全文获取类型
收费全文 | 4591篇 |
免费 | 494篇 |
国内免费 | 231篇 |
专业分类
化学 | 460篇 |
晶体学 | 3篇 |
力学 | 398篇 |
综合类 | 86篇 |
数学 | 3855篇 |
物理学 | 514篇 |
出版年
2023年 | 74篇 |
2022年 | 126篇 |
2021年 | 135篇 |
2020年 | 184篇 |
2019年 | 156篇 |
2018年 | 142篇 |
2017年 | 154篇 |
2016年 | 187篇 |
2015年 | 113篇 |
2014年 | 204篇 |
2013年 | 339篇 |
2012年 | 231篇 |
2011年 | 222篇 |
2010年 | 170篇 |
2009年 | 236篇 |
2008年 | 246篇 |
2007年 | 219篇 |
2006年 | 227篇 |
2005年 | 213篇 |
2004年 | 158篇 |
2003年 | 177篇 |
2002年 | 163篇 |
2001年 | 136篇 |
2000年 | 133篇 |
1999年 | 112篇 |
1998年 | 96篇 |
1997年 | 79篇 |
1996年 | 65篇 |
1995年 | 76篇 |
1994年 | 37篇 |
1993年 | 36篇 |
1992年 | 40篇 |
1991年 | 43篇 |
1990年 | 34篇 |
1989年 | 25篇 |
1988年 | 36篇 |
1987年 | 26篇 |
1986年 | 23篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 34篇 |
1981年 | 13篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 11篇 |
1977年 | 22篇 |
1976年 | 18篇 |
1975年 | 5篇 |
1974年 | 3篇 |
排序方式: 共有5316条查询结果,搜索用时 15 毫秒
1.
2.
对人教版高中化学教科书新设计的“研究与实践”栏目的主题内容、功能价值进行分析,就如何充分发挥该栏目的教学功能和价值,发展学生的化学学科核心素养,提出了创设教学情境线索、开发为研究性学习课题、开发为校本选修课程、开发为STEM课程等实施策略。 相似文献
3.
Claudius Gros 《Entropy (Basel, Switzerland)》2021,23(2)
Human societies are characterized by three constituent features, besides others. (A) Options, as for jobs and societal positions, differ with respect to their associated monetary and non-monetary payoffs. (B) Competition leads to reduced payoffs when individuals compete for the same option as others. (C) People care about how they are doing relatively to others. The latter trait—the propensity to compare one’s own success with that of others—expresses itself as envy. It is shown that the combination of (A)–(C) leads to spontaneous class stratification. Societies of agents split endogenously into two social classes, an upper and a lower class, when envy becomes relevant. A comprehensive analysis of the Nash equilibria characterizing a basic reference game is presented. Class separation is due to the condensation of the strategies of lower-class agents, which play an identical mixed strategy. Upper-class agents do not condense, following individualist pure strategies. The model and results are size-consistent, holding for arbitrary large numbers of agents and options. Analytic results are confirmed by extensive numerical simulations. An analogy to interacting confined classical particles is discussed. 相似文献
4.
在分析政府监管下医院间医疗信息分享特征的基础上,结合我国当前正在推行的医联体医院间信息分享运作模式,引入梅特卡夫定律并考虑患者评价的影响,分析了监管部门与医院各自的利益组成,建立了监管部门与医院两者之间的演化博弈模型,并采用复制动态方程研究了不同情形下医院间信息分享的演化博弈轨迹。研究表明,政府通过监管并建立激励惩罚机制等引导措施对医院最终达到的演化稳定态具有极大影响;降低医院主体信息分享的风险成本、规范提高医院分享信息的质量、引导患者增强对医院信息分享的关注、制定有吸引力和威慑力的奖惩政策,是促进医院医疗信息分享的关键。研究结果可为政府监管部门预测医院间的信息分享趋势和制定精准化政策以促进分享提供参考。 相似文献
5.
