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   529篇
  免费   57篇
  国内免费   22篇
  608篇
  2023年   6篇
  2022年   11篇
  2021年   17篇
  2020年   18篇
  2019年   12篇
  2018年   12篇
  2017年   8篇
  2016年   24篇
  2015年   31篇
  2014年   31篇
  2013年   32篇
  2012年   49篇
  2011年   47篇
  2010年   18篇
  2009年   19篇
  2008年   37篇
  2007年   26篇
  2006年   26篇
  2005年   26篇
  2004年   20篇
  2003年   24篇
  2002年   19篇
  2001年   7篇
  2000年   6篇
  1999年   8篇
  1998年   8篇
  1997年   5篇
  1996年   6篇
  1995年   3篇
  1994年   6篇
  1993年   2篇
  1992年   4篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1987年   1篇
  1986年   5篇
  1985年   4篇
  1982年   3篇
  1980年   1篇
  1979年   5篇
  1978年   3篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1973年   2篇
  1972年   2篇
  1971年   3篇
排序方式: 共有608条查询结果,搜索用时 15 毫秒
251.
252.
Understanding habitat quality and landscape connectivity and exploring corridors connecting habitat patches are crucial for conservation, particularly for species distributed among isolated populations. The Sichuan golden snub-nosed monkey, Rhinopithecus roxellana, is an Endangered primate species endemic to mountainous forests in China. Its easternmost distribution lies in the Shennongjia area, which harbors an isolated subspecies, R. roxellana hubeiensis. Unfortunately, it has experienced significant habitat loss, fragmentation, and dramatic population decline in recent decades, primarily due to increased human disturbance. To quantify habitat quality, identify suitable habitat patches, and detect possible linkages among these patches for R. roxellana hubeiensis, we conducted habitat suitability assessments and landscape connectivity analyses in the Shennongjia area based on a set of environmental factors. We created a habitat quality model and a movement cost surface for the Shennongjia area based on a habitat suitability index, graph theory, expert knowledge, field experience, and information from the literature. Our results show that suitable habitat for R. roxellana hubeiensis in Shennongjia is fragmented and limited, and that this is particularly true for highly suitable habitats. We detected six core habitat patches and six least-cost paths and corridors. Our study does not provide accurate distributions of the monkeys and their habitat use. However, it identifies the most feasible and traversable habitats and corridors, which should be conservation priorities for this subspecies, and provides valuable guidance for reevaluating habitat conservation plans.  相似文献   
253.
254.
第二掌骨长度与身高   总被引:2,自引:0,他引:2  
贾勉  颜政 《人类学学报》1989,8(3):240-244
本文通过对青藏高原海拔3000—4000米地区藏族、汉族7—18岁青少年1468人第二掌骨长度与身高的调查,探讨了二者的内在联系及规律。结果表明:第二掌骨长度与身高的增长近乎平行趋势,该二者之间存在着较高程度的正相关。第二掌骨长度/身高指数比较恒定,以第二掌骨长度推算身高是简便可行的。  相似文献   
255.
Psychological stress evokes rapid changes to the cardiovascular and neuroendocrine systems, responses that can become habituated following repeated exposure. This study, comprising of two phases, suggests that the immune system follows a similar trend. Phase 1: 15 healthy subjects (aged between 26 and 56 years) provided capillary blood samples before and after completing three basic tasks using, in turn, two automotive touch screen interfaces (Interface 1—antecedent version, Interface 2—improved version). Using a chemiluminescent technique termed leukocyte coping capacity (LCC), the ability of leukocytes to produce reactive oxygen species in vitro was assessed. Significant differences in leukocyte activity were shown between treatment groups, where the greatest post-test decrease occurred after using Interface 1. Phase 2: a randomly selected sub-group (n = 4) underwent weekly repeat testing using both interfaces. Significant differences in post-test leukocyte reactivity were exhibited between test weeks for each interface—the magnitude of response decreasing with successive exposure.  相似文献   
256.
257.
Modified quantum mechanical calculations predict the binding enthalpies of saccharide inhibitors of lysozyme to within a few kilocalories of experimental measurements.  相似文献   
258.
Partial resistance to Phytophthora sojae in soybean is controlled by multiple quantitative trait loci (QTL). With traditional QTL mapping approaches, power to detect such QTL, frequently of small effect, can be limited by population size. Joint linkage QTL analysis of nested recombinant inbred line (RIL) populations provides improved power to detect QTL through increased population size, recombination, and allelic diversity. However, uniform development and phenotyping of multiple RIL populations can prove difficult. In this study, the effectiveness of joint linkage QTL analysis was evaluated on combinations of two to six nested RIL populations differing in inbreeding generation, phenotypic assay method, and/or marker set used in genotyping. In comparison to linkage analysis in a single population, identification of QTL by joint linkage analysis was only minimally affected by different phenotypic methods used among populations once phenotypic data were standardized. In contrast, genotyping of populations with only partially overlapping sets of markers had a marked negative effect on QTL detection by joint linkage analysis. In total, 16 genetic regions with QTL for partial resistance against P. sojae were identified, including four novel QTL on chromosomes 4, 9, 12, and 16, as well as significant genotype-by-isolate interactions. Resistance alleles from PI 427106 or PI 427105B contributed to a major QTL on chromosome 18, explaining 10–45 % of the phenotypic variance. This case study provides guidance on the application of joint linkage QTL analysis of data collected from populations with heterogeneous assay conditions and a genetic framework for partial resistance to P. sojae.  相似文献   
259.

