全文获取类型
收费全文 | 1952篇 |
免费 | 97篇 |
国内免费 | 11篇 |
专业分类
化学 | 1401篇 |
晶体学 | 23篇 |
力学 | 65篇 |
数学 | 163篇 |
物理学 | 408篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 57篇 |
2021年 | 62篇 |
2020年 | 59篇 |
2019年 | 51篇 |
2018年 | 37篇 |
2017年 | 41篇 |
2016年 | 62篇 |
2015年 | 55篇 |
2014年 | 75篇 |
2013年 | 139篇 |
2012年 | 148篇 |
2011年 | 151篇 |
2010年 | 91篇 |
2009年 | 86篇 |
2008年 | 151篇 |
2007年 | 118篇 |
2006年 | 121篇 |
2005年 | 91篇 |
2004年 | 100篇 |
2003年 | 53篇 |
2002年 | 75篇 |
2001年 | 32篇 |
2000年 | 42篇 |
1999年 | 18篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 20篇 |
1995年 | 10篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2060条查询结果,搜索用时 15 毫秒
161.
Dongjoon Lee Jong-Chan Park Keum Sim Jung Jiyeong Kim Ji Sung Jang Sunghoon Kwon Min Soo Byun Dahyun Yi Gihwan Byeon Gijung Jung Yu Kyeong Kim Dong Young Lee Sun-Ho Han Inhee Mook-Jung 《Experimental & molecular medicine》2022,54(1):61
The deposition of beta-amyloid (Aβ) in the brain precedes the onset of symptoms such as cognitive impairment in Alzheimer’s disease (AD); therefore, the early detection of Aβ accumulation is crucial. We previously reported the applicability of the QPLEXTM Alz plus assay kit for the prescreening of Aβ accumulation. Here, we tested the specific application of the kit in a large cohort of cognitively normal (CN) individuals of varying ages for the early detection of Aβ accumulation. We included a total of 221 CN participants with or without brain Aβ. The QPLEXTM biomarkers were characterized based on age groups (1st–3rd tertile) and across various brain regions with cerebral amyloid deposition. The 3rd tertile group (>65 years) was found to be the most suitable age group for the application of our assay kit. Receiver operating characteristic curve analysis showed that the area under the curve (AUC, discrimination power) was 0.878 with 69.7% sensitivity and 98.4% specificity in the 3rd tertile group. Additionally, specific correlations between biomarkers and cerebral amyloid deposition in four different brain regions revealed an overall correlation with general amyloid deposition, consistent with previous findings. Furthermore, the combinational panel with plasma Aβ1–42 levels maximized the discrimination efficiency and achieved an AUC of 0.921 with 95.7% sensitivity and 67.3% specificity. Thus, we suggest that the QPLEXTM Alz plus assay is useful for prescreening brain Aβ levels in CN individuals, especially those aged >65 years, to prevent disease progression via the early detection of disease initiation.Subject terms: Alzheimer''s disease, Neural ageing, ELISA 相似文献
162.
163.
TaeYoung Kim Minwon Suh Soon Jae Kwon Tae Hee Lee Jong Eun Kim You Jong Lee Joo Hyung Kim MunPyo Hong Kwang S. Suh 《Macromolecular rapid communications》2009,30(17):1477-1482
We report that poly(3,4‐ethylenedioxythiophene) derived from poly(ionic liquid) (PEDOT:PIL) constitutes a unique polymeric hole‐injecting material capable of improving device lifetime in organic light‐emitting diodes (OLEDs). Imidazolium‐based poly(ionic liquid)s were engineered to impart non‐acidic and non‐aqueous properties to PEDOT without compromising any other properties of PEDOT. A fluorescent OLED was fabricated using PEDOT:PIL as a hole‐injection layer and subjected to a performance evaluation test. In comparison with a control device using a conventional PEDOT‐based material, the device with PEDOT:PIL was found to achieve a significant improvement in terms of device lifetime. This improvement was attributed to a lower indium content in the PEDOT:PIL layer, which can be also interpreted as the effective protection characteristics of PEDOT:PIL for indium extraction from the electrodes.
