全文获取类型
收费全文 | 15770篇 |
免费 | 1388篇 |
国内免费 | 1341篇 |
专业分类
18499篇 |
出版年
2024年 | 45篇 |
2023年 | 232篇 |
2022年 | 476篇 |
2021年 | 764篇 |
2020年 | 632篇 |
2019年 | 714篇 |
2018年 | 704篇 |
2017年 | 511篇 |
2016年 | 688篇 |
2015年 | 1034篇 |
2014年 | 1240篇 |
2013年 | 1264篇 |
2012年 | 1460篇 |
2011年 | 1310篇 |
2010年 | 887篇 |
2009年 | 730篇 |
2008年 | 782篇 |
2007年 | 702篇 |
2006年 | 688篇 |
2005年 | 555篇 |
2004年 | 483篇 |
2003年 | 514篇 |
2002年 | 396篇 |
2001年 | 243篇 |
2000年 | 211篇 |
1999年 | 204篇 |
1998年 | 138篇 |
1997年 | 112篇 |
1996年 | 115篇 |
1995年 | 109篇 |
1994年 | 93篇 |
1993年 | 57篇 |
1992年 | 78篇 |
1991年 | 64篇 |
1990年 | 60篇 |
1989年 | 44篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 34篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1962年 | 2篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Coleifolides A and B,Two New Sesterterpenoids from the Aerial Parts of Scutellaria coleifolia H.Lév. 下载免费PDF全文
Shin‐ichiro Kurimoto Jian‐Xin Pu Han‐Dong Sun Yoshihisa Takaishi Yoshiki Kashiwada 《化学与生物多样性》2015,12(8):1200-1207
Coleifolides A and B ( 1 and 2 ), two new sesterterpenoids with a β‐methyl‐α,β‐unsaturated‐γ‐lactone moiety, were isolated from the aerial parts of Scutellaria coleifolia H.Lév . (Lamiaceae), together with three known compounds. Their structures were elucidated by NMR and MS examinations. Coleifolides A and B were concluded to be partially racemic compounds by the HPLC analysis using a chiral column or introduction of chiral derivatizing agents. The absolute configuration of the major isomer was determined by analyses of the CD spectrum as well as NMR data of (R)‐ and (S)‐2‐NMA derivatives. Coleifolides A and B are structurally similar to manoalide derivatives, previously isolated from marine sponges, and appear to be the first examples of this type of compounds being isolated from higher plants. 相似文献
952.
Merosesquiterpenoids and Ten‐Membered Macrolides from a Soft Coral‐Derived Lophiostoma sp. Fungus 下载免费PDF全文
Cai‐Juan Zheng Chang‐Lun Shao Min Chen Zhi‐Gang Niu Dong‐Lin Zhao Chang‐Yun Wang 《化学与生物多样性》2015,12(9):1407-1414
One new merosesquiterpenoid, craterellin D ( 1 ), along with one known analog, craterellin A ( 2 ), and five known ten‐membered macrolides, 3 – 7 , were isolated from a soft coral‐derived Lophiostoma sp. fungus. The absolute configuration of 1 was established based on biogenetic consideration with the co‐isolated analog 2 , whose configuration was determined by modified Mosher's method and single‐crystal X‐ray diffraction analysis using CuKα radiation. The absolute configuration of 3 was determined by X‐ray diffraction analysis using CuKα radiation. Compounds 2 and 3 showed antibacterial activities against Bacillus cereus with a MIC value of 3.12 μM . 相似文献
953.
Tellurium@Ordered Macroporous Carbon Composite and Free‐Standing Tellurium Nanowire Mat as Cathode Materials for Rechargeable Lithium–Tellurium Batteries 下载免费PDF全文
954.
The Effect of Antisite Disorder and Particle Size on Li Intercalation Kinetics in Monoclinic LiMnBO3 下载免费PDF全文
In materials containing 1D lithium diffusion channels, cation disorder can strongly affect lithium intercalation processes. This work presents a model to explain the unusual transport properties of monoclinic LiMnBO3, a material determined by scanning electron microscopy and synchrotron X‐ray diffraction to contain a wide particle size distribution and Mn/Li antisite disorder. First‐principles calculations indicate that Mn occupying Li sites obstruct the 1D lithium diffusion channel along the [001] direction. While channel blockage by the antisites significantly lowers Li mobility in large particles, Li kinetics in small particles and particle surfaces are found to be less sensitive to the presence of antisite disorder. Thus, in an electrode containing a large particle size distribution, smaller particles have higher Li mobility, and the measured Li diffusivity as determined by potentiostatic intermittent titration test varies as a function of particle size. The Li capacity in monoclinic LiMnBO3 is kinetically controlled by the fraction of large particles with antisite disorder, but is not intrinsically limited. These results strongly suggest that particle nanosizing will significantly enhance the electrochemical performance of LiMnBO3. 相似文献
955.
