全文获取类型
收费全文 | 401篇 |
免费 | 34篇 |
国内免费 | 124篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 6篇 |
地球物理 | 35篇 |
地质学 | 38篇 |
海洋学 | 349篇 |
天文学 | 3篇 |
综合类 | 88篇 |
自然地理 | 30篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 15篇 |
2020年 | 22篇 |
2019年 | 14篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 38篇 |
2013年 | 42篇 |
2012年 | 24篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 27篇 |
2008年 | 38篇 |
2007年 | 16篇 |
2006年 | 31篇 |
2005年 | 23篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有559条查询结果,搜索用时 15 毫秒
181.
利用TAIL-PCR(Thermal Asymmetric Interlaced PCR)方法克隆节杆菌A3 ftsq基因序列,基于生物信息学软件分别进行ftsq序列同源性分析、蛋白质FtsQ跨膜域及三级结构预测,初步预测该基因所编码蛋白FtsQ的功能.结果表明:节杆菌A3 ftsq基因全序列1035 bp,编码氨基酸344个;节杆菌A3 ftsq基因与谷氨酸棒状杆菌、结核分枝杆菌和天蓝色链霉菌ftsq亲缘关系比较近,与大肠杆菌、枯草芽孢杆菌、新月柄杆菌和肺炎链球菌亲缘关系比较远;节杆菌蛋白质FtsQ为一次跨膜蛋白,包括膜内域(1-114氨基酸残基)、跨膜域(115-139氨基酸残基)和膜外域(140-344氨基酸残基);空间结构预测节杆菌FtsQ膜内域和跨膜域空间结构缺失.因此,节杆菌A3 FtsQ蛋白与大肠杆菌、枯草芽孢杆菌FtsQ膜内域在长度和空间结构存在显著不同,其膜内域较长,较长的膜内域段可能取代了缺失的FtsA的功能,辅助Z环的锚定和下游蛋白的吸附.当节杆菌A3处于电离、辐射、寒冷等极端环境时,ftsq或许是节杆菌生存的必须基因;当节杆菌处于实验条件温度为20℃,营养充足,ftsq则可能是非必须基因.节杆菌A3 FtsQ在细菌细胞分裂时可能通过与上游蛋白、下游蛋白相互作用,确定细胞分裂位点和速度;同时FtsQ参与合成肽聚糖,一方面,促使细胞内陷皱缩,细胞一分为二;另一方面,FtsQ合成厚厚的细胞壁以适应极端环境的需要. 相似文献
182.
根据刘次全研究员等发现的蛋白质与其编码mRNA二级结构之间可能存在着二级结构单元数目间的对应关系 ,首次尝试参照P53蛋白质N/C末端的编码mRNA二级结构预测P53蛋白质N/C末端相应的二级结构。预测结果显示 ,在P53蛋白质N端 1 -93残基肽段可能存在四个α螺旋结构 (1 4-2 6 ,38-4 6 ,51 -56 ,6 8-70aa)。在P53蛋白质C端单体聚合区以后的区域可能存在另外两个α螺旋 (36 8-373,381 -388aa)。在P53蛋白质N/C端末知二级结构的预测区域内没有发现β层片结构。这些预测结果与法国蛋白质生物和化学研究所 (IBCP)多重序列联配蛋白质二级结构预测方法对照 (其准确率为 73.2 0 %左右 ) ,结果基本一致。在此工作基础上 ,将P53蛋白质N/C端预测的二级结构在SGI-INDIGO2 工作站上分别构建出三维构象模型。与分子生物学研究的资料对照 ,这两个模型较好的解释了P53蛋白质N/C末端特定的生物功能在三维结构上的相应特点。此外 ,在SGI -INDIGO2 工作站上 ,首次选择和利用P53蛋白质突变研究近十年积累的大量资料 ,以及P53蛋白质核心区三维晶体结构数据资料 ,对Arg1 75,Arg 2 49,和Arg 2 48三个P53蛋白质高频率突变点的十种不同的残基替换做了分子动力学研究。结果发现 ,P53蛋白质核心区在经历 1 2 ps的分子动力学过程后 ,其三 相似文献
183.
INTRODUCTIONThemetabolisminfishincludesstandardmetabolism(RS)routinemetabolism(RR),specificdynamicaction(SDA)andactivemetabolism(RA),relatedas: RT=RS RR SDA RAwhereRSisthemetabolismofthefishatrest;RRthemetabolismoftheroutinelyactivefish;SDAthemetabolismofth… 相似文献
184.
Joseph E. Salisbury Douglas Vandemark Christopher W. Hunt Janet W. Campbell Wade R. McGillis William H. McDowell 《Estuarine, Coastal and Shelf Science》2008
The partial pressure of carbon dioxide (pCO2) in estuary-plume systems is related to the internal processes of net organic metabolism and physical mixing, but is also strongly influenced by biogeochemical inputs from the land and ocean. Surface layer pCO2, stimulated fluorescence of chlorophyll (f-chl) and colored organic matter (f-com), and beam attenuation at 660 nm (c-660) were measured during three seasonal surveys of the Kennebec (ME) and Merrimack (MA) estuary-plume systems. These estuaries are both supplied by large New England Rivers and separated by less than 150 km, but significant differences were often observed in the distributions of surface pCO2 and optical variables. High pCO2 concentrations were generally associated with high f-com, while lower pCO2 concentrations were associated with high f-chl and c-660. Using simple regression models, optical measurements were used to estimate chlorophyll and total organic carbon concentrations. Results suggest that labile riverine carbon is responsible for sustaining supersaturated pCO2 conditions and that phytoplankton productivity, likely driven by inputs of riverine dissolved inorganic nitrogen, is responsible for pCO2 undersaturation. Although optical variables are often related to surface pCO2, the results suggest that efforts to retrieve pCO2 in complex waters using optical data may be enhanced using a site-specific, multivariate approach. 相似文献
185.
