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   3577篇
  免费   285篇
  国内免费   143篇
林业   453篇
农学   213篇
基础科学   112篇
  379篇
综合类   1603篇
农作物   93篇
水产渔业   463篇
畜牧兽医   438篇
园艺   83篇
植物保护   168篇
  2024年   8篇
  2023年   87篇
  2022年   120篇
  2021年   133篇
  2020年   105篇
  2019年   138篇
  2018年   87篇
  2017年   126篇
  2016年   175篇
  2015年   145篇
  2014年   187篇
  2013年   206篇
  2012年   229篇
  2011年   258篇
  2010年   183篇
  2009年   207篇
  2008年   191篇
  2007年   230篇
  2006年   210篇
  2005年   157篇
  2004年   147篇
  2003年   117篇
  2002年   88篇
  2001年   100篇
  2000年   59篇
  1999年   39篇
  1998年   42篇
  1997年   42篇
  1996年   25篇
  1995年   28篇
  1994年   25篇
  1993年   27篇
  1992年   11篇
  1991年   25篇
  1990年   11篇
  1989年   7篇
  1988年   9篇
  1987年   7篇
  1986年   3篇
  1985年   1篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
  1981年   2篇
  1979年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有4005条查询结果,搜索用时 281 毫秒
41.
为获得营养均衡的调制牛奶,满足人体的多种营养需求,添加多种维生素和矿物质,设计出一款适用于糖尿病人、亚健康人群、体重管理、皮肤管理等人群饮用的低血糖生成指数(Glycemic Index,GI)的牛奶。稳定性试验结果表明,静置12 天后,牛奶无显著脂肪上浮,体系稳定性良好;人体GI值试验结果表明,调制牛奶的餐后血糖值上升和下降均较葡萄糖餐后血糖值平稳,有较好稳定餐后血糖的效果,表明开发的调制牛奶为低GI食品(GI值=22.86)。人体饱腹感试验结果显示,和普通纯牛奶对比,调制牛奶具有显著提高饱腹感的效果。  相似文献   
42.
随着社会经济水平日益提升,越来越多的人饲养宠物作为伴侣,与此同时宠物诊疗机构如春笋般蓬勃发展。然而其在发展中存在诸多问题,尤以使用人用药品问题最为突出。论文从药品使用现状、原因、管理等方面,对动物诊疗机构人用药品使用现象进行分析并提出一些建议,旨在进一步规范动物诊疗机构临床用药,使其良性发展。  相似文献   
43.
Participation in conservation programs is often viewed as a necessity, but understanding of this participation is limited. This research takes a different approach by also examining participation in non-conservation-related activities. Questionnaires (N = 339) were administered in four Brazilian coastal communities where the national sea turtle conservation project conducts monitoring and outreach. Employing social capital as a conceptual framework, measurements included participation in civic, community, and social activities along with group participation and collective action. Confirmatory factor analysis was used for validating measures of social capital and conservation perceptions. Structural equation modeling indicated that social capital has a positive relationship with participation in sea turtle conservation, suggesting that general levels of participation and community norms of participation could be just as influential as conservation perceptions to engage communities in conservation. Information gained by deconstructing participation may be used to design and target conservation programs, improving overall participation.  相似文献   
44.
Previous studies have established a bovine mammary gland epithelia cells in vitro model by the adenovirus-mediated telomerase (hTERT-bMGEs). The present study was conducted to confirm whether hTERT-bMGEs were effective target cells to improve the efficiency of transgenic expression and somatic cell nuclear transfer (SCNT). To accomplish this, a mammary-specific vector encoding human lysozyme and green fluorescent protein was used to verify the transgenic efficiency of hTERT-bMGEs, and untreated bovine mammary gland epithelial cells (bMGEs) were used as a control group. The results showed that the hTERT-bMGEs group had much higher transgenic efficiency and protein expression than the bMGEs group. Furthermore, the nontransgenic and transgenic hTERT-bMGEs were used as donor cells to evaluate the efficiency of SCNT. There were no significant differences in rates of cleavage or blastocysts or hatched blastocysts of cloned embryos from nontransgenic hTERT-bMGEs at passage 18 and 28 groups (82.8% vs. 81.9%, 28.6% vs. 24.8%, 58.6% vs. 55.3%, respectively) and the transgenic group (80.8%, 26.5% and 53.4%); however, they were significantly higher than the bMGEs group (71.2%, 12.8% and 14.8%), (p < 0.05). We confirmed that hTERT-bMGEs could serve as effective target cells for improving development of somatic cell cloned cattle embryos.  相似文献   
45.
