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   400篇
  免费   56篇
  国内免费   118篇
测绘学   43篇
大气科学   69篇
地球物理   100篇
地质学   108篇
海洋学   121篇
天文学   41篇
综合类   36篇
自然地理   56篇
  2024年   1篇
  2023年   4篇
  2022年   8篇
  2021年   10篇
  2020年   11篇
  2019年   19篇
  2018年   13篇
  2017年   15篇
  2016年   18篇
  2015年   29篇
  2014年   37篇
  2013年   37篇
  2012年   35篇
  2011年   18篇
  2010年   17篇
  2009年   34篇
  2008年   39篇
  2007年   30篇
  2006年   26篇
  2005年   27篇
  2004年   18篇
  2003年   11篇
  2002年   22篇
  2001年   7篇
  2000年   10篇
  1999年   17篇
  1998年   14篇
  1997年   9篇
  1996年   6篇
  1995年   7篇
  1994年   3篇
  1993年   3篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1988年   2篇
  1985年   2篇
  1983年   1篇
  1981年   1篇
  1954年   1篇
  1915年   1篇
  1905年   2篇
  1900年   1篇
  1897年   1篇
排序方式: 共有574条查询结果,搜索用时 31 毫秒
1.
26S蛋白酶体是真核生物中一种具有ATP依赖性的蛋白酶复合体,主要通过泛肽途径选择性降解细胞内与代谢调控、细胞周期有关的功能蛋白及异常蛋白,参与多种细胞活动的调控过程。26S蛋白酶体由具有催化活性的20S亚复合体和一个具有调节作用的19S亚复合体组成,其中19S亚复合体中的ATP酶亚基是调节26S蛋白酶体活性的重要组件。本通过简并引物PCR手段,从软体动物合浦珠母贝(Pinctada fucata)中扩增到参与构成19S亚复合体的S4和S7(MSS1)两个亚基的基因片段。这两个基因片段所编码的ATP酶组件包含有Gx4GKT,DEID,SAT和H/QRxGRxxR等26S蛋白酶体ATP酶亚基的共同功能基序。这是首次在软体动物中报道26S蛋白酶体的ATP酶亚基基因序列,为研究软体动物中26S蛋白酶体的结构与功能奠定了分子基础。  相似文献   
2.
Zooplankton sampling has been carried out by the Continuous Plankton Recorder (CPR) survey since the 1930s enabling the study of long-term changes in plankton populations, the elucidation of seasonal patterns of abundance, and more recently providing zooplankton biomass estimates for ecosystem models. Data for zooplankton abundance collected by CPR tows in the Western English Channel (between 1988 and 1998) were compared to vertically integrated samples collected from station L4 off Plymouth, UK. Comparisons were made for locally abundant copepods (including Acartia, Calanus, Para/Pseudocalanus, Centropages, Oithona and Temora) collected by CPR and WP-2 nets. All dominant species recorded at L4 were also common to the CPR data. However, the position of the taxa in the two datasets was not equivalent. Seasonal cycles revealed by CPR data were significantly similar to those recorded throughout the water column at L4 for most taxa. However, absolute levels of abundance differed for the two datasets: abundances were underestimated by CPR samples when compared to those of vertically integrated samples by a factor of between 2 and 35, with the exception of Centropages. The differing mesh sizes (200 and 270 μm) of the WP-2 net and CPR mesh could only partially explain these differences in abundance, implying that the behaviour of individual taxa and their depth in the water column also influenced the abundance recorded.  相似文献   
3.
4.
作者引入 I(L)值完全下半连续映射 ,研究其性质。利用 I(L)值完全下半连续映射定义I(L)值完全诱导空间 ,给出 I(L)值完全诱导空间的拓扑基的表达形式 ,证得两个 I(L)值完全诱导空间的映射是连续映射的充分必要条件 ,并建立了乘积空间的 I(L)值完全诱导空间与 I(L)值完全诱导空间的乘积空间的联系  相似文献   
5.
Satish  Choy 《Marine Ecology》1988,9(3):227-241
Abstract. Routine monthly samples of the commercially important portunid crab Liocarcimtx puber and the sympatric but ecologically separated L. holsatus were collected from the waters and shores around the Gowcr Peninsula, South Wales, between November 1983 and September 1985.
The pubertal moult in L. puber occurred at 38 mm CW (carapace width) (females) and 42 mm CW (males). In L. holsatus this occurred at 17 mm (females) and 18.5 mm CW (males). The median size of ovigcrous females was 49.2 ± 6.7 mm CW in L. puber and 26.5 ± 2.0 mm CW in L. holsatus.
