全文获取类型
收费全文 | 17074篇 |
免费 | 466篇 |
国内免费 | 119篇 |
专业分类
化学 | 12376篇 |
晶体学 | 149篇 |
力学 | 388篇 |
数学 | 2146篇 |
物理学 | 2600篇 |
出版年
2023年 | 77篇 |
2022年 | 96篇 |
2021年 | 185篇 |
2020年 | 242篇 |
2019年 | 221篇 |
2018年 | 173篇 |
2017年 | 158篇 |
2016年 | 325篇 |
2015年 | 320篇 |
2014年 | 380篇 |
2013年 | 732篇 |
2012年 | 1007篇 |
2011年 | 1276篇 |
2010年 | 616篇 |
2009年 | 517篇 |
2008年 | 1116篇 |
2007年 | 1111篇 |
2006年 | 1182篇 |
2005年 | 1206篇 |
2004年 | 1012篇 |
2003年 | 824篇 |
2002年 | 809篇 |
2001年 | 235篇 |
2000年 | 234篇 |
1999年 | 191篇 |
1998年 | 209篇 |
1997年 | 217篇 |
1996年 | 273篇 |
1995年 | 177篇 |
1994年 | 169篇 |
1993年 | 156篇 |
1992年 | 131篇 |
1991年 | 126篇 |
1990年 | 84篇 |
1989年 | 87篇 |
1988年 | 87篇 |
1987年 | 92篇 |
1986年 | 71篇 |
1985年 | 135篇 |
1984年 | 136篇 |
1983年 | 101篇 |
1982年 | 104篇 |
1981年 | 129篇 |
1980年 | 124篇 |
1979年 | 85篇 |
1978年 | 95篇 |
1977年 | 73篇 |
1976年 | 66篇 |
1975年 | 81篇 |
1973年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Hualong Song Simon J. Allison Viktor Brabec Hannah E. Bridgewater Jana Kasparkova Hana Kostrhunova Vojtech Novohradsky Roger M. Phillips Jitka Pracharova Nicola J. Rogers Samantha L. Shepherd Peter Scott 《Angewandte Chemie (International ed. in English)》2020,59(34):14677-14685
Monosaccharides are added to the hydrophilic face of a self‐assembled asymmetric FeII metallohelix, using CuAAC chemistry. The sixteen resulting architectures are water‐stable and optically pure, and exhibit improved antiproliferative selectivity against colon cancer cells (HCT116 p53+/+) with respect to the non‐cancerous ARPE‐19 cell line. While the most selective compound is a glucose‐appended enantiomer, its cellular entry is not mainly glucose transporter‐mediated. Glucose conjugation nevertheless increases nuclear delivery ca 2.5‐fold, and a non‐destructive interaction with DNA is indicated. Addition of the glucose units affects the binding orientation of the metallohelix to naked DNA, but does not substantially alter the overall affinity. In a mouse model, the glucose conjugated compound was far better tolerated, and tumour growth delays for the parent compound (2.6 d) were improved to 4.3 d; performance as good as cisplatin but with the advantage of no weight loss in the subjects. 相似文献
962.
Rhea C. Garcellano John R. Cort Syed G. A. Moinuddin Scott G. Franzblau Rui Ma 《Natural product research》2020,34(8):1175-1179
AbstractCoronaridine (1) was isolated from the CH2Cl2 root extract of Tabernaemontana ternifolia. The structure of 1 was established from 1D- and 2D-NMR and HR-ESIMS experiments, and by comparison with reported spectroscopic data. To date, this is the first report of compound 1 from T. ternifolia, introduced as new Tabernaemontana species from Philippines in 2005 on the basis of morphological characters. Coronaridine, an iboga-type indole alkaloid, has been isolated from over 50 Tabernaemontana species and can thus be inferred as a chemotaxonomic marker of the genus. T. ternifolia has a distinct arrangement of leaves not known in the genus, but is variable in other genera. Its isolation from endemic T. ternifolia establishes its position in the genus and supports the claim that coronaridine is a chemical marker of the genus Tabernaemontana. Interestingly, coronaridine exhibited relatively weak activity against Mycobacterium tuberculosis H37Rv (MIC 82.64?μg/mL) (Rifampicin MIC 0.05?μg/mL). 相似文献
963.
Meccanica - This study concerns the response of a spherical drop, attached to a sinusoidally vibrating wall. Given that the drop is spherical, the model is more realistic than that of a 2D drop... 相似文献
964.
Roselis A. Landaeta Aponte Andreas Luxenburger Scott A. Cameron Alex Weymouth-Wilson Richard H. Furneaux Lawrence D. Harris Benjamin J. Compton 《Molecules (Basel, Switzerland)》2022,27(7)
Bile acid receptors have been identified as important targets for the development of new therapeutics to treat various metabolic and inflammatory diseases. The synthesis of new bile acid analogues can help elucidate structure–activity relationships and define compounds that activate these receptors selectively. Towards this, access to large quantities of a chenodeoxycholic acid derivative bearing a C-12 methyl and a C-13 to C-14 double bond provided an interesting scaffold to investigate the chemical manipulation of the C/D ring junction in bile acids. The reactivity of this alkene substrate with various zinc carbenoid species showed that those generated using the Furukawa methodology achieved selective α-cyclopropanation, whereas those generated using the Shi methodology reacted in an unexpected manner giving rise to a rearranged skeleton whereby the C ring has undergone contraction to form a novel spiro–furan ring system. Further derivatization of the cyclopropanated steroid included O-7 oxidation and epimerization to afford new bile acid derivatives for biological evaluation. 相似文献
965.
