全文获取类型
收费全文 | 99044篇 |
免费 | 694篇 |
国内免费 | 819篇 |
出版年
2023年 | 47篇 |
2022年 | 147篇 |
2021年 | 280篇 |
2020年 | 124篇 |
2019年 | 158篇 |
2018年 | 11974篇 |
2017年 | 10768篇 |
2016年 | 7606篇 |
2015年 | 884篇 |
2014年 | 609篇 |
2013年 | 752篇 |
2012年 | 4636篇 |
2011年 | 13148篇 |
2010年 | 12189篇 |
2009年 | 8399篇 |
2008年 | 9995篇 |
2007年 | 11584篇 |
2006年 | 473篇 |
2005年 | 692篇 |
2004年 | 1155篇 |
2003年 | 1170篇 |
2002年 | 937篇 |
2001年 | 377篇 |
2000年 | 266篇 |
1999年 | 105篇 |
1998年 | 51篇 |
1997年 | 61篇 |
1996年 | 48篇 |
1994年 | 32篇 |
1993年 | 52篇 |
1992年 | 83篇 |
1991年 | 111篇 |
1990年 | 81篇 |
1989年 | 68篇 |
1988年 | 85篇 |
1987年 | 62篇 |
1986年 | 41篇 |
1985年 | 55篇 |
1984年 | 56篇 |
1983年 | 59篇 |
1980年 | 33篇 |
1979年 | 39篇 |
1978年 | 43篇 |
1977年 | 33篇 |
1976年 | 34篇 |
1975年 | 30篇 |
1974年 | 40篇 |
1972年 | 271篇 |
1971年 | 299篇 |
1970年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
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
202.
203.
204.
205.
Eric Delson 《Journal of Mammalian Evolution》2007,14(3):198-199
206.
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
207.
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
208.
Erythrocyte samples from 101 individuals, originally from Punjab and living at the time of investigation in England, were screened for glucose-6-phosphate dehydrogenase (G6PD) variants by Beutler’s fluorescent spot test and standard cellulose acetate gel (Cellogel) electrophoresis. All but 2 of the 40 males in the study were found to be indistinguishable from normal G6PD B. One of the variants had 2% of the normal activity and resembled G6PD Mediterranean in electrophoretic behaviour. The other variant showed 52% of the normal activity and migrated slower than G6PD B in Cellogel with about half of the normal band intensity. A set of physicochemical characteristics of the variant determined by conventional methods distinguished it from the variants reported so far. It was designated as G6PD Punjab, and the corresponding allele asG6PD PUN. The most striking feature of G6PD Punjab is a remarkable alteration in its electrophoretic behaviour after dialysis. 相似文献
209.
RepC protein encoded by plasmid pT181 has single-stranded endonuclease and topoisomerase-like activities. These activities may be involved in the initiation (and termination) of pT181 replication by a rolling circle mechanism. RepC protein cleaves the bottom strand of DNA within the origin of replication at a single, specific site when the DNA is in the supercoiled or linear (double or single-stranded) form. We have found that RepC protein will also cleave single-stranded DNA at sites other than the origin of replication. We have mapped the secondary cleavage sites on pT181 DNA. When the DNA is in the supercoiled, or linear, double-stranded form, only the primary site within the origin is cleaved. However, when the DNA is present in the single-stranded form, several strong and weak cleavage sites are observed. The DNA sequence at these cleavage sites shows a strong similarity with the primary cleavage site. The presence of Escherichia coli SSB protein inhibited cleavage at all of the secondary nick sites while the primary nick site remained susceptible to cleavage. 相似文献
210.