全文获取类型
收费全文 | 1758篇 |
免费 | 110篇 |
国内免费 | 9篇 |
专业分类
化学 | 1539篇 |
晶体学 | 9篇 |
力学 | 18篇 |
数学 | 91篇 |
物理学 | 220篇 |
出版年
2023年 | 20篇 |
2022年 | 15篇 |
2021年 | 20篇 |
2020年 | 33篇 |
2019年 | 48篇 |
2018年 | 40篇 |
2017年 | 17篇 |
2016年 | 44篇 |
2015年 | 64篇 |
2014年 | 62篇 |
2013年 | 102篇 |
2012年 | 128篇 |
2011年 | 129篇 |
2010年 | 86篇 |
2009年 | 63篇 |
2008年 | 136篇 |
2007年 | 101篇 |
2006年 | 133篇 |
2005年 | 126篇 |
2004年 | 108篇 |
2003年 | 75篇 |
2002年 | 63篇 |
2001年 | 14篇 |
2000年 | 22篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1967年 | 4篇 |
排序方式: 共有1877条查询结果,搜索用时 515 毫秒
991.
Ohta K Koketsu E Nagase Y Takahashi N Watanabe H Yoshimatsu M 《Chemical & pharmaceutical bulletin》2011,59(9):1133-1140
Direct scandium- and lanthanum-catalyzed etherifications of propargyl alcohols 1 and 6 in MeNO?-H?O provided propargyl ethers 3, 4 and 7 in high yields. In addition, reactions of 1 and 6 with thiols exclusively yielded the corresponding propargyl sulfides. 相似文献
992.
We investigated dynamics of group decision making on complex problems when agents can form mental models of others from discussion history. Results indicated that as the agents' memory capacity increases, the group reaches superficial consensus more easily. Surprisingly, however, the shared mental model of the problem develops only within a limited area of the problem space, because incorporating knowledge from others into one's own knowledge quickly creates local agreement on where relevant solutions are, leaving other potentially useful solutions beyond the scope of discussion. The mechanisms stifling group‐level exploration and their implications for decision making research are discussed. © 2010 Wiley Periodicals, Inc. Complexity 16: 49–57, 2011 相似文献
993.
Hirofumi Shimizu Shintarou Nagase Masanori Ikeda 《Applied Physics A: Materials Science & Processing》2011,104(3):929-934
We investigated a variation of frequency-dependent alternating current (AC) surface photovoltages (SPVs) in thermally oxidized,
chromium-contaminated, n-type silicon (Si) wafers. As previously reported, immediately after rinsing in Cr-contaminated solution,
a Cr(OH)3–Si contact causes a Schottky-barrier-type AC SPV on n-type Si. Upon oxidation at 373 K for 10 min, the Schottky barrier collapses
and, with further oxidation, a metal-induced negative oxide charge, due to atomic bridging of (CrOSi)− and/or CrO2-\mathrm{CrO}_{2}^{-} networks, definitely grows over time in SiO2. For samples oxidized at temperatures between 823 and 1023 K for 30 min, the observed AC SPV gives evidence that the metal-induced
negative oxide charge causes a strongly inverted state of the Si surface. At oxidation temperatures higher than 1023 K and
/or for an oxidation time longer than 60 min, the level height of the AC SPV is reduced, implying that the strongly inverted
state changes into a less depleted state, whilst, finally, the AC SPV disappears. In this case, the collapse of the (CrOSi)− and/or CrO2-\mathrm{CrO}_{2}^{-} networks is anticipated, with a possible change into Cr2O3. The existence of the (CrOSi)− and/or CrO2-\mathrm{CrO}_{2}^{-} networks has also been confirmed in p-type Si wafers. 相似文献
994.
A new terthiophene based ligand (L = 3-(2-pryridyl)-5-(2,2′:5′,2″-terthien-3′-yl) pyrazole was synthesized. The reaction of Ni(BF4)2·6H2O, L and nBu4N[Fe(CN)3tp∗] (tp∗ = tris(3,5-dimethylpyrazol-1-yl)borohyrdide) with NaBPh4 in MeOH/acetone yielded a cyanide bridged tetranuclear complex [Fe2Ni2(CN)6(tp∗)2(L)4](BPh4)2 (1). The electrochemical properties of both 1 and L were investigated, and magnetic susceptibility measurements of 1 were conducted, revealing that ferromagnetic interactions were operative within the tetranuclear core. 相似文献
995.
In this paper, we describe a method to enhance the fluorescence signal of mutagen detection using SOS response-induced green fluorescence protein (GFP) in genetically modified Escherichia coli using a multi-layered substrate. To generate E. coli that express SOS response-induced GFP, we constructed a plasmid carrying the RecA promoter located upstream of the GFP gene and used it to transform E. coli BL21. The transformed strain was incubated with mitomycin C (MMC), a typical mutagen, and then immobilized on a multi-layered substrate with Ag and a thin Al(2)O(3) layer on a glass slide. Since the multi-layered substrate technique is an optical technique with potential to enhance the fluorescence of fluorophore placed on top of the substrate, the multi-layered substrate was expected to improve the fluorescence signal of mutagen detection. We obtained an average 14-fold fluorescence enhancement of MMC-induced GFP in the concentration range 1 to 1000 ng/ml. In addition, the lower detection limit of MMC was improved using this technique, and was estimated to be 1 ng/ml because of an enlargement of the difference between the blank and the signal of 1 ng/ml of MMC. 相似文献
996.
