全文获取类型
收费全文 | 32992篇 |
免费 | 691篇 |
国内免费 | 823篇 |
专业分类
教育 | 18228篇 |
科学研究 | 6832篇 |
各国文化 | 154篇 |
体育 | 2067篇 |
综合类 | 1728篇 |
文化理论 | 189篇 |
信息传播 | 5308篇 |
出版年
2024年 | 6篇 |
2023年 | 35篇 |
2022年 | 348篇 |
2021年 | 952篇 |
2020年 | 682篇 |
2019年 | 390篇 |
2018年 | 357篇 |
2017年 | 439篇 |
2016年 | 412篇 |
2015年 | 1064篇 |
2014年 | 1591篇 |
2013年 | 2090篇 |
2012年 | 2423篇 |
2011年 | 2600篇 |
2010年 | 2537篇 |
2009年 | 2224篇 |
2008年 | 2349篇 |
2007年 | 2509篇 |
2006年 | 2508篇 |
2005年 | 2100篇 |
2004年 | 1112篇 |
2003年 | 998篇 |
2002年 | 1016篇 |
2001年 | 930篇 |
2000年 | 579篇 |
1999年 | 552篇 |
1998年 | 384篇 |
1997年 | 257篇 |
1996年 | 235篇 |
1995年 | 167篇 |
1994年 | 173篇 |
1993年 | 100篇 |
1992年 | 97篇 |
1991年 | 62篇 |
1990年 | 43篇 |
1989年 | 53篇 |
1988年 | 32篇 |
1987年 | 4篇 |
1986年 | 19篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
961.
Wei Wu Kai Liu Yanjie Li Zhenhai Yu Desheng Wu Yuting Shao Shihang Na Gang Li Ruizhen Huang Tao Xiang Jianlin Luo 《国家科学评论(英文版)》2020,7(1):21
Exploration of superconductivity in Cr-based compounds has attracted considerable interest because only a few Cr-based superconductors (CrAs, A2Cr3As3 and ACr3As3 (A = K, Rb, Cs, Na)) have been discovered so far and they show an unconventional pairing mechanism. We report the discovery of bulk superconductivity at 5.25 K in chromium nitride in Pr3Cr10-xN11 with a cubic lattice structure. A relatively large upper critical field of Hc2(0) ∼ 12.6 T is determined, which is larger than the estimated Pauli-paramagnetic pair-breaking magnetic field. The material has a large electronic specific-heat coefficient of 170 mJ K−2 mol−1—about 10 times larger than that estimated by the electronic structure calculation, which suggests that correlations between 3d electrons are very strong in Pr3Cr10-xN11, and thus quantum fluctuations might be involved. Electronic structure calculations show that the density of states at the Fermi energy are contributed predominantly by Cr 3d electrons, implying that the superconductivity results mainly from the condensation of Cr 3d electrons. Pr3Cr10-xN11 represents a rare example of possible unconventional superconductivity emerging in a 3D system with strong electron correlations. Nevertheless, clarification of the specific pairing symmetry needs more investigation. 相似文献
962.
Wenbo Pang Xu Cheng Haojie Zhao Xiaogang Guo Ziyao Ji Guorui Li Yiming Liang Zhaoguo Xue Honglie Song Fan Zhang Zheng Xu Lei Sang Wen Huang Tiefeng Li Yihui Zhang 《国家科学评论(英文版)》2020,7(2):342
The manufacture of 3D mesostructures is receiving rapidly increasing attention, because of the fundamental significance and practical applications across wide-ranging areas. The recently developed approach of buckling-guided assembly allows deterministic formation of complex 3D mesostructures in a broad set of functional materials, with feature sizes spanning nanoscale to centimeter-scale. Previous studies mostly exploited mechanically controlled assembly platforms using elastomer substrates, which limits the capabilities to achieve on-demand local assembly, and to reshape assembled mesostructures into distinct 3D configurations. This work introduces a set of design concepts and assembly strategies to utilize dielectric elastomer actuators as powerful platforms for the electro-mechanically controlled 3D assembly. Capabilities of sequential, local loading with desired strain distributions allow access to precisely tailored 3D mesostructures that can be reshaped into distinct geometries, as demonstrated by experimental and theoretical studies of ∼30 examples. A reconfigurable inductive–capacitive radio-frequency circuit consisting of morphable 3D capacitors serves as an application example. 相似文献
963.
Jing-Yang Hu Zi-Qian Hao Laurent Frantz Shi-Fang Wu Wu Chen Yun-Fang Jiang Hong Wu Wei-Min Kuang Haipeng Li Ya-Ping Zhang Li Yu 《国家科学评论(英文版)》2020,7(4):798
Pangolins are among the most critically endangered animals due to heavy poaching and worldwide trafficking. However, their demographic histories and the genomic consequences of their recent population declines remain unknown. We generated high-quality de novo reference genomes for critically endangered Malayan (Manis javanica, MJ) and Chinese (M. pentadactyla, MP) pangolins and re-sequencing population genomic data from 74 MJs and 23 MPs. We recovered the population identities of illegally traded pangolins and previously unrecognized genetic populations that should be protected as evolutionarily distinct conservation units. Demographic reconstruction suggested environmental changes have resulted in a population size fluctuation of pangolins. Additionally, recent population size declines due to human activities have resulted in an increase in inbreeding and genetic load. Deleterious mutations were enriched in genes related to cancer/diseases and cholesterol homeostasis, which may have increased their susceptibility to diseases and decreased their survival potential to adapt to environmental changes and high-cholesterol diets. This comprehensive study provides not only high-quality pangolin reference genomes, but also valuable information concerning the driving factors of long-term population size fluctuations and the genomic impact of recent population size declines due to human activities, which is essential for pangolin conservation management and global action planning. 相似文献
964.
