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   6214篇
  免费   529篇
  国内免费   8篇
  6751篇
  2023年   47篇
  2022年   107篇
  2021年   263篇
  2020年   120篇
  2019年   160篇
  2018年   165篇
  2017年   146篇
  2016年   250篇
  2015年   414篇
  2014年   421篇
  2013年   412篇
  2012年   590篇
  2011年   555篇
  2010年   306篇
  2009年   273篇
  2008年   419篇
  2007年   318篇
  2006年   310篇
  2005年   270篇
  2004年   233篇
  2003年   209篇
  2002年   176篇
  2001年   37篇
  2000年   27篇
  1999年   42篇
  1998年   36篇
  1997年   24篇
  1996年   18篇
  1995年   18篇
  1994年   18篇
  1993年   15篇
  1992年   22篇
  1991年   19篇
  1990年   27篇
  1989年   21篇
  1988年   15篇
  1987年   13篇
  1986年   10篇
  1985年   18篇
  1984年   16篇
  1983年   11篇
  1982年   12篇
  1981年   9篇
  1979年   9篇
  1977年   11篇
  1976年   13篇
  1975年   17篇
  1973年   16篇
  1970年   9篇
  1962年   8篇
排序方式: 共有6751条查询结果,搜索用时 10 毫秒
991.
Strategic use of oral toxicants could allow for practical and sustainable control schemes for the invasive common carp (Cyprinus carpio, or ‘carp’) if a toxicant selectively targeted carp and not native species. In this study, we incorporated antimycin-a (ANT-A), a known fish toxicant, into a corn-based bait and conducted a series of experiments to determine its toxicity, leaching rate, and species-specificity. Our results showed that ANT-A was lethal to carp at doses ≥ 4 mg/kg and that the amount of ANT-A that leached out of the bait in 72 h was not lethal to carp or bluegill (Lepomis macrochirus). Species-specificity trials were conducted in 227 L tanks, in which carp were stocked with three native species representing families that occur sympatrically with carp in our study region: the fathead minnow (Pimephales promelas), yellow perch (Perca flavescens) and bluegill. These trials showed high mortality of carp (46%) and fathead minnows (76%) but no significant mortality of perch or bluegill. Finally, a pond study, which used the same species composition except for fathead minnows, resulted in 37% morality among adult carp and no mortality among perch or bluegill. Our results suggest that corn-based bait that contains ANT-A could be used to selectively control carp in ecosystems dominated by percids or centrarchids, such as lakes across the Great Plains ecoregion of North America, where carp are especially problematic.  相似文献   
992.
993.
Ecosystem service (ES) evidence and arguments can mobilize support for biodiversity conservation. However, the ES concept’s impact on the ground seems unclear: It is reliant upon a range of pre-requisites at the science-policy nexus and it tends to be science-driven and demanding in terms of data and required capacity. The TEEB stepwise approach (The Economics of Ecosystems and Biodiversity for Local and Regional Policy Makers, Earthscan, London, 2012) guides purpose-driven ES assessments and seeks to enhance the usefulness of the ES concept in difficult real-world settings. An application of this approach has not yet been appraised. Also, beyond the instrumental use of ES data (e.g. for the design of payment schemes for ES), there is little documented experience with strategically using ES arguments for mobilizing financial resources for conservation. As many other countries, Côte d’Ivoire does not have a strong knowledge base on ecosystem services (ES). Such circumstances can preclude the use of the ES concept for convincing potential donors to co-finance conservation. We examine the recent ES assessment for the Parc national de Taï (PNT), Côte d’Ivoire, which followed the TEEB stepwise approach. We look at process, results and outcomes to address three questions: (i) How did study results contribute to mobilizing funds for the PNT? (ii) In which ways was the TEEB stepwise approach useful in practice? (iii) What lessons can be drawn for ES assessments geared to conservation finance?  相似文献   
994.
995.
