全文获取类型
收费全文 | 7504篇 |
免费 | 407篇 |
国内免费 | 313篇 |
专业分类
8224篇 |
出版年
2023年 | 87篇 |
2022年 | 139篇 |
2021年 | 177篇 |
2020年 | 147篇 |
2019年 | 279篇 |
2018年 | 285篇 |
2017年 | 128篇 |
2016年 | 159篇 |
2015年 | 243篇 |
2014年 | 397篇 |
2013年 | 484篇 |
2012年 | 301篇 |
2011年 | 479篇 |
2010年 | 381篇 |
2009年 | 411篇 |
2008年 | 449篇 |
2007年 | 457篇 |
2006年 | 389篇 |
2005年 | 380篇 |
2004年 | 237篇 |
2003年 | 238篇 |
2002年 | 256篇 |
2001年 | 174篇 |
2000年 | 147篇 |
1999年 | 144篇 |
1998年 | 129篇 |
1997年 | 109篇 |
1996年 | 111篇 |
1995年 | 60篇 |
1994年 | 74篇 |
1993年 | 60篇 |
1992年 | 68篇 |
1991年 | 49篇 |
1990年 | 43篇 |
1989年 | 39篇 |
1988年 | 42篇 |
1987年 | 39篇 |
1986年 | 32篇 |
1985年 | 50篇 |
1984年 | 51篇 |
1983年 | 31篇 |
1982年 | 62篇 |
1981年 | 40篇 |
1980年 | 33篇 |
1979年 | 33篇 |
1978年 | 30篇 |
1977年 | 16篇 |
1975年 | 13篇 |
1974年 | 19篇 |
1973年 | 9篇 |
排序方式: 共有8224条查询结果,搜索用时 0 毫秒
31.
K. D. Hahn F. Buck H. Rüterjans B. K. Chernov K. G. Skryabin M. P. Kirpichnikov 《European biophysics journal : EBJ》1985,12(2):87-95
The 17 base pair operator O
R
3 oligonucleotide, which is the preferential binding site for the Cro repressor of phage , was studied by two-dimensional NMR spectroscopy. A sequential assignment procedure based on two-dimensional Nuclear Overhauser Effect (NOESY) and scalar coupling correlated (COSY) NMR spectroscopy, together with the knowledge of the oligodesoxynucleotide sequence, made it possible to assign the non-exhangeable base protons and the H1 and the H2-H2 sugar protons of the O
R
3 operator DNA. The pattern of the observed NOE connectivities is consistent with a right-handed helical DNA structure. The base and sugar proton assignments provide the necessary information for further studies of the O
R
3 operator — Cro repressor interaction.Abbreviations COSY
correlated spectroscopy
- FID
free induction decay
- NOE
nuclear Overhauser effect
- NOESY
nuclear Overhauser effect spectroscopy
- RD
relaxation delay
- TSP
sodium 3-trimethylsilyl-(2,2,3,3-2H4)propionate
- EDTA
sodium ethylendiamine tetraacetate 相似文献
32.
Structural comparison of the two distinct sugar binding sites in wheat germ agglutinin isolectin II 总被引:12,自引:0,他引:12
C S Wright 《Journal of molecular biology》1984,178(1):91-104
33.
本文研究了杨尺蠖核型多角体病毒(AciNPV)蛋白质特性,用反复调等电点法,从AciNPV的多角体蛋白中分离到A,B两种蛋白,Sepharose 6B柱层析和超离心沉降分析表明,两者均为一个峰纯,沉降系数(S20w)分别为4.9和8.9,对A蛋白进行了16种氨基酸组成分析,Glu、Asp和Leu含量高于其它氨基酸,不含Cys,用SDS-聚丙烯酰胺凝胶电泳和免疫双扩散法分析表明,用两倍体积饱和硫酸铵沉淀法制备的多角体蛋白,与提纯的多角体A、B蛋白之间无差异,多角体蛋白结构多肽由6种组成,分子量在12500—54000道尔顿范围内,其中32000是多角体蛋白的主要多肽,病毒粒子结构多肽和核衣壳蛋白分别由19和7个多肽组成,分子量范围分别在89000~13000和34000~13000之间,间接试验结果表明,在AciNPV中有碱性蛋白酶活性存在。 相似文献
34.
Summary When the red-light grown protonema ofAdiantum capillus-veneris was transferred to the dark, the nucleus ceased its migration ca. 5 hours before cell plate formation (Mineyuki andFuruya 1980). To see whether the nucleus was held by some cytoplasmic structure during nuclear positioning, protonemata were treated with various centrifugal forces at different stages of the cell cycle. Nuclei of G1 phase were easily displaced by centrifugation at 360×g for 15 minutes, but those of G2 or M phase were not displaced by it, suggesting that the nuclei were held by some cytoplasmic elements in G2 or M phase. This nuclear anchoring was not detectable in protonemata that were treated with 5mM colchicine. With this treatment, the nucleus did not stop its migration at late G2 and moved even in prophase. And the retardation of organelle movement which was observed in cytoplasm on the lateral side of the nucleus after the cessation of premitotic nuclear migration (Mineyuki andFuruya 1984) was not observed in the presence of colchicine. Thus the nuclei appear to be held by colchicine-sensitive structure in cytoplasm between the lateral surface of the nucleus and cell wall during the premitotic nuclear positioning. Electron micrographs showing cytoplasmic microtubules were consistent with the idea.Abbreviations PPN
Premitotic positioning of the nucleus
- L region
Cytoplasm between the lateral surface of the nucleus and cell wall (seeMineyuki
et al. 1984) 相似文献
35.
