全文获取类型
收费全文 | 373001篇 |
免费 | 29330篇 |
国内免费 | 355篇 |
出版年
2018年 | 8856篇 |
2017年 | 8597篇 |
2016年 | 8097篇 |
2015年 | 5360篇 |
2014年 | 6348篇 |
2013年 | 9055篇 |
2012年 | 11809篇 |
2011年 | 16668篇 |
2010年 | 12238篇 |
2009年 | 11326篇 |
2008年 | 14316篇 |
2007年 | 15934篇 |
2006年 | 9049篇 |
2005年 | 9292篇 |
2004年 | 8989篇 |
2003年 | 9018篇 |
2002年 | 8678篇 |
2001年 | 15590篇 |
2000年 | 15482篇 |
1999年 | 11751篇 |
1998年 | 3569篇 |
1997年 | 3681篇 |
1996年 | 3531篇 |
1995年 | 3226篇 |
1994年 | 3149篇 |
1993年 | 3070篇 |
1992年 | 9211篇 |
1991年 | 9000篇 |
1990年 | 9065篇 |
1989年 | 8657篇 |
1988年 | 8066篇 |
1987年 | 7654篇 |
1986年 | 6883篇 |
1985年 | 7193篇 |
1984年 | 5722篇 |
1983年 | 4983篇 |
1982年 | 3498篇 |
1981年 | 3258篇 |
1980年 | 3004篇 |
1979年 | 5380篇 |
1978年 | 4131篇 |
1977年 | 3776篇 |
1976年 | 3678篇 |
1975年 | 4284篇 |
1974年 | 4591篇 |
1973年 | 4716篇 |
1972年 | 4650篇 |
1971年 | 4253篇 |
1970年 | 3373篇 |
1969年 | 3149篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Bock (1963) showed that in the years 1956-60 early season sprays achieved good control of coffee berry disease (CBD) in East Rift areas of Kenya. In recent years, however, this spray programme has given erratic and often very poor results. In field experiments in 1966 yields of main (late) crop were increased from 151 to 652 kg/ha by early season sprays but in 1967 practically no control of the disease was achieved. Of the fungicides examined captafol was superior to copper; ‘Tuzet’, the best antisporulant, gave the poorest control. Analysis of the data indicates that this large seasonal variation depends on the very different inter-relationships between rainfall, cropping pattern and timing of sprays which obtained in the 2 years. The hypothesis that early-season sprays achieve control of CBD mainly by reducing the sporulating capacity of the maturing bark is questioned. The view is put forward that the protectant action of these sprays has been underestimated. 相似文献
994.
We report that membrane vesicles of Escherichia coli contain protein-binding sites for acyl carrier protein. Scatchard analysis of the binding indicates a dissociation constant around 0.35 micrometers and a maximum number of protein-binding sites around 50 pmol per mg of membrane protein. Binding is on the inner membrane while the outer membrane is devoid of binding sites. These results are consistent with the fact that some acyl carrier protein-dependent enzymes implicated in phospholipid- and membrane-derived oligosaccharide biosynthesis are localized in the cytoplasmic membrane. 相似文献
995.
N. N. Tzvelev 《The Botanical review》1989,55(3):141-203
Originally published in Russian as number 37 of Komarov Readings, 1987. Translated by Victoria V. Michaelova, Brigham Young
University, Provo, Utah 84602. Translation edited by Arthur Cronquist, New York Botanical Garden, New York, and approved by
the author. A few additions have been made to account for very recent literature. 相似文献
996.
Iu V Kotelevtsev D D Spitkovski? S N Orlov Iu V Postnov 《Biulleten' eksperimental'no? biologii i meditsiny》1989,108(11):608-609
26 male F2 hybrids between spontaneously hypertensive (SHR) and normotensive control (WKY) rats (SHRxWKY)F2 were segregated according to their c-src genotype into SS and WW homozygous groups, corresponding to SHR or WKY and WS heterozygous group. Na, K cotransport in erythrocytes in the WW group was equal to that of WKY and differs significantly from that of WS and SS groups (the rate of Na, K cotransport in latter groups was close to that of SHR). Ca content of RBC in WW group was equal to that of WKY, lower than that of WS and SS groups which in turn was significantly lower than in SHR, indicating polygenic control of the trait. Authors conclude that the c-src locus itself or some other loci inherited in conjunction with c-src determines both the increase of Na, K cotransport and calcium content in erythrocytes of SHR. 相似文献
997.
The behavioral effects of opiate agonists and antagonists were studied on the female aggression model. Mu-agonist buprenorphine more selectively decreased maternal aggression than kappa-agonist tifluadom. Kappa-agonists (bremazocine, tifluadom) increased passive defence in lactating female rats. Ethopharmacological data shows predominant involvement of brain mu-opiate receptor system in the integrative processes of maternal behavior and maternal aggression in particular. 相似文献
998.
999.
A mathematical model of autoimmunity is developed. This model is a system of two nonlinear differential equations, which describe the concentration dynamics of tissue cells and agressive lymphocytes. An analysis of the solutions shows that this model reproduces general behaviour of autoimmune diseases. 相似文献
1000.
Summary The a-c electrical properties of bipolar membranes separating equal strength solutions of the same uni-univalent electrolyte are analyzed for the case where both ions have equal mobilities. Two membrane models are treated. In one, the fixed-charge density is assumed to be constant throughout the membrane. In the other, the membrane is regarded as comprising an array of pores separated by walls through which the fixed charge is spread uniformly. Experimental results are reported for the a-c electrical properties of a bipolar membrane prepared from a single polyolephine sheet and immersed in KCl solutions of various concentrations. It is found that the data can be interpreted using the pore model. 相似文献