全文获取类型
收费全文 | 1019篇 |
免费 | 26篇 |
国内免费 | 6篇 |
专业分类
化学 | 714篇 |
晶体学 | 6篇 |
力学 | 24篇 |
数学 | 121篇 |
物理学 | 186篇 |
出版年
2022年 | 15篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 22篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 28篇 |
2015年 | 23篇 |
2014年 | 24篇 |
2013年 | 71篇 |
2012年 | 55篇 |
2011年 | 59篇 |
2010年 | 33篇 |
2009年 | 39篇 |
2008年 | 58篇 |
2007年 | 42篇 |
2006年 | 41篇 |
2005年 | 36篇 |
2004年 | 38篇 |
2003年 | 30篇 |
2002年 | 31篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1995年 | 11篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1969年 | 6篇 |
排序方式: 共有1051条查询结果,搜索用时 15 毫秒
51.
Harsha K. Tripathy S. V. Nair Manju Rama Murthy Bestha Vinay Kiran Sreekanth Dittakavi Ramesh Mullangi 《Biomedical chromatography : BMC》2022,36(8):e5387
In this study, we report the development and validation of an LC–tandem mass spectrometry method for the simultaneous quantitation of bendamustine and copanlisib in mouse plasma as per the US FDA regulatory guidelines. The sample processing involves extraction of bendamustine and copanlisib along with internal standard (IS; warfarin) from 50 μL mouse plasma using a liquid–liquid extraction method. The chromatographic separation of bendamustine, copanlisib and the IS was achieved on an Atlantis dC18 column using an isocratic mobile phase (5 mM ammonium acetate:methanol, 20:80 v/v). Bendamustine, copanlisib and the IS eluted at 0.88, 1.39 and 0.74 min, respectively, with a total run time of 2.5 min. The calibration curve ranged from 3.99–2996 and 4.33–3248 ng/mL for bendamustine and copanlisib, respectively. Inter- and intra-day precision and accuracy, stability in processed samples and upon storage, dilution integrity and incurred sample reanalysis were investigated for both the analytes. The intra- and inter-day precisions were in the ranges of 2.01%–5.05% and 2.74%–6.13% and 1.98%–7.64 and 8.62%–9.04% for bendamustine and copanlisib, respectively. Stability studies showed that both analytes were stable on bench top for 6 h, in auto-sampler for 24 and at −80°C for 30 days. The validated method was successfully applied to a pharmacokinetic study in mice. 相似文献
52.
Philippe Schwaller Riccardo Petraglia Valerio Zullo Vishnu H. Nair Rico Andreas Haeuselmann Riccardo Pisoni Costas Bekas Anna Iuliano Teodoro Laino 《Chemical science》2020,11(12):3316
We present an extension of our Molecular Transformer model combined with a hyper-graph exploration strategy for automatic retrosynthesis route planning without human intervention. The single-step retrosynthetic model sets a new state of the art for predicting reactants as well as reagents, solvents and catalysts for each retrosynthetic step. We introduce four metrics (coverage, class diversity, round-trip accuracy and Jensen–Shannon divergence) to evaluate the single-step retrosynthetic models, using the forward prediction and a reaction classification model always based on the transformer architecture. The hypergraph is constructed on the fly, and the nodes are filtered and further expanded based on a Bayesian-like probability. We critically assessed the end-to-end framework with several retrosynthesis examples from literature and academic exams. Overall, the frameworks have an excellent performance with few weaknesses related to the training data. The use of the introduced metrics opens up the possibility to optimize entire retrosynthetic frameworks by focusing on the performance of the single-step model only.We present an extension of our Molecular Transformer model combined with a hyper-graph exploration strategy for automatic retrosynthesis route planning without human intervention. 相似文献
53.
Khalid Naim Manjeet Singh Sachin Sharma Dr. Rajesh V. Nair Prof. Paloth Venugopalan Dr. Subash Chandra Sahoo Dr. Prakash P. Neelakandan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(52):11979-11984
The design of molecular compounds that exhibit flexibility is an emerging area of research. Although a fair amount of success has been achieved in the design of plastic or elastic crystals, realizing multidimensional plastic and elastic bending remains challenging. We report herein a naphthalidenimine–boron complex that showed size-dependent dual mechanical bending behavior whereas its parent Schiff base was brittle. Detailed crystallographic and spectroscopic analysis revealed the importance of boron in imparting the interesting mechanical properties. Furthermore, the luminescence of the molecule was turned-on subsequent to boron complexation, thereby allowing it to be explored for multimode optical waveguide applications. Our in-depth study of the size-dependent plastic and elastic bending of the crystals thus provides important insights in molecular engineering and could act as a platform for the development of future smart flexible materials for optoelectronic applications. 相似文献
54.
John Bacsa Maurice Okello Pankaj Singh Vasu Nair 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(3):285-288
The conformation and tautomeric structure of (Z)‐4‐[5‐(2,6‐difluorobenzyl)‐1‐(2‐fluorobenzyl)‐2‐oxo‐1,2‐dihydropyridin‐3‐yl]‐4‐hydroxy‐2‐oxo‐N‐(2‐oxopyrrolidin‐1‐yl)but‐3‐enamide, C27H22F3N3O5, in the solid state has been resolved by single‐crystal X‐ray crystallography. The electron distribution in the molecule was evaluated by refinements with invarioms, aspherical scattering factors by the method of Dittrich et al. [Acta Cryst. (2005), A 61 , 314–320] that are based on the Hansen–Coppens multipole model [Hansen & Coppens (1978). Acta Cryst. A 34 , 909–921]. The β‐diketo portion of the molecule exists in the enol form. The enol –OH hydrogen forms a strong asymmetric hydrogen bond with the carbonyl O atom on the β‐C atom of the chain. Weak intramolecular hydrogen bonds exist between the weakly acidic α‐CH hydrogen of the keto–enol group and the pyridinone carbonyl O atom, and also between the hydrazine N—H group and the carbonyl group in the β‐position from the hydrazine N—H group. The electrostatic properties of the molecule were derived from the molecular charge density. The molecule is in a lengthened conformation and the rings of the two benzyl groups are nearly orthogonal. Results from a high‐field 1H and 13C NMR correlation spectroscopy study confirm that the same tautomer exists in solution as in the solid state. 相似文献
55.
