attract increasing attention as photosensitisers and photoredox catalysts. Such applications generally rely on sufficiently long excited state lifetimes and efficient bimolecular quenching, which leads to there being few examples of successful usage of Fe–NHC complexes to date. Here, we have employed [Fe(iii)(btz)3]3+ (btz = (3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene))) in the addition of alkyl halides to alkenes and alkynes via visible light-mediated atom transfer radical addition (ATRA). Unlike other Fe–NHC complexes, [Fe(iii/ii)(btz)3]3+/2+ benefits from sizable charge transfer excited state lifetimes ≥0.1 ns in both oxidation states, and the Fe(iii) 2LMCT and Fe(ii) 3MLCT states are strong oxidants and reductants, respectively. The combined reactivity of both excited states enables efficient one-electron reduction of the alkyl halide substrate under green light irradiation. The two-photon mechanism proceeds via reductive quenching of the Fe(iii) 2LMCT state by a sacrificial electron donor and subsequent excitation of the Fe(ii) product to its highly reducing 3MLCT state. This route is shown to be more efficient than the alternative, where oxidative quenching of the less reducing Fe(iii) 2LMCT state by the alkyl halide drives the reaction, in the absence of a sacrificial electron donor.An iron complex with N-heterocyclic carbene ligands engages in efficient photoredox catalysis via excited state electron transfer reactions of its Fe(ii) and Fe(iii) oxidation states. 相似文献
104.
Herbal remedia are widely employed in folk medicine, and have been more and more often studied and considered in the treatment of several infections. Sarcoptic mange (scabies, when referring to human patients) is a highly contagious skin disease caused by Sarcoptes scabiei (sarcoptiformes, Sarcoptinae), an astigmatid mite which burrows into the epidermis, actively penetrating the stratum corneum. This parasitosis negatively affects livestock productions and represents a constraint on animal and human health. The treatment relies on permethrine and ivermectine but, since these molecules do not have ovicidal action, more than a single dose should be administered. Toxicity, the possible onset of parasite resistance, the presence of residues in meat and other animal products and environmental contamination are the major constraints. These shortcomings could be reduced by the use of plant extracts that have been in vitro or in vivo checked against these mites, sometimes with promising results. The aim of the present study was to review the literature dealing with the treatment of both scabies and sarcoptic mange by plant-derived agents, notably essential oils. 相似文献
105.
Simona Dedoni Valeria Avdoshina Chiara Camoglio Carlotta Siddi Walter Fratta Maria Scherma Paola Fadda 《Molecules (Basel, Switzerland)》2022,27(13)
COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global pandemic that might lead to very serious consequences. Notably, mental status change, brain confusion, and smell and taste disorders along with neurological complaints have been reported in patients infected with SARS-CoV-2. Furthermore, human brain tissue autopsies from COVID-19 patients show the presence of SARS-CoV-2 neuroinvasion, which correlates with the manifestation of meningitis, encephalitis, leukocyte infiltration, and neuronal damage. The olfactory mucosa has been suggested as a way of entry into the brain. SARS-CoV-2 infection is also known to provoke a hyper-inflammatory reaction with an exponential increase in the production of pro-inflammatory cytokines leading to systemic responses, even in the absence of direct infection of brain cells. Angiotensin-converting enzyme 2 (ACE2), the entry receptor of SARS-CoV-2, has been extensively demonstrated to be present in the periphery, neurons, and glial cells in different brain regions. To dissect the details of neurological complications and develop therapies helping COVID-19 survivors regain pre-infection quality of life, the development of robust clinical models is highly warranted. Several human angiotensin-converting enzyme 2 (hACE2) transgenic mouse models have been developed and used for antiviral drug screening and vaccine development, as well as for better understanding of the molecular pathogenetic mechanisms of SARS-CoV-2 infection. In this review, we summarize recent results from the studies involving two such mouse models, namely K18- and CAG-hACE2 transgenics, to evaluate the direct and indirect impact of SARS-CoV-2 infection on the central nervous system. 相似文献
106.
In this paper, we prove some inequalities between intrinsic and extrinsic curvature invariants, namely the normalized -Casorati curvatures and the scalar curvature of statistical submanifolds in Kenmotsu statistical manifolds of constant -sectional curvature that are endowed with semi-symmetric metric connection. Furthermore, we investigate the equality cases of these inequalities. We also describe an illustrative example. 相似文献
107.
Predoana Luminita Atkinson Irina Karaj Dániel Attila Odhiambo Vincent Otieno Bakos László Péter Nagyné Kovács Teodóra Pandele-Cusu Jeanina Petrescu Simona Rusu Adriana Szilágyi Imre M. Pokol György Zaharescu Maria 《Journal of Thermal Analysis and Calorimetry》2021,143(4):2893-2900
Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications... 相似文献
108.
Roberta Cassano Massimo Cuconato Gabriella Calviello Simona Serini Sonia Trombino 《Molecules (Basel, Switzerland)》2021,26(4)
Melanoma is one of the most aggressive forms of skin cancer, with few possibilities for therapeutic approaches, due to its multi-drug resistance and, consequently, low survival rate for patients. Conventional therapies for treatment melanoma include radiotherapy, chemotherapy, targeted therapy, and immunotherapy, which have various side effects. For this reason, in recent years, pharmaceutical and biomedical research has focused on new sito-specific alternative therapeutic strategies. In this regard, nanotechnology offers numerous benefits which could improve the life expectancy of melanoma patients with very low adverse effects. This review aims to examine the latest advances in nanotechnology as an innovative strategy for treating melanoma. In particular, the use of different types of nanoparticles, such as vesicles, polymers, metal-based, carbon nanotubes, dendrimers, solid lipid, microneedles, and their combination with immunotherapies and vaccines will be discussed. 相似文献
109.
110.
Binyamin Schwarz 《Israel Journal of Mathematics》1963,1(1):11-21
n particles (beads) of different masses are mounted at equally spaced points along a string which in itself is weightless,
of unit tension and fixed at its endpoints. Given the set of masses, it is shown that the principal frequency of this loaded
string becomes minimal if they are arranged decreasing from the center in as nearly a symmetrical order as possible. If a
strictly symmetrical increasing arrangement of the masses exists, then this arrangement gives the maximum of the principal
frequency.
Sponsored by the Mathematics Research Center, United States Army under Contract No. DA-11-022-ORD-2059, University of Wisconsin,
Madison. 相似文献