全文获取类型
收费全文 | 3838篇 |
免费 | 91篇 |
国内免费 | 20篇 |
专业分类
化学 | 2236篇 |
晶体学 | 22篇 |
力学 | 233篇 |
数学 | 748篇 |
物理学 | 710篇 |
出版年
2023年 | 24篇 |
2022年 | 62篇 |
2021年 | 65篇 |
2020年 | 58篇 |
2019年 | 69篇 |
2018年 | 49篇 |
2017年 | 58篇 |
2016年 | 133篇 |
2015年 | 105篇 |
2014年 | 108篇 |
2013年 | 223篇 |
2012年 | 238篇 |
2011年 | 228篇 |
2010年 | 154篇 |
2009年 | 132篇 |
2008年 | 218篇 |
2007年 | 226篇 |
2006年 | 188篇 |
2005年 | 171篇 |
2004年 | 199篇 |
2003年 | 146篇 |
2002年 | 146篇 |
2001年 | 48篇 |
2000年 | 36篇 |
1999年 | 40篇 |
1998年 | 43篇 |
1997年 | 48篇 |
1996年 | 57篇 |
1995年 | 44篇 |
1994年 | 44篇 |
1993年 | 32篇 |
1992年 | 37篇 |
1991年 | 29篇 |
1990年 | 28篇 |
1989年 | 18篇 |
1988年 | 33篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 44篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 33篇 |
1980年 | 28篇 |
1979年 | 29篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1974年 | 17篇 |
排序方式: 共有3949条查询结果,搜索用时 15 毫秒
991.
We apply the method of Dalgarno and Lewis to scattering states and discuss the choice of the unperturbed model in order to have a convergent perturbation series for the phase shift. We show that a recently proposed approach is a particular case of the method of Dalgarno and Lewis. 相似文献
992.
Damiana Scuteri Laura Rombol Takafumi Hayashi Chizuko Watanabe Shinobu Sakurada Kengo Hamamura Tsukasa Sakurada Paolo Tonin Giacinto Bagetta Luigi A. Morrone Maria Tiziana Corasaniti 《Molecules (Basel, Switzerland)》2022,27(15)
Chronic pain is one of the most common causes of the need for clinical evaluation, acquiring more importance in the elderly with cognitive impairment. Reduced self-reporting capabilities cause unrelieved pain contributing to the development of agitation. Safe and effective pain treatment can afford the management of agitation without the serious increase in death risk associated with neuroleptics. To this aim, the essential oil of bergamot (BEO), proven by rigorous evidence to have strong preclinical anti-nociceptive and anti-allodynic properties, has been engineered (NanoBEO, patent EP 4003294) to allow randomized, double-blind, placebo-controlled trials (BRAINAID, ). The present study: (1) assesses the analgesic effects of a single therapeutic dose of NanoBEO, as supplied by an airless dispenser for clinical translation, in models of inflammatory, neuropathic, and sensitization types of pain relevant to clinic; (2) provides a dose–response analysis of the efficacy of NanoBEO on scratching behavior, a typical behavioral disturbance occurring in dementia. A single therapeutic dose of NanoBEO confirms efficacy following thirty minutes pre-treatment with capsaicin and on the central sensitization phase induced by formalin. Moreover, it has an ID50 of 0.6312 mg and it is efficacious on static and dynamic mechanical allodynia. Altogether, the gathered results strengthen the potential of NanoBEO for clinical management of pain and agitation. NCT04321889相似文献
993.
994.
995.
We propose to measure the universal constant of gravity G in space by means of a small scale planetary system in geosynchronous orbit; test particle satellites of different nuclear composition and with different distances from the central mass would allow one to check possible variations with material and distance. With current technology G can be measured with a relative accuracy of 10−5 or better depending on the capability of controlling some perturbations which act at the level of 10−6 (i.e. ≈ 10−11 cm s−2; however, particular dynamical configurations mutuated from celestial mechanics should allow detection of differential effects with composition and distance (if any) to at least 10−6. Distance variations will be detected only if acting on a distance scale of 10 m. 相似文献
996.
997.
