全文获取类型
收费全文 | 5968篇 |
免费 | 652篇 |
国内免费 | 747篇 |
专业分类
化学 | 4452篇 |
晶体学 | 76篇 |
力学 | 276篇 |
综合类 | 77篇 |
数学 | 913篇 |
物理学 | 1573篇 |
出版年
2024年 | 15篇 |
2023年 | 115篇 |
2022年 | 197篇 |
2021年 | 212篇 |
2020年 | 253篇 |
2019年 | 265篇 |
2018年 | 221篇 |
2017年 | 223篇 |
2016年 | 281篇 |
2015年 | 314篇 |
2014年 | 363篇 |
2013年 | 530篇 |
2012年 | 522篇 |
2011年 | 512篇 |
2010年 | 400篇 |
2009年 | 370篇 |
2008年 | 436篇 |
2007年 | 361篇 |
2006年 | 333篇 |
2005年 | 234篇 |
2004年 | 182篇 |
2003年 | 126篇 |
2002年 | 131篇 |
2001年 | 79篇 |
2000年 | 76篇 |
1999年 | 69篇 |
1998年 | 47篇 |
1997年 | 47篇 |
1996年 | 38篇 |
1995年 | 20篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 21篇 |
1979年 | 13篇 |
1978年 | 24篇 |
1977年 | 17篇 |
1976年 | 12篇 |
1975年 | 11篇 |
排序方式: 共有7367条查询结果,搜索用时 0 毫秒
61.
62.
An analytical method for the separation and quantification of Sb(III) and Sb(V) using anion chromatography with ICP-MS is presented. The optimum conditions for the separation of the antimony species were established with 15 mmol/L nitric acid at pH 6 as eluent system on a PRP-X100 column. The retention times for antimony(V) and antimony(III) were 85 s and 300 s with detection limits of 0.06 μg/L and 0.29 μg/L, respectively. The proposed method was applied to cell extracts of Leishmania donovani, which were incubated with antimony(III) and antimony(V). Some metabolism seemed to occur within the cells. 相似文献
63.
64.
Fluorine substitution on a solute can have a significant effect on solute solubility in a given solvent and fluorine substitution on a solvent can also have a significant effect on solvent quality. The effect of fluorine is demonstrated with the phase behavior data for bis(p-tolyl)propane (BTP) compared to bis(p-tolyl)hexafluoropropane (BTHFP) in supercritical carbon dioxide, 1,1-difluoroethane (F152a), and 1,1,1,2-tetrafluoroethane (F134a). Semifluorinated BTHFP is more soluble than non-fluorinated BTP in all three solvents, especially CO2. The CO2–BTP system exhibits solid solubility behavior while the CO2–BTHFP system exhibits liquid–liquid–vapor (LLV) behavior near the critical point of CO2. Although the two dipolar hydrofluorocarbons (HFC) are better solvents than CO2 for these two aromatic solid compounds, F152a is the superior HFC solvent, especially for BTP, because F152a has a smaller molar volume and a larger effective dipole moment than F134a. LLV behavior is also observed for the F134a–BTP system near the critical point of F134a although the F134a–BTHFP, F152a–BTP, and F152a–BTHFP systems all appear to exhibit type-I phase behavior and no liquid–liquid immiscibility near the respective critical points. 相似文献
65.
Dr. Sarah Desmons Yu Zhou Dr. Dan Zhang Dr. Carlos Jarava-Barrera Dr. Anaïs Coffinet Dr. Antoine Simonneau Dr. Laure Vendier Prof. Dr. Gen Luo Dr. Sébastien Bontemps 《European journal of organic chemistry》2023,26(30):e202300525
The hydroboration of CO2 into bis(boryl)acetal (BBA) compounds is an important transformation, since it enabled to selectively reduce CO2 by 4e- and to subsequently use the BBA compounds as C1 and Cn sources. However, the influence of the nature of the boryl moieties on the reactivity of BBA compounds has not been evaluated so far. In the present study, four BBA compounds – including two new ones – were reacted with 2,6-diisopropylaniline to afford the expected imine. Significant differences in the rate of the reaction from minutes to weeks have been observed depending on the BBA used, showing the importance of the nature of the boryl moieties. Theoretical investigations enabled to propose a mechanism involving the addition of the aniline to the BBA as the rate-determining step and to determine that the steric hindrance of the BBA compounds is the main factor driving the rate of this condensation reaction. 相似文献
66.
This article deals with the solution properties of poly(vinylpyrrolidone) (PVP) in salt and surfactant environment. The cloud point (CP) of PVP has been found to be induced by the salts NaCl, KCl, KBr, Na2SO4, MgSO4, and Na3PO4. On the basis of CP values for a salt at different [PVP], the energetics of the clouding process have been estimated. The effect of the surfactant, sodium dodecyl sulfate (SDS), on the salt-induced CP has also been studied, and reduction in CP at low [SDS] and increase in CP at high [SDS] have been observed. The water vapor adsorption of PVP has been determined by isopiestic method. The results display a BET Type III isotherm whose analysis has helped to obtain the monolayer capacity of PVP and formation of multilayer on it. The solvation of PVP in a solution of water and a water-isopropanol mixture has been determined by conductometry from which contribution of the individual components were estimated. The interaction of PVP with SDS in solution led to formation of a complex entity, which has been studied also by conductometry adopting a binding-equilibrium scheme. SDS has been found to undergo two types of binding as monomers in the pre- critical aggregation concentration (CAC) range and as small clusters in the post CAC region. The stoichiometries of binding and binding constant were evaluated. 相似文献
67.
