全文获取类型
收费全文 | 5568篇 |
免费 | 1283篇 |
国内免费 | 425篇 |
专业分类
化学 | 2963篇 |
晶体学 | 15篇 |
力学 | 76篇 |
综合类 | 14篇 |
数学 | 62篇 |
物理学 | 4146篇 |
出版年
2024年 | 26篇 |
2023年 | 48篇 |
2022年 | 286篇 |
2021年 | 307篇 |
2020年 | 349篇 |
2019年 | 299篇 |
2018年 | 245篇 |
2017年 | 318篇 |
2016年 | 377篇 |
2015年 | 340篇 |
2014年 | 595篇 |
2013年 | 499篇 |
2012年 | 425篇 |
2011年 | 431篇 |
2010年 | 338篇 |
2009年 | 367篇 |
2008年 | 356篇 |
2007年 | 349篇 |
2006年 | 222篇 |
2005年 | 181篇 |
2004年 | 133篇 |
2003年 | 109篇 |
2002年 | 93篇 |
2001年 | 65篇 |
2000年 | 84篇 |
1999年 | 70篇 |
1998年 | 62篇 |
1997年 | 54篇 |
1996年 | 44篇 |
1995年 | 28篇 |
1994年 | 25篇 |
1993年 | 17篇 |
1992年 | 22篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 1篇 |
1982年 | 9篇 |
1980年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有7276条查询结果,搜索用时 15 毫秒
921.
Looking inside the human body fascinated mankind for thousands of years. Current diagnostic and therapy methods are often limited by inadequate sensitivity, specificity and spatial resolution. Raman imaging may bring revolution in monitoring of disease and treatment. The main advantage of Raman imaging is that it gives spatial information about various chemical constituents in defined cellular organelles in contrast to conventional methods (liquid chromatography/mass spectrometry, NMR, HPLC) that rely on bulk or fractionated analyses of extracted components. We demonstrated how Raman imaging can drive the progress on breast cancer just unimaginable a few years ago. We looked inside human breast ducts answering fundamental questions about location and distribution of various biochemical components inside the lumen, epithelial cells of the duct and the stroma around the duct during cancer development. We have identified Raman candidates as diagnostic markers for breast cancer prognosis: carotenoids, mammaglobin, palmitic acid and sphingomyelin as key molecular targets in ductal breast cancer in situ, and propose the molecular mechanisms linking oncogenes with lipid programming. 相似文献
922.
A simple Schiff-base derivative with salicylaldehyde moieties as fluorescent probe 1 was reported by aggregation-induced emission (AIE) characterization for the detection of metal ions. Spectral analysis revealed that probe 1 was highly selective and sensitive to Al3+. The probe 1 was also subject to minimal interference from other common competitive metal ions. The detection limit of Al3+ was 0.4 μM, which is considerably lower than the World Health Organization standard (7.41 μM), and the acceptable level of Al3+ (1.85 μM) in drinking water. The Job's plot and the results of 1H-NMR and FT-IR analyses indicated that the binding stoichiometry ratio of probe 1 to Al3+ was 1:2. Probe 1 demonstrated a fluorescence-enhanced response upon binding with Al3+ based on AIE characterization. This response was due to the restricted molecular rotation and increased rigidity of the molecular assembly. Probe 1 exhibited good biocompatibility, and Al3+ was detected in live cells. Therefore, probe 1 is a promising fluorescence probe for Al3+ detection in the environment. 相似文献
923.
A rhodamine spirolactam derivative (1) bearing a hydrophilic carboxylic acid group is developed as a fluorescent chemodosimeter for bivalent mercury ions (Hg2+) in 100% aqueous solution. It exhibits a highly sensitive “turn-on” fluorescent response toward Hg2+ with a 42-fold fluorescence intensity enhancement under 1 equiv. of Hg2+ added. The chemodosimeter can be applied to the quantification of Hg2+ with a linear range covering from 3.0 × 10−7 to 1.0 × 10−5 M and a detection limit of 9.7 × 10−8 M. Most importantly, the fluorescence changes of the chemodosimeter are remarkably specific for Hg2+ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the experiment results show that the response behavior of 1 towards Hg2+ is pH independent in neutral condition (pH 5.0–8.0) and the response is fast (response time less than 3 min). Furthermore, the ring-opening mechanism of the rhodamine spirolactam induced by Hg2+ was supported by NMR, MS, and DFT theoretical calculations. In addition, the proposed chemodosimeter has been used to detect Hg2+ in water samples and image Hg2+ in living cells with satisfying results. 相似文献
924.
