全文获取类型
收费全文 | 9546篇 |
免费 | 1844篇 |
国内免费 | 2154篇 |
专业分类
测绘学 | 568篇 |
大气科学 | 1845篇 |
地球物理 | 2473篇 |
地质学 | 4941篇 |
海洋学 | 993篇 |
天文学 | 570篇 |
综合类 | 870篇 |
自然地理 | 1284篇 |
出版年
2024年 | 32篇 |
2023年 | 157篇 |
2022年 | 428篇 |
2021年 | 497篇 |
2020年 | 422篇 |
2019年 | 493篇 |
2018年 | 548篇 |
2017年 | 537篇 |
2016年 | 531篇 |
2015年 | 490篇 |
2014年 | 532篇 |
2013年 | 563篇 |
2012年 | 542篇 |
2011年 | 576篇 |
2010年 | 561篇 |
2009年 | 562篇 |
2008年 | 543篇 |
2007年 | 523篇 |
2006年 | 347篇 |
2005年 | 381篇 |
2004年 | 321篇 |
2003年 | 280篇 |
2002年 | 315篇 |
2001年 | 343篇 |
2000年 | 321篇 |
1999年 | 412篇 |
1998年 | 314篇 |
1997年 | 333篇 |
1996年 | 276篇 |
1995年 | 253篇 |
1994年 | 176篇 |
1993年 | 193篇 |
1992年 | 157篇 |
1991年 | 95篇 |
1990年 | 71篇 |
1989年 | 89篇 |
1988年 | 80篇 |
1987年 | 39篇 |
1986年 | 34篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1958年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
31.
本矿床是我国金红石矿床重要的成因及工业类型,为具有特定化学成分的岩石在特定变质条件下形成的。本文通过对大量数据的处理,查明了化学成分与成矿的关系:高Al2O3、MgO、Fe2O3+FeO、K2O、P2O5、H2O+、MnO,低SiO2、CaO、Na2O、CO2、S等,利于钛富集;高TiO2、MgO、P2O5、S,低SiO2、CaO、K2O、Al2O3、Fe2O3/FeO,利于金红石形成;高Sc、Zr、Ni、Zn及La/Yb,低Y、Nb、Th、Cd、Ba、Be、ΣREE,利于金红石纯度提高。对研究矿床成因及寻找新的同类矿床等有重要意义 相似文献
32.
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
33.
Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase. 相似文献
34.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
35.
含有多重极点的有理真分式展开为部分分式,不需要计算低阶导数。列出被求函数的各阶导数的关系式,画出各阶导数作为节点的信号流图。该图无环路,既直观表现出各高阶导数的相互关系及影响的单向性,也使求节点增益的梅森公式特别简便。该方法将求高阶导数问题简化为代数运算,特别适合于编制成计算机程序 相似文献
36.
1IntroductionOne of the key factors related to basin geody-namics is deep process controlling formation and evolution of sedimentary basin. Depth and tempera-ture of asthenosphere,existence of mantle plume,occurrence of mantle melting,and amounts of melts under depressurization during thinning of lithosphere are controlling factors influenced formation and characteristics of extensional basin directly (Li,1994). Rifting is probably governed by frictional forces exerted on the base of litho… 相似文献
37.
Study is made on a 45 km-long artificial ecosystem without irrigation in Tengger desert on the basis of long-term ecological monitoring and ecohydrological fundamentals. Changes in water allocation, utilization, cycle and balance patterns in more than 40-year evolution of the soil-plant system are analyzed. The formation of a drought horizon in shrub rhizosphere and its effect, ecohydrological function of the crust and its effect on the soil-plant system change are discussed. Driven by water self-regulation and water stress, the soil-plant system is going to develop towards the steppe desert to ensure more effective use and optimum collocation of water resource.
相似文献38.
本文通过数值求解带电粒子与Alfven波湍动相互作用的动力学方程,得到了相对论电子在射电喷流中被加速随时间演化的解.高能电子可以加速到Lorentz因子γy~106,且形成稳态的幂律谱,尽管其谱指数S≈l比观测值小,但粒子加速时间约为1012-1014秒,小于射电斑的寿命107年.粒子能谱指数几乎与Alfven波谱指数和能量损失函数无关.能量损失对加速上限有较大影响. 相似文献
39.
Michael Boylan-Kolchin Chung-Pei Ma Eliot Quataert 《Monthly notices of the Royal Astronomical Society》2005,362(1):184-196
We carry out numerical simulations of dissipationless major mergers of elliptical galaxies using initial galaxy models that consist of a dark matter haloes and a stellar bulge with properties consistent with the observed fundamental plane. By varying the density profile of the dark matter haloes [standard Navarro, Frenk & White (NFW) profile versus adiabatically contracted NFW profile], the global stellar to dark matter mass ratio and the orbit of the merging galaxies, we are able to assess the impact of each of these factors on the structure of the merger remnant. Our results indicate that the properties of the remnant bulge depend primarily on the angular momentum and energy of the orbit; for a cosmologically motivated orbit, the effective radius and velocity dispersion of the remnant bulge remain approximately on the fundamental plane. This indicates that the observed properties of elliptical galaxies are consistent with significant growth via late dissipationless mergers. We also find that the dark matter fraction within the effective radius of our remnants increases after the merger, consistent with the hypothesis that the tilt of the fundamental plane from the virial theorem is due to a varying dark matter fraction as a function of galaxy mass. 相似文献
40.