全文获取类型
收费全文 | 49085篇 |
免费 | 7133篇 |
国内免费 | 3844篇 |
学科分类
工业技术 | 60062篇 |
出版年
2024年 | 195篇 |
2023年 | 977篇 |
2022年 | 1503篇 |
2021年 | 1856篇 |
2020年 | 2026篇 |
2019年 | 1894篇 |
2018年 | 1710篇 |
2017年 | 1979篇 |
2016年 | 2074篇 |
2015年 | 2122篇 |
2014年 | 2819篇 |
2013年 | 3103篇 |
2012年 | 3397篇 |
2011年 | 3451篇 |
2010年 | 2412篇 |
2009年 | 2785篇 |
2008年 | 2580篇 |
2007年 | 3149篇 |
2006年 | 2886篇 |
2005年 | 2382篇 |
2004年 | 1970篇 |
2003年 | 1857篇 |
2002年 | 1606篇 |
2001年 | 1446篇 |
2000年 | 1290篇 |
1999年 | 1043篇 |
1998年 | 894篇 |
1997年 | 824篇 |
1996年 | 656篇 |
1995年 | 621篇 |
1994年 | 543篇 |
1993年 | 353篇 |
1992年 | 334篇 |
1991年 | 268篇 |
1990年 | 254篇 |
1989年 | 226篇 |
1988年 | 111篇 |
1987年 | 70篇 |
1986年 | 60篇 |
1985年 | 53篇 |
1984年 | 52篇 |
1983年 | 42篇 |
1982年 | 41篇 |
1981年 | 32篇 |
1980年 | 34篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1959年 | 8篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
101.
本文采用粉末冶金法制备了不同成分的PSZ/Mo复合材料。并对其密度、弹性模量和热膨胀系数进行了测量和分析 ,用XRD进行了物相分析。实验结果表明 :纳米氧化锆的烧结性能比金属钼好 ;弹性模量估算选用简单混合法则进行计算时应进行修正 ;钼和氧化锆在烧结时不发生化学反应。通过热压PSZ/Mo功能梯度材料的断口扫描分析发现 :虽然金属钼和纳米氧化锆具有一定增韧作用 ,但材料断裂方式仍以脆性断裂为主 相似文献
102.
1 IntroductionThestickingpointofassociationrulealgorithmsdependsoneffectivelyfindingallcorrelationpatternsthatsatisfyvaluerequirementinthemagnanimityofdata.Butthealgorithmsalsobringanegativeef fect:thenumberofassociationrulesisverylarge.Alsoinformation… 相似文献
103.
A novel series of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] (p(NIPAM‐co‐EMA)) microgels was prepared by the surfactant‐free radical polymerization of N‐isopropylacrylamide (NIPAM) with ethyl methacrylate (EMA). The shape, size dispersity and volume‐phase transition behavior of the microgels were investigated by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The transmission electron micrographs and DLS results showed that microgels with narrow distributions were prepared. It was shown from UV–Vis, DLS and DSC measurements that the volume‐phase transition temperature (VPTT) of the p(NIPAM‐co‐EMA) microgels decreased with increasing incorporation of EMA, but the temperature‐sensitivity was impaired when more EMA was incorporated, causing the volume‐phase transition of the microgels to become more continuous. It is noteworthy that incorporation of moderate amounts of EMA could not only lower the VPTT but also enhance the temperature‐sensitivity of the microgels. The reason for this phenomenon could be attributed to changes in the complicated interactions between the various molecules. Copyright © 2004 Society of Chemical Industry 相似文献
104.
The miscibility and phase behavior of ternary blends containing dimethylpolycarbonate (DMPC), tetramethylpolycarbonate (TMPC) and poly[styrene‐co‐(methyl methacrylate)] copolymer (SMMA) have been explored. Ternary blends containing polystyrene (PS) instead of SMMA were also examined. Blends of DMPC with SMMA copolymers (or PS) did not form miscible blends regardless of methyl methacrylate (MMA) content in copolymers. However, DMPC blends with SMMA (or PS) blends become miscible by adding TMPC. The miscible region of ternary blends is compared with the previously determined miscibility region of binary blends having the same chemical components and compositions. The region where the ternary blends are miscible is much narrower than that of binary blends. Based on lattice fluid theory, the observed phase behavior of ternary blends was analyzed. Even though the term representing the Gibbs free energy change of mixing for certain ternary blends had a negative value, blends were immiscible. It was revealed that a negative value of the Gibbs free energy change of mixing was not a sufficient condition for miscible ternary blends because of the asymmetry in the binary interactions involved in ternary blends. Copyright © 2004 Society of Chemical Industry 相似文献
105.
106.
107.
�Ĵ������Ȼ�����������б�����Դ̽�� 总被引:11,自引:0,他引:11
本文应用天然气中甲烷、乙烷的碳同位素,甲烷的氢同位素,汞含量及天然气成分等指标,探讨了四川盆地天然气成因分类;并结合地质情况对气源层进行了探讨。 相似文献
108.
The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium
vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition
points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO3, RbVO3 and CsVO3, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition
temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric
state and depends upon sodium concentration. 相似文献
109.
110.