全文获取类型
收费全文 | 15476篇 |
免费 | 2571篇 |
国内免费 | 1911篇 |
专业分类
化学 | 11341篇 |
晶体学 | 227篇 |
力学 | 861篇 |
综合类 | 147篇 |
数学 | 1613篇 |
物理学 | 5769篇 |
出版年
2024年 | 63篇 |
2023年 | 318篇 |
2022年 | 563篇 |
2021年 | 575篇 |
2020年 | 589篇 |
2019年 | 652篇 |
2018年 | 526篇 |
2017年 | 510篇 |
2016年 | 719篇 |
2015年 | 734篇 |
2014年 | 933篇 |
2013年 | 1233篇 |
2012年 | 1431篇 |
2011年 | 1547篇 |
2010年 | 1037篇 |
2009年 | 1010篇 |
2008年 | 1015篇 |
2007年 | 990篇 |
2006年 | 800篇 |
2005年 | 683篇 |
2004年 | 580篇 |
2003年 | 443篇 |
2002年 | 414篇 |
2001年 | 350篇 |
2000年 | 328篇 |
1999年 | 252篇 |
1998年 | 218篇 |
1997年 | 170篇 |
1996年 | 185篇 |
1995年 | 148篇 |
1994年 | 157篇 |
1993年 | 118篇 |
1992年 | 115篇 |
1991年 | 94篇 |
1990年 | 87篇 |
1989年 | 77篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 42篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Zhong‐Lu You Hai‐Liang Zhu 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(12):m623-m624
The title complex, [Ag(C7H5O2)(C4H5N3)]n, is a polymer based on a mononuclear silver(I)‐centered fragment. The AgI atom is trigonally coordinated by two N atoms from two 2‐aminopyrimidine ligands and one O atom from one benzoate anion, giving zigzag polymeric chains with an [–Ag—N—C—N–]n backbone running along the a axis. It is proposed that intermolecular hydrogen bonding drives the formation of the chain polymer. 相似文献
992.
Asanuma H Toda T Murayama K Liang X Kashida H 《Journal of the American Chemical Society》2010,132(42):14702-14703
A new foldamer, acyclic threoninol nucleic acid (aTNA), has been synthesized by tethering each of the genetic nucleobases A, G, C, and T to d-threoninol molecules, which were then incorporated as building blocks into a scaffold bearing phosphodiester linkages. We found that with its fully complementary strand in an antiparallel fashion, the aTNA oligomer forms an exceptionally stable duplex that is far more stable than corresponding DNA or RNA duplexes, even though single-stranded aTNA is rather flexible and thus does not take a preorganized structure. 相似文献
993.
Meriles CA Jiang L Goldstein G Hodges JS Maze J Lukin MD Cappellaro P 《The Journal of chemical physics》2010,133(12):124105
Magnetic resonance imaging can characterize and discriminate among tissues using their diverse physical and biochemical properties. Unfortunately, submicrometer screening of biological specimens is presently not possible, mainly due to lack of detection sensitivity. Here we analyze the use of a nitrogen-vacancy center in diamond as a magnetic sensor for nanoscale nuclear spin imaging and spectroscopy. We examine the ability of such a sensor to probe the fluctuations of the "classical" dipolar field due to a large number of neighboring nuclear spins in a densely protonated sample. We identify detection protocols that appropriately take into account the quantum character of the sensor and find a signal-to-noise ratio compatible with realistic experimental parameters. Through various example calculations we illustrate different kinds of image contrast. In particular, we show how to exploit the comparatively long nuclear spin correlation times to reconstruct a local, high-resolution sample spectrum. 相似文献
994.
A series of bipolar-transporting europium(III) complexes containing carbazole and oxadiazole units were synthesized and characterized. Two intense UV absorption bands at around 286 nm and 352 nm, and sharply red emissions peaked at 614 nm were observed for these europium complexes in dichloromethane. Importantly, the bipolar-transporting europium(III) complexes exhibited higher thermal stability, more intense UV absorption at 286 nm and twofold increased photoluminescent quantum yield compared to the reported red chromophore of tri(dibenzoylmethane) (1,10-phenanthroline) europium(III). 相似文献
995.
996.
