全文获取类型
收费全文 | 10215篇 |
免费 | 386篇 |
国内免费 | 151篇 |
专业分类
化学 | 6930篇 |
晶体学 | 95篇 |
力学 | 380篇 |
综合类 | 1篇 |
数学 | 1609篇 |
物理学 | 1737篇 |
出版年
2022年 | 104篇 |
2021年 | 110篇 |
2020年 | 185篇 |
2019年 | 162篇 |
2018年 | 122篇 |
2017年 | 118篇 |
2016年 | 244篇 |
2015年 | 199篇 |
2014年 | 255篇 |
2013年 | 492篇 |
2012年 | 556篇 |
2011年 | 675篇 |
2010年 | 378篇 |
2009年 | 301篇 |
2008年 | 587篇 |
2007年 | 551篇 |
2006年 | 530篇 |
2005年 | 519篇 |
2004年 | 487篇 |
2003年 | 337篇 |
2002年 | 356篇 |
2001年 | 130篇 |
2000年 | 113篇 |
1999年 | 85篇 |
1998年 | 98篇 |
1997年 | 138篇 |
1996年 | 178篇 |
1995年 | 118篇 |
1994年 | 98篇 |
1993年 | 117篇 |
1992年 | 88篇 |
1991年 | 104篇 |
1990年 | 98篇 |
1989年 | 81篇 |
1988年 | 80篇 |
1987年 | 73篇 |
1986年 | 75篇 |
1985年 | 135篇 |
1984年 | 143篇 |
1983年 | 106篇 |
1982年 | 126篇 |
1981年 | 113篇 |
1980年 | 104篇 |
1979年 | 86篇 |
1978年 | 117篇 |
1977年 | 97篇 |
1976年 | 88篇 |
1975年 | 72篇 |
1974年 | 72篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A series of homo- and copolymers of acrylonitrile was prepared under radical initiation in DMF solutions. The thermal and flammability characteristics of these polymers were evaluated through thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and by limiting oxygen index (LOI) measurements. The thermal degradation behaviours of the polymers were assessed primarily with a view to designing comonomers, for acrylonitrile-based polymers, bearing flame retardant moieties. Broadly speaking, in LOI tests acrylic-based comonomers were found to improve fire performance. For instance, the incorporation of methacrylic acid gave a limiting oxygen index value of 26.4 at 30.9 mol% loading, and an intumescent char was produced upon burning. 相似文献
952.
Complexes of sodium poly(4-styrenesulfonate) (NaPSS) and poly(diallyldimethylammonium chloride) (PDADMAC) were formed on mixing equimolar solutions in high salt concentration. Under ultracentrifugal fields, the complex precipitates were transformed into compact polyelectrolyte complexes (CoPECs), which showed extensive porosity. The mechanical properties of CoPECS make them attractive for bioimplants and tissue engineering applications. Free NaPSS chains in the closed pores of CoPECs create excess osmotic pressure, which controls the pore size and contributes to the mechanical resistance of the material. The mechanical properties of CoPECs, modulated by the ionic strength of the doping medium, were studied by uniaxial tensile testing and the stress-strain data were fit to a three-element Maxwell model which revealed at least two regimes of stress relaxation. 相似文献
953.
Rower JE Bushman LR Hammond KP Kadam RS Aquilante CL 《Biomedical chromatography : BMC》2010,24(12):1300-1308
Gemfibrozil, a fibric acid hypolipidemic agent, is increasingly being used in clinical drug–drug interaction studies as an inhibitor of drug metabolizing enzymes and drug transporters. The validation of a fast, accurate and precise LC/MS method is described for the quantitative determination of gemfibrozil in an EDTA‐anticoagulated human plasma matrix. Briefly, gemfibrozil was extracted from human plasma by an acetonitrile protein precipitation method. The assay was reproducible with intra‐assay precision between 1.6 and 10.7%, and inter‐assay precision ranging from 4.4 to 7.8%. The assay also showed good accuracy, with intra‐assay concentrations within 85.6–108.7% of the expected value, and inter‐assay concentrations within 89.4–104.0% of the expected value. The linear concentration range was between 0.5 and 50 µg/mL with a lower limit of quantitation of 0.5 µg/mL when 125 µL of plasma were extracted. This LC/MS method yielded a quick, simple and reliable protocol for determining gemfibrozil concentrations in plasma and is applicable to clinical pharmacokinetic studies. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
954.