Jony Javorski Eckert Fabio Mazzariol Santiciolli Elvis Bertoti Eduardo dos Santos Costa Fernanda Cristina Corrêa Ludmila Corrêa de Alkmin e Silva 《基于设计的结构力学与机械力学》2018,46(2):238-253
In the present work, the Adaptive-Weight Genetic Algorithm was employed in order to determine the gear shifting strategies that allow an automobile to work in the best compromise among fuel consumption, engine emissions, and vehicle performance. For the assessment of each of the three objective functions, a simulation model based on engine data and on the well-established equations of the longitudinal dynamics was developed. The driving cycle chosen for the calculations was the FTP-75, which takes into account both cold and hot starts, meaning that the transient operation during the warm-up of the catalyst is also considered. 相似文献
6.
受不可逆损失的影响,热光伏能量转换器件在高品位热能回收与利用方面受到限制.本文揭示不可逆损失来源,提供热光伏能量转换器件性能提升方案.利用半导体物理和普朗克热辐射理论,确定热光伏能量转换器件在理想条件下的最大效率.进而考虑Auger与Shockley-Reed-Hall非辐射复合和不可逆传热损失对光伏电池的电学、光学和热学特性的影响,预测热光伏器件优化性能.确定功率密度、效率和光子截止能量的优化区间.结果表明:相比于理想热光伏器件,非理想热光伏器件的开路电压、短路电流密度和效率有所降低;优化热光伏电池电压、光子截止能量和热源温度,可提升器件的功率密度和效率.通过对比发现理论与实验结果较一致,所得结果可为实际热光伏能量转换器件的研制提供理论指导. 相似文献
7.
Piotr Bajger Mariusz Bodzioch Urszula Foryś 《Mathematical Methods in the Applied Sciences》2020,43(18):10671-10689
We consider a two-compartment model of chemotherapy resistant tumour growth under angiogenic signalling. Our model is based on the one proposed by Hahnfeldt et al. (1999), but we divide tumour cells into sensitive and resistant subpopulations. We study the influence of antiangiogenic treatment in combination with chemotherapy. The main goal is to investigate how sensitive are the theoretically optimal protocols to changes in parameters quantifying the interactions between tumour cells in the sensitive and resistant compartments, that is, the competition coefficients and mutation rates, and whether inclusion of an antiangiogenic treatment affects these results. Global existence and positivity of solutions and bifurcations (including bistability and hysteresis) with respect to the chemotherapy dose are studied. We assume that the antiangiogenic agents are supplied indefinitely and at a constant rate. Two optimisation problems are then considered. In the first problem a constant, indefinite chemotherapy dose is optimised to maximise the time needed for the tumour to reach a critical (fatal) volume. It is shown that maximum survival time is generally obtained for intermediate drug dose. Moreover, the competition coefficients have a more visible influence on survival time than the mutation rates. In the second problem, an optimal dosage over a short, 30-day time period, is found. A novel, explicit running penalty for drug resistance is included in the objective functional. It is concluded that, after an initial full-dose interval, an administration of intermediate dose is optimal over a broad range of parameters. Moreover, mutation rates play an important role in deciding which short-term protocol is optimal. These results are independent of whether antiangiogenic treatment is applied or not. 相似文献
8.
9.
10.
Quantitative determination of omega-6 and omega-3 polyunsaturated fatty acids in human plasma and urine with high accuracy and precision provides significant information to monitor the underlying etiology of several diseases. In this regard, liquid chromatography-mass spectrometry is a good choice owing to its great selectivity and sensitivity. Additionally, the hybrid quadrupole–time of flight–mass spectrometer systems provides easy identification of target compounds with superior mass measurements. In this study, an analytical method has been developed for simple, accurate and simultaneous determination of linoleic acid, arachidonic acid, docosahexaenoic acid and eicosapentaenoic acid in a short chromatographic analysis period. The developed method is suitable for the quantitative detection of these four compounds with detection limits ranging between 1.1–3.0 ng ml−1 and its applicability was assessed in human urine and plasma samples. As a result, acceptable accuracy (between 83 and 111%) and good precision (<6%) were obtained for target compounds using matrix matching calibration strategy. 相似文献