全文获取类型
收费全文 | 61613篇 |
免费 | 973篇 |
国内免费 | 439篇 |
专业分类
测绘学 | 1302篇 |
大气科学 | 4071篇 |
地球物理 | 12053篇 |
地质学 | 22063篇 |
海洋学 | 5849篇 |
天文学 | 14178篇 |
综合类 | 110篇 |
自然地理 | 3399篇 |
出版年
2022年 | 390篇 |
2021年 | 733篇 |
2020年 | 728篇 |
2019年 | 844篇 |
2018年 | 1727篇 |
2017年 | 1549篇 |
2016年 | 1836篇 |
2015年 | 940篇 |
2014年 | 1675篇 |
2013年 | 3214篇 |
2012年 | 1920篇 |
2011年 | 2579篇 |
2010年 | 2363篇 |
2009年 | 3048篇 |
2008年 | 2561篇 |
2007年 | 2772篇 |
2006年 | 2491篇 |
2005年 | 1799篇 |
2004年 | 1750篇 |
2003年 | 1697篇 |
2002年 | 1676篇 |
2001年 | 1497篇 |
2000年 | 1355篇 |
1999年 | 1112篇 |
1998年 | 1116篇 |
1997年 | 1119篇 |
1996年 | 905篇 |
1995年 | 889篇 |
1994年 | 836篇 |
1993年 | 737篇 |
1992年 | 720篇 |
1991年 | 672篇 |
1990年 | 688篇 |
1989年 | 687篇 |
1988年 | 625篇 |
1987年 | 739篇 |
1986年 | 654篇 |
1985年 | 813篇 |
1984年 | 855篇 |
1983年 | 795篇 |
1982年 | 715篇 |
1981年 | 751篇 |
1980年 | 645篇 |
1979年 | 629篇 |
1978年 | 600篇 |
1977年 | 580篇 |
1976年 | 516篇 |
1975年 | 519篇 |
1974年 | 496篇 |
1973年 | 542篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
361.
362.
An automatic sample changer based upon a commercially available 20-port rotary valve has been developed for use in automated seawater nutrient analyses. All parts exposed to seawater are of stainless steel, Teflon®, or Kel-F®. The sampler has proven to be rugged and efficient in both shore and shipboard laboratories. 相似文献
363.
Mindhola River estuary, which receives industrial waste containing high concentrations of fluoride, and Purna River estuary, which is free from fluoride contamination, have been investigated. While fluoride behaved conservatively in Purna River estuary, significant deviation from the theoretical dilution line (TDL) in the chlorinity range 0·5–8‰ was observed in Mindhola River estuary due to the externally added fluoride which largely remained in solution. The excess of fluroide over the theoretically calculated value was at a maximum around a chlorinity of 3‰. High natural fluoride content of the river waters resulted in F/Cl ratios exceeding 300 × 10−5 at low chlorinities. The ratio decreased rapidly with increasing chlorinity and the value near to that of seawater was observed at chlorinities above 14‰. 相似文献
364.
Samples were studied from each color change along six gravity cores from nearshore to deep-sea areas in the Gulf of Mexico. Analytical methods and techniques used to characterize the sediments were X-ray diffraction, differential thermal analysis, cation exchange capacity, particle size distribution and fractionation of the clay-size material with the supercentrifuge. 相似文献
365.
A simple sand trap is used to measure swash and backwash bedload transport rates on intertidal profiles. Data from sixty-eight beach experiments are used to calculate a mean value of 12.78 kg m?4s?2 for the calibration coefficient in the Bagnold beach equation. 相似文献
366.
Yurii D. Shuisky 《Marine Geology》1989,90(4):289-296
With the very extensive coastline in the north and northeast and the relatively shorter coastlines in the south, cheniers in the USSR can occur in a great variety of climatological conditions ranging from subarctic to subtropical. Cheniers in the USSR have been studied since approximately 1900, the investigations being mainly concerned with the palaeogeographical aspects. Since the 1960's, investigations have focussed on contemporary morphodynamics. Chenier formation appears to depend largely on the relative influence that marine and fluvial factors have on the formation of marginal deltaic plains. Research in this field is briefly reviewed. 相似文献
367.
Descriptive Analysis and Classification of Benthic Communities in Some Mediterranean Coastal Lagoons (Central Italy) 总被引:3,自引:0,他引:3
Abstract. Benthic samples were taken seasonally at 32 stations in five coastal lagoons of Central Italy (Fogliano, Monaci, Caprolace, Fondi, and Lungo) during a two-year period (1982–1984). Composition and distribution of benthic populations in each lagoon as well as seasonal trends of species richness, density, diversity, and redundancy are presented and discussed.
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
368.
Extensive surveys were made to establish the concentrations of several metals (Zn, Cd, Pb, Cu and Hg) in various marine organisms from different parts of the Adriatic Sea in the period from 1979 to 1985. The results obtained are based on analyses which were performed in conjunction with carefully tested procedures. Proper sampling, sample storage, treatment of samples and final analytical determination has excluded artefacts which would influence the accuracy, or cause contamination and/or trace metal losses.The metal concentrations in shellfish from the coastal areas of the Adriatic Sea are in the range of the lowest values obtained for similar organisms from other localities throughout the Mediterranean Sea. Special attention has been paid to the anthropogenic influence on trace metal concentrations in organisms living in the vicinity of domestic sewage and/or industrial waste-water outflows. 相似文献
369.
The paper deals with a numerical integrated procedure to calculate the effects of the interaction between sea waves and a tripod-type steel gravity platform. The main aspects to be taken into account for a reliable wave loading analysis of such a new type of platform are emphasized. Among them, the field perturbation effect due to the large bodies presence is analysed. Finally, some principal results in terms of structure global loads obtained by the numerical integrated procedure are presented. 相似文献
370.