全文获取类型
收费全文 | 3659篇 |
免费 | 112篇 |
国内免费 | 17篇 |
专业分类
化学 | 2837篇 |
晶体学 | 31篇 |
力学 | 41篇 |
数学 | 95篇 |
物理学 | 784篇 |
出版年
2023年 | 15篇 |
2021年 | 34篇 |
2020年 | 33篇 |
2019年 | 44篇 |
2018年 | 28篇 |
2017年 | 24篇 |
2016年 | 67篇 |
2015年 | 57篇 |
2014年 | 65篇 |
2013年 | 138篇 |
2012年 | 187篇 |
2011年 | 243篇 |
2010年 | 114篇 |
2009年 | 129篇 |
2008年 | 209篇 |
2007年 | 232篇 |
2006年 | 218篇 |
2005年 | 230篇 |
2004年 | 203篇 |
2003年 | 175篇 |
2002年 | 158篇 |
2001年 | 112篇 |
2000年 | 85篇 |
1999年 | 81篇 |
1998年 | 43篇 |
1997年 | 45篇 |
1996年 | 31篇 |
1995年 | 42篇 |
1994年 | 30篇 |
1993年 | 30篇 |
1992年 | 39篇 |
1991年 | 34篇 |
1990年 | 38篇 |
1989年 | 28篇 |
1988年 | 24篇 |
1987年 | 36篇 |
1986年 | 22篇 |
1985年 | 40篇 |
1984年 | 40篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 37篇 |
1980年 | 28篇 |
1979年 | 48篇 |
1978年 | 28篇 |
1977年 | 22篇 |
1976年 | 15篇 |
1975年 | 20篇 |
1974年 | 25篇 |
1973年 | 15篇 |
排序方式: 共有3788条查询结果,搜索用时 15 毫秒
1.
2.
3.
Simultaneous quantification of leukotrienes and hydroxyeicosatetraenoic acids in cell culture medium using liquid chromatography/tandem mass spectrometry 下载免费PDF全文
Leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) are important bioactive lipid mediators that participate in various pathophysiological processes. To advance understanding of the mechanisms that regulate these mediators in physiological and pathological processes, an analytical method using liquid chromatography/tandem mass spectrometry for the simultaneous quantification of LTB4, LTC4, LTD4, LTE4, 5‐HETE, 8‐HETE, 12‐HETE and 15‐HETE in cell culture media was developed. A Supel?‐Select HLB solid‐phase extraction cartridge was used for sample preparation. The compounds were separated on a C18 column using gradient elution with acetonitrile–water–formic acid (20:80:0.1, v/v/v) and acetonitrile–formic acid (100:0.1, v/v). The calibration curves of LTB4, LTD4, LTE4 and HETEs were linear in the range of 0.025–10 ng/mL, and the calibration curve of LTC4 was linear in the range of 0.25–10 ng/mL. Validation assessment showed that the method was highly reliable with good accuracy and precision. The stability of LTs and HETEs was also investigated. Using the developed method, we measured LTs and HETEs in the culture supernatant of the human mast cell line HMC‐1. The present method could facilitate investigations of the mechanisms that regulate the production, release and signaling of LTs and HETEs. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
ABSTRACTQM(UB3LYP)/MM(AMBER) calculations were performed for the locations of the transition structure (TS) of the oxygen–oxygen (O–O) bond formation in the S4 state of the oxygen-evolving complex (OEC) of photosystem II (PSII). The natural orbital (NO) analysis of the broken-symmetry (BS) solutions was also performed to elucidate the nature of the chemical bonds at TS on the basis of several chemical indices defined by the occupation numbers of NO. The computational results revealed a concerted bond switching (CBS) mechanism for the oxygen–oxygen bond formation coupled with the one-electron transfer (OET) for water oxidation in OEC of PSII. The orbital interaction between the σ-HOMO of the Mn(IV)4–O(5) bond and the π*-LUMO of the Mn(V)1=O(6) bond plays an important role for the concerted O–O bond formation for water oxidation in the CaMn4O6 cluster of OEC of PSII. One electron transfer (OET) from the π-HOMO of the Mn(V)1=O(6) bond to the σ*-LUMO of the Mn(IV)4–O(5) bond occurs for the formation of electron transfer diradical, where the generated anion radical [Mn(IV)4–O(5)]-? part is relaxed to the ?Mn(III)4?…?O(5)- structure and the cation radical [O(6)=Mn(V)1]+ ? part is relaxed to the +O(6)–Mn(IV)1? structure because of the charge-spin separation for the electron-and hole-doped Mn–oxo bonds. Therefore, the local spins are responsible for the one-electron reductions of Mn(IV)4->Mn(III)4 and Mn(V)1->Mn(IV)1. On the other hand, the O(5)- and O(6)+ sites generated undergo the O–O bond formation in the CaMn4O6 cluster. The Ca(II) ion in the cubane- skeleton of the CaMn4O6 cluster assists the above orbital interactions by the lowering of the orbital energy levels of π*-LUMO of Mn(V)1=O(6) and σ*-LUMO of Mn(IV)4–O(5), indicating an important role of its Lewis acidity. Present CBS mechanism for the O–O bond formation coupled with one electron reductions of the high-valent Mn ions is different from the conventional radical coupling (RC) and acid-base (AB) mechanisms for water oxidation in artificial and native photosynthesis systems. The proton-coupled electron transfer (PC-OET) mechanism for the O–O bond formation is also touched in relation to the CBS-OET mechanism. 相似文献
5.
