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   94970篇
  免费   380篇
  国内免费   812篇
  2023年   20篇
  2022年   78篇
  2021年   111篇
  2020年   64篇
  2019年   94篇
  2018年   11888篇
  2017年   10727篇
  2016年   7553篇
  2015年   721篇
  2014年   414篇
  2013年   490篇
  2012年   4347篇
  2011年   12943篇
  2010年   12057篇
  2009年   8268篇
  2008年   9838篇
  2007年   11401篇
  2006年   305篇
  2005年   547篇
  2004年   996篇
  2003年   1032篇
  2002年   788篇
  2001年   274篇
  2000年   174篇
  1999年   44篇
  1998年   12篇
  1997年   28篇
  1996年   20篇
  1995年   11篇
  1994年   12篇
  1993年   42篇
  1992年   27篇
  1991年   57篇
  1990年   16篇
  1989年   21篇
  1988年   23篇
  1987年   19篇
  1984年   14篇
  1983年   19篇
  1982年   7篇
  1981年   8篇
  1975年   7篇
  1973年   7篇
  1972年   251篇
  1971年   277篇
  1965年   13篇
  1962年   24篇
  1956年   5篇
  1944年   12篇
  1940年   10篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
A male sterile line was isolated in marigold (Tagetes erecta L.) and cytological analysis determined this to be a novel genic male sterility trait (Tems). Through the use of amplified fragment length polymorphisms (AFLPs) and bulked segregant analysis (BSA), tightly linked markers of Tems were identified with a view towards a map-based cloning strategy. It was found that spontaneous homeotic conversion of floral organs was the underlying cause of the male sterility in this marigold line. Thus, petals of male sterile plants resembled sepal-like structures and the stamens were partially converted to styles, although without the full characteristics or function of the true style organs. We have constructed a fine marker-based map for the Tems gene. This is intended to provide a tool for marker assisted selection (MAS) strategies in hybrid breeding and map-based cloning strategies for the male sterility locus. We discuss the significance of this spontaneously derived genic male sterility trait relating to the homeotic conversion of floral organs in marigold.  相似文献   
192.
The role of CCN proteins in vivo is only just becoming understood. A prototypical member of the CCN family, CCN3 suppresses proliferation. In a study in press, Shimoyama and colleagues show that mice lacking CCN3 have a hyperproliferative response to vascular injury. These data, along with other recent observations, suggest that CCN3 may represent a novel therapy for hyperproliferative diseases.  相似文献   
193.
In this paper we propose that the internal bracketing of a word with more than two morphemes is reflected in the phonetic implementation. We hypothesize that embedded forms show more phonetic reduction than forms at higher structural levels (‘Embedded Reduction Hypothesis’). This paper tests the prediction of the Embedded Reduction Hypothesis with triconstituent compounds. The analysis of the durational properties of almost 500 compound tokens shows that there is a lengthening effect on the non-embedded constituent, and a shortening effect on the adjacent embedded constituent. Yet, this predicted effect of embedding interacts with other lexical factors, above all the bigram frequency of the embedded compound. At a theoretical level, these effects mean that the durational properties of the cross-boundary constituents are indicative of the hierarchical structure and of the strength of the internal boundary of triconstituent compounds. Hence, morphological structure is reflected in the speech signal.  相似文献   
194.
195.
196.
197.
198.
The influence of moulded hay (Alternaria alternata, Epicoccum nigrum, Mucor racemosus, Ulocladium chartarum) and the efficiency of Vitamin B1 substitution to cope these effects on rumen protozoa was investigated using the longterm rumen simulation technique (RUSITEC) for about 25 days. Moulded hay affected medium-sized protozoa to a different extent (Alternaria alternata: ?16 %, Epicoccum nigrum: ?27 %, Mucor racemosus: ?9 %, Ulocladium chartarum: +2 %). The vitamin B1 substitution had positive effects during the feeding of Mucor racemosus and Ulocladium chartarum.  相似文献   
199.
An isolated rat liver was perfused with deoxynivalenol (DON) at a dose of 3 mg in a recirculating perfusion system. To identify glucuronide conjugates equal amounts of bile samples, perfusate and liver homogenates were incubated with and without (control) a β-glucuronidase preparation and analyzed by thin layer chromatography and capillary gas liquid chromatography — chemical ionization mass spectrometry. A total of 40.4% of the administered dose of DON was found to be conjugated with glucuronic acid (perfusate 20.4%, bile 19.2%, liver 0.8%), while only 1.3% of the parent DON (perfusate 1.1%, bile 0.2%) was detected. The cleavage of DON-glucuronide was demonstrated by incubating DON-glucuronide containing bile samples with intestine contents under anaerobic conditions.  相似文献   
200.
Effects of tissue position (viz. outer vs inner mesocarp) and heat treatment (48°C, 20 min) on variations in polygalacturonase (EC 3.2.1.15 and EC 3.2.1.67) activity and ripening of fruits of Carica papaya L. cv. Backcross Solo were investigated. Polygalacturonase activity increased during ripening concomitantly with an increase in tissue softness and soluble polyuronide level. Throughout ripening, inner mesocarp tissue was softer and contained higher polygalacturonase activity than outer mesocarp tissue. Titratable acidity as well as ß-galactosidase (EC 3.2.1.23) activity also increased during ripening; however, unlike polygalacturonase, their level or activity was lower in inner than in outer mesocarp. Ascorbic acid could partially account for the increase in titratable acidity during ripening but contributed very little to the differences in titratable acid levels between outer and inner mesocarp. Heat treatment had no effect on either fruit softness or titratable acidity, but it markedly reduced the increase in ascorbic acid and polygalacturonase activity during ripening. Ripening, as reflected by changes in tissue softness and polygalacturonase activity, progressed outwardly from the interior towards the exterior of the fruit. The effect of heat treatment in suppressing polygalacturonase activity was relatively greater in inner than in outer mesocarp, suggesting that sensitivity of the enzyme to heat treatment may vary with stage of ripeness of the tissue.  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