全文获取类型
收费全文 | 4166篇 |
免费 | 145篇 |
国内免费 | 18篇 |
专业分类
化学 | 2884篇 |
晶体学 | 40篇 |
力学 | 106篇 |
数学 | 332篇 |
物理学 | 967篇 |
出版年
2023年 | 21篇 |
2022年 | 71篇 |
2021年 | 95篇 |
2020年 | 79篇 |
2019年 | 69篇 |
2018年 | 59篇 |
2017年 | 45篇 |
2016年 | 122篇 |
2015年 | 114篇 |
2014年 | 141篇 |
2013年 | 231篇 |
2012年 | 319篇 |
2011年 | 356篇 |
2010年 | 190篇 |
2009年 | 176篇 |
2008年 | 272篇 |
2007年 | 251篇 |
2006年 | 233篇 |
2005年 | 230篇 |
2004年 | 171篇 |
2003年 | 158篇 |
2002年 | 139篇 |
2001年 | 92篇 |
2000年 | 90篇 |
1999年 | 75篇 |
1998年 | 59篇 |
1997年 | 33篇 |
1996年 | 50篇 |
1995年 | 45篇 |
1994年 | 48篇 |
1993年 | 44篇 |
1992年 | 32篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有4329条查询结果,搜索用时 15 毫秒
71.
T. Itagaki E. Rokuta H.‐S. Kuo K. Nomura T. Ishikawa B.‐L. Cho I.‐S. Hwang T. T. Tsong C. Oshima 《Surface and interface analysis : SIA》2007,39(4):299-303
We observed field emission microscopy (FEM) patterns of noble‐metal (NM) covered W nano‐tips with three different apex structures fabricated by field evaporation. Each of the three tips was terminated with a single atom, three atoms or ten atoms. We investigated the temporal changes in the FEM of these tips to discuss the stabilities in the spatial distributions of the field emission (FE) beams. The single‐atom tip showed two characteristics that were superior to the others. First, the beams emitted from the single‐atom tip were the most collimated among the three tips (the semi‐cone angle of 1.0° , FWHM). Second, adsorption of residual gas had little influence on FE from the single‐atom tip, while the other tips were easily contaminated even at ultra high vacuum, resulting in the emission fluctuation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
72.
Effective isolation of magnesium lithospermate B and its inhibition of aldose reductase and fibronectin on mesangial cell line 总被引:4,自引:0,他引:4
Jung M Lee HC Ahn CW Park W Choi S Kim H Cho D Lee GT Li HR 《Chemical & pharmaceutical bulletin》2002,50(8):1135-1136
We developed an effective isolation method of magnesium lithospermate B from Salviae miltiorrhizae Radix and found for the first time that magnesium lithospermate B shows strong in vitro inhibition (IC50=0.04 microM) of aldose reductase (AR), 2.5 times than that of clinically used epalrestat (IC50=0.1 microM) and accumulation of fibronectin dose dependently. 相似文献
73.
Jeon JH Cho SY Kim CW Shin DM Kwon JC Choi KH Kim IG 《Experimental & molecular medicine》2002,34(6):496-499
Human papillomavirus E7 (HPV E7) is a viral oncoprotein that plays an important role in cervical carcinogenesis through binding with retinoblastoma protein (Rb). Inactivation of Rb by E7 is necessary but not sufficient for cellular transformation, suggesting other protein-protein interactions are required for E7-mediated cellular transformation aside from the interaction with Rb. However, studies on the oncogenic function of HPV E7 have been limited by its poor immunoreactivity. In this report, we show that the fixation of purified recombinant HPV E7 on blotted nitrocellulose membrane with glutaldehyde markedly enhanced the immunoreactivity of HPV E7 protein. Using HeLa and Caski cell lines which are infected with HPV 18 and HPV 16, respectively, we demonstrated that native HPV E7 proteins also could be detected by this method. These results therefore can provide the experimental conditions for detection of HPV E7 proteins with greater sensitivity and may help to analyze E7 functions. 相似文献
74.
Suzuki-Miyaura coupling was achieved on a variety of aryl chlorides by using di(2,6-dimethylmorpholino)phenylphosphine (L1) as a bulky electron-rich monoaryl phosphine ligand. We report the couplings of various chlorobenzenes and heteroaryl chlorides. 相似文献
75.
A stable inorganic-organic hybrid multilayer film with homogeneous and dense inorganic nanoparticle deposition was constructed by coating ZrO2 nanoparticles with poly(4-sodium styrenesulfonate) (PSS) and irradiating multilayer film assembled from PSS-coated ZrO2 nanoparticles and a diazo-resin (DR). 相似文献
76.
