全文获取类型
收费全文 | 940篇 |
免费 | 12篇 |
国内免费 | 4篇 |
专业分类
化学 | 708篇 |
晶体学 | 26篇 |
力学 | 5篇 |
数学 | 63篇 |
物理学 | 154篇 |
出版年
2023年 | 4篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2016年 | 6篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 29篇 |
2012年 | 28篇 |
2011年 | 40篇 |
2010年 | 19篇 |
2009年 | 20篇 |
2008年 | 45篇 |
2007年 | 62篇 |
2006年 | 57篇 |
2005年 | 42篇 |
2004年 | 48篇 |
2003年 | 39篇 |
2002年 | 38篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 15篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 22篇 |
1981年 | 15篇 |
1980年 | 27篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 8篇 |
1971年 | 4篇 |
1970年 | 5篇 |
排序方式: 共有956条查询结果,搜索用时 218 毫秒
941.
Nakamura R Hamada N Ichida H Tokunaga F Kanematsu Y 《The Journal of chemical physics》2007,127(21):215102
The ultrafast photoinduced dynamics of photoactive yellow protein in aqueous solution were studied at room temperature by femtosecond fluorescence spectroscopy using an optical Kerr-gate technique. Coherent oscillations of the wave packet were directly observed in the two-dimensional time-energy map of ultrafast fluorescence with 180 fs time resolution and 5 nm spectral resolution. The two-dimensional map revealed that four or more oscillatory components exist within the broad bandwidth of the fluorescence spectrum, each of which is restricted in the respective narrow spectral region. Typical frequencies of the oscillatory modes are 50 and 120 cm(-1). In the landscape on the map, the oscillatory components were recognized as the ridges which were winding and descending with time. The amplitude of the oscillatory and winding behaviors is a few hundred cm(-1), which is the same order as the frequencies of the oscillations. The mean spectral positions of the oscillatory components in the two-dimensional map are well explained by considering the vibrational energies of intramolecular modes in the electronic ground state of the chromophore. The entire view of the wave packet oscillations and broadening in the electronic excited state, accompanied by fluorescence transitions to the vibrational sublevels belonging to the electronic ground state, was obtained. 相似文献
942.
Hirashita T Shiraki F Onishi K Ogura M Araki S 《Organic & biomolecular chemistry》2007,5(13):2154-2158
The successive double allylation of cyclopropenes with allylindium sesquiiodide and allyl iodide proceeded with a cis-addition mode in the presence of other organometallics (e.g. Grignard reagent, cuprate, Et(2)Zn and Et(3)Al), giving the corresponding cis-diallylcyclopropanes in high yields. 相似文献
943.
944.
Fumio Hamada Kyoko Ishikawa Yutaka Higuchi Youichi Akagami Akihiko Ueno 《Journal of inclusion phenomena and macrocyclic chemistry》1996,25(4):283-294
-Cyclodextrin with appended fluorescein (1) has been prepared as a sensor and a charge-changeable receptor for detecting organic compounds including terpenoids, carboxylic acids and bile acids. Compound1 has cationic, neutral and anionic forms depending on the pH of the solutions. The anionic form of1 at about neutral pH exhibits the highest sensing ability for carboxylic acids and bile acids, while at alkaline pH it detects hardly any of the guests examined. The high sensitivity and selectivity of the anionic form of1 at around neutral pH for acidic guests seems to be caused by the hydrogen bond between the phenoxide anion moiety of fluorescein and acidic guests. The neutral form of1 exhibits little sensing ability for all the guests, but the cationic form shows comparatively higher sensing ability for the guests examined. 相似文献
945.
Y. Oya Y. Onishi H. Miyauchi T. Nakahata Y. Nishikawa K. Okuno S. Tanaka 《Journal of Radioanalytical and Nuclear Chemistry》2007,272(3):639-644
The D2
+ was irradiated into SiC up to the saturation and thereafter He+ irradiation was performed to elucidate interaction mechanism between hydrogen isotope retained in SiC and irradiated energetic
He+ by means of X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). It was found that D was trapped
by both of Si and C by D2
+ irradiation and only D bound to Si interacted with irradiated He+ in the initial He+ irradiation stage. Some damaged structures were introduced into SiC by both of D2
+ and He+ irradiation. By heating after the irradiation experiments, most of SiC structure was recovered at the temperature above 1000
K. However, some free C was migrated toward the surface and aggregated on the surface of SiC. This fact indicates that the
C impurity would contaminate the plasma and/or the tritium breeding materials, which is thought to be contacted with the SiC
inserts. 相似文献
946.
