全文获取类型
收费全文 | 54414篇 |
免费 | 1142篇 |
国内免费 | 842篇 |
专业分类
化学 | 22326篇 |
晶体学 | 315篇 |
力学 | 3359篇 |
数学 | 17532篇 |
物理学 | 12866篇 |
出版年
2023年 | 407篇 |
2021年 | 501篇 |
2020年 | 686篇 |
2019年 | 398篇 |
2018年 | 785篇 |
2017年 | 1009篇 |
2016年 | 1069篇 |
2015年 | 891篇 |
2014年 | 1243篇 |
2013年 | 3136篇 |
2012年 | 2334篇 |
2011年 | 2963篇 |
2010年 | 2106篇 |
2009年 | 2253篇 |
2008年 | 2900篇 |
2007年 | 2950篇 |
2006年 | 2915篇 |
2005年 | 2508篇 |
2004年 | 1899篇 |
2003年 | 1723篇 |
2002年 | 1551篇 |
2001年 | 1482篇 |
2000年 | 1117篇 |
1999年 | 1086篇 |
1998年 | 707篇 |
1997年 | 543篇 |
1996年 | 656篇 |
1995年 | 521篇 |
1994年 | 538篇 |
1993年 | 458篇 |
1992年 | 520篇 |
1991年 | 448篇 |
1990年 | 483篇 |
1989年 | 389篇 |
1988年 | 399篇 |
1987年 | 378篇 |
1986年 | 351篇 |
1985年 | 777篇 |
1984年 | 814篇 |
1983年 | 466篇 |
1982年 | 697篇 |
1981年 | 740篇 |
1980年 | 722篇 |
1979年 | 717篇 |
1978年 | 742篇 |
1977年 | 665篇 |
1976年 | 617篇 |
1975年 | 513篇 |
1974年 | 528篇 |
1973年 | 597篇 |
排序方式: 共有10000条查询结果,搜索用时 37 毫秒
1.
《Arabian Journal of Chemistry》2022,15(10):104139
Pressure oxidation leaching behavior of chalcopyrite in sulfuric acid solution from 110 °C to 150 °C were investigated by in-situ electrochemical methods. Leaching experiments under saturated vapor pressure conditions were used to simulate the anoxic environment that may be encountered in industrial applications. Scanning electron microscope and X-ray photoelectron spectroscopy were used to characterize the morphology and the chemical status of chalcopyrite surface. Results show that the copper extraction was increased with the increase of leaching temperature. Under the optimal leaching conditions under saturated vapor pressure, the copper and iron extraction are 8.3% and 29.8%, respectively. When the temperature increased from 110 °C to 150 °C, the self-corrosion potential and electrochemical reaction resistance firstly increased and then decreased. In contrast, the resistance of the passive film was always increased with the increase of temperature. The electrochemical study results indicated that the increase in temperature affected the oxidation of chalcopyrite by altering the kinetics of the cathodic reaction and the anodic passivation. Both the self-corrosion current density (icorr) and rate constant were affected by the reduction of Fe(III). The XPS results show that elemental sulfur and H3O(Fe3(SO4)2(OH)6) were the main leaching solid products. The formation of H3O(Fe3(SO4)2(OH)6) not only caused a decrease in cathodic reaction kinetics, but also increased the resistance of mass transfer process. Due to the faster release of iron, copper-rich sulphides were formed, which mixed with the elemental sulfur and/or H3O(Fe3(SO4)2(OH)6) led to coverage of the chalcopyrite surface. 相似文献
2.
3.
4.
5.
Automotive proton exchange membrane fuel cell stacks need to meet manufacturer specified rated beginning-of-life (BOL) performance before being assembled into vehicles and shipped off to customers. The process of “breaking-in” of a freshly assembled stack is often referred to as “conditioning.” It has become an intensely researched area especially in automotive companies, where imminent commercialization of fuel cell electric vehicles (FCEVs) demands a short, energy- and cost-efficient, and practical conditioning protocol. Significant advances in reducing the conditioning time from 1 to 2 days to as low as 4h or less, in some cases without the use of additional inert gases such as nitrogen, and with minimal use of hydrogen, and specialized test stations will be discussed. 相似文献
6.
7.
A reflective subuniverse in homotopy type theory is an internal version of the notion of a localization in topology or in the theory of ∞-categories. Working in homotopy type theory, we give new characterizations of the following conditions on a reflective subuniverse L: (1) the associated subuniverse of L-separated types is a modality; (2) L is a modality; (3) L is a lex modality; and (4) L is a cotopological modality. In each case, we give several necessary and sufficient conditions. Our characterizations involve various families of maps associated to L, such as the L-étale maps, the L-equivalences, the L-local maps, the L-connected maps, the unit maps , and their left and/or right orthogonal complements. More generally, our main theorem gives an overview of how all of these classes related to each other. We also give examples that show that all of the inclusions we describe between these classes of maps can be strict. 相似文献
8.
9.
《Journal of voice》2022,36(2):292.e23-292.e28
10.