全文获取类型
收费全文 | 19107篇 |
免费 | 1211篇 |
国内免费 | 917篇 |
专业分类
系统科学 | 1842篇 |
丛书文集 | 442篇 |
教育与普及 | 283篇 |
理论与方法论 | 324篇 |
现状及发展 | 945篇 |
研究方法 | 31篇 |
综合类 | 17366篇 |
自然研究 | 2篇 |
出版年
2024年 | 81篇 |
2023年 | 168篇 |
2022年 | 324篇 |
2021年 | 339篇 |
2020年 | 273篇 |
2019年 | 161篇 |
2018年 | 956篇 |
2017年 | 987篇 |
2016年 | 712篇 |
2015年 | 569篇 |
2014年 | 697篇 |
2013年 | 762篇 |
2012年 | 1072篇 |
2011年 | 1716篇 |
2010年 | 1630篇 |
2009年 | 1274篇 |
2008年 | 1368篇 |
2007年 | 1558篇 |
2006年 | 685篇 |
2005年 | 583篇 |
2004年 | 576篇 |
2003年 | 546篇 |
2002年 | 631篇 |
2001年 | 592篇 |
2000年 | 413篇 |
1999年 | 372篇 |
1998年 | 256篇 |
1997年 | 279篇 |
1996年 | 247篇 |
1995年 | 245篇 |
1994年 | 204篇 |
1993年 | 205篇 |
1992年 | 153篇 |
1991年 | 147篇 |
1990年 | 140篇 |
1989年 | 117篇 |
1988年 | 96篇 |
1987年 | 47篇 |
1986年 | 22篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1967年 | 1篇 |
1960年 | 1篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
Hydrothermal reactions of oxalic acid(H2ox) and 2-sulfobenzoic acid(H2L) with lanthanide oxide or hydroxide yielded five lanthanide oxalatosulfocarboxylates.They have a general formula [Ln2L2(ox)(H2O)6]n[Ln = La(1),Nd(2),Eu(3),Gd(4),Tb(5)].Their structures were characterized by single crystal X-ray diffraction,powder X-ray diffraction(PXRD),infrared(IR) spectroscopy,elemental analysis(EA),and thermogravimetric analysis(TGA).1-5 are isostructural coordination polymers and feature one-dimensional(1D) chains,which are extended into 3D supramolecular frameworks through inter-chain hydrogen bonds between coordinated H2O donors and oxygen acceptors from carboxylate,sulfonate and oxalate groups.In addition,the solid-state photoluminescence properties of the Nd(2),Eu(3) and Tb(5) derivatives have been measured at room temperature.The Eu and Tb-containing coordination polymers(CPs) exhibit intense red and green luminescence emissions,respectively,with lifetimes in the order of millisecond. 相似文献
972.
973.
974.
在Belle实验B±→K±ω道的物理分析中,对神经元网络法和Fisher判别法在压制连续过程本底应用中的性能进行了比较研究.应用神经元网络法可以获得对BB信号事例42.3%的选择效率和99.2%的连续过程本底排除水平;应用Fisher判别法可以获得57.9%的信号事例选择效率和98.6%的连续过程本底排除水平. 相似文献
975.
Bi2Se3 thin films were electrochemically deposited on Ti and indium tin oxide-coated glass substrates, respectively, at room temperature,
using Bi(NO3)3·5H2O and SeO2 as starting materials in diluted HNO3 solution. A conventional three-electrode cell was used with a platinum sheet as a counter electrode, and a saturated calomel
electrode was used as a reference electrode. The films were annealed in argon atmosphere. The influence of cold isostatic
pressing before annealing on the microstructure and thermoelectric properties of the films was investigated. X-ray diffraction
analysis indicates that the film grown on the indium tin oxide-coated glass substrate is pure rhombohedral Bi2Se3, and the film grown on the Ti substrate consists of both rhombohedral and orthorhombic Bi2Se3. 相似文献
976.
We investigated the dynamic properties of a two-section composite chain of beads under vertical vibration.By analyzing the chain’s motion,including phase-shift,mean dilation,center-of-mass displacement,and energy,we found that with different bead arrangements,the chain behaved in different ways.We believe that interaction existing at the interface between bead sections provides the underlying cause.This interaction causes different energy in different arrangements,which leads to different dynamic characteristics. 相似文献
977.
为了得到填料-高压微雾对组合式空调机组的降温效果,测试1台55 000m3/h风量的填料-高压微雾组合式空调机组.采用对比方法,将5种不同的测试的降温效果进行对比.实验数据表明,高压微雾和填料上采用三维布水相结合对空调机组的降温最为显著.从研究结果上看,高压微雾不仅是人们传统认识上的加湿器,还是一台良好的冷却器,能够对空气进行降温,满足一些场所降温的需要,具有广泛的应用范围. 相似文献
978.
Sheng-jun Li Yuan Lin Wei-wei Tan Jing-bo Zhang Xiao-wen Zhou Jin-mao Chen Zeng Chen 《矿物冶金与材料学报》2010,17(1):92-97
The ZnO-modified TiO2 electrode was prepared by adding Zn(CH3COO)2·2H2O to the TiO2 colloid during the sol-gel production process, and was used in dye-sensitized solar cells (DSCs). The open circuit voltage
(V
OC) and fill factor (ff) of the cells were improved significantly. The performances of the ZnO-modified TiO2 electrode such as dark current, transient photocurrent, impedance, absorption spectra, and flat band potential (V
fb) were investigated. It is found that the interface charge recombination impedance increases and V
fb shifts about 200 mV toward the cathodic potential. The effect mechanism of ZnO modification on the performance of DSCs may
be that ZnO occupies the surface states of the TiO2 film. 相似文献
979.
用Broyden法来求解带不可微项的非线性方程,在弱条件下,通过构造优序列,给出了解的存在性与收敛性定理以及相应的证明. 相似文献
980.
A larger-scale Zr70Pd30 alloy system has been simulated using molecular dynamics (MD) to investigate structure evolution in Zr70Pd30 metallic glass. The simulated pair distribution function of Zr70Pd30 metallic glass agrees well with the experimental results. Voronoi polyhedron analysis indicates that the icosahedra are not
randomly distributed in space, but form characteristic intercrossed icosahedral clusters with medium-range order. Intercrossed
icosahedral clusters are the dominant local configurations in Zr70Pd30 metallic glass and probably cause the quasicrystalline phase discovered in Zr70Pd30 metallic glass. 相似文献