全文获取类型
收费全文 | 343716篇 |
免费 | 4592篇 |
国内免费 | 1337篇 |
专业分类
化学 | 190086篇 |
晶体学 | 4670篇 |
力学 | 13713篇 |
综合类 | 8篇 |
数学 | 41943篇 |
物理学 | 99225篇 |
出版年
2021年 | 2063篇 |
2020年 | 2473篇 |
2019年 | 2455篇 |
2018年 | 2313篇 |
2017年 | 2231篇 |
2016年 | 4663篇 |
2015年 | 3912篇 |
2014年 | 5247篇 |
2013年 | 15473篇 |
2012年 | 12468篇 |
2011年 | 15309篇 |
2010年 | 9396篇 |
2009年 | 9252篇 |
2008年 | 14138篇 |
2007年 | 14193篇 |
2006年 | 13856篇 |
2005年 | 12690篇 |
2004年 | 11368篇 |
2003年 | 9946篇 |
2002年 | 9745篇 |
2001年 | 10569篇 |
2000年 | 8159篇 |
1999年 | 6492篇 |
1998年 | 5264篇 |
1997年 | 5085篇 |
1996年 | 5166篇 |
1995年 | 4656篇 |
1994年 | 4457篇 |
1993年 | 4273篇 |
1992年 | 4712篇 |
1991年 | 4558篇 |
1990年 | 4243篇 |
1989年 | 4038篇 |
1988年 | 4319篇 |
1987年 | 3991篇 |
1986年 | 3844篇 |
1985年 | 5640篇 |
1984年 | 5676篇 |
1983年 | 4616篇 |
1982年 | 5058篇 |
1981年 | 5041篇 |
1980年 | 4800篇 |
1979年 | 4877篇 |
1978年 | 4869篇 |
1977年 | 4842篇 |
1976年 | 4787篇 |
1975年 | 4694篇 |
1974年 | 4512篇 |
1973年 | 4654篇 |
1972年 | 2659篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as
hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as
provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.
In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested
hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development
of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
12.
13.
A. J. Parsons S. D. J. Inglethorpe D. J. Morgan A. C. Dunham 《Journal of Thermal Analysis and Calorimetry》1997,48(1):49-62
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday 相似文献
14.
15.
16.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
17.
Chromatographia - A theoretical model is used to predict retention times of divalent metal cations in single-column ion chromatography using one or more ligands in the eluent. Stability constants... 相似文献
18.
19.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
20.
J. Escudi C. Couret H. Ranaivonjatovo J. Satge 《Coordination chemistry reviews》1994,130(1-2):427-480
During the last 10 years, several compounds of the type Ge=X (X = C, Ge, N, P, S) have been isolated as monomers. The stabilization of such derivatives, which are generally highly polymerizable, was achieved by using very bulky groups both on the germanium atom and on the heteroelement X. Conjugation (particularly in a few germenes and germaimines) and intramolecular or intermolecular coordination with oxygen or nitrogen, also contributes, in some cases, to the stabilization. The X-ray analyses of such compounds show a significant bond shortening of the double bond (8–10%) relative to the corresponding single bond and a planar or nearly planar germanium. These doubly bonded germanium derivatives are usually thermally stable but must be handled in an inert atmosphere because of their high sensitivity to oxygen and moisture; they are extremely reactive, much more than the corresponding carbon analogues. Nearly quantitative additions on the double bond have been observed with electrophiles and nucleophiles, and various types of cycloadditions also occur. Except in one case, a germylene behavior has not been observed, proving that such compounds retain their structural integrity in solution. 相似文献