Linping Mu Zhiqun He Prof. Xiangfei Kong Guanbao Hui Min Xu Chunjun Liang Dr. Xiping Jing Dr. Andrzej Danel Dr. Ewa Kulig Dr. 《Chemphyschem》2010,11(12):2623-2629
Pyrazolo[3,4‐b]quinoline derivatives are reported to be highly efficient organic fluorescent materials suitable for applications in light‐emitting devices. Although their fluorescence remains stable in organic solvents or in aqueous solution even in the presence of H2O, halide salts (LiCl), alkali (NaOH) and weak acid (acetic acid), it suffers an efficient quenching process in the presence of protic acid (HCl) in aqueous or ethanolic solution. This quenching process is accompanied by a change in the UV spectrum, but it is reversible and can be fully recovered. Both steady‐state and transient fluorescence spectra of 1‐phenyl‐3,4‐dimethyl‐1H‐pyrazolo‐[3,4‐b]quinoline (PAQ5) during quenching are measured and analyzed. It is found that a combined dynamic and static quenching mechanism is responsible for the quenching processes. The ground‐state proton‐transfer complex [PAQ5 ??? H+] is responsible for static quenching. It changes linearly with proton concentration [H+] with a bimolecular association constant KS=1.95 M ?1 controlled by the equilibrium dissociation of HCl in ethanol. A dynamic quenching constant KD=22.4 M ?1 is obtained by fitting to the Stern–Volmer equation, with a bimolecular dynamic quenching rate constant kd=1.03×109 s?1 M ?1 under ambient conditions. A change in electron distribution is simulated and explains the experiment results. 相似文献
997.
998.
Three pyridyl functionalized bis(pyrazol‐1‐yl)methanes, namely 2‐[(4‐pyridyl)methoxyphenyl] bis(pyrazol‐1‐yl)methane (L1), 2‐[(4‐pyridyl)methoxyphenyl]bis(3,5‐dimethylpyrazol‐1‐yl)methane (L2) and 2‐[(3‐pyridyl)methoxyphenyl]bis(pyrazol‐1‐yl)methane (L3) have been synthesized by the reactions of (2‐hydroxyphenyl)bis(pyrazol‐1‐yl)methanes with chloromethylpyridine. Treatment of these three ligands with R2SnCl2 (R = Et, n‐Bu or Ph) yields a series of symmetric 2:1 adducts of (L)2SnR2Cl2 (L = L1, L2 or L3), which have been confirmed by elemental analysis and NMR spectroscopy. The crystal structures of (L2)2Sn(n‐Bu)2Cl2·0.5C6H14 and (L3)2SnEt2Cl2 determined by X‐ray crystallography show that the functionalized bis(pyrazol‐1‐yl)methane acts as a monodentate ligand through the pyridyl nitrogen atom, and the pyrazolyl nitrogen atoms do not coordinate to the tin atom. The cytotoxic activity of these complexes for Hela cells in vitro was tested. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
999.
Xiaogang Hu Guimei Dai Jiajing Huang Tingting Ye Huajun Fan Tang Youwen Ying Yu Yong Liang 《Journal of chromatography. A》2010,1217(38):5875-5882
A molecularly imprinted polymer (MIP) with metolachlor as template was firstly coated on stainless steel fiber through chemical bonding strategy to solve the fragility problem of silica fiber substrate for solid-phase microextraction. The surface pretreatment of stainless steel fiber and the polymerization conditions were investigated systematically to enhance the preparation feasibility and MIP coating performance, and then a porous and highly cross-linked MIP coating with 14.8-μm thickness was obtained with over 200 times re-usability which was supported by non-fragile stainless steel fiber adoption. The MIP coating possessed specific selectivities to metolachlor, its metabolites and other chloroacetanilide herbicides with the factors of 1.1–4.6. Good extraction capacities of metolachlor, propisochlor and butachlor were found with MIP coating under quick adsorption and desorption kinetics, and the detection limits of 3.0, 9.6 and 38 μg L−1 were achieved, respectively. Moreover, the MIP-coated stainless steel fiber was evaluated for trace metolachlor, propisochlor and butachlor extraction in the spiked soybean and corn samples, and the enrichment factors of 54–60, 27–31 and 15–20 were obtained, respectively. 相似文献
1000.
We report the construction of three-dimensional (3D) colloidal crystal arrays (CCA) and hollow colloidal crystal arrays (HCCA) derived from the self-assembly of polyelectrolytes (PE)-coated polystyrene (PS) particles and their use as models of high surface area systems to immobilize peroxidase (POD). POD molecules could infiltrate into the deep layers of CCA and HCCA through their interconnected pores and strongly adsorbed at the PE shell of the colloidal particles. And the total enzyme loading amount and bioactivities increased linearly with the thickness of the CCA till ca. 10 mum. Compared with flat substrates with the same geometrical area, CCA and HCCA exhibit much higher enzyme loading abilities (approximately 43 and 53 times respectively) and the resulting bioactivities (approximately 35 and 41 times respectively) due to their inherently higher surface area and 3D interconnected porous structures. In addition, HCCA could load approximately 30% more POD than CCA because some POD molecules could infiltrate into the interior of the hollow capsule under salt condition. 相似文献