全文获取类型
收费全文 | 222篇 |
免费 | 8篇 |
国内免费 | 11篇 |
专业分类
化学 | 156篇 |
力学 | 1篇 |
综合类 | 1篇 |
数学 | 17篇 |
物理学 | 66篇 |
出版年
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 22篇 |
2012年 | 18篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 16篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1993年 | 1篇 |
排序方式: 共有241条查询结果,搜索用时 31 毫秒
101.
Vincensini D Dedieu V Eliat PA Vincent C Bailly C de Certaines J Joffre F 《Magnetic resonance imaging》2007,25(3):293-302
Vascular permeability (k(ep), min(-1)) and extracellular volume fraction (v(e)) are tissue parameters of great interest to characterize malignant tumor lesions. Indeed, it is well known that tumors with high blood supply better respond to therapy than poorly vascularized tumors, and tumors with large extracellular volume tend to be more malignant than tumors showing lower extracellular volume. Furthermore, the transport of therapeutic agents depends on both extracellular volume fraction and vessel permeability. Thus, before treatment, these tissue parameters may prove useful to evaluate tumor aggressiveness and to predict responsiveness to therapy and variations during cytotoxic therapies could allow to assess treatment efficacy and early modified therapy schedules in case of poor responsiveness. As a consequence, there is a need to develop methods that could be routinely used to determine these tissue parameters. In this work, blood-tissue permeability and extracellular volume fraction information were derived from magnetic resonance imaging dynamic longitudinal relaxation rate (R(1)) mapping obtained after an intravenous bolus injection of Gd-DTPA in a group of 92 female patients with breast lesions, 68 of these being histologically proven to be with carcinoma. For the sake of comparison, 24 benign lesions were studied. The measurement protocol based on two-dimensional gradient echo sequences and a monoexponential plasma kinetic model was that validated in the occasion of previous animal experiments. As a consequence of neoangiogenesis, results showed a higher permeability in malignant than in benign lesions, whereas the extracellular volume fraction value did not allow any discrimination between benign and malignant lesions. The method, which can be easily implemented whatever the imaging system used, could advantageously be used to quantify lesion parameters (k(ep) and v(e)) in routine clinical imaging. Because of its large reproducibility, the method could be useful for intersite comparisons and follow-up studies. 相似文献
102.
Karel Pomeisl Jaroslav Kví?ala Antonín Klásek Vladislav Kubelka Jan ?ejka 《Tetrahedron》2007,63(42):10549-10561
3-(Fluoroacyloxy)quinoline-2,4(1H,3H)-diones react with triethyl phosphite to afford either the product of the Perkow reaction or the corresponding 4-ethoxyquinolin-2(1H)-one. In both reactions, the fluorocarboxylate anion acts as the leaving group. For the corresponding 3-(fluoroiodoacetoxy) derivative this observation precludes the application of the intramolecular Wittig-Horner synthesis to modify quinoline-2,4(1H,3H)-diones by the annulation of a fluorinated but-2-enolide moiety. 相似文献
103.
I. Al-Saleh M. Al-Zahrani M. Al-Shanshoury G. Mohammed N. Shinwari I. Al-Doush P. Basile 《Chromatographia》2002,55(7-8):457-461
Summary Comparative analytical quantitation of DDE, DDD, and DDT in human milk, by gas chromatography with mass spectrometric and
electron capture detection (GC-MS and GC-ECD) has been studied by use of 513 samples of milk from lactating mothers participating
in a World Health Organization special study. Although Correlation between thep,p-DDE concentrations measured by GC-ECD and GC-MSD was excellent (r=0.950,P<0.0001) and correlation was significant and moderate forp,p-DDD andp,p-DDT, the best precision was obtained by use of GC-MS. This study has therefore demonstrated that GC-MSD is a useful tool
for determining the concentration of DDT and its metabolites, because it enables simultaneous detection and confirmation. 相似文献
104.
J. Kritzenberger G. Bernhardt R. Gust P. Pistor H. Schönenberger H. Yersin 《Monatshefte für Chemie / Chemical Monthly》1993,124(5):587-604
Summary The syntheses of dichlorobis(cycloalkylamine)platinum(II) complexes withcis andtrans cycloalkylamine ligands [cis-PtCl2(C3H5NH2)2 tocis-PtCl2(C8H15NH2)2 (3–8) andtrans-PtCl2(C7H13NH2)2 (9) andtrans-PtCl2(C8H15NH2)2 (10)] are described. The distinction betweencis andtrans isomers was achieved by1H-NMR spectroscopy. The antitumor activity was determined on the cell proliferation of the human MDA-MB-231 breast cancer cell line during long-term drug exposure. The complexes with small cycloalkylamine ligands (3–6) were inferior, those with large cycloalkylamine ligands were comparable (7) or superior (8) to cisplatin. Surprisingly, thecis/trans isomers7/9 and8/10 were equally active. All cycloalkylamine ligands were inactive. IR-spectroscopic studies showed that the size of the cycloalkylamine ring does not lead to significant differences in the Pt-Cl binding strength. Therefore it is assumed that the markedly stronger antitumor activity of the higher homologues,7–10, is not the result of a faster reaction with bionucleophils such as DNA. A possible explanation of the high activity of7–10 is the strong lipophilicity of the complexes. This assumption was confirmed by toxicity tests against confluent cultures.In memory of Professor Dr. Günter Gliemann, late director of the Institut für Physikalische und Theoretische Chemie, Universität Regensburg. 相似文献
105.