M. Coleman M.C. Geddes C.N.A. Trotman 《International Journal of Salt Lake Research》1998,7(2):171-180
Parartemia is a genus of brine shrimp endemic to Australia which is related to the more widespread and economically importantArtemia sp. The expression of a multimeric haemoglobin molecule inArtemia is well documented but inParartemia only trace levels of a possible haemoglobin have been observed. In this paper we describe the DNA sequence of a domain of
a haemoglobin molecule inParartemia. The derived amino acid sequence suggests that the possible date of divergence about 85 million years ago of the two genera
predates the divergence of the C and T polymers ofArtemia haemoglobin. This date would correlate with the physical and temporal isolation of Australia in the late Mesozoic. 相似文献
186.
187.
188.
Comparative study on the allergenicity of different Litopenaeus vannamei extract solutions 总被引:1,自引:0,他引:1
WU Lisha LIN Haixin WANG Guoying LU Zongchao CHEN Guanzhi LIN Hong and LI Zhenxing 《中国海洋大学学报(英文版)》2014,13(1):157-162
Allergen extracts are widely used for allergy diagnosis and treatment. The application of shrimp extract is hampered due to the low protein concentration and the inconsistent allergenicity. Extracting solutions are considered to be the primary limiting factor of protein extraction from crustaceans. This study aimed to select an optimal solution for shrimp protein extraction by comparing the allergenicity of different shrimp extracts. The effect of 7 existing or modified extracting solutions were evaluated, including the glycerol-NaCl solution, the glycerol Cocaine's solution, the buffered saline solution, the Cocaine's solution, the Glucose leaching solution, 1 mol L-1 KCl solution, and 0.01 mol L-1 phosphate buffered saline solution with and without dithiothreitolor(DTT). The quantitative(protein concentration) and qualitative parameters(SDS-PAGE protein patterns and immuno-reactivity) were determined using the sodium dodecyl sulfate polyacrylamide gel electrophoresis, enzyme linked immunosorbent assay and immunoblotting assay. Results showed that the 1 mol L-1 KCl solution with DTT was optimal for shrimp protein extraction, which yielded high concentration and allergenicity in the protein extract, including major and minor allergens. The 1 mol L-1 KCl solution with DDT is proposed for preparation of shrimp extract and associated allergy diagnosis, as well as potential applications for other crustaceans. 相似文献
189.
KONG Lingfeng WANG Zhaoping YU Ruihai LI Qi WANG Rucai 《中国海洋大学学报(英文版)》2007,6(4):383-386
The glycogen content and the activities of two key enzymes in glycogen metabolism, glycogen phosphorylase and gly- cogen synthetase, in the gonad of diploid and triploid Pacific oysters (Crassostrea gigas) were compared during maturation. The glycogen content in the gonad of diploids decreased with gametogenesis (by 85.7%), but the glycogen content in the gonad of trip- loids did not vary significantly. Activity of glycogen phosphorylase (GP) in the gonad of diploids decreased with gametogenesis (by 55.5%), while GP activity of triploids did not vary significantly during maturation. Activity of glycogen synthetase (GS) in the gonad of diploids increased slightly with gametogenesis, reaching a peak in June. Activity of GS declined sharply from June to July, which might be due to gonad spawning. GS activity of triploid oysters in spawning time (July and August) was significantly higher than that in other months, which might be explained with a ‘compensating’ mechanism for the higher glycogen content in triploids. 相似文献
190.
【目的】探究不同碳水化合物与蛋白质水平配合饲料对光裸星虫(Sipunculus nudus)稚虫生长及体壁营养成分的影响。【方法】以碳水化合物/蛋白质质量分数分别为39.46%/20.67%(EG1组)、34.97%/24.02%(EG2组)、30.48%/27.37%(EG3组)、25.99%/30.72%(EG4组)和21.50%/34.07%(EG5组)的饲料,饲喂体质量为(2.45±0.40)g的光裸星虫稚虫12周,测定稚虫的生长指标及体壁一般营养成分及氨基酸组成。【结果】随着碳水化合物水平降低、蛋白质水平升高,各饲料组光裸星虫的增重率和特定生长率均呈先升后降的趋势,其中EG2组的增重率和特定生长率显著性高于其余4组(P<0.05);EG2组的存活率显著高于EG3组、EG5组(P<0.05),但与EG1组、EG4组差异不显著(P>0.05);不同碳水化合物蛋白质水平饲料会影响光裸星虫稚虫体壁的水分及其干物质的粗蛋白、粗脂肪、灰分、蛋氨酸、异亮氨酸、缬氨酸、亮氨酸、丙氨酸、天冬氨酸、谷氨酸、酪氨酸和精氨酸的含量(P<0.05),而各组的其他氨基酸含量、必需氨基酸总量、呈味氨基酸总量、氨基酸总量则差异不显著(P>0.05)。【结论】当饲料碳水化合物/蛋白质质量分数为34.97%/24.02%时,光裸星虫增重率和特定生长率最高,且不会影响其体壁的氨基酸总量、必需氨基酸和呈味氨基酸含量。 相似文献