Paulson Mathew Satheesh K. Nair K. M. Sreedhar V. N. Rajasekharan Pillai 《合成通讯》2013,43(16):2157-2161
When α‐oxoketene dithioacetals 1a–n were treated with the bromine complex of a copolymer of 1‐vinyl‐2‐pyrrolidone and 4‐vinylpyridine, the corresponding thiolcarboxylates 2a–n were formed in excellent yields. The reaction also works with other 1‐vinyl‐2‐pyrrolidone‐derived polymers as well as commercially available polyvinylpyrrolidone–bromine complexes. The method is suitable for preparing aliphatic, aromatic, and γ,δ‐unsaturated β‐oxothiolcarboxylates. 相似文献
56.
Visalini Nair‐Shalliker Mark Clements Michael Fenech Bruce K Armstrong 《Photochemistry and photobiology》2013,89(1):208-214
Solar ultraviolet‐B radiation (UVB) is essential for epidermal vitamin D production. We aimed to quantitate the relationship between personal solar UV exposure and serum 25hydroxy vitamin D (25[OH]D) concentration. Blood was collected for 25(OH)D analysis in 207 South Australian adults aged 27–61 years. At the time of blood collection, each participant completed a questionnaire, which included a calendar for recall of sun exposure in the preceding 16 weeks. We examined the association between solar UV exposure and serum 25(OH)D graphically from smoothed scatter plots, and modeled it using multiple linear regression, with age, sex and body mass index as covariates. Estimated erythemal solar UV exposure in the 6 weeks before blood collection best predicted serum 25(OH)D concentrations. Serum 25(OH)D rose with increasing personal solar UV exposure to a maximum of about 89 nmol L?1 at an estimated mean weekly solar erythemal UV exposure of about 1230 mJ cm?2. The maximum was the same after accounting for clothing coverage and was reached at an estimated whole body equivalent exposure to ambient UV of ca 700 mJ cm?2. These results suggest that an average maximum serum 25(OH)D of ca 89 nmol L?1 is achieved from sun exposure in a healthy Australian adult population. 相似文献
57.
The O-glycosidation reaction of 1-O-acetyl-2,3-dideoxy-DL-pent-2-enopyran - 4 -ulose catalysed by the environmentally accepted and inexpensive industrial catalyst Montmorillonite K-10 clay with variety of alcohols in high yield is reported. 相似文献
58.
We give the first evidence that the director tilt angle can be reduced by electric fields in the tilted smectic phase of banana-shaped molecules. In these phases the value of polarization is determined by the molecular packing and no electro-clinic effect is expected. Our studies show that high electric fields eventually induce a meta-stable phase with zero director tilt. The tilted phase slowly recovers at low fields. We propose that the field-induced quenching of the layer fluctuations is responsible for the observed effects. 相似文献
59.
Employing actinic light to alter/stabilise a particular thermodynamic phase via the photo-isomerisation of the constituent molecules is an interesting tool to investigate soft matter from a new dimension. This article focuses on our recent results on several aspects of these non-equilibrium phase transitions, which are isothermal in nature. We specifically discuss (i) the influence of different parameters, such as confinement, applied electric field, pressure etc., on the dynamics associated with both the photochemical transition driving the equilibrium nematic to the non-equilibrium isotropic phase and the thermal back relaxation recovering the nematic phase, (ii) unique light-driven disorder–order transition in a reentrant system, (iii) dynamic self-assembly of the smectic A phase, which is stabilised only in the presence of actinic light, (iv) novel temperature-intensity phase diagrams and an example of primary and secondary photo-ferroelectric effects in an antiferroelectric smectic C system. These results highlight the fact that the actinic light can be used as a new tool to study phase transitions and the associated critical phenomena that could also bring about effects that are not seen in equilibrium situations. 相似文献
60.
Rajeev Rajasekharan‐Nair Dean Moore Dr. Kirsten Chalmers Dr. Dawn Wallace Louise M. Diamond Lisa Darby Dr. David R. Armstrong Dr. John Reglinski Dr. Mark D. Spicer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(7):2487-2495
The alkylation reactions of soft scorpionates are reported. The hydrotris(S‐alkyl‐methimazolyl)borate dications (alkyl=methyl, allyl, benzyl), which were prepared by the reaction of TmMe anion and primary alkyl halides, have been isolated and structurally characterised. The reaction is, however, not universally successful. DFT analysis of these alkylation reactions (C?S versus B? H alkylation) indicates that the observed outcome is driven by kinetic factors. Extending the study to incorporate alternative imine thiones (mercaptobenzothiazole, bz; thiazoline, tz) led to the structural characterisation of di[aquo‐μ‐aquohydrotris(mercaptobenzothiazolyl)boratosodium], which contains sodium atoms in the κ3‐S,S,S coordination mode. Alkylation of Na[Tbz] and Na[tzTtz] leads to decomposition resulting in the formation of the simple S‐alkylated heterocycles. The analysis of the species involved in these reactions shows an inherent weakness in the B? N bond in soft scorpionates, which has implications for their use in more advanced chemistry. 相似文献