164.
Effects of post-annealing on electrical properties of amorphous Ga-doped Zn–Sn–O semiconductor films
Dong-Ho Kim Hye-Ri Kim Jung-Dae Kwon Gun-Hwan Lee Juyun Park Yong-Cheol Kang 《Journal of Non》2012,358(18-19):2616-2619
We investigated the effect of post-annealing on the electrical properties of amorphous gallium-zinc-tin oxide (a-GZTO) films with different Ga contents. The films were deposited at room temperature by sputtering and annealed in air for 1 h. It was found that the doping with Ga, which acts as the carrier suppressor, contributes to the thermal stability of characteristic properties of a-GZTO thin films. The film with a small amount of Ga showed significant variations in carrier concentration according to the annealing temperature. Increases in carrier concentration and mobility can be ascribed to the reduction of subgap density of states by annealing. After annealing at 400 °C, however, the enrichment of Zn cations in surface region resulted in considerable changes in chemical bonding states and consequently, the carrier concentration decreased by two orders of magnitude for the low Ga-doped ZTO film. 相似文献
165.
Joong-Ho Kwon Myung-Woo Byun Kang-Soo Kim Il-Jun Kang 《Radiation Physics and Chemistry》2000,57(3-6):309-313
The hygienic, physicochemical, and organoleptic qualities of white ginseng were monitored during 6 months under accelerated conditions (40°C, 90% r.h.) by observing its microbial populations, disinfestation, and some quality attributes following either gamma irradiation at 2.5–10 kGy or commercial phosphine (PH3) fumigation. In a comparative study, both treatments were found to be effective for disinfecting the stored samples. Phosphine showed no appreciable decontaminating effects on microorganisms contaminated including coliforms, while 5 kGy irradiation was sufficient to control all microorganisms related to the quality of the packed samples. Irradiation at 5 kGy caused negligible changes in physicochemical attributes of the samples, such as ginsenosides, amino acids, fatty acids, and organoleptic properties, whereas phosphine fumigation was found detrimental to sensory flavor (P<0.01). Quality deterioration occurred in the commercially-packed samples was in the following order: the control, 10 kGy-, phosphine-, and 2.5–5 kGy-treated samples. Accordingly, irradiation at <5 kGy was found to be an effective alternative to phosphine fumigation for white ginseng. 相似文献
166.
Sun Hwa Lee Li Xu Dr. Byeong Kwon Park Yuri V. Mironov Dr. Soo Hyun Kim Young Ju Song Cheal Kim Prof. Dr. Youngmee Kim Dr. Sung‐Jin Kim Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4678-4685
Two new tetranuclear chalcocyanide cluster complexes, [{Mn(saloph)H2O}4Re4Q4(CN)12]?4 CH3OH? 8 H2O (saloph=N,N′‐o‐phenylenebis(salicylidenaminato), Q=Se ( 1 ‐Se), Te ( 2 ‐Te)), have been synthesized by the diffusion of a methanolic solution of [PPh4]4[Re4Q4(CN)12] into a methanolic solution of [Mn(saloph)]+. The structure of 2 ‐Te has been determined by X‐ray crystallography. These rhenium cluster‐supported [MnIII(saloph)] complexes have been found to efficiently catalyze a wide range of olefin epoxidations under mild experimental conditions in the presence of meta‐chloroperbenzoic acid (mCPBA). Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants MnV?O, MnIV?O, and MnIII? OOC(O)R. Evidence in support of this interpretation has been derived from reactivity and Hammett studies, H218O‐exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. Moreover, it has been observed that the participation of MnV?O, MnIV?O, and MnIII? OOC(O)R can be controlled by changing the substrate concentration. This mechanism provides the greatest congruity with related oxidation reactions that employ certain Mn complexes as catalysts. 相似文献
167.
