全文获取类型
收费全文 | 19554篇 |
免费 | 3350篇 |
国内免费 | 3443篇 |
专业分类
化学 | 15258篇 |
晶体学 | 361篇 |
力学 | 1145篇 |
综合类 | 296篇 |
数学 | 2412篇 |
物理学 | 6875篇 |
出版年
2024年 | 18篇 |
2023年 | 268篇 |
2022年 | 392篇 |
2021年 | 512篇 |
2020年 | 667篇 |
2019年 | 779篇 |
2018年 | 675篇 |
2017年 | 669篇 |
2016年 | 920篇 |
2015年 | 999篇 |
2014年 | 1125篇 |
2013年 | 1507篇 |
2012年 | 1723篇 |
2011年 | 1744篇 |
2010年 | 1350篇 |
2009年 | 1397篇 |
2008年 | 1495篇 |
2007年 | 1378篇 |
2006年 | 1318篇 |
2005年 | 1071篇 |
2004年 | 994篇 |
2003年 | 851篇 |
2002年 | 1019篇 |
2001年 | 785篇 |
2000年 | 544篇 |
1999年 | 469篇 |
1998年 | 319篇 |
1997年 | 224篇 |
1996年 | 187篇 |
1995年 | 161篇 |
1994年 | 144篇 |
1993年 | 118篇 |
1992年 | 84篇 |
1991年 | 87篇 |
1990年 | 70篇 |
1989年 | 61篇 |
1988年 | 41篇 |
1987年 | 32篇 |
1986年 | 36篇 |
1985年 | 37篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1968年 | 3篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
乳腺癌是当前最常见的恶性肿瘤之一,其电子病历数据可用于挖掘隐含规律,对治疗与预后分析有重要意义。通过与乳腺科医生合作,选择合适的预测模型和可视化方法,搭建了一个基于电子病历的乳腺癌群组和治疗方案可视分析系统。首先,对具有高维属性的病人进行降维和聚类处理,形成病人群组,并采用南丁格尔图、词云和时间轴可视化方法,直观展示病人群组间特征的差异;然后,用支持向量机(support vector machine,SVM)模型预测治疗方案,用平行坐标、矩阵热力图和分类图分别展示属性相关性、训练后的特征权重和预测结果;最后,用真实案例验证了系统在群组分析、治疗方案及病人属性关联分析中的有效性,从而较好地帮助医生选择合适的治疗方案。 相似文献
2.
针对大温差条件下固井水泥浆在固井过程中可能存在的悬浮失稳问题,本研究采用水溶液自由基聚合法来合成具有疏水缔合结构的聚合物作为悬浮稳定剂(PAAN)。通过红外光谱仪、凝胶渗透色谱仪、热重分析仪、高温流变仪、SEM、紫外分光光度计等表征PAAN的结构,发现PAAN随温度升高,形成分子间疏水缔合网状结构,保证了体系的粘度,从而起到有效的悬浮稳定作用。研究发现在40~110 ℃下,0.6%加量的PAAN可以保证固化后的水泥石柱顶部和底部密度差<0.01 g/cm3,且水泥浆稠化时间基本不变,表明PAAN可以保证水泥浆体系具有良好的悬浮稳定效果,且对水泥浆的其他性能无不良影响。 相似文献
3.
Yaoli Wang Yan Liang Huixiang Sheng Jin Wang Junjie Wang Shunhao He Mengdan Guan Yaqi Chen Prof. Gang Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(2):e202103709
Surface plasmon can trigger or accelerate many photochemical reactions, especially useful in energy and environmental industries. Recently, molecular adsorption has proven effective in modulating plasmon-mediated photochemistry, however the realized chemical reactions are limited and the underlying mechanism is still unclear. Herein, by using in situ dark-field optical microscopy, the plasmon-mediated oxidative etching of silver nanoparticles (Ag NPs), a typical hot-hole-driven reaction, is monitored continuously and quantitatively. The presence of thiol or thiophenol molecules is found essential in the silver oxidation. In addition, the rate of silver oxidation is modulated by the choice of different thiol or thiophenol molecules. Compared with the molecules having electron donating groups, the ones having electron accepting groups accelerate the silver oxidation dramatically. The thiol/thiophenol modulation is attributed to the modulation of the charge separation between the Ag NPs and the adsorbed thiol or thiophenol molecules. This work demonstrates the great potential of molecular adsorption in modulating the plasmon-mediated photochemistry, which will pave a new way for developing highly efficient plasmonic photocatalysts. 相似文献
4.
