全文获取类型
收费全文 | 3067篇 |
免费 | 507篇 |
国内免费 | 496篇 |
专业分类
化学 | 2413篇 |
晶体学 | 55篇 |
力学 | 211篇 |
综合类 | 64篇 |
数学 | 297篇 |
物理学 | 1030篇 |
出版年
2024年 | 11篇 |
2023年 | 60篇 |
2022年 | 147篇 |
2021年 | 148篇 |
2020年 | 144篇 |
2019年 | 154篇 |
2018年 | 121篇 |
2017年 | 145篇 |
2016年 | 159篇 |
2015年 | 198篇 |
2014年 | 202篇 |
2013年 | 251篇 |
2012年 | 296篇 |
2011年 | 276篇 |
2010年 | 216篇 |
2009年 | 222篇 |
2008年 | 216篇 |
2007年 | 190篇 |
2006年 | 160篇 |
2005年 | 138篇 |
2004年 | 77篇 |
2003年 | 69篇 |
2002年 | 75篇 |
2001年 | 59篇 |
2000年 | 63篇 |
1999年 | 39篇 |
1998年 | 34篇 |
1997年 | 27篇 |
1996年 | 23篇 |
1995年 | 27篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 8篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 1篇 |
1983年 | 7篇 |
1982年 | 1篇 |
1979年 | 3篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4070条查询结果,搜索用时 15 毫秒
951.
952.
953.
A new set-up for microwave-assisted acid hydrolysis (MAAH) with high efficiency and reproducibility to degrade proteins into
peptides for mass spectrometry analysis is described. It is based on the use of an inexpensive domestic microwave oven and
can be used for low volume protein solution digestion. This set-up has been combined with liquid chromatography electrospray
ionization quadrupole time-of-flight mass spectrometry (LC-ESI QTOF MS) for mapping protein sequences and characterizing phosphoproteins.
It is demonstrated that for bovine serum albumin (BSA), with a molecular mass of about 67,000 Da, 1292 peptides (669 unique
sequences) can be detected from a 2 μg hydrolysate generated by trifluoroacetic acid (TFA) MAAH. These peptides cover the
entire protein sequence, allowing the identification of an amino acid substitution in a natural variant of BSA. It is shown
that for a simple phosphoprotein containing one phosphoform, β-casein, direct analysis of the hydrolysate generates a comprehensive
peptide map that can be used to identify all five known phosphorylation sites. For characterizing a complex phosphoprotein
consisting of different phosphoforms with varying numbers of phosphate groups and/or phosphorylation sites, such as bovine
αs1-casein, immobilized metal-ion affinity chromatography (IMAC) is used to enrich the phosphopeptides from the hydrolysate,
followed by LC-ESI MS analysis. The MS/MS data generated from the initial hydrolysate and the phosphopeptide-enriched fraction,
in combination with MS analysis of the intact protein sample, allow us to reveal the presence of three different phosphoforms
of bovine αs1-casein and assign the phosphorylation sites to each phosphoform with high confidence. 相似文献
954.
Pt-doped mesoporous indium oxide (In2O3) has been successfully obtained by a simple and effective in situ nanocasting method. The resultant samples were characterized by XRD, FE-SEM, TEM, N2 physisorption, XPS and EDX. The gas sensing properties for hydrogen sulfide (H2S) of the Pt-doped mesoporous In2O3 specimens were also examined. The results exhibit those In2O3 specimens possess much higher response to H2S even at low concentration of 2 ppm and a lower optimum working temperature of 150 °C. A possible mechanism was also provided to explain the improvement of the sensing properties. 相似文献
955.
It has been envisioned that carbon nanotubes could promote electron‐transfer reactions when used as electrode materials in electrochemical cells. In the present study, calf thymus DNA was electrochemically oxidized at an electrode modified with multiwalled carbon nanotubes. The potentials for DNA oxidation at pH 7.0 were found to be 0.71 and 0.81 V versus SCE, corresponding to the oxidation of guanine and adenine residues, respectively. An initial oxidation of adenine was observed in the first scan, which was followed by a quasi‐reversible redox process of the oxidation product in the subsequent scans. 相似文献
956.