A sweep optical frequency synthesizer is demonstrated by using a frequency-stabilized optical frequency comb and injection-locked distributed-Bragg-reflector (DBR) laser diode. The injection-locked DBR laser acts as a single-frequency filter and, simultaneously, a high-gain amplifier of the optical frequency comb. The frequency instability of the heterodyne beat signal between two independently injection-locked DBR lasers is measured to be 2.3 x 10(-16) at 1 s averaging time. The output frequency of the sweep optical frequency synthesizer can be precisely tuned over 1 GHz, and a saturated absorption spectrum of the Cs D2 line at 852 nm is recorded by the injected DBR laser. 相似文献
168.
This paper reports the investigation of the nanostructured surface morphology of novel arborescent polyisobutylene-block-polystyrene (PIB-PS) copolymers, in comparison with linear PS-PIB-PS triblock copolymers, using atomic force microscopy (AFM) in tapping mode. Arborescent PIB-PS samples displayed interesting new phase morphologies, which changed dramatically upon annealing but remained irregular. Linear PS-PIB-PS samples showed morphologies similar to those previously found by transmission electron microscopy (TEM) in cryomicrotomed bulk samples, ranging from spherical/cylindrical to lamellar nanometer-sized discreet PS phases dispersed in a continuous PIB matrix. Annealing the samples resulted in more ordered structures.Three-dimensional AFM image and section analysis indicated a height difference between PIB and PS in the block copolymers, which became more prominent during annealing. This feature was verified on compression moulded and protein coated samples. The arborescent PIB-PS materials displayed thermoplastic elastomeric behaviour with a tensile strength between 7 and 10 MPa and elongation ranging from 1000% to 1830%. In comparison, linear triblock samples had a tensile strength between 7 and 20 MPa and elongation ranging from 380% to 640%. Block copolymers with irregular elastomeric midsegments may emerge as a new class of TPEs. 相似文献
169.
Magnetically separable Pd catalyst for highly selective epoxide hydrogenolysis under mild conditions
A magnetically separable palladium catalyst was synthesized simply through a sol-gel process incorporating palladium nanoparticles and superparamagnetic iron oxide nanoparticles in aluminum oxyhydroxide matrix, which is highly active and selective for epoxide hydrogenolysis at room temperature under 1 atm H2. The catalyst was recycled for 25 times without loss of the activity. 相似文献
170.
Choi EY Kim D Hong BK Kwon HM Song YG Byun KH Park HY Whang KC Kim HS 《Experimental & molecular medicine》2002,34(6):391-400
Chlamydia pneumoniae infection implicated as an important etiologic factor of atherosclerosis, especially in coronary artery disease (CAD), was found in vitro to be associated with the induction of matrix metalloproteinases (MMPs). An extracellular matrix metalloproteinase inducer (EMMPRIN)/ membrane-type 1 matrix metalloproteinase (MT1-MMP) system which induces and activates MMPs, is suggested to be functional and were upregulated in the failing myocardium. However, the upstream regulation of MMPs by C. pneumoniae within atheroma itself remains unclear. We evaluated the seroepidemiologic study of C. pneumoniae infection in CAD patients (n= 391) and controls (n=97) and performed histopathological and in vitro analysis in atherosclerotic vascular tissues obtained from patients with seropositive to C. pneumoniae (n=20), by using immunochemistry for C. pneumoniae, EMMPRIN/MT1-MMP, MMP-2, and MMP-9. The seropositive rates of both anti-C. pneumoniae IgG and IgA were 56.7% in CAD group and 43.3% in control group (P=0.033). Seropositive rate was increased in subgroups of CAD patients without conventional coronary risk factors compared to those with conventional risk factors. Immunoreactivities of EMMPRIN, MT1-MMP, MMP-2, and MMP-9 were increased in the atheromatous plaque itself, predominantly in immunoreactive macrophages/mononuclear cells to C. pneumoniae. Furthermore, Western blot analysis showed that EMMPRIN and MMP-2 were detected more prominently in atherosclerotic tissues infected with C. pneumoniae compared to control tissues. Zymographic analysis revealed that activities of MMP-2 and MMP-9 were more increased in atherosclerotic tissues infected with C. pneumoniae compared to control tissues. The present study demonstrated upstream regulation of MMPs can be induced by C. pneumoniae within atheromatous plaque itself. These findings help to understand the potential role of C. pneumoniae in the progression of atherosclerosis. 相似文献