全文获取类型
收费全文 | 40405篇 |
免费 | 4352篇 |
国内免费 | 12篇 |
出版年
2021年 | 498篇 |
2020年 | 349篇 |
2019年 | 428篇 |
2018年 | 553篇 |
2017年 | 524篇 |
2016年 | 901篇 |
2015年 | 1630篇 |
2014年 | 1576篇 |
2013年 | 2108篇 |
2012年 | 2397篇 |
2011年 | 2108篇 |
2010年 | 1459篇 |
2009年 | 1335篇 |
2008年 | 1829篇 |
2007年 | 1811篇 |
2006年 | 1630篇 |
2005年 | 1580篇 |
2004年 | 1489篇 |
2003年 | 1282篇 |
2002年 | 1292篇 |
2001年 | 1232篇 |
2000年 | 1237篇 |
1999年 | 1101篇 |
1998年 | 595篇 |
1997年 | 545篇 |
1996年 | 544篇 |
1995年 | 537篇 |
1994年 | 494篇 |
1993年 | 517篇 |
1992年 | 1010篇 |
1991年 | 754篇 |
1990年 | 770篇 |
1989年 | 761篇 |
1988年 | 654篇 |
1987年 | 596篇 |
1986年 | 611篇 |
1985年 | 711篇 |
1984年 | 533篇 |
1983年 | 415篇 |
1982年 | 342篇 |
1981年 | 313篇 |
1980年 | 253篇 |
1979年 | 379篇 |
1978年 | 344篇 |
1977年 | 242篇 |
1976年 | 227篇 |
1975年 | 196篇 |
1974年 | 290篇 |
1973年 | 250篇 |
1972年 | 189篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Dane Bicanic Darko Dimitrovski Svjetlana Luterotti Ksenija Marković Charlotte van Twisk Josephus G. Buijnsters Otto Dóka 《Food biophysics》2010,5(1):24-33
The trans-lycopene content of fresh tomato homogenates was assessed by means of the laser photoacoustic spectroscopy, the laser optothermal
window, micro-Raman spectroscopy, and colorimetry; none of these methods require the extraction from the product matrix prior
to the analysis. The wet chemistry method (high-performance liquid chromatography) was used as the absolute quantitative method.
Analytical figures of merit for all methods were compared statistically; best linear correlation was achieved for the chromaticity
index a* and chroma C*. 相似文献
92.
93.
H. van Keulen 《Plant and Soil》1981,58(1-3):205-229
94.
95.
Maria D Mjaavatten Désirée van der Heijde Till Uhlig Anne J Haugen Halvor Nygaard Göran Sidenvall Knut Helgetveit Tore K Kvien 《Arthritis research & therapy》2010,12(3):R76
Introduction
We wanted to assess the importance of the levels of anti-citrullinated peptide antibody (anti-CCP) and immunoglobulin M (IgM) rheumatoid factor (RF) in predicting development of persistent arthritis from undifferentiated arthritis (UA), and to investigate whether there is an added predictive value for persistent arthritis in testing for both anti-CCP and IgM RF. 相似文献96.
97.
Induction of the nodA promoter of Rhizobium leguminosarum Sym plasmid pRL1JI by plant flavanones and flavones. 总被引:24,自引:16,他引:8 下载免费PDF全文
S A Zaat C A Wijffelman H P Spaink A A van Brussel R J Okker B J Lugtenberg 《Journal of bacteriology》1987,169(1):198-204
An expression vector containing the Rhizobium leguminosarum nodA promoter cloned in front of the Escherichia coli lacZ gene was used to characterize the properties of the R. leguminosarum nodA gene-inducing compound(s) present in sterile root exudate of the host plant Vicia sativa L. subsp. nigra (L.). The major inducing compound was flavonoid in nature, most likely a flavanone. The commercially available flavonoids naringenin (5,7,4'-trihydroxyflavanone), eriodictyol (5,7,3'4'-tetrahydroxyflavanone), apigenin (5,7,4'-trihydroxyflavone), and luteolin (5,7,3',4'-tetrahydroxyflavone) induced the nodA promoter to the same level as the root exudate. On the basis of chromatographic properties, it was concluded that none of these compounds is identical to the inducer that is present in root exudate. The induction of the nodA promoter by root exudate and by the most effective inducer naringenin was very similar, as judged from the genetic requirements and the kinetics of induction. 相似文献
98.
99.
100.
Immunochemical study of nutritionally variant streptococci 总被引:11,自引:0,他引:11
Nutritionally variant streptococci (NVS) have been characterized by their growth as satellite colonies around colonies of staphylococci or several other gram-positive or gram-negative bacterial strains. The majority of the NVS strains were isolated from patients with subacute bacterial endocarditis. Organisms identified as NVS were subdivided into three serotypes by rocket-line electrophoresis and hemagglutination inhibition assays. Ninety-nine of 103 strains expressed one or more of the three serotype antigens; however, a group antigen was not demonstrated in the various extracts of these streptococci. Surface protein studies confirmed the NVS differentiation into serotypes. Serotype I organisms expressed surface protein(s) specific for the serotype, whereas the serotype II and III NVS demonstrated common protein(s) on their surface. Furthermore, SDS extraction released a greater amount of radioiodinatable surface protein from serotypes I and III bacteria than serotype II. Finally, there was no correlation between the serotype or the disease of the patients from which the NVS strains were isolated. 相似文献