全文获取类型
收费全文 | 29007篇 |
免费 | 4118篇 |
国内免费 | 2700篇 |
专业分类
化学 | 19932篇 |
晶体学 | 269篇 |
力学 | 1909篇 |
综合类 | 273篇 |
数学 | 3296篇 |
物理学 | 10146篇 |
出版年
2024年 | 30篇 |
2023年 | 570篇 |
2022年 | 542篇 |
2021年 | 817篇 |
2020年 | 1099篇 |
2019年 | 1058篇 |
2018年 | 881篇 |
2017年 | 781篇 |
2016年 | 1228篇 |
2015年 | 1177篇 |
2014年 | 1487篇 |
2013年 | 1994篇 |
2012年 | 2579篇 |
2011年 | 2685篇 |
2010年 | 1665篇 |
2009年 | 1637篇 |
2008年 | 1743篇 |
2007年 | 1677篇 |
2006年 | 1501篇 |
2005年 | 1231篇 |
2004年 | 946篇 |
2003年 | 798篇 |
2002年 | 755篇 |
2001年 | 565篇 |
2000年 | 561篇 |
1999年 | 609篇 |
1998年 | 559篇 |
1997年 | 549篇 |
1996年 | 618篇 |
1995年 | 505篇 |
1994年 | 465篇 |
1993年 | 387篇 |
1992年 | 365篇 |
1991年 | 318篇 |
1990年 | 248篇 |
1989年 | 202篇 |
1988年 | 160篇 |
1987年 | 135篇 |
1986年 | 125篇 |
1985年 | 119篇 |
1984年 | 88篇 |
1983年 | 60篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 17篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Li-Hua Su Tian-Ze Li Yun-Bao Ma Chang-An Geng Xiao-Yan Huang Xin Zhang Zhen Gao Ji-Jun Chen 《中国化学》2022,40(1):104-114
Inspired by the intriguing structures and remarkable activities of sesquiterpenoid dimers,12 new sesquiterpenoid dimers,artematrovirenolides A—D(1—4)and artematrolides S—Z(8—12),were isolated from the EtOAc fraction of Artemisia atrovirens through a bioactivity-guided approach.Their structures were elucidated by comprehensive spectroscopic data and absolute configuration was assigned based on single crystal X-ray diffraction data and ECD calculations.Structurally,all compounds are presumably formed via[4+2]cycloaddition involving three connecting model.Compounds 1—4 are four novel hetero-dimeric[4+2]Diels-Alder adducts dimerized from a rotundane-type unit and a guaiane-type monomer,and compounds 5—12 are eight new homo-dimeric[4+2]adducts derived from two guaianolide moieties.A putative biosynthetic pathway for compounds 1—4 was also proposed.Compounds 4,6,7,and 10 demonstrated moderate cytotoxicity against HepG2,SMMC-7721,and Huh7 cell lines with IC50 values ranging from 9.3 to 62.3μmol/L.Interestingly,compounds 5 and 11 manifested cytotoxicity with IC50 values of 13.6 and 12.8(HepG2),18.5 and 13.1(SMMC-7721),and 16.5 and 19.4μmol/L(Huh7),respectively,which were equivalent to the positive control,sorafenib.This investigation suggests that compounds 5 and 11 might be considered as potent antihepatoma candidates and deserve further structural modification and mechanism study. 相似文献
22.
Nonlinear Dynamics - This paper mainly investigates the dynamics of the non-resonant and near-resonant Hopf–Hopf bifurcations caused by the interaction of the lateral and yaw motion in a... 相似文献
23.
本文基于新的Kronecker型替换,给出两个由黑盒表示的稀疏多项式的新确定性插值算法.令f∈R[x1,……,xn]是一个稀疏黑盒多项式,其次数上界为D.当R是C或者是有限域时,相对于已有算法,新算法具有更好的计算复杂度或者关于D的复杂度更低.特别地,对于一般黑盒模型,D是复杂度中的主要因素,而在所有的确定性算法中,本文的第二个算法的复杂度关于D是最低的. 相似文献
24.
Journal of Applied Spectroscopy - The speciation of extracted chromium from ZSM-5 into an ionic liquid (IL) was studied using X-ray absorption near-edge structure (XANES) spectroscopy. The main... 相似文献
25.
In this paper,we consider the deformed Hermitian-Yang-Mills equation on closed almost Hermitian manifolds.In the case of the hypercritical phase,we derive a priori estimates under the existence of an admissible C-subsolution.As an application,we prove the existence of solutions for the deformed Hermitian-Yang-Mills equation under the condition of existence of a supersolution. 相似文献
26.
27.
28.
Russian Journal of Organic Chemistry - A rapid and efficient catalytic approach has been proposed for the synthesis of dimethyl 2-[2-(aryl-amino)but-3-en-1-yl]- and... 相似文献
29.
Journal of Thermal Analysis and Calorimetry - A complete analysis of the thermal process about melamine was presented, in which different methods were applied to determine the characteristic of the... 相似文献
30.
Bo Huang Hirokazu Kobayashi Tomokazu Yamamoto Takaaki Toriyama Syo Matsumura Yoshihide Nishida Katsutoshi Sato Katsutoshi Nagaoka Masaaki Haneda Wei Xie Yusuke Nanba Michihisa Koyama Fenglong Wang Shogo Kawaguchi Yoshiki Kubota Hiroshi Kitagawa 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2252-2257
Ru is an important catalyst in many types of reactions. Specifically, Ru is well known as the best monometallic catalyst for oxidation of carbon monoxide (CO) and has been practically used in residential fuel cell systems. However, Ru is a minor metal, and the supply risk often causes violent fluctuations in the price of Ru. Performance‐improved and cost‐reduced solid‐solution alloy nanoparticles of the Cu‐Ru system for CO oxidation are now presented. Over the whole composition range, all of the CuxRu1?x nanoparticles exhibit significantly enhanced CO oxidation activities, even at 70 at % of inexpensive Cu, compared to Ru nanoparticles. Only 5 at % replacement of Ru with Cu provided much better CO oxidation activity, and the maximum activity was achieved by 20 at % replacement of Ru by Cu. The origin of the high catalytic performance was found as CO site change by Cu substitution, which was investigated using in situ Fourier transform infrared spectra and theoretical calculations. 相似文献