全文获取类型
收费全文 | 20830篇 |
免费 | 1601篇 |
国内免费 | 26篇 |
出版年
2023年 | 111篇 |
2022年 | 160篇 |
2021年 | 322篇 |
2020年 | 247篇 |
2019年 | 276篇 |
2018年 | 468篇 |
2017年 | 442篇 |
2016年 | 592篇 |
2015年 | 739篇 |
2014年 | 925篇 |
2013年 | 1164篇 |
2012年 | 1642篇 |
2011年 | 1591篇 |
2010年 | 915篇 |
2009年 | 714篇 |
2008年 | 1151篇 |
2007年 | 1274篇 |
2006年 | 1072篇 |
2005年 | 1036篇 |
2004年 | 959篇 |
2003年 | 906篇 |
2002年 | 829篇 |
2001年 | 434篇 |
2000年 | 438篇 |
1999年 | 293篇 |
1998年 | 225篇 |
1997年 | 180篇 |
1996年 | 175篇 |
1995年 | 184篇 |
1994年 | 167篇 |
1993年 | 143篇 |
1992年 | 159篇 |
1991年 | 149篇 |
1990年 | 146篇 |
1989年 | 130篇 |
1988年 | 134篇 |
1987年 | 108篇 |
1986年 | 107篇 |
1985年 | 120篇 |
1984年 | 117篇 |
1983年 | 116篇 |
1982年 | 120篇 |
1981年 | 114篇 |
1980年 | 91篇 |
1979年 | 102篇 |
1978年 | 99篇 |
1977年 | 98篇 |
1976年 | 82篇 |
1974年 | 72篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Catherine Ronin Herman van Halbeek Johannah GM Mutsaers Johannes F G Vliegenthart 《Glycoconjugate journal》1987,4(3):247-254
The lipid-linked precursor ofN-type glycoprotein oligosaccharides was isolated from porcine thyroid microsomes after in cubation with UDP[3H] Glucose. The carbohydrate was released from dolichol pyrophosphate by mild acid hydrolysis, purified by gel filtration and characterized by 500-MHz1H-NMR spectroscopy in combination with enzymatic degradation. The parent oligosaccharide was found to be Glc3Man9Glc-NAc2. The three glucose residues are present in the linear sequence Glcα1-2Glα1-3 Glc, the latter being α(1-3)-linked to one of the mannose residues. In order to establish the branch location of the triglucosyl unit, the parent compound was digested with jack-bean α-mannosidase. The oligosaccharide product was purified by gel filtration, and identified by1H-NMR as Glc3Man5GlcNAc2 lacking the mannose residues A, D2, B and D3. Therefore, the structure of the precursor oligosaccharide is as follows: $$\begin{gathered} c b a D_1 C 4 \hfill \\ Glc\alpha 1 - 2Glc\alpha 1 - 3Glc\alpha 1 - 3Man\alpha 1 - 2Man\alpha 1 - 2Man\alpha 1 \hfill \\ 3 \swarrow 3 2 1 \hfill \\ Man\alpha 1 - 2Man\alpha 1 Man\beta 1 - 4GlcNAc\beta 1 - 4GlcNAc \hfill \\ D_{2 } A 3 6 \hfill \\ Man\alpha 1 \hfill \\ 6 \hfill \\ Man\alpha 1 - 2Man\alpha 1 \nwarrow 4 \hfill \\ D_3 B \hfill \\ \end{gathered} $$ 相似文献
42.
Osmoregulation in Escherichia coli by accumulation of organic osmolytes: betaines,glutamic acid,and trehalose 总被引:42,自引:0,他引:42
Like other cyanobacteria, Chlorogloeopsis fritschii contained as major lipid classes monogalactosyldiacyl-glycerols, digalactosyldiacylglycerols, sulfoquinovosyldiacylglycerols and diacylglycerophosphoglycerols. In addition to these lipid classes this cyanobacterium also contained small amounts of diacylglycerophosphocholines and sterols, predominantly lanosterol, thus showing similarity to photosynthetic eukaryotes. Dark incubated cells contained larger proportions of the latter two lipid classes than light grown cells. Like other prokaryotes, C. fritschii lacked linolenic acid (18:3) in its lipids. Lipids from the thylakoids were richer in palmitoleic acid (16:1) than those of whole cells. There was no effect of light on the patterns of constituent fatty acids of lipids from C. fritschii, in contrast to photosynthetic eukaryotes.Abbreviations MGDG
Monogalactosyldiacylglycerols
- PA
Phosphatidic acids
- PE
Diacylglycerophosphoethanolamines
- PG
Diacylglycerophosphoethanolamines
- DGDG
Digalactosyldiacylglycerols
- SQDG
Sulfoquinovosyldiacylglycerols
- PC
Diacylglycerophosphocholines 相似文献
43.
Alberto Barros M. Carmo Tavares Sérgio Castedo M. Salomé Pereira M. Purificação Tavares M. Almeida e Costa 《Human genetics》1987,75(4):388-390
Summary A double balanced reciprocal translocation involving four chromosomes, t(1;19;6;14) (1p11; 19p11; 6q25; 14q21), was found in the phenotypically normal husband in a couple referred because of repeated abortions. Reciprocal translocations, t(6;14), had been transmitted by his mother, his father being apparently homozygous for a translocation comprising pairs 1 and 19-t(1;19)(1;19). The genetic consequences of this complex chromosomal rearrangement are analyzed. 相似文献
44.
