全文获取类型
收费全文 | 33271篇 |
免费 | 2874篇 |
国内免费 | 118篇 |
出版年
2021年 | 437篇 |
2020年 | 284篇 |
2019年 | 431篇 |
2018年 | 503篇 |
2017年 | 410篇 |
2016年 | 641篇 |
2015年 | 1024篇 |
2014年 | 1140篇 |
2013年 | 1610篇 |
2012年 | 1786篇 |
2011年 | 1682篇 |
2010年 | 1241篇 |
2009年 | 983篇 |
2008年 | 1465篇 |
2007年 | 1405篇 |
2006年 | 1373篇 |
2005年 | 1210篇 |
2004年 | 1269篇 |
2003年 | 1210篇 |
2002年 | 1255篇 |
2001年 | 1078篇 |
2000年 | 978篇 |
1999年 | 898篇 |
1998年 | 459篇 |
1997年 | 432篇 |
1996年 | 356篇 |
1995年 | 345篇 |
1994年 | 279篇 |
1993年 | 331篇 |
1992年 | 602篇 |
1991年 | 590篇 |
1990年 | 546篇 |
1989年 | 473篇 |
1988年 | 420篇 |
1987年 | 386篇 |
1986年 | 372篇 |
1985年 | 439篇 |
1984年 | 403篇 |
1983年 | 351篇 |
1982年 | 273篇 |
1981年 | 274篇 |
1980年 | 250篇 |
1979年 | 312篇 |
1978年 | 267篇 |
1977年 | 308篇 |
1976年 | 290篇 |
1975年 | 283篇 |
1974年 | 290篇 |
1973年 | 260篇 |
1972年 | 235篇 |
排序方式: 共有10000条查询结果,搜索用时 258 毫秒
51.
52.
L. Chaerle F. De Boever M. Van Montagu & D. Van Der Straeten 《Plant, cell & environment》2001,24(1):15-25
Pending cell death was visualized by thermographic imaging in bacterio‐opsin transgenic tobacco plants. Cell death in these plants was characterized by a complex lesion phenotype. Isolated cell death lesions were preceded by a colocalized thermal effect, as previously observed at sites infected by tobacco mosaic virus (TMV) ( Chaerle et al. 1999 Nature Biotechnology 17, 813–816). However, in most cases, a coherent front of higher temperature, trailed by cell death, initiated at the leaf base and expanded over the leaf lamina. In contrast to the homogenous thermal front, cell death was first visible close to the veins, and subsequently appeared as discrete spots on the interveinal tissue, as cell death spread along the veins. Regions with visible cell death had a lower temperature because of water evaporation from damaged cells. In analogy with previous observations on the localized tobacco–TMV interaction ( Chaerle et al. 1999 ), the kinetics of thermographic and continuous gas exchange measurements indicated that stomatal closure preceded tissue collapse. Localized spontaneous cell death could also be presymptomatically visualized in the Arabidopsis lsd2 mutant. 相似文献
53.
Paul H. De Kruif 《The Journal of general physiology》1922,4(4):387-393
A distinct difference in acid agglutination optimum for Type D (bacillus of rabbit septicemia) and its mutant form, Type G, has been observed. The optimum for Type D lies between pH 3.5 and pH 3.0. This changes during mutation, the resulting Type G mutants having in general an optimum lying between pH 4.7 and pH 3.8. The constancy of the optimum for Type D is very strict, while that for Type G is slightly less so. The variation is never so great as to cause an overlapping of optima and consequent failure of differentiation. These acid agglutination optima are in the nature of physical constants for the two types and would imply a fundamental difference in the chemical constitution of the organisms. Animal passage, far from causing a reversion of the mutant Type G to the primordial Type D form, brings about a still greater instability in the presence of H ions. 相似文献
54.
55.
A cholinergic proteolipid fraction (i.e. a hydrophobic lipoprotein) was separated from the of the cow, using affinity chromatography with the lipophilic gel Sephadex LH-20 and p-phenyltrimethylamonium as the active group. High affinity binding studies showed that only the specific fraction, desorbed after an acetylcholine (or acid) pulse, and corresponding to 0,72% of the proteolipids, is the one that binds the cholinergic ligands. The binding of (3H)atropine and (14C)d-tubocurarine demonstrated that there are 814 picomoles/g fresh tissue of muscarinic sites and only 76 picomoles/g of nicotinic sites. The specific radioactivity for (3H)atropine is 10,000 nmoles/g protein, suggesting a high degree of purification of the specific cholinergic proteolipid. 相似文献
56.
57.
Siddhartha Kumar Bhaumik Manoj Kumar Singh Subir Karmakar Tripti De 《Glycoconjugate journal》2009,26(6):663-673
As compared to cutaneous leishmaniasis, vaccination against visceral leishmaniasis (VL) has received limited attention. In
this study, we demonstrate for the first time that an UDP-Galactose: N-acetylglucosamine β 1–4 galactosyltransferase (GenBank Accession No. EF159943) expressing attenuated LD clonal population (A-LD) is able to confer protection against the experimental challenge with the virulent LD AG83 parasite. A-LD was also effective in established leishmania infection. The vaccinated animals showed both cell mediated
(in vitro T-cell proliferation, and DTH response) and humoral responses (Th1 type). These results demonstrate the potential of the
attenuated clones as an immunotherapeutic and immunoprophylactic agent against visceral leishmaniasis. 相似文献
58.
59.
Arnold N. Onyango 《Chemistry and physics of lipids》2012,165(7):777-786
Small reactive carbonyl compounds (RCCs) such as formaldehyde, acetaldehyde, acrolein, crotonaldehyde, glyoxal, methylglyoxal, glycolaldehyde, glycidaldehyde, and 2-butene-1,4-dial are involved in carbonyl and oxidative stress-related physiological disorders. While some evidence indicates that lipid oxidation could be an important source of these compounds in vivo, this has sometimes been doubted because the mechanisms of their formation thereby are poorly understood. Here, representative literature supporting the significant formation of these compounds during lipid oxidation under physiologically relevant conditions are highlighted, and the strengths and weaknesses of previously proposed mechanisms of their formation thereby are considered. In addition, based on the current understanding of lipid oxidation chemistry, some new pathways of their formation are suggested. The suggested pathways also generate 4-hydroxy-2-butenal, a precursor of the carcinogen furan, whose endogenous formation in tissues has hitherto not been seriously considered. 相似文献
60.
A linkage analysis of the murine Mos gene, which codes for the c-mos proto-oncogene, was performed in 88 backcross progeny of an interspecies cross of laboratory mice and Mus spretus. Linkage was tested for four different genes on mouse chromosome 4: Aco-1, Mup-1, b, and Ifb. The gene order (from centromere) with intervening percentage recombination is Mos-15.9 (+/- 3.9)-Aco-1-5.6 (+/- 2.4)-Mup-1-3.4 (+/- 1.9)-b-5.6 (+/- 2.4)-Ifb. These results confirm the previous assignment of Mos to chromosome 4 on the basis of segregation in somatic cell hybrids (D. Swan et al., 1982, J. Virol. 44: 752-754) and show furthermore that Mos and the Ifa/Ifb clusters are not tightly linked as a group of intronless genes, but are separated by a map distance of 30.6 +/- 4.9 recombination units. The linkage data obtained in the present study place Mos in a region compatible with the physical map (D. W. Threadgill and J. E. Womack, 1988, Genomics 3: 82-86). 相似文献