全文获取类型
收费全文 | 43773篇 |
免费 | 8329篇 |
国内免费 | 16046篇 |
专业分类
化学 | 31606篇 |
晶体学 | 1866篇 |
力学 | 3438篇 |
综合类 | 1974篇 |
数学 | 6758篇 |
物理学 | 22506篇 |
出版年
2024年 | 130篇 |
2023年 | 413篇 |
2022年 | 1592篇 |
2021年 | 1535篇 |
2020年 | 1503篇 |
2019年 | 1479篇 |
2018年 | 1406篇 |
2017年 | 2165篇 |
2016年 | 1547篇 |
2015年 | 2201篇 |
2014年 | 2673篇 |
2013年 | 3396篇 |
2012年 | 3299篇 |
2011年 | 3703篇 |
2010年 | 3754篇 |
2009年 | 3914篇 |
2008年 | 4430篇 |
2007年 | 3852篇 |
2006年 | 3902篇 |
2005年 | 3402篇 |
2004年 | 2646篇 |
2003年 | 1899篇 |
2002年 | 1883篇 |
2001年 | 2039篇 |
2000年 | 2139篇 |
1999年 | 1249篇 |
1998年 | 692篇 |
1997年 | 547篇 |
1996年 | 542篇 |
1995年 | 445篇 |
1994年 | 460篇 |
1993年 | 437篇 |
1992年 | 463篇 |
1991年 | 251篇 |
1990年 | 306篇 |
1989年 | 253篇 |
1988年 | 259篇 |
1987年 | 252篇 |
1986年 | 176篇 |
1985年 | 134篇 |
1984年 | 157篇 |
1983年 | 145篇 |
1982年 | 99篇 |
1981年 | 96篇 |
1980年 | 62篇 |
1979年 | 73篇 |
1978年 | 25篇 |
1977年 | 17篇 |
1965年 | 20篇 |
1964年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
采用气相色谱-质谱(GC-MS)选择离子监测法(SIM),建立了准确可靠、灵敏度高、快速简便的测定维生素C泡腾片中甜蜜素含量的新方法.样品中的甜蜜素衍生后用有机试剂提取,在选择离子模式下进行测定,以保留时间和特征离子比例进行定性,单离子定量.甜蜜素的线性范围为0.05-10mg/L,检出限为0.6mg/kg,回收率为90.5%-96.9%,相对标准偏差小于4.4%.方法分析所用时间短,结果准确可靠,选择性好,适用于维生素C泡腾片中甜蜜素含量的检验. 相似文献
142.
The wavelet and harmonic filtering method suggested by Zalevsky and Ouzieli is introduced in this paper and adopted in our volume holographic image recognition system. This composite filter combines several scaled versions of the cascaded wavelet and harmonic filter, obtaining high discrimination ability and wide dynamic range of rotation and scale deformations. Optical experiments are conducted to demonstrate the validity and practicability of the algorithm. To the best of our knowledge, this is the first report of using this algorithm in a volume holographic system. Moreover, the separate correlation approach proposed in this paper greatly simplifies the manufacturing process and reduces the cost of the system. 相似文献
143.
Let R be a ring. R is called right AP-injective if, for any a ∈ R, there exists a left ideal of R such that lr(a) = Ra (?) Xa. We extend this notion to modules. A right .R-module M with 5 = End(MR) is called quasi AP-injective if, for any s ∈ S, there exists a left ideal Xs of S such that ls(Ker(s)) = Ss (?) Xs. In this paper, we give some characterizations and properties of quasi AP-injective modules which generalize results of Page and Zhou. 相似文献
144.
研究全稳定广义生灭最小Q过程的可配称性,获得广义生灭最小Q过程是可配称的充分必要条件,以及最小Q过程是唯一的可配称Q过程的充分必要条件. 相似文献
145.
146.
Prisoner's Dilemma Game with Heterogeneous Influential Effect on Regular Small-World Networks 下载免费PDF全文
The effect of heterogeneous influence of different individuals on the maintenance of co-operative behaviour is studied in an evolutionary Prisoner's Dilemma game with players located on the sites of regular small-world networks. The players interacting with their neighbours can either co-operate or defect and update their states by choosing one of the neighbours and adopting its strategy with a probability depending on the pay off difference. The selection of the neighbour obeys a preferential rule: the more influential a neighbour, the larger the probability it is picked. It is found that this simple preferential selection rule can promote continuously the co-operation of the whole population with the strengthening of the disorder of the underlying network. 相似文献
147.
Design and Fabrication of 1.06 μm Resonant-Cavity Enhanced Reflective Modulator with GaInAs/GaAs Quantum Wells 下载免费PDF全文
A resonant-cavity enhanced reflective optical modulator is designed and fabricated, with three groups of three highly strained InGaAs/GaAs quantum wells in the cavity, for low voltage and high contrast ratio operation. The quantum wells are positioned in antinodes of the optical standing wave. The modulator is grown in a single growth step in an molecular beam epitaxy system, using GaAs/AlAs distributed Bragg reflectors as both the top and bottom mirrors. Results show that the reflection device has a modulation extinction of 3 dB at -4.5 V bias. 相似文献
148.
The conceptual design of a cryogenic system at temperature 2 K for the Peking University Free Electron Laser (PKU-FEL) facility is carried out. In order to minimize the scale of the cryogenic system and the running cost, the superconducting accelerator and the superconducting injector will mainly run at a long-pulsed mode. Optimization of the 2-K cryogenic system is carried out based on the heat load estimation and running parameters. Total cooling power of 52.5 W for the long-pulsed mode is necessary for the PKU cryogenic system. The PKU cryogenic system will be the first 2-K system for accelerators in China and will provide experience for similar facilities. 相似文献
149.
本文对广义风险过程中的渐近方差作了非参数估计,得出并证明了两个定理,为广义风险过程中破产概率的区间估计作了理论准备. 相似文献
150.
乌骨鸡磷脂侧链脂肪酸的GC-MS分析 总被引:1,自引:1,他引:0
用氯仿:甲醇(2:1)超声提取乌骨鸡总磷脂,丙酮脱油精制后,经皂化、甲酯化处理,应用GC-MS联用技术对其侧链脂肪酸组成进行分析,并以面积归一法,计算各脂肪酸的相对百分含量.结果显示,乌骨鸡总磷脂中含有硬脂酸27.46%、花生四烯酸21.39%、油酸18.22%、亚油酸16.67%、棕榈酸12.13%、二十二碳六烯酸(DHA) 2.26%、二十碳三烯酸1.71%、棕榈油酸0.16%.不饱和脂肪酸和多不饱和脂肪酸的含量分别为60.41%和42.03%.乌骨鸡磷脂侧链脂肪酸中高比例的多不饱和脂肪酸和花生四烯酸含量是乌骨鸡磷脂的显著特征. 相似文献