Xier Luo Yu Zhou Bing Zhang Yi Zhang Xiaobo Wang Tong Feng Zhipeng Li Kuiqing Cui Zhiqiang Wang Chan Luo Hui Li Yanfei Deng Fenghua Lu Jianlin Han Yongwang Miao Huaming Mao Xiaoyan Yi Cheng Ai Shigang Wu Alun Li Zhichao Wu Zijun Zhuo Do Da Giang Bikash Mitra Mohammad Farhad Vahidi Shahid Mansoor Sahar Ahmed Al-Bayatti Eka Meutia Sari Neena Amatya Gorkhali Sigit Prastowo Laiba Shafique Guoyou Ye Qian Qian Baoshan Chen Deshun Shi Jue Ruan Qingyou Liu 《国家科学评论(英文版)》2020,7(3):686
Domesticated buffaloes have been integral to rice-paddy agro-ecosystems for millennia, yet relatively little is known about the buffalo genomics. Here, we sequenced and assembled reference genomes for both swamp and river buffaloes and we re-sequenced 230 individuals (132 swamp buffaloes and 98 river buffaloes) sampled from across Asia and Europe. Beyond the many actionable insights that our study revealed about the domestication, basic physiology and breeding of buffalo, we made the striking discovery that the divergent domestication traits between swamp and river buffaloes can be explained with recent selections of genes on social behavior, digestion metabolism, strengths and milk production. 相似文献
965.
Yanhua Qu Chunhai Chen Ying Xiong Huishang She Yong E Zhang Yalin Cheng Shane DuBay Dongming Li Per G P Ericson Yan Hao Hongyuan Wang Hongfeng Zhao Gang Song Hailin Zhang Ting Yang Chi Zhang Liping Liang Tianyu Wu Jinyang Zhao Qiang Gao Weiwei Zhai Fumin Lei 《国家科学评论(英文版)》2020,7(1):113
Known as the ‘third polar region’, the Qinghai-Tibet Plateau represents one of the harshest highland environments in the world and yet a number of organisms thrive there. Previous studies of birds, animals and humans have focused on well-differentiated populations in later stages of phenotypic divergence. The adaptive processes during the initial phase of highland adaptation remain poorly understood. We studied a human commensal, the Eurasian Tree Sparrow, which has followed human agriculture to the Qinghai-Tibet Plateau. Despite strong phenotypic differentiation at multiple levels, in particular in muscle-related phenotypes, highland and lowland populations show shallow genomic divergence and the colonization event occurred within the past few thousand years. In a one-month acclimation experiment investigating phenotypic plasticity, we exposed adult lowland tree sparrows to a hypoxic environment and did not observe muscle changes. Through population genetic analyses, we identified a signature of polygenic adaptation, whereby shifts in allele frequencies are spread across multiple loci, many of which are associated with muscle-related processes. Our results reveal a case of positive selection in which polygenic adaptation appears to drive rapid phenotypic evolution, shedding light on early stages of adaptive evolution to a novel environment. 相似文献
966.
Cong Liu Feng An Paria S M Gharavi Qinwen Lu Junkun Zha Chao Chen Liming Wang Xiaozhi Zhan Zedong Xu Yuan Zhang Ke Qu Junxiang Yao Yun Ou Zhiming Zhao Xiangli Zhong Dongwen Zhang Nagarajan Valanoor Lang Chen Tao Zhu Deyang Chen Xiaofang Zhai Peng Gao Tingting Jia Shuhong Xie Gaokuo Zhong Jiangyu Li 《国家科学评论(英文版)》2020,7(1):84
Complex oxides with tunable structures have many fascinating properties, though high-quality complex oxide epitaxy with precisely controlled composition is still out of reach. Here we have successfully developed solution-based single-crystalline epitaxy for multiferroic (1-x)BiTi(1-y)/2FeyMg(1-y)/2O3–(x)CaTiO3 (BTFM–CTO) solid solution in large area, confirming its ferroelectricity at the atomic scale with strong spontaneous polarization. Careful compositional tuning leads to a bulk magnetization of 0.07 ± 0.035 μB/Fe at room temperature, enabling magnetically induced polarization switching exhibiting a large magnetoelectric coefficient of 2.7–3.0 × 10−7 s/m. This work demonstrates the great potential of solution processing in large-scale complex oxide epitaxy and establishes novel room-temperature magnetoelectric coupling in epitaxial BTFM–CTO film, making it possible to explore a much wider space of composition, phase, and structure that can be easily scaled up for industrial applications. 相似文献
967.
968.
随着超市快速发展,竞争的日趋激烈,作为超市主要利润来源的商品销售利润水平却在下降,超市生存和发展的秘密是什么?单一的向下游(顾客)要利润已经无法使超市更好发展。因此超市的赢利模式日趋多样化和复杂化。 相似文献
969.
企业战略决策是一个非结构化的过程,其形成机制难以清晰描述。本文讲述了如何利用MATLAB神经网络工具箱建立BP网络模型,结合BorlandC Builder具有的丰富可视化组件和SQLServer的数据库管理功能,调用MATLAB引擎进行混合编程,本文还讨论了编程设计过程,使系统能够辅助企业做出科学化的战略决策。 相似文献
970.