全文获取类型
收费全文 | 384301篇 |
免费 | 80805篇 |
国内免费 | 101957篇 |
专业分类
测绘学 | 64538篇 |
大气科学 | 74313篇 |
地球物理 | 67539篇 |
地质学 | 197188篇 |
海洋学 | 66645篇 |
天文学 | 6860篇 |
综合类 | 40137篇 |
自然地理 | 49843篇 |
出版年
2024年 | 4490篇 |
2023年 | 15808篇 |
2022年 | 19203篇 |
2021年 | 20243篇 |
2020年 | 15631篇 |
2019年 | 22786篇 |
2018年 | 21582篇 |
2017年 | 14468篇 |
2016年 | 15930篇 |
2015年 | 19576篇 |
2014年 | 26416篇 |
2013年 | 24273篇 |
2012年 | 25941篇 |
2011年 | 26534篇 |
2010年 | 25490篇 |
2009年 | 24865篇 |
2008年 | 24453篇 |
2007年 | 22668篇 |
2006年 | 21748篇 |
2005年 | 18797篇 |
2004年 | 17665篇 |
2003年 | 16232篇 |
2002年 | 14449篇 |
2001年 | 13461篇 |
2000年 | 11025篇 |
1999年 | 8740篇 |
1998年 | 6186篇 |
1997年 | 5367篇 |
1996年 | 4862篇 |
1995年 | 4582篇 |
1994年 | 4313篇 |
1993年 | 4126篇 |
1992年 | 4104篇 |
1991年 | 3699篇 |
1990年 | 3504篇 |
1989年 | 3723篇 |
1988年 | 3895篇 |
1987年 | 3790篇 |
1986年 | 3217篇 |
1985年 | 3266篇 |
1984年 | 2951篇 |
1983年 | 2766篇 |
1982年 | 2279篇 |
1981年 | 1714篇 |
1980年 | 1273篇 |
1979年 | 801篇 |
1978年 | 392篇 |
1959年 | 311篇 |
1958年 | 332篇 |
1957年 | 315篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
761.
762.
Isabella A. Abbott 《中国海洋湖沼学报》1995,(4)
A new species of Liagora,L.perennis sp.nov.from Hawai’i,is described.Unlike dpecies of this genus in China,it is carpotetrasporangial,and at the place of expected carposporangia bears cruciately di-vided tetrasporangia,a detail which differentiates it from the usual species of Liagora without tetraspores that have been reported in China.Notes are provided on other Liagora species that have an impact on the taxonomy of species found in China. 相似文献
763.
以首都圈地区现今活动断层上近20年的位移测量资料为依据,用二维线弹性有限元对该区断层的活动特征进行了拟合,并结合有关资料讨论了该区的地震危险性。结果表明:1977-1986年间该区主压应力优势方位与华北较一致,约为N45°-80°E;1986-1990年其主压应力方向向北偏转,约为N5°-60°E;1990年至现在其主压应力又向东偏转,角度大于第一阶段,约为N80°-95°E。该区的张家口-延庆一带近期有发生中强震的可能;丰镇-阳高-大同地区和凉城-古营盘地区应力较高,也应引起注意。 相似文献
764.
本文介绍了1993年12月29日一个SF/C1.9耀斑过程的HeI10830A的二维光谱观测和资料的初步分析,主要结果如下:(1)在直接拼出的HeI 10830A单色象上未发现有Rust提出的强度超过连续谱的耀斑亮点,但在剩余强度图上的确发现有四个小区相对周围变亮,其强度在耀斑爆发过程中有明显变化;(2)所有HeI 10830A“亮区”均落在Hα耀斑亮区内,反之则不一定有对应;(3)HeI 108 相似文献
765.
本文介绍了对时序垂直角观测值进行谱分析的方法和所得到的结论。使以往对于大气折射影响及其变化规律的定性认识得以定量化。 相似文献
766.
767.
From elements formed in interstellar furnaces to humans peering back at the stars, the evolution of life has been a long, intricate and perhaps inevitable process. Life as we know it requires a planet orbiting a star at just the right distance so that water can exist in liquid form. It needs a rich supply of chemicals and energy sources. On Earth, the combination of chemistry and energy generated molecules that evolved ways of replicating themselves and of passing information from one generation to the next. Thus, the thread of life began. This chart traces the thread, maintained by DNA molecules for much of its history, as it weaves its way through the primitive oceans, gaining strength and diversity along the way. Organisms eventually moved onto the land, where advanced forms, including humans, ultimately arose. Finally, assisted by a technology of its own making, life has reached back out into space to understand its own origins, to expand into new realms, and to seek other living threads in the cosmos. 相似文献
768.
Theoretical rotational excitation rates were computed for C3H2 in collisions with He atoms at temperatures from 30 to 120 K. The intermolecular forces were obtained from accurate self-consistent field and perturbation theory calculations, and collision dynamics were treated within the infinite-order sudden approximation. The accuracy of the latter was examined by comparing with the more exact coupled states approximation. 相似文献
769.
Chandna RC Sharma D 《Population geography : a journal of the Association of Population Geographers of India》1987,9(1-2):45-55
Using a sample of 885 females (1/2 of all married women of reproductive age), this study examines the role of education as a determinant of fertility among couples in Kullu town of Himachol Pradesh, India. Of the 885 respondents, only 149 were illiterate. The average family size was 2.88. Findings reveal that 1) the average family size was largest for illiterate respondents (3.57) and for illiterate males (3.76); 2) average family size declined consistently after the middle level of education to 1.29 for post graduate respondents and 2.33 for post graduate males; 3) a negative correlation exists between fertility and education of both husband and wife, with the wife's education having a stronger negative correlation with fertility; and 4) couples with an educational level of matriculation and above have a distinctly smaller family size than those less educated. 相似文献
770.