Quantification of a mixture of peptides in solution was achieved by disposable patterned hydrophilic chip based matrix-assisted laser desorption/ionization mass spectrometric imaging(MALDI MSI).Compared with other quantitative methods for peptides in solution, this method is label-free and does not require separation of the multiple components of the solution before analysis. Uniform hydrophilic spots and high mass accuracy measurements provided confident identification and quantitative analysis of imaged compounds. The linear correlation between concentration and grayscale of image in the range of 5 fmol/μ L to 1 pmol/μ L was obtained for all four peptides. Good sensitivity and excellent reproducibility were also achieved. The method expands the application of MALDI MSI from tissues to solutions. 相似文献
925.
目的探讨急性脑梗死患者脑微出血的发病情况及其危险因素。方法选择急性脑梗死患者75例,男51例,女24例,年龄42~83(64.9±10.8)岁。行头颅CT、磁敏感成像(SWI)检查,依据脑微出血检出的结果分成阳性组(23例)与阴性组(52例),比较两组的一般资料,探讨脑微出血发病的危险因素。结果SWI检查的检出率比CT检出率高(χ2=27.17,P<0.05)。阳性组年龄、高血压病、糖尿病患病率均较阴性组高,差异均有统计学意义(均P<0.05);两组性别、血脂异常、心房颤动、冠心病、吸烟、饮酒情况比较,差异均无统计学意义(均P>0.05)。logistic回归分析显示年龄增长、高血压病是脑微出血的独立危险因素(P<0.05)。结论急性脑梗死患者合并存在脑微出血的比例高,SWI检查是检测脑微出血的敏感方法,年龄大、高血压病与脑微出血的发生密切相关。 相似文献
926.
Micropatterning of the Ferroelectric Phase in a Poly(vinylidene difluoride) Film by Plasmonic Heating with Gold Nanocages
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jianhua Li Miaoxin Yang Xiaojun Sun Dr. Xuan Yang Dr. JiaJia Xue Dr. Chunlei Zhu Prof. Hong Liu Prof. Younan Xia 《Angewandte Chemie (International ed. in English)》2016,55(44):13828-13832
Polymer thin films with patterned ferroelectric domains are attractive for a broad range of applications, including the fabrication of tactile sensors, infrared detectors, and non‐volatile memories. Herein, we report the use of gold nanocages (AuNCs) as plasmonic nanostructures to induce a ferroelectric–paraelectric phase transition in a poly(vinylidene fluoride) (PVDF) thin film by leveraging its photothermal effect. This technique allows us to generate patterned domains of ferroelectric PVDF within just a few seconds. The incorporation of AuNCs significantly enhances the pyroelectric response of the ferroelectric film under near‐infrared irradiation. We also demonstrate the use of such patterned ferroelectric films for near‐infrared sensing/imaging. 相似文献
927.
Imaging of Oxygen Diffusion in Individual Platinum/Ce2Zr2Ox Catalyst Particles During Oxygen Storage and Release
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Hirosuke Matsui Dr. Nozomu Ishiguro Kaori Enomoto Dr. Oki Sekizawa Prof. Dr. Tomoya Uruga Prof. Dr. Mizuki Tada 《Angewandte Chemie (International ed. in English)》2016,55(39):12022-12025
The spatial distribution of Ce3+ and Ce4+ in each particle of Ce2Zr2Ox in a three‐way conversion catalyst system was successfully imaged during an oxygen storage/release cycle by scanning X‐ray absorption fine structure (XAFS) using hard X‐ray nanobeams. For the first time, nano‐XAFS imaging visualized and identified the modes of non‐uniform oxygen diffusion from the interface of Pt catalyst and Ce2Zr2Ox support and the active parts in individual catalyst particles. 相似文献
928.
