全文获取类型
收费全文 | 386篇 |
免费 | 14篇 |
专业分类
化学 | 278篇 |
力学 | 35篇 |
数学 | 13篇 |
物理学 | 74篇 |
出版年
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 11篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 10篇 |
2012年 | 24篇 |
2011年 | 24篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 22篇 |
2006年 | 14篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 19篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1955年 | 1篇 |
1944年 | 1篇 |
排序方式: 共有400条查询结果,搜索用时 0 毫秒
81.
Smriti KoodanjeriAjit R Pradhan Lakshmi S KaanumalleV Ramamurthy 《Tetrahedron letters》2003,44(15):3207-3210
1-Naphthyl phenyl acylates upon irradiation in solution yield eight products via β-cleavage process. However, excitation of these molecules as included in γ-cyclodextrin results in a single product (>95%). This medium dependent product selectivity is attributed to conformational and translational restrictions enforced on the reactant as well as intermediates by the cyclodextrin cavity. 相似文献
82.
83.
Kuniyil Prabhakaran Birgit Schwenzer Steven P. DenBaars 《Applied Surface Science》2007,253(10):4773-4776
Nanoparticles of gallium nitride, synthesized by a low-temperature reaction between triethyl gallium and ammonia, were introduced onto silicon wafers containing a thin layer of chemically prepared silicon dioxide. At room temperature, the nanoparticles form unstructured agglomerates on the surface. However, upon annealing the samples beyond the decomposition temperature of the silicon dioxide layer, the gallium nitride particles self-organize to form triangular structures. The pattern formation is attributed to the domain separation associated with the (1 × 1)-(7 × 7) surface phase transformation followed by selective incorporation of the nanoparticles. 相似文献
84.
85.
86.
87.
Fragment angular distributions in heavy ion-induced fission reactions have been analysed in terms of a two component model—fission
following compound nucleus formation and fast fission events. It is seen that, contrary to the general assumption, fast fission
competes with compound nucleus fission even when the composite system is formed with a spin less than the rotating liquid
drop model limit for vanishing fission barrier. 相似文献
88.
89.
Viswanathan R Prabhakaran EN Plotkin MA Johnston JN 《Journal of the American Chemical Society》2003,125(1):163-168
The scope of aryl radical additions to the nitrogen of azomethines is described. Aryl, trifluoromethyl alkyl, and alpha,beta-unsaturated ketimines engage in regioselective aryl-nitrogen bond formation via 5-exo cyclizations of an aryl radical to azomethine nitrogen. Selectivity for carbon-nitrogen over carbon-carbon bond formation is generally high (>95:5) and competes only with direct aryl radical reduction by stannane (0-10%). Alpha-ketoimines are a promising new class of carbon radical acceptors for which no competitive aryl radical reduction is observed. The reaction conditions are pH-neutral and are therefore among the mildest methods available for amination of an aromatic ring. The ketimines examined did not suffer from competitive reduction by stannane, offering an advantage over the use of diazo and azide functional groups as nitrogen sources for carbon radicals. The free radical-mediated aryl amination was sequenced with the O'Donnell phase transfer-catalyzed enantioselective alkylation strategy of glycinyl imine to provide either enantiomer of indoline alpha-amino acids with high ee. These new constrained phenyl alanine derivatives are now readily available for evaluation across a variety of applications. 相似文献
90.
S. R. Naidu N. M. Bhide K. V. Prabhakaran E. M. Kurian 《Journal of Thermal Analysis and Calorimetry》1995,44(6):1449-1462
Nitroaminoguanidine (NAG) has been investigated as regards its thermal decomposition characteristics using simultaneous thermal analysis, infrared spectroscopy, X-ray diffraction and polarising microscopy. XRD studies show thatNAG crystal belongs to the tetragonal system. The crystal structure parameters are found to be:a=17.063±0.005Å,b=17.063±0.005Å,c=5.155±0.005Å andc/a axial ratio=0.302. Under non-isothermal conditions,NAG decomposed apparently in one stage with a loss in weight of 80%. But the thermal decomposition ofNAG in the solid phase under isothermal conditions proceeded through three stages. Both the first and the second stages obeyed theA-E (Avrami Erofee'v) equation forn=1. The 3rd stage is too slow and kinetics has not been attempted. The rate parameters for the first and second stages have been evaluated. Gaseous decomposition products detected using the IR gas cell are NH3, NO2, HCN, N2O, CO and CO2. High temperature IR studies indicate preferential deamination reaction initially indicating breaking of N?NH2 and C?NH2 bonds leading to NH2 radical formation. Addition of diphenylamine, a known chain inhibitor, decelerated the thermal decomposition, supporting a radical chain reaction. 相似文献