全文获取类型
收费全文 | 26407篇 |
免费 | 389篇 |
国内免费 | 220篇 |
专业分类
测绘学 | 537篇 |
大气科学 | 1959篇 |
地球物理 | 5334篇 |
地质学 | 9184篇 |
海洋学 | 2119篇 |
天文学 | 6130篇 |
综合类 | 54篇 |
自然地理 | 1699篇 |
出版年
2021年 | 172篇 |
2020年 | 207篇 |
2019年 | 222篇 |
2018年 | 518篇 |
2017年 | 478篇 |
2016年 | 588篇 |
2015年 | 464篇 |
2014年 | 634篇 |
2013年 | 1232篇 |
2012年 | 752篇 |
2011年 | 1046篇 |
2010年 | 892篇 |
2009年 | 1241篇 |
2008年 | 1068篇 |
2007年 | 1075篇 |
2006年 | 992篇 |
2005年 | 828篇 |
2004年 | 847篇 |
2003年 | 808篇 |
2002年 | 749篇 |
2001年 | 696篇 |
2000年 | 643篇 |
1999年 | 575篇 |
1998年 | 586篇 |
1997年 | 578篇 |
1996年 | 440篇 |
1995年 | 423篇 |
1994年 | 383篇 |
1993年 | 336篇 |
1992年 | 314篇 |
1991年 | 278篇 |
1990年 | 305篇 |
1989年 | 290篇 |
1988年 | 236篇 |
1987年 | 321篇 |
1986年 | 260篇 |
1985年 | 349篇 |
1984年 | 385篇 |
1983年 | 375篇 |
1982年 | 338篇 |
1981年 | 315篇 |
1980年 | 312篇 |
1979年 | 286篇 |
1978年 | 312篇 |
1977年 | 263篇 |
1976年 | 269篇 |
1975年 | 275篇 |
1974年 | 234篇 |
1973年 | 239篇 |
1972年 | 158篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A mechanically-actuated locking-compass was designed for mounting on corers to record equipment orientation during the sampling process, thereby providing magnetic orientation data on the recovered deep-sea core. Locking occurs upon impact by the corer with the sea-floor; after retrieval, the device is easily unlocked and reset for another station. Compass construction makes use of commercially available parts, requires no welding and little machining, and thus allows inexpensive and easy assembly at sea. 相似文献
992.
R.F. Lee B. Dornseif F. Gonsoulin K. Tenore R. Hanson 《Marine environmental research》1981,5(2):125-143
Addition of a heavy oil to a Spartina salt marsh in the autumn resulted in high concentrations of polycyclic aromatic hydrocarbons in sediment and benthic animals. The highest concentrations of phenanthrene, chrysene and fluoranthene in the sediment were 112, 105 and 75 ng/g sediment, respectively. These concentrations rapidly decreased during the 20 week period following the spill. The times for these hydrocarbons to decrease to 50% of their highest values, i.e. half-life, were approximately 100, 70 and 30 days in sediment, mussels and oysters, respectively. Benthic macrofauna species showed three responses to oil addition which included no change, an increase, or a decrease in the population. No changes were noted in populations of fiddler crabs (Uca pugnax), oysters (Crassostrea virginica), and mussels (Modiolus demissus). Mud snails (Nassarius obsoleta) increased in density after the spill due to immigration of adult snails from untreated areas to scavenge on animals killed by the oil. Many of the adult periwinkles (Littorina irrorata) were killed by the oil. In the spring, juvenile periwinkles recolonised to oiled areas as a result of larvae settling. 相似文献
993.
G.F. Humphrey 《Marine Policy》1981,5(3):270-271
The deliberations at UNCLOS have been watched with great interest by individual marine scientists and by those who have attended as observers on behalf of scientific groups. Most of all these scientists have been apprehensive that their ability (freedom) to carry out research would be significantly limited by many of the provisions of the ICNT. In fact, one author goes as far as to state that progress has been made, largely at the expense of the marine research scientist1. 相似文献
994.
