全文获取类型
收费全文 | 8048篇 |
免费 | 724篇 |
国内免费 | 508篇 |
专业分类
化学 | 600篇 |
晶体学 | 47篇 |
力学 | 919篇 |
综合类 | 60篇 |
数学 | 1829篇 |
物理学 | 1614篇 |
综合类 | 4211篇 |
出版年
2024年 | 28篇 |
2023年 | 82篇 |
2022年 | 131篇 |
2021年 | 180篇 |
2020年 | 145篇 |
2019年 | 196篇 |
2018年 | 198篇 |
2017年 | 220篇 |
2016年 | 229篇 |
2015年 | 259篇 |
2014年 | 381篇 |
2013年 | 584篇 |
2012年 | 428篇 |
2011年 | 504篇 |
2010年 | 375篇 |
2009年 | 481篇 |
2008年 | 427篇 |
2007年 | 536篇 |
2006年 | 466篇 |
2005年 | 423篇 |
2004年 | 348篇 |
2003年 | 392篇 |
2002年 | 352篇 |
2001年 | 286篇 |
2000年 | 257篇 |
1999年 | 198篇 |
1998年 | 168篇 |
1997年 | 164篇 |
1996年 | 144篇 |
1995年 | 120篇 |
1994年 | 95篇 |
1993年 | 76篇 |
1992年 | 77篇 |
1991年 | 70篇 |
1990年 | 56篇 |
1989年 | 50篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 22篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有9280条查询结果,搜索用时 15 毫秒
101.
The Kringle-1 structure of plasminogen (PGK-1), the Kringle-2 structure of tissue plasminogen activator (PAK-2) and the Kringle structure of prourokinase (UKK) has been modeled on the basis of the three-dimensional structure of Kringle-1 of prothrombin (PTK-1) at 2.8 resolution. The predicted three-dimensional structure of these Kringles shows that the binding site of PGK-1 is characterized by an apparent dipolar site, the polar parts of which are separated by a hydrophobic region. PAK-2 possesses the anionic center but has not a cationic binding center which might be provided by a guanidinium group from Arg-69 located adjacent to the Arg-71 position. UKK possesses neither the anionic binding center nor the cationic center which are probably the main reason for the poor fibrin specificity of urokinase. 相似文献
102.
MoS2 nanotube coated SWNT (Single wall carbon nanotube) bundles have been successfully prepared by adsorbing (NH4)2MoS4 onto SWNT bundles and subsequent heat treatment under H2 at 900 ℃ in a tube furnace. The morphologies, structure and composition of the as-prepared sample were investigated by XRD, SEM, HRTEM coupled with EDS. The formation mechanism has also been preliminarily discussed. 相似文献
103.
Faqiong Zhao Liqin Liu Fei Xiao Jiangwen Li Rui Yan Shuangshuang Fan Baizhao Zeng 《Electroanalysis》2007,19(13):1387-1393
An ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium hexafluorophosphate, BMIMPF6)‐single‐walled carbon nanotube (SWNT) gel modified glassy carbon electrode (BMIMPF6‐SWNT/GCE) is fabricated. At it the voltammetric behavior and determination of p‐nitroaniline (PNA) is explored. PNA can exhibit a sensitive cathodic peak at ?0.70 V (vs. SCE) in pH 7.0 phosphate buffer solution on the electrode, resulting from the irreversible reduction of PNA. Under the optimized conditions, the peak current is linear to PNA concentration over the range of 1.0×10?8–7.0×10?6 M, and the detection limit is 8.0×10?9 M. The electrode can be regenerated by successive potential scan in a blank solution for about 5 times and exhibits good reproducibility. Meanwhile, the feasibility to determine other nitroaromatic compounds (NACs) with the modified electrode is also tested. It is found that the NACs studied (i.e., p‐nitroaniline, p‐nitrophenol, o‐nitrophenol, m‐nitrophenol, p‐nitrobenzoic acid, and nitrobenzene) can all cause sensitive cathodic peaks under the conditions, but their peak potentials and peak currents are different to some extent. Their peak currents and concentrations show linear relationships in concentration ranges with about 3 orders of magnitude. The detection limits are 8.0×10?9 M for p‐nitroaniline, 2.0×10?9 M for p‐nitrophenol, 5.0×10?9 M for o‐nitrophenol, 5.0×10?9 M for m‐nitrophenol, 2.0×10?8 M for p‐nitrobenzoic acid and 8.0×10?9 M for nitrobenzene respectively. The BMIMPF6‐SWNT/GCE is applied to the determination of NACs in lake water. 相似文献
104.