Wilkes JG Rafii F Sutherland JB Rushing LG Buzatu DA 《Rapid communications in mass spectrometry : RCM》2006,20(16):2383-2386
Pyrolysis mass spectrometry (PyMS) was investigated as a rapid tool to distinguish potential bioterror hoax materials from samples containing pathogenic bacteria. A pyrolysis time-of-flight (TOF) mass spectrometer equipped with an alternative ionization technique, metastable atom bombardment (MAB), was used to produce sample spectra. These spectra were analyzed by principal component and discriminant analysis for pattern recognition. Materials investigated were two strains of Vibrio parahaemolyticus, one of which produced the tdh toxin, two Salmonella enterica serotypes, a biological mosquito control product containing spores of Bacillus thuringiensis, and several white to off-white powders (which could be used as hoax materials), such as flour, corn starch, methyl cellulose, and xanthan gum. PyMS distinguished bacterial samples from hoax materials. Furthermore, pattern analysis differentiated Vibrios from Salmonellae, Salmonella enterica Anatum from S. enterica Heidelberg, and the two V. parahaemolyticus strains from each other. The B. thuringiensis mixture was distinguished from other bacteria and powders, suggesting that PyMS with pattern recognition may differentiate samples containing pathogens, including Bacillus spp., from nonbiological agents and that it can be a rapid method for detection of bacteria. MS data acquisition took only 7 min for each sample. 相似文献
68.
The syntheses and biological evaluation of six epothilone D analogues are reported. These side-chain variants of the (E)-9,10-didehydroepothilone scaffold contain C-15 thiazole appendages that are derived from bromomethyl ketone intermediates. Although each of these analogues is less cytotoxic than the parent (E)-9,10-didehydroepothilone D, three maintain IC(50) values in the double-digit nanomolar range against both susceptible and resistant cell lines. 相似文献
69.
Jianjun Zou Dingwei Wu Dawei Xiao Dan Qi Li Liu Li Ding Guangji Wang 《Chromatographia》2009,69(5-6):453-458
A sensitive and specific liquid chromatography–electrospray ionization–tandem mass spectrometry method has been developed and validated for the quantification of huperzine A in human plasma. After the addition of trimetazidine, the internal standard (IS) and sodium hydroxide, plasma samples were extracted using 5 mL ethyl acetate. The compounds were separated on an Agilent Zorbax SB C18 column (100 mm × 2.1 mm ID, dp 3.5 μm) using an elution system of 10 mM ammonium acetate solution–methanol–formic acid (18:82:0.1, v/v) as the mobile phase. The quantification of target compounds was obtained by using multiple reaction monitoring (MRM) transitions: m/z 243.1, 210.1 and 267.2, 166.0 were measured in positive mode for huperzine A and IS. Linearity was established for the range of concentrations 0.01–4.0 ng mL?1 with a coefficient of correlation (r) of 0.9991. The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.01 ng mL?1. The method has been successfully applied to study the pharmacokinetics of huperzine A in healthy male Chinese volunteers. 相似文献
70.
This work focuses on the systematic investigation of the influences of pyrimidine-based thioether ligand geometries and counteranions on the overall molecular architectures. A N-containing heterocyclic dithioether ligand 2,6-bis(2-pyrimidinesulfanylmethyl)pyridine (L1) and three structurally related isomeric bis(2-pyrimidinesulfanylmethyl)benzene (L2-L4) ligands have been prepared. On the basis of the self-assembly of CuX (X = I, Br, Cl, SCN, or CN) and the four structurally related flexible dithioether ligands, we have synthesized and characterized 10 new metal-organic entities, Cu4(L1)2I4 1, Cu4(L1)2Br4 2, [Cu2(L2)2I2.CH3CN]n 3, [Cu(L3)I]n 4, [Cu(L3)Br]n 5, [Cu(L3)CN]n 6, [Cu(L4)CN]n 7, [Cu2(L4)I2]n 8, [Cu2(L4)(SCN)2]n 9, and [[Cu6I5(L4)3](BF4).H2O]n 10, by elemental analyses, IR spectroscopy, and X-ray crystallography. Single-crystal X-ray analyses show that the 10 Cu(I) complexes possess an increasing dimensionality from 0D (1 and 2) to 1D (3-5) to 2D (6-9) to 3D (10), which indicates that the ligand geometry takes an essential role in the framework formation of the Cu(I) complexes. The influence of counteranions and pi-pi weak interactions on the formation and dimensionality of these coordination polymers has also been explored. In addition, the photoluminescence properties of Cu(I) coordination polymers 4-10 in the solid state have been studied. 相似文献