全文获取类型
收费全文 | 89890篇 |
免费 | 2756篇 |
国内免费 | 2797篇 |
专业分类
化学 | 33777篇 |
晶体学 | 1032篇 |
力学 | 7365篇 |
综合类 | 206篇 |
数学 | 33200篇 |
物理学 | 19863篇 |
出版年
2023年 | 258篇 |
2022年 | 366篇 |
2021年 | 538篇 |
2020年 | 598篇 |
2019年 | 589篇 |
2018年 | 10834篇 |
2017年 | 10715篇 |
2016年 | 6685篇 |
2015年 | 1541篇 |
2014年 | 1146篇 |
2013年 | 1391篇 |
2012年 | 4970篇 |
2011年 | 11661篇 |
2010年 | 6559篇 |
2009年 | 6948篇 |
2008年 | 7556篇 |
2007年 | 9567篇 |
2006年 | 1034篇 |
2005年 | 1942篇 |
2004年 | 1999篇 |
2003年 | 2336篇 |
2002年 | 1359篇 |
2001年 | 558篇 |
2000年 | 519篇 |
1999年 | 351篇 |
1998年 | 375篇 |
1997年 | 275篇 |
1996年 | 299篇 |
1995年 | 214篇 |
1994年 | 152篇 |
1993年 | 167篇 |
1992年 | 114篇 |
1991年 | 118篇 |
1990年 | 96篇 |
1989年 | 99篇 |
1988年 | 83篇 |
1987年 | 72篇 |
1986年 | 75篇 |
1985年 | 62篇 |
1984年 | 46篇 |
1983年 | 43篇 |
1982年 | 46篇 |
1981年 | 41篇 |
1980年 | 51篇 |
1979年 | 47篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
31.
Dongping Wang Jie Dong Wenjing Fan Prof. Dr. Xiang-Ai Yuan Prof. Dr. Jian Han Prof. Dr. Jin Xie 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(22):8508-8512
An unprecedented Mn(I)-catalyzed selective hydroarylation and hydroalkenylation of unsaturated amides with commercially available organic boronic acids is reported. Alkenyl boronic acids have been successfully employed for the first time in Mn(I)-catalyzed carbon–carbon bond formation. A wide array of β-alkenylated amide products can be obtained in moderate to good yields, which offers practical access to five- and six-membered lactams. This protocol has predictable regio- and chemoselectivity, excellent functional group compatibility and ease of operation in air, representing a significant step-forward towards manganese-catalyzed C−C coupling. 相似文献
32.
33.
34.
Abstract Gastrodigenin, also known as 4-hydroxybenzyl alcohol (HBA), is one of the main components of Gastrodia elata, which is a perfect lead compound of natural products. In order to get new active compounds, we modified the structure of HBA through esterification with carboxylic acid, and got a series of derivatives in which 4-hydroxybenzyl alcohol 2-naphthoate (NHBA) showed stronger antidepressant activity than HBA. In this paper, we firstly evaluated the antidepressant activity of NHBA by tail suspension test (TST) and forced swimming test (FST). Then, we carried out the biochemical assay and western blot to determine its mechanism. The results displayed that NHBA could increase the content of serotonin, dopamine, norepinephrine, γ-aminobutyric acid, brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) in mice brain. It suggested that NHBA exhibited an antidepressant-like effect through monoaminergic system, GABAergic system and BDNF/TrkB signaling pathways. 相似文献
35.
Guangrui Chen Yuxing Yan Dr. Jie Wang Prof. Yong Sik Ok Guiyuan Zhong Prof. Bu Yuan Guan Prof. Yusuke Yamauchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19831-19836
Mesoporous core–shell nanostructures with controllable ultra-large open channels in their nanoshells are of great interest. However, soft template-directed cooperative assembly to mesoporous nanoshells with highly accessible pores larger than 30 nm, or even above 50 nm into macroporous range, remains a significant challenge. Herein we report a general approach for precisely tailored coating of hierarchically macro-/mesoporous polymer and carbon shells, possessing highly accessible radial channels with extremely wide pore size distribution from ca. 10 nm to ca. 200 nm, on diverse functional materials. This strategy creates opportunities to tailor the interfacial assembly of irregular mesostructured nanounits on core materials and generate various core–shell nanomaterials with controllable pore architectures. The obtained Fe,N-doped macro-/mesoporous carbon nanoshells show enhanced electrochemical performance for the oxygen reduction reaction in alkaline condition. 相似文献
36.
37.
The sunset diagram of λφ4 theory is evaluated numerically in cutoff scheme and a nonzero finite term(in accordance with dimensional regularization (DR) result) is found in contrast to published calculations. This findingdramatically reduces the critical couplings for symmetry breaking in the two-loop effective potential discussed in ourprevious work. 相似文献
38.
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
39.
关于绝对半素环和绝对半素根 总被引:3,自引:0,他引:3
张宪君 《纯粹数学与应用数学》1993,9(2):57-60
本文了绝对半素环的概念,研究了绝对半素与与半素环及素环之间的关系,讨论了由全体绝对半素环类决定的上根--绝对半半素根及其性质。 相似文献
40.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective. 相似文献