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   780684篇
  免费   95041篇
  国内免费   420篇
  2016年   8507篇
  2015年   12961篇
  2014年   14926篇
  2013年   20772篇
  2012年   23727篇
  2011年   23672篇
  2010年   16032篇
  2009年   15243篇
  2008年   21714篇
  2007年   22309篇
  2006年   20875篇
  2005年   20133篇
  2004年   19955篇
  2003年   19313篇
  2002年   18738篇
  2001年   34296篇
  2000年   34736篇
  1999年   27999篇
  1998年   10722篇
  1997年   11365篇
  1996年   10916篇
  1995年   10326篇
  1994年   10175篇
  1993年   10001篇
  1992年   23584篇
  1991年   22846篇
  1990年   22480篇
  1989年   21805篇
  1988年   20077篇
  1987年   19740篇
  1986年   18109篇
  1985年   18189篇
  1984年   15114篇
  1983年   13197篇
  1982年   10547篇
  1981年   9397篇
  1980年   8949篇
  1979年   14544篇
  1978年   11691篇
  1977年   10563篇
  1976年   9961篇
  1975年   10800篇
  1974年   11626篇
  1973年   11414篇
  1972年   10219篇
  1971年   9478篇
  1970年   8109篇
  1969年   7664篇
  1968年   6842篇
  1967年   6173篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
741.
Ten patients with advanced progressive adenocarcinoma of the prostate were treated with a long acting analogue of gonadotrophin releasing hormone. Eight of these patients responded to treatment in terms of pain relief and clinical regression of tumour. Serum gonadotrophin and testosterone concentrations were significantly suppressed by the end of the second week of treatment, testosterone concentrations being comparable with those achieved by castration. The two patients who failed to respond had both relapsed previously when receiving conventional treatment, and neither showed any endocrine response to the analogue. Superagonists of gonadotrophin releasing hormone may be the treatment of choice in adenocarcinoma of the prostate, but further trials are required to establish long term safety and efficacy.  相似文献   
742.
743.
The pericarp of Chinese gooseberries is green due to the presenceof low concentrations of chlorophylls. On a f. wt basis thereis about 1.5 times more tetrapyrollic pigments (chlorophyllsand related compounds) in the outer pericarp than in the innerpericarp, whereas the carotenoid pigment values only showed1.25 times more in the outer than in the inner part of the fruit.The drying of Chinese gooseberries at 40 °C for 40 h resultedin the loss of at least half the tetrapyrollic pigments andof carotenoids. Chlorophylls a and b were converted to chlorophyllides,pheophytins and pheophorbides. Chloroplasts in the outer pericarp are clustered closely aroundthe nucleus and have a well-defined grana and inter-granal membranesystem. In the inner pericarp the chloroplasts are again clusteredaround the nucleus and there is a proliferation of inter-granalmembranes. In dried tissue the limiting membrane of chloroplastswas completely dispersed whereas some of the internal membranesremained intact. Actinidia chinensis Planch., Chinese gooseberry, Kiwi fruit, pigments, chloroplast structure  相似文献   
744.
745.
A total of 2,377 C 57 Bl/6M mice were assigned to control groups and experimental groups exposed to tritiated water administered as a pulse injection or in drinking water, at a dose of 1.0 microCi per injection or per ml of drinking water. Weanlings were observed for the duration of life span. Data analysis was based on two coefficient estimates (1) individual carcinogenic induction coefficient and (2) specific tumorigenic induction coefficient. The carcinogenic potency of tritium was found to be dual in nature in enhancing the absolute induction of lymphocytic lymphomas in both sexes as well as their relative induction in competition with reticulo-endothelial tumors of other types.  相似文献   
746.
In carps living since 4 months at 6, 20 or 30 degrees C, epinephrine or glucagon injections produce increase in plasma glucose but affect only slightly liver glycogen: lower is the temperature, slower and longer are the effect. Insulin injection induces more or less delayed hypoglycaemia according to temperature acclimatization; decrease in blood glucose is accompanied by a slight increase of glycogen in all tissues at 6 degrees C and on the contrary by a very strong depletion of this polysaccharide in liver and even heart at 20 and 30 degrees C.  相似文献   
747.
748.
749.
750.
The importance of oxygen availability in the embryonation of the infective egg stages of the gastrointestinal nematode parasite Heterakis gallinarum was studied in the laboratory. Unembryonated H. gallinarum eggs were kept under either aerobic conditions by gassing with oxygen, or anaerobic conditions by gassing with the inert gas nitrogen, under a range of constant temperatures. Oxygenated eggs embryonated at a rate influenced by temperature. Conversely, eggs treated with nitrogen showed no embryonation although when these eggs were transferred from nitrogen to oxygen gas after 60 days of treatment, embryonation occurred. This demonstrated that oxygen is an essential requirement for H. gallinarum egg development, although undeveloped eggs remain viable, even after 60 days in low oxygen conditions. The effects of climate on the biology of free-living stages studied under constant laboratory conditions cannot be applied directly to the field where climatic factors exhibit daily cycles. The effect of fluctuating temperature on development was investigated by including an additional temperature group in which H. gallinarum eggs were kept under daily temperature cycles between 12 and 22°C. Cycles caused eggs to develop significantly earlier than those in the constant mean cycle temperature, 17°C, but significantly slower than those in constant 22°C suggesting that daily temperature cycles had an accelerating effect on H. gallinarum egg embryonation but did not accelerate to the higher temperature. These results suggest that daily fluctuations in temperature influence development of the free-living stages and so development cannot be accurately predicted on the basis of constant temperature culture.  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