全文获取类型
收费全文 | 1446篇 |
免费 | 308篇 |
国内免费 | 669篇 |
专业分类
化学 | 1169篇 |
晶体学 | 56篇 |
力学 | 115篇 |
综合类 | 44篇 |
数学 | 254篇 |
物理学 | 785篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 76篇 |
2021年 | 66篇 |
2020年 | 53篇 |
2019年 | 50篇 |
2018年 | 46篇 |
2017年 | 66篇 |
2016年 | 51篇 |
2015年 | 67篇 |
2014年 | 122篇 |
2013年 | 141篇 |
2012年 | 133篇 |
2011年 | 145篇 |
2010年 | 161篇 |
2009年 | 141篇 |
2008年 | 165篇 |
2007年 | 145篇 |
2006年 | 135篇 |
2005年 | 107篇 |
2004年 | 73篇 |
2003年 | 50篇 |
2002年 | 54篇 |
2001年 | 66篇 |
2000年 | 72篇 |
1999年 | 43篇 |
1998年 | 27篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有2423条查询结果,搜索用时 15 毫秒
981.
基于虚拟仪器的微机电系统动态特性测试仪设计 总被引:1,自引:0,他引:1
设计了一种基于虚拟仪器的微机电系统动态特性测试仪,主要用于微机电系统的频谱测试和静态特性测试.该仪器采用PCI总线24位高性能数据采集卡,使用虚拟仪器技术进行设计和开发,采用扫频方法给待测系统输入一系列由低频到高频的正弦激励信号,进而分析出该系统响应和激励之间的关系.其频率范围为0.01Hz-10 kHz,并能在关键频率附近增加测试的频率点以提高精度.试验表明,该仪器的最大幅值误差小于0.2dB,最大相位误差小于0.7°,同时具有较高的可靠性和扩展性.该仪器自动化程度高,并具有良好的人机交互特性,可实时显示测试数据并绘制曲线,并在测试完成后进行数据分析处理,最后自动生成报表. 相似文献
982.
KONG De-Nian XIE Zai-Lai LI Jian-Rong FENG Mei-Ling HUANG Xiao-Ying 《结构化学》2009,28(11):1373-1380
Two lanthanide selenite-carboxylate (LSC) compounds, namely, [Ln8(SeO3)4(2,6- pdc)8(H2O)10]·2H2O (Ln = Pr 1, Sm 2; 2,6-pdcH2 = pyridine-2,6-dicarboxylic acid) have been hydrothermally synthesized and structurally characterized. Both compounds possess two-dimensional layer structures constructed by Ln8(SeO3)4(2,6-pdc)8(H2O)10 clusters connected to each other via bridging carboxylate groups. The structures are further extended into three-dimensional architectures through extensive inter-layer H-bonding between coordinated water molecules and carboxylate groups. The luminescent properties and thermal stability of both compounds have been investigated. 相似文献
983.
WANG Hai-Feng LIN Zhen-Quan KONG Xiang-Mu 《理论物理通讯》2006,46(6):1113-1120
Two catalyzed-birth models of n-species (n ≥ 2) aggregates with exchange-driven growth processes are proposed and compared. In the first one, the exchange reaction occurs between any two aggregates Ak^m and Af^m of the same species with the rate kernels Km(k,j)= Kmkj (m = 1, 2,... ,n, n ≥ 2), and aggregates of A^n species catalyze a monomer-birth of A^l species (l = 1, 2 , n - 1) with the catalysis rate kernel Jl(k,j) -Jlkj^v. The kinetic behaviors are investigated by means of the mean-field theory. We find that the evolution behavior of aggregate-size distribution ak^l(t) of A^l species depends crucially on the value of the catalysis rate parameter v: (i) ak^l(t) obeys the conventional scaling law in the case of v ≤ 0, (ii) ak^l(t) satisfies a modified scaling form in the case of v 〉 0. In the second model, the mechanism of monomer-birth of An-species catalyzed by A^l species is added on the basis of the first model, that is, the aggregates of A^l and A^n species catalyze each other to cause monomer-birth. The kinetic behaviors of A^l and A^n species are found to fall into two categories for the different v: (i) growth obeying conventional scaling form with v ≤ 0, (ii) gelling at finite time with v 〉 0. 相似文献
984.
算子[b,TΩ,α]表示由lipschitz函数b与带有齐次核的分数次积分算子TΩ,α生成的交换子.本文主要研究该交换子在Herz型Hardy空间上的有界性,得到了它是从HKq1^η,p(R^n)到Kq2^η,p(R^n)有界的. 相似文献
985.
在约束锥拓扑内部为空时利用集合的拟内部的概念给出了带约束的向量均衡问题的弱有效解的充分性和必要性条件。作为它的应用,还给出了带约束的向量变分不等式、向量优化问题的弱有效解的最优性条件。 相似文献
986.
To enhance the relative movement of domains, we inserted a random sequence of fifteen-peptide into the three domains of L-aspartase. By means of directed screening, the three isoforms of monomeric, dimmeric and tetrameric enzymes were obtained. Compared to the wild-type tetrameric L-asparease, these mutants remained 19. 7%, 42.3%, and 92% of the enzyme activity, respectively. Moreover, the examination of enzyme properties revealed that their kcat, and KM changed in varying degrees, and the optimum pH shifted towards acidic pH, while the dependence of the activity of enzyme on Mg^2 concentration and thermostability increased. Therefore this strategy provides a novel approach to directed evolution of enzymes. 相似文献
987.
988.
989.
990.
Cross-Section Measurements for Reactions on Platinum Isotopes in the Neutron Energy Range of 13.5 to 14.6MeV 下载免费PDF全文
Cross-sections for (n,2n) and (n,p) reactions have been measured on platinum isotopes at the neutron energies of 13.5 to 14.6 MeV using the activation technique. Data were reported for the following reactions: Pt(n,2n)197m+gPt,198Pt(n,2n)197mPt,192Pt(n,2n)191Pt, 194Pt(n,p)194Ir, 195Pt(n, p)195mIr, and 196Pt(n,p)196mIr. At the neutron energies of 13.5, 14.1 and 14.6 MeV, the cross sections in mb are 2038±159, 1919±73 and 1836±68 for 198Pt(n,2n)197m+gPt reaction; 974±37, 1055±39 and 1042±39 for 198Pt(n, 2n)197mPt reaction, respectively. The cross sections are 1680±103, 1810±67 and 2047±97 for 192Pt(n,2n)191Pt reaction, and 1.0±0.2, 1.6±0.2 and 1.8±0.2 for 195Pt(n, p)195mIr reaction, respectively, at energies of 14.1, 14.4 and 14.6MeV. At 14.1 and 14.4 MeV neutron energies, the cross sections are 3.8±0.4 and 5.4±0.5 for 194Pt(n,p)194Ir reaction. While, the data are (1.13±0.07) and (1.18±0.06) mb at energies of 13.5 and 14.4 MeV, respectively, for 196Pt(n,p)196mIr reaction.The neutron fluences were determined using the monitor reaction 93Nb(n, 2n)92mNb or 27Al(n, a)24Na. A comparison was made between the present cross sections and the collected data for the measured reactions. 相似文献