Background

Neuroinflammation is a key cascade after cerebral ischemia. Excessive production of proinflammatory mediators in ischemia exacerbates brain injury. Cold-inducible RNA-binding protein (CIRP) is a newly discovered proinflammatory mediator that can be released into the circulation during hemorrhage or septic shock. Here, we examine the involvement of CIRP in brain injury during ischemic stroke.

Methods

Stroke was induced by middle cerebral artery occlusion (MCAO). In vitro hypoxia was conducted in a hypoxia chamber containing 1% oxygen. CIRP and tumor necrosis factor-α (TNF-α) levels were assessed by RT-PCR and Western blot analysis.

Results

CIRP is elevated along with an upregulation of TNF-α expression in mouse brain after MCAO. In CIRP-deficient mice, the brain infarct volume, induction of TNF-α, and activation of microglia are markedly reduced after MCAO. Using microglial BV2 cells, we demonstrate that hypoxia induces the expression, translocation, and release of CIRP, which is associated with an increase of TNF-α levels. Addition of recombinant murine (rm) CIRP directly induces TNF-α release from BV2 cells and such induction is inhibited by neutralizing antisera to CIRP. Moreover, rmCIRP activates the NF-κB signaling pathway in BV2 cells. The conditioned medium from BV2 cells exposed to hypoxia triggers the apoptotic cascade by increasing caspase activity and decreasing Bcl-2 expression in neural SH-SY5Y cells, which is inhibited by antisera to CIRP.

Conclusion

Extracellular CIRP is a detrimental factor in stimulating inflammation to cause neuronal damage in cerebral ischemia.

General significance

Development of an anti-CIRP therapy may benefit patients with brain ischemia.  相似文献   
260.
Alpha-momorcharin (??-MMC) is a ribosome-inactivating protein (RIP) with excellent cytotoxicity to tumor cells. However, its strong immunogenicity and short plasma half-life limit its clinical applications. To overcome this, we have to PEGylated ??-MMC using a branched 20?kDa (mPEG) 2-Lys-NHS. Homogeneous mono-, di- and tri-PEGylated ??-MMCs were synthesized, purified and characterized. In vitro and in vivo analysis indicated that the serial PEG-conjugates preserved moderate anti-tumor activity with 36% acute toxicity and at most 66% immunogenicity decrease. These results suggested the potential application of ??-MMC-PEG conjugates as an anti-tumor agent.  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