全文获取类型
收费全文 | 30768篇 |
免费 | 149篇 |
国内免费 | 278篇 |
专业分类
化学 | 11689篇 |
晶体学 | 285篇 |
力学 | 1426篇 |
综合类 | 12篇 |
数学 | 9216篇 |
物理学 | 8567篇 |
出版年
2021年 | 93篇 |
2020年 | 70篇 |
2019年 | 65篇 |
2018年 | 1232篇 |
2017年 | 1480篇 |
2016年 | 766篇 |
2015年 | 621篇 |
2014年 | 533篇 |
2013年 | 771篇 |
2012年 | 3240篇 |
2011年 | 2430篇 |
2010年 | 1880篇 |
2009年 | 1618篇 |
2008年 | 673篇 |
2007年 | 690篇 |
2006年 | 673篇 |
2005年 | 4504篇 |
2004年 | 3966篇 |
2003年 | 2329篇 |
2002年 | 537篇 |
2001年 | 321篇 |
2000年 | 128篇 |
1999年 | 208篇 |
1998年 | 141篇 |
1997年 | 97篇 |
1996年 | 69篇 |
1995年 | 70篇 |
1994年 | 74篇 |
1993年 | 48篇 |
1992年 | 200篇 |
1991年 | 176篇 |
1990年 | 148篇 |
1989年 | 115篇 |
1988年 | 120篇 |
1987年 | 63篇 |
1986年 | 51篇 |
1985年 | 54篇 |
1984年 | 43篇 |
1983年 | 36篇 |
1982年 | 45篇 |
1979年 | 34篇 |
1976年 | 88篇 |
1975年 | 42篇 |
1974年 | 49篇 |
1973年 | 54篇 |
1972年 | 42篇 |
1970年 | 34篇 |
1969年 | 37篇 |
1968年 | 36篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
1.
Mariam Hakami Dr. Geetanjali Deokar Jasmin Smajic Dr. Nitin M. Batra Prof. Pedro M. F. J. Costa 《化学:亚洲杂志》2021,16(11):1466-1474
In the last decade, catalytic chemical vapor deposition (CVD) has been intensively explored for the growth of single-layer graphene (SLG). Despite the scattering of guidelines and procedures, variables such as the surface texture/chemistry of catalyst metal foils, carbon feedstock, and growth process parameters have been well-scrutinized. Still, questions remain on how best to standardize the growth procedure. The possible correlation of procedures between different CVD setups is an example. Here, two thermal CVD reactors were explored to grow graphene on Cu foil. The design of these setups was entirely distinct, one being a “showerhead” cold-wall type, whereas the other represented the popular “tubular” hot-wall type. Upon standardizing the Cu foil surface, it was possible to develop a procedure for cm2-scale SLG growth that differed only by the carrier gas flow rate used in the two reactors. 相似文献
2.
3.
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
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.
E. C. Ferreira J. A. P. da Costa J. A. K. Freire G. A. Farias V. N. Freire 《Applied Surface Science》2002,190(1-4):191-194
Confined excitons in non-abrupt GaAs/AlxGa1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al0.3Ga0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces. 相似文献
9.
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
10.
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