全文获取类型
收费全文 | 95218篇 |
免费 | 407篇 |
国内免费 | 812篇 |
出版年
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 23篇 |
2018年 | 11867篇 |
2017年 | 10695篇 |
2016年 | 7483篇 |
2015年 | 638篇 |
2014年 | 355篇 |
2013年 | 387篇 |
2012年 | 4317篇 |
2011年 | 12902篇 |
2010年 | 12064篇 |
2009年 | 8283篇 |
2008年 | 9880篇 |
2007年 | 11466篇 |
2006年 | 375篇 |
2005年 | 607篇 |
2004年 | 1060篇 |
2003年 | 1105篇 |
2002年 | 858篇 |
2001年 | 329篇 |
2000年 | 221篇 |
1999年 | 78篇 |
1998年 | 31篇 |
1997年 | 42篇 |
1996年 | 27篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 38篇 |
1992年 | 76篇 |
1991年 | 81篇 |
1990年 | 49篇 |
1989年 | 41篇 |
1988年 | 48篇 |
1987年 | 43篇 |
1986年 | 33篇 |
1985年 | 29篇 |
1984年 | 29篇 |
1983年 | 33篇 |
1982年 | 15篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1972年 | 248篇 |
1971年 | 277篇 |
1970年 | 12篇 |
1965年 | 15篇 |
1962年 | 25篇 |
1944年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
191.
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
192.
193.
194.
195.
196.
Eric Delson 《Journal of Mammalian Evolution》2007,14(3):198-199
197.
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
198.
Jerzy Chelkowski Piotr Zajkowski Marcin Zawadzki Juliusz Perkowski 《Mycotoxin Research》1987,3(1):25-32
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
199.
Using Toyopearl and cyclohexane: cyclohexanol solvent, fourCl-containing Chls were separated from 36Cl-labeled cells ofthe blue-green, Plectonema boryanum. In normally grown cells,all four Cl-containing chlorophylls amounted to less than 1/2,000of the total Chi and about 1/50 of P700, values much lower thanpreviously reportedcontents of Chi RC I, and varied from algato alga. The level of Cl-containing Chi was markedly enhancedwhen the cells were poisoned with methyl viologen. These resultssuggests that these Cl-containing Chls are not related to thereaction center of PS I. (Received June 23, 1987; Accepted September 17, 1987) 相似文献
200.
In vitro splicing of a chicken delta-crystallin pre-mRNA in a mammalian nuclear extract 总被引:6,自引:0,他引:6
An in vitro splicing system was constructed using portions of chicken delta-crystallin pre-mRNA synthesized in vitro and a HeLa nuclear extract. Analysis of the reaction products revealed that about 25% of the pre-mRNA was precisely spliced at 30 degrees C in 2 h under the standard conditions. The other major products of the reaction detected were a 5'-exon fragment and three RNA species showing unusual electrophoretic mobilities on polyacrylamide gels. Structural analyses showed that these three RNAs contain a branch (lariat) structure as seen in the in vitro splicing reactions of human beta-globin, adenovirus, and yeast pre-mRNAs. In addition, methylation at the N-7 position of the blocking guanosine of the 5'-terminal cap structure of pre-mRNA has been suggested to play an important role in the splicing reaction. 相似文献