全文获取类型
收费全文 | 101247篇 |
免费 | 715篇 |
国内免费 | 816篇 |
出版年
2022年 | 52篇 |
2021年 | 81篇 |
2020年 | 62篇 |
2019年 | 65篇 |
2018年 | 11901篇 |
2017年 | 10728篇 |
2016年 | 7595篇 |
2015年 | 849篇 |
2014年 | 550篇 |
2013年 | 853篇 |
2012年 | 4700篇 |
2011年 | 13309篇 |
2010年 | 12296篇 |
2009年 | 8510篇 |
2008年 | 10261篇 |
2007年 | 11879篇 |
2006年 | 775篇 |
2005年 | 1007篇 |
2004年 | 1531篇 |
2003年 | 1453篇 |
2002年 | 1227篇 |
2001年 | 392篇 |
2000年 | 275篇 |
1999年 | 141篇 |
1998年 | 120篇 |
1997年 | 109篇 |
1996年 | 93篇 |
1995年 | 87篇 |
1994年 | 77篇 |
1993年 | 89篇 |
1992年 | 117篇 |
1991年 | 128篇 |
1990年 | 86篇 |
1989年 | 77篇 |
1988年 | 88篇 |
1987年 | 69篇 |
1986年 | 56篇 |
1985年 | 48篇 |
1984年 | 51篇 |
1983年 | 49篇 |
1982年 | 34篇 |
1981年 | 35篇 |
1980年 | 44篇 |
1979年 | 33篇 |
1978年 | 26篇 |
1977年 | 33篇 |
1975年 | 21篇 |
1972年 | 253篇 |
1971年 | 280篇 |
1962年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
Feedbacks between nutrient cycling and vegetation predict plant species coexistence and invasion 总被引:5,自引:0,他引:5
To investigate the role of species‐specific litter decomposability in determining plant community structure, we constructed a theoretical model of the codevelopmental dynamics of soil and vegetation. This model incorporates feedback between vegetation and soil. Vegetation changes the nutrient conditions of soil by affecting mineralization processes; soil, in turn, has an impact on plant community structure. The model shows that species‐level traits (decomposability, reproductive and competitive abilities) determine whether litter feedback effects are positive or negative. The feedback determines community‐level properties, such as species composition and community stability against invasion. The model predicts that positive feedback may generate multiple alternative steady states of the plant community, which differ in species richness or community composition. In such cases, the realized state is determined by initial abundance of co‐occurring species. Further, the model shows that the importance of species‐level traits depends on environmental conditions such as system fertility. 相似文献
203.
204.
205.
206.
Eric Delson 《Journal of Mammalian Evolution》2007,14(3):198-199
207.
208.
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
209.
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
210.
Takashi Yamashita Naoto Tonouchi Takeshi Uozumi Teruhiko Beppu 《Molecular & general genetics : MGG》1987,210(3):462-467
Summary The aspartic protease gene of a zygomycete fungus Mucor pusillus was expressed in Saccharomyces cerevisiae under the control of the yeast GAL7 promoter. A putative preproenzyme with an NH2-terminal extension of 66 amino acids directed by the gene was processed in yeast cells and the mature enzyme, whose NH2-terminus was identical to that of the Mucor enzyme, was efficiently secreted into the medium at a concentration exceeding 150 mg/l. The enzyme secreted from the recombinant yeast was more glycosylated than the native Mucor enzyme but its enzymatic properties were almost identical with those of the native enzyme, which has been used as a milk coagulant in cheese manufacture. 相似文献