全文获取类型
收费全文 | 4284篇 |
免费 | 213篇 |
国内免费 | 17篇 |
专业分类
化学 | 2759篇 |
晶体学 | 16篇 |
力学 | 86篇 |
数学 | 659篇 |
物理学 | 994篇 |
出版年
2023年 | 29篇 |
2022年 | 37篇 |
2021年 | 63篇 |
2020年 | 81篇 |
2019年 | 78篇 |
2018年 | 75篇 |
2017年 | 78篇 |
2016年 | 182篇 |
2015年 | 147篇 |
2014年 | 126篇 |
2013年 | 237篇 |
2012年 | 293篇 |
2011年 | 317篇 |
2010年 | 182篇 |
2009年 | 132篇 |
2008年 | 266篇 |
2007年 | 230篇 |
2006年 | 195篇 |
2005年 | 214篇 |
2004年 | 178篇 |
2003年 | 163篇 |
2002年 | 146篇 |
2001年 | 58篇 |
2000年 | 45篇 |
1999年 | 54篇 |
1998年 | 42篇 |
1997年 | 33篇 |
1996年 | 47篇 |
1995年 | 26篇 |
1994年 | 40篇 |
1993年 | 46篇 |
1992年 | 50篇 |
1991年 | 30篇 |
1990年 | 39篇 |
1989年 | 35篇 |
1988年 | 41篇 |
1987年 | 29篇 |
1986年 | 30篇 |
1985年 | 57篇 |
1984年 | 35篇 |
1983年 | 23篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 26篇 |
1977年 | 23篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1974年 | 23篇 |
1973年 | 20篇 |
排序方式: 共有4514条查询结果,搜索用时 671 毫秒
911.
Christopher J. H. Smalley Harriet E. Hoskyns Colan E. Hughes Duncan N. Johnstone Tom Willhammar Mark T. Young Christopher J. Pickard Andrew J. Logsdail Paul A. Midgley Kenneth D. M. Harris 《Chemical science》2022,13(18):5277
We report the crystal structure of a new polymorph of l-tyrosine (denoted the β polymorph), prepared by crystallization from the gas phase following vacuum sublimation. Structure determination was carried out by combined analysis of three-dimensional electron diffraction (3D-ED) data and powder X-ray diffraction (XRD) data. Specifically, 3D-ED data were required for reliable unit cell determination and space group assignment, with structure solution carried out independently from both 3D-ED data and powder XRD data, using the direct-space strategy for structure solution implemented using a genetic algorithm. Structure refinement was carried out both from powder XRD data, using the Rietveld profile refinement technique, and from 3D-ED data. The final refined structure was validated both by periodic DFT-D calculations, which confirm that the structure corresponds to an energy minimum on the energy landscape, and by the fact that the values of isotropic 13C NMR chemical shifts calculated for the crystal structure using DFT-D methodology are in good agreement with the experimental high-resolution solid-state 13C NMR spectrum. Based on DFT-D calculations using the PBE0-MBD method, the β polymorph is meta-stable with respect to the previously reported crystal structure of l-tyrosine (now denoted the α polymorph). Crystal structure prediction calculations using the AIRSS approach suggest that there are three other plausible crystalline polymorphs of l-tyrosine, with higher energy than the α and β polymorphs.A new polymorph of l-tyrosine is reported, with the crystal structure determined by combined analysis of 3D-ED data and powder XRD data, augmented by information from periodic DFT-D calculations and solid-state 13C NMR data. 相似文献
912.
Roberto Fernndez-Acosta Claudia Iriarte-Mesa Daniel Alvarez-Alminaque Behrouz Hassannia Bartosz Wiernicki Alicia M. Díaz-García Peter Vandenabeele Tom Vanden Berghe Gilberto L. Pardo Andreu 《Molecules (Basel, Switzerland)》2022,27(13)
The use of nanomaterials rationally engineered to treat cancer is a burgeoning field that has reported great medical achievements. Iron-based polymeric nano-formulations with precisely tuned physicochemical properties are an expanding and versatile therapeutic strategy for tumor treatment. Recently, a peculiar type of regulated necrosis named ferroptosis has gained increased attention as a target for cancer therapy. Here, we show for the first time that novel iron oxide nanoparticles coated with gallic acid and polyacrylic acid (IONP–GA/PAA) possess intrinsic cytotoxic activity on various cancer cell lines. Indeed, IONP–GA/PAA treatment efficiently induces ferroptosis in glioblastoma, neuroblastoma, and fibrosarcoma cells. IONP–GA/PAA-induced ferroptosis was blocked by the canonical ferroptosis inhibitors, including deferoxamine and ciclopirox olamine (iron chelators), and ferrostatin-1, the lipophilic radical trap. These ferroptosis inhibitors also prevented the lipid hydroperoxide generation promoted by the nanoparticles. Altogether, we report on novel ferroptosis-inducing iron encapsulated nanoparticles with potent anti-cancer properties, which has promising potential for further in vivo validation. 相似文献
913.