Robert D. Barrows Mark J. Dresel Thomas J. Emge Paul R. Rablen Spencer Knapp 《Molecules (Basel, Switzerland)》2022,27(1)
The amidation reaction of a tetrahydroisoquinolin-1-one-4-carboxylic acid is a key step in the multi-kilogram-scale preparation of the antimalarial drug SJ733, now in phase 2 clinical trials. In the course of investigating THIQ carboxamidations, we found that propanephosphonic acid anhydride (T3P) is an effective reagent, although the yield and byproducts vary with the nature and quantity of the base. As a control, the T3P reaction of a 3-(2-thienyl) THIQ was performed in the absence of the amine, and the products were characterized: among them are three dimeric allenes and two dimeric lactones. A nucleophile-promoted ketene dimerization process subject to subtle steric and stereoelectronic effects accounts for their formation. Two novel monomeric products, a decarboxylated isoquinolone and a purple, fused aryl ketone, were also isolated, and mechanisms for their formation from the ketene intermediate are proposed. 相似文献
966.
Fatemeh Fadaei Michelle Seifert Joshua R. Raymond David eha Natalia Kulik Babak Minofar Mark P. Heitz 《Molecules (Basel, Switzerland)》2022,27(1)
Ionic liquids (ILs) have become nearly ubiquitous solvents and their interactions with biomolecules has been a focus of study. Here, we used the fluorescence emission of DAPI, a groove binding fluorophore, coupled with molecular dynamics (MD) simulations to report on interactions between imidazolium chloride ([Imn,1]+) ionic liquids and a synthetic DNA oligonucleotide composed entirely of T/A bases (7(TA)) to elucidate the effects ILs on a model DNA duplex. Spectral shifts on the order of 500–1000 cm−1, spectral broadening (~1000 cm−1), and excitation and emission intensity ratio changes combine to give evidence of an increased DAPI environment heterogeneity on added IL. Fluorescence lifetimes for DAPI/IL solutions yielded two time constants 0.15 ns (~80% to 60% contribution) and 2.36–2.71 ns for IL up to 250 mM. With DNA, three time constants were required that varied with added IL (0.33–0.15 ns (1–58% contribution), ~1.7–1.0 ns (~5% contribution), and 3.8–3.6 ns (94–39% contribution)). MD radial distribution functions revealed that π-π stacking interactions between the imidazolium ring were dominant at lower IL concentration and that electrostatic and hydrophobic interactions become more prominent as IL concentration increased. Alkyl chain alignment with DNA and IL-IL interactions also varied with IL. Collectively, our data showed that, at low IL concentration, IL was primarily bound to the DNA minor groove and with increased IL concentration the phosphate regions and major groove binding sites were also important contributors to the complete set of IL-DNA duplex interactions. 相似文献
967.
There have now been a number of experimental studies on the preparation and elastomeric properties of random bimodal networks of polydimethylsiloxane. The mole per cent of the short chains and their molecular masses covered a wide range, thus resulting in various polydisperse chain-length distributions. The networks were studied with regard to their stress-strain isotherms in elongation, and values of their moduli in the large-deformation (phantom) limit were found to depend on the chain-length distribution. This Important result is in disagreement with phantom network theory, which assumes the elastic modulus is dependent only on the mean value of chain lengths such that the cycle rank of the network is preserved. The effective functionality of the long chains was found to depend on the number of short chains present. Better agreement with experiment was obtained when account was taken of the connectivity of the very short chains, in what is essentially a bimodal distribution of both network chain lengths and cross-link functionalities. Relevant here is the fact that as the degree of chemical cross-linking Increases, the shear modulus G moves away from the affine limit, toward the phantom limit. This increase toward phantom behavior is presumably due to the fact that the mutual interspersion of chains is less when the chains are shorter, even in the small-strain region. 相似文献
968.
Navindra Keerthisinghe Matthew S. Christian Anna A. Berseneva Gregory Morrison Vladislav V. Klepov Mark D. Smith Hans-Conrad zur Loye 《Molecules (Basel, Switzerland)》2022,27(1)
The solvothermal synthesis, structure determination and optical characterization of five new metastable halometallate compounds, [1,10-phenH][Pb3.5I8] (1), [1,10-phenH2][Pb5I12]·(H2O) (2), [1,10-phen][Pb2I4] (3), [1,10-phen]2[Pb5Br10] (4) and [1,10-phenH][SbI4]·(H2O) (5), are reported. The materials exhibit rich structural diversity and exhibit structural dimensionalities that include 1D chains, 2D sheets and 3D frameworks. The optical spectra of these materials are consistent with bandgaps ranging from 2.70 to 3.44 eV. We show that the optical behavior depends on the structural dimensionality of the reported materials, which are potential candidates for semiconductor applications. 相似文献
969.
970.