全文获取类型
收费全文 | 917401篇 |
免费 | 98989篇 |
国内免费 | 491篇 |
专业分类
1016881篇 |
出版年
2018年 | 9534篇 |
2017年 | 9187篇 |
2016年 | 12726篇 |
2015年 | 16913篇 |
2014年 | 19419篇 |
2013年 | 28112篇 |
2012年 | 31826篇 |
2011年 | 32008篇 |
2010年 | 21315篇 |
2009年 | 19084篇 |
2008年 | 28015篇 |
2007年 | 28762篇 |
2006年 | 26895篇 |
2005年 | 25737篇 |
2004年 | 25321篇 |
2003年 | 24052篇 |
2002年 | 23202篇 |
2001年 | 41903篇 |
2000年 | 41860篇 |
1999年 | 33323篇 |
1998年 | 11330篇 |
1997年 | 11929篇 |
1996年 | 11195篇 |
1995年 | 10327篇 |
1994年 | 10239篇 |
1993年 | 10022篇 |
1992年 | 27066篇 |
1991年 | 25924篇 |
1990年 | 25366篇 |
1989年 | 24843篇 |
1988年 | 22846篇 |
1987年 | 21470篇 |
1986年 | 19985篇 |
1985年 | 19998篇 |
1984年 | 16324篇 |
1983年 | 13979篇 |
1982年 | 10603篇 |
1981年 | 9467篇 |
1980年 | 9043篇 |
1979年 | 15431篇 |
1978年 | 11927篇 |
1977年 | 10863篇 |
1976年 | 10120篇 |
1975年 | 11099篇 |
1974年 | 11839篇 |
1973年 | 11616篇 |
1972年 | 10546篇 |
1971年 | 9520篇 |
1970年 | 8311篇 |
1969年 | 7756篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests. 相似文献
53.
A A Sukhopiatkina O S Bat A V Levitskaia V G Potapova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(4):80-81
The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures. 相似文献
54.
55.
56.
57.
François Frappier Andrée Marquet 《Biochemical and biophysical research communications》1981,103(4):1288-1293
[3-14C, 35S]-L-cysteine was tested as precursor of biotin in Achromobacter IVSW. No significant incorporation was observed, in contradiction with the data previously reported. On the other hand, Achromobacter IVSW converts [3H, 14C]-dethiobiotin into biotin. This suggests that biotin is biosynthesized in Achromobacter according to the classical dethiobiotin pathway. 相似文献
58.
59.
V A Berezin E N Zhmarev I A Brodskaia G M Shevchenko L S Zashko 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(7):68-70
The content of neurospecific proteins S-100, GFA and D2 was measured in malignant cerebral tumors by electrophoresis with the use of monospecific antisera. Concomitant measurement of proteins S-100 and GFA is a more reliable diagnostic criterion as to the tumor histogenesis than study of each protein alone. D2 protein appeared to be the most stable specific marker. 相似文献
60.
Demonstration that a chemically synthesized BPV1 oncoprotein and its C-terminal domain function to induce cellular DNA synthesis 总被引:17,自引:0,他引:17
Bovine papillomavirus type 1 contains the smallest known oncogene (ORF E5), encoding a hydrophobic 44 amino acid protein. To study the biochemical functions of the E5 oncoprotein, we have chemically synthesized it and several deletion mutant peptides. We demonstrate induction of cellular DNA synthesis in growth-arrested cells by microinjection of E5 oncoprotein. This activity can be broken down into two functionally distinguishable domains. Remarkably, the first domain, which alone is sufficient to induce cellular DNA synthesis, contains only the C-terminal 13 amino acids. This is the smallest known protein fragment that can autonomously activate cellular DNA synthesis. The second domain is the hydrophobic middle region, which by itself fails to induce cellular DNA synthesis but confers a 1000-fold increase in specific activity. The N-terminal one-third of the molecule is dispensable for induction of DNA synthesis. 相似文献