全文获取类型
收费全文 | 3047篇 |
免费 | 108篇 |
国内免费 | 14篇 |
专业分类
化学 | 2487篇 |
晶体学 | 30篇 |
力学 | 29篇 |
数学 | 205篇 |
物理学 | 418篇 |
出版年
2023年 | 18篇 |
2022年 | 18篇 |
2021年 | 22篇 |
2020年 | 44篇 |
2019年 | 47篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 60篇 |
2015年 | 58篇 |
2014年 | 94篇 |
2013年 | 194篇 |
2012年 | 147篇 |
2011年 | 185篇 |
2010年 | 123篇 |
2009年 | 112篇 |
2008年 | 193篇 |
2007年 | 173篇 |
2006年 | 194篇 |
2005年 | 200篇 |
2004年 | 174篇 |
2003年 | 147篇 |
2002年 | 148篇 |
2001年 | 50篇 |
2000年 | 42篇 |
1999年 | 27篇 |
1998年 | 39篇 |
1997年 | 32篇 |
1996年 | 26篇 |
1995年 | 16篇 |
1994年 | 29篇 |
1993年 | 15篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 21篇 |
1986年 | 18篇 |
1985年 | 34篇 |
1984年 | 48篇 |
1983年 | 28篇 |
1982年 | 40篇 |
1981年 | 44篇 |
1980年 | 27篇 |
1979年 | 25篇 |
1978年 | 18篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 15篇 |
1974年 | 17篇 |
1973年 | 11篇 |
排序方式: 共有3169条查询结果,搜索用时 21 毫秒
141.
Cp(2)Ti[P(OEt)(3)](2)-promoted reactions of 2-(alk-1-yn-1-yl)-2-(trialkylsilyl)-1,3-dithianes (RS)(2)C(Si)CCR with terminal olefins and carbonyl compounds produced (trialkylsilylethynyl)cyclopropanes and 1-(trialkylsilyl)alk-3-en-1-ynes, respectively. These compounds were suggest to be produced via the formation of intermediary titanium alpha-(trialkylsilylethynyl)carbene complexes Cp(2)Ti=C(R)CCSi in preference to their regioisomers, alpha-(trialkylsilyl)alkynylcarbene complexes Cp(2)Ti=C(Si)CCR. 相似文献
142.
Koji Nakabayashi Masaki Kawano Prof. Dr. Tatsuhisa Kato Prof. Dr. Ko Furukawa Dr. Shin‐ichi Ohkoshi Prof. Dr. Toshiya Hozumi Dr. Makoto Fujita Prof. Dr. 《化学:亚洲杂志》2007,2(1):164-170
We show a new approach to manipulating the through‐space spin–spin interaction by utilizing the confined cavity of a self‐assembled M6L4 coordination cage. The coordination cage readily encapsulates stable organic radicals in solution, which brings the spin centers of the radicals closer to each other. In sharp contrast to the fact that the radical in solution in the absence of the cage is in a doublet state, in the presence of the cage through‐space spin–spin interaction is induced through cage‐encapsulation effects in solution as well as in the solid state, resulting in the triplet state of the complex. These results were confirmed by ESR spectroscopy and X‐ray crystallography. The quantity of triplet species generated by encapsulation in the cage increases with increasing affinity of the radicals to the cage. We estimated the affinity between several types of guests and the cage in solution by cyclic voltammetry. We also demonstrate that the through‐space interaction of organic radicals within the self‐assembled coordination cage can be controlled by external stimuli such as heat or pH. 相似文献
143.
Takiue T Hirose D Murakami D Sakamoto H Matsubara H Aratono M 《The journal of physical chemistry. B》2005,109(34):16429-16434
The interfacial tension gamma of the hexane solution of 1H,1H-perfluorononanol (FDFC(9)OH) and its omega-hydrogenated analogue, 1H,1H,9H-perfluorononanol (HDFC(9)OH), against water was measured as a function of pressure and concentration at 298.15 K in order to clarify the effect of omega-dipole on the orientation of fluorononanol molecules from the viewpoint of volume. The adsorbed films of both alcohols exhibit two kinds of phase transitions among three different states: the gaseous, expanded, and condensed states. The partial molar volume changes of adsorption - in the expanded and condensed states were evaluated and compared between the two systems. The - values of both alcohols are negative, and thus the alcohol molecules have smaller volume in the adsorbed film than in the bulk solution. Furthermore, the value was obtained through the evaluation of by the density measurement of the bulk hexane solution. It was found that the value of HDFC(9)OH is smaller than that of FDFC(9)OH in the condensed state. On the basis of three matters concerning the molecular structure of alcohols, the occupied area at the interface, and the orientation of FDFC(9)OH in the adsorbed film deduced from the earlier results of X-ray reflectivity measurement, the mean tilt angle of HDFC(9)OH from the interface normal in the condensed film was estimated to be 15 degrees . The thermodynamic estimation demonstrated here is highly valuable one to provide structure information on an adsorbed film. 相似文献
144.
