全文获取类型
收费全文 | 49687篇 |
免费 | 20583篇 |
国内免费 | 44961篇 |
专业分类
测绘学 | 3673篇 |
大气科学 | 23575篇 |
地球物理 | 16652篇 |
地质学 | 41938篇 |
海洋学 | 17707篇 |
天文学 | 1623篇 |
综合类 | 5965篇 |
自然地理 | 4098篇 |
出版年
2024年 | 247篇 |
2023年 | 624篇 |
2022年 | 1262篇 |
2021年 | 1634篇 |
2020年 | 2663篇 |
2019年 | 5978篇 |
2018年 | 6359篇 |
2017年 | 6042篇 |
2016年 | 6237篇 |
2015年 | 5365篇 |
2014年 | 5072篇 |
2013年 | 5718篇 |
2012年 | 5371篇 |
2011年 | 5177篇 |
2010年 | 5083篇 |
2009年 | 4388篇 |
2008年 | 3549篇 |
2007年 | 3659篇 |
2006年 | 3108篇 |
2005年 | 2992篇 |
2004年 | 3106篇 |
2003年 | 2867篇 |
2002年 | 2580篇 |
2001年 | 2388篇 |
2000年 | 2161篇 |
1999年 | 2465篇 |
1998年 | 2332篇 |
1997年 | 2394篇 |
1996年 | 1966篇 |
1995年 | 1835篇 |
1994年 | 1633篇 |
1993年 | 1556篇 |
1992年 | 1278篇 |
1991年 | 975篇 |
1990年 | 874篇 |
1989年 | 720篇 |
1988年 | 617篇 |
1987年 | 470篇 |
1986年 | 395篇 |
1985年 | 299篇 |
1984年 | 320篇 |
1983年 | 214篇 |
1982年 | 237篇 |
1981年 | 166篇 |
1980年 | 136篇 |
1979年 | 128篇 |
1978年 | 60篇 |
1977年 | 51篇 |
1972年 | 45篇 |
1971年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
The purpose of this work was to reinvestigate the existing hydrogeological conceptual model of the basin of Madrid, Spain. A cumulative chemical isotopic diagram which enabled the distinction between different groups of water as well as calculation of the mode of their blending was used for this investigation. It was found that the groups of discharge were lighter in their isotopic composition than that of recharge. The previous explanation of this fact, backed by carbon-14 dating, was the long residence time due to flow lines going down to depths of more than 1000 m. This flow model assumes homogenous conditions to these depths. This assumption can not be supported by evidence from deep wells. Thus a modified model is suggested which maintains homogenous conditions only to about 300 m and a deep confined aquifer below containing paleowater. The higher degree of depletion of this water has been explained by a colder climate on top of an altitude effect. Another interesting observation was the correlation between the isotopic composition of the rains, the month of the rain event and the composition of the recharge group groundwater. It could be seen that the winter rains resemble the groundwater composition, which shows that practically all the spring and summer rains were evapotranspirated. 相似文献
104.
介绍一种自行设计和加工的直接雾化石墨炉进样装置的结构、工作原理和操作方法。该装置由微机控制与石墨炉加热程序同步工作,可以实现自动控制和自动测量。对雾化进样石墨炉分析的仪器参数和实验条件进行了研究和选择。结果表明,该装置与石墨炉结合具有自动化程度高、重现性好、样品利用率高和分析速度快等特点。 相似文献
105.
106.
107.
Dolmatova L. S. Eliseykina M. G. Timchenko N. F. Kovaleva A. L. Shitkova O. A. 《中国海洋湖沼学报》2003,21(4):293-304
Pure fraction (92%–95%) of phagocytes (FP) and a mixture of amoebocytes (62%) and morula cells (38%)-FPMC- of the holothurianEupentacta fraudatrix' (Holothuroidea, Dendrochirota) were obtained by using ficoll-verographine step gradient. Basal production of reactive oxygen species (ROS) in FP quantified
by using reduction of nitroblue tetrazolium (NBT) was more than twice that in FPMC. Thermostable toxin ofYersinia pseudotuberculosis (TST) at different concentrations (0.2; 0.5; 2.5 μg/ml, but not 0.1 μg/ml) stimulated NBT reduction in FPMC after 24 h incubation.
In FP, TST at concentrations of 0.1 and 0.2 μg/ml inhibited and at concentrations of 0.5 and 2.5 μg/ml stimulated NBT reduction
after 24 h incubation. Maximal effect was observed in FP and FPMC at TST concentrations of 0.5 and 0.2 μg/ml, respectively.