Timothy W. Bumpus Prof. Dr. Jeremy M. Baskin 《Angewandte Chemie (International ed. in English)》2016,55(42):13155-13158
Phosphatidic acid (PA) is a potent lipid secondary messenger, the synthesis of which is tightly regulated in both space and time. Established tools for detecting PA involve ex vivo analysis and do not provide information on the subcellular locations where this lipid is synthesized. Here, a chemoenzymatic strategy for imaging sites of cellular PA synthesis by phospholipase D (PLD) enzymes is reported. PLDs were found to be able to catalyze phospholipid head‐group exchange with alkynols to generate alkyne‐labeled PA analogues within cells. Subsequent fluorophore tagging through Cu‐catalyzed azide–alkyne cycloaddition enabled both visualization by fluorescence microscopy and quantification by HPLC. Our studies revealed several intracellular sites of PLD‐mediated PA synthesis. We envision applications of this approach to dissect PA‐dependent signaling pathways, image PLD activity in disease, and remodel intracellular membranes with new functionality. 相似文献
929.
Koushik Sarkar Prof. Parthasarathi Dastidar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18963-18974
A mixed ligand approach was exploited to synthesize a new series of MnII‐based coordination polymers (CPs), namely, CP1 {[Mn(μ‐dpa)(μ‐4,4′‐bp)]?MeOH}∞, CP2 {[Mn3(μ‐dpa)3(2,2′‐bp)2]}∞, CP3 {[Mn3(μ‐dpa)3(1,10‐phen)2]?2 H2O}∞, CP4 {[Mn(μ‐dpa)(μ‐4,4′‐bpe)1.5]?H2O}∞, CP5 {[Mn2(μ‐dpa)2(μ‐4,4′‐bpe)2]? DEF}∞, and CP6 {[Mn(μ‐dpa)(μ‐4,4′‐bpe)1.5]? DMA}∞ (dpa=3,5‐dicarboxyphenyl azide, 2,2′‐bp=2,2′‐bipyridine, 1,10‐phen=1,10‐phenanthroline, 4,4′‐bpe=1,2‐bis(4‐pyridyl)ethylene, 4,4′‐bp=4,4′‐bipyridine, DEF=N,N‐diethylformamide, DMA=N,N‐dimethylacetamide), to develop multifunctional CPs. Various techniques, such as single‐crystal X‐ray diffraction (SXRD), FTIR spectroscopy, elemental analysis, and thermogravimetric analysis, were employed to fully characterize these CPs. The majority of the CPs displayed a four‐connected sql topology, whereas CP4 and CP6 exhibited a two‐dimensional SnS network architecture, which was further entangled in a polycatenation mode. Compound CP1 displayed an open framework structure. The CPs were scaled down to the nanoregime in a ball mill for cell imaging studies. Whereas CP2 and CP4 were employed for cell imaging with RAW264.7 cells, CP1 was exploited for both cell imaging and heterogeneous catalysis in a cyanosilylation reaction. 相似文献
930.
Quantitative,In Situ Visualization of Metal‐Ion Dissolution and Transport Using 1H Magnetic Resonance Imaging
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Joshua M. Bray Prof. Alison J. Davenport Prof. Karl S. Ryder Dr. Melanie M. Britton 《Angewandte Chemie (International ed. in English)》2016,55(32):9394-9397
Quantitative mapping of metal ions freely diffusing in solution is important across a diverse range of disciplines and is particularly significant for dissolution processes in batteries, metal corrosion, and electroplating/polishing of manufactured components. However, most current techniques are invasive, requiring sample extraction, insertion of an electrode, application of an electric potential or the inclusion of a molecular sensor. Thus, there is a need for techniques to visualize the distribution of metal ions non‐invasively, in situ, quantitatively, in three dimensions (3D) and in real time. Here we have used 1H magnetic resonance imaging (MRI) to make quantitative 3D maps showing evolution of the distribution of Cu2+ ions, not directly visible by MRI, during the electrodissolution of copper, with high sensitivity and spatial resolution. The images are sensitive to the speciation of copper, the depletion of dissolved O2 in the electrolyte and show the dissolution of Cu2+ ions is not uniform across the anode. 相似文献