全文获取类型
收费全文 | 3911篇 |
免费 | 587篇 |
国内免费 | 499篇 |
专业分类
测绘学 | 1471篇 |
大气科学 | 369篇 |
地球物理 | 928篇 |
地质学 | 947篇 |
海洋学 | 369篇 |
天文学 | 200篇 |
综合类 | 447篇 |
自然地理 | 266篇 |
出版年
2024年 | 8篇 |
2023年 | 38篇 |
2022年 | 127篇 |
2021年 | 150篇 |
2020年 | 150篇 |
2019年 | 193篇 |
2018年 | 147篇 |
2017年 | 233篇 |
2016年 | 215篇 |
2015年 | 233篇 |
2014年 | 228篇 |
2013年 | 266篇 |
2012年 | 274篇 |
2011年 | 280篇 |
2010年 | 186篇 |
2009年 | 247篇 |
2008年 | 258篇 |
2007年 | 268篇 |
2006年 | 264篇 |
2005年 | 207篇 |
2004年 | 187篇 |
2003年 | 138篇 |
2002年 | 117篇 |
2001年 | 84篇 |
2000年 | 92篇 |
1999年 | 72篇 |
1998年 | 69篇 |
1997年 | 49篇 |
1996年 | 33篇 |
1995年 | 46篇 |
1994年 | 35篇 |
1993年 | 25篇 |
1992年 | 18篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有4997条查询结果,搜索用时 15 毫秒
991.
刘清耀 《中国天文和天体物理学报》1988,(2)
本文给出了一个确定大熊W型双星质量比的近似方法。如果知道大熊W型双星的周期P、主子星表面有效温度T_p和主次食深差△m,可通过该文导出的一个公式算得质量比。对21个大熊W双星进行了计算,结果表明用该方法确定的质量比同分光或测光质量比符合较好。 相似文献
992.
J. A. López Ortí A. López García R. López Machí 《Celestial Mechanics and Dynamical Astronomy》1992,53(4):311-322
The equilibrium configurations of close binary systems are analyzed. The autogravitational, centrifugal and tidal potentials are expanded in Clairaut's coordinates. From the set of the total potential angular terms an integral equations system is derived. The reduction of them to ordinary differential equations and the determination of the boundary conditions allow a formulation of the problem in terms of a single variable. 相似文献
993.
Michael Bauer 《Astrophysics and Space Science》2005,296(1-4):255-260
A method is presented to include irradiation effects in the modeling of over-contact binaries. The Roche potential is numerically
modified in a way to account for mechanical effects of the mutual irradiation of the two binary components. The efficiency
of radiative interaction is parametrized by means of the fraction of radiative over gravitational forces for each component
of the binary. The modified Roche geometry is implemented as binary model in an eclipse light curve solution code, which is
based on the general Wilson–Devinney scheme. As an example the method is applied to the early-type over-contact system V606
Cen. 相似文献
994.
Virginia Trimble 《Journal of Astrophysics and Astronomy》1984,5(4):389-402
Supernovae of both Type I (hydrogen-poor) and Type II (hydrogen-rich) can be expected to occur among binary stars. Among massive
stars (>10 M•), the companion makes it more difficult for the primary to develop an unstable core of >1.4.M• while still retaining
the extended, hydrogen-rich envelope needed to make a typical Type II light curve. Among 1–10 M• stars, on the other hand,
a companion plays a vital role in currently popular models for Type I events, by transferring material to the primary after
it has become a stable white dwarf, and so driving it to conditions where either core collapse or explosive nuclear burning
will occur. Several difficulties (involving nucleosynthesis, numbers and lifetimes of progenitors, the mass-transfer mechanism,etc.) still exist in these models. Some of them are overcome by a recent, promising scenario in which the secondary also evolves
to a degenerate configuration, and the two white dwarfs spiral together to produce a hydrogen-free explosion, long after single
stars of the same initial masses have ceased to be capable of fireworks. 相似文献
995.
