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   33788篇
  免费   6375篇
  国内免费   8210篇
测绘学   2151篇
大气科学   6729篇
地球物理   8564篇
地质学   17289篇
海洋学   4175篇
天文学   1402篇
综合类   3769篇
自然地理   4294篇
  2024年   120篇
  2023年   534篇
  2022年   1562篇
  2021年   1779篇
  2020年   1539篇
  2019年   1742篇
  2018年   2045篇
  2017年   1777篇
  2016年   1997篇
  2015年   1642篇
  2014年   2040篇
  2013年   2081篇
  2012年   1940篇
  2011年   2045篇
  2010年   1961篇
  2009年   1897篇
  2008年   1716篇
  2007年   1585篇
  2006年   1280篇
  2005年   1301篇
  2004年   950篇
  2003年   951篇
  2002年   917篇
  2001年   949篇
  2000年   1055篇
  1999年   1550篇
  1998年   1268篇
  1997年   1284篇
  1996年   1221篇
  1995年   1017篇
  1994年   897篇
  1993年   792篇
  1992年   647篇
  1991年   452篇
  1990年   373篇
  1989年   292篇
  1988年   261篇
  1987年   192篇
  1986年   158篇
  1985年   110篇
  1984年   79篇
  1983年   69篇
  1982年   61篇
  1981年   39篇
  1980年   42篇
  1979年   37篇
  1978年   24篇
  1977年   16篇
  1975年   18篇
  1958年   25篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
101.
The variation in the orbital period of the W UMa type contact binary V502 Oph is analyzed. The orbital period exhibits a wavelike variation with a periodicity of 23.0 years and an amplitude of △P = 1.24×10~(-6) days superimposed on secular decrease of dP/dt = 1.68×10-7 day per year. The long-term decrease may be accompanied by the contraction of the secondary at a rate of 83 m per year and a mass transfer rate from the primary to the secondary of 4.28×10~8 M per year. The short-term oscillation may be explained by the presence of a third component. Orbital elements of the third body and its possible mass are presented.  相似文献   
102.
The new polyenzyme method for making gravy fromHarengula zunasi offal involves protein enzymolysis with flavorase after proper alkaline and neutral protease levels were established by orthogonal trials to select the best hydrolytic conditions for processing offal with alkaline and neutral protease. The conditions for the polyenzyme method were pH of 7.0, temperature of 50°C, alkaline and neutral protease concentration of 1.5% respectively, hydrolysis time of 120 min, and flavorase concentration of 2.0%, for 60 min. The new gravy-making technology yields a nutritious and delicious gravy containing 40.3% of total essential amino acids, with delicious amino acids Glu, Asp, Gly, Ala, Pro and Ser comprising 49.5%, total and amino nitrogen being respectively 1.9 and 1.1 g/100 g (amino acid nitrogen being 61.0% of total nitrogen), The polyenzyme method was used to make 14.8% protein gravy fromHarengula zunasi offal. In addition, inorganic elements, the phosphorus content is the highest. This project was aided financially by the Guangdong Science and Technology Office (No. 2KM06002S).  相似文献   
103.
1INTRODUCTION Since the first use in human genetic research in1966,allozyme has become the most popular genetic marker for population genetics studies for almost all groups of animals and plants(Lewontin and Hubby,1966;Murphy et al.,1996).In the past seve…  相似文献   
104.
105.
黑色高岭石粘土岩,是铜川王石凹煤矿石炭纪煤系地层顶部,五号煤层的上部一层稳定的煤矸石。经偏光显微镜及费氏台测试光性特征、化学试验及分析鉴定表明,这是一种由高岭石组成的,成分很纯、颗粒大、结晶良好的高岭石粘土岩。据微量元素含量分析,此高岭石系淡水沉积物。  相似文献   
106.

The characteristics of red karst weathering crust in the research region can be divided into three subtypes. The first one includes the silicon to aluminum ratio, the composition of the clay minerals, etc., and reflects the weak action of de-silicon and aluminum enrichment. The second one, for example the granularity, shows that the viscous action is strong. The third one, such as the CaCO3 content and pH value, has regional difference in a large scale, which is consistent with the condition of modern scenery, so it is not important as for the ancient environment.

  相似文献   
107.

The pyroxenite xenoliths in the volcanic rocks of Hoh Xil consist of clinopyroxenes and orthopyroxenes. The mineral composition of these pyroxenes is similar to that of mantle xenoliths including peridotite and pyroxenite from China and abroad, and different from that of granulites. The pyroxenes formed at 1101–1400°C (averaging 1250°C) and under 30–60 kb (averaging 46 kb). We deduced that the magma was derived from the mantle at a depth of more than 150 km, which fits in with the geophysical conclusion that the low-velocity layer existed in the mantle under 150 km.

  相似文献   
108.
Free radical scavenging abilities of polypeptide from Chlamys farreri   总被引:1,自引:0,他引:1  
1 INTRODUCTION Active oxygen free radicals can damage cell structure, even kill the cells, causing aging and cer- tain serious diseases (Bors et al., 1989). Usually, the production and scavenging of active oxygen free radicals are in balance in healthy hu…  相似文献   
109.
110.
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F obs = 3 + F intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem v must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem v corr and logZ have a good correlation.  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