全文获取类型
收费全文 | 706篇 |
免费 | 39篇 |
国内免费 | 3篇 |
出版年
2021年 | 10篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2016年 | 9篇 |
2015年 | 21篇 |
2014年 | 28篇 |
2013年 | 30篇 |
2012年 | 43篇 |
2011年 | 44篇 |
2010年 | 37篇 |
2009年 | 18篇 |
2008年 | 37篇 |
2007年 | 41篇 |
2006年 | 17篇 |
2005年 | 31篇 |
2004年 | 23篇 |
2003年 | 22篇 |
2002年 | 29篇 |
2001年 | 24篇 |
2000年 | 27篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1981年 | 6篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1970年 | 5篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1956年 | 3篇 |
排序方式: 共有748条查询结果,搜索用时 812 毫秒
11.
K. S. Kumarasinghe F. Zapata G. Kovacs D. L. Eskew S. K. A. Danso 《Plant and Soil》1986,90(1-3):293-299
Summary The symbiotic association of the water fernAzolla with the blue-green algaAnabaena azollae can fix 30–60 kg N ha–1 per rice cropping season. The value of this fixed N for rice production, however, is only realized once the N is released from theAzolla biomass and taken up by the rice plants. The availability of N applied asAzolla or as urea was measured in field experiments by two15N methods. In the first,Azolla caroliniana (Willd.) was labelled with15N in nutrient solution and incorporated into the soil at a rate of 144 kg N ha–1. The recovery ofAzolla-N in the above ground parts of rice [Oryza sativa (L) cv. Nucleoryza] was found to be 32% vs. 26% for urea applied at a rate of 100 kg N/ha; there was no significant difference in recovery. In the second, 100 kg N/ha of15N-urea was applied separately or in combination with either 250 or 330 kg N ha–1 of unlabelledAzolla. At the higher rate, the recovery ofAzolla-N was significantly greater than that of urea. There was a significant interaction when both N sources were applied together, which resulted in a greater recovery of N from each source in comparison to that source applied separately. Increasing the combined urea andAzolla application rate from 350 kg N ha–1 to 430 kg N ha–1 increased the N yield but had no effect on the dry matter yield of rice plants. The additional N taken up at the higher level of N application accumulated to a greater extent in the straw compared to the panicles. Since no assumptions need to be made about the contribution of soil N in the method using15N-labelledAzolla, this method is preferable to the15N dilution technique for assessing the availability ofAzolla-N to rice. Pot trials usingAzolla stored at –20°C or following oven-drying showed that both treatments decreased the recovery of N by one third in comparison to freshAzolla. 相似文献
12.
K N Pandey W J Kovacs T Inagami 《Biochemical and biophysical research communications》1985,133(2):800-806
We have found that atrial natriuretic factor (ANF) has a profound effect on testicular cells in altering intracellular cyclic nucleotide levels as well as progesterone secretion. Using clonal cultured Leydig tumor cells we found that 1 X 10(-8)M ANF caused a two thousand-fold elevation in the accumulation of cellular cGMP and inhibited cAMP in treated cells by more than 90% as compared to the controls. ANF (1 X 10(-8)M) also significantly inhibited gonadotropin-stimulated accumulation of cAMP in response to bovine luteinizing hormone (bLH) or human chorionic gonadotropin (hCG). Gonadotropin-stimulated progesterone secretion was inhibited by ANF (1 X 10(-10) - 1 X 10(-9)M) in these cultured Leydig tumor cells. Approximately 50% inhibition of progesterone secretion was observed at the peptide concentration of 1 X 10(-9) M. 相似文献
13.
14.
