全文获取类型
收费全文 | 2590篇 |
免费 | 332篇 |
国内免费 | 180篇 |
专业分类
化学 | 1655篇 |
晶体学 | 21篇 |
力学 | 92篇 |
综合类 | 3篇 |
数学 | 187篇 |
物理学 | 610篇 |
无线电 | 534篇 |
出版年
2024年 | 5篇 |
2023年 | 51篇 |
2022年 | 38篇 |
2021年 | 93篇 |
2020年 | 74篇 |
2019年 | 76篇 |
2018年 | 86篇 |
2017年 | 55篇 |
2016年 | 101篇 |
2015年 | 103篇 |
2014年 | 112篇 |
2013年 | 153篇 |
2012年 | 194篇 |
2011年 | 226篇 |
2010年 | 150篇 |
2009年 | 131篇 |
2008年 | 174篇 |
2007年 | 154篇 |
2006年 | 138篇 |
2005年 | 160篇 |
2004年 | 113篇 |
2003年 | 80篇 |
2002年 | 77篇 |
2001年 | 52篇 |
2000年 | 57篇 |
1999年 | 51篇 |
1998年 | 33篇 |
1997年 | 38篇 |
1996年 | 31篇 |
1995年 | 38篇 |
1994年 | 23篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有3102条查询结果,搜索用时 593 毫秒
41.
Tønder JE Olesen PH Hansen JB Begtrup M Pettersson I 《Journal of computer-aided molecular design》2001,15(3):247-258
A study of a series of compounds with agonistic effect at the alpha4beta2 nicotinic acetylcholine receptors resulted in an improved pharmacophore model as well as a CoMFA model. The pharmacophore was composed of three pharmacophoric elements: (1) a site point (a) corresponding to a protonated nitrogen atom, (2) a site point (b) corresponding to an electronegative atom capable of forming a hydrogen bond, and (3) the centre of a heteroaromatic ring or a C=O bond (c). The pharmacophoric elements were related by the following parameters: (a-b) 7.3-8.0 A, (a-c) 6.5-7.4 A, and the angle between the two distance vectors (delta bac) 30.4-35.8 degrees. In addition to this, a stereoselective CoMFA model was developed, which showed good predictability even for compound classes not present in the training set. 相似文献
42.
In this paper, we investigate dual problems for nonconvex set-valued vector optimization via abstract subdifferential. We first introduce a generalized augmented Lagrangian function induced by a coupling vector-valued function for set-valued vector optimization problem and construct related set-valued dual map and dual optimization problem on the basic of weak efficiency, which used by the concepts of supremum and infimum of a set. We then establish the weak and strong duality results under this... 相似文献
43.
Zheng J. Maharaj C. Liu J. Chai H. Liu H. Dear J. P. 《Mechanics of Composite Materials》2022,58(1):125-140
Mechanics of Composite Materials - In this research, the maximum stress, Hashin, Puck, LaRC03, and Northwestern University (NU) criteria are analyzed based literature data, analytical results... 相似文献
44.
Fangzin Fu Hongyu Li Dongsheng Zhu Qunxin Fang Huade Pan Edward R. T. Tiekink Franois Kayser Monique Biesemans Ingrid Verbruggen Rudolph Willem Marcel Gielen 《Journal of organometallic chemistry》1995,490(1-2):163-171
The synthesis and characterization by 1H, 13C, 119Sn NMR and 119Sn Mössbauer spectroscopy of (Z)-1-[2-(triphenylstannyl)vinyl]-1-cycloheptanol,
(1), and (Z)-1-[2-tri-p-tolylstannyl)vinyl-1-cycloheptanol,
(2), are described, together with their halodemetallation by I2, Br2 and ICIl to yield derivatives of the types
(Ar = phenyl or p-tolyl, N = 1, 2; X = I, Br, Cl, respectively). The solid-state structures of four compounds have been determined by X-ray diffraction analysis. In the crystals of
(1) and
(2) the Sn atom has a tetrahedral geometry distorted towards trigonal bipyramid as a consequence of a close intramolecular contact with the hydroxyl O(1) atom of 2.742(3) Å and 2.768(3) Å, respectively. A trigonal bipyramidal geometry is found in
(12) and
(4), in which significant Sn---O(1) interactions are noted [2.437(8) Å and 2.407(8) Å, respectively]. 相似文献
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
Full-size image
45.
