全文获取类型
收费全文 | 373篇 |
免费 | 20篇 |
专业分类
化学 | 307篇 |
力学 | 9篇 |
数学 | 18篇 |
物理学 | 59篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 17篇 |
2013年 | 17篇 |
2012年 | 29篇 |
2011年 | 33篇 |
2010年 | 23篇 |
2009年 | 18篇 |
2008年 | 30篇 |
2007年 | 32篇 |
2006年 | 25篇 |
2005年 | 20篇 |
2004年 | 19篇 |
2003年 | 20篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1909年 | 2篇 |
1908年 | 1篇 |
1905年 | 4篇 |
排序方式: 共有393条查询结果,搜索用时 531 毫秒
41.
Density Functional Theory and post‐Hartree Fock calculations reveal an unusual energy profile for Zn? S and Zn? N bond dissociation reactions in several [Zn(SR)4]2? and [Zn(Im)(SR)3]? complexes. The Zn? S bond dissociation in tetrathiolate dianions, which is highly exothermic in the gas phase, proceeds through a late transition state which can be rationalized on the basis of an avoided crossing resulting from Coulomb repulsion between the anionic fragments and ligand‐to‐metal charge‐transfer in the [Zn(SR)4]2? complexes. When solvation models for water, DMSO, or acetonitrile are included, some complexes become stable while others are metastable, so this constitutes the first theoretical model which is in full agreement with the experimental data for various [Zn(SR)4]2?, [Zn(SR)3]?, and [Zn(Im)(SR)3]? complexes. The analysis given here indicates that the Zn(Cys)4 and Zn(His)(Cys)3 cores of numerous proteins are metastable with respect to Zn? S and Zn? N bond dissociation, respectively. This is consistent with the kinetic lability at the zinc‐centers and illustrates that in nature, thermodynamic stability is imparted upon the zinc cores by the protein environment. 相似文献
42.
43.
44.
Methods are developed and analyzed for estimating the distance to a local minimizer of a nonlinear programming problem. One estimate, based on the solution of a constrained convex quadratic program, can be used when strict complementary slackness and the second-order sufficient optimality conditions hold. A second estimate, based on the solution of an unconstrained nonconvex, nonsmooth optimization problem, is valid even when strict complementary slackness is violated. Both estimates are valid in a neighborhood of a local minimizer. An active set algorithm is developed for computing a stationary point of the nonsmooth error estimator. Each iteration of the algorithm requires the solution of a symmetric, positive semidefinite linear system, followed by a line search. Convergence is achieved in a finite number of iterations. The error bounds are based on stability properties for nonlinear programs. The theory is illustrated by some numerical examples. 相似文献
45.
Delphine Chan‐Seng Michael K. Georges 《Journal of polymer science. Part A, Polymer chemistry》2006,44(13):4027-4038
Living radical polymerizations of styrene were performed under emulsion atom transfer radical polymerization conditions with latexes prepared by a nanoprecipitation technique recently developed for the stable free‐radical polymerization process. Latexes were prepared by the precipitation of a solution of low‐molecular‐weight polystyrene in acetone into a solution of a surfactant in water. The resulting particles were swollen with styrene and then heated. The effects of various surfactants and hydrophobic ligands, the reaction temperature, and the ligand/copper(I) bromide ratio were studied. The best results were obtained with the nonionic surfactant Brij 98 in combination with the hydrophobic ligand N,N‐bis(2‐pyridylmethyl)octadecylamine and a ligand/copper(I) bromide ratio of 1.5 at a reaction temperature of 85–90 °C. Under these conditions, latexes with good colloidal stability with average particle diameters of 200 nm were obtained. The molecular weight distributions of the polystyrenes were narrow, although the experimental molecular weights were slightly larger than the theoretical ones because not all the macroinitiator appeared to reinitiate. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4027–4038, 2006 相似文献
46.
Marie Kueny-StotzHind Mamlouk-Chaouachi Delphine Felder-Flesch 《Tetrahedron letters》2011,52(22):2906-2909
In the last decade, methods for the precise localization of sentinel lymph node (SLN) have drawn tremendous attention by oncology surgeons and researchers in the field of medical diagnosis. The accurate identification and characterization of lymph nodes by imaging has important therapeutic and prognostic significance in patients with newly diagnosed cancers. The SLN is the first lymph node that receives lymphatic drainage from the site of a primary tumor. Two biocompatible dendronized phosphonates, one bearing a Patent Blue (PB VF) dye at its periphery, where synthesized. Indeed, such a blue dye is currently injected to label the lymph node system for its per-operative detection. Therefore, developing chemistry of Patent Blue VF to optimize early diagnosis is of great current interest. 相似文献
47.
