全文获取类型
收费全文 | 5015篇 |
免费 | 173篇 |
国内免费 | 23篇 |
专业分类
化学 | 3503篇 |
晶体学 | 49篇 |
力学 | 106篇 |
数学 | 395篇 |
物理学 | 1158篇 |
出版年
2023年 | 25篇 |
2022年 | 95篇 |
2021年 | 119篇 |
2020年 | 102篇 |
2019年 | 89篇 |
2018年 | 66篇 |
2017年 | 51篇 |
2016年 | 143篇 |
2015年 | 136篇 |
2014年 | 170篇 |
2013年 | 273篇 |
2012年 | 358篇 |
2011年 | 404篇 |
2010年 | 208篇 |
2009年 | 198篇 |
2008年 | 304篇 |
2007年 | 298篇 |
2006年 | 281篇 |
2005年 | 247篇 |
2004年 | 201篇 |
2003年 | 185篇 |
2002年 | 162篇 |
2001年 | 101篇 |
2000年 | 107篇 |
1999年 | 94篇 |
1998年 | 72篇 |
1997年 | 41篇 |
1996年 | 60篇 |
1995年 | 52篇 |
1994年 | 55篇 |
1993年 | 52篇 |
1992年 | 44篇 |
1991年 | 25篇 |
1990年 | 38篇 |
1989年 | 27篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 29篇 |
1985年 | 30篇 |
1984年 | 14篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1974年 | 12篇 |
1973年 | 11篇 |
1958年 | 23篇 |
排序方式: 共有5211条查询结果,搜索用时 0 毫秒
141.
In the capillary electrophoretic separation of primary amine enantiomers using (+)-(18-crown-6)-tetracarboxylic acid (18C6H4) as a chiral selector, the presence of run buffer constituents such as tris(hydroxymethyl)aminomethane (Tris) or Na+ competing with analytes for 18C6H4, diminishes the effectiveness of 18C6H4. In order to determine appropriate buffer systems for 18C6H4, various run buffer cationic components including Tris, 1,3-bis[tris(hydroxymethyl)methylamino]propane, bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane, triethanolamine, tetramethylammonium, and Na+ were compared. Quantitative studies of the effects of the competitive constituents were carried out by measuring the electrophoretic mobilities of histidine as a function of the 18C6H4 concentration. We also derived a simple equation to estimate the optimal chiral selector concentration for a maximum mobility difference in the presence of a competitive inhibitor. 相似文献
142.
Conductance data are reported for NaI, KI, RbI, CsI, NH4I, NaClO4, and KClO4 in propylene carbonate at 25°C in the concentration range 1×10–4 –8.3×10–3M. Analysis of the data with the current conductance theories indicates negligible ion-association, strong cation-solvent and weak anion-solvent interactions. 相似文献
143.
Hanna Barchanska Piotr Markowski Magdalena Strzebin 《International journal of environmental analytical chemistry》2018,98(6):493-505
A simple, fast and sensitive analytical method was developed for the quantification of herbicide mesotrione (MES) and its degradation products: 4-(methylsulfonyl)-2-nitrobenzoic acid (MNBA) and 2-amino-4-(methylsulfonyl) benzoic acid (AMBA) using differential pulse voltammetry (DPV). Voltammetric measurements were performed using glassy carbon electrode (GCE). Potential range, pH of the electrolyte and the scan rate were optimised to achieve the lowest detection limits of analytes. The optimal conditions were obtained in a Britton–Robinson (BR) buffer at pH 4.0 for MNBA and at pH 6.0 for MES and AMBA, with the scan rate 0.08 V/s. The potential V for (1) nitro and carbonyl groups of MES, (2) nitro group of MNBA and (3) amino group of AMBA, obtained under optimised conditions, was plotted as a function of a peak current (I). The I(V) dependencies were measured for the following concentration ranges: 0.5–5.0 µM for the nitro group of MES and MNBA, 0.75–5.0 µM and 0.50–8.5 µM for the carbonyl groups of MES, and 0.25–8.5 µM for amino group of AMBA; whereas, the limit of detection was in range 0.07–0.23 µM (20–80 µg/L). The proposed method is the first one that allows the determination of both MES and its degradation products. The practical applicability of these newly developed voltammetric methods was verified by direct determination of MES and its degradation products in model samples of drinking and surface water. 相似文献
144.
