全文获取类型
收费全文 | 3789篇 |
免费 | 111篇 |
国内免费 | 23篇 |
专业分类
化学 | 3183篇 |
晶体学 | 53篇 |
力学 | 41篇 |
数学 | 164篇 |
物理学 | 482篇 |
出版年
2023年 | 22篇 |
2022年 | 23篇 |
2021年 | 42篇 |
2020年 | 57篇 |
2019年 | 51篇 |
2018年 | 32篇 |
2017年 | 31篇 |
2016年 | 66篇 |
2015年 | 76篇 |
2014年 | 88篇 |
2013年 | 191篇 |
2012年 | 214篇 |
2011年 | 274篇 |
2010年 | 142篇 |
2009年 | 144篇 |
2008年 | 302篇 |
2007年 | 234篇 |
2006年 | 294篇 |
2005年 | 254篇 |
2004年 | 223篇 |
2003年 | 200篇 |
2002年 | 187篇 |
2001年 | 50篇 |
2000年 | 63篇 |
1999年 | 46篇 |
1998年 | 34篇 |
1997年 | 38篇 |
1996年 | 40篇 |
1995年 | 37篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 29篇 |
1984年 | 33篇 |
1983年 | 16篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 25篇 |
1979年 | 14篇 |
1978年 | 17篇 |
1976年 | 11篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1973年 | 10篇 |
排序方式: 共有3923条查询结果,搜索用时 125 毫秒
991.
Computational study on the reaction mechanism of the key thermal [4 + 4] cycloaddition reaction in the biosynthesis of epoxytwinol A 总被引:1,自引:0,他引:1
[reaction: see text] The key [4 + 4] cycloaddition in the biosynthesis of epoxytwinol A has been established by theoretical calculations to comprise of three processes. The first step is formation of the C8-C8' bond generating a biradical intermediate. Next, rotation about the C8-C8' bond occurs, and finally the C1-C1' bond is formed. Biradicals stabilized by conjugation and two hydrogen bonds are essential for realization of this rare thermal [4 + 4] cycloaddition. 相似文献
992.
Rekharsky MV Yamamura H Kawai M Osaka I Arakawa R Sato A Ko YH Selvapalam N Kim K Inoue Y 《Organic letters》2006,8(5):815-818
[STRUCTURE: SEE TEXT] A unique ternary 1:1:1 cucurbit[6]uril (CB[6])-cyclodextrin (CD)-dihexylammonium (DHA) complex was designed and noncovalently synthesized in stepwise fashion: first, CB[6] interacts strongly with DHA to form a 1:1 complex; second, addition of CD into the solution of the 1:1 complex leads to the exclusive formation of the 1:1:1 ternary complex. The ternary complex was characterized by various experimental techniques including ITC, NMR, and ESI-MS. 相似文献
993.
[reaction: see text] A concise method for the preparation of isochromene carboxylates has been developed by the regioselective 1,6-addition of various nucleophiles such as Grignard reagents, alkoxide, and cyanide onto benzopyranylidenetungsten(0) complexes, followed by iodine oxidation of the addition intermediates. 相似文献
994.
Osaka T Matsunaga T Nakanishi T Arakaki A Niwa D Iida H 《Analytical and bioanalytical chemistry》2006,384(3):593-600
Magnetic nanoparticles have been attracting much interest as a labeling material in the fields of advanced biological and
medical applications such as drug delivery, magnetic resonance imaging, and array-based assaying. In this review, synthesis
of iron oxide magnetic nanoparticles via a reverse micelle system and modification of their surface by an organosilane agent
are discussed. Furthermore, as a practical biological assay system, the magnetic detection of biomolecular interactions is
demonstrated by using the combination of a patterned substrate modified with a self-assembled monolayer and the magnetic nanoparticles. 相似文献
995.
Hexadecanaphthalenes (S,S,S,S,S,S,S,S,S,S,S,S,S,S,S)-4b and (S,S,S,S,S,S,S,R,S,S,S,S,S,S,S)-4b that possess two tetraphenylporphyrins (TPP) on the upper and lower naphthalene rings were synthesized. Long-range exciton-coupled CD in the Soret region of TPP (about 66 A) was observed. [structure: see text] 相似文献
996.
