全文获取类型
收费全文 | 25128篇 |
免费 | 4498篇 |
国内免费 | 3412篇 |
专业分类
化学 | 17616篇 |
晶体学 | 329篇 |
力学 | 1651篇 |
综合类 | 236篇 |
数学 | 2894篇 |
物理学 | 10312篇 |
出版年
2024年 | 96篇 |
2023年 | 510篇 |
2022年 | 912篇 |
2021年 | 975篇 |
2020年 | 1110篇 |
2019年 | 1012篇 |
2018年 | 956篇 |
2017年 | 850篇 |
2016年 | 1230篇 |
2015年 | 1296篇 |
2014年 | 1509篇 |
2013年 | 1942篇 |
2012年 | 2329篇 |
2011年 | 2319篇 |
2010年 | 1668篇 |
2009年 | 1592篇 |
2008年 | 1770篇 |
2007年 | 1562篇 |
2006年 | 1356篇 |
2005年 | 1124篇 |
2004年 | 850篇 |
2003年 | 689篇 |
2002年 | 660篇 |
2001年 | 556篇 |
2000年 | 475篇 |
1999年 | 478篇 |
1998年 | 399篇 |
1997年 | 305篇 |
1996年 | 325篇 |
1995年 | 298篇 |
1994年 | 273篇 |
1993年 | 222篇 |
1992年 | 196篇 |
1991年 | 200篇 |
1990年 | 197篇 |
1989年 | 148篇 |
1988年 | 122篇 |
1987年 | 94篇 |
1986年 | 80篇 |
1985年 | 87篇 |
1984年 | 48篇 |
1983年 | 48篇 |
1982年 | 37篇 |
1981年 | 28篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
J.Z. Tao 《Journal of solid state chemistry》2003,173(1):45-48
X-ray diffraction data for TaO2F from 20 to 400 K show a thermal expansion so low that we cannot be certain whether it is positive or negative. We estimate the absolute value of the thermal expansion coefficient to be less than 6×10−7/K. This then is comparable to that of amorphous SiO2 and is apparently unique behavior for a cubic material over such a large temperature range. 相似文献
62.
The millimeter wave spectrum of the isotopically substituted CO dimer, (13C16O)2, has been studied for the first time, confirming and extending a recent infrared study. Eighty-seven transitions in the 77-180 GHz region have been assigned and analyzed in terms of a model-independent term value scheme involving 57 rotational levels with J=0-8. The levels can be classified into 7 “stacks” which have symmetry classifications of either A−/B+ or A+/B− and K-values of either 0 or 1. For the normal isotope, symmetry and nuclear spin statistics cause alternate rotational levels to be missing, but for (13C16O)2 all levels are present with an intensity alternation of 1:3 between A and B symmetries. The four A−/B+ stacks have not previously been observed, and the lowest of them establishes the tunneling splitting of (13C16O)2 to be 3.769 cm−1, slightly larger than the (12C16O)2 value of 3.731 cm−1. A large amount of precise experimental data is now available for the CO dimer, which should lead to greater theoretical insight into its structure and tunneling dynamics. 相似文献
63.
研究了钍与5-(对羧基苯偶氮)-8-羟基喹啉(5-CPAHQ)的显色反应条件:在阳离子表面活性剂十六烷基三甲基溴化铵(CTMAB)存在下,pH4.4-5.4缓冲介质中,形成稳定的橙红色络合物,最大吸收波长为490nm,ε=1.10×105L·mol-1·cm-1,钍在0-9μg/25mL范围内符合比尔定律。用TBP萃淋树脂分离,该方法可用于测定矿石中的微量钍。 相似文献
64.
投资理论告诉人们,应尽量使投资分散化.但许多投资在实际投资中却常常违背这一原则.本从一个调面分析在一个等均值和有一个无风险资产的均方世界里,交易成本的存在,会使投资产生很强的违背分散化原则的动机。 相似文献
65.
Yanqing Tian Xiaohe Xu Yingying Zhao Xinyi Tang Fengyu Su Xiaoguang Zhao Enle Zhou 《Liquid crystals》1995,19(3):295-300
The synthesis of three new series of chiral Schiff's bases containing benzilideneaniline and 2-hydroxybenzilideneaniline moieties as mesogenic cores is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements were used to study the phase transition temperatures and behaviour. The results reveal that most of these materials show chiral smectic mesomorphism. 相似文献
66.
Consideringsystem:x=φ(y)-F(x),y=-g(x){(E)inwhichF(x)=∫x0f(t)dt,f(x),g(x),φ(y)arecontinuous,andsatisfytheconditionswhichensur... 相似文献
67.
SINGLE MACHINE SCHEDULING WITH CONTROLLABLE PROCESSING TIMES AND COMPRESSION COSTS (PART I:EQUAL TIMES AND COSTS) 总被引:1,自引:0,他引:1
Most papers in scheduling research have treated individual job processing times as fixed parameters. However, in many practical situations, a manager may control processing time by realloeating resources. In this paper, authors consider a machine scheduling problemwith controllable processing times. In the first part of this paper, a special case where the pro-cessing times and compression costs are uniform among jobs is discussed. Theoretical results are derived that aid in developing an O(n^2) algorithm to slove the problem optimally. In the second part of this paper, authors generalize the discussion to general case, An effective heuristic to the genera/ problem will be presented. 相似文献
68.
Z P Li C S Tang J Y Su 《Science in China. Series B, Chemistry, life sciences & earth sciences》1991,34(5):599-605
Results from a systematic experiment on isolated perfused rat heart and isolated myocytes of adult rat showed that the mechanism of calcium influx during myocardial ischemia-reperfusion is due to the development of intracellular sodium overload during ischemic period; on reperfusion, the high intracellular Na+ content activated the reverse direction of Na(+)-Ca2+ exchange over myocardial sarcolemma (SL), thus a large quantity of extracellular Ca2+ fluxed over the SL to the intracellular space, forming a condition of intracellular Ca2+ overload, which leads to irreversible damage of the myocardium. 相似文献
69.
70.
本文来自于作者的实践。介绍了加工方法及测量问题。重点叙述了加工中的一些关键,同时也提供了国内外在这方面的进展情况。 相似文献