Osamu Hisatomi Makoto Ishikawa Akira Tonosaki Fumio Tokunaga 《Photochemistry and photobiology》1997,66(6):792-795
Abstract— A visual pigment was extracted from lamprey retina and was expressed in cultured mammalian cells (293S) using a cDNA fragment isolated from lamprey retina. The extracted pigment, a putative lamprey rhodopsin, had an absorption maximum at 503 nm. The recombinant lamprey rhodopsin, reconstituted with 11- cis -retinal, showed an absorption maximum at about 500 nm. Both pigments reacted with an anti-bovine rhodopsin antibody (Rh29), which recognizes the short photoreceptor cells in lamprey retina. Unlike rhodopsins of higher vertebrates, the lamprey rhodopsin bleached gradually in the presence of 100 m M hydroxylamine even in the dark. Our results suggest that, despite its high similarities with other vertebrate rhodopsins, lamprey rhodopsin has a character different from those of higher vertebrates. 相似文献
947.
Ariga K Nakanishi T Hill JP Shirai M Okuno M Abe T Kikuchi J 《Journal of the American Chemical Society》2005,127(34):12074-12080
Various amino acid-carrying amphiphiles were synthesized, and the pK values of the attached amino acid residues were investigated at the air-water interface and in aqueous vesicles using pi-A isotherm measurements, (1)H NMR titration, and IR spectroscopy in reflection-adsorption mode. The epsilon-amino group of the Lys residue embedded at the air-water interface displays a significant pK shift (4 or 5 unit) compared with that observed in bulk water, while the pK shift in aqueous vesicles was not prominent (ca. 1 unit). Moreover, pK values of the amino acids at the air-water interface can be tuned simply by control of the subphase ionic strength as well as by molecular design of the amphiphiles. A simple equation based on the dominant contribution by the electrostatic energy to the pK shift reproduces well the surface pressure difference between protonated and unprotonated species, suggesting a reduction in the apparent dielectric constant at the air-water interface. Hydrolysis of a p-nitrophenyl ester derivative was used as a model reaction to demonstrate the use of the Lys-functionalized monolayer. Efficient hydrolysis was observed, even at neutral pH, after tuning of pK for the Lys residue in the monolayer, which is a similar case to that occurring in biological catalysis. 相似文献
948.
N-Tosylaziridine was found to be a useful substrate for cycloaddition reaction with carbon dioxide. The reaction was successfully catalyzed by lithium bromide under atmospheric pressure to give the corresponding five-membered cyclic urethane, N-tosyl-1,3-oxazolidin-2-one, selectively. It was found that electron-donating nature of the substituent at 2-position of N-tosylaziridine accelerated the reaction, and this tendency allowed us to estimate the reaction mechanism. 相似文献
949.
We explain the molecular mechanism of the effect of urea and glycerol cosolvents on the partial molar volume (PMV) change associated with the pressure denaturation of staphylococcal nuclease (SNase) protein recently observed in experiments. Native and denatured conformations of SNase are produced by using molecular dynamics simulations in water, and the PMV is obtained from the integral equation theory of molecular liquids called 3D-RISM, which is based on statistical mechanics. The PMV of the native SNase in water predicted by 3D-RISM theory is in good agreement with experiment. The PMV changes associated with pressure denaturation in water and in water-urea and water-glycerol mixtures are qualitatively reproduced. By analyzing the results obtained, we found two interesting cosolvent effects on the PMV: (1) both urea and glycerol cosolvents increase the PMVs of both native and denatured SNase compared to those in water and (2) both urea and glycerol cosolvents increase the PMV of denatured SNase more than that of native SNase. We also showed that these two observations can be explained in terms of the thermal volume, which is related to the packing effect of solvent molecules. 相似文献
950.
Fumio Maruyama 《Journal of solid state chemistry》2005,178(10):3020-3026
We calculated the molecular field coefficients, nFeFe and nRFe (R=Sm, Gd, Tb, Ho and Tm), for R2Fe17−xGax and the values of nFeFe and nSmFe for R2Fe17−xTx (T=Al and Si) using the experimental values of the Curie temperature. The values of nFeFe increase in spite of the decrease of μFe for 0?x?5. The values of nSmFe have large values when the magnetic anisotropy is axial. For 6?x?8, the values of nFeFe, nHoFe and nTmFe increase largely, which is related to the change of the easy magnetization direction. For Y2Fe17−xTx (T=Ga and Al), the values of nFeFe have a maximum value with increasing those of μFe. With increasing V−1, the values of nFeFe have a maximum value around the same value of V−1 for Y2Fe17−xTx (T=Ga and Al). For Y2Fe17−xSix, the values of nFeFe increase with increasing V−1. 相似文献