956.
Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements 下载免费PDF全文
Yubo Chen Wei Zhou Dong Ding Meilin Liu Francesco Ciucci Moses Tade Zongping Shao 《Liver Transplantation》2015,5(18)
Solid oxide fuel cells (SOFCs) represent one of the cleanest and most efficient options for the direct conversion of a wide variety of fuels to electricity. For example, SOFCs powered by natural gas are ideally suited for distributed power generation. However, the commercialization of SOFC technologies hinges on breakthroughs in materials development to dramatically reduce the cost while enhancing performance and durability. One of the critical obstacles to achieving high‐performance SOFC systems is the cathodes for oxygen reduction reaction (ORR), which perform poorly at low temperatures and degrade over time under operating conditions. Here a comprehensive review of the latest advances in the development of SOFC cathodes is presented: complex oxides without alkaline earth metal elements (because these elements could be vulnerable to phase segregation and contaminant poisoning). Various strategies are discussed for enhancing ORR activity while minimizing the effect of contaminant on electrode durability. Furthermore, some of the critical challenges are briefly highlighted and the prospects for future‐generation SOFC cathodes are discussed. A good understanding of the latest advances and remaining challenges in searching for highly active SOFC cathodes with robust tolerance to contaminants may provide useful guidance for the rational design of new materials and structures for commercially viable SOFC technologies. 相似文献
957.
958.
Yadong Yang Xunong Dong Bingbing Xie Nan Ding Juan Chen Yongjun Li Qian Zhang Hongzhu Qu Xiangdong Fang 《基因组蛋白质组与生物信息学报(英文版)》2015,13(1):46-50
Publicly-accessible resources have promoted the advance of scientific discovery. The era of genomics and big data has brought the need for collaboration and data sharing in order to make effective use of this new knowledge. Here, we describe the web resources for cancer genomics research and rate them on the basis of the diversity of cancer types, sample size, omics data comprehensiveness, and user experience. The resources reviewed include data repository and analysis tools; and we hope such introduction will promote the awareness and facilitate the usage of these resources in the cancer research community. 相似文献
959.
Hui Li Kun‐Ling Lang Hai‐Bin Fu Chang‐Peng Shen Fang‐Hao Wan Dong Chu 《Insect Science》2015,22(6):761-767
The cotton mealybug, Phenacoccus solenopsis Tinsley, is a serious and invasive pest. At present, genetic resources for studying P. solenopsis are limited, and this negatively affects genetic research on the organism and, consequently, translational work to improve management of this pest. In the present study, expressed sequence tags (ESTs) were analyzed from a normalized complementary DNA library of P. solenopsis. In addition, EST‐derived microsatellite loci (also known as simple sequence repeats or SSRs) were isolated and characterized. A total of 1107 high‐quality ESTs were acquired from the library. Clustering and assembly analysis resulted in 785 unigenes, which were classified functionally into 23 categories according to the Gene Ontology database. Seven EST‐based SSR markers were developed in this study and are expected to be useful in characterizing how this invasive species was introduced, as well as providing insights into its genetic microevolution. 相似文献
960.
Yunxia Fang Jiang Hu Jie Xu Haiping Yu Zhenyuan Shi Guosheng Xiong Li Zhu Dali Zeng Guangheng Zhang Zhenyu Gao Guojun Dong Meixian Yan Longbiao Guo Yonghong Wang Qian Qian 《植物学报(英文版)》2015,57(2):151-161
The aerial parts of higher plants are generated from the shoot apical meristem(SAM). In this study, we isolated a small rice(Oryza sativa L.) mutant that showed premature termination of shoot development and was named mini rice 1(mini1). The mutant was first isolated from a japonica cultivar Zhonghua11(ZH11) subjected to ethyl methanesulfonate(EMS)treatment. With bulked segregant analysis(BSA) and map-based cloning method, Mini1 gene was finally fine-mapped to an interval of 48.6 kb on chromosome 9. Sequence analyses revealed a single base substitution from G to A was found in the region, which resulted in an amino acid change from Gly to Asp.The candidate gene Os09g0363900 was predicted to encode a putative adhesion of calyx edges protein ACE(putative HOTHEAD precursor) and genetic complementation experiment confirmed the identity of Mini1. Os09g0363900 contains glucose-methanol-choline(GMC) oxidoreductase and NAD(P)-binding Rossmann-like domain, and exhibits high similarity to Arabidopsis HOTHEAD(HTH). Expression analysis indicated Mini1 was highly expressed in young shoots but lowly in roots and the expression level of most genes involved in auxin biosynthesis and signal transduction were reduced in mutant.We conclude that Mini1 plays an important role in maintaining SAM activity and promoting shoot development in rice. 相似文献