During radiotherapy of cancer, neighboring normal cells may receive sub-lethal doses of radiation. To investigate whether such low levels of radiation modulate normal cell responses to death stimuli, primary cultured human fibroblasts were exposed to various doses of gamma-rays. Analysis of cell viability using an exclusion dye propidium iodide revealed that the irradiation up to 10 Gy killed the fibroblasts only to a minimal extent. In contrast, the cells efficiently lost their viability when exposed to 0.5-0.65 mM H(2)O(2). This type of cell death was accompanied by JNK activation, and was reversed by the use of a JNK-specific inhibitor SP600125. Interestingly, H(2)O(2) failed to kill the fibroblasts when these cells were pre-irradiated, 24 h before H(2)O(2) treatment, with 0.25-0.5 Gy of gamma-rays. These cytoprotective doses of gamma-rays did not enhance cellular capacity to degrade H(2)O(2), but elevated cellular levels of p21(Cip/WAF1), a p53 target that can suppress H(2)O(2)-induced cell death by blocking JNK activation. Consistently, H(2)O(2)-induced JNK activation was dramatically suppressed in the pre-irradiated cells. The overall data suggests that ionizing radiation can impart normal fibroblasts with a survival advantage against oxidative stress by blocking the process leading to JNK activation. 相似文献
77.
Photophysical properties of porphyrin tapes 总被引:1,自引:0,他引:1
Cho HS Jeong DH Cho S Kim D Matsuzaki Y Tanaka K Tsuda A Osuka A 《Journal of the American Chemical Society》2002,124(49):14642-14654
The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso-meso, beta-beta, beta-beta positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, approximately 500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of approximately 1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from approximately 4.5 ps for the T2 dimer to approximately 0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes were observed to be in a sharp contrast to those of the orthogonal porphyrin arrays. The PPP-SCI calculated charge-transfer probability indicates that the lowest excited state of the porphyrin tapes (Tn) resembles a Wannier-type exciton closely, whereas the lowest excited state of the directly linked porphyrin arrays can be considered as a Frenkel-type exciton. Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials. 相似文献
78.
Dong Hyun KimHyun Il Cho Taehyoung ZyungLee-Mi Do Ki-Min BarkGap Chul Shin Sung Chul Shin 《European Polymer Journal》2002,38(1):133-137
New tetradentate Schiff-base polymers, in which phenylene units alternate with salicylideneiminato units, have been prepared by condensation of 2,5-(didodecyloxy)-1,4-bis(3-formyl-4-hydroxyphenyl)benzene (DFHB) with appropriate diamines in a mixed solution of CHCl3/toluene/acetic acid with 31-79% yields. DFHB as the key building block was prepared by the Suzuki reaction of 2,5-(didodecyloxy)benzene-1,4-diboronic acid with 5-bromosalicylaldehyde in a two-phase solution of tetrahydrofuran/water in the presence of NaHCO3/Pd(PPh3)4 in 45% yield. The molecular structures of the prepared compounds were identified by spectroscopy. Their absorption spectroscopic profiles have been analyzed. 相似文献
79.
Young Hyun Cho Wanno Lee Kun Ho Chung Geun Sik Choi Chang Woo Lee 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(3):531-538
The seasonal variation of the 7Be activities in air and the size distribution of the 7Be aerosols were studied by using a continuous air sampler and a five stage cascade impactor. The mean monthly activity level
of 7Be at the Korea Atomic Energy Research Institute (KAERI) site varied from 0.5 to 4.8 Bq·m−3 and revealed a seasonal variation, in which the 7Be activity levels were high in winter and low in summer. The mass size distribution showed a bi-modal distribution with a
higher peak around 0.49 μm and a smaller peak between 3 μm and 7.2 μm. The activity median aerodynamic diameter (AMAD) decreased
with increasing ambient 7Be concentrations. The mean residence times by using a mean growth rate of 0.004 μm·h−1 were estimated to be 2.5–6.4 days. The AMAD has an increasing tendency with higher relative humidity. It seemed that the
high humidity condition facilitated the growth of the aerosol, resulting in increased deposition rates of the aerosols and
the low 7Be content in the surface air. The AMAD of the 7Be aerosols increased with an increasing temperature, but the temperature dependency of AMAD should be explained with geological
and meteorological conditions. 相似文献
80.
Jung HW La SJ Kim JY Heo SK Kim JY Wang S Kim KK Lee KM Cho HR Lee HW Kwon B Kim BS Kwon BS 《Experimental & molecular medicine》2003,35(6):501-508
Herpes virus entry mediator (HVEM) is a newly discovered member of the tumor necrosis factor receptor (TNFR) superfamily that has a role in herpes simplex virus entry, in T cell activation and in tumor immunity. We generated mAb against HVEM and detected soluble HVEM (SHVEM) in the sera of patients with various autoimmune diseases. HVEM was constitutively expressed on CD4(+) and CD8(+) T cells, CD19(+) B cells, CD14(+) monocytes, neutrophils and dendritic cells. In three-way MLR, mAb 122 and 139 were agonists and mAb 108 had blocking activity. An ELISA was developed to detect sHVEM in patient sera. sHVEM levels were elevated in sera of patients with allergic asthma, atopic dermatitis and rheumatoid arthritis. The mAbs discussed here may be useful for studies of the role of HVEM in immune responses. Detection of soluble HVEM might have diagnostic and prognostic value in certain immunological disorders. 相似文献