Matsumori N Tanada N Nozu K Okazaki H Oishi T Murata M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(31):8568-8575
A lipid raft is a cholesterol (Chol)-rich microdomain floating in a sea of lipid bilayers. Although Chol is thought to interact preferentially with sphingolipids such as sphingomyelin (SM), rather than with glycerophospholipids, the origin of the specific interaction has remained unresolved, primarily because of the high mobility of lipid molecules and weak intermolecular interactions. In this study, we synthesized SM-Chol conjugates with functionally designed linker portions to restrain Chol mobility and examined their formation of ordered membranes by a detergent insolubility assay, fluorescence anisotropy experiments, and fluorescence-quenching assay. In all of the tests, membranes prepared from the conjugates showed properties of ordered domains comparable to a SM-Chol (1:1) membrane. To gain insight into the structure of bilayers composed from the conjugates, we performed molecular dynamics simulations with 64 molecules of the conjugates, which suggested that the conjugates form a stable bilayer structure by bending at the linker portion and, mostly, reproduce the hydrogen bonds between the SM and Chol portions. These results imply that the molecular recognition between SM and Chol in an ordered domain is essentially reproduced by the conjugated molecules and, thus, demonstrates that these conjugate molecules could potentially serve as molecular probes for understanding molecular recognition in lipid rafts. 相似文献
997.
Oshige M Kawasaki S Takano H Yamaguchi K Kurita H Mizuno T Matsuura S Mizuno A Katsura S 《Journal of fluorescence》2011,21(3):1189-1194
Direct observation studies of single molecules have revealed molecular behaviors usually hidden in the ensemble and time-averaging
of bulk experiments. Direct single DNA molecule analysis of DNA metabolism reactions such as DNA replication, repair, and
recombination is necessary to fully understand these essential processes. Intercalation of fluorescent dyes such as YOYO-1
and SYTOX Orange has been the standard method for observing single molecules of double-stranded DNA (dsDNA), but effective
fluorescent dyes for observing single molecules of single-stranded DNA (ssDNA) have not been found. To facilitate direct single-molecule
observations of DNA metabolism reactions, it is necessary to establish methods for discriminating ssDNA and dsDNA. To observe
ssDNA directly, we prepared a fusion protein consisting of the 70 kDa DNA-binding domain of replication protein A and enhanced
yellow fluorescent protein (RPA-YFP). This fusion protein had ssDNA-binding activity. In our experiments, dsDNA was stained
by SYTOX Orange and ssDNA by RPA-YFP, and we succeeded in staining ssDNA and dsDNA by using RPA-YFP and SYTOX Orange simultaneously. 相似文献
998.
Yoshifumi Sasano Hiroki Tanaka Yohei Haketa Yoichi Kobayashi Yukihide Ishibashi Tatsuki Morimoto Ryuma Sato Yasuteru Shigeta Nobuhiro Yasuda Tsuyoshi Asahi Hiromitsu Maeda 《Chemical science》2021,12(28):9645
In this study, charged π-electronic species are observed to develop stacking structures based on electrostatic and dispersion forces. iπ–iπ Interaction, defined herein, functions for the stacking structures consisting of charged π-electronic species and is in contrast to conventional π–π interaction, which mainly exhibits dispersion force, for electronically neutral π-electronic species. Establishing the concept of iπ–iπ interaction requires the evaluation of interionic interactions for π-electronic ion pairs. Free base (metal-free) and diamagnetic metal complexes of 5-hydroxy-10,15,20-tris(pentafluorophenyl)porphyrin were synthesized, producing π-electronic anions upon the deprotonation of the hydroxy unit. Coexisting cations in the ion pairs with porphyrin anions were introduced as the counter species of the hydroxy anion as a base for commercially available cations and as ion-exchanged species, via Na+ in the intermediate ion pairs, for synthesized π-electronic cations. Solid-state ion-pairing assemblies were constructed for the porphyrin anions in combination with aliphatic tetrabutylammonium (TBA+) and π-electronic 4,8,12-tripropyl-4,8,12-triazatriangulenium (TATA+) cations. The ordered arrangements of charged species, with the contributions of the charge-by-charge and charge-segregated modes, were observed according to the constituent charged building units. The energy decomposition analysis (EDA) of single-crystal packing structures revealed that electrostatic and dispersion forces are important factors in stabilizing the stacking of π-electronic ions. Furthermore, crystal-state absorption spectra of the ion pairs were correlated with the assembling modes. Transient absorption spectroscopy of the single crystals revealed the occurrence of photoinduced electron transfer from the π-electronic anion in the charge-segregated mode.π-Electronic ion pairs comprising porphyrin-based π-electronic anions have exhibited characteristic assembling modes and resulting electronic properties such as solid-state absorption and photoinduced electron transfer. 相似文献
999.
In order to reveal the anticlastogenic potency of aspirin, we evaluated the suppressive ability of aspirin on chromosome aberrations induced by X-ray. Aspirin at doses of 0.5, 5 and 50 mg/kg was administrated intraperitoneally or orally at 0.5 h after or before the X-ray irradiation. The anticlastogenic activity of aspirin on chromosome aberrations induced by X-ray was determined in the mouse micronucleus test and alkaline single cell gel electrophoresis (SCG) assay in vivo. The frequency by polychromatic erythrocytes with micronuclei (MNPCEs) was decreased by about 19–61% at 0.5 h after and about 23–62% at 0.5 h before the X-ray irradiation. DNA damage by X-ray was significantly decreased by oral administration of aspirin at 0.5 h after or before the X-ray irradiation for the SCG assay. We consider aspirin can be used as preventive agents against exposure of X-ray. 相似文献
1000.