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   3000篇
  免费   293篇
  国内免费   168篇
  3461篇
  2023年   23篇
  2022年   19篇
  2021年   39篇
  2020年   63篇
  2019年   85篇
  2018年   90篇
  2017年   113篇
  2016年   105篇
  2015年   80篇
  2014年   131篇
  2013年   177篇
  2012年   63篇
  2011年   112篇
  2010年   69篇
  2009年   136篇
  2008年   124篇
  2007年   166篇
  2006年   155篇
  2005年   118篇
  2004年   99篇
  2003年   106篇
  2002年   119篇
  2001年   94篇
  2000年   99篇
  1999年   80篇
  1998年   83篇
  1997年   71篇
  1996年   75篇
  1995年   69篇
  1994年   83篇
  1993年   61篇
  1992年   44篇
  1991年   47篇
  1990年   55篇
  1989年   38篇
  1988年   41篇
  1987年   34篇
  1986年   42篇
  1985年   45篇
  1984年   25篇
  1983年   15篇
  1982年   23篇
  1981年   30篇
  1980年   27篇
  1979年   23篇
  1978年   23篇
  1977年   10篇
  1976年   7篇
  1974年   5篇
  1973年   6篇
排序方式: 共有3461条查询结果,搜索用时 15 毫秒
891.
892.
893.
This study evaluated the length-weight relationships (LWRs) for three teleost fish species sampled from the Stung Russei Chrum River basin, Kingdom of Cambodia. The fish were collected during two dry seasons (April 2019 and November 2019) and one rainy season (October 2018) using monofilament trammel nets (2–12 cm mesh size), cast net (mesh size 2 cm) and scoop-nets (mesh size with 0.3 cm). Results showed that all fitted regressions were highly significant and the coefficients of determination (r2) were high. This study expanded the value of maximum total length for Cyclocheilichthys apogon and Poropuntius laoensis while reported the wider ranges of total mass for Poropuntius laoensis. Moreover, our present study also provided the novel LWRs records for Hemibagrus filamemtus.  相似文献   
894.
Lisa Åkesson 《Ethnos》2013,78(3):326-347
This article examines migrant remittances through the lens of anthropological theories of gift relationships. I explore remittance transactions as perceived and practised by people in Cape Verde, a country in which many households receive money from abroad. The article highlights three key dimensions. The first dimension is the transactors' (senders and receivers of remittances) relations and obligations to each other, the second is the degree to which remittances are seen as voluntary gifts or, alternatively, as elements in an obligatory reciprocal exchange, and the third is the relation between the transactors and money as an object of exchange. I argue that these dimensions together open up for a holistic understanding of the dynamic interplay between remittances and relationships. In contrast to mainstream remittance studies, with their conventional focus on economic rationality, this is an approach that illuminates what remittances mean, as social practice, to those involved.  相似文献   
895.
896.
Abstract

The New Zealand proctotrupid Fustiserphus intrudens (Smith) was reared from two species of Tingena (Lepidoptera: Oecophoridae) feeding on leaf litter in Nothofagus forest. Host relationships in the Proctotrupidae are discussed.  相似文献   
897.
《Anthrozo?s》2013,26(2):279-294
ABSTRACT

This paper examines the variations in dog owners' attitudes toward, treatment of, and interactions with, animals. Based on 28 in-depth interviews with dog owners from a county in the Midwestern United States, I demonstrate that pets are an important part of many people's lives, often providing companionship, entertainment, and meaningful interactions; however, there are notable, distinct variations in how people relate to them. Pet owners typically exhibit one of three orientations toward pets: “dominionistic,” “humanistic,” or “protectionistic.” The dominionistic have relatively low regard for their pets, valuing them primarily for the uses they provide, such as protection. Those employing the humanistic orientation elevate their pets to the status of surrogate humans and value their pets primarily for the affective benefits they enjoy from their close attachments. The protectionistic have high regard for both pets and animals more generally. They view pets as valuable companions and as creatures with their own interests. This typology offers insights for understanding the source and variety of the often ambiguous and contradictory relations between people and pets. I argue that individual characteristics and experiences impact how people understand and relate to animals, in large part, because they represent exposure to different cultural messages. I suggest that these orientations represent three sets of distinct cultural logics, each with distinct histories and contemporary sources.  相似文献   
898.
899.
The exploitation of cheap and efficient electrocatalysts is the key to make energy‐related electrocatalytic techniques commercially viable. In recent years, transition metal phosphides (TMPs) electrocatalysts have gained a great deal of attention owing to their multifunctional active sites, tunable structure, and composition, as well as unique physicochemical properties. This review summarizes the up‐to‐date progress on TMPs in energy‐related electrocatalysis from diversified synthetic methods, ingenious‐modulated strategies, and novel applications. In order to set forth theory–structure–performance relationships upon TMPs, the corresponding reaction mechanisms, electrocatalytsts' structure/composition designs and desired electrochemical performance are jointly discussed, along with demonstrating their practical electrocatalytic applications in overall water splitting, metal–air batteries, lithium–sulfur batteries, etc. In the end, some underpinning issues and research orientations of TMPs toward efficient energy‐related electrocatalysis are briefly proposed.  相似文献   
900.
Electrostatic interactions between phosphate anions and Toll-like receptor 4 / Myeloid differentiation factor-2 (TLR4/MD-2) protein complexes of human, murine, equine and canine species were computed. Such knowledge can provide mechanistic information about recognising LPS-like ligands, since anionic phosphate groups belong to the structural features of LPS with their diphosphorylated diglucosamine backbone. Sequence composition analyses, electrostatic interaction potentials and docked energies as well as molecular dynamics studies evaluated the phosphate interactions within the triangular LPS binding site (wedge). According to electrostatic analyses, human, horse and dog wedges possess phosphate-binding sites with indistinct positive and negative charge distributions, but the murine wedge shows a unique strong negative net charge at the site where antagonists bind in other species (Pan). Docking of a phosphate mono-anion (probe) confirmed its repulsion at this Pan site, but the Pag site of the murine wedge attracted the probe. It is occupied by phosphate groups of agonists in other species (Pag). Molecular dynamics trajectories show a variable degree of random walk across the wedges, that is, not following electrostatic preferences (neither Pag nor Pan). In summary, two opposing electrostatic patterns exist –murine versus human, equine and canine species – all of which reflect the potential dual activity mode of under-acylated ligands such as lipid IVA.  相似文献   
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