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   338802篇
  免费   38669篇
  国内免费   148篇
  377619篇
  2018年   3270篇
  2017年   3009篇
  2016年   4394篇
  2015年   6147篇
  2014年   7186篇
  2013年   9983篇
  2012年   11337篇
  2011年   11391篇
  2010年   7655篇
  2009年   6770篇
  2008年   9825篇
  2007年   10101篇
  2006年   9382篇
  2005年   9005篇
  2004年   9093篇
  2003年   8642篇
  2002年   8542篇
  2001年   14782篇
  2000年   14851篇
  1999年   11820篇
  1998年   4175篇
  1997年   4244篇
  1996年   4039篇
  1995年   3876篇
  1994年   3871篇
  1993年   3752篇
  1992年   9933篇
  1991年   9481篇
  1990年   9283篇
  1989年   9028篇
  1988年   8403篇
  1987年   8037篇
  1986年   7269篇
  1985年   7361篇
  1984年   6083篇
  1983年   5332篇
  1982年   4190篇
  1981年   3713篇
  1980年   3525篇
  1979年   6113篇
  1978年   4563篇
  1977年   4291篇
  1976年   3987篇
  1975年   4317篇
  1974年   4669篇
  1973年   4741篇
  1972年   4370篇
  1971年   4077篇
  1970年   3451篇
  1969年   3350篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
95.
Six hundred foramina transversaria (FT) of the axis vertebrae of 4 population groups were examined for the presence of erosion of the lateral articular mass. Of these, 127 (21%) and 72 (12%) presented with moderate and marked erosion, respectively. Evidence is presented incriminating the tortuosity of the vertebral artery as well as congenital factors in the etiology of the erosion of the FT. Attention is drawn to the possible correlation between angulation of the transverse process of the axis and erosion of the FT.  相似文献   
96.
Two internal herinias of the intestines were found in adult males. One was a large translucent avascular membranous sac contining the small intestine from the duodenojejunal flexure to a point 6 in. proximal to the ileocaecal junction. The other was a peritoneal sac enclosing the small intestine, appendix, caecum and 6 in. of the ascending colon. The mesenteric and colic vessels were normal. Both hernias conformed to PAPEZ's concept of the so-called paraduodenal hernia that the hernial sac is derived from the umbilical coelom. The authors suggest that most of the so-called paraduodenal hernias are derived from the embryonic umbilical peritoneal diverticulum rather than from the peritoneal recesses or mesentery of the colon.  相似文献   
97.
98.
The liver and kidney of rat underwent severe histopathological lesions when treated with a single bolus dose of carbendazim, a fungicide, particularly affecting the hepatocytes and the renal corpuscles, respectively. The effects appear to be manifestations of the microtubule-disrupting activity of carbendazim. Treatment of carbendazim-treated rats with the powder of tuberous root of Withania somnifera (Ashwagandha) for 48 days resulted in complete cure of these organs. The results indicate that Withania somnifera would be an effective curative for carbendazim-induced histopathological changes in the liver and kidney.  相似文献   
99.
In a medium containing 40 g ethanol l–1, laccase production by Trametes versicolor was 2.6 unit per ml of the supernatant, which was over 20 times higher than that without ethanol. Laccase activity with ethanol was quite comparable to that with the well-known inducers such as veratryl alcohol, xylidine and guaiacol. With other white-rot fungi, Coriolus hirsutus and Grifola frondosa, ethanol had a similar stimulatory effect on laccase production.  相似文献   
100.
Changes in yield and quality of fresh tomatoes in response toair vapour pressure deficit (VPD) and plant fruit load werestudied under Mediterranean summer conditions. Plants thinnedto three or six fruits per truss were grown in two compartments,one at a VPD below 1.5 kPa, the other without VPD control. Theseasonal trend in fruit yield and quality was assessed fromApril to September by weekly measurement of number, fresh weightand dry matter content of harvested fruits, together with theoccurrence of blossom-end-rot (BER) and cracking. On two occasions,in July and September, sugar and acid content was measured atthree ripening stages. The seasonal decrease in fresh yieldwas attenuated at low VPD, because of higher individual fruitfresh weight, especially at low fruit load. Low VPD decreasedoccurrence of BER but like low fruit load, it increased fruitcracking. Fruit dry matter content was lower at low VPD, butwas unaffected by fruit load. Sugar content and the ratio ofsugars:acids was increased at high VPD and low fruit load, withinteractive effects depending on season and ripening stage.The influence of VPD on acid content differed with fruit loadand also changed during ripening and between seasons. Resultsshowed that water was the main limiting factor for growth offruits picked in July; at this time, reducing fruit load topromote mean fruit size had negative effects on BER and cracking.Reducing VPD reduced BER but had a negative effect on crackingand diluted both the dry matter and sugar content. For fruitsharvested later in summer, these negative effects were attenuatedbecause fruit growth was also carbon limited. Copyright 2000Annals of Botany Company Lycopersicon esculentum Mill., tomato, water and carbon stress, yield, quality, dry matter, sugar, acid, BER, volatile composition  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