全文获取类型
收费全文 | 325054篇 |
免费 | 3094篇 |
国内免费 | 951篇 |
专业分类
化学 | 178312篇 |
晶体学 | 4971篇 |
力学 | 13815篇 |
综合类 | 11篇 |
数学 | 32665篇 |
物理学 | 99325篇 |
出版年
2018年 | 2601篇 |
2016年 | 4448篇 |
2015年 | 3054篇 |
2014年 | 4530篇 |
2013年 | 13332篇 |
2012年 | 9463篇 |
2011年 | 11928篇 |
2010年 | 8086篇 |
2009年 | 8063篇 |
2008年 | 10900篇 |
2007年 | 11112篇 |
2006年 | 10533篇 |
2005年 | 9633篇 |
2004年 | 8756篇 |
2003年 | 7783篇 |
2002年 | 7710篇 |
2001年 | 9362篇 |
2000年 | 7178篇 |
1999年 | 5659篇 |
1998年 | 4629篇 |
1997年 | 4627篇 |
1996年 | 4431篇 |
1995年 | 4124篇 |
1994年 | 4019篇 |
1993年 | 3769篇 |
1992年 | 4464篇 |
1991年 | 4416篇 |
1990年 | 4254篇 |
1989年 | 4255篇 |
1988年 | 4138篇 |
1987年 | 4082篇 |
1986年 | 3810篇 |
1985年 | 5157篇 |
1984年 | 5263篇 |
1983年 | 4334篇 |
1982年 | 4675篇 |
1981年 | 4495篇 |
1980年 | 4368篇 |
1979年 | 4627篇 |
1978年 | 4989篇 |
1977年 | 4739篇 |
1976年 | 4712篇 |
1975年 | 4498篇 |
1974年 | 4515篇 |
1973年 | 4526篇 |
1972年 | 2978篇 |
1971年 | 2568篇 |
1968年 | 2887篇 |
1967年 | 3101篇 |
1966年 | 2628篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The reaction of CH3 with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 1013 cm3/mol-s was measured for removal of OH by CH3. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (?75%) for the removal of OH by CH3 at these conditions is their combination to form CH3OH. Rate coefficients of (5.3 ± 0.8) × 1012 and (9.0 ± 1.4) × 1012 cm3/mol-s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure. 相似文献
112.
W. Knoll W. Hickel M. Sawodny J. Stumpe H. Knobloch 《Fresenius' Journal of Analytical Chemistry》1991,341(3-4):272-278
Summary We report on novel optical techniques, based on evanescent waves, for the characterization of polymer surfaces and thin films. We first describe photo-ablation studies with polysilane films investigated by surface plasmon microscopy, a technique which is particularly well-suited for ultrathin samples. Thicker films that are homogeneous enough to carry optical waveguide modes can be characterized with high lateral resolution by the recently developed waveguide microscopy. We demonstrate this for a thin film of a solid polyelectrolyte. Finally, we report on surface plasmon field-enhanced Raman-spectroscopic and -imaging investigations of ultrathin Langmuir-Blodgett-Kuhn-layers of cadmium arachidate.W. Hickel is now with HOECHST AG, Angewandte Physik, W-6230 Frankfurt 80 相似文献
113.
Novel 3-phenyloxy substituted propane-1,2-diol derivatives, 4-(4-n-hexyloxyphenyl)-butane-1,2-diol and 4-(trans-4-n-pyropylcyclohexyl)-butane-1,2-diol have been synthesized and their thermal behaviour has been studied. These compounds exhibit thermotropic and, after addition of water, also lyotropic liquid-crystalline behaviour. The clearing temperatures of the smectic mesophases were found to be strongly dependent on the alkyl chain length and on the structural units that link the aromatic ring to the alkyl chain and to the diol unit. The behaviour of the aromatic compounds is compared with that of the cyclohexane derivative. Thereby it has been realized that the mesophase stability of the amphiphilic diols incorporating a rigid unit is largely determined by both, the molecular geometry (molecular shape and intramolecular flexibility) and the amphiphilic structural pattern. 相似文献
114.
The equations describing the behaviour of temperature/flow microsensorsemploy-ing polysilicon thermistors form a degenerate nonlinearparabolic system. One special feature is that different equationsof this system are to be satisfied on different domains. Bymeans of supersolutions and subsolutions, the maximum principle,and fixed point arguments, the authors show the existence ofsolutions to the equations. 相似文献
115.
F. J. M. Farley 《Zeitschrift fur Physik C Particles and Fields》1992,56(Z1):S88-S96
Measurements of the anomalous magnetic moment of the muon are reviewed. The emphasis is put on the first one of a series of
three CERN experiments which led to an experimental value ofa=1165922.9 (8.5)·10−9 (±7.2ppm), and which compares well with the present theoretical resulta=1165919.2 (1.8)·10−9 (±1.5ppm). 相似文献
116.
R. P. Spielmann Jin Zhen H. J. Triebel V. Nicolas M. Heller E. Bü cheler 《Magnetic resonance imaging》1992,10(6):893-901
To correlate the appearance of poststenotic jets on gradient echo images with features of localized Doppler spectra of the jets, we studied an in vitro model of steady flow-through stenoses of 86, 96, and 99% area reduction. As fluids, water and a 40% glycerol solution in water were used. MRI was performed with a 1.5 T whole body imager and gradient echo images were obtained in planes parallel to the direction of flow. Doppler spectra were acquired separately from the MR measurements at 1 cm intervals for a distance of 10 cm downstream from the stenosis. Poststenotic signal void was observed for water and for the 40% glycerol solution only if the mean velocity within the stenosis exceeded a limit of 50–60 cm/sec. On the MR images, the jets could be divided into two segments: A proximal jet segment of uniform width equal to the diameter of the stenosis, followed by a distal jet segment which was characterized by broadening and then dissipating signal void. Except for the 99% stenosis, a high signal intensity core was present within the proximal jet segment. In the proximal jet segment, the Doppler measurements showed a low temporal fluctuation of the maximal flow velocity and only little flow opposite to the main flow direction. In the distal jet segment, the velocity fluctuation and the intensity of reverse flow increased sharply. The high signal intensity core of the jet was associated with a poststenotic zone of constant maximal flow velocity. The results demonstrate a close relationship between characteristic features of poststenotic jets in MRI and pulsed Doppler sonography. 相似文献
117.
118.
B. Griepink E. A. Maier P. Quevauviller H. Muntau 《Fresenius' Journal of Analytical Chemistry》1991,339(9):599-603
Summary The Community Bureau of Reference (BCR) has undertaken the production of a wide range of certified reference materials (CRMs) for the improvement of accuracy and measurement harmony in various areas of concern at European Community level. This paper provides an overview of the sectors of the BCR-programme in the field of environment i.e. for water systems (water, sediment, biota), soil analysis (soil, fertiliser, waste), plant analysis (aquatic and terrestrial plants), analysis related to animals (e.g. muscle or liver) or man (e.g. industry and food). 相似文献
119.
120.