Nitrogen-containing heterocycles represent the majority of FDA-approved small-molecule pharmaceuticals. Herein, we describe a synthetic method to produce saturated N-heterocyclic drug scaffolds with an internal alkyne for elaboration. The treatment of N,N-dimethylhydrazinoalkenes with Et2Zn, followed by a Cu(I)-catalyzed cross-coupling with 1-bromoalkynes, results in piperidines and pyrrolidines with a good yield. Five examples are reported and a proposed mechanism for the Cu(I)-catalyzed cross-coupling is presented. 相似文献
914.
With an ever-growing emphasis on sustainable synthesis, aerobic C–H activation (the use of oxygen in air to activate C–H bonds) represents a highly attractive conduit for the development of novel synthetic methodologies. Herein, we report the air mediated functionalisation of various saturated heterocycles and ethers via aerobically generated radical intermediates to form new C–C bonds using acetylenic and vinyl triflones as radical acceptors. This enables access to a variety of acetylenic and vinyl substituted saturated heterocycles that are rich in synthetic value. Mechanistic studies and control reactions support an aerobic radical-based C–H activation mechanism.Herein we disclose a novel method for the aerobic C–H activation of ethereal-based heterocycles to generate various α-functionalised building blocks. 相似文献
915.
Dr. Miguel Ángel Revuelta-Maza Elena de las Heras Dr. Montserrat Agut Prof. Santi Nonell Prof. Tomás Torres Dr. Gema de la Torre 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(15):4955-4963
Herein, the photodynamic activity of phthalocyanine (pc)-assembled nanoparticles against bacterial strains is demonstrated. The photosensitizers (PS) studied in this work are two chiral ZnIIPcs ( PS-1 and PS-2 ), with an AABB geometry (where A and B refer to differently substituted isoindole constituents). They contain differently functionalized, chiral binaphthyloxy-linked A isoindole units, which determine the hydrophobicity of the system, and cationic methyl pyridinium moieties in the other two isoindoles to embody hydrophilicity. Both compounds have the ability to self-assemble into nanoparticles in aqueous media and have proved efficient in the photo-inactivation of Staphylococcus aureus and Escherichia coli, selected as models of Gram-positive and Gram-negative bacteria. The average size of the nanoparticles was determined by substitution at the binaphthyl core and, in turn, influences the toxicity of the PS. Thus, PS-1 , presenting a nonsubstituted binaphthyl core, forms larger nanoparticles with a larger cationic surface than the octyl-functionalized PS-2 . Although both PSs present similar structure and photophysical features, the self-assembled nanostructures of PS-1 are more effective at killing both types of strain, showing an outstanding photo-inactivation capacity with the Gram-negative E. coli. 相似文献
916.
917.
This article is concerned with the Stokes system with nonhomogeneous source terms and nonhomogeneous Dirichlet boundary condition. First, we reformulate the problem in its dual mixed form, and then, we study its corresponding well-posedness. Next, in order to circumvent the well-known Babuška-Brezzi condition, we analyze a stabilized formulation of the resulting approach. Additionally, we endow the scheme with an a posteriori error estimator that is reliable and efficient. Finally, we provide numerical experiments that illustrate the performance of the corresponding adaptive algorithm and support its use in practice. 相似文献
918.
919.
920.
R. Zeisler S. F. Stone R. P. Viscidi E. H. Cerny 《Journal of Radioanalytical and Nuclear Chemistry》1993,167(2):445-452
The feasibility of performing immunoassays with colloidal gold labels and detection of198Au by neutron activation has been demonstrated with measurements of human immunoglobulin and of serum antibodies to human immunodeficiency virus type 1. The detection sensitivity achieved after activation in a high flux reactor or with a water moderated252Cf source, by gamma-counting or by autoradiography, is similar to the sensitivity obtained with absorbance measurements in the more common enzyme immunoassays. The reactor based neutron activation assay allows detection of 10–16 mol of analyte in routine operation with possible extension to 10–20 mol. The sensitivity with the 1.3 Ci252Cf source is limited to about 10–15 mol. The practical limitations of the assay's sensitivity at this point are due to background signals from reagents and/or nonspecific binding of the gold labeled reagent. 相似文献