首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   12283篇
  免费   148篇
  国内免费   70篇
测绘学   245篇
大气科学   769篇
地球物理   2388篇
地质学   4751篇
海洋学   1251篇
天文学   2565篇
综合类   48篇
自然地理   484篇
  2022年   147篇
  2021年   220篇
  2020年   213篇
  2019年   239篇
  2018年   540篇
  2017年   448篇
  2016年   504篇
  2015年   208篇
  2014年   433篇
  2013年   638篇
  2012年   491篇
  2011年   602篇
  2010年   589篇
  2009年   666篇
  2008年   603篇
  2007年   597篇
  2006年   510篇
  2005年   333篇
  2004年   324篇
  2003年   295篇
  2002年   285篇
  2001年   258篇
  2000年   264篇
  1999年   184篇
  1998年   192篇
  1997年   174篇
  1996年   117篇
  1995年   138篇
  1994年   117篇
  1993年   102篇
  1992年   74篇
  1991年   103篇
  1990年   100篇
  1989年   68篇
  1988年   81篇
  1987年   100篇
  1986年   82篇
  1985年   108篇
  1984年   103篇
  1983年   106篇
  1982年   87篇
  1981年   83篇
  1980年   100篇
  1979年   88篇
  1978年   89篇
  1977年   78篇
  1976年   61篇
  1975年   65篇
  1974年   71篇
  1973年   65篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Frenzel, B., Pfister, C. & Gläser, B. (eds.) 1992: European Climate Reconstructed from Documentary Data: Methods and Results.  相似文献   
42.
Several measurements have been performed to find antiprotons in the primary cosmic radiation. Because it is difficult to get completely separated secondary produced antiprotons primary ones, calculations based on accelerator results have been performed for the flux of secondary produced antideuterons and antihelium.  相似文献   
43.
Book review     
N. O. Weiss 《Solar physics》1985,96(2):423-423
  相似文献   
44.
The results of detailed studies and interpretations are presented for composition variations, structural properties and the phase state of hydrocarbon fluids from subsalt pools of the Pre-Caspian depression. These data serve as a basis for substantiating the existence of several types of condensate, and identifying the locations of the main centres of fluid generation. The basic geological-geochemical conditions controlling the composition of condensate and free gases have been determined as well as their present phase state. A set of basic criteria is proposed as well as prognostic maps for the condensate and free gas composition, and the pool phase states.  相似文献   
45.
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   
46.
47.
Some results following from two contemporary photographical programs (Slovakia and Japan) for persistent meteor train spectra are compared. It shows that even though both programs are not too different according to their lenses and films used, the spectral interval detected is very different. In this respect prism as a dispersion element is more favourable than the grating with blaze wavelength near 610 nm. However, some results previously assumed as typicai for presented persistent trains-e.g. the forbidden Herzberg O2 emission, the NO2 continuum and OH red emissions-seem to be substanciated especially due to higher and linear dispersion of those grating spectra.  相似文献   
48.
49.
50.
The role in radiative association of narrow resonances arising from quasi-bound levels is examined. For the rate coefficient the contribution from such levels is readily calculated in terms of the Einstein A -coefficient from bound rovibrational levels generated using a suitable alternative boundary condition. By locating systematically all the quasi-bound levels, an enhancement by more than an order of magnitude of the rate coefficient for Li(2s) + H(1s) association above about 600 K is obtained. The effect on the LiH abundance in the early Universe is no more than an increase of a factor of 3 for limited ranges of values of the redshift. For the Li(2p) state the effect of narrow resonances appears to have been taken into account in previous calculations.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号