全文获取类型
收费全文 | 60879篇 |
免费 | 422篇 |
国内免费 | 1128篇 |
专业分类
测绘学 | 2085篇 |
大气科学 | 3659篇 |
地球物理 | 11463篇 |
地质学 | 25841篇 |
海洋学 | 4513篇 |
天文学 | 10333篇 |
综合类 | 2248篇 |
自然地理 | 2287篇 |
出版年
2022年 | 488篇 |
2021年 | 709篇 |
2020年 | 756篇 |
2019年 | 826篇 |
2018年 | 6340篇 |
2017年 | 5458篇 |
2016年 | 4162篇 |
2015年 | 843篇 |
2014年 | 1493篇 |
2013年 | 2058篇 |
2012年 | 2566篇 |
2011年 | 4537篇 |
2010年 | 3752篇 |
2009年 | 4240篇 |
2008年 | 3605篇 |
2007年 | 4279篇 |
2006年 | 1787篇 |
2005年 | 1088篇 |
2004年 | 1211篇 |
2003年 | 1194篇 |
2002年 | 988篇 |
2001年 | 810篇 |
2000年 | 681篇 |
1999年 | 430篇 |
1998年 | 458篇 |
1997年 | 474篇 |
1996年 | 337篇 |
1995年 | 358篇 |
1994年 | 335篇 |
1993年 | 281篇 |
1992年 | 284篇 |
1991年 | 290篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 258篇 |
1987年 | 260篇 |
1986年 | 191篇 |
1985年 | 301篇 |
1984年 | 302篇 |
1983年 | 295篇 |
1982年 | 274篇 |
1981年 | 269篇 |
1980年 | 282篇 |
1979年 | 203篇 |
1978年 | 242篇 |
1977年 | 204篇 |
1976年 | 183篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The Cone-in-Cone Structure and Its Origin 总被引:1,自引:0,他引:1
Morphostructural investigation of carbonate cone-in-cone formations allows to conclude that they belong to self-organizing (dissipative, according to I. Prigogine's terminology) systems of the geological past formed in a thermogradient field at the expense of energy of heat and mass transfer (Prigogine and Stengers, 1984). First, the fluid-convective metasomatic hypothesis unites and reconciles the most well-known hypotheses that previously seemed to be incompatible and transforms them to rather consistent particular cases of a more intricate multistage geological phenomenon. Second, it helps to identify the morphologically and genetically analogous noncarbonate structures that mimic biogenic ones. The probable indicative role of cone-in-cone structure in the mapping of fluid-conducting systems is a consequence of the proposed hypothesis. 相似文献
42.
Astrakhantsev G. P. Minina T. R. Petrova N. A. Poloskov V. N. Rukhovets L. A. 《Water Resources》2003,30(2):209-220
A zoobenthos submodel is included in an ecosystem model. The new model is used to assess the role of zoobenthos in the phosphorus exchange at the water–bed interface, in particular, the phosphorus cycle in the water body ecosystem is described more accurately. The calculated zoobenthos distribution over the bed of a lake can be used in modeling the lake ichthyocenoses. 相似文献
43.
44.
The evolution of views and practical decisions regarding the problem of collecting payment for the use of surface waters with regard to their quality in the former USSR and present-day Ukraine is discussed. A simple and feasible method is proposed for differentitation of regional (basin) rates of payment for the use of surface water in Ukraine with allowance made for its quality assessed based on a system of environmental classifications. 相似文献
45.
46.
47.
The study of REE distribution in the clay fraction of sedimentary rocks from two coalfields made it possible to distinguish
several types of REE distribution, which correlate with their mineral composition. It is shown that the REE fractionation
was related to the mineral reconstruction of the primary clay fraction and some detrital minerals in the course of postsedimentary
transformations of rocks during diagenesis, early catagenesis, and beginning of late catagenesis. These transformations were
governed by several factors, such as the composition of sediments; hydrochemical features of accumulation environment; the
chemical composition, dynamics, and feeding sources of pore solutions; the porosity and permeability of sediments and rocks;
and the content of organic matter and its reaction ability. 相似文献
48.
A 2D finite volume model for bebris flow and its application to events occurred in the Eastern Pyrenees 总被引:1,自引:0,他引:1
V.MEDINA A.BATEMAN M.HüRLIMANN Ph.D student Sediment Transport Research Group Department of Engineering Hydraulic Marine Environmental Engineering Technical University of Catalonia 《国际泥沙研究》2008,23(4):348-360
FLATModel is a 2D finite volume code that contains several original approaches to improve debris-flow simulation. Firstly, FLATModel incorporates a "stop-and-go" technique in each cell to allow continuous collapses and remobilizations of the debris-flow mass. Secondly, flow velocity and consequently yield stress is directly associated with the type of rheology to improve boundary accuracy. Thirdly, a simple approach for entrainment is also included in the model to analyse the effect of basal erosion of debris flows. FLATMODEL was tested at several events that occurred in the Eastern Pyrenees and simulation results indicated that the model can represent rather well the different characteristics observed in the field. 相似文献
49.
Twenty-year temperature and precipitation extremes and their projected future changes are evaluated in an ensemble of climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), updating a similar study based on the CMIP3 ensemble. The projected changes are documented for three radiative forcing scenarios. The performance of the CMIP5 models in simulating 20-year temperature and precipitation extremes is comparable to that of the CMIP3 ensemble. The models simulate late 20th century warm extremes reasonably well, compared to estimates from reanalyses. The model discrepancies in simulating cold extremes are generally larger than those for warm extremes. Simulated late 20th century precipitation extremes are plausible in the extratropics but uncertainty in extreme precipitation in the tropics and subtropics remains very large, both in the models and the observationally-constrained datasets. Consistent with CMIP3 results, CMIP5 cold extremes generally warm faster than warm extremes, mainly in regions where snow and sea-ice retreat with global warming. There are tropical and subtropical regions where warming rates of warm extremes exceed those of cold extremes. Relative changes in the intensity of precipitation extremes generally exceed relative changes in annual mean precipitation. The corresponding waiting times for late 20th century extreme precipitation events are reduced almost everywhere, except for a few subtropical regions. The CMIP5 planetary sensitivity in extreme precipitation is about 6 %/°C, with generally lower values over extratropical land. 相似文献
50.
Diurnal variation of deep cloud systems over the Indian region using INSAT-1B pixel data 总被引:1,自引:0,他引:1
Summary
Among the various time scales of deep clouds, diurnal variation is found to be prominent over the tropics. The present study
examines the diurnal variation in the number and area cover associated with the cloud systems over the tropical Indian region
using INSAT-1B pixel data. Three periods, namely, April–May 1988, July–August 1988, and January–February 1989 are considered.
The dependence of diurnal characteristics on the temperature threshold, life duration and size of cloud systems, and land-sea
contrast has been explored. The diurnal characteristics of cloud systems living for more than a day have been studied for
the first time. It is shown that cloud systems exhibit strong diurnal dependence at the coldest temperature threshold used
(201 K). Also, the diurnal variation is more for larger cloud systems and for longer living systems. In general, more deep
cloud activity is found from the satellite data during the pre-dawn and early morning hours. Precipitation is enhanced during
morning to early noon hours. Further, using data from a recent field experiment, clear evidence of diurnal variation in precipitation
over the Bay of Bengal is also presented.
Received March 20, 2000/Revised October 3, 2000 相似文献