Jaguars and pumas are threatened species in Brazil’s Atlantic Forest, especially at the borders of protected areas. This article assessed the influence of emotions, attitudes, existence value, and agency credibility on acceptability of big cats among rural residents living adjacent to two protected areas in this forest. Data from self-administrated questionnaires (= 326) indicated those with positive attitudes toward big cats (β = .28, < .001), those who valued the existence of big cats (β = .14, < .05), those who would feel sorrow if big cats disappeared (β = .21, < .001), and those who considered the managing agency as credible (β = .16, = .002) were more accepting of big cats. The model provided theoretical and practical insights into large carnivore conservation. For example, given the significance of agency credibility, a positive relationship between park authorities and residents is crucial for big cat conservation.  相似文献   
46.
47.
Human commensal species take advantage of anthropogenic conditions that are less likely to be challenged by the selective pressures of natural environments. Their morphological and physiological phenotypes can therefore dissociate from habitat characteristics. Understanding how these species adjust their morphological and physiological traits across latitudinal gradients is fundamental to uncovering the eco-physiological strategies underlying coping mechanisms. Here, we studied morphological traits in breeding Eurasian tree sparrows (ETSs; Passer montanus) among low-latitude (Yunnan and Hunan) and middle-latitude (Hebei) localities in China. We then compared body mass; lengths of bill, tarsometatarsus, wing, total body, and tail feather; and baseline and capture stress-induced levels of plasma corticosterone (CORT) and the metabolites including glucose (Glu), total triglyceride (TG), free fatty acid (FFA), total protein, and uric acid (UA). None of the measured morphological parameters varied with latitude except in the Hunan population, which demonstrated longer bills than those in other populations. Stress-induced CORT levels significantly exceeded baseline levels and decreased with increasing latitude, but total integrated CORT levels did not vary with latitude. Capture stress-induced significantly increased Glu levels and decreased TG levels, independent of site. However, the Hunan population had significantly higher baseline CORT, baseline and stress-induced FFA levels, but lower UA levels, which differed from other populations. Our results suggest that rather than morphological adjustments, physiological adjustments are mainly involved in coping mechanisms for middle-latitude adaptation in ETSs. It is worth investigating whether other avian species also exhibit such dissociation from external morphological designs while depending on physiological adjustments.  相似文献   
48.
Under the background of the new rural construction in China, it is an important scientific question and an urgent social task to construct the harmonious society and to achieve the sustainable regional development on how to construct concentrative residence and manage the human habitat environment in the fast industrializing and typically urbanizing area. This paper analyzed the problems in the construction of the human habitat envi- ronment in the rural area of southern Jiangsu, discussed the methodologies of planning and design for rural con- centrative residence, researched the human habitat environment improvement technologies, and put forward the resolution of the recycling community for the rural inhabitation, which aimed at demonstrating the practicing in rapidly urbanizing regions.  相似文献   
49.
Earning report is a main accounting report that transmits earning information to users. It is the core of financial reports system. Earning information is significant to users' decision making. This paper studies the respond of stock trading volume to earning report and draws the curve of trading volume before and after earning report. This paper further does a regression analysis of accidental earning and abnormal return rate, and draws the relation curve of them on the earning report date to prove stock trading volume does have remarkable respond to earning report. This research is significant to either lessen small investors blindness investment and help them make reasonable forecast to markets and regulate the disclosure of listed companies.  相似文献   
50.
Improves investment decision method NPV method by introducing risk. This paper CAPM and certainty equivalent wealthare applied because of NCF'S volatility of venture capital projects, on the basis of which, debt capital is introduced. the dissertation derives a levered risky project's NPV formula, which broadens applying range and lessens constrain conditions. For risky projects investment decision, the research provides a new theoretical basis.  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