全文获取类型
收费全文 | 6490篇 |
免费 | 1276篇 |
国内免费 | 1501篇 |
专业分类
测绘学 | 834篇 |
大气科学 | 843篇 |
地球物理 | 1512篇 |
地质学 | 3508篇 |
海洋学 | 1015篇 |
天文学 | 107篇 |
综合类 | 577篇 |
自然地理 | 871篇 |
出版年
2024年 | 58篇 |
2023年 | 215篇 |
2022年 | 231篇 |
2021年 | 238篇 |
2020年 | 214篇 |
2019年 | 300篇 |
2018年 | 283篇 |
2017年 | 179篇 |
2016年 | 174篇 |
2015年 | 254篇 |
2014年 | 357篇 |
2013年 | 324篇 |
2012年 | 387篇 |
2011年 | 368篇 |
2010年 | 345篇 |
2009年 | 322篇 |
2008年 | 320篇 |
2007年 | 328篇 |
2006年 | 362篇 |
2005年 | 331篇 |
2004年 | 303篇 |
2003年 | 269篇 |
2002年 | 265篇 |
2001年 | 244篇 |
2000年 | 258篇 |
1999年 | 167篇 |
1998年 | 154篇 |
1997年 | 160篇 |
1996年 | 157篇 |
1995年 | 120篇 |
1994年 | 113篇 |
1993年 | 131篇 |
1992年 | 132篇 |
1991年 | 143篇 |
1990年 | 137篇 |
1989年 | 119篇 |
1988年 | 90篇 |
1987年 | 94篇 |
1986年 | 80篇 |
1985年 | 65篇 |
1984年 | 65篇 |
1983年 | 64篇 |
1982年 | 54篇 |
1981年 | 31篇 |
1980年 | 44篇 |
1979年 | 14篇 |
1964年 | 13篇 |
1959年 | 20篇 |
1958年 | 20篇 |
1957年 | 22篇 |
排序方式: 共有9267条查询结果,搜索用时 390 毫秒
971.
激电工作使用的电极排列有多种,应根据工作目的、地质条件和需要信息量选其一种进行工作,否则不但得不到预期效果,而且浪费资金。遗憾的是有这种倾向,某种电极排列得到偏爱,不分场合照例使用,对其它电极排列的特点则考虑不多。论述各种电极排列优缺点的文章不多,虽通过模型实验结 相似文献
972.
在勘探工作的各个阶段上(选择初勘对象,将储量划分为表内矿和表外矿,合理地开发已探明的储量)的矿床评价问题,都与矿石工业品位指标的确定有密切的联系.目前,批发价格仍然是确定矿石品位指标的经济依据.根据这个原则,开采能有盈利的储量,即在工业利用的一定期间能回收基建投资的矿产资源,才算作表内矿量.但是经验证明,根据批发价格确定矿石品位指标的做法,往往导致不良的后果.例 相似文献
973.
前言早在1951年,就认识到剩余磁化强度对岩体的磁异常有影响.后来研究结果证明,在测定的地质体磁异常中,剩余磁化强度可以超过感应磁化强度.古地磁测定岩体剩余磁化强度常用的方法,包括在野外采集岩石标本和在室内测定标本的磁化方向.可是在海丘研究中,有些作者指出,其磁化方向可以根据磁异常与测深法所测得的海丘形状和位置进行对比来确定.本文目的在于证明,可以根据地质体重,磁异常的空间关系来确定其磁化方向,从而获 相似文献
974.
扎瓦里茨基法(简称扎氏法,下同)是常用的岩石化学计算方法之一。在计算时过去是靠小型电算器或笔算,这种手算方式在样品数目很多时往往容易出错,且效率低、时间长。近年来虽出现了用ALGOL、BCY语言为扎氏法编写的程序,采用电子计算机运算,但因数据纸带穿孔,造成检查、修改麻烦,而且计算时要到电算站上机,所以不易推广。可是微型电子计算机比其他大、中、小电算机具有使用方便、成本低等优点。当前很多单位都购买了这种微型机,这样就为计算扎氏法提供了条件。一般微型机软件都配有 相似文献
975.
Challenges in global ballast water management 总被引:3,自引:0,他引:3
Endresen Ø Lee Behrens H Brynestad S Bjørn Andersen A Skjong R 《Marine pollution bulletin》2004,48(7-8):615-623
Ballast water management is a complex issue raising the challenge of merging international regulations, ship's specific configurations along with ecological conservation. This complexity is illustrated in this paper by considering ballast water volume, discharge frequency, ship safety and operational issues aligned with regional characteristics to address ecological risk for selected routes. A re-estimation of ballast water volumes gives a global annual level of 3500 Mton. Global ballast water volume discharged into open sea originating from ballast water exchange operations is estimated to approximately 2800 Mton. Risk based decision support systems coupled to databases for different ports and invasive species characteristics and distributions can allow for differentiated treatment levels while maintaining low risk levels. On certain routes, the risk is estimated to be unacceptable and some kind of ballast water treatment or management should be applied. 相似文献
976.