Edoardo Raciti Sai Manoj Gali Michele Melchionna Giacomo Filippini Arianna Actis Mario Chiesa Manuela Bevilacqua Paolo Fornasiero Maurizio Prato David Beljonne Roberto Lazzaroni 《Chemical science》2022,13(34):9927
Graphitic carbon nitride (gCN) is an important heterogeneous metal-free catalytic material. Thermally induced post-synthetic modifications, such as amorphization and/or reduction, were recently used to enhance the photocatalytic response of these materials for certain classes of organic transformations, with structural defects possibly playing an important role. The knowledge of how these surface modifications modulate the photocatalytic response of gCN is therefore not only interesting from a fundamental point of view, but also necessary for the development and/or tuning of metal-free gCN systems with superior photo-catalytic properties. Herein, employing density functional theory calculations and combining both the periodic and molecular approaches, in conjunction with experimental EPR measurements, we demonstrate that different structural defects on the gCN surface generate distinctive radical defect states localized within the electronic bandgap, with only those correlated with amorphous and reduced gCN structures being photo-active. To this end, we (i) model defective gCN surfaces containing radical defect states; (ii) assess the interactions of these defects with the radical precursors involved in the photo-driven alkylation of electron-rich aromatic compounds (namely perfluoroalkyl iodides); and (iii) describe the photo-chemical processes triggering the initial step of that reaction at the gCN surface. We provide a coherent structure/photo-catalytic property relationship on defective gCN surfaces, elaborating how only specific defect types act as binding sites for the perfluoroalkyl iodide reagent and can favor a photo-induced charge transfer from the gCN surface to the molecule, thus triggering the perfluoroalkylation reaction.The nature of radical defects governs the photocatalytic activity of graphitic carbon nitride. 相似文献
998.
Valentina Stoppa Edoardo Battistel Marco Baron Paolo Sgarbossa Andrea Biffis Gregorio Bottaro Lidia Armelao Cristina Tubaro 《Molecules (Basel, Switzerland)》2022,27(13)
The use of alkynyl gold(I) complexes covers different research fields, such as bioinorganic chemistry, catalysis, and material science, considering the luminescent properties of the complexes. Regarding this last application, we report here the synthesis of three novel dinuclear gold(I) complexes of the general formula [(diNHC)(Au-C≡CPh)2]: two Au-C≡CPh units are connected by a bridging di(N-heterocyclic carbene) ligand, which should favor the establishment of semi-supported aurophilic interactions. The complexes can be easily synthesized through mechanochemistry upon reacting the pristine dibromido complexes [(diNHC)(AuBr)2] with phenylacetylene and KOH. Interestingly, we were also able to isolate the monosubstituted complex [(diNHC)(Au-C≡CPh)(AuBr)]. The gold(I) species were fully characterized by multinuclear NMR spectroscopy and mass spectrometry. The emission properties were also evaluated, and the salient data are comparable to those of analogous compounds reported in the literature. 相似文献
999.
Extended Reaction Scope of Thiamine Diphosphate Dependent Cyclohexane‐1,2‐dione Hydrolase: From CC Bond Cleavage to CC Bond Ligation 下载免费PDF全文
Dipl.‐Chem. Sabrina Loschonsky Dipl.‐Chem. Tobias Wacker Simon Waltzer Dr. Pier Paolo Giovannini Prof. Dr. Michael J. McLeish Prof. Dr. Susana L. A. Andrade Prof. Dr. Michael Müller 《Angewandte Chemie (International ed. in English)》2014,53(52):14402-14406
ThDP‐dependent cyclohexane‐1,2‐dione hydrolase (CDH) catalyzes the C? C bond cleavage of cyclohexane‐1,2‐dione to 6‐oxohexanoate, and the asymmetric benzoin condensation between benzaldehyde and pyruvate. One of the two reactivities of CDH was selectively knocked down by mutation experiments. CDH‐H28A is much less able to catalyze the C? C bond formation, while the ability for C? C bond cleavage is still intact. The double variant CDH‐H28A/N484A shows the opposite behavior and catalyzes the addition of pyruvate to cyclohexane‐1,2‐dione, resulting in the formation of a tertiary alcohol. Several acyloins of tertiary alcohols are formed with 54–94 % enantiomeric excess. In addition to pyruvate, methyl pyruvate and butane‐2,3‐dione are alternative donor substrates for C? C bond formation. Thus, the very rare aldehyde–ketone cross‐benzoin reaction has been solved by design of an enzyme variant. 相似文献
1000.
John Hanna El‐Nakat Noha Ghanem Paolo Yammine Gary Willett Keith Fisher 《International journal of quantum chemistry》2007,107(6):1367-1372
Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR/MS) offers the opportunity for gas phase cluster formation reactions at very low pressures and at temperatures that are different from room temperature. Reactions take place with single positive‐charge metal ions that are normally +2, +3, +4, etc., charged in solution. The ions formed are detected by measuring the current induced by their cyclotron rotation, but they cannot be physically separated and collected. Collision‐induced dissociation (CID) is widely used for ion‐structure determination via the fragmentation of the excited ions. CID study aims to determine the relationship between the Vpp [peak‐to‐peak voltage of the radiofrequency (rf) pulse] and the mass‐to‐charge (m/z) ratio, which will be used for the calculation of the center‐of‐mass translational kinetic energy (Ekcm) of the excited ion under investigation. CID studies are restricted to stable ions with relatively high abundance. Nevertheless, with the evolution of computational chemistry, such problems can be overcome whereby CID calculations will be used to provide the substantial parameters for computer software, such as the Gaussian 03 program, for the structure determination of the less stable NixS anions. The latter constitutes the core for our current research. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献