Addition of catalase (0.7 μg/ml) to the cells treated with TST (2.5 μg/ml) was followed by a decrease in NBT reduction compared
to that under toxin treatment alone. TST stimulated superoxide dismutase activity in concentration-dependent manner (maximum
at 0.5 μg/ml concentration in FP) after 24 h treatment, and this stimulation was prevented by a commercial catalase. Plant
lectin concanavalin A stimulated NBT reduction more than 5-fold in FPMC compared to the control. With addition of TST, lectin
stimulated ROS to lesser extent than that with lectin alone. When catalase, TST, and lectin were added into the FPMC simultaneously,
ROS increase was similar to that under lectin treatment alone. On the whole, data obtained indicated that ROS generation in
holothurian coelomocytes especially occurs in both stimulated and not stimulated phagocytes, and that changes in ROS production
by these cells may be one of the mechanisms of antibacterial protection of holothurians.
This work was financially supported by the Russian Foundation for Fundamental Research Grant (No. 00-04-48949). 相似文献
108.
地倾斜台站数字化、模拟观测数据频率特性研究 总被引:2,自引:2,他引:0
分析了四川、云南的部分地倾斜数字化观测与模拟观测资料的特性,从频率范围,周期10天以上的FFT谱特性,固体潮波振幅,相位特征值等方面,论述了地倾斜数字化资料较模拟记录资料的信息组成变化,并对资料的分析与应用进行了初步探讨。 相似文献
109.
1StrongtideandastronomicalconditionsPartial solar eclipse occurred 4 times in 1964, 1982 and 2000 respectively. Time interval is about 3 Saros periods (one Saros period is 18 years and 10.33~11.33 days). Total lunar eclipse occurred 2 times in 1964 and 2000 respectively and 3 times in 1982. However, there was no lunar eclipse in 1966, 1984 and 2002. It seems that they had similar astro-nomical conditions and the best was in 1982. The studies about the effect of tide on the global climate… 相似文献
110.
Himalayan magmatism and porphyry copper–molybdenum mineralization in the Yulong ore belt, East Tibet
Summary ?The NW–SE-trending Yulong porphyry Cu–Mo ore belt, situated in the Sanjiang0 area of eastern Tibet, is approximately 400 km
long and 35 to 70 km wide. Complex tectonic and magmatic processes during the Himalayan epoch have given rise to favorable
conditions for porphyry-type Cu–Mo mineralization.
Porphyry masses of the Himalayan epoch in the Yulong ore belt are distributed in groups along regional NW–SE striking tectonic
lineaments. They were emplaced mainly into Triassic and Lower Permian sedimentary-volcanic rocks. K–Ar und U–Pb isotopic datings
give an intrusion age range of 57–26 Ma. The porphyries are mainly of biotite monzogranitic and biotite syenogranitic compositions.
Geological and geochemical data indicate that the various porphyritic intrusions in the belt had a common or similar magma
source, are metaluminous to peraluminous, Nb–Y–Ba-depleted, I-type granitoids, and belong to the high-K calc-alkaline series.
Within the Yulong subvolcanic belt a number of porphyry stocks bear typical porphyry type Cu–Mo alteration and mineralization.
The most prominent porphyry Co–Mo deposits include Yulong, Malasongduo, Duoxiasongduo, Mangzong and Zhanaga, of which Yulong
is one of the largest porphyry Cu (Mo) deposits in China with approximately 8 × 106 tons of contained Cu metal. Hydrothermal alteration at Yulong developed around a biotite–monzogranitic porphyry stock that
was emplaced within Upper Triassic limestone, siltstone and mudstone. The earliest alteration was due to the effects of contact
metamorphism of the country rocks and alkali metasomatism (potassic alteration) within and around the porphyry body. The alteration
of this stage was accompanied by a small amount of disseminated and veinlet Cu–Mo sulfide mineralization. Later alteration–mineralization
zones form more or less concentric shells around the potassic zone, around which are distributed a phyllic or quartz–sericite–pyrite
zone, a silicification and argillic zone, and a propylitic zone.
Fluid inclusion data indicate that three types of fluids were involved in the alteration–mineralization processes: (1) early
high temperature (660–420 °C) and high salinity (30–51 wt% NaCl equiv) fluids responsible for the potassic alteration and
the earliest disseminated and/or veinlet Cu–Mo sulfide mineralization; (2) intermediate unmixed fluids corresponding to phyllic
alteration and most Cu–Mo sulfide mineralization, with salinities of 30–50 wt% NaCl equiv and homogenization temperatures
of 460–280 °C; and (3) late low to moderate temperature (300–160 °C) and low salinity (6–13 wt% NaCl equiv) fluids responsible
for argillic and propylitic alteration. Hydrogen and oxygen isotopic studies show that the early hydrothermal fluids are of
magmatic origin and were succeeded by increasing amounts of meteoric-derived convective waters. Sulfur isotopes also indicate
a magmatic source for the sulfur in the early sulfide mineralization, with the increasing addition of sedimentary sulfur outward
from the porphyry stock.
Received August 29, 2001; revised version accepted May 1, 2002
Published online: November 29, 2002 相似文献