M. F. Kovacs Jr. 《Plant and Soil》1971,34(1):441-451
Summary We detected aromatic and aliphatic acids in root and seed exudates of aseptic cultures of pea, cotton and barley plants by
thin-layer and gas-liquid chromatography. There were traces of p-hydroxybenzoic acid in the root and seed exudates of all
three plant species. Acid hydrolysis of pea and barley seed exudates yielded p-hydroxybenzoic, and of cotton seed exudates
yielded p-coumaric acid, as the predominant aromatic acid constituents of materials exuded by the germinating seeds. Lactic
was the predominant aliphatic acid detected in pea and barley root exudates whereas malic acid was predominant in cotton exudates.
With the exception of citric acid in peas, malic acid was the predominant acid found in pea, cotton and barley seed exudates.
The germinating seed was responsible for a large portion of the total aliphatic and aromatic acid exudation of the seedling
plant grown aseptically for 14 days.
Trade names are used in this publication only to provide scientific information. Their use does not constitute a guarantee
of the products named and does not signify that they are approved by the U.S. Department of Agriculture to the exclusion of
others of suitable composition. 相似文献
15.
D D Belsham E Rosenmann F A Pereira S G Williams M K Turney W J Kovacs L E Faber K Wrogemann 《Journal of steroid biochemistry》1989,33(3):389-394
Analysis of soluble proteins from human genital skin fibroblasts by two-dimensional polyacrylamide gel electrophoresis reveals an abundant protein doublet of mol. wt 56,000 with isoelectric points (pI) of 6.7 and 6.5. This protein is absent in non-genital skin fibroblasts as well as in genital skin fibroblasts of most patients with complete forms of androgen insensitivity. The protein specifically binds androgen. A protein of similar estimated molecular weight (58,000) from human genital skin fibroblasts has recently been found to be covalently radiolabelled by the affinity ligand dihydrotestosterone 17 beta-bromoacetate (DHT-BA). In the present study these proteins have been found to be indistinguishable on one- and two-dimensional gel electrophoresis. Antibodies raised against the 56 kDa pI 6.7/6.5 protein also recognized the protein covalently radiolabelled by DHT-BA. A third protein of estimated mol. wt 59,000 has been found to be associated with several steroid hormone receptor complexes but has no known ligand binding activity. This protein was found to be clearly separable from the 56/58 kDa protein on two-dimensional gel electrophoresis as it has a more acidic pI of approximately 5.4. Furthermore, antibodies against the 59 kDa protein do not recognize the 56 kDa species, and vice versa. 相似文献
16.
Differentiation-dependent expression of the brown adipocyte uncoupling protein gene: regulation by peroxisome proliferator-activated receptor gamma. 总被引:5,自引:1,他引:4
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
I B Sears M A MacGinnitie L G Kovacs R A Graves 《Molecular and cellular biology》1996,16(7):3410-3419
Uncoupling protein (UCP) is expressed only in brown adipocytes and is responsible for the unique thermogenic properties of this cell type. The novel brown preadipocyte cell line, HIB-1B, expresses UCP in a strictly differentiation-dependent manner. Transgenic mice studies have shown that a region from kb -2.8 to -1.0 of the marine UCP gene is required for brown adipocyte-specific expression. Subsequent analysis identified a potent 220-bp enhancer from kb -2.5 to -2.3. We show that this enhancer is active only in differentiated HIB-1B adipocytes, and we identify a peroxisome proliferator-activated receptor gamma (PPARgamma) response element, referred to as UCP regulatory element 1 (URE1), within the enhancer. URE1 has differentiation-dependent enhancing activity in HIB-1B cells and is required for enhancer action, since mutations of URE1 that block protein binding abolish enhancer activity. We also show that PPAR gamma antibodies block binding to URE1 of nuclear extracts from cultured brown adipocytes and from the brown adipose tissue of cold-exposed mice. Protein binding to URE1 increases substantially during differentiation of HIB-1B preadipocytes, and PPAR-gamma mRNA levels increase correspondingly. Although forced expression of PPAR gamma and retinoid X receptor alpha activates the enhancer in HIB-1B preadipocytes, these receptors are not capable of activating the enhancer in NIH 3T3 fibroblasts. Our results show that PPAR gamma is a regulator of the differentiation-dependent expression of UCP and suggest that there are additional factors in HIB-1B cells required for brown adipocyte-specific UCP expression. 相似文献
17.
