全文获取类型
收费全文 | 28986篇 |
免费 | 93篇 |
国内免费 | 272篇 |
专业分类
化学 | 10666篇 |
晶体学 | 265篇 |
力学 | 1374篇 |
综合类 | 12篇 |
数学 | 8926篇 |
物理学 | 8108篇 |
出版年
2020年 | 37篇 |
2018年 | 1192篇 |
2017年 | 1443篇 |
2016年 | 706篇 |
2015年 | 546篇 |
2014年 | 467篇 |
2013年 | 657篇 |
2012年 | 3129篇 |
2011年 | 2307篇 |
2010年 | 1797篇 |
2009年 | 1541篇 |
2008年 | 564篇 |
2007年 | 612篇 |
2006年 | 610篇 |
2005年 | 4450篇 |
2004年 | 3933篇 |
2003年 | 2322篇 |
2002年 | 489篇 |
2001年 | 286篇 |
2000年 | 93篇 |
1999年 | 178篇 |
1998年 | 112篇 |
1997年 | 74篇 |
1996年 | 47篇 |
1995年 | 42篇 |
1994年 | 46篇 |
1992年 | 172篇 |
1991年 | 157篇 |
1990年 | 136篇 |
1989年 | 112篇 |
1988年 | 102篇 |
1987年 | 57篇 |
1986年 | 41篇 |
1985年 | 40篇 |
1984年 | 34篇 |
1983年 | 26篇 |
1979年 | 31篇 |
1978年 | 25篇 |
1976年 | 81篇 |
1975年 | 41篇 |
1974年 | 40篇 |
1973年 | 49篇 |
1972年 | 39篇 |
1971年 | 25篇 |
1970年 | 34篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1967年 | 32篇 |
1966年 | 37篇 |
1923年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
1.
Watanabe Sou Senzaki Tatsuya Shibata Atsuhiro Nomura Kazunori Takeuchi Masayuki Nakatani Kiyoharu Matsuura Haruaki Horiuchi Yusuke Arai Tsuyoshi 《Journal of Radioanalytical and Nuclear Chemistry》2019,322(3):1273-1277
Journal of Radioanalytical and Nuclear Chemistry - Extraction chromatography flow-sheet employing octyl(phenyl)-N,N-diisobutylcarbonoylmethylphosphine oxide and bis(2-ethylhexyl) hydrogen phosphate... 相似文献
2.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
3.
It is an important issue to clarify the minimum required size of a specimen for the accurate measurement of oblique incidence absorption coefficient. Investigation is made on the basis of experimental studies in a laboratory, using Aoshima's time stretched pulse technique. Measurements are carried out for glass fiber with thickness of 50 and 100 mm as highly absorbing materials and for ceramic with a thickness of 52 mm as relatively low absorbing material. The tested surface areas range from 0.0625 to 42 m2 for glass fiber and from 0.1563 to 39.168 m2 for ceramics. The absorption coefficients are determined at incidence angles from 0 to 45° in increments of 15°. With consideration of an active surface bounded by ellipse orbit, the minimum required surface area is 16 m2 with a ratio of length to width of about 1.25. This value is twice the area size of the active surface, which is calculated from the geometry of source and microphone, and the width of the temporal window. 相似文献
4.
The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported. 相似文献
5.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
6.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
7.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
8.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献
9.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented. 相似文献
10.
Micha? Chmielewski 《Tetrahedron letters》2004,45(31):6007-6010
Comparison of the anion binding properties of a series of uncharged macrocyclic tetraamides reveal significant effects of the receptor's size on the strength of its anion complexes. This study allowed for estimation of the optimal size of a macroring for complexation of common anions. 相似文献