全文获取类型
收费全文 | 34825篇 |
免费 | 6574篇 |
国内免费 | 8355篇 |
专业分类
测绘学 | 1840篇 |
大气科学 | 7751篇 |
地球物理 | 9344篇 |
地质学 | 17207篇 |
海洋学 | 4037篇 |
天文学 | 1698篇 |
综合类 | 3887篇 |
自然地理 | 3990篇 |
出版年
2024年 | 98篇 |
2023年 | 515篇 |
2022年 | 1423篇 |
2021年 | 1586篇 |
2020年 | 1369篇 |
2019年 | 1478篇 |
2018年 | 1893篇 |
2017年 | 1695篇 |
2016年 | 2039篇 |
2015年 | 1616篇 |
2014年 | 2052篇 |
2013年 | 1985篇 |
2012年 | 1769篇 |
2011年 | 1869篇 |
2010年 | 1961篇 |
2009年 | 1954篇 |
2008年 | 1768篇 |
2007年 | 1699篇 |
2006年 | 1370篇 |
2005年 | 1251篇 |
2004年 | 1023篇 |
2003年 | 1048篇 |
2002年 | 1016篇 |
2001年 | 987篇 |
2000年 | 1219篇 |
1999年 | 1832篇 |
1998年 | 1515篇 |
1997年 | 1466篇 |
1996年 | 1367篇 |
1995年 | 1149篇 |
1994年 | 1091篇 |
1993年 | 947篇 |
1992年 | 773篇 |
1991年 | 606篇 |
1990年 | 469篇 |
1989年 | 415篇 |
1988年 | 366篇 |
1987年 | 219篇 |
1986年 | 202篇 |
1985年 | 140篇 |
1984年 | 101篇 |
1983年 | 73篇 |
1982年 | 105篇 |
1981年 | 66篇 |
1980年 | 43篇 |
1979年 | 38篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1958年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
61.
调查了潜蝇在湛江市的发生与为害情况,结果表明,美洲斑潜蝇(LiriomyzaSatiuaeBlanchard)是为害作物潜蝇的优势种,包括有6个科18种,年间发生有6个为害高峰期。应用绿潜宝、乐果、巴丹等药剂在发生为害高峰期的峰前、中、后三次用药,防治效果维持70%以上。 相似文献
62.
63.
Zhang Chuanling 《地球科学与环境学报》1997,(1)
文中详细地论述了新疆阿尔泰哈巴河一带古生代火山岩的地质、岩石化学、稀土元素地球化学特征。将其分为三个类型,认为火山岩是在陆缘裂陷槽的区域构造背景下发生和演化的。对各类型火山岩岩浆来源,上升模式也做了初步讨论。 相似文献
64.
本文首先用有限元方法对几种不同的地形模型进行了分析。所得的结论是:由于实际地球表面地形的起伏不平,水准测量资料与地形之间具有相关性,即水准点高程变化与该点高程之间呈相关性。最后,本文对今后水准测量资料的分析处理提出了建议。 相似文献
65.
66.
概略地叙述了西宁地区的泥石流形成条件和形成机理,并将西宁地区泥石流划分为稀性泥石流类及泥石质泥石流种类。在此基础上提出防治泥石流灾害的意见。 相似文献
67.
68.
Hong-Guang Wang Guo-Jun Qiao Ren-Xin XuDepartment of Astronomy Peking University Beijing 《中国天文和天体物理学报》2003,3(5):443-452
The inner vacuum gap model has become the foundation stone of most theories on pulsar radio emission. The fundamental picture of this model is the sparking, which was conjectured to be induced by magnetic absorption of background gamma photons. However, a question is, can the sparking be triggered in the millisecond pulsars (MSPs) with magnetic fields (B) only about 108 G? We investigate this problem by including the pair production above the inner gap. Under the assumption that the magnetic field is dipolar, our results show the background gamma-ray emission can not be the key factor that triggers the sparking, at least not in MSPs with B - 108 G, if the temperature in the polar cap region is only so high as is observed (< 4 × 106 K). Some other mechanisms are required. 相似文献
69.
H. L. Xu S. Svanberg R. D. Cowan P.-H. Lefèbvre P. Quinet E. Biémont 《Monthly notices of the Royal Astronomical Society》2003,346(2):433-440
Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd ii in the energy range 20 500–32 500 cm−1 . For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree–Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0–1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology. 相似文献
70.
The response of natural vegetation to climate change is of global concern. In this research, an aggregated Holdridge Life Zone System was used to study the possible response of life zones in China under doubled atmospheric CO2 concentration with the input climatic parameters at 0.5×0.5° resolution of longitude and latitude from NCAR regional climate model 2 (RegCM2) coupled with the CSIRO global climate model. The results indicate that the latitudinal distribution of life zones would become irregular because of the complicated climate change. In particular, new life zones, such as subtropical desert (SD), tropical desert (TDE) and tropical thorn woodland (TTW), would appear. Subtropical evergreen broadleaved forest (SEBF), tropical rainforest and monsoon forest (TRF), SD, TDE and TTW zones would appear in the northeastern China. Cool-temperate mixed coniferous and broadleaved forest (CMC) and warm-temperate deciduous broadleaved forest (WDBF) zones would appear at latitudes 25–35°N. The temperate desert (TD) in the western China would become Tibetan high-cold plateau (THP), SEBF, WDBF and temperate steppe (TS), and a large part of THP would be replaced by TRF, TDE, SEBF, TS and TTW. The relative area (distribution area/total terrestrial area) of CMC, TRF, TDE and TTW zone would increase about 3%, 21%, 3% and 6%, respectively. However, the relative area of SEBF, TS, TD and THP would decrease about 5%, 3%, 19% and 4%, respectively. In all, the relative area of forests (CCF, CMC, WDBF, SEBF, TRF) would increase about 15%, but the relative area of desert (TD, SD, TDE, and TTW) and THP would decrease about 9% and 4%, respectively. Therefore, responses of different life zones in China to climate change would be dramatic, and nationwide corridors should be considered for the conservation of migrating species under climate change. 相似文献