Eubacterial components similar to small nuclear ribonucleoproteins: identification of immunoprecipitable proteins and capped RNAs in a cyanobacterium and a gram-positive eubacterium. 总被引:1,自引:0,他引:1
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)
S A Kovacs J O'Neil J Watcharapijarn C Moe-Kirvan S Vijay V Silva 《Journal of bacteriology》1993,175(7):1871-1878
Small nuclear ribonucleoprotein (snRNP) particles play an important role in the processing of pre-mRNA. snRNPs have been identified immunologically in a variety of cells, but none have ever been observed in prokaryotic systems. This report provides the first evidence for the presence of snRNP-like components in two types of prokaryotic cells: those of the cyanobacterium Synechococcus leopoliensis and those of the gram-positive eubacterium Bacillus subtilis. These components consist of snRNP-immunoreactive proteins and RNAs, including some with the snRNP-unique 5' m2,2,7G (m3G) cap. Immunoreactivity was determined by immunoprecipitation procedures, with either antinuclear-antibody-positive (RNP- and Sm-monospecific) patient sera or a m3G monoclonal antibody, with radiolabelled cell extracts that were preadsorbed with antinuclear-antibody-negative sera. S. leopoliensis immunoprecipitates showed the presence of high-molecular-mass proteins (14 to 70 kDa) and RNAs (138 to 243 nucleotides) that are analogous in size to proteins and RNAs found in human (HEp-2) cell immunoprecipitates but absent in Escherichia coli immunoprecipitates. Thin-layer chromatography of S. leopoliensis immunoprecipitates confirmed the presence of a capped nucleotide similar to a capped nucleotide in HEp-2 immunoprecipitates; no such nucleotide was observed in E. coli immunoprecipitates. Immunoreactive RNAs (117-170 nucleotides) were identified in a second eubacterium, B. subtilis, as well. This work suggests that snRNPs or their evolutionary predecessors predate the emergence of eukaryotic cells. 相似文献
18.
19.
Heat-tolerant methanotrophic bacteria from the hot water effluent of a natural gas field. 总被引:3,自引:1,他引:2
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
L Bodrossy J C Murrell H Dalton M Kalman L G Puskas K L Kovacs 《Applied microbiology》1995,61(10):3549-3555
Methanotrophic bacteria were isolated from a natural environment potentially favorable to heat-tolerant methanotrophs. An improved colony plate assay was developed and used to identify putative methanotrophic colonies with high confidence. Fourteen new isolates were purified and partially characterized. These new isolates exhibit a DNA sequence homology of up to 97% with the conserved regions in the mmoX and mmoC genes of the soluble methane monooxygenase (MMO)-coding gene cluster of Methylococcus capsulatus Bath. The copper regulation of soluble MMO expression in the same isolates, however, differs from that of M. capsulatus Bath, as the new isolates can tolerate up to 0.8 microM copper without loss of MMO activity while a drastic reduction of MMO activity occurs already at 0.1 microM copper in M. capsulatus Bath. The isolates can be cultivated and utilized at elevated temperatures, and their copper- and heat-tolerant MMO activity makes these bacteria ideal candidates for future biotechnological use. 相似文献
20.
The changes in concentrations of a number of trace elements have been determined by neutron activation analysis in tumor, liver, and blood serum of host animals, following local irradiation of a solid tumor (3924A Morris hepatoma). These trace element changes are compared to the changes observed in a parallel study of the effects of the chemotherapeutic agent 5-fluorouracil on the same tumor. Since the changes in some of the trace elements parallel the changes in pathological and biochemical factors resulting from the insult of radiation on the tumor, these trace elements may be valuable markers in the clinical evaluation of therapeutic response and as monitors of the long term effects of cancer therapy. 相似文献