全文获取类型
收费全文 | 463篇 |
免费 | 44篇 |
国内免费 | 225篇 |
专业分类
测绘学 | 92篇 |
大气科学 | 3篇 |
地球物理 | 53篇 |
地质学 | 54篇 |
海洋学 | 379篇 |
综合类 | 116篇 |
自然地理 | 35篇 |
出版年
2024年 | 7篇 |
2023年 | 13篇 |
2022年 | 19篇 |
2021年 | 28篇 |
2020年 | 25篇 |
2019年 | 35篇 |
2018年 | 30篇 |
2017年 | 35篇 |
2016年 | 39篇 |
2015年 | 39篇 |
2014年 | 63篇 |
2013年 | 53篇 |
2012年 | 45篇 |
2011年 | 37篇 |
2010年 | 33篇 |
2009年 | 20篇 |
2008年 | 30篇 |
2007年 | 27篇 |
2006年 | 29篇 |
2005年 | 15篇 |
2004年 | 22篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有732条查询结果,搜索用时 15 毫秒
11.
本研究首先从施氏鲟(Acipenser schrenckii)性腺转录组中获得nanos1(Asnanos1)基因全长c DNA,并对其序列的准确性和特征分别进行PCR验证和生物信息学分析。进一步利用荧光定量RT-PCR技术检测Asnanos1基因在雌、雄施氏鲟的性腺、心脏、鳃、脑、肾、肝脏、脾脏等组织中的表达量。利用荧光定量RT-PCR技术检测Asnanos1基因在雌、雄施氏鲟的性腺、心脏、鳃、脑、肾、肝脏、脾脏等组织中的表达量。结果显示:Asnanos1的c DNA全长为1 389 bp,其中,5′非编码区(UTR)为414 bp,3′UTR为279 bp,ORF为696 bp。该基因共编码231个氨基酸。Asnanos1基因在施氏鲟除心脏以外的各组织中均有表达,在雌、雄鱼的鳃、脑、肾、肝脏、脾脏等组织中表达量无显著差异,但在卵巢中的表达量显著高于其他各组织(P0.05)。所得到的结果可为人工培育全雌施氏鲟苗种提供一些基础资料。 相似文献
12.
利用泥蚶(Tegillarca granosa)铁蛋白原核表达工程菌获得的重组铁蛋白,通过圆二色光谱分析蛋白二级结构,扫描电镜和电感耦合等离子质谱研究重组铁蛋白富集Fe~(2+)、Mn~(2+)、Cd~(2+)、Cr~(3+)、Hg~(2+)、Pb~(2+)和As~(3+)等7种重金属离子的特性,同时探索利用重组铁蛋白修饰丝网印刷电极,设计和制备重组铁蛋白检测Pb~(2+)和Cd~(2+)浓度的电化学生物传感器。结果表明复性成功的铁蛋白多为完整的?-螺旋结构,而复性不成功的蛋白聚集体则多为无规卷曲。重组铁蛋白的直径和形态与富集的离子种类有关。泥蚶铁蛋白对单一金属离子Fe~(2+)和Mn~(2+)的富集凸显优势。对两种混合金属离子的富集大多表现为竞争关系。但重组铁蛋白对Hg~(2+)和As~(3+)混合组的富集量明显高于单一金属离子组的富集量,对Hg~(2+)和As~(3+)混合组的富集表现出协同促进作用。重组铁蛋白传感器对Pb~(2+)和Cd~(2+)溶液的最低检测限为10μg/L。 相似文献
13.
克隆得到缢蛏天然抗性相关巨噬蛋白2(Sc-Nramp2)基因的cDNA全长序列3 681 bp,该基因的开放阅读框有1 776 bp,编码591个氨基酸,预测分子量为65.86 kDa;其结构具有Slc11蛋白家族的典型特征,包括有10个典型的跨膜结构和2个糖基化位点。Sc-Nramp2基因3'-UTR有2个类似于脊椎动物Nramp2中铁反应控制蛋白结合位点;同源性分析表明,Sc-Nramp2和太平洋牡蛎Nramp2-like的同源性最高为71.6%。实时荧光定量PCR结果表明,Sc-Nramp2基因在闭壳肌、外套膜、肝胰腺、斧足、水管和鳃6个组织中均有表达,其中肝胰腺中的表达量最高,其次是鳃,与其他组织均有极显著性差异(P<0.01);注射副溶血弧菌后,肝胰腺中Sc-Nramp2基因的表达量较对照组显著上调(P<0.01),且表达量呈现先上升后下降的趋势,在12 h时达到最大表达量,推测Sc-Nramp2基因参与了缢蛏非特异性免疫应答反应。 相似文献
14.