The currents and surface level oscillations in the Sea of Azov ensuing from contraction of the mouth of Taganrog Bay are computed using the grid technique on the basis of a numerical solution to the system of quasi-linear, degenerate, parabolic, partial derivative equations (shallow-water equations). It is demonstrated what changes are to be expected in the dynamics of the Sea of Azov should this project be realized. The computations were carried out for typical wind directions.Translated by Vladimir A. Puchkin. 相似文献
995.
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
996.
Abstract. The oxygen consumption of Eudendrium glomeratum was measured monthly, throughout the period of active presence of the species in the field, to obtain indications on its physiological condition in the different phases of the cycle. Sets of one hundred polyps were assayed in the laboratory under normothermic (according to field temperature: 14–19°C) and hyperthermic conditions (22–25°C). The different response to identical temperatures at the extremes of the cycle, together with a differential ability to face stressful conditions in the same periods, suggests that other factors, besides temperature, regulate the seasonal cycle of Eudendrium glomeratum. 相似文献
997.
Abstract. The proximate composition of the various components of Posidonia oceanica is given in terms of gravimetric and energetic level and amount of plants from 2 depths at Port-Cros (Var. France). The level of proximate constituents differed little between the leaves (regardless of age) and the roots, but the rhizome contained much more soluble carbohydrate and less structural carbohydrate and ash. Because of this, the energy level in the leaves was more in terms of organic material and less in terms of total material than the energy level in the rhizome. The leaves of a P. oceanica shoot at 2 m depth in July contained 1.6 g organic material. 29.0 kJ. The weight and energy of the soluble carbohydrate in the rhizome from the base of the leaves to the 18th sheath scale decreased by ca. 40% from October to March and increased by ca. 100% from March to July. 相似文献
998.
Kazufumi Takayanagi George T. F. Wong Margaret J. Filardo 《Journal of Oceanography》1989,45(2):129-133
Nitrate reductase activity and the concentrations of selenite and selenate were monitored for six months at the mouth of Chesapeake Bay (USA). A positive correlation was found between nitrate reductase activity and the concentration of selenite, suggesting that selenite may be formed in coastal waters and nitrate reductase may be involved in the process. 相似文献
999.
The radiometers on board the satellites ERS-1, TOPEX/Poseidon, ERS-2, GFO, Jason-1, and Envisat measure brightness temperatures at two or three different frequencies to determine the total columnal water vapor content and wet tropospheric path delay, a major correction to the altimeter range measurements. In order to asses the long-term stability of the path delay, the radiometers are calibrated against vicarious cold and hot references, against each other, and against several atmospheric models. Four of these radiometers exhibit significant drifts in at least one of the channels, resulting in yet unmodeled errors in path delay of up to 1 mm/year, thus limiting the accuracy at which global sea level rise can be inferred from the altimeter range measurements. 相似文献
1000.
Sylvie Labroue Philippe Gaspar Joel Dorandeu Oz Zanif F. Mertz Patrick Vincent Denis Choquet 《Marine Geodesy》2004,27(3):453-481
The Jason-1 sea state bias (SSB) is analyzed in depth from the first year of GDR products. Compared to previous missions, this work benefits from two aspects of the empirical determination of the SSB from the altimetric data themselves. First, from a methodological point of view, a nonparametric technique (NP) has been developed and largely tested on TOPEX/Poseidon 1, GFO and Envisat data. The NP estimator has proven to be a useful tool in the SSB estimation, and it is now mature enough to be used for a refined analysis. On the other hand, the SSB can be extracted from three different data sets (crossovers, collinear data, and residuals) with different characteristics. It is then possible to cross calibrate various estimations of the SSB models and to determine the most accurate one. A systematic comparison is made between these different estimates for the Jason-1 altimeter. The collinear and crossover data sets yield very similar estimates despite their difference of spatial and temporal distributions. These SSB models assure consistency with the TOPEX mission when comparing Jason-1 and TOPEX residuals during the tandem phase. Thanks to the present work, the impact of the short wavelengths filtering on the SSB estimation is evidenced. More generally, our understanding of potential errors affecting the sea surface height and their impact onto the SSB estimation is also improved. 相似文献