全文获取类型
收费全文 | 60335篇 |
免费 | 5249篇 |
国内免费 | 2475篇 |
出版年
2023年 | 502篇 |
2022年 | 985篇 |
2021年 | 1758篇 |
2020年 | 1220篇 |
2019年 | 1509篇 |
2018年 | 1557篇 |
2017年 | 1135篇 |
2016年 | 1770篇 |
2015年 | 3025篇 |
2014年 | 3433篇 |
2013年 | 3909篇 |
2012年 | 4926篇 |
2011年 | 4749篇 |
2010年 | 2931篇 |
2009年 | 2579篇 |
2008年 | 3507篇 |
2007年 | 3373篇 |
2006年 | 3090篇 |
2005年 | 2781篇 |
2004年 | 2721篇 |
2003年 | 2483篇 |
2002年 | 2274篇 |
2001年 | 990篇 |
2000年 | 831篇 |
1999年 | 885篇 |
1998年 | 682篇 |
1997年 | 577篇 |
1996年 | 514篇 |
1995年 | 469篇 |
1994年 | 499篇 |
1993年 | 406篇 |
1992年 | 501篇 |
1991年 | 470篇 |
1990年 | 394篇 |
1989年 | 359篇 |
1988年 | 345篇 |
1987年 | 277篇 |
1986年 | 273篇 |
1985年 | 314篇 |
1984年 | 307篇 |
1983年 | 274篇 |
1982年 | 282篇 |
1981年 | 239篇 |
1980年 | 217篇 |
1979年 | 180篇 |
1978年 | 182篇 |
1977年 | 148篇 |
1976年 | 154篇 |
1975年 | 134篇 |
1974年 | 150篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Nadine B. Carozzi Gregory W. Warren Nalini Desai Susan M. Jayne Richard Lotstein Douglas A. Rice Stephen Evola Michael G. Koziel 《Plant molecular biology》1992,20(3):539-548
Insecticidal transgenic tobacco plants containing a truncated Bacillus thuringiensis cryIA(b) crystal protein (ICP) gene expressed from the CaMV 35S promoter were analyzed for ICP gene expression under field and greenhouse conditions over the course of a growing season. We present new information on temporal and tissue-specific expression of a CaMV 35S/cryIA(b) gene. Levels of cryIA(b) protein and mRNA were compared in both homozygous and hemizygous lines throughout plant development. Levels of ICP mRNA and protein increased during plant development with a pronounced rise in expression at the time of flowering. Homozygous ICP lines produced higher levels of ICP than the corresponding hemizygous lines. ELISA analysis of different tissues in the tobacco plant showed ICP gene expression in most tissues with a predominance of ICP in older tissue. All transgenic ICP tobacco lines which were studied in the field and greenhouse contained 400 ng to 1 g ICP per gram fresh weight in leaves from the mid-section of the plant at flowering. The amounts of ICP produced by field lines were directly comparable to levels observed in greenhouse-grown plants. 相似文献
992.
993.
994.
Methane oxidation rates were measured in boreal forest soils using seven techniques that provide a range of information on soil CH4 oxidation. These include: (a) short-term static chamber experiments with a free-air (1.7 ppm CH4) headspace, (b) estimating CH4 oxidation rates from soil CH4 distributions and (c)222Rn-calibrated flux measurements, (d) day-long static chamber experiments with free-air and amended (+20 to 2000 PPM CH4) headspaces, (e) jar experiments on soil core sections using free-air and (f) amended (+500 ppm CH4) headspaces, and (g) jar experiments on core sections involving tracer additions of14CH4. Short-term unamended chamber measurements,222Rn-calibrated flux measurements, and soil CH4 distributions show independently that the soils are capable of oxidizing atmospheric CH4 at rates ranging to < 2 mg m–2 d–1. Jar experiments with free-air headspaces and soil CH4 profiles show that CH4 oxidation occurs to a soil depth of 60 cm and is maximum in the 10 to 20 cm zone. Jar experiments and chamber measurements with free-air headspaces show that CH4 oxidation occurs at low (< 0.9 ppm) thresholds. The14CH4-amended jar experiments show the distribution of end products of CH4 oxidation; 60% is transformed to CO2 and the remainder is incorporated in biomass. Chamber and jar experiments under amended atmospheres show that these soils have a high capacity for CH4 oxidation and indicate potential CH4 oxidation rates as high as 867 mg m–2 d–1. Methane oxidation in moist soils modulates CH4 emission and can serve as a negative feedback on atmospheric CH4 increases. 相似文献
995.
Complex patterns of linkage disequilibrium in the Huntington disease region. 总被引:11,自引:8,他引:3
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M E MacDonald C Lin L Srinidhi G Bates M Altherr W L Whaley H Lehrach J Wasmuth J F Gusella 《American journal of human genetics》1991,49(4):723-734
The genetic defect causing Huntington disease (HD) has been mapped to 4p16.3 by linkage analysis using DNA markers. Two apparently contradictory classes of recombination events in HD kindreds preclude precise targeting of efforts to clone the disease gene. Here, we report a new recombination event that increases support for an internal candidate region of 2.5 Mb between D4S10 and D4S168. Analysis of 23 DNA polymorphisms in 4p16.3 revealed a complex pattern of association with the disease gene that failed to narrow the size of the candidate region. The degree of linkage disequilibrium did not show a continuous increase across the physical map, nor was a region of extreme disequilibrium identified. Markers displaying no association with the disorder were interspersed with and, in many cases, close to markers displaying significant disequilibrium. Comparison of closely spaced marker pairs on normal and HD chromosomes, as well as analysis of haplotypes across the HD region, suggest that simple recombination subsequent to a single original HD mutation cannot easily explain the pool of HD chromosomes seen today. A number of different mechanisms could contribute to the diversity of haplotypes observed on HD chromosomes, but it is likely that there has been more than one and possibly several independent origins of the HD mutation. 相似文献
996.