Moulting and copulation occurred between spring and autumn, the moulting period of males being earlier than that of the females. Ovigcrous L. holsatus were recorded throughout the year, with highest proportions between February and April. L. puber were ovigcrous mainly between January and March; none was recorded between September and November. The number of eggs of the wild brood (range: 39,000–280,000 for L. holsatus and 40.000–262.000 for L. puber ) was related to female body size as y = 3.099.51 c0.1126x, r = 0.90, n = 21 and y = 6,335.98 c0.051x, r = 0.88, n = 23, respectively, where y = number of eggs and x = carapace width (mm).
Following successful copulation, females of both species were able to spawn more than once during an intcrmoult period.  相似文献   
6.
刘升发 《台湾海峡》1997,16(2):229-232
本文报道芽腺属吸虫一新种,即矶鲈芽腺吸虫,新种LecithocladiumparapristipomatissP.nov.,虫体大小1.24~1.74×0.25~0.45mm;虫卵18~22×9~12μm。  相似文献   
7.
采用病原分离与鉴定、人工感染试验等方法,在对养殖牙鲆病例进行发病情况、病理变化特征检验的基础上,进行病原学检验。结果表明,此病例属于由弧菌属(VibrioPacini1854)细菌引起的败血感染症。经对12株纯培养菌(HQ010712-1—HQ010712-12)进行形态特征、理化特性等表观分类学指征的检验,选择代表菌株(HQ010712-1株)进行16S rRNA基因的测定与系统发育学分析等,判定为弧菌属的一个新种。将HQ010712-1株送中国典型培养物保藏中心(CCTCC)进行了复核鉴定与分类定名,依据分离地定名为秦皇岛弧菌(Vibrioqinhuangdaorasp.nov.);参考菌株为HQ010712-1。  相似文献   
8.
种植盐地碱蓬修复滨海盐渍土效果的研究   总被引:25,自引:0,他引:25  
利用盐生植物——盐地碱蓬进行天津河口滨海盐碱地的生物修复。通过比较种植盐地碱蓬土壤和对照土壤的电导率、有机质和微生物数量的差异等研究了其修复效果。结果表明,种植区碱蓬根际土壤的电导率与对照土壤相比下降了13%;有机质和总氮与对照土壤相比分别增加43%和18%;根际土壤的微生物数量明显增加,放线菌和真菌分别比对照增加了5倍和16倍。根际微生物优势种群的盐耐受性结果显示,部分根际土壤的优势种群的盐耐受性明显下降,耐盐性较低的微生物种群已成为优势种群。以上结果表明,种植盐地碱蓬对改善滨海盐碱地的生态有明显的效果。  相似文献   
9.
Lateral moraines constructed along west to east sloping outlet glaciers from mountain centred, pre-last glacial maximum (LGM) ice fields of limited extent remain largely preserved in the northern Swedish landscape despite overriding by continental ice sheets, most recently during the last glacial. From field evidence, including geomorphological relationships and a detailed weathering profile including a buried soil, we have identified seven such lateral moraines that were overridden by the expansion and growth of the Fennoscandian ice sheet. Cosmogenic 10Be and 26Al exposure ages of 19 boulders from the crests of these moraines, combined with the field evidence, are correlated to episodes of moraine stabilisation, Pleistocene surface weathering, and glacial overriding. The last deglaciation event dominates the exposure ages, with 10Be and 26Al data derived from 15 moraine boulders indicating regional deglaciation 9600 ± 200 yr ago. This is the most robust numerical age for the final deglaciation of the Fennoscandian ice sheet. The older apparent exposure ages of the remaining boulders (14,600-26,400 yr) can be explained by cosmogenic nuclide inheritance from previous exposure of the moraine crests during the last glacial cycle. Their potential exposure history, based on local glacial chronologies, indicates that the current moraine morphologies formed at the latest during marine oxygen isotope stage 5. Although numerous deglaciation ages were obtained, this study demonstrates that numerical ages need to be treated with caution and assessed in light of the geomorphological evidence indicating moraines are not necessarily formed by the event that dominates the cosmogenic nuclide data.  相似文献   
10.
益母草水苏碱对钉螺生理生化的影响   总被引:1,自引:1,他引:1  
本实验研究了益母草水苏碱对钉螺糖原和总蛋白的生理生化影响:大于0.80g/L益母草水苏碱能够显著降低钉螺体内的糖原含量,减少幅度从11.68%到76.16%;益母草水苏碱也能够在一定程度上降低钉螺体内的蛋白质含量(从5.66%到13.69%),但减少量不及糖原显著;灭螺植物对钉螺的致死作用可能更多与钉螺组织细胞中的能量代谢有关。  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