Nan Wu 《Analytica chimica acta》2009,653(1):103-967
A novel and highly selective optical sensor with molecularly imprinted polymer (MIP) film was fabricated and investigated. The optical sensor head employing a medium finesse molecularly imprinted polymer film has been fabricated and characterised. A blank polymer and formaldehyde imprinted polymer were using methacrylic acid as the functional monomer and the ethylene glycol dimethacrylate as a crosslinker. The transduction mechanism is discussed based on the changes of optical intensity of molecularly imprinted polymer film acting as an optical reflected sensor. Template molecules, which diffused into MIP, could cause film density, and refractive index change, and then induce measurable optical reflective intensity shifts. Based on the reflective intensity shifts, an optical reflection detection of formaldehyde was achieved by illuminating MIP with a laser beam. For the same MIP, the reflective intensity shift was proportional to the amount of template molecule. This optical sensor, based on an artificial recognition system, demonstrates long-time stability and resistance to harsh chemical environments. As the research moves forward gradually, we establish the possibilities of quantitative analysis primly, setting the groundwork to the synthesis of the molecular imprinted optical fiber sensor. The techniques show good reproducibility and sensitivity and will be of significant interest to the MIPcommunity. 相似文献
957.
Su-Ping He Gui-Yu Tan Gang Li Wei-Ming Tan Tie-Gui Nan Bao-Min Wang Zhao-Hu Li Qing X. Li 《Analytical and bioanalytical chemistry》2009,393(4):1297-1303
Artemisinin is an endoperoxide sesquiterpene lactone isolated from the Chinese medicinal plant Artemisia annua L. It has been widely used in South-East Asia and Africa as an effective drug against sensitive and multidrug-resistant Plasmodium falciparum malaria. A monoclonal antibody (mAb), designated as 3H2, was generated with artesunate–bovine serum albumin conjugate as
the immunogen. mAb 3H2 was used to develop a highly sensitive and specific indirect competitive enzyme-linked immunosorbent
assay (icELISA) for artemisinin. The concentration of analyte producing 50% of inhibition (IC50) and the working range of the icELISA were 1.3 and 0.2–5.8 ng/mL, respectively. The mAb 3H2 recognized the artemisinin analogs
artesunate, dihydroartemisinin, and artemether with cross-reactivity of 650%, 57%, and 3%, respectively, but negligibly recognized
deoxyartemisinin and the artemisinin precursors arteannuin B and artemisinic acid. The average recoveries of artemisinin fortified
in A. annua samples at concentrations from 156 to 5,000 μg/g determined by icELISA ranged from 91% to 98%. The icELISA was applied for
the determination of artemisinin in different wild A. annua samples and the results were confirmed by high-performance liquid chromatography (HPLC) analysis. The correlation coefficient
(R
2) between the two assays was larger than 0.99, demonstrating a good agreement between the icELISA and HPLC results. This ELISA
is suitable for quality assurance of A. annua L. materials.
Figure
Artemisia annua plant and antimalarial drugs derived from artemisinin 相似文献
958.
Ranked-set sampling (RSS) often provides more efficient inference than simple random sampling (SRS). In this article, we propose
a systematic nonparametric technique, RSS-EL, for hypothesis testing and interval estimation with balanced RSS data using
empirical likelihood (EL). We detail the approach for interval estimation and hypothesis testing in one-sample and two-sample
problems and general estimating equations. In all three cases, RSS is shown to provide more efficient inference than SRS of
the same size. Moreover, the RSS-EL method does not require any easily violated assumptions needed by existing rank-based
nonparametric methods for RSS data, such as perfect ranking, identical ranking scheme in two groups, and location shift between
two population distributions. The merit of the RSS-EL method is also demonstrated through simulation studies.
This work was supported by National Natural Science Foundation of China (Grant No. 10871037) 相似文献
959.
By combining the semiempirical density-functional based tight-binding optimization with density-functional theory single-point energy calculation at the PBE1PBE/6-311G level, we propose an efficient computational approach to determine lowest-energy structures of large-sized carbon fullerenes. Our studies show that C(92) (D(3): 28) and C(94) (C(2): 43) are the new leading candidates for the lowest-energy structures of C(92) and C(94). Moreover, for the first time, the lowest-energy structures of C(98)-C(110) are identified on the basis of the density-functional theory calculation. The lowest-energy isomers C(102) (C(1): 603) and C(108) (D(2): 1771) are readily isolated experimentally because they are much lower in energy than their other low-lying IPR isomers. 相似文献
960.
Xu N Powell DR Cheng L Richter-Addo GB 《Chemical communications (Cambridge, England)》2006,(19):2030-2032
The NO ligand in the formally {FeNO}6 compound [Fe(oep)(NO)(thiolate)] is bent, and does not impart a significant structural trans effect to the Fe-S bond. 相似文献