全文获取类型
收费全文 | 2585篇 |
免费 | 225篇 |
专业分类
2810篇 |
出版年
2021年 | 42篇 |
2020年 | 23篇 |
2019年 | 35篇 |
2018年 | 43篇 |
2017年 | 23篇 |
2016年 | 54篇 |
2015年 | 89篇 |
2014年 | 96篇 |
2013年 | 129篇 |
2012年 | 145篇 |
2011年 | 149篇 |
2010年 | 102篇 |
2009年 | 82篇 |
2008年 | 110篇 |
2007年 | 128篇 |
2006年 | 114篇 |
2005年 | 94篇 |
2004年 | 94篇 |
2003年 | 90篇 |
2002年 | 73篇 |
2001年 | 77篇 |
2000年 | 68篇 |
1999年 | 60篇 |
1998年 | 34篇 |
1997年 | 34篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 47篇 |
1991年 | 37篇 |
1990年 | 31篇 |
1989年 | 40篇 |
1988年 | 37篇 |
1987年 | 41篇 |
1986年 | 34篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1979年 | 33篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 15篇 |
1974年 | 29篇 |
1973年 | 17篇 |
1972年 | 21篇 |
1970年 | 17篇 |
1967年 | 15篇 |
排序方式: 共有2810条查询结果,搜索用时 15 毫秒
1.
Ouenzar Bouchra Hartmann Caroline Rode Andre Benslimane Abdelali 《Plant Molecular Biology Reporter》1998,16(3):263-269
We have developed a new mini-procedure for isolation of total cellular DNA from date palm (Phoenix dactylifera L.). The procedure, which does not use liquid nitrogen, has proved useful due to temporary disruptions in supplies of liquid nitrogen that occur in countries where date palm trees are cultivated. DNA suitable for RFLP and PCR analyses is obtained. 相似文献
2.
3.
4.
We describe a new tracer method to measure unidirectional fluxes of Li+, despite the lack of any utilizable radioisotope of lithium. This method uses the purified stable isotopes, 6Li and 7Li, detected with an ion-probe microanalyser. The accuracy is comparable to that obtained for other ions (e.g., Na+) with radiotracers.The method has been applied to frog skin with both faces bathed in a 20% lithium/80% sodium medium. Sodium and lithium unidirectional fluxes have been measured simultaneously. The results are consistent with lithium being actively pumped, the outflux of lithium being, however, much larger than that of sodium. 相似文献
5.
Ana Isabell Paulino Aud Larsen Gunnar Bratbak Dale Evens Svein Rune Erga Einar Bye-Ingebrigtsen 《Marine Biology Research》2018,14(5):421-435
Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by Skeletonema marinoi and Chaetoceros socialis, and other Chaetoceros and Thalassiosira spp. Blooms of the haptophytes Phaeocystis pouchetii and Emiliania huxleyi were irregular and in some years totally absent. Although E. huxleyi was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes. 相似文献
6.
Dipl. Landw. Wilhelm Hartmann Dr. Kurt Zschau 《Archives Of Phytopathology And Plant Protection》2013,46(6):523-538
In den Jahren 1987 bis 1989 wurden die Auswirkungen und Effekte eines kombinierten Befalls des Winterweizens mit Sitobion avenae (Fabr.) und Puccinia recondita Rob.ex Desm. f.sp.tritici Erikss. untersucht. Dabei wurde das Verhalten der Schaderregerpopulationen und die Einflußnahme auf das Ertragsgeschehen bei separatem und simultanem Befall erfaßt. Während bei starkem Befall der oberen Blattetagen mit P.recondita eine Förderung der Aphidenpopulation an den Ähren der befallenen Pflanzen registriert werden konnte, war bei schwachem Braunrostbefall keine Einflußnahme auf die Blattläuse nachweisbar. Durch das kombinierte Auftreten beider Schaderreger kann es zu Reduktionen bei der Kornmasse/Ähre und bei der Tausendkornmasse kommen, die größer sind, als die Summe der Verluste bei Einzelbefall. Ähren stark braunrostbefallener Winterweizenpflanzen wurden zeitiger von S.avenae angeflogen und schneller besiedelt als diese von gesunden Kontrollpflanzen. Als Ursache für die Förderung der Populationsentwicklung von S.avenae werden durch P.recondita induzierte Veränderungen im Angebot an freien Aminosäuren in der Wirtspflanze diskutiert. 相似文献
7.
Ultrastructural demonstration of NAD-pyrophosphorylase activity (E.C.2.7.7.1) in isolated mouse liver nuclei was investigated with the use of an electronhistochemical procedure based on the precipitation of pyrophosphate ions with lead ions under conditions permitting simultaneous ATPase inhibition by formaldehyde/ethanol prefixation. In isolated mouse liver nuclei activity of NAD-pyrophosphorylase was found in nucleoli, in interchromatin granules, coiled bodies and strand-like structures in nucleoplasm. 相似文献
8.
9.
The interstitial matrix of human carcinomas and sarcomas transplanted to the nude mouse: immunolocalization of some human and murine components 总被引:1,自引:0,他引:1
10.
Regulation of nitrogenase activity by oxygen in Azospirillum brasilense and Azospirillum lipoferum. 总被引:10,自引:6,他引:4
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The nitrogenase activity of the microaerophilic bacteria Azospirillum brasilense and A. lipoferum was completely inhibited by 2.0 kPa of oxygen (approximately 0.02 atm of O2) in equilibrium with the solution. The activity could be partially recovered at optimal oxygen concentrations of 0.2 kPa. In contrast to the NH4+ switch off, no covalent modification of the nitrogenase reductase (Fe protein) was involved, as demonstrated by Western-blotting and 32P-labeling experiments. However, the inhibition of the nitrogenase activity under anaerobic conditions was correlated with covalent modification of the Fe protein. In contrast to the NH4+ switch off, no increase in the cellular glutamine pool and no modification of the glutamine synthetase occurred under anaerobic switch-off conditions. Therefore, a redox signal, independent of the nitrogen control of the cell, may trigger the covalent modification of the nitrogenase reductase of A. brasilense and A. lipoferum. 相似文献