Eosin Y staining of proteins in polyacrylamide gels. 总被引:1,自引:0,他引:1
A staining method is described in which various proteins in polyacrylamide gels can be stained by using eosin Y. After a brief incubation of a polyacrylamide gel in an acidic solution of 1% eosin Y, various proteins, including human erythrocyte membrane sialoglycoproteins which are not detectable by Coomassie blue R-250 (CB), can be detected with a sensitivity of 10 ng protein. This is far more sensitive than CB staining and is comparable to the sensitivity of silver staining. In a Western blot, the antigenicity of an eosin Y stained protein is retained. In addition, proteins on an immunoblot sheet can be detected by eosin Y staining. The method described is rapid, sensitive, and reproducible with various proteins in polyacrylamide gels and has the added advantage of also staining sialoglycoproteins. 相似文献
997.
黄芫花提取物对V79细胞和WB肝细胞的生物...:1.... 总被引:3,自引:0,他引:3
A Chinese herb, wikstroemia Chamaedaphen (WC) extract, recently has been shown to be a potential tumor promoting agent on uterine cervical carcinoma induced by HSV-2 or MCA in mice. To determine whether the tumor promoting effects of WC extract were mediated through inhibition of gap junctional intercellular communication (GJIC) with relation to cellular growth, experiments were conducted on Chinese hamster V79 cells and rat WB liver cells by utilization of SLDT method for GJIC detection and cell growth curve examination, 3H-TdR incorporation, mitotic index (MI) and Flow Cytometry (FCM) methods. TPA was used for comparative purpose. WC extract inhibited GJIC and stimulated cell growth in a dose (2-200 micrograms/ml) and time (0-72 hr)-dependent manner in both cell lines. Both WC extract and TPA treatments increased V79 cell growth rate. The average cell doubling-time was decreased from 36.5 hr in control V79 cells to 28.2 hr in WC extract (10 micrograms/ml) and 20.9 hr in TPA (50 ng/ml) treatment by the 3rd day. Stimulating effect of both drugs on DNA synthesis of V79 cells was demonstrated. The results of FCM and MI indicated that the cell number of M-phase cells was increased after drug treatment. It is suggested that (1) tumor promoting effect of WC extract might be mediated through inhibition of GJIC: (2) inhibition of GJIC is closely correlated with increased cell growth rate and entry of cell division cycle. 相似文献
998.
999.
Alcohol and aldehyde dehydrogenase genotypes and alcoholism in Chinese men. 总被引:29,自引:4,他引:25
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
H R Thomasson H J Edenberg D W Crabb X L Mai R E Jerome T K Li S P Wang Y T Lin R B Lu S J Yin 《American journal of human genetics》1991,48(4):677-681
The liver enzymes alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which are responsible for the oxidative metabolism of ethanol, are polymorphic in humans. An allele encoding an inactive form of the mitochondrial ALDH2 is known to reduce the likelihood of alcoholism in Japanese. We hypothesized that the polymorphisms of both ALDH and ADH modify the predisposition to development of alcoholism. Therefore, we determined the genotypes of the ADH2, ADH3, and ALDH2 loci of alcoholic and nonalcoholic Chinese men living in Taiwan, using leukocyte DNA amplified by the PCR and allele-specific oligonucleotides. The alcoholics had significantly lower frequencies of the ADH2*2, ADH3*1, and ALDH2*2 alleles than did the nonalcoholics, suggesting that genetic variation in both ADH and ALDH, by modulating the rate of metabolism of ethanol and acetaldehyde, influences drinking behavior and the risk of developing alcoholism. 相似文献
1000.
Fifty mesophilic and five moderately thermophilic strains of acidophilic heterotrophic bacteria were tested for the ability to reduce ferric iron in liquid and solid media under aerobic conditions; about 40% of the mesophiles (but none of the moderate thermophiles) displayed at least some capacity to reduce iron. Both rates and extents of ferric iron reduction were highly strain dependent. No acidophilic heterotroph reduced nitrate or sulfate, and (limited) reduction of manganese(IV) was noted in only one strain (Acidiphilium facilis), an acidophile which did not reduce iron. Insoluble forms of ferric iron, both amorphous and crystalline, were reduced, as well as soluble iron. There was evidence that, in at least some acidophilic heterotrophs, iron reduction was enzymically mediated and that ferric iron could act as a terminal electron acceptor. In anaerobically incubated cultures, bacterial biomass increased with increasing concentrations of ferric but not ferrous iron. Mixed cultures of Thiobacillus ferrooxidans or Leptospirillum ferrooxidans and an acidophilic heterotroph (SJH) produced sequences of iron cycling in ferrous iron-glucose media. 相似文献