Platinum concentration in silicone breast implant material and capsular tissue by ICP-MS 总被引:2,自引:0,他引:2
Maharaj SV 《Analytical and bioanalytical chemistry》2004,380(1):84-89
Inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine the concentration of platinum (Pt) in silicone breast implant gel (range, 0.26–48.90 g g–1 Pt; n=15), elastomer (range, 3.05–28.78 g g–1 Pt; n=7), double lumen (range, 5.79–125.27 g g–1 Pt; n=7), foam (range, 5.79–8.36 g g–1 Pt; n=2), and capsular tissue (range, 0.003–0.272 g g–1 Pt; n=15). The results show that very high levels of Pt are present in the encasing elastomer, double lumen, and foam envelope materials. Silicone breast implants can be a source of significant Pt exposure for individuals with these implants. 相似文献
106.
Identification and quantification of tamoxifen and four metabolites in serum by liquid chromatography-tandem mass spectrometry 总被引:1,自引:0,他引:1
Gjerde J Kisanga ER Hauglid M Holm PI Mellgren G Lien EA 《Journal of chromatography. A》2005,1082(1):6-14
We have developed a method for the determination of tamoxifen (tam) and its metabolites 4-hydroxytamoxifen (4OHtam), N-demethyltamoxifen (NDtam), N-dedimethyltamoxifen (NDDtam), tamoxifen-N-oxide (tamNox), and 4-hydroxy-N-demethyltamoxifen (4OHNDtam) in 50 microl human serum. Serum proteins were precipitated with acetonitrile. Deuterated-tamoxifen (D5 tam) was added as internal standard. Sample supernatant was injected into an on-line reversed-phase extraction column coupled with a C18 analytical column and analytes were detected by tandem mass spectrometry. The lower limits of quantification were 0.25 ng/mL for 4OHtam, NDtam and tam, 1.0 ng/mL for NDDtam and tamNox. Ranges of within- and between-day variation were 2.9-15.4% and 4.4-12.9%, respectively. 相似文献
107.
With a 511-slit one-dimensional (1D) Hadamard mask and a highly sensitive linear charge-coupled device (CCD), spatial multiplexing is performed and a programmable Hadamard transform (HT) microscopic fluorescence imaging system was developed. The system can generate 511×512 pixel format images for small samples. Sensitivity, signal to noise ratio, imaging speed and spatial resolution of this system were discussed. The results show that the system can be applied for single-cell imaging sensitively in a short time. Spatial resolution up to 0.24 μm/pixel, which is close to the resolution limit of the conventional optical microscope, has been obtained under oil lens. The weak native fluorescence imaging for pollen cells can be realized within 1 min. The system has been applied for multi-parameter evaluation of tumor malignancy based on nuclear DNA ploidy measurements for one breast tumor specimen. The result indicates that the system has good application prospect in cell biology and medicine. 相似文献
108.
J. Rodríguez Flores J. J. Berzas Nevado G. Castañeda Peñalvo M. I. Rodríguez Cáceres 《Chromatographia》2002,56(5-6):283-288
Summary A micellar electrokinetic capillary chromatography (MEKC) method has been developed for quantification of four drugs-tamoxifen,
anastrozole, letrozole, and methotrexate—used to treat advanced breast cancer. Separation was performed at 25°C and 25kV,
with 20mm borate buffer (pH 9.2) containing 40mm sodium dodecylsulfate as electrolyte solution. Under these conditions analyses were performed in 12 min. The linearity of
the response was investigated for the concentration range 2.0–20.0 mg L−1. The intra-day residual standard deviation (n=4 graphs) between the slopes of the calibration graphs was acceptable for the four drugs studied. Detection limits (signal-to-noise
ratio=3) were below 1 mg L−1 for all the compounds. The simplicity, precision, and sensitivity of MEKC proved suitable for quality control of pharmaceutical
preparations used to treat advanced breast cancer. Six different pharmaceutical preparations, each containing one of the above-mentioned
drugs, were successfully analyzed. 相似文献
109.
Thirty-two breast milk samples provided voluntarily by healthy women living in the Dongting Lake area were investigated by
Inductively Coupled Plasma Mass Spectrometry (ICP/MS). Eleven minor and trace elements (Na, Mg, K, Ca, Mn, Fe, Cu, Zn, As,
Se and Pb) were quantified and compared with literature reports. The results provide useful data for further studies in the
nutritional field.
Author for correspondence. E-mail: zhengmh@mail. rcees.ac.cn
Received September 4, 2002; accepted February 11, 2003
Published online May 15, 2003 相似文献
110.
To investigate the mechanism of the anti-tumor activity of cinobufacini on the breast cancer cell line T-47D,the inhibitory effect of cinobufacini on the proliferation of T-47D was detected via MTT assay and the morphological changes of T-47D and HBL-100 cells caused by cinobufacini were observed with an inverted microscope.Cell apoptosis and cell cycle stages were detected by flow cytometry analysis.The effects of cinobufacini on the expression of active-form and pro-form of caspase-3 were assessed by Western blot analysis.Cinobufacini dramatically inhibited T-47D proliferation in a dose-and time-dependent manner.We found that more than 20% of T-47D cells were killed after treatment with 20 mg/mL cinobufacini for 24 h in vitro.After 6 d of treatment with 20 mg/mL cinobufacini,the cell survival rate decreased by more than 40%.Flow cytometric analysis demonstrated that cinobufacini induced significant apoptosis and changes of the cell cycle distribution of T-47D cells.We used breast cell line HBL-100 as the control,the above experiments except cell cycle analysis showed that cinobufacini more obviously induced the apoptosis of T-47D cells than that of HBL-100 cells.Western blot analysis confirmed the protein expression of active caspase-3 increased with increasing the dose of cinobufacini.These results indicate that cinobufacini induces the apoptosis of T-47D cells via the up-regulation of caspase-3. 相似文献