36.
The herbicide glyphosate (N-phosphonomethyl glycine) is a potent reversible inhibitor of the 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase activity of the purified arom multienzyme complex from Neurospora crassa. Inhibition of the EPSP synthase reaction by glyphosate is competitive with respect to phosphoenolpyruvate, with K(i) 1.1 microM, and uncompetitive with respect to shikimate-3-phosphate. The kinetic patterns are consistent with a compulsory order sequential mechanism in which either PEP or glyphosate can bind to an enzyme: shikimate-3-phosphate complex. 相似文献
37.
The incidence of lethal parasites in the larvae of a Tipula paludosa population was monitored for two seasons. The proportions of larvae infected with Tipula iridescent virus (TIV) and a tachinid insect were similar to those in previously studied populations, whereas the proportions of larvae infected with Tipula nuclear polyhedrosis virus (NPV) and a spore-forming bacterium (SFB) were higher. Conservative estimates of mortality due to these four agents were 10.7% in 1977–1978 and 7.7% in 1978–1979. The mean population density and the proportion of SFB-infected larvae were lower in 1978–1979 than in 1977–1978, while the proportion of NPV-infected larvae was higher. In 1979 the proportion of NPV-infected larvae was positively correlated with population density, which was highest in the wettest part of the study area. In both seasons the proportion of SFB-infected larvae was negatively correlated with population density. Larvae infected with the NPV or the SFB became pallid at an advanced stage of infection, but, although infected larvae were found throughout the larval period, pallid larvae were only found in the later part. It is suggested that larvae become infected in an early instar, then the infections slowly develop throughout the remainder of the larval period. Five larvae were found with mixed infections; four were infected with the SFB and NPV, while the fifth was infected with the SFB and TIV. 相似文献
38.
Graham P. Allaway 《Journal of invertebrate pathology》1983,42(3):357-368
The structure of the inclusion bodies (IBs) of three multiply enveloped nuclear polyhedrosis viruses (MNPVs), one singly enveloped NPV (SNPV), two granulosis viruses (GVs) and one cytoplasmic polyhedrosis virus (CPV) were compared. A method was devised to calculate the numbers of virus particles and nucleocapsids in IBs using data from light microscopy and thin sections. The three MNPVs, from Agrotis segetum (English and Polish virus isolates) and Mamestra brassicae had similar concentrations of virus particles ranging from 17.3 to 19.6 per μm3 of IB. Plusia gamma SNPV had a higher density of 59.6 virus particles per μm3 of IB, which partly compensated for its having smaller IBs (mean volume 0.65 μm3) than the MNPVs (2.60–9.71 μm3). The English A. segetum MNPV isolate had the most nucleocapsids in each virus particle (mean, 4.04) and the largest IBs (mean volume, 9.71 μm3), giving 674 nucleocapsids per IB on average. The GVs, from A. segetum and Pieris brassicae, mainly contained one nucleocapsid per IB. P. gamma CPV IBs had a much higher density of virus particles than the baculoviruses (260 per μm3 compared with 17–60 per μm3). These data are discussed in relation to the biological properties of these viruses, and possible adaptational advantages of alternative IB designs are considered. 相似文献
39.
Twelve singly embedded isolates (SEV) and two multiply embedded isolates (MEV) of nuclear polyhedrosis viruses from Heliothis larvae were compared by time-mortality assays in neonate H. zea larvae. The isolates could be separated into six groups based on differences in the 50% survival time (ST50) values. Isolates with identical restriction endonuclease (REN) profiles did not differ significantly in their ST50 values, whereas isolates with several different REN cleavage sites also had significantly different ST50 values. With the exception of one isolate from India, the singly embedded isolates acted faster than the multiply embedded isolates. 相似文献
40.
L.Charles Dickinson James C.W. Chien 《Biochemical and biophysical research communications》1973,51(3):587-592
Single crystals of horse CoHb were obtained by reduction of CoHb+ crystals with dithionite. Epr measurements showed that the g? and Coà tensors are both axial and share the same principal axis systems. Of the four subunits, the “heme” normals of C? and d? subunits ãb?plane 29 ± 1° from b?; they have the same orientation as the hemes in methemoglobin. The normals of “hemes” à and B? are 47 above the ãb? plane as compared to 16° in methemoglobin. 相似文献