The Mg2+ -dependent activity of the tonoplast pyrophosphatase (PPase) was investigated by measuring proton transport and by using the acridine orange technique on intact vacuoles of the aquatic liverwort Riccia fluitans L. In solutions with both Mg2+ and pyrophosphate present, a number of complexes are formed, which could all influence the enzymatic and hence the transport activity of the PPase. Therefore, the individual concentrations of these complexes were calculated and their contributions to proton transport across the tonoplast were tested. From these experiments we conclude that Mg2+ has three different roles: (i) Mg2+ stimulates transport activity of the PPase. (ii) Mg2 PPi inhibits PPase-mediated H+ transport, (iii) MgPPi * (= MgPPi 2- + MgHPPi - ) is the substrate with an apparent K1/2 = 5–10 μM, with no discrimination between MgPPi 2- and MgHPPi - . 相似文献
45.
Growth line analysis of diagenetically altered scleractinians is only possible if carbonate diagenesis has followed the pathway of aragonite leaching and coeval formation of low magnesium calcite. All other possibilities of aragonite transformation into calcite exclude the preservation of this growth line banding. Examples of these diagenetic patterns are found in the Pleistocene of Barbados. 相似文献
46.
Biosynthesis of the Cyanogenic Glucoside Dhurrin in Seedlings of Sorghum bicolor (L.) Moench and Partial Purification of the Enzyme System Involved 总被引:3,自引:1,他引:2
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The cyanogenic glucoside dhurrin is rapidly synthesized in etiolated seedlings of Sorghum bicolor (L.) Moench. The dhurrin content of the seedlings increases sigmoidally with the germination time. Shoots of 10 centimeters height contain 850 nanomoles of dhurrin per shoot corresponding to 6% of the dry weight. The biosynthetic activity sharply rises upon germination and reaches a maximum level of 10 nanomoles dhurrin/(hour × shoot) after 48 hours when the shoots are 3 centimeters high. This maximum level is followed by a sharp decline in activity when germination time exceeds 65 hours. Dhurrin and the dhurrin-synthesizing enzyme system are primarily located in the upper part of the etiolated shoot where both are evenly distributed between the coleoptile, the primary leaves and the upper 0.5 centimeter of the first internode including the shoot apex. Dhurrin constitutes 30% of the dry weight of the upper 1.2 centimeter of 10 centimeter high shoots. The seed and root contain neither dhurrin nor the dhurrin-synthesizing enzyme system. The codistribution of dhurrin and the enzyme system throughout the seedling indicates that production and storage sites are located within the same cell. Purification of the dhurrin-synthesizing enzyme by gel filtration or by sucrose gradient centrifugations results in a tenfold increase in specific activity. Further purification is accompained by a decline in specific activity due to loss of essential components as demonstrated by reconstitution experiments. 相似文献
47.
L. O. e Silva S. P. Singh M. A. Pastor-Corrales 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,78(5):619-624
Summary Inheritance of resistance to common bacterial blight in the trifoliate leaf, plant canopy, and pods was controlled by a single major gene. Additive followed by dominance effects were more important than epistatic interactions. Narrow-sense heritability values ranged from 0.18 to 0.87 for trifoliate leaf, from 0.26 to 0.76 for canopy, and from 0.11 to 0.36 for pods. Observed gains from selection for resistance were higher than expected gains. Implications of these results in breeding for resistance are discussed. 相似文献
48.
Gerd Reuter Roland Schauer Claudia Szeiki Johannis P Kamerling Johannes FG Vliegenthart 《Glycoconjugate journal》1989,6(1):35-44
Periodate oxidation of terminalN-acetyl- andN-glycoloylneuraminic acid residues in the mucins from edible bird nest substance and pig submandibular gland, respectively, can be carried out under conditions which exclusively give rise to the formation of the C-7 analogues of these sialic acids. In contrast, the C-8 compounds can be obtained in a maximum yield of about 40%. Under identical conditions,N-glycoloylneuraminic acid is oxidized about 1.5 times faster than theN-acetylated derivative. After release of the sialic acids by acid hydrolysis, the characterization of the oxidation products was carried out by TLC, by GLC and GLC-MS of the corresponding pertrimethylsilyl derivatives, and by 500-MHz1H-NMR spectroscopy. In addition, molar response factors for GLC analysis and extinction coefficients in the orcinol/Fe3+/HCl assay were determined. 相似文献
49.
Glutamate dehydrogenase in disrupted mitochondrial preparations is activated by L-leucine to a much greater extent than is the purified enzyme. A factor, or factors, responsible for modulating the sensitivity of L-leucine is lost during the purification of the enzyme. Although both cardiolipin and phosphatidylserine are inhibitors of the enzyme, only the inhibition by the former phospholipid is reversed by L-leucine. The inhibition of glutamate dehydrogenase by its binding to cardiolipin in the disrupted mitochondrial preparations and its relief by L-leucine could account for the greater sensitivity of such preparations to activation by that amino acid. 相似文献
50.
Protoplast cultures were prepared from hypocotyls of ten spring rapeseed cultivars. Protoplasts from all genotypes tested formed calli, and shoots were regenerated from calli of nine of the genotypes at frequencies varying from 15 to 76%. The regenerating cultivars fell into a high regenerating group (>60% and a low regenerating group <25%). 相似文献