全文获取类型
收费全文 | 16720篇 |
免费 | 1203篇 |
国内免费 | 13篇 |
出版年
2023年 | 46篇 |
2022年 | 144篇 |
2021年 | 298篇 |
2020年 | 180篇 |
2019年 | 283篇 |
2018年 | 386篇 |
2017年 | 346篇 |
2016年 | 586篇 |
2015年 | 821篇 |
2014年 | 1016篇 |
2013年 | 1067篇 |
2012年 | 1448篇 |
2011年 | 1316篇 |
2010年 | 891篇 |
2009年 | 709篇 |
2008年 | 1063篇 |
2007年 | 919篇 |
2006年 | 853篇 |
2005年 | 770篇 |
2004年 | 779篇 |
2003年 | 628篇 |
2002年 | 513篇 |
2001年 | 435篇 |
2000年 | 411篇 |
1999年 | 306篇 |
1998年 | 139篇 |
1997年 | 125篇 |
1996年 | 92篇 |
1995年 | 89篇 |
1994年 | 78篇 |
1993年 | 61篇 |
1992年 | 156篇 |
1991年 | 109篇 |
1990年 | 92篇 |
1989年 | 86篇 |
1988年 | 55篇 |
1987年 | 59篇 |
1986年 | 48篇 |
1985年 | 60篇 |
1984年 | 39篇 |
1983年 | 33篇 |
1982年 | 29篇 |
1981年 | 28篇 |
1980年 | 27篇 |
1979年 | 28篇 |
1978年 | 35篇 |
1976年 | 21篇 |
1975年 | 28篇 |
1974年 | 26篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
A group of 16 German Landrace sows, nursing 155 piglets, was used for the demonstration of the effect of 20 mg of the progestogen megestrol acetate, administered orally from Day 8 to 21 post-partum, on milk production, milk composition and piglet weight. Eight sows remained untreated. Megestrol acetate treatment increased significantly milk yield by 35% and piglet weight at weaning (Day 35) by 30% over controls. A carryover effect after cessation of drug treatment was dtected, which kept milk production at an increased level for 8 more days. 相似文献
73.
Strains of coagulase-positive staphylococci which were nontypable with the routine typing set of phages could be typed by lysogeny with phage-propagating strains as indicators and with ultraviolet induction. About 10% of the strains could be typed without induction. About 36% of them could be typed by this method when ultraviolet irradiation was used as an inducing agent. The phage groups from which the majority of the nontypable staphylococci originated were easily identified by this method of typing. 相似文献
74.
75.
The assay of yeast ureidoglycolatase 总被引:6,自引:0,他引:6
76.
1. Cellulose decomposition in forest and orchard soils was investigated by studying the breakdown of boiled and washed cellophane in the soils and in vitro. Decomposition occurred from quick to slow in the order: orchard on clay soil, forest on clay soil, forest on sandy loam, and in the latter in the order: calcareous mull, acid mull and mor. 2. In the different forest soils which were investigated the rate of decomposition was parallel to their water capacity. It slowed down considerably when the water content of the soil decreased, especially after the wilting point was reached. 3. Of the fungi isolated from these soils, those from orchard soil — 5% to 50%Fusarium spp. — were among the fastest decomposers of cellulose. This agrees with, and may explain the high rate of decomposition in orchard soil. 4. Decomposition in pure culture is quicker than in soil. As filtersterilized soil extract checked the decomposition in pure culture, but heat-sterilized soil extract did not, an extractable but heat-sensitive substance may be one retarding factor. 相似文献
77.
I. E. Den Dooren De Jong Miss M. S. Dauvillier W. B. Roman 《Antonie van Leeuwenhoek》1961,27(1):337-361
Summary The formation of adipocere is a process occurring under virtually anaerobic conditions in which human fat is converted into
a complex of saturated fatty acids by a great variety of bacterial species occurring in and on the decomposing body. 相似文献
78.
79.
Evolution of eye lens crystallins: the stress connection 总被引:21,自引:0,他引:21
Crystallins, the structural proteins of the eye lens, ensure the transparency and integrity of the lens throughout life. Recent sequence comparisons have shown that evolution has recruited crystallins among already existing heat-shock proteins and stress-inducible enzymes. 相似文献
80.
IL-4 blocks the up-regulation of IL-2 receptors induced by IL-2 in normal human B cells 总被引:6,自引:0,他引:6
A negative influence of IL-4 on the IL-2-induced B cell proliferation and differentiation has recently been reported. In this study, we have further investigated a role of IL-4 on human tonsillar B cell proliferation and IL-2R expression. IL-4 enhanced Staphylococcus aureus Cowan 1 strain (SAC)-induced B cell proliferation, reaching the peak on day 3. However, from day 4, IL-4 inhibited IL-2-induced proliferation. In the cross-linking study, IL-4 enhanced the density of 125I-IL-2-binding protein at low affinity binding condition (2 nM of 125I-IL-2) in SAC-activated B cells. However, IL-4 blocked the enhancement in the density of 125I-IL-2-binding proteins induced by IL-2, from day 3, in both high (50 pM of 125I-IL-2) and low affinity binding conditions, suggesting that IL-4 is able to block IL-2-induced IL-2R up-regulation. This was confirmed by a binding study: B cells that cultured for 3 days with SAC plus IL-2 expressed an average of 180 +/- 20 high affinity receptors/cell with a Kd of 12 pM and 5800 +/- 500 low affinity receptors/cell with a Kd of 980 pM. By coculturing with IL-4, high affinity receptors were almost undetectable and the expression of low affinity receptors was reduced by more than 80%. IL-4-mediated inhibition of IL-2-induced IL-2R expression does not seem to be due to the direct interaction between IL-4 and cell surface receptors, inasmuch as preincubation of cells with IL-4 for 60 min at 37 degrees C did not alter the binding of 125I-IL-2 to cells previously cultured for 3 days with SAC plus IL-2. These data suggest that IL-4 has a capacity to block the up-regulation of the high as well as low affinity IL-2R-induced by IL-2 in normal human B cells, and could provide a possible explanation for the decreased responsiveness of B cells to IL-2 in the presence of IL-4. 相似文献