15.
In crustaceans, the male sexual dif ferentiation and maintenance are specially regulated by androgenic gland(AG). However, little is known about the genes involved in the regulation process.RNA-Seq was performed on AG with ejaculatory duct(AG_ED) and ejaculatory duct(ED) as control in Eriocheir sinensis, one of the most important economic and ?shery crabs with typically sex dimorphism. A total of 925 unigenes were identi?ed as dif ferentially expressed genes(DEGs) and the expression of nine genes randomly selected was con?rmed by qRT-PCR. 667 unigenes were up-regulated in AG_ED, being supposed to be AG preferential genes. Among them, the full length of i nsulin-like androgenic gland factor( IAG) cDNA named as Es-IAG was obtained as a logo gene of AG, which together with the genes i nsulin-like receptor( INR), and s ingle insulin binding domain protein( SIBD), might constitute the sex regulation pathway. Several sex related genes were identi?ed, and their function will have to be investigated. Also,the identi?cation of j uvenile hormone epoxide hydrolase 1( JHEH1), ecdysteroid 22-hydroxylase( DIB) and e cdysone receptor( ECR) preliminarily clari?ed the molecular regulation mechanism of eyestalk-AG-testis axis, which plays important roles in molting and reproduction. The results will enhance our understanding for the molecular basis of the AG involved in male sex regulation in crabs. 相似文献
16.
Thermal impact of typical high‐density residential, industrial, and commercial land uses is a major concern for the health of aquatic life in urban watersheds, especially in smaller, cold, and cool‐water streams. This is the first study of its kind that provides simple easy‐to‐use equations, developed using gene expression programming (GEP) that can guide the assessment and the design of urban stormwater management systems to protect thermally sensitive receiving streams. We developed 3 GEP models using data collected during 3 years (2009–2011) from 4 urban catchments; the first GEP model predicts event mean temperature at the inlet of the pond; the second model predicts the stormwater temperature at the outlet of the pond; and the third model predicts the temperature of the stormwater after flowing through a cooling trench and before discharging to the receiving stream. The new models have high correlation coefficients of 0.90–0.94 and low prediction uncertainty of less than 4% of the median value of the predicted runoff temperatures. Sensitivity analysis shows that climatic factors have the highest influence on the thermal enrichment followed by the catchment characteristics and the key design variables of the stormwater pond and the cooling trench. The general method presented here is easily transferable to other regions of the world (but not necessarily the exact equations developed here); also through sensitivity and parametric analysis, we gained insight on the key factors and their relative importance in modelling thermal enrichment of urban stromwater runoff. 相似文献
17.
Over the past few decades, earthquake engineering research mainly focused on the effects of strong seismicshaking. After the 1999 earthquakes in Turkey and Taiwan, and thanks to numerous cases where fault rupture causedsubstantial damage to structures, the importance of faulting-induced deformation has re-emerged. This paper, along withits companion (Part Ⅱ), exploits parametric results of finite element analyses and centrifuge model testing in developing afour-step semi-analytical approach for analysis of dip-slip (normal and thrust) fault rupture propagation through sand, itsemergence on the ground surface, and its interaction with raft foundations. The present paper (Part Ⅰ) focuses on the effectsof faulting in the absence of a structure (i.e., in the free-field). The semi-analytical approach comprises two-steps: the firstdeals with the rupture path and the estimation of the location of fault outcropping, and the second with the tectonically-induced displacement profile at the ground surface. In both cases, simple mechanical analogues are used to derive simplifiedsemi-analytical expressions. Centrifuge model test data, in combination with parametric results from nonlinear finite elementanalyses, are utilized for model calibration. The derived semi-analytical expressions are shown to compare reasonably wellwith more rigorous experimental and theoretical data, thus providing a useful tool for a first estimation of near-fault seismichazard. 相似文献
18.
19.
20.
Wiesław Wiśniewolski Janusz Górczyński Wiesław Madry 《Aquatic Sciences - Research Across Boundaries》1989,51(3):249-259
Width of the first ray of the pectoral fin has been measured in two places for 154 young and 89 adult wels. Statistical relationships between the above characters and fish length as well as its maturity and sex have been proved. Three models of discriminant function for identification of adult fish sex have been derived and verified. The accuracy of sex separation has been 89,5% in a standard sample of wels, and 90,6% in a routine sample, after an adjustment in the procedure. 相似文献