全文获取类型
收费全文 | 4065篇 |
免费 | 925篇 |
国内免费 | 951篇 |
专业分类
测绘学 | 79篇 |
大气科学 | 462篇 |
地球物理 | 2270篇 |
地质学 | 2051篇 |
海洋学 | 575篇 |
天文学 | 72篇 |
综合类 | 113篇 |
自然地理 | 319篇 |
出版年
2024年 | 11篇 |
2023年 | 40篇 |
2022年 | 108篇 |
2021年 | 131篇 |
2020年 | 164篇 |
2019年 | 203篇 |
2018年 | 194篇 |
2017年 | 205篇 |
2016年 | 250篇 |
2015年 | 221篇 |
2014年 | 267篇 |
2013年 | 309篇 |
2012年 | 215篇 |
2011年 | 248篇 |
2010年 | 199篇 |
2009年 | 302篇 |
2008年 | 305篇 |
2007年 | 278篇 |
2006年 | 282篇 |
2005年 | 218篇 |
2004年 | 208篇 |
2003年 | 193篇 |
2002年 | 150篇 |
2001年 | 173篇 |
2000年 | 148篇 |
1999年 | 135篇 |
1998年 | 153篇 |
1997年 | 105篇 |
1996年 | 116篇 |
1995年 | 92篇 |
1994年 | 67篇 |
1993年 | 55篇 |
1992年 | 42篇 |
1991年 | 34篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 20篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有5941条查询结果,搜索用时 15 毫秒
81.
In the process of steam stimulation exploitation of viscous crude oil, the injected water, at high temperature and under high pressure, reacts intensively with the host rock. This kind of water–rock interaction in Liaohe Shuguang Oil Field was studied on the basis of analysis of water composition changes, laboratory experiments, mineral saturation indices analysis, and mass balance calculation. Compared with the injected water, the changes of the composition of discharged water are mainly the distinct decrease of pH, Na+, SiO2 and Cl−, as well as the increase of K+, Ca2+, Mg2+, SO
4
2−
and HCO
3
−
. Laboratory experiments under field conditions showed: the dissolution sequence of minerals quantitatively is quartz>potassium feldspar>albite, and the main change of clay minerals is the conversion of kaolinite to analcime. Mass balance calculation indicated during the process of steam stimulation, large quantities of analcime are precipitated with the dissolution of large amounts of quartz, kaolinite, potassium feldspar, and CO2. These results correlated very well with the experimental results. The calculated results of Liaohe Shuguang Oil Field showed that during the steam stimulation for viscous crude oil, the amounts of minerals dissolved (precipitated) are huge. To control the clogging of pore spaces of oil reservoirs, increased study of water–rock interaction is needed. 相似文献
82.
Mongolian gerbils (Meriones unguiculatus) and Daurian pikas (Ochotona dauurica) are two key small mammal species in the Inner Mongolian grasslands, China. Mongolian gerbils displayed density-dependent population growth, but the time lag of density dependence was short and within season. The spring–autumn population growth rate was inversely related to population density in Mongolian gerbils of the Erdos desert grasslands. The autumn–spring population growth rate of Mongolian gerbils was inversely related to winter precipitation. Precipitation had stronger effects on the population growth of gerbils during the non-breeding season. The monthly population growth rate of Daurian pikas was positively related to the monthly precipitation and was inversely related to population density in central Inner Mongolia. Daurian pikas select habitats with tall plants. Increased precipitation enhances plant production and increases the height of plants in arid and semi-arid regions. This enhancement of plant height might increase the population growth of Daurian pikas. Mongolian gerbils live in short grasslands. Increased winter precipitation might result in higher winter mortality of Mongolia gerbils, or taller plants might supress gerbil population growth in wet years. Therefore, responses of small mammal species to changes in precipitation depend on the life history of small mammals and changes in vegetation induced by climatic changes. 相似文献
83.
84.
In this study, hydrogeologic and hydrochemical information from the Mersin-Erdemli groundwater system were integrated and
used to determine the main factors and mechanisms controlling the chemistry of groundwaters in the area and anthropogenic
factors presently affecting them. The PHREEQC geochemical modeling demonstrated that relatively few phases are required to
derive water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area
fall into four categories: (1) silicate weathering reactions; (2) dissolution of salts; (3) precipitation of calcite, amorphous
silica and kaolinite; (4) ion exchange. As determined by multivariate statistical analysis, anthropogenic factors show seasonality
in the area where most contaminated waters related to fertilizer and fungicide applications that occur during early summer
season. 相似文献
85.
S-S. Xu A. F. Nieto-Samaniego S. A. Alaniz-Álvarez L. G. Velasquillo-Martínez 《International Journal of Earth Sciences》2006,95(5):841-853
The power-law exponent (n) in the equation: D=cL
n
, with D = maximum displacement and L = fault length, would be affected by deviations of fault trace length. (1) Assuming n=1, numerical simulations on the effect of sampling and linkage on fault length and length–displacement relationship are done in this paper. The results show that: (a) uniform relative deviations, which means all faults within a dataset have the same relative deviation, do not affect the value of n; (b) deviations of the fault length due to unresolved fault tip decrease the values of n and the deviations of n increase with the increasing length deviations; (c) fault linkage and observed dimensions either increase or decrease the value of n depending on the distribution of deviations within a dataset; (d) mixed deviations of the fault lengths are either negative or positive and cause the values of n to either decrease or increase; (e) a dataset combined from two or more datasets with different values of c and orders of magnitude also cause the values of n to deviate. (2) Data including 19 datasets and spanning more than eight orders of fault length magnitudes (10−2–105 m) collected from the published literature indicate that the values of n range from 0.55 to 1.5, the average value being 1.0813, and the peak value of n
d (double regression) is 1.0–1.1. Based on above results from the simulations and published data, we propose that the relationship between the maximum displacement and fault length in a single tectonic environment with uniform mechanical properties is linear, and the value of n deviated from 1 is mainly caused by the sampling and linkage effects. 相似文献
86.
《中国地球化学学报》2006,25(B08):127-128
87.
88.
异常形态、分布严格受推覆断裂控制,范围大、浓集中心明显,浓度变化及因子载荷表明。区内找Ag、Pb有利,而Sb又为其最佳指示元素。 相似文献
89.
90.
Sandro Fuzzi Maria Cristina Facchini Stefano Decesari Emanuela Matta Mihaiela Mircea 《Atmospheric Research》2002,64(1-4)
We have recently set up a new procedure for characterising the water soluble organic compounds (WSOC) in fog water, for which information is still rather limited. Fog samples collected during the 1998–1999 fall–winter season in the Po Valley (Italy) were analysed following this procedure, which allows a quantitative determination of three main classes of organic compounds (neutral species, mono- and di-carboxylic acids, polycarboxylic acids), together accounting for ca. 85% of the total WSOC. This procedure also provides information on the main chemical characteristics of these three classes of compounds (functional groups, aliphatic vs. aromatic character, etc.). The enhanced chemical knowledge on fog/cloud chemical composition opens new scenarios as far as chemical and microphysical processes in clouds and fogs are concerned. 相似文献