全文获取类型
收费全文 | 51039篇 |
免费 | 10337篇 |
国内免费 | 18261篇 |
专业分类
化学 | 37004篇 |
晶体学 | 2322篇 |
力学 | 4060篇 |
综合类 | 2043篇 |
数学 | 8286篇 |
物理学 | 25922篇 |
出版年
2024年 | 138篇 |
2023年 | 550篇 |
2022年 | 1930篇 |
2021年 | 1853篇 |
2020年 | 1795篇 |
2019年 | 1753篇 |
2018年 | 1611篇 |
2017年 | 2468篇 |
2016年 | 1758篇 |
2015年 | 2606篇 |
2014年 | 3188篇 |
2013年 | 4227篇 |
2012年 | 4154篇 |
2011年 | 4357篇 |
2010年 | 4469篇 |
2009年 | 4594篇 |
2008年 | 5228篇 |
2007年 | 4591篇 |
2006年 | 4551篇 |
2005年 | 3983篇 |
2004年 | 3040篇 |
2003年 | 2231篇 |
2002年 | 2216篇 |
2001年 | 2245篇 |
2000年 | 2315篇 |
1999年 | 1376篇 |
1998年 | 738篇 |
1997年 | 590篇 |
1996年 | 576篇 |
1995年 | 503篇 |
1994年 | 544篇 |
1993年 | 516篇 |
1992年 | 431篇 |
1991年 | 314篇 |
1990年 | 312篇 |
1989年 | 339篇 |
1988年 | 274篇 |
1987年 | 223篇 |
1986年 | 173篇 |
1985年 | 135篇 |
1984年 | 126篇 |
1983年 | 139篇 |
1982年 | 115篇 |
1981年 | 98篇 |
1980年 | 73篇 |
1979年 | 63篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1971年 | 16篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
UJ24型电位差计使用时出现的故障,可以利用数字万用表排查故障,提出排查方案,进行维修与调节,使它尽快恢复到最佳工作状态,这样既节省厂家的维修时间又节省学校的维修费用。 相似文献
2.
Qin Yin Shou-Guo Wang Xiao-Wei Liang De-Wei Gao Jun Zheng Shu-Li You 《Chemical science》2015,6(7):4179-4183
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation. 相似文献
3.
Highly dispersed palladium nanoclusters incorporated in amino‐functionalized silica spheres for the selective hydrogenation of succinic acid to γ‐butyrolactone 下载免费PDF全文
Highly dispersed palladium nanoclusters incorporated on amino‐functionalized silica sphere surfaces (Pd/SiO2‐NH2) were fabricated by a simple one‐pot synthesis utilizing 3‐(2‐aminoethylamino)propyltrimethoxysilane (AAPTS) as coordinating agent. Uniform palladium nanoclusters with an average size of 1.1 nm can be obtained during the co‐condensation of tetraethyl orthosilicate and AAPTS owing to the strong interaction between palladium species and amino groups in AAPTS. The palladium particle size can be controlled by addition of AAPTS and plays a significant role in the catalytic performance. The Pd/SiO2‐NH2 catalyst exhibits high catalytic activity for succinic acid hydrogenation with 100% conversion and 94% selectivity towards γ‐butyrolactone using 1,4‐dioxane as solvent at 240°C and 60 bar for 4 h. Moreover, the Pd/SiO2‐NH2 catalyst is robust and readily reusable without loss of its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
4.
Dr. Wan‐Ling Liu Ni‐Shin Yang Ya‐Ting Chen Stephen Lirio Cheng‐You Wu Prof. Chia‐Her Lin Prof. Hsi‐Ya Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):115-119
A green and sustainable strategy synthesizes clinical medicine warfarin anticoagulant by using lipase‐supported metal–organic framework (MOF) bioreactors (see scheme). These findings may be beneficial for future studies in the industrial production of chemical, pharmaceutical, and agrochemical precursors. 相似文献
5.
6.
本文在一类 Lp位势V(x)下建立了广义Schrodinger算子H=(-Δ)m+V(x)在C∞0(Rn)上的本质自伴性,给出了H的本质谱的分布. 相似文献
7.
首先在Contingent切锥意义下界定了Banach空间中非空集合的伪切锥和伪凸性的概念,并讨论了相应的性质,然后针对可微优化问题,在广义凸性假设下,建立了最优性条件。 相似文献
8.
9.
LIU Jixue ZHANG Sanguo & CHEN Xiru Department of Statistics Finance University of Science Technology of China Hefei China Department of Mathematics Graduate School of Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,49(6):752-769
This paper studies the linear EV model when replicate observations are made only on independent variables. We construct the estimates of regression coefficients and prove the consistency and asymptotic normality under some proper conditions. Results obtained reveal the difference between the case where the independent and dependent variables are observed repeatedly and simultaneously and the case studied in this article. 相似文献
10.
DING Bin-Gang ZHANG Da-Li LU Ding-Hui 《理论物理通讯》2006,46(1):113-118
We calculate the binding energies of Ni, Cu, Xe, Cs, Pt, Au, Np, Pu isotope chains using two interaction parameter sets NL-3 and NL-Z, and compared the relative errors of the even-even nuclei with those of odd-even nuclei and odd-odd nuclei. We find that the errors of binding energy of odd-even and odd-odd nuclei are not bigger than the one of even-even nuclei. The result shows that comparing with even-even nuclei, there is no systematic error and approximation in the calculations of the binding energy of odd-even and odd-odd nuclei with relativistic mean-field theory. In addition, the result is explained theoretically. 相似文献