将有机物2,5-二溴对苯二甲酸(H2L1)和2,2′-联吡啶(L2)作为双配体,使用溶剂热法和七水合硫酸锌(ZnSO4·7H2O)、六水合硝酸钴(Co(NO3)2·6H2O)分别反应,得到配合物[Zn(L1)(L2)(H2O)]n(1)和配合物[Co(L1)(L2)(H2O)]n(2)。采用单晶X射线衍射、元素分析、红外光谱、紫外光谱、荧光光谱、热重分析等测试方法对这两种物质进行分析研究。单晶测试结果表明配合物1是单斜晶系,以Zn2+配位连接L2-1与L2形成一维链状结构,各条链在分子间氢键和π…π共轭作用下有规律地堆叠形成三维网络结构。配合物2是三斜晶系,Co1离子和Co1i离子由H2L1上的羧酸氧原子O4和O4i连接,形成双齿螯合的配位结构单元,以Co2+配位连接 L2-1和L2形成二维网格结构,各层在O—H…O分子间氢键和范德瓦耳斯力作用下有规律的堆叠形成三维网络结构。配合物1和2均含有芳香杂环、羧基杂环和氮杂环,具有良好的荧光性质和热稳定性,最大发射波长分别为345 nm和333 nm。 相似文献
5.
Yao Wen Chen Yangfan Li Jiangling Yang Jian Ren Shan Liu Weizao Liu Qingcai 《Research on Chemical Intermediates》2022,48(5):1813-1829
Research on Chemical Intermediates - Industrial wastewater is becoming a universal environmental problem, wherein toxic organic compounds are important sources of pollution. For the degradation... 相似文献
6.
Yin Qingqing Xu Fen Sun Lixian Li Yaying Liao Lumin Wang Tao Guan Yanxun Xia Yongpeng Zhang Chenchen Wei Sheng Zhang Huanzhi Li Bin 《Journal of Thermal Analysis and Calorimetry》2022,147(12):6583-6592
Journal of Thermal Analysis and Calorimetry - Polyethylene glycol (PEG) is widely used as phase change materials (PCMs). However, the leakage and low thermal conductivity issues restrict its... 相似文献
7.
Dr. Sirinapa Wongwilawan Dr. Doyun Kim Dr. Thien S. Nguyen Wonki Lim Prof. Dr. Sheng Li Prof. Dr. Cafer T. Yavuz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(72):e202202340
Through accumulation, mercury contamination in aquatic systems still poses serious health risks despite the strict regulations on drinking water and industrial discharge. One effective strategy against this is adsorptive removal, in which a suitably functionalized porous material is added to water treatment protocols. Thiol (SH) group-grafted structures perform commendably; however, insufficient attention is paid to the cost, scalability, and reusability or how the arrangement of sulfur atoms could affect the HgII binding strength. We used an inexpensive and scalable porous covalent organic polymer (COP-130) to systematically introduce thiol functional groups with precise chain lengths and sulfur content. Thiol-functionalized COP-130 demonstrates enhanced wettability and excellent HgII uptake of up to 936 mg g−1, with fast kinetics and exceptionally high selectivity. These Hg adsorbents are easily regenerated with HCl and can be used at least six times without loss of capacity even after treatment with strong acid, a rare performance in the domain of Hg-removal research. 相似文献
8.
Dr. Hongying Tang Jian Gao Prof. Yidong Wang Prof. Nanwen Li Dr. Kang Geng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202064
Great efforts have been conducted to develop high temperature proton exchange membrane fuel cell (HT-PEMFC) due to its features of enhanced electrocatalyst reactivity, simplified hydrothermal management system and high CO tolerance of catalysts, and remarkable progress has been achieved. However, the easy leaching of phosphoric acid (PA) from the membranes during operation limits its commercial scale-up in complicated environments. This concept here mainly focuses on the recent developments for mitigation of PA loss in PEMs. The probable mechanisms of PA loss are proposed. The approaches to improve PA retention for example via introduction of phosphonic acid by covalent bond, using ion-pairs interaction and siphoning effect, and blending with inorganic nanoparticles are described in detail. Among these strategies, the siphoning effect from the intrinsic microporous PEMs is the most efficient and enables the cell to operate flexibly within a broad temperature range. Therefore, this concept may provide new ideas for the scientists to retain PA, to improve the cell performance and expand the potential applications of PA doped PEMs at elevated humidity and wide temperature range. 相似文献
9.
Fluid Dynamics - The collapse of cavitation bubbles in a hydraulic system generates localized zones of high temperature and pressure and, under certain conditions, luminescence. In this study, we... 相似文献
10.