全文获取类型
收费全文 | 343749篇 |
免费 | 2792篇 |
国内免费 | 893篇 |
专业分类
化学 | 165735篇 |
晶体学 | 5109篇 |
力学 | 16786篇 |
综合类 | 2篇 |
数学 | 51418篇 |
物理学 | 108384篇 |
出版年
2020年 | 1827篇 |
2019年 | 2123篇 |
2018年 | 11002篇 |
2017年 | 11824篇 |
2016年 | 7915篇 |
2015年 | 3492篇 |
2014年 | 4160篇 |
2013年 | 11441篇 |
2012年 | 12399篇 |
2011年 | 22238篇 |
2010年 | 13635篇 |
2009年 | 13610篇 |
2008年 | 19404篇 |
2007年 | 22905篇 |
2006年 | 8675篇 |
2005年 | 14646篇 |
2004年 | 10496篇 |
2003年 | 9633篇 |
2002年 | 7617篇 |
2001年 | 7443篇 |
2000年 | 5731篇 |
1999年 | 4302篇 |
1998年 | 3682篇 |
1997年 | 3683篇 |
1996年 | 3519篇 |
1995年 | 3316篇 |
1994年 | 3115篇 |
1993年 | 3156篇 |
1992年 | 3446篇 |
1991年 | 3499篇 |
1990年 | 3314篇 |
1989年 | 3254篇 |
1988年 | 3334篇 |
1987年 | 3212篇 |
1986年 | 3111篇 |
1985年 | 4158篇 |
1984年 | 4334篇 |
1983年 | 3579篇 |
1982年 | 3932篇 |
1981年 | 3807篇 |
1980年 | 3686篇 |
1979年 | 3766篇 |
1978年 | 4045篇 |
1977年 | 3824篇 |
1976年 | 4099篇 |
1975年 | 3593篇 |
1974年 | 3705篇 |
1973年 | 4038篇 |
1972年 | 2510篇 |
1971年 | 1938篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Umie F.M. Haziz Rosenani A. Haque Shun-Ze Zhan Hassan H. Abdallah Mohd R. Razali 《应用有机金属化学》2020,34(10):e5818
The synthesis and characterizations for a series of dinuclear gold (I)-di-NHC complexes, 1–8 through the trans-metalation method of their respective silver (I)-di-NHC complexes, i–viii are reported (where NHC = N-heterocyclic carbene). The successful complexation of a series of unusual non-symmetrical and symmetrical di-NHC ligands, 3,3'-(ethane-1,2-diyl)-1-alkylbenzimidazolium-1'-butylbenzimidazolium (with alkyl = methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, benzyl) with the gold (I) ions are suggested by elemental analysis, Fourier transform-infrared, 1H- and 13C-NMR data. The 13C-NMR spectra of 1–8 show a singlet sharp peak in the range of 190.00–192.00 ppm, indicating the presence of a carbene carbon that bonded to the gold (I) ion. From single crystal X-ray diffraction data, the structure of complex 6 with the formula of [di-NHC-Au (I)]2·2PF6 is obtained [where NHC = 3,3'-(ethane-1,2-diyl)-1-hexylbenzimidazolium-1'-butylbenzimidazolium]. The photophysical study in solid state of 6 displays an intense photoluminescence with a strong emission maxima, λem = 480 nm, upon excitation at 340 nm at room temperature. Interestingly, the emission maximum at 77 K shows a structural character with a strong peak at 410 nm, a medium at 433 nm and a weak at 387 nm, accompanied by a tail band to about 500 nm. 相似文献
102.
103.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and... 相似文献
104.
105.
Vanessa R. Machado Louis P. Sandjo Giovanni L. Pinheiro Milene H. Moraes Mario Steindel Moacir G. Pizzolatti 《Natural product research》2018,32(3):275-281
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase. 相似文献
106.
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
107.
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
108.
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
109.
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
110.