全文获取类型
收费全文 | 19069篇 |
免费 | 2259篇 |
国内免费 | 3646篇 |
专业分类
测绘学 | 1506篇 |
大气科学 | 2922篇 |
地球物理 | 2822篇 |
地质学 | 7266篇 |
海洋学 | 2018篇 |
天文学 | 5400篇 |
综合类 | 1038篇 |
自然地理 | 2002篇 |
出版年
2024年 | 42篇 |
2023年 | 168篇 |
2022年 | 411篇 |
2021年 | 473篇 |
2020年 | 514篇 |
2019年 | 617篇 |
2018年 | 537篇 |
2017年 | 592篇 |
2016年 | 640篇 |
2015年 | 749篇 |
2014年 | 1023篇 |
2013年 | 1168篇 |
2012年 | 1144篇 |
2011年 | 1219篇 |
2010年 | 1175篇 |
2009年 | 1598篇 |
2008年 | 1651篇 |
2007年 | 1533篇 |
2006年 | 1462篇 |
2005年 | 1270篇 |
2004年 | 1105篇 |
2003年 | 958篇 |
2002年 | 784篇 |
2001年 | 707篇 |
2000年 | 646篇 |
1999年 | 557篇 |
1998年 | 450篇 |
1997年 | 298篇 |
1996年 | 207篇 |
1995年 | 226篇 |
1994年 | 210篇 |
1993年 | 205篇 |
1992年 | 119篇 |
1991年 | 85篇 |
1990年 | 78篇 |
1989年 | 63篇 |
1988年 | 60篇 |
1987年 | 23篇 |
1986年 | 35篇 |
1985年 | 38篇 |
1984年 | 30篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 15篇 |
1976年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Linux 防火墙的研究与设计 总被引:4,自引:0,他引:4
阐述了Linux2.4内核的防火墙Linux的原理,并分析了netfilter的设计与实现,叙述了Linux的动态地址转换,介绍了在Linux下基于netfilter架构如何开发自己的防火墙并给出具体实例。 相似文献
122.
123.
124.
125.
Based on the Germany Koldwey Station's 1994-2003 conventional observation hourly data, this paper conducts a statistical analysis on the short-term climate characteristics for an arctic tundra region (Ny-(A)lesund island) where our first arctic expedition station (Huanghe Station) was located. Affected by the North Atlantic warming current, this area has a humid temperate climate, and the air temperature at Ny-(A)lesund rose above 0 ℃ even during deep winter season during our research period. The wind speed in this area was low and appeared most at southeast direction. We find that the temperature at Ny-(A)lesund rose in the faster rate (0.68 ℃/10 a) than those at the whole Arctic area. Compared with the floating ices where our expedition conducted in the Arctic, Ny-(A)lesund was warmer and more humid and had lower wind speed. Comparison of the near surface air temperature derived by NCEP/NCAR reanalysis to the conventional measurements conducted at the Koldwey site in Ny-(A)lesund area shows a good agreement for winter season and a significant difference for summer season. 相似文献
126.
127.
128.
P. G. Jonker M. van der Klis C. Kouveliotou M. Méndez W. H. G. Lewin T. Belloni 《Monthly notices of the Royal Astronomical Society》2003,346(2):684-688
We have observed the eclipsing low-mass X-ray binary MS 1603.6+2600 with Chandra for 7 ks. The X-ray spectrum is well fit with a single absorbed power law with an index of ∼2. We find a clear sinusoidal modulation in the X-ray light curve with a period of 1.7 ± 0.2 h , consistent with the period of 1.85 h found before. However, no (partial) eclipses were found. We argue that if the X-ray flare observed in earlier X-ray observations was a type I X-ray burst, then the source can only be an accretion disc corona source at a distance of ∼11–24 kpc (implying a height above the Galactic disc of ∼8–17 kpc). It has also been proposed in the literature that MS 1603.76+2600 is a dipper at ∼75 kpc. We argue that, in this dipper scenario, the observed optical properties of MS 1603.6+2600 are difficult to reconcile with the optical properties one would expect on the basis of comparisons with other high-inclination, low-mass X-ray binaries, unless the X-ray flare was not a type I X-ray burst. In that case, the source can be a nearby soft X-ray transient accreting at a quiescent rate, as was proposed by Hakala et al., or a high-inclination source at ∼15–20 kpc. 相似文献
129.
Mineral assemblages in Al2O3‐rich, SiO2‐ and K2O‐poor metapelitic rocks from the western Odenwald Crystalline Complex (Variscan Mid‐German Crystalline Rise, southern Germany) include corundum, spinel, cordierite, sillimanite, garnet and staurolite. Quartz is absent from almost all samples. Therefore, the applicability of conventional geothermobarometry is very limited or even impossible. Detailed petrographic investigation on selected samples permits inference of the sequence of appearance and disappearance of several mineral assemblages. The recognition of such partial re‐equilibration stages and their associated mineral assemblages, together with mineral stabilities predicted from KFMASH pseudosections, enables the determination of the pressure‐temperature (P–T) trajectories experienced by these rocks during the Variscan metamorphism. The rocks were metamorphosed under low‐P/high‐T conditions and underwent an anti‐clockwise P–T evolution. A pressure increase from about 2 kbar to 4 ± 0.5 kbar was accompanied by heating. Peak metamorphic conditions were reached at pressures of 4 ± 0.5 kbar and temperatures of at least 640 °C, probably even higher. The retrograde evolution is characterised by near‐isobaric cooling from ≥ 640 °C to approximately 550 °C. The rocks underwent the anti‐clockwise evolution in a subduction‐related magmatic arc setting. The close spatial association of the low‐P/high‐T rocks with recently discovered metabasic eclogites in the eastern part of the Odenwald Crystalline Complex may indicate a fossil paired metamorphic belt in the Central European Variscides. 相似文献
130.