首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22409篇
  免费   2046篇
  国内免费   2632篇
  27087篇
  2024年   56篇
  2023年   221篇
  2022年   496篇
  2021年   867篇
  2020年   699篇
  2019年   911篇
  2018年   904篇
  2017年   739篇
  2016年   1009篇
  2015年   1400篇
  2014年   1670篇
  2013年   1794篇
  2012年   2058篇
  2011年   1960篇
  2010年   1390篇
  2009年   1244篇
  2008年   1389篇
  2007年   1279篇
  2006年   1106篇
  2005年   1048篇
  2004年   906篇
  2003年   864篇
  2002年   771篇
  2001年   437篇
  2000年   318篇
  1999年   268篇
  1998年   234篇
  1997年   185篇
  1996年   133篇
  1995年   103篇
  1994年   95篇
  1993年   68篇
  1992年   84篇
  1991年   62篇
  1990年   43篇
  1989年   50篇
  1988年   42篇
  1987年   25篇
  1986年   21篇
  1985年   24篇
  1984年   14篇
  1983年   15篇
  1982年   16篇
  1981年   8篇
  1980年   6篇
  1979年   8篇
  1977年   4篇
  1972年   7篇
  1970年   5篇
  1965年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
栖息地破碎化、人为干扰等因素影响着中华鬣羚(Capricornis sumatraensis)的生存.目前,中华鬣羚的行为研究还比较匮乏,因此有必要构建中华鬣羚的行为谱及PAE (posture-act-environment)编码系统,以期促进其基础行为资料的完善,为深入开展科学研究和保护工作奠定基础.本文旨在:(1...  相似文献   
972.
Orphan genes are genetic innovations that lack homologs in other lineages. Orphan genes can rapidly originate and become substantially functional, yet the mechanisms underlying their origins are still largely unknown in plants. Here, we investigated the origin of orphan genes in the Oryza sativa ssp. japonica “Nipponbare” genome using genome‐wide comparisons with 10 closely related Oryza species. We identified a total of 37 orphan genes in the Nipponbare genome that show short sequence lengths, elevated GC content, and absence of introns. Interestingly, half of the identified orphan genes originated by way of a distinctive mechanism that involved the generation of new coding sequences through independent and rapid divergence within the inserted transposable element. Our results provide valuable insight into genetic innovations in the model rice genome that formed on a very short timescale.  相似文献   
973.
A new trinickel(II) complex bridged by N‐[3‐(dimethylamino)propyl]‐ N ′‐(2‐hydroxylphenyl)oxamido (H3pdmapo), namely [Ni3(pdmapo)2(H2O)2]?4CH3OH, was synthesized and characterized by X‐ray single‐crystal diffraction and other methods. In the molecule, two symmetric cis‐ pdmapo3? mononickel(II) complexes as a “complex ligand” using the carbonyl oxygen atoms coordinate to the center nickel(II) ion situated on an inversion point. The Ni···Ni distance through the oxamido bridge is 5.2624(4) Å. The center nickel(II) ion and the lateral ones have octahedral and square‐planar coordination geometries, respectively. In the crystal, a three‐dimensional supramolecular network dominated by hydrogen bonds is observed. The reactivity toward DNA/protein bovine serum albumin (BSA) revealed that the complex could interact with herring sperm DNA (HS‐DNA) through the intercalation mode and quench the intrinsic fluorescence of BSA via a static mechanism. The in vitro anticancer activities suggested that the complex is active against the selected tumor cell lines.  相似文献   
974.
We reported an integrated platform to explore serum protein variant pattern in cancer and its utility as a new class of biomarker panel for diagnosis. On the model study of serum amyloid A (SAA), we employed nanoprobe‐based affinity mass spectrometry for enrichment, identification and quantitation of SAA variants from serum of 105 gastric cancer patients in comparison with 54 gastritis patients, 54 controls, and 120 patients from other cancer. The result revealed surprisingly heterogeneous and most comprehensive SAA bar code to date, which comprises 24 SAA variants including SAA1‐ and SAA2‐encoded products, polymorphic isoforms, N‐terminal–truncated forms, and three novel SAA oxidized isotypes, in which the variant‐specific peptide sequence were also confirmed by LC‐MS/MS. A diagnostic model was developed for dimension reduction and computational classification of the 24 SAA‐variant bar code, providing good discrimination (AUC = 0.85 ± 3.2E?3) for differentiating gastric cancer group from gastritis and normal groups (sensitivity, 0.76; specificity, 0.81) and was validated with external validation cohort (sensitivity, 0.71; specificity, 0.74). Our platform not only shed light on the occurrence and modification extent of under‐represented serum protein variants in cancer, but also suggested a new concept of diagnostic platform by serum protein variant profile.  相似文献   
975.
976.
In this work, a freestanding NiS2/FeS holey film (HF) is prepared after electrochemical anodic and chemical vapor deposition treatments. With the combination of good electrical conductivity and holey structure, the NiS2/FeS HF presents superior electrochemical performance, due to the following reasons: (i) Porous structure of HF provides a large surface area and more active sites/channels/pathways to enhance the ion/mass diffusion. Moreover, the porous structure can reduce the damage from the volumetric expansion. (ii) The as‐prepared electrode combines the current collector (residual NiFe alloy) and active materials (sulfides) together, thus reducing the resistance of the electrode. Additionally, the good conductivity of HF can improve electron transport. (iii) Sulfides are more stable as active materials than sulfur, showing only a small capacity decay while retaining high cyclability performance. This work provides a promising way to develop high energy and stable electrode for Li‐S battery.  相似文献   
977.
978.
CCT家族基因广泛参与植物花期的调控过程,粗山羊草(Aegilops tauschii Coss.)作为小麦D基因组供体,给小麦带来新的花期及适应性相关基因。研究粗山羊草CCT家族基因不仅可为小麦进化、驯化和演变规律提供参考,还有助于认识粗山羊草作为杂草的生态适应性。粗山羊草基因组中26个CCT基因进化分析后发现Group A、Group C、GroupH和Group G中的13个Aet CCT成员出现了快速进化;Group A中有42.1%的位点存在正选择效应,表明快速进化提高了粗山羊草的适应性。基因结构分析表明CCT结构域在Aet CCT家族中保守性很高,但不同基因内含子和外显子的排布差异较大,特异Motif可能是不同亚家族基因间功能差异的重要原因。Aet CCT4、Aet CCT7、Aet CCT8、Aet CCT11、Aet CCT12、Aet CCT16、Aet CCT17、Aet CCT19、Aet CCT21和Aet CCT22的表达具有明显的"生物钟效应",呈现出24 h的节律性表达,且基本都处于快速进化的Group A、Group C、GroupH和Group I。研究结果表明,这些成员可能参与花期调控等生长发育过程,在粗山羊草的适应性形成过程中发挥了作用。  相似文献   
979.
980.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号