全文获取类型
收费全文 | 1107篇 |
免费 | 32篇 |
国内免费 | 187篇 |
专业分类
化学 | 1109篇 |
晶体学 | 14篇 |
力学 | 4篇 |
综合类 | 1篇 |
物理学 | 198篇 |
出版年
2024年 | 1篇 |
2023年 | 25篇 |
2022年 | 19篇 |
2021年 | 18篇 |
2020年 | 25篇 |
2019年 | 32篇 |
2018年 | 16篇 |
2017年 | 27篇 |
2016年 | 17篇 |
2015年 | 33篇 |
2014年 | 28篇 |
2013年 | 42篇 |
2012年 | 78篇 |
2011年 | 49篇 |
2010年 | 51篇 |
2009年 | 69篇 |
2008年 | 50篇 |
2007年 | 72篇 |
2006年 | 86篇 |
2005年 | 59篇 |
2004年 | 62篇 |
2003年 | 45篇 |
2002年 | 38篇 |
2001年 | 44篇 |
2000年 | 34篇 |
1999年 | 50篇 |
1998年 | 39篇 |
1997年 | 30篇 |
1996年 | 27篇 |
1995年 | 25篇 |
1994年 | 21篇 |
1993年 | 27篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1966年 | 1篇 |
排序方式: 共有1326条查询结果,搜索用时 531 毫秒
111.
The combined derivative spectrophotometry developed in this paper is a new method, which can be used to determine multicomporent mixture simultaneously and may improve the sensitivity and accuracy of the measurement remarkably. Two practical tests were carried out to verify the correctness of the theory, and the results are satisfactory. 相似文献
112.
Numerous analogies between organic and inorganic chemistry have emerged in recent years. The most prominent example is the isolobal relationship. Many reactions have shown that metal-metal double and triple bonds exhibit a pattern of reactivity similar to that of alkenes and alkynes. In compounds containing a σ2π4 triple bond between molybdenum and tungsten atoms, the M? M bond order can be increased from three to four by reductive elimination or decreased from three to two or one by oxidative addition. Complexes with M?M bonds can be used to prepare clusters or can serve as catalysts. In this review relationships between structure (electronic and stereochemical) and reactivity that are characteristic for modern inorganic chemistry are discussed. 相似文献
113.
Two new molybdenum (VI) monophosphates CsMoO2PO4 and TlMoO2PO4 have been synthesized by solid state chemistry. Their structure were determined from single crystal X-ray diffraction studies. The frameworks MoO2PO4 delimit tunnels in which are located the univalent cations. Structural relationships between the different monophosphates of the AMoO2PO4 series with A = Ag, Na, K, Tl, Cs, are presented in which two kinds of frameworks appear owing to the size of the univalent cations. 相似文献
114.
Using density functional theory methods, we have studied carbon trioxide, its adsorption and dissociation on Ag(100). In the gas phase, two isomers are found, D3h and C2v, with the latter of 2.0 kcal mol?1 lower in energy at the PW91PW91/6?31G(d) level. For CO3 on Ag(100), the calculated adsorption energy is 91.2 and 89.1 kcal mol?1 for the bi‐coord perpendicular and tri‐coord parallel structures, respectively. Upon the adsorption, 0.50 ~ 0.56 electron is transferred from silver to CO3, indicative of significant ionic characters of the adsorbate‐surface bonding. In addition, the geometry of CO3 is largely changed by its strong interaction with silver. For CO3(ad) → O(ad) + CO2(gas), the energy barrier is calculated to be 19.8 kcal mol?1 through the bi‐coord path. The process is endothermic with an enthalpy change of +17.3 ~ +26.7 kcal mol?1 and the weakly chemisorbed CO2 is identified as an intermediate on the potential energy surface. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
115.
Chemoselective reduction of azides catalyzed by molybdenum xanthate by using phenylsilane as the hydride source 总被引:1,自引:0,他引:1
Mahagundappa R. Maddani 《Tetrahedron》2010,66(1):329-8551
A chemoselective, neutral, and efficient strategy for the reduction of azides to corresponding amines catalyzed by dioxobis(N,N,-diethyldithiocarbamato) molybdenum complex (1, MoO2[S2CNEt2]2) in the presence of phenylsilane is discovered. This chemoselective reduction strategy tolerates a variety of reducible functional groups. 相似文献
116.
