全文获取类型
收费全文 | 1945篇 |
免费 | 118篇 |
国内免费 | 9篇 |
专业分类
化学 | 1537篇 |
晶体学 | 19篇 |
力学 | 41篇 |
数学 | 146篇 |
物理学 | 329篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 22篇 |
2021年 | 43篇 |
2020年 | 36篇 |
2019年 | 43篇 |
2018年 | 32篇 |
2017年 | 35篇 |
2016年 | 94篇 |
2015年 | 65篇 |
2014年 | 97篇 |
2013年 | 187篇 |
2012年 | 171篇 |
2011年 | 163篇 |
2010年 | 115篇 |
2009年 | 89篇 |
2008年 | 111篇 |
2007年 | 111篇 |
2006年 | 117篇 |
2005年 | 97篇 |
2004年 | 79篇 |
2003年 | 75篇 |
2002年 | 97篇 |
2001年 | 31篇 |
2000年 | 25篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2072条查询结果,搜索用时 328 毫秒
991.
Disposable integrated microfluidic biochip for blood typing by plastic microinjection moulding 总被引:1,自引:0,他引:1
Blood typing is the most important test for both transfusion recipients and blood donors. In this paper, a low cost disposable blood typing integrated microfluidic biochip has been designed, fabricated and characterized. In the biochip, flow splitting microchannels, chaotic micromixers, reaction microchambers and detection microfilters are fully integrated. The loaded sample blood can be divided by 2 or 4 equal volumes through the flow splitting microchannel so that one can perform 2 or 4 blood agglutination tests in parallel. For the purpose of obtaining efficient reaction of agglutinogens on red blood cells (RBCs) and agglutinins in serum, we incorporated a serpentine laminating micromixer into the biochip, which combines two chaotic mixing mechanisms of splitting/recombination and chaotic advection. Relatively large area reaction microchambers were also introduced for the sake of keeping the mixture of the sample blood and serum during the reaction time before filtering. The gradually decreasing multi-step detection microfilters were designed in order to effectively filter the reacted agglutinated RBCs, which show the corresponding blood group. To achieve the cost-effectiveness of the microfluidic biochip for disposability, the biochip was realized by the microinjection moulding of COC (cyclic olefin copolymer) and thermal bonding of two injection moulded COC substrates in mass production with a total fabrication time of less than 20 min. Mould inserts of the biochip for the microinjection moulding were fabricated by SU-8 photolithography and the subsequent nickel electroplating process. Human blood groups of A, B and AB have been successfully determined with the naked eye, with 3 microl of the whole sample bloods, by means of the fabricated biochip within 3 min. 相似文献
992.
We present a simple cell docking method induced by receding meniscus to capture non-adherent yeast cells onto microwells inside a microfluidic channel. Microwells were fabricated either by capillary moulding of UV curable polyurethane acrylate (PUA) onto glass substrate or direct replica moulding of poly(dimethyl siloxane) (PDMS). A cell suspension of the budding yeast, Saccharomyces cerevisiae, was introduced into the microfluidic channel by surface tension driven capillary flow and a receding meniscus was subsequently generated by evaporation. As the meniscus progressed, one to multiple yeast cells were spontaneously captured onto microwells by lateral capillary force created at the bottom of the meniscus. Using this cell-based platform, we observed the response of yeast cells upon stimulation by a mating pheromone (alpha-factor) by monitoring the expression of green fluorescent protein (GFP) with time. It was observed that alpha-factor triggered the expression of GFP at 60 min after stimulation and the fluorescence intensity was sustained for an additional 60 min without changes. 相似文献
993.
The influence of Bi modification of Pt anode catalyst on the performance of direct formic acid fuel cells was investigated. Compared with the unmodified Pt anode, the Bi modified Pt (PtBi(m)) electrode prepared by under-potential deposition (UPD) caused faster electrocatalytic oxidation of formic acid at the same value of the overpotential, and thus, PtBi(m) resulted in an increase in the power performance of direct formic acid fuel cells. Electrochemical impedance spectra helped to explain the difference of performance between the unmodified Pt and Bi modified Pt electrodes. Solution conductivity and dehydration phenomena occurring in highly concentrated formic acid solutions can also explain the higher power performance of PtBi(m). 相似文献
994.
Schiff’s base condensation of 2,6-diformyl-4-R-phenol and affords 34-membered macrocyclic tetraiminodiphenol compounds, (R = H and R′ = iPr, 1; R = Me and R′ = iPr, 2; R = F and R′ = iPr, 3; R = Me and R′ = Et, 4; R = F and R′ = Et, 5) in good yields (47-62%), from which dinuclear nickel complexes, (R = H and R′ = iPr, 6; R = Me and R′ = iPr, 7; R = F and R′ = iPr, 8) are prepared. Molecular structures of 2, dipotassium salt of 1, and 7 were confirmed by X-ray crystallography. Addition of B(C6F5)3 to a toluene solution of 6-8 gives insoluble precipitates which show good activity for ethylene polymerization. 相似文献
995.
