全文获取类型
收费全文 | 79105篇 |
免费 | 1429篇 |
国内免费 | 1942篇 |
专业分类
测绘学 | 2627篇 |
大气科学 | 5705篇 |
地球物理 | 15572篇 |
地质学 | 31849篇 |
海洋学 | 6162篇 |
天文学 | 13916篇 |
综合类 | 2386篇 |
自然地理 | 4259篇 |
出版年
2022年 | 493篇 |
2021年 | 789篇 |
2020年 | 761篇 |
2019年 | 854篇 |
2018年 | 6227篇 |
2017年 | 5422篇 |
2016年 | 4197篇 |
2015年 | 1224篇 |
2014年 | 1716篇 |
2013年 | 2951篇 |
2012年 | 2993篇 |
2011年 | 5219篇 |
2010年 | 4278篇 |
2009年 | 5166篇 |
2008年 | 4314篇 |
2007年 | 4932篇 |
2006年 | 2624篇 |
2005年 | 1875篇 |
2004年 | 1975篇 |
2003年 | 1862篇 |
2002年 | 1698篇 |
2001年 | 1324篇 |
2000年 | 1216篇 |
1999年 | 955篇 |
1998年 | 1004篇 |
1997年 | 952篇 |
1996年 | 803篇 |
1995年 | 783篇 |
1994年 | 682篇 |
1993年 | 575篇 |
1992年 | 606篇 |
1991年 | 543篇 |
1990年 | 610篇 |
1989年 | 538篇 |
1988年 | 482篇 |
1987年 | 599篇 |
1986年 | 488篇 |
1985年 | 603篇 |
1984年 | 694篇 |
1983年 | 621篇 |
1982年 | 618篇 |
1981年 | 574篇 |
1980年 | 570篇 |
1979年 | 511篇 |
1978年 | 482篇 |
1977年 | 470篇 |
1976年 | 428篇 |
1975年 | 416篇 |
1974年 | 423篇 |
1973年 | 483篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
251.
Dolmatova L. S. Eliseykina M. G. Timchenko N. F. Kovaleva A. L. Shitkova O. A. 《中国海洋湖沼学报》2003,21(4):293-304
Pure fraction (92%–95%) of phagocytes (FP) and a mixture of amoebocytes (62%) and morula cells (38%)-FPMC- of the holothurianEupentacta fraudatrix' (Holothuroidea, Dendrochirota) were obtained by using ficoll-verographine step gradient. Basal production of reactive oxygen species (ROS) in FP quantified
by using reduction of nitroblue tetrazolium (NBT) was more than twice that in FPMC. Thermostable toxin ofYersinia pseudotuberculosis (TST) at different concentrations (0.2; 0.5; 2.5 μg/ml, but not 0.1 μg/ml) stimulated NBT reduction in FPMC after 24 h incubation.
In FP, TST at concentrations of 0.1 and 0.2 μg/ml inhibited and at concentrations of 0.5 and 2.5 μg/ml stimulated NBT reduction
after 24 h incubation. Maximal effect was observed in FP and FPMC at TST concentrations of 0.5 and 0.2 μg/ml, respectively.
Addition of catalase (0.7 μg/ml) to the cells treated with TST (2.5 μg/ml) was followed by a decrease in NBT reduction compared
to that under toxin treatment alone. TST stimulated superoxide dismutase activity in concentration-dependent manner (maximum
at 0.5 μg/ml concentration in FP) after 24 h treatment, and this stimulation was prevented by a commercial catalase. Plant
lectin concanavalin A stimulated NBT reduction more than 5-fold in FPMC compared to the control. With addition of TST, lectin
stimulated ROS to lesser extent than that with lectin alone. When catalase, TST, and lectin were added into the FPMC simultaneously,
ROS increase was similar to that under lectin treatment alone. On the whole, data obtained indicated that ROS generation in
holothurian coelomocytes especially occurs in both stimulated and not stimulated phagocytes, and that changes in ROS production
by these cells may be one of the mechanisms of antibacterial protection of holothurians.
This work was financially supported by the Russian Foundation for Fundamental Research Grant (No. 00-04-48949). 相似文献
252.
The present paper reports 9 species of pontoniine shrimps collected from Hainan IS-land ,South China Sea ,by the Joint Chinese-German Marine Biology Expeditions,in which Peri-climenaeus arabicus (Calman,1939) and Periclimenaeus hecate (Nobili,1904) are recorded for the first time from Hainan Island. 相似文献
253.
Lightning discharge generated in the protoplanetary nebula is viewed as a temporally isolated surge in the flow of electrically charged particles, similar to that of terrestrial lightning. If the current is intense enough, a powerful circular impulse magnetic field is generated around the instantaneous virtual electric conductor. Such magnetic field is capable of magnetizing dust grains containing ferromagnetic components present in its vicinity to their saturation levels. As a result, dust grains attract one another, forming the aggregates. This magnetically driven attraction suggests an important process possibly operational at an early stage of the planetary accretion. Based on both a classical model for electric conductor, and the theory of Lienard–Wiechert electromagnetic potentials, our calculations show that the magnetic impulse due to a discharge channel of a few cm in diameter transferring a charge of about 104 electrons reaches as high as 10 T. At these magnetic fields, the ferromagnetic dust grains, and possibly the already-formed larger aggregates as well, are easily magnetized to the saturation levels, producing compact clusters exhibiting permanent magnetic moments. 相似文献
254.
255.
256.
257.
Flux pile-up magnetic reconnection is traditionally considered only for incompressible plasmas. The question addressed in this paper is whether the pile-up scalings with resistivity are robust when plasma compressibility is taken into account. A simple analytical argument makes it possible to understand why the transition from a highly compressible limit to the incompressible one is difficult to discern in typical simulations spanning a few decades in resistivity. From a practical standpoint, however, flux pile-up reconnection in a compressible plasma can lead to anomalous electric resistivity in the current sheet and flare-like energy release of magnetic energy in the solar corona. 相似文献
258.
259.
APPLICATION OF GEOGRAPHICAL PARAMETER DATABASE TO ESTABLISHMENT OF UNIT POPULATION DATABASE 总被引:1,自引:1,他引:0
Now GIS is turning into a good tool in handling geographical, economical, and population data, so we can obtain more and more information from these data. On the other hand, in some cases, for a calamity, such as hurricane, earthquake, flood, drought etc., or a decision-making, such as setting up a broadcasting transmitter, building a chemical plant etc., we have to evaluate the total population in the region influenced by a calamity or a project. In this paper, a method is put forward to evaluate the population in such special region. Through exploring the correlation of geographical parameters and the distribution of people in the same region by means of quantitative analysis and qualitative analysis, unit population database (1km× 1km) is established. In this way, estimating the number of people in a special region is capable by adding up the population in every grid involved in this region boundary. The geographical parameters are obtained from topographic database and DEM database on the scale of 相似文献
260.