全文获取类型
收费全文 | 49376篇 |
免费 | 485篇 |
国内免费 | 329篇 |
专业分类
测绘学 | 1300篇 |
大气科学 | 3631篇 |
地球物理 | 9274篇 |
地质学 | 20671篇 |
海洋学 | 3590篇 |
天文学 | 9233篇 |
综合类 | 189篇 |
自然地理 | 2302篇 |
出版年
2020年 | 137篇 |
2019年 | 129篇 |
2018年 | 3497篇 |
2017年 | 3307篇 |
2016年 | 2108篇 |
2015年 | 426篇 |
2014年 | 450篇 |
2013年 | 1181篇 |
2012年 | 1670篇 |
2011年 | 3602篇 |
2010年 | 3360篇 |
2009年 | 3633篇 |
2008年 | 2949篇 |
2007年 | 3599篇 |
2006年 | 875篇 |
2005年 | 1240篇 |
2004年 | 1129篇 |
2003年 | 1181篇 |
2002年 | 976篇 |
2001年 | 621篇 |
2000年 | 638篇 |
1999年 | 575篇 |
1998年 | 552篇 |
1997年 | 563篇 |
1996年 | 461篇 |
1995年 | 463篇 |
1994年 | 442篇 |
1993年 | 410篇 |
1992年 | 380篇 |
1991年 | 327篇 |
1990年 | 379篇 |
1989年 | 296篇 |
1988年 | 341篇 |
1987年 | 377篇 |
1986年 | 326篇 |
1985年 | 481篇 |
1984年 | 523篇 |
1983年 | 529篇 |
1982年 | 422篇 |
1981年 | 432篇 |
1980年 | 456篇 |
1979年 | 382篇 |
1978年 | 396篇 |
1977年 | 346篇 |
1976年 | 382篇 |
1975年 | 341篇 |
1974年 | 382篇 |
1973年 | 366篇 |
1972年 | 233篇 |
1971年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
431.
432.
433.
The influence of salinity on the solubility of Zn and Cd sulphides in the Scheldt estuary 总被引:2,自引:0,他引:2
In the estuary of the river Scheldt, where an oxygen gradient exists in addition to the salinity gradient, redox processes will be of major importance for trace metal mobilisation. In this study, the influence of salinity and pH on the redox processes of dissolved Zn and Cd sulphides is investigated together with the effects on the ratio of the dissolved Zn and Cd concentrations. The speciation of these metals is calculated with the chemical equilibrium programme
+. Zn sulphides are oxidised at lower oxygen concentrations than Cd sulphides, due to lower stability constants, causing a sudden increase or peak in the dissolved Zn/Cd ratio. The formation of dissolved Cd chloride complexes when oxidation occurs at high salinities (S=15) increases the mobility of Cd, causing a decrease in the Zn/Cd peak of the total dissolved concentrations. The peak is three to four times smaller at S=15 than when oxidation occurs at S=2. The simple model calculations compare very well with field data. The Scheldt estuary is suitable to illustrate these calculations. In the 1970s, the anoxic part of the estuary reached S=15–20, but since the early 1980s it has dropped to S=2–10. Historic data on metals in the estuary from 1978, 1987 and the 1990s were used to compare with the equilibrium calculations. The increase of the dissolved Zn/Cd peak at low salinity as a consequence, of the decreasing anoxic region is confirmed well by the data. The good agreement between model calculations and field data is a proof of the extreme importance of redox processes for the solubility of Zn and Cd sulphides in the estuary. 相似文献
434.
We perform the analysis of the time spectra of four tsunamis generated in the Black Sea by the earthquakes of 26.07.1927,
11.09.1927, 26.12.1939, and 12.07.1966. For the analysis of the spectra, we used digitized marigrams obtained for 12 points
of the Black-Sea coast. The obtained spectra are, as a rule, multimode and have 1–4 spectral maxima. One maximum corresponds
to the periods typical of tsunami waves and the other maxima correspond to the oscillations of the sea level with lower frequencies.
It seems likely that the events of tsunami are accompanied by low-frequency oscillations of the level caused by the atmospheric
forcing, seiches, or other factors. In numerous cases, the oscillations from the predominant energy range lie outside the
characteristic range of periods of the tsunami waves.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 21–30, September–October, 2007. 相似文献
435.
A global survey of the distribution of dissolved CO2 taking advantage of sampling opportunities provided by the World Ocean Circulation Experiment: World Hydrographic Program (WOCE-WHP) is being carried out through 1995. Goals include the measurement of oceanic inorganic carbon transport and the development of a data base from which future fossil-fuel CO2 build-up can be monitored. The analytical method selected for total carbon dioxide (CT) is gas extraction of acidified seawater with coulometric titration of the acid formed by the resultant carbon dioxide and monoethanolamine. To combine high accuracy and precision (± 1.5 μmol/kg for CT ≥ 2000 μmol/kg) with a high rate of analysis, we have modified an automated single-parameter system. Following prototype development between 1987 and 1990, an instrument emerged with the acronym Somma standing for single-operator multiparameter metabolic analyzer. Improved functional and operating procedures have integrated electronic calibration, CO2 gas calibration, and sample analysis with automated pressure, temperature, and conductivity (salinity) sensing into a single convenient transportable package. 相似文献
436.
James W. Murray Robert Leborgnelt Yves Dandonneau 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)
This special issue is the third and final volume containing results from the JGOFS Process Study in the equatorial Pacific. Most of the Study in the equational Pacific. Most of the contributions evolved either from the US JGOFS workshop in 1994 on the equatorial Pacific in Scottsdale, AZ or from the NATO Advanced Research Workshop on the Carbon Cycle of the Equatorial Pacific in 1995 in Noumea, New Caledonia. 相似文献
437.
438.
Three data sets of suspensate concentrations, collected under different sampling plans, were analyzed to develop a minimal sampling period, consistent with a predetermined precision. Individual samples collected during any part of a given day were within ±50% of the daily average. In the main channel of the estuary, a monthly sampling scheme closely approximated a weekly pattern; however, seasonal sampling was unsatisfactory. Outside the main channel, weekly, monthly, and seasonal sampling patterns did not differ greatly. Variability in suspensate concentrations must be considered when calculating sediment flux in estuarine and coastal waters. 相似文献
439.
We study the processes of global self-regulation of Earth’s biota (GAIA-theory) by applying the method of adaptive balance of causes proposed by the authors. By using, as an example, the Daisy World model constructed by this method, we reveal the phenomenon of preservation of the mean temperature of Earth’s surface due
to the presence of the vegetation cover. We develop an integral model of global natural, social, and economic processes in
which the World Ocean is one of the factors regulating the amount of greenhouse gases in the atmosphere. The decrease in the
amount of greenhouse gases in the atmosphere caused by the GAIA-effects increases the number of hurricanes and floods on the Earth. As a result, the levels of ecological and social hazards
for the mankind become much higher. To eliminate these threats, it is necessary to intensify the processes of self-organization
of the society realized via the improvement of education, development of science, and global regulation of the competition
for natural resources. We present the results of numerical experiments performed by using the model demonstrating possible
scenarios of global development with regard for the processes of self-organization of the society.
__________
Translated From Morskoi Gidrofizicheskii Zhurnal, No. 3, Pp. 62–80, May–June, 2007. 相似文献
440.