A new thermodynamic calculation procedure is introduced to predict the equilibrium conditions of multicomponent gas hydrates containing hydrogen. This new approach utilizes an excess Gibbs potential term to account for second- or higher-order water-cavity distortions due to the presence of multiple guest species. The excess Gibbs potential describes changes in reference chemical potentials according to different compositions of guest mixtures in the hydrate phase. To determine the equilibrium conditions of multicomponent gas hydrates, the excess Gibbs potential term is incorporated to the Lee-Holder model along with the Zele-Lee-Holder cell distortion model. For binary gas hydrates between hydrogen and the other gas molecule, the predicted equilibrium pressure deviates within 10-20% from the experimental value. For the ternary and quaternary mixture hydrates, the model prediction is reasonably good but its error increases with increasing pressure and temperature under the presence of THF. 相似文献
996.
997.
Yun B Kim Jae K Ryu Hong J Lee In J Lim Dongsun Park Min C Lee Seung U Kim 《BMC neuroscience》2010,11(1):42
Background
Midkine (MK), a member of the heparin-binding growth factor family, which includes MK and pleiotrophin, is known to possess neurotrophic and neuroprotective properties in the central nervous system. Previous studies have shown that MK is an effective neuroprotective agent in reducing retinal degeneration caused by excessive light and decreasing hippocampal neuronal death in ischemic gerbil brain. The present study was undertaken to investigate whether MK acts as an anticonvulsant in kainic acid (KA)-induced seizure in mouse and blocks KA-mediated neuronal cell death in hippocampus. 相似文献998.
This paper presents a 900-1700 nm hyper-spectral imaging spectrometer which offers low distortions, a low F-number, a compact size, an easily-fabricated design and a low cost (is presented in this paper). The starting point for its optical design is discussed according to the geometrical aberration theory and Rowland circle condition. It is shown that these methods are useful in designing a push-broom hyper-spectral imaging spectrometer that has an aperture of f/2.4, modulation transfer functions of less than 0.8 at 25 cycles/mm, and spot sizes less than 10 μm. A prototype of the optimized hyper-spectral imaging spectrometer has been fabricated using a high precision machine and the experimental demonstration with the fabricated hyper-spectral imaging spectrometer is presented. 相似文献
999.
Myeon‐Cheon Choi Jae‐Chul Hwang Chiwan Kim Youngkyoo Kim Chang‐Sik Ha 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):5189-5197
We synthesized new polynorbornene dicarboximide (PCaNI) functionalized with hole‐transporting carbazole moieties and its copolymer (PCaNA) by ring‐opening metathesis polymerization (ROMP), where the PCaNA was further reacted with 3‐amino‐triethoxysilane to prepare PCaNI/silica hybrid. We also investigated the feasibility of PCaNI and PCaNI/silica hybrid (PCaSi) as a hole‐transporting material for hybrid organic light emitting devices (HOLEDs). To improve the performance of the PCaNI‐based HOLEDs, N,N′‐diphenyl‐N,N′‐(3‐methylphenyl)‐[1,1′‐biphenyl]‐4‐4′‐diamine (TPD) was also introduced into the PCaNI matrix. Results showed that PCaNI exhibited high glass transition temperature (~260 °C) and high optical transparency in the visible region. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of PCaNI were measured as 5.6 and 2.2 eV, while the TPD‐doped PCaNI showed 5.7 eV (HOMO) and 2.6 eV (LUMO). The PCaNI/silica hybrid nanolayers showed excellent solvent resistance due to the formation of covalent bonds between ITO and PCaNI. The HOLEDs with PCaNI/TPD or PCaSi/TPD hybrid nanolayers exhibited relatively higher luminance (~10,000 cd/m2), lower operating voltage (~6.5 V at 300 cd/m2), and higher current efficiency (~2.7 cd/A). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
1000.
Jin Young Choi Soo Jung Lee Sung Joong Lee Semin Park Jung Han Lee Jae‐Han Shim A. M. Abd El‐Aty Jong‐Sung Jin Euh‐Duck Jeong Won Sup Lee Sung Chul Shin 《Journal of separation science》2010,33(9):1192-1197
The skin of Vitis coignetiae Pulliat (meoru) grown wild in the Republic of Korea was analyzed for anthocyanins via HPLC coupled to ESI‐MS/MS in positive ion mode. Chromatographic separation was conducted via RP HPLC using a C18 column, with a 50‐min gradient from 0 to 80% methanol in water containing 0.5% formic acid. A total of 18 anthocyanins were identified. Among them, nine compounds were newly determined by comparing the retention time (tR) and mass fragmentation patterns with those of the previously reported anthocyanins for other grape varieties: malvidin hexose, peonidin 3‐galactoside, malvidin 3‐galactoside, cyanidin, petunidin, petunidin 3‐(6″‐coumaroyl)‐5‐diglucoside, peonidin, malvidin, and malvidin 3‐(6″‐coumaroyl)‐5‐diglucoside. The antioxidant activity of the V. coignetiae Pulliat anthocyanins was determined via 2,2‐diphenyl‐2‐picrylhydrazyl radical scavenging and 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical cation assays in a range of concentration from 25 to 500 mg/L. The capacity increased with concentration. The IC50 values, defined as the concentration of sample required to scavenge 50% of free radicals, were calculated as follows: 189.63±11.31 mg/L and 141.29±6.70 mg/L for 2,2‐diphenyl‐2‐picrylhydrazyl and 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical cation, respectively. The antioxidant activity of the V. coignetiae Pulliat anthocyanins is substantially higher than that of ascorbic acid and is similar to the effects of the extracts obtained from other grape varieties. 相似文献