Chih-Ching Chien Chian-Chiao Hong Po-Chi Soo Yu-Hong Wei Shan-Yu Chen Mei-Ling Cheng Yi-Ming Sun 《Applied biochemistry and biotechnology》2010,162(8):2355-2364
Polyhydroxyalkanoates are polyesters synthesized by numerous microorganisms. These polyesters are biodegradable and have similar
properties to those of conventional plastics. Cupriavidus taiwanensis strain 184 is phylogenetically related to the well-known polyhydroxybutyrate (PHB) producer Ralstonia eutropha (Cupriavidus necator) and is also shown to be able to accumulate significant amounts of PHB. In this study, we cloned the PHB synthesis genes
(phaCAB) from C. taiwanensis 184 into Escherichia coli for biosynthesis of PHB. The recombinant E. coli strains were able to synthesize significant amounts of PHB. The PHB amounted to about 66∼70% of total cell material of these
recombinant strains. 相似文献
955.
Victor J. Bellitto Mikhail I. Melnik Daniel N. Sorensen Joseph C. Chang 《Journal of Thermal Analysis and Calorimetry》2010,102(2):557-562
We studied the surface and thermal properties of seven different varieties of cyclotrimethylene-trinitramine (RDX) crystalline
explosives from five manufacturers using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The specific
varieties of the RDX studied were acquired from the previous Reduced Sensitivity RDX Round Robin program. They were chosen
because intensive characterization of the materials already existed including shock sensitivity and cyclotetramethylene-tetranitramine
(HMX) impurity levels. AFM scans revealed a diversity of surface defects. To quantify the surface defects on the crystalline
surface of the RDX particles, surface roughness measurements were acquired. Statistical analysis was undertaken to correlate
the observed surface, HMX impurity levels, and DSC thermal curve properties with the known shock sensitivities of the material.
It was determined that a statistically significant relationship exists between surface roughness and the shock sensitivity
of the material while no relationship was observed between the DSC thermal properties and either surface roughness or shock
sensitivity. The HMX content greatly affected the thermal properties of RDX but was uncorrelated with the shock sensitivity. 相似文献
956.
957.
Uranium-carbon bond reactivity has been investigated with the bis(tethered silylalkyl) uranium metallocene (η5:κ1-C5Me4SiMe2CH2)2U, 1. Tert-butyl nitrile, tBuCN, inserts into both of the tethered U-C bonds to produce the bis(tethered ketimide) complex [η5:κ1-C5Me4SiMe2CH2C(tBu)N]2U, 2, which has unusually bent U-N-C bond angles. Carbon dioxide also inserts into both U-C bonds of 1 yielding the bis(tethered carboxylate) (C5Me4SiMe2CH2CO2)2U, 3. Neither PhCCPh nor PhCCH insert into the U-C bonds, but PhCCH cleaves the silylalkyl tethers in 1 to generate (C5Me4SiMe3)1? ligands in the complex (C5Me4SiMe3)2U(CCPh)2, 4. 相似文献
958.
Harry J. Sterling Joseph D. Batchelor David E. Wemmer Evan R. Williams 《Journal of the American Society for Mass Spectrometry》2010,21(6):1045-1049
Electrospray ionization (ESI) mass spectrometry (MS) is a powerful method for analyzing the active forms of macromolecular
complexes of biomolecules. However, these solutions often contain high concentrations of salts and/or detergents that adversely
effect ESI performance by making ion formation less reproducible, causing severe adduction or ion suppression. Many methods
for separating complexes from nonvolatile additives are routinely used with ESI-MS, but these methods may not be appropriate
for complexes that require such stabilizers for activity. Here, the effects of buffer loading using concentrations of ammonium
acetate ranging from 0.22 to 1.41 M on the ESI mass spectra of a solution containing a domain truncation mutant of a σ54 activator from Aquifex aeolicus were studied. This 44.9 kDa protein requires the presence of millimolar concentrations of Mg2+, BeF3−, and ADP, (at ∼60 °C) to assemble into an active homo-hexamer. Addition of ammonium acetate can improve signal stability
and reproducibility, and can significantly lower adduction and background signals. However, at higher concentrations, the
relative ion abundance of the hexamer is diminished, while that of the constituent monomer is enhanced. These results are
consistent with loss of enzymatic activity as measured by ATP hydrolysis and indicate that the high concentration of ammonium
acetate interferes with assembly of the hexamer. This shows that buffer loading with ammonium acetate is effective for obtaining
ESI signal for complexes that require high concentrations of essential salts, but can interfere with formation of, and/or
destabilize complexes by disrupting crucial electrostatic interactions at high concentration. 相似文献
959.
960.