全文获取类型
收费全文 | 32364篇 |
免费 | 1652篇 |
国内免费 | 3091篇 |
专业分类
测绘学 | 2144篇 |
大气科学 | 3568篇 |
地球物理 | 6447篇 |
地质学 | 15687篇 |
海洋学 | 2173篇 |
天文学 | 1960篇 |
综合类 | 2809篇 |
自然地理 | 2319篇 |
出版年
2024年 | 30篇 |
2023年 | 123篇 |
2022年 | 273篇 |
2021年 | 369篇 |
2020年 | 256篇 |
2019年 | 365篇 |
2018年 | 5069篇 |
2017年 | 4301篇 |
2016年 | 2959篇 |
2015年 | 652篇 |
2014年 | 560篇 |
2013年 | 538篇 |
2012年 | 1530篇 |
2011年 | 3255篇 |
2010年 | 2490篇 |
2009年 | 2818篇 |
2008年 | 2360篇 |
2007年 | 2834篇 |
2006年 | 489篇 |
2005年 | 627篇 |
2004年 | 776篇 |
2003年 | 713篇 |
2002年 | 689篇 |
2001年 | 444篇 |
2000年 | 416篇 |
1999年 | 384篇 |
1998年 | 264篇 |
1997年 | 253篇 |
1996年 | 197篇 |
1995年 | 176篇 |
1994年 | 177篇 |
1993年 | 128篇 |
1992年 | 106篇 |
1991年 | 74篇 |
1990年 | 80篇 |
1989年 | 47篇 |
1988年 | 55篇 |
1987年 | 39篇 |
1986年 | 27篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 21篇 |
1981年 | 34篇 |
1980年 | 29篇 |
1979年 | 5篇 |
1976年 | 8篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1958年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Corrosion behavior of steel in the juncture area of sea clay and sand was studied. The results show that galvanic corrosion occurred between steel samples buried in sea clay and sand, and that the polarity of the galvanic cell reversed after some testing later. The cause of reversing of polarity is discussed. 相似文献
32.
We have studied the optical historical light curves of two Active Galactic Nuclei (AGNs): OJ287 and 3C345. We find a linear
dependence between the magnitude and the logarithm of the length of the time the objects stay below this magnitude. The relation
may originate from a fractal structure of the light curve.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
33.
Ken Ebisawa Aya Kubota Tsunefumi Mizuno Piotr Życki 《Astrophysics and Space Science》2001,276(1):11-14
The Ultra-luminous Compact X-ray Sources (ULXs)in nearby spiral galaxies and the Galactic super-luminaljet sources sharethe common spectral characteristic that they haveextremely high disk temperatures which cannot be explainedin the framework of the standard accretion disk modelin the Schwarzschild metric. We have calculated an extreme Kerr disk model to examine if the Kerr disk model can instead explain the observed `too hot' accretion disk spectra.We found that the Kerr disk spectrum becomes significantly hardercompared to the Schwarzschild disk only when the disk is highlyinclined.For super-luminal jet sources, which are known to beinclined systems, the Kerr disk model may thuswork if we choose proper values for the black hole angular momentum. For the ULXs, however, the Kerr disk interpretation will be problematic,as is is highly unlikely that their accretion disks are preferentiallyinclined. 相似文献
34.
在20℃、4℃、-10℃、-20℃四种温度下贮藏马面卵巢,对其中磷脂含量的变化进行了测定,并利用薄层层析分析测定了不同温度下贮存3d后马面卵巢中磷脂各组分的相对百分比。结果表明马面卵巢中磷脂的损失率随贮藏温度的上升而增加;在不同温度下贮藏3d,磷脂各组分的相对百分比都发生了变化;随贮藏温度的升高磷脂酰胆碱的降解速度大大加快,所占的百分比快速下降,而溶血磷脂酰胆碱的比例有不同程度的增加。相对而言,-20℃下贮藏数天,磷脂的含量及组分的变化较小。 相似文献
35.
Hong Lin Zhang Douglas H. Sampson 《Monthly notices of the Royal Astronomical Society》2001,322(3):433-437
Calculations are made of the resonance contribution to electron-impact excitation of H-like 13 C and Li-like 23 Na, 25 Mg, 27 Al and 29 Si to the upper hyperfine levels that produce millimetre (mm) lines of likely astrophysical interest. The resonance contribution is found to be very important for these Li-like ions, considerably more important than for Li-like 57 Fe considered previously. However, resonances are found to be rather unimportant for H-like 13 C. The effect of radiative decay on the resonance contribution is found to be insignificant in all of the present calculations. 相似文献
36.
37.
CLIMATICTRENDINDICATEDBYVARIATIONSOFGLACIERSANDLAKESINTHETIANSHANMOUNTAINS¥HuRuji;YangChuande;MaHong;JiangFengqing(XinjiangIn... 相似文献
38.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
39.
Simulation of double cold cores of the 35°N section in the Yellow Sea with a wave-tide-circulation coupled model 总被引:1,自引:0,他引:1
Based on the MASNUM wave-tide-circulation coupled numerical model, the temperature structure along 35°N in the Yellow Sea
was simulated and compared with the observations. One of the notable features of the temperature structure along 35°N section
is the double cold cores phenomena during spring and summer. The double cold cores refer to the two cold water centers located
near 122°E and 125°E from the depth of 30m to bottom. The formation, maintenance and disappearance of the double cold cores
are discussed. At least two reasons make the temperature in the center (near 123°E) of the section higher than that near the
west and east shores in winter. One reason is that the water there is deeper than the west and east sides so its heat content
is higher. The other is invasion of the warm water brought by the Yellow Sea Warm Current (YSWC) during winter. This temperature
pattern of the lower layer (from 30m to bottom) is maintained through spring and summer when the upper layer (0 to 30m) is
heated and strong thermocline is formed. Large zonal span of the 35°N section (about 600 km) makes the cold cores have more
opportunity to survive. The double cold cores phenomena disappears in early autumn when the west cold core vanishes first
with the dropping of the thermocline position.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献
40.
Technique for Controlling Spread of Limnotic Oncomelania 总被引:1,自引:0,他引:1
Schistosomiasis is a parasitic disease mostly found in areas along the Changjiang River of China. The disease is spread solely through an intermediary named oncomelania, so its spread of schistosomiasis can be controlled by properly designing water intakes which prevent oncomelania from entering farming land or residential areas. This paper reports a successful design process and a new oncomelania-free intake device. The design of the new intake is based on a sound research program in which extensive experimental studies were carried out to gain knowledge of oncomelania eco-hydraulic behavior and detailed flow field information through CFD simulation. 相似文献