A copper(I)-catalyzed reaction of a variety of 4-aryl-pent-4-enoates with nosyliminoiodane generated in situ provides the corresponding 5-aryl-5-nosylamidomethylbutyrolactones. The reaction presumably proceeds via an aziridine intermediate, which could be isolated in one case. 相似文献
48.
Quantitative and sensitive detection of rare mutations using droplet-based microfluidics 总被引:2,自引:0,他引:2
Pekin D Skhiri Y Baret JC Le Corre D Mazutis L Salem CB Millot F El Harrak A Hutchison JB Larson JW Link DR Laurent-Puig P Griffiths AD Taly V 《Lab on a chip》2011,11(13):2156-2166
Somatic mutations within tumoral DNA can be used as highly specific biomarkers to distinguish cancer cells from their normal counterparts. These DNA biomarkers are potentially useful for the diagnosis, prognosis, treatment and follow-up of patients. In order to have the required sensitivity and specificity to detect rare tumoral DNA in stool, blood, lymph and other patient samples, a simple, sensitive and quantitative procedure to measure the ratio of mutant to wild-type genes is required. However, techniques such as dual probe TaqMan(?) assays and pyrosequencing, while quantitative, cannot detect less than ~1% mutant genes in a background of non-mutated DNA from normal cells. Here we describe a procedure allowing the highly sensitive detection of mutated DNA in a quantitative manner within complex mixtures of DNA. The method is based on using a droplet-based microfluidic system to perform digital PCR in millions of picolitre droplets. Genomic DNA (gDNA) is compartmentalized in droplets at a concentration of less than one genome equivalent per droplet together with two TaqMan(?) probes, one specific for the mutant and the other for the wild-type DNA, which generate green and red fluorescent signals, respectively. After thermocycling, the ratio of mutant to wild-type genes is determined by counting the ratio of green to red droplets. We demonstrate the accurate and sensitive quantification of mutated KRAS oncogene in gDNA. The technique enabled the determination of mutant allelic specific imbalance (MASI) in several cancer cell-lines and the precise quantification of a mutated KRAS gene in the presence of a 200,000-fold excess of unmutated KRAS genes. The sensitivity is only limited by the number of droplets analyzed. Furthermore, by one-to-one fusion of drops containing gDNA with any one of seven different types of droplets, each containing a TaqMan(?) probe specific for a different KRAS mutation, or wild-type KRAS, and an optical code, it was possible to screen the six common mutations in KRAS codon 12 in parallel in a single experiment. 相似文献
49.
Dr. Valérie Alain‐Rizzo Delphine Drouin‐Kucma Cédric Rouxel Dr. Issa Samb Jérémy Bell Dr. Patrick Y. Toullec Dr. Véronique Michelet Dr. Isabelle Leray Dr. Mireille Blanchard‐Desce 《化学:亚洲杂志》2011,6(4):1080-1091
A series of rod‐shaped and related three‐branched push–pull derivatives containing phosphane oxide or phosphane sulfide (PO or PS)—as an electron‐withdrawing group conjugated to electron‐donating groups, such as amino or ether groups, with a conjugated rod consisting of arylene–vinylene or arylene–ethynylene building blocks—were prepared. These compounds were efficiently synthesized by a Grignard reaction followed by Sonogashira coupling. Their photophysical properties including absorption, emission, time‐resolved fluorescence, and two‐photon absorption (TPA) were investigated with special attention to structure–property relationships. These fluorophores show high fluorescence quantum yields and solvent‐dependent experiments reveal that efficient intramolecular charge transfer occurs upon excitation, thereby leading to highly polar excited states, the polarity of which can be significantly enhanced by playing on the end groups and conjugated linker. Rod‐shaped and related three‐branched systems show similar fluorescence properties in agreement with excitation localization on one of the push–pull branches. By using stronger electron donors or replacing the arylene–ethynylene linkers with an arylene–vinylene one induces significant redshifts of both the low‐energy one‐photon absorption and TPA bands. Interestingly, a major enhancement in TPA responses is observed, whereas OPA intensities are only weakly affected. Similarly, phosphane oxide derivatives show similar OPA responses than the corresponding sulfides but their TPA responses are significantly larger. Finally, the electronic coupling between dipolar branches promoted by common PO or PS acceptor moieties induces either slight enhancement of the TPA responses or broadening of the TPA band in the near infrared (NIR) region. Such behavior markedly contrasts with triphenylamine‐core‐mediated coupling, which gives evidence for the different types of interactions between branches. 相似文献