An experimental study on the Reynolds stress tensor was conducted in the three-dimensional flow in the plane turbulent wall jet induced by an isolated streamwise vortex generated by the half-delta wing mounted on the wall. Oscillation of the angle of attack of the wing induced a periodic perturbation in the strength of the streamwise vortex. Analysis by triple velocity decomposition and phase averaging shows that the oscillation induces periodic variations in the strength, radius, and position of the streamwise vortex center. The effect of periodic perturbation manifests itself in the magnitude of the Reynolds stress components
and
Simulations prove that the periodic variations in the strength, radius, and position of the vortex center can generate an apparent shear stress, denoted herein as
相似文献
997.
Ohmori K Katsuki H Chiba H Honda M Hagihara Y Fujiwara K Sato Y Ueda K 《Physical review letters》2006,96(9):093002
The quantum interference of two molecular wave packets has been precisely controlled in the B electronic state of the I2 molecule by using a pair of fs laser pulses whose relative phase is locked within the attosecond time scale and its real-time evolution has been observed by another fs laser pulse. It is clearly observed that the temporal evolution changes drastically as a function of the relative phase between the locked pulses, allowing us to read both amplitude and phase information stored in the wave functions of the molecular ensemble. 相似文献
998.
To verify the high-pressure formation of the bulk metallic glass in elemental Zr and Ti, which Zhang and Zhao [Nature (London) 430, 332 (2004)] and Y. Wang et al. [Phys. Rev. Lett. 95, 155501 (2005)] recently reported, the high-pressure states were investigated by our newly developed in situ angle-dispersive x-ray diffraction using a two-dimensional detector and x-ray transparent anvils. Despite the disappearance of all the Bragg peaks in the one-dimensional energy-dispersive data, two-dimensional angle-dispersive data showed several intense Bragg spots even at the conditions where the amorphization was reported. This finding suggests that Zr and Ti do not transform into an amorphous state, but that their grain size becomes large, which causes the missing Bragg peaks in energy-dispersive data. 相似文献
999.
Intermolecular interaction and a concentration-quenching mechanism of phosphorescent Ir(III) complexes in a solid film 总被引:1,自引:0,他引:1
Solid-state self-quenching processes of highly efficient Ir(III) phosphorescent emitters are investigated by the measurement of thin film photoluminescence quantum efficiency and transient lifetime as a function of doping concentration in a host matrix. The radiative decay rate constant is found to be independent from the average distance between dopant molecules (R), and the concentration-quenching rate constant is shown to be dependent on R(-6). The quenching dependence on R strongly suggests that luminescent concentration quenching in a phosphorescent Ir(III) complex:host film is controlled by dipole-dipole deactivating interactions as described by the F?rster energy transfer model. 相似文献
1000.
Ito M Ogino H Oshima H Shiraki N Shibamoto Y Kasai H Mase M Kawamura Y Miyati T 《Magnetic resonance imaging》2006,24(5):625-630
PURPOSE: A newly developed contrast material, CH3-DTPA-Gd (NMS60), a trimer containing 3 Gd(3+) atoms per molecule, has been shown to offer greater enhancement and longer vascular retention than gadopentetate dimeglumine (Gd-DTPA) in animals. We report on our early phase II study on NMS60 in brain tumor patients together with supplementary investigations. METHODS AND MATERIALS: The longitudinal relaxation rate (R(1)=1/T(1)) and the transverse relaxation rate (R(2)*=1/T(2)*) of NMS60 and Gd-DTPA were determined at 20 degrees C in water at 1.5 T. An NMS60 dose of 0.1 or 0.2 mmol (Gd)/kg was randomly assigned and administered to 10 patients (five women, five men; mean age: 49 years) with brain tumors. Safety and contrast-enhancing ability of NMS60 were evaluated. Dual dynamic contrast-enhanced T(1) and R(2)* studies (DUCE imaging) were also carried out in two patients. RESULTS: Regarding the relaxivity per Gd, R(1) and R(2)* of NMS60 were 9.5 and 11.0 (mmol/L x s)(-1), respectively, compared to 4.8 and 7.2 (mmol/L x s)(-1) for Gd-DTPA. Although a transient slight increase of alanine aminotransferase was observed in one case, no other adverse reactions were observed after administration of NMS60. Contrast enhancement by NMS60 was excellent at both concentrations, and when tumor detectability was assessed with a five-point scale, the diagnostic usefulness was 4 or higher in all cases. In DUCE imaging, NMS60 appeared to show high signal intensity, when compared with the data obtained separately for Gd-DTPA. CONCLUSION: NMS60 had a high contrasting effect and little toxicity, and is expected to be clinically useful. 相似文献