Intermediate term earthquake prediction in the area of Greece: Application of the algorithm M8 总被引:1,自引:0,他引:1
The 3 strongest earthquakes,M7.0, which have occurred since 1973 in the area of Greece were preceded by a specific increase of the earthquake activity in the lower magnitude range. This activation is depicted by algorithm M8. This algorithm of intermediate term earthquake prediction was originally designed for diagnosis by Times of Increased Probability (TIPs) of the strongest earthquake,M8.0 worldwide (Keilis-Borok andKossobokov, 1984). At present the algorithm is retrospectively tested for smaller magnitudes in different seismic regions (Keilis-Borok andKossobokov, 1986, 1988). A TIP refers to a time period of 5 years and an area whose linear size is proportional and several times larger than that of the incipient earthquake source. Altogether the TIPs diagnosed by the algorithm M8 in the area of Greece occupy less than 20% and the Times of Expectation (TEs) about 10% of the total space-time domain considered. Also there is a current TIP for the southeastern Aegean sea and 1988–1992. It may specify the long-term prediction given inWyss andBaer (1981a,b).The results of this study are further evidence favoring applicability of algorithm M8 in diverse seismotectonic environment and magnitude ranges and support indirectly the hypothesis of self-similarity of the earthquake activity. It also implies the possibility of intermediate term prediction of the strongest earthquakes in the area of Greece. 相似文献
996.
夏季降水日数的准确预测,对于保障农业、运输业、电力等行业的有序进行具有重要现实意义.利用连云港市气象局提供的1951—2012年夏季降水数据对连云港地区的降水日数特征进行分析,难以直观地发现夏季降水日数随时间分布的规律.为进一步探索降水日数的发生规律,结合国家气候中心网站提供的多种气候因子数据,基于CART决策树算法构建了连云港地区夏季降水日数是否偏多与是否偏少的分类与预测模型.该模型可以发现在多种气候因子不同条件下,夏季降水日数是否偏多(偏少)的规律,模型的分类与预测都具有良好的效果.利用52 a的数据样本训练模型,模型的训练准确率为90.38%(86.54%),再用剩余10 a数据样本检验模型,测试准确率为80%(80%),并且得到规则集,方便气象业务人员使用以及决策服务人员参考.同时,为降水日数的预测提供了数据挖掘的新思路. 相似文献
997.
Amine Ait-Ouahmed Didier Josselin Fen Zhou 《International journal of geographical information science》2018,32(2):367-398
Car-sharing system with electric cars is a very convenient service for urban transportation: it allows users to pick up a vehicle at a station and rent it during a short time. To manage this kind of system in the best way, it is necessary to solve the critical problem of vehicle stock imbalance across the stations. Several decision levels must be considered to balance the car distribution by taking into account the quality of service and the system operation cost. To this end, a linear programming model is proposed to formalize the problem in a mathematical framework, which allows the computation of optimal vehicle distribution strategies. To make our solution time efficient and usable for solving large problems, a greedy algorithm and a tabu search algorithm are proposed. These two algorithms are applied to the Auto Bleue network in Nice and its surrounding (France) using extensive simulations. Besides, an integrated mapping method is provided within the Geographical Information System QGIS to estimate flows and their locations. Numerical results demonstrate that the tabu search algorithm is able to find near-optimal solutions and good compromises between client satisfaction, number of staff agents and vehicles used, and computing time. 相似文献
998.
999.
以2009年以来江西省地震台网记录到的86个ML2.5以上地震事件的波形资料为研究对象,通过遗传算法获得介质的品质因子和台站场地响应,并在此基础上计算地震的震源谱参数。结果显示,江西地区Q值与频率f的关系式为Q(f)=323.1f0.505 9;大部分台站的场地响应在频率域表现为平坦型,整体上与台站基岩性质相符;近震级ML与地震矩M0在单对数坐标下呈线性关系,地震矩与拐角频率呈负相关特征,应力降与地震矩之间没有显著相关性;震源半径与应力降存在显著的双对数关系。 相似文献
1000.
提出一种求解不等式约束秩亏平差问题的新算法,该算法将先验信息表示为不等式形式,并与秩亏平差模型构成不等式约束秩亏平差模型。结合Karush-Kuhn-Tucker条件可将该模型转化为线性互补问题,然后利用Lemke算法求解,克服了秩亏网中必要起算数据不足的问题,能保证解的唯一性。最后,模拟附先验信息的秩亏的GPS观测网,并结合多种经典的秩亏平差方法,验证了Lemke算法在处理不等式约束秩亏问题上的有效性。 相似文献