全文获取类型
收费全文 | 3387篇 |
免费 | 549篇 |
国内免费 | 836篇 |
专业分类
测绘学 | 200篇 |
大气科学 | 638篇 |
地球物理 | 927篇 |
地质学 | 1759篇 |
海洋学 | 416篇 |
天文学 | 113篇 |
综合类 | 349篇 |
自然地理 | 370篇 |
出版年
2024年 | 17篇 |
2023年 | 52篇 |
2022年 | 158篇 |
2021年 | 157篇 |
2020年 | 133篇 |
2019年 | 158篇 |
2018年 | 205篇 |
2017年 | 184篇 |
2016年 | 172篇 |
2015年 | 146篇 |
2014年 | 220篇 |
2013年 | 228篇 |
2012年 | 190篇 |
2011年 | 195篇 |
2010年 | 198篇 |
2009年 | 202篇 |
2008年 | 165篇 |
2007年 | 178篇 |
2006年 | 131篇 |
2005年 | 109篇 |
2004年 | 120篇 |
2003年 | 102篇 |
2002年 | 82篇 |
2001年 | 111篇 |
2000年 | 142篇 |
1999年 | 127篇 |
1998年 | 104篇 |
1997年 | 122篇 |
1996年 | 126篇 |
1995年 | 97篇 |
1994年 | 98篇 |
1993年 | 81篇 |
1992年 | 60篇 |
1991年 | 37篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1936年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有4772条查询结果,搜索用时 31 毫秒
21.
22.
本文以~3H—TdR掺入法观察911对小鼠脾淋巴细胞增殖反应的影响并用CTLL细胞检测了其对IL—2的作用。体外实验结果表明,911对小鼠脾淋巴细胞增殖反应有明显的增强作用,以0.5μg/ml的浓度效果最为明显,相对增殖指数RPI可达200%;体内实验则以5mg/kg体重ip,连续7d效果最好,相对增殖指数RPI可达176%;911用药组小鼠IL—2的产生量均高于对照组,以5mg/kg和10mg/kg效果最好。以上实验证明,这一多糖是一种有希望的新免疫调节药物。 相似文献
23.
24.
25.
以松辽盆地地质资料为基础,介绍了应力场和张裂缝预测的计算方法。通过了各种岩性的张破裂概率隶属函数,预测松辽盆地酉部张裂缝区的分布。据此,为今后的油气勘探提出了几点认识和建议。 相似文献
26.
研究了青岛市南、市北、四方三区交警在服用排铅奶粉(LeadExcretingMilkPow-der,LEMP)前后,体内粪铅含量变化情况。实验结果表明,服用LEMP后,粪铅含量先呈上升趋势,达到最高值后,又呈下降趋势。在整个实验过程中,粪铅含量四方区最高,而市南区最低。服用LEMP前,三区交警粪铅平均含量为0.687mg/kg,服用7d后达到峰值(1.96mg/kg,P<0.01),第15d降到1.61(mg/kg)(P<0.05),表明LEMP能排除体内铅起到预防铅中毒的作用 相似文献
27.
This article presents results from a series of Ko-consolidated compression and extension triaxial tests on specimens from undisturbed samples of Hong Kong Marine Deposits (HKMD). To investigate the strain-rate effects, a total of seven Ko-consolidated triaxial tests were conducted including four compression tests and three extension tests. After Ko-consolidation, the triaxial test specimens were sheared at step-changed axial strain rates under three different confining pressures of 50 kPa, 150 kPa, and 400 kPa, respectively. The step-changed strain rates were applied in the following order: +2%/h, +0.2%/h, +20%/h, -2%/h (unloading) and +2%/h (reloading) for the four compression tests and -2%/h, -0.2%/h, -20%/h, +2%/h (unloading) and -2%/h (reloading) for the three extension tests. The results are reported and analyzed in the paper. The results show that the strain rate effects, the stress-strain characteristics, and the effective stress paths of the specimens for tests in a compression state are different from those for tests in an extension stage. One order of magnitude increase in axial strain rate causes an average 8.6% increase in undrained shear strength for compression tests and a 12.1% increase for extension tests. It is also found that the failure mode of the specimens in compression is different from that in extension. The stress-strain behavior of specimens shows strain-softening and a clear shear band in compression tests, but strain-hardening without any clear shear band in extension tests for the same absolute value of axial strain. 相似文献
28.
Total dissolved selenium and selenium species have been measured in the Rhône river delta and the Gulf of Lions within the framework of the EROS-2000 project. The Rhône river concentration of total selenium averages 2.30 nM with important variations related to river discharge. During estuar-ine mixing, the concentrations of total dissolved selenium, selenite and selenate (calculated as the difference between total dissolved and selenite) decrease linearly with increasing salinity, without significant interconversion between selenium species. In the open Mediterranean waters of the Gulf of Lions the total dissolved selenium increases from 0.5 nM in the surface waters to 0.9 nM in the deep waters. Organic selenium has been observed in Mediterranean deep water, an observation which is different from those from the Atlantic and the Pacific Oceans. The distributions of total inorganic selenium (Σ5e), selenite and selenate are strongly related to phosphate and silicate concentrations as observed previously for the major oceans. 相似文献
29.
-Combined refraction and diffraction models in the form of linear parabolic approximation are derived through smallparameter method. More strictly theoretical basis and more accuracy in the models than Lozano's (1980) are obtained. Some theoretical defects in Liu's model (1985) with consideration of current are not only found but also eliminated. More strict and accurate models are, therefore, presented in this paper.The calculation results and analysis in applying the models to actual wave field with consideration of bottom friction will be given in the following paper. 相似文献
30.