全文获取类型
收费全文 | 248805篇 |
免费 | 1592篇 |
国内免费 | 427篇 |
专业分类
化学 | 115514篇 |
晶体学 | 3899篇 |
力学 | 13152篇 |
综合类 | 3篇 |
数学 | 38142篇 |
物理学 | 80114篇 |
出版年
2021年 | 1093篇 |
2020年 | 1249篇 |
2019年 | 1341篇 |
2018年 | 10556篇 |
2017年 | 11391篇 |
2016年 | 6709篇 |
2015年 | 2499篇 |
2014年 | 2653篇 |
2013年 | 6563篇 |
2012年 | 9392篇 |
2011年 | 18705篇 |
2010年 | 11493篇 |
2009年 | 11544篇 |
2008年 | 16452篇 |
2007年 | 19869篇 |
2006年 | 5723篇 |
2005年 | 11881篇 |
2004年 | 8068篇 |
2003年 | 7676篇 |
2002年 | 5553篇 |
2001年 | 5748篇 |
2000年 | 4326篇 |
1999年 | 3146篇 |
1998年 | 2179篇 |
1997年 | 2248篇 |
1996年 | 2281篇 |
1995年 | 2044篇 |
1994年 | 2027篇 |
1993年 | 1831篇 |
1992年 | 2305篇 |
1991年 | 2395篇 |
1990年 | 2249篇 |
1989年 | 2205篇 |
1988年 | 2192篇 |
1987年 | 2201篇 |
1986年 | 2017篇 |
1985年 | 2500篇 |
1984年 | 2533篇 |
1983年 | 2027篇 |
1982年 | 2024篇 |
1981年 | 1865篇 |
1980年 | 1852篇 |
1979年 | 2153篇 |
1978年 | 2233篇 |
1977年 | 2102篇 |
1976年 | 2058篇 |
1975年 | 1925篇 |
1974年 | 1903篇 |
1973年 | 1975篇 |
1972年 | 1276篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Peter T. Smith Younghoon Kim Dr. Bahiru Punja Benke Prof. Kimoon Kim Prof. Christopher J. Chang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4932-4937
We report a supramolecular strategy for promoting the selective reduction of O2 for direct electrosynthesis of H2O2. We utilized cobalt tetraphenylporphyrin (Co-TPP), an oxygen reduction reaction (ORR) catalyst with highly variable product selectivity, as a building block to assemble the permanently porous supramolecular cage Co-PB-1(6) bearing six Co-TPP subunits connected through twenty-four imine bonds. Reduction of these imine linkers to amines yields the more flexible cage Co-rPB-1(6). Both Co-PB-1(6) and Co-rPB-1(6) cages produce 90–100 % H2O2 from electrochemical ORR catalysis in neutral pH water, whereas the Co-TPP monomer gives a 50 % mixture of H2O2 and H2O. Bimolecular pathways have been implicated in facilitating H2O formation, therefore, we attribute this high H2O2 selectivity to site isolation of the discrete molecular units in each supramolecule. The ability to control reaction selectivity in supramolecular structures beyond traditional host–guest interactions offers new opportunities for designing such architectures for a broader range of catalytic applications. 相似文献
72.
Mathematical Notes - An algorithm is presented which determines in a finite number of steps whether an initial finite binary automaton is spherically transitive. Since the class of deterministic... 相似文献
73.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
74.
75.
Lebedev V. T. Serebrov A. P. 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2020,14(1):1-5
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques - A method for studying the magnetic dynamics of endofullerenes M@C2n (2n = 60, 70, …) and their derivatives,... 相似文献
76.
77.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献
78.
N. I. Golovina G. N. Nechiporenko G. G. Nemtsev G. P. Dolganova V. P. Roshchupkin D. B. Lempert G. B. Manelis 《Russian Journal of Applied Chemistry》2007,80(1):24-30
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined. 相似文献
79.
Yu. V. Pokonova 《Russian Journal of Applied Chemistry》2007,80(12):2163-2164
Kinetic, sorption and selectivity properties of commercial adsorbents are improved by adding petroleum residues (tar asphaltene concentrates) 13% of whole mass. Obtained adsorbents can be used for selective extraction of nobel metals from multicomponent polymetallic solutions of heavy metals and fro sewages purification for removing arsenic. 相似文献
80.
G. Panina 《Central European Journal of Mathematics》2003,1(2):157-168
All 3-dimensional convex polytopes are known to be rigid. Still their Minkowski differences (virtual polytopes) can be flexible
with any finite freedom degree. We derive some sufficient rigidity conditions for virtual polytopes and present some examples
of flexible ones. For example, Bricard's first and second flexible octahedra can be supplied by the structure of a virtual
polytope. 相似文献