Liver cancer is the sixth most common cancer worldwide and 3rd most common cause of cancer-related death. Hepatocellular carcinoma (HCC) represents more than 90% of primary liver cancer and is a major public health problem. Due to the advanced stages of HCC at the time of diagnosis, utilizing the conventional treatment for solid tumors frequently ends with treatment failure, recurrence, or poor survival. HCC is highly refractory to chemotherapy and other systemic treatments, and locoregional therapies or selective internal radiation therapies are largely palliative. Considering how the pathogenesis of HCC often induces an immunosuppressed state which is further amplified by post-treatment recurrence and reactivation, immunostimulation provides a potential novel approach for the treatment of HCC. Immune response(s) of the body may be potentiated by immunomodulation of various effector cells such as B-cells, T-cells, Treg cells, natural killer cells, dendritic cells, cytotoxic T-lymphocytes, and other antigen-presenting cells; cellular components such as genes and microRNA; and molecules such as proteins, proteoglycans, surface receptors, chemokines, and cytokines. Targeting these effectors individually has helped in the development of newer therapeutic approaches; however, combinational therapies targeting multi-faceted biomarkers have yielded better results. Still, there is a need for further research to develop novel therapeutic strategies which may act as either complementary or an alternative treatment to the standard therapy protocols of HCC. This review focuses on potential cellular and molecular targets, as well as the role of virotherapy and combinational therapy in the treatment of HCC.  相似文献   
996.
997.
The conformational equilibria of integral membrane proteins have proven extremely difficult to characterize within native lipid bilayers. To circumvent technical issues, investigations of the structure and stability of α‐helical membrane proteins are often carried out in mixed micelle or bicelle solvents that mimic the membrane and facilitate measurements of reversible folding. Under these conditions, the energetics of membrane protein folding are typically proportional to the mole fraction of an anionic detergent in the micelle. However, investigations of the folding and unfolding of bacteriorhodopsin (bR) surprisingly revealed that the folding rate is also highly sensitive to the bulk molar concentration of lipids and detergents. We show here that this rate enhancement coincides with changes in bicelle size and suggest this effect arises through restriction of the conformational search space during folding. In conjunction with previous mutagenic studies, these results provide additional evidence that a topological search limits the rate of bR folding. Furthermore, this finding provides insights into the manner by which micellar and bicellar environments influence the conformational stability of polytopic membrane proteins.  相似文献   
998.
999.
Raised progesterone during the menstrual cycle is associated with suppressed physiological immune responses, reducing the probability that the immune system will compromise the blastocyst's development. The Compensatory Prophylaxis Hypothesis proposes that this progesterone-linked immunosuppression triggers increased disgust responses to pathogen cues, compensating for the reduction in physiological immune responses by minimizing contact with pathogens. Although a popular and influential hypothesis, there is no direct, within-woman evidence for correlated changes in progesterone and pathogen disgust. To address this issue, we used a longitudinal design to test for correlated changes in salivary progesterone and pathogen disgust (measured using the pathogen disgust subscale of the Three Domain Disgust Scale) in a large sample of women (N?=?375). Our analyses showed no evidence that pathogen disgust tracked changes in progesterone, estradiol, testosterone, or cortisol. Thus, our results provide no support for the Compensatory Prophylaxis Hypothesis of variation in pathogen disgust.  相似文献   
1000.
Raised progesterone during the menstrual cycle is associated with suppressed physiological immune responses, reducing the probability that the immune system will compromise the blastocyst's development. The Compensatory Prophylaxis Hypothesis proposes that this progesterone-linked immunosuppression triggers increased disgust responses to pathogen cues, compensating for the reduction in physiological immune responses by minimizing contact with pathogens. Although a popular and influential hypothesis, there is no direct, within-woman evidence for correlated changes in progesterone and pathogen disgust. To address this issue, we used a longitudinal design to test for correlated changes in salivary progesterone and pathogen disgust (measured using the pathogen disgust subscale of the Three Domain Disgust Scale) in a large sample of women (N = 375). Our analyses showed no evidence that pathogen disgust tracked changes in progesterone, estradiol, testosterone, or cortisol. Thus, our results provide no support for the Compensatory Prophylaxis Hypothesis of variation in pathogen disgust.  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