Minato M Sekimizu R Uchida D Ito T 《Dalton transactions (Cambridge, England : 2003)》2004,(21):3695-3698
Treatment of eta(3)-allyl compound [Cp(2)Mo(eta(3)-C(3)H(5))](+)(1; Cp =eta(5)-C(5)H(5)) with MH (M = Li, Na) resulted in reduction of the allyl ligand to give propane. Deuterium-labeling studies were used to trace the origins and fates of the hydrogen atoms. The mechanism is discussed in light of the HSAB principle. The studies showed that the formation of propane can be explained by 1,2-hydrogen migration from the central to the terminal carbon of the allyl ligand, and the subsequent double nucleophilic addition of the hydride at the central carbon. 相似文献
145.
Shin-ichi NayaHisashi Miyama Kenji YasuTohru Takayasu Makoto Nitta 《Tetrahedron》2003,59(10):1811-1821
Three-step reactions starting from 2-chlorotropone with barbituric acid afforded novel 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (9·BF4−), which is the isoelectronic compound of the 5-ethyl-3-methyllumiflavinium ion. The stability of cation 9 is expressed by the pKR+ value, which was determined spectrophotometrically, as ca. 6.0. The electrochemical reduction of 9 exhibited low reduction potential at −0.58 (V vs Ag/AgNO3), upon cyclic voltammetry (CV). In a search for the reactivity, reactions of 9·BF4− with some nucleophiles, hydroxide, hydride, amines, thiols, and methanol, were carried out to exhibit that the introduction of nucleophiles is dependent on the nucleophile itself. The photo-induced oxidation reactions of some alcohols catalyzed by 9·BF4− under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compound 9·BF4−], suggesting the oxidizing function of 9·BF4− toward alcohols in the autorecycling process. The UV-vis and fluorescence spectra of 9 were studied to suggest the electron transfer from alcohols to the excited 9. 相似文献
146.
An(a, b)-n-fan means a union ofn internally disjoint paths. Menger's theorem states that a graphG has an(a, b)-n-fan if and only ifG isn-connected betweena andb. We show thatG contains edge-disjoint(a, b)-n-fans if and only if for anyk withk0min{n–1, |V(G)|–2} and for any subsetX ofV(G)-{a, b} with cardinalityk, G-X is (n-k)-edge-connected betweena andb. 相似文献
147.
148.
This paper studies the heavily trimmed sums (*)
[ns] + 1
[nt]
X
j
(n)
, where {X
j
(n)
}
j = 1
n
are the order statistics from independent random variables {X
1,...,X
n
} having a common distributionF. The main theorem gives the limiting process of (*) as a process oft. More smoothly trimmed sums like
j = 1
[nt]
J(j/n)X
j
(n)
are also discussed. 相似文献
149.
We revealed that in ATX-S10.Na(II)(13,17-bis (1-carboxypropionyl) carbamoylethyl-8-etheny-2-hydroxy-3-hydroxyiminoethylidene-2,7,12,18-tetraethyl porphyrin sodium)-mediated photodynamic therapy using 667 nm nanosecond-pulsed light excitation at a peak intensity of 2.0 MW/cm(2), phototoxicity increased with decreasing pulse repetition rate in the range of 5-30 Hz for A549 cell cultures. To examine the relation between the reaction mechanism and measured phototoxicity, we carefully measured the kinetics of photochemical oxygen consumption and photobleaching during irradiation of ATX-S10.Na(II)-sensitized A549 monolayer cultures. Measurements of oxygen consumption with a microelectrode, which was performed just above the cells, showed that there was no significant difference between the magnitudes of decrease in oxygen at the three repetition rates at the same cumulative fluence. Loss of ATX-S10.Na(II) fluorescence intensity also exhibited little repetition rate dependence when compared at the same cumulative fluence. We investigated the correlation between oxygen consumption and photobleaching during irradiation and obtained "fluorescence-oxygen diagrams." The diagrams showed dynamic changes between oxygen-dependent and oxygen-independent photobleaching at the higher repetition rates of 10 and 30 Hz, whereas such change was not clearly seen over the whole irradiation time at 5 Hz. These results suggest that the reduced phototoxicity at high repetition rates might be due to an oxygen-independent reaction. We presumed that the change in the reaction mechanism was associated with the local concentrations of the photosensitizer and oxygen in cells during irradiation. 相似文献
150.
An automated analyzer for vancomycin in rat plasma by column-switching high-performance liquid chromatography (HPLC) with UV detection was developed. The method includes in-line extraction of vancomycin by ion-exchange cartridge column and a separation on a reversed-phase column with UV detection at 215 nm. Plasma samples were diluted by mobile phase solution and directly injected to HPLC. Vancomycin was quantitatively recovered from rat plasma samples. The separation was completed within 15 min. The calibration curve was linear over the range from 0.5 to 100 microg/mL with the detection and quantification limits of 0.5 microg/mL (2.5 ng on column; signal-to-noise ratio = 3). The values of precision in intra- and inter-day assays (n = 3) were less than 1.92 and 3.69%, respectively. This method does not require time-consuming pre-treatment and is suitable for the routine assay of plasma samples. 相似文献