Thomas Höche Wolfgang NeumannSaeid Esmaeilzadeh Reinhard UeckerMarkus Lentzen Christian Rüssel 《Journal of solid state chemistry》2002,166(1):15-23
Sr2TiSi2O8 single crystals were grown by Czochralski pulling and from a high-temperature solution. X-ray diffractometry revealed the modulated crystal structure of Sr2TiSi2O8 to belong to the 5D superspace group P4bm (−α, α, 1/2; α, α, 1/2) with α=0.3. Atomic positions, anisotropic displacement factors and positional modulation parameters for Sr2TiSi2O8 are determined and discussed. The positional modulation is further investigated by electron diffraction and high-resolution transmission electron microscopy. In the latter experiments, the 2D modulation appears to be superimposed by some 1D modulation waves. This effect is discussed in terms of growth conditions. 相似文献
105.
P.V. Pogodin A.A. Lagunin D.A. Filimonov M.C. Nicklaus V.V. Poroikov 《SAR and QSAR in environmental research》2019,30(10):759-773
ABSTRACTExisting data on structures and biological activities are limited and distributed unevenly across distinct molecular targets and chemical compounds. The question arises if these data represent an unbiased sample of the general population of chemical-biological interactions. To answer this question, we analyzed ChEMBL data for 87,583 molecules tested against 919 protein targets using supervised and unsupervised approaches. Hierarchical clustering of the Murcko frameworks generated using Chemistry Development Toolkit showed that the available data form a big diffuse cloud without apparent structure. In contrast hereto, PASS-based classifiers allowed prediction whether the compound had been tested against the particular molecular target, despite whether it was active or not. Thus, one may conclude that the selection of chemical compounds for testing against specific targets is biased, probably due to the influence of prior knowledge. We assessed the possibility to improve (Q)SAR predictions using this fact: PASS prediction of the interaction with the particular target for compounds predicted as tested against the target has significantly higher accuracy than for those predicted as untested (average ROC AUC are about 0.87 and 0.75, respectively). Thus, considering the existing bias in the data of the training set may increase the performance of virtual screening. 相似文献
106.
一种液晶环氧树脂固化中扩散控制动力学研究 总被引:3,自引:0,他引:3
根据扩散控制反应的基本原理 ,建立了合适的反应模型 ,描述了 4 ,4′ 二 ( 2 ,3 环氧丙氧基 )偶氮苯(DGEAP) / 4,4′ 二氨基二苯甲烷 (DDM)环氧树脂的固化行为 .该模型认为 ,随着环氧基团反应程度的提高 ,基团的反应半径将受到影响 .当体系中出现了介晶基元的有序排列时 ,与之相连的反应基团的分布也受到影响 ,有序区内的局部浓度将变大 ,产生假浓度效应 ,并最终影响扩散控制反应动力学 .通过与普通环氧树脂固化动力学的比较 ,证实了这一效应 . 相似文献
107.
108.
Preparation and Characterization of Three-dimensionally Ordered Crystalline Macroporous CeO2 总被引:2,自引:0,他引:2
Xi Yan ZHANG Tong Wen WANG Wen Qing JIANG Di WU Ling LIU Ai Hong DUAN 《中国化学快报》2005,16(8):1109-1112
Three-dimensional ordered macroporous (3DOM) materials are of great potential importance in catalysis, selective separation, sensor arrays and communications with optical band gaps1. Many results in the synthesis of 3DOM materials have been reported, such as closed-packed silica spheres or polystyrenes (PS) templating routes for silica2, metal oxides1-6 and metals7. Recently, poly(methyl methacrylate) (PMMA) colloidal crystal templates have been used to prepare 3DOM materials of metals8,… 相似文献
109.
By the use of time domain reflectometry method, dielectric measurements were carried out on dimethylformamide‐2‐nitrotoluene solvent mixtures in the frequency range 10 MHz‐20 GHz, at various temperatures from 15 °C to 45 °C. These solvent mixtures as well as pure solvents display a Debye type dispersion. Their frequency dependent dielectric properties can be summarized by the three parameters in the Debye equation: a static permittivity, permittivity at high frequency and a dielectric relaxation time constant. The free energy of activation for dipolar relaxation process and the Kirkwood correlation factor were determined using these fitting parameters for these solvent mixtures at various concentrations and temperatures. By using these dielectric parameters, the excess permittivity and excess inverse relaxation time is obtained. The excess permittivity is found to be positive for all concentrations and temperatures whereas the excess inverse relaxation time is negative. 相似文献
110.
The post-translational modifications of the 96 kDa protein dynamin A from Dictyostelium discoideum were analyzed using Q-TOF mass spectrometry. The accurate molecular mass of the intact protein revealed a covalent modification causing an additional mass of 42 Da. The modification could be identified as N-terminal acetylation by tandem mass spectrometry. Extracted ion chromatograms for the a(1) and b(1) ion of the tryptic T1 peptide were used to detect the acetylated peptide within 54 nanoelectrospray ionization tandem mass spectra. Owing to the accurate molecular mass of the intact protein, additional covalent modifications could be excluded. In addition to the covalent modification, the domain structure of dynamin A was determined by applying a combination of limited proteolysis, sodium dodecylsulfate polyacrylamide gel electrophoresis, automated tandem mass spectrometry and protein database searching. 相似文献