Lee SK Cho JM Goo Y Shin WS Lee JC Lee WH Kang IN Shim HK Moon SJ 《Chemical communications (Cambridge, England)》2011,47(6):1791-1793
A highly processable, new semiconducting polymer, PCDTTz, based on alternating thiazolothiazole and carbazole units was synthesized. The new polymer exhibited a field-effect carrier mobility of up to 3.8 × 10(-3) cm(2) V(-1) s(-1) and bulk heterojunction solar cells made from PCDTTz produced a power conversion efficiency of 4.88% under AM 1.5 G (100 mW cm(-2)) conditions. 相似文献
145.
Li R Stumpfe D Vogt M Geppert H Bajorath J 《Journal of chemical information and modeling》2011,51(10):2507-2514
We introduce a method to determine a structural distance between any pair of molecular scaffolds. The development of this approach was motivated by the need to accurately evaluate scaffold hopping studies in virtual screening and medicinal chemistry and assess the degree of difficulty involved in facilitating a transition from one structure to another. In order to consistently derive structural distances, scaffolds of different composition and topology are subjected to molecular editing procedures that abstract from original scaffolds in a defined manner until compositional and topological equivalence can be established. Pairs of corresponding scaffold representations are transformed into one-dimensional atom sequences that are aligned using approaches adapted from biological sequence comparison. From best scoring atom sequence alignments, interscaffold distances are derived. The algorithm is evaluated at different levels including the analysis of a series of model scaffolds with defined chemical changes, a scaffold library, and scaffolds from reference compounds and hits of successful virtual screening applications. It is demonstrated that chemically intuitive scaffold distances are obtained for pairs of scaffolds with varying composition and topology. Distance threshold values for close and remote structural relationships between scaffolds are also determined. The methodology is made publicly available in order to provide a basis for a consistent assessment of scaffold hopping ability and to aid in the evaluation and comparison of virtual screening methods. 相似文献
146.
147.
148.
Cho KB Hirao H Chen H Carvajal MA Cohen S Derat E Thiel W Shaik S 《The journal of physical chemistry. A》2008,112(50):13128-13138
This study directly compares the active species of heme enzymes, so-called Compound I (Cpd I), across the heme-thiolate enzyme family. Thus, sixty-four different Cpd I structures are calculated by hybrid quantum mechanical/molecular mechanical (QM/MM) methods using four different cysteine-ligated heme enzymes (P450(cam), the mutant P450(cam)-L358P, CPO and NOS) with varying QM region sizes in two multiplicities each. The overall result is that these Cpd I species are similar to each other with regard to many characteristic features. Hence, using the more stable CPO Cpd I as a model for P450 Cpd I in experiments should be a reasonable approach. However, systematic differences were also observed, and it is shown that NOS stands out in most comparisons. By analyzing the electrical field generated by the enzyme on the QM region, one can see that (a) the protein exerts a large influence and modifies all the Cpd I species compared with the gas-phase situation and (b) in NOS this field is approximately planar to the heme plane, whereas it is approximately perpendicular in the other enzymes, explaining the deviating results on NOS. The calculations on the P450(cam) mutant L358P show that the effects of removing the hydrogen bond between the heme sulfur and L358 are small at the Cpd I stage. Finally, Mossbauer parameters are calculated for the different Cpd I species, enabling future comparisons with experiments. These results are discussed in the broader context of recent findings of Cpd I species that exhibit large variations in the electronic structure due to the presence of the substrate. 相似文献
149.
Baoxin Zhang Haijuan Zhang Miao Zhong Song Wang Qianhe Xu Dong-Hyung Cho Hongdeng Qiu 《中国化学快报》2020,31(1):133-135
Cysteine(Cys) plays a pivotal role in many physiological and pathological processes,including detoxification and protein synthesis.The abnormal levels of Cys are linked to many diseases.In this study,a novel red-emitting off-on fluorescent probe Cys-TCF was masterly constructed for discriminative detection of Cys.After a series of experimental assessment,Cys-TCF displayed higher selectivity and sensitivity for Cys over other biothilols with a low detection limit(0.04 μmol/L).More notably,the pro... 相似文献
150.