全文获取类型
收费全文 | 4565篇 |
免费 | 139篇 |
国内免费 | 181篇 |
专业分类
教育 | 3182篇 |
科学研究 | 705篇 |
各国文化 | 46篇 |
体育 | 220篇 |
综合类 | 296篇 |
文化理论 | 12篇 |
信息传播 | 424篇 |
出版年
2024年 | 3篇 |
2023年 | 27篇 |
2022年 | 46篇 |
2021年 | 114篇 |
2020年 | 125篇 |
2019年 | 102篇 |
2018年 | 92篇 |
2017年 | 83篇 |
2016年 | 109篇 |
2015年 | 133篇 |
2014年 | 159篇 |
2013年 | 278篇 |
2012年 | 355篇 |
2011年 | 245篇 |
2010年 | 171篇 |
2009年 | 247篇 |
2008年 | 331篇 |
2007年 | 376篇 |
2006年 | 414篇 |
2005年 | 305篇 |
2004年 | 298篇 |
2003年 | 198篇 |
2002年 | 155篇 |
2001年 | 119篇 |
2000年 | 95篇 |
1999年 | 72篇 |
1998年 | 45篇 |
1997年 | 42篇 |
1996年 | 42篇 |
1995年 | 20篇 |
1994年 | 16篇 |
1993年 | 22篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有4885条查询结果,搜索用时 140 毫秒
941.
QIN Feng CHEN Jiang-ping ZHANG Wen-feng CHEN Zhi-jiu 《浙江大学学报(A卷英文版)》2007,8(2):197-204
INTRODUCTION Metal hydrides are special alloys which absorb and desorb hydrogen reversibly. At room temperature, metal hydrides could absorb as much hydrogen as liquid hydrogen of the same volume under much lower pressure and much higher temperature (Güther and Otto, 1999). Massive reaction heat is generated accompanying this reaction, which could be used for waste heat recovery, solar energy utilization and re-frigeration with no side effect to environment (Izhvanov et al., 1996). Con… 相似文献
942.
Lukáš Babka 《Slavic & East European Information Resources》2017,18(3-4):165-184
This study focuses on the visual collections in the holdings of the Slavonic Library (a section of the National Library of the Czech Republic). The library holdings also include unique collections relevant to the topic of Russian and Ukrainian emigration: collections of visual art, ex libris, posters and flyers by Ukrainian émigrés (1918–1945), and a collection of invitations and flyers by Russian émigrés (1918–1945). Rudolf H?lka’s collection of photographs, dating back to the 1920s, captures a series of ethnographic, folkloric, and architectonic phenomena which no longer exist. Moreover, Russian posters from the period of WWI, from the revolutionary year of 1917, and the subsequent civil war are equally fascinating as are banknotes from the same period and region. 相似文献
943.
Copper(II) hydroxide (as the rarely occurring mineral spertiniite) is formed under alkaline, oxidising conditions. It has been observed as a naturally occurring corrosion product of brass in sea water. But most occurrences on copper alloys are due to conservation treatments using basic solutions (sodium hydroxide or ammonia) or to intentional patination. Classical brass centrepieces (c. 1800), ‘cleaned’ with ammonia solution, developed a blue spertiniite patina in gaps, where evaporation was hindered. Additional to the danger of stress corrosion cracking this is another reason now outlawing this treatment. Copper pigment layers will transform to copper hydroxide when exposed to bases. The treatment of basic copper salts with bases has been used intentionally in the production of Bremen blue and similar pigments which can be composed of copper hydroxide as well. 相似文献
944.
张惠玲 《安徽科技学院学报》2003,17(2):170-172
AutoCAD2 0 0 0和AutoCAD2 0 0 2为用户提供了两种绘图环境 :世界坐标系WCS(WorldCoord :natesystem)和用户坐标系UCS(UserCoord :nateSystem)。对一般的机械图形而言 ,整个绘图过程在WCS环境下进行即可 ,但在绘制较复杂的机械三维实体 ( 3DimensionObject)图的过程中 ,适当地设置UCS绘图环境 ,WCS和UCS交替使用 ,给我们绘图带来的简捷是单一的WCS绘图环境下无可比拟的。本文就在绘制三维实体图形时如何充分灵活应用UCS ,设置最佳绘图环境加以阐述。 相似文献
945.
主要介绍向量测度中的一些结论,并给出一个渐近鞅是L1(μ,X)有界渐近鞅而不是(B)有界的。 相似文献
946.
朱艳娥 《忻州师范学院学报》2006,22(3):18-21
晋语是指山西及其毗连地区有入声的语言。它不仅在语音上有其独特特点,在词汇、语法上也别具特色。文章从“圪”字的构词方式出发,分析了“圪”头词中“圪”的性质。且在基础上,讨论了晋语的构词方式。 相似文献
947.
TisiW_(12)O_(40)/TiO_2的合成、表征及催化活性 总被引:1,自引:0,他引:1
本文报道了非均相固载型杂多酸盐催化剂TiSiW12O40/TiO2的制备方法,并用IR、XRD谱对该催化剂进行了表征,研究了该催化剂的催化活性.实验表明,在以苯为带水剂时,催化剂的用量为反应液的0.5%,醇酸摩尔比为1.20∶1,酯化反应时间为2h,乙酸正丁酯的收率达76.8%,超过硫酸、磷钨酸催化水平. 相似文献
948.
张昌斌 《赣南师范学院学报》1993,(Z1)
本文将振幅的概念推广到映第一可数空间到度量空间的映射,证明了这类映射的连续点之集必为可数个开集之交,挥广了若干经典的结论。我们还证明了:映第二可数的T_1空间到度量空间的映射的极限存在但不连续的点只有可数个;给出了这一结论在积分论上的应用。 相似文献
949.
Objectives: To directly compare the quality of harmonic imaging (HI) and fundamental imaging (FI) in fetal echocardiography and to determine any differences in image quality between the two modalities. Methods: Fetal echocardiograms were performed with the use of FI and HI in 58 fetuses, image quality and visualization of left and right atria, left and right ventricles, mitral and tricuspid valves, aortic and pulmonary valves, left and right ventricular outflow tracts were evaluated and compared between FI and HI. Results: Mean HI scores were higher than mean FI scores (2.73±0.43 vs 2.16±0.69, P<0.001)for all the cardiovascular structures evaluated. Compared with FI, HI improved the image quality and visualization of fetal cardiac structures in subjects with both good (2.73±0.43 vs 2.88±0.32, P<0.001) and suboptimal (1.65±0.41 vs 2.58±0.47, P<0.001) echocardiographic windows. The interobserver correlation coefficient for the grading scores was 0.74 (P<0.001). Conclusions: harmonic imaging enhances and improves the image quality of fetal echocardiography; and has important potential role in cardiac imaging in the fetus. 相似文献
950.
The State Transition Equation (STE) based method to automatically generate the parallel CRC circuits for any generator polynomial
or required amount of parallelism is presented. The parallel CRC circuit so generated is partially optimized before being
fed to synthesis tools and works properly in our LAN transceiver. Compared with the cascading method, the proposed method
gives better timing results and significantly reduces the synthesis time, in particular.
Project (No. 60271010) supported by the National Natural Science Foundation of China 相似文献