Schmidt H Bich Ha N Pfannkuche J Amann H Kronfeldt HD Kowalewska G 《Marine pollution bulletin》2004,49(3):229-234
The laboratory characterization of a field-operable surface-enhanced Raman scattering sensor (SERS optode) is presented for the detection of aromatic hydrocarbons in seawater. The sensor has been developed for deployment with a robust underwater spectrograph. To meet the demands of the harsh seawater application, sol-gel derived SERS substrates were used. The calibration curves of six PAHs were determined to be of Langmuir adsorption isotherm type with limits of detection ranging from the microg l(-1) to ng l(-1) level. The experimentally determined adsorption constants varied strongly with the molecular weight of the analytes and correlated with their solubility. A mixture of five PAHs dissolved in seawater was investigated to demonstrate the utility of this method for screening. Emphasis was put on the interference from suspended particulate matter (SPM). The Raman measurement with backscattering configuration was shown to be immune against turbidities up to 1000 NTU. The physico-chemical interference arising from adsorption by the sediment was measured on-line by adding sediment to a PAH-spiked solution. According to the calibration curve, the PAH concentration decrease corresponded to more than 98% of the analyte being scavenged by the sediment. 相似文献
977.
978.
Sokołowski A Wołowicz M Hummel H Smolarz-Górska K Fichet D Radenac G Thiriot-Quiévreux C Namieśnik J 《Marine pollution bulletin》2004,49(1-2):17-22
Recent studies of the Baltic clam Macoma balthica (L.) from the southern Baltic (the Gulf of Gdansk) have revealed striking morphological, histological and cytogenetic features. Strong deformation of the shell, including elongation of the posterior end and the appearance of an easily visible flexure in this part, has been recorded. The population contribution of the deformed blunt shelled ("irregular") clams ranged from 0% to 65% and tended to increase with depth. The morphologically "irregular" clams had higher accumulated tissue concentrations of trace metals (As, Ag, Cd, Pb, Cu and Zn), indicating a different metal handling ability. Adverse conditions in deeper water regions of the Gulf (e.g. hypoxia, hydrogen sulphide, elevated bioavailability of contaminants) have been suggested as inducers of the phenotypical changes (morphological deformation) in part of the population and, in parallel, of the specific physiological adaptations that result in higher metal accumulation in the "irregular" clams. Cytogenetic and histological analyses showed the presence of tumours in gill cells and digestive system of the affected clams, the prevalence of disseminated neoplasia ranging from 0% to 94% depending on the site. The disease was manifested by a modified karyotype (i.e. an abnormal number and morphology of chromosomes), a higher activity of nucleolar organizer regions (AgNORs), and tissue lesions (enlarged cells, actively proliferative with pleomorphic nuclei). Bottom sediments showed acute toxicity and have been proposed as a source of an initialising carcinogenic factor. However, none of the ecotoxicological studies provided was successful in the clear demonstration of a single (or multifactorial) agent that can account for the disseminated neoplasia. 相似文献
979.
新疆阔尔真阔腊金矿床成矿流体包裹体研究 总被引:16,自引:1,他引:15
新疆西北部阔尔真阔腊金矿床是产于海西期岛弧型钙碱性火山岩中的火山晚期热液型金矿床。流体包裹体研究表明,成矿阶段(Ⅰ)包裹体为气相包裹体,均一温度为308~396℃,盐度为5.86~8.41wt%NaCl;主成矿阶段(Ⅱ、Ⅲ)为气液包裹体,均一温度分别为209~276℃(Ⅱ)、119~198℃(Ⅲ),盐度分别为5.11~7.86wt%NaCl(Ⅱ)、2.74~6.17wt%NaCl(Ⅲ)。石英流体包裹体成分测定采用分阶段法,有效地排除了不同成矿阶段包裹体成分的影响,准确地测出了成矿阶段(Ⅰ)和主成矿阶段(Ⅱ、Ⅲ)包裹体的成分,结果表明成矿流体具Na^ -H^--Cl^--H2O型中低温、低盐特征,金主要以金硫络合物的形式迁移,金矿化是在还原条件下进行。主成矿阶段包裹体中水的氢同位素组成为-83.97~-89.07‰,氧同位素组成为1.8~3.2‰,成矿流体是岩浆热液与古大气降水混合而成。流体混合及水-岩反应是造成本区金沉淀成矿的主要因素。 相似文献
980.
Rosenberg R Blomqvist M C Nilsson H Cederwall H Dimming A 《Marine pollution bulletin》2004,49(9-10):728-739
The aim of this study is to develop a new method for classification of marine benthic quality according to the European Union Water Framework Directive. Tolerance values to environmental disturbance were determined in an objective analysis for benthic species along the Swedish west coast by using 4676 samples from 257 stations. Based on a combination of the species tolerance values, abundance and diversity, a benthic quality index (BQI) was calculated for the assessment of environmental status at a particular station. The qualification of BQI was evaluated in relation to known spatial and temporal gradients of disturbance. 相似文献