Jonas Sävmarker 《Tetrahedron letters》2010,51(52):6886-6889
Stille-type carbonylative cross-couplings, employing palladium catalysis and Mo(CO)6 as the carbon monoxide carrier, were used for the preparation of deoxybenzoins. Straightforward transformations were conveniently performed in closed vessels at 100 °C, providing the products in good yields. Benzyl bromides and chlorides were used as coupling partners with aryl and heteroaryl stannanes. This mild three-component carbonylation employs the destabilizing agent DBU to promote smooth release of carbon monoxide from Mo(CO)6, which made this protocol operationally simple and minimized the formation of Stille diarylmethane products. 相似文献
117.
The novel tridentate chiral ligand 2,6-bis{[(1R,2S,4R)-2-hydroxy-1,3,3-trimethyl-bicyclo[2.2.1]hept-2-yl]}pyridine (1) was readily prepared by reaction of 2,6-dilithiopyridine with (R)-(−)-fenchone. Reaction of 1 with [MoO2(acac)2] resulted in the formation of the new metal-oxo five-coordinated complex [MoO2(ONO)] (2) [ONO = (1 – 2H)]. The reactivity of 2 has been studied and the derivatives [MoS2(ONO)] (3) and [MoO(O2)(ONO)] (4) were prepared. The compounds 1–4 have been characterised by 1H and 13C{1H} NMR, microanalysis and IR spectroscopy. Furthermore, the molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction. The behaviour of 2 as catalyst in oxotransfer and in nucleophilic substitution of propargylic alcohols reactions has been tested. 相似文献
118.
Jian Chen Prof. Shanghui Chen Dongyu Lu Weihong Zhang Fangyan Xie Weiguang Xie Dr. Li Gong Chengxin Wang Prof. 《Chemphyschem》2010,11(12):2546-2549
Raman spectroscopic analysis is performed on WO3 nanowires at room temperature at pressures from ambient conditions to 45 GPa. Linear dependence of the first‐order Raman signal on various high‐pressure (HP) sections is observed. Upon increasing the applied pressure, the WO3 nanowires undergo four phase transitions at pressures around 1.7, 4.6, 21.5, and 26.2 GPa, which are all less than that reported for bulk WO3. When the pressure is up to 42.5 GPa, a new high‐pressure phase (HP5) appears. This phase has never been reported and is not reversible while unloading the pressure. 相似文献
119.
A cellulose triacetate (CTA) membrane containing trioctylphosphine oxyde (TOPO) as carrier and 2-nitrophenyloctyl ether (NPOE) as a plasticizer was prepared. The membrane CTA + NPOE + TOPO was characterised using chemical techniques as well as Fourier Transform InfraRed (FTIR) spectroscopy, X-ray diffraction and Scanning Electron Microscopy (SEM). The CTA membrane is characterised by well-defined pores; these pores are completely filled with the NPOE and carrier. Surfaces of membranes with TOPO are smooth. The systems constituted by the mixture of CTA + NPOE, CTA + NPOE + TOPO do not give any diffraction. This can be due to the absence of crystallization within the membrane. On the other hand, this result should be attributable to the amorphous state of the structure, which permits us to eliminate the mechanism of transfer of the ions by electron jump. A comparative study of transport across a polymer inclusion membrane (PIM) and a supported liquid membrane (SLM) containing the same carrier in chloroform has shown that uranium or molybdenum transport efficiency was increased using PIM instead of SLM. PIM showed higher stability than SLM, the flux of transport remain constant in the former case after 2 weeks. 相似文献
120.
Yughandhar Sreedhar Neelam Rekha Dasari P. Reddy Prasad M. Sankar Nayak 《Journal of Saudi Chemical Society》2010,14(2):149-155
A novel analytical reagent 4-(2-hydroxy phenyl ethaminodiol), benzene-1,3-diol(4-2-HPEDB-1,3,D) was synthesized for the determination of molybdenum(VI). The present paper reveals the detailed study of electroanalytical behaviour for [Mo-(4-2-HPEDB-1,3,D)] complex under optimized conditions. The peak obtained for [Mo-(4-2-HPEDB-1,3,D)] prevent the interference of foreign ions which shows the sensitivity of the proposed method. The linearity was maintained at the concentration range of 0.5–200 μg/mL at pH 4.5 with correlation factor 0.9997. The present method was successfully applied for the analysis of molybdenum(VI) in biological fluids and plant material. The results obtained from the proposed method show good agreement with reference method. 相似文献