6.
R. Bairava Ganesh Hitoshi Matsuo Takahiro Kawamura Yoshihiro Kangawa Koji Arafune Yoshio Ohshita Masafumi Yamaguchi Koichi Kakimoto 《Journal of Crystal Growth》2008,310(11):2697-2701
Multicrystalline silicon was grown by unidirectional solidification method using the accelerated crucible rotation technique. The application of the accelerated crucible rotation technique in unidirectional solidification method induced growth striations across the axial direction of the grown crystal. This striation pattern was observed from carbon concentration distribution, obtained by using Fourier transform infrared spectroscopy. The generated striation pattern was found to be weak and discontinuous. Some striations were absent, probably due to back melting, caused during each crucible rotation. From the growth striations and applied time period in crucible rotation, the growth rate was estimated by using Fourier transformation analysis. 相似文献
7.
Hiroshi Noguchi Masanori Ueda Yoshinobu Baba Masako Takasu 《Journal of Polymer Science.Polymer Physics》2003,41(12):1316-1322
The electrophoresis of DNA chains in uncrosslinked polymer solutions with a Brownian dynamics simulation with an anisotropic friction tensor was analyzed. According to the degree of anisotropy, three types of migration behavior are obtained: fluctuation without or with periodicity between U‐shaped and compact conformations, or migration with linear conformation. We found good agreement between our simulation results and the direct observations of DNA by fluorescence microscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1316–1322, 2003 相似文献
8.
Yasuhiro Ikezoe Sadahiro Ishizaki Hiroharu Yui Masanori Fujinami Tsuguo Sawada 《Analytical sciences》2004,20(3):435-440
The oscillation of the interfacial tension and electrical potential at a water/nitrobenzene interface was observed with homologous anionic surfactant molecules, sodium-alkyl-sulfates. Concerning small molecules with a short hydrophobic carbon chain, the oscillation period and amplitude decreased with a decrease of the length of the alkyl chain. On the other hand, when surfactant molecules with a long hydrophobic carbon chain were used, no remarkable periodic oscillation occurred after the first oscillation. In all systems, an interfacial flow by Marangoni convection was observed when the oscillation took place. By monitoring the movement of carbon powder scattered on the liquid/liquid interface with a CCD camera, we could observe that the liquid/liquid interface expanded outward from the area on which the surfactant molecules adsorbed when the oscillation occurred. When the small molecule was used, the speed of expansion of the interface (flow speed) was small and shrinkage followed by expansion of the interface repeatedly occurred. However, when the large molecule was used, the flow speed was large and expansion occurred only one time. These results show that hydrodynamic factors and surface activities are important in chemical oscillation systems. 相似文献
9.
Takashi Yoshitake Ryuji Iizuka Kaoru Fujino Osamu Inoue Kenji Yamagata Hitoshi Nohta Masatoshi Yamaguchi 《Analytical sciences》2004,20(12):1687-1690
An improved high-performance liquid-chromatographic (HPLC) assay for the simultaneous determination of serotonin (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) in human urine is reported. Following the automated precolumn derivatization of urinary 5-HT and 5-HIAA with benzylamine, the derivatives are separated by isocratic elution on a reversed-phase C18 semi-microbore column, and are fluorometrically detected at an excitation wavelength of 345 nm and an emission wavelength of 480 nm. The detection limits of 5-HT and 5-HIAA are 7 and 5 nmol/l in urine (0.7 and 0.5 fmol/20-microl injection). The proposed automatic method permits a highly selective and sensitive determination of 5-HT and 5-HIAA in human urine without any sample purification. 相似文献
10.
Norikazu Yamaguchi 《Mathematical Methods in the Applied Sciences》2005,28(13):1507-1526
In this paper we are concerned with the initial boundary value problem of the micropolar fluid system in a three dimensional bounded domain. We study the resolvent problem of the linearized equations and prove the generation of analytic semigroup and its time decay estimates. In particular, Lp–Lq type estimates are obtained. By use of the Lp–Lq estimates for the semigroup, we prove the existence theorem of global in time solution to the original nonlinear problem for small initial data. Furthermore, we study the magneto‐micropolar fluid system in the final section. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献