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   102109篇
  免费   8321篇
  国内免费   36篇
  110466篇
  2021年   901篇
  2018年   1369篇
  2017年   1260篇
  2016年   1738篇
  2015年   1870篇
  2014年   2248篇
  2013年   3130篇
  2012年   3498篇
  2011年   3578篇
  2010年   2629篇
  2009年   2242篇
  2008年   3214篇
  2007年   3196篇
  2006年   3004篇
  2005年   2844篇
  2004年   2795篇
  2003年   2714篇
  2002年   2527篇
  2001年   4571篇
  2000年   4319篇
  1999年   3350篇
  1998年   1112篇
  1997年   1085篇
  1996年   977篇
  1995年   882篇
  1994年   891篇
  1992年   2545篇
  1991年   2561篇
  1990年   2543篇
  1989年   2316篇
  1988年   2145篇
  1987年   2069篇
  1986年   1892篇
  1985年   1901篇
  1984年   1565篇
  1983年   1353篇
  1982年   985篇
  1981年   919篇
  1979年   1500篇
  1978年   1172篇
  1977年   1060篇
  1976年   1019篇
  1975年   1198篇
  1974年   1313篇
  1973年   1395篇
  1972年   1248篇
  1971年   1072篇
  1970年   970篇
  1969年   1008篇
  1968年   876篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
Inheritance of barley nuclear genes responsible for various morphological marker traits was studied in hybrid populations F2 and Fa. Nine marker genes showed deviation from Mendelian monogenic inheritance depending on the cross direction and maternal cytoplasm. Segregation biases to both recessive mutant and dominant normal phenotypes were observed. Mechanisms of the segregation bias related to cytoplasm substitution in iso- and alloplasmic lines are discussed.  相似文献   
93.
The composition of the phospholipid-bound fatty acids in the spermatozoa of the turkey, Meleagris gallopavo, and fowl, Gallus domesticus, was studied. The types of fatty acids were similar in the two birds. The ratio of polyunsaturated : saturated fatty acids was generally low but slightly higher in the turkey than in the fowl. The significance of the findings in relation to the origin of the semen collected in these gallinaceous birds and the greater difficulty of freezing turkey spermatozoa was discussed.  相似文献   
94.
The surface sediments collected from the intertidal and shallow marine (0–20 m) regimes of Jason Bay, South China Sea contain calcareous nannoplankton assemblages in whichGephyrocapsa oceanica comprises 99% of the assemblage. The calcareous nannoplankton diversity is very low and the abundance of species tends to increase with both depth and distance offshore and becomes abundant in samples from water depths of 18 m and 20 m.Emiliania huxleyi is absent from all studied samples. The sediments from the intertidal regime contained rare calcareous nannoplankton.  相似文献   
95.
96.
Collozoum inerme (Müller) is a colonial Radiolarian containing numerous cells bound in a common gelatinous matrix. The cells do not possess a skeleton as observed in many unicellular Radiolaria, but the cytoplasmic organization is similar. The cells are multinucleate and a complex system of cellular processes containing mitochondria, Golgi, and numerous vacuoles radiate out from the nuclear region. The endoplasm is connected to the ectoplasm across a double membrane boundary by thin cytoplasmic strands called fusules whose structure resemble those in unicellular Radiolaria. The ectoplasm contains a lacy network of vacuoles containing an osmiophilic substance. Rhizopodia emerge from the ectoplasmic sheath. Some are thin and densely granular. Larger diameter rhizopodia, containing less dense cytoplasm, sequester the zooxanthellae which present a typical dinoflagellate fine structure. Some of the zooxanthellae are apparently cultivated since they are sometimes observed dividing and persist in large numbers when colonies are cultivated under illumination for several weeks in the laboratory. However, colonies maintained in the dark have a decline in number of zooxanthellae and light microscopic examination shows they are being drawn into the ectoplasm of the radiolarian cells. Electron microscopic examination of zooxanthellae drawn into the ectoplasm sheath indicates they are digested. C. inerme is a remarkable example of a simple cellular aggregate that has exploited its colonial habit to culture algae and use them as food thus possibly enhancing the viability of the colony.  相似文献   
97.
Power spectra and coherence function of EEG of various cortical areas of both hemispheres were analyzed in 9 patients with extremely protracted loss of consciousness. Five patients were in the state of posttraumatic apallic syndrome lasting for more than 4 years in one patient, and 4-9 months with successive lethal outcome in 4 patients. One patient for more than 2 years was in a state of areactivity to external signals. In 3 patients the process of recovery of consciousness and speech began in 1-2 months. At the apallic syndrome, only low-frequency EEG components were present in spectrograms, and the values of coherence function were sharply decreased. With recovering consciousness and speech, a gradual appearance of alpha-activity was observed as well as an increase of coherence values at the frequency of the alpha-rhythm. The recovery of intercentral EEG relations in the motor-verbal cortical area was shown to play a special role in further normalization of connections in the cerebral cortex.  相似文献   
98.
99.
100.
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