T. Sandrock T. Danger E. Heumann G. Huber B. H. T. Chai 《Applied physics. B, Lasers and optics》1994,58(2):149-151
We report, to our knowledge for the first time, Continuous Wave (CW) laser emission at room temperature of Pr:LiYF4 (Pr.YLF) at six wavelengths: 522, 545, 607, 639.5, 720 and 907.4 nm. The pump source was an argon-ion laser tuned to a wavelength of = 457.9 nm. The maximum output powers at 522 nm (3Pi 3H5) and 639.5 nm (3P0 3F2) were 144 and 266 mW, respectively. We also observed CW laser action of Pr:GdLiF4 (Pr: GLF) at = 639 nm and of Pr:KYF4 (Pr: KYF) at = 642.5 nm. 相似文献
46.
Yi Sun Kuanxin Zhang Run Chai Yueda Wang Xianhong Rui Kang Wang Huaxia Deng Hongfa Xiang 《Advanced functional materials》2023,33(36):2303020
Considered the promising anode material for next-generation high-energy lithium-ion batteries, SiOx has been slow to commercialize due to its low initial Coulombic efficiency (ICE) and unstable solid electrolyte interface (SEI) layer, which leads to reduced full-cell energy density, short cycling lives, and poor rate performance. Herein, a novel strategy is proposed to in situ construct an artificial hybrid SEI layer consisting of LiF and Li3Sb on a prelithiated SiOx anode via spontaneous chemical reaction with SbF3. In addition to the increasing ICE (94.5%), the preformed artificial SEI layer with long-term cycle stability and enhanced Li+ transport capability enables a remarkable improvement in capacity retention and rate capability for modified SiOx. Furthermore, the full cell using Li(Ni0.8Co0.1Mn0.1)O2 and a pre-treated anode exhibits high ICE (86.0%) and capacity retention (86.6%) after 100 cycles at 0.5 C. This study provides a fresh insight into how to obtain stable interface on a prelithiated SiOx anode for high energy and long lifespan lithium-ion batteries. 相似文献
47.
Wireless Personal Communications - To investigate the effect of nano-potassium silicate on the expression of glutamine (GLN) family gene, amino acid (AAs) componentand volatile metabolites (VMs)... 相似文献
48.
[reaction: see text] A novel cycloaldol approach to the isobenzofuran core common to many of the eunicellin diterpenes is described. The cycloaldol precursor was prepared by aldol addition of (S)-(+)-carvone and methacrolein followed by etherification to a glycolate ester. Chemoselective enolization of the glycolate ester led to the cycloaldol adduct in high yield and diastereoselectivity. An oxidative rearrangement-allylic diazene rearrangement sequence established the requisite cis ring fusion. 相似文献
49.
Z. F. Chai Q. F. Qian X. Q. Feng P. Q. Zhang N. Q. Liu W. Y. Feng M. X. Kuang H. Y. Wang Y. Z. Zhang 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(1):153-156
The occupational health impact of atmospheric pollution on exposed workers at one iron and steel complex was studied by instrumental neutron activation analysis of workers' hair samples and medical examination. The experimental results indicate that there is a positive correlation between the high inhalation amounts of iron and other trace elements by the exposed workers and the symptom of their high blood pressure and hypoglycemia, which implies that the atmospheric environment polluted by iron and steel industry has an adverse health impact on the exposed workers. The measures to relieve and abate the occupational diseases caused by air-borne particulate matter should be taken 相似文献
50.
Hood BL Lucas DA Kim G Chan KC Blonder J Issaq HJ Veenstra TD Conrads TP Pollet I Karsan A 《Journal of the American Society for Mass Spectrometry》2005,16(8):1221-1230
With advancements in the analytical technologies and methodologies in proteomics, there is great interest in biomarker discovery in biofluids such as serum and plasma. Current hypotheses suggest that the low molecular weight (LMW) serum proteome possesses an archive of clipped and cleaved protein fragments that may provide insight into disease development. Though these biofluids represent attractive samples from which new and more accurate disease biomarkers may be found, the intrinsic person-to-person variability in these samples complicates their discovery. Mice are one of the most extensively used animal models for studying human disease because they represent a highly controllable experimental model system. In this study, the LMW serum proteome was compared between xenografted tumor-bearing mice and control mice by differential labeling utilizing trypsin-mediated incorporation of the stable isotope of oxygen, 18O. The digestates were combined, fractionated by strong cation exchange chromatography, and analyzed by nanoflow reversed-phase liquid chromatography coupled online with tandem mass spectrometry, resulting in the identification of 6003 proteins identified by at least a single, fully tryptic peptide. Almost 1650 proteins were identified and quantitated by two or more fully tryptic peptides. The methodology adopted in this work provides the means for future quantitative measurements in comparative animal models of disease and in human disease cohorts. 相似文献