全文获取类型
收费全文 | 67435篇 |
免费 | 4860篇 |
国内免费 | 3662篇 |
出版年
2024年 | 85篇 |
2023年 | 824篇 |
2022年 | 1393篇 |
2021年 | 1645篇 |
2020年 | 1530篇 |
2019年 | 1996篇 |
2018年 | 1983篇 |
2017年 | 1487篇 |
2016年 | 1654篇 |
2015年 | 2288篇 |
2014年 | 3520篇 |
2013年 | 4799篇 |
2012年 | 2572篇 |
2011年 | 3387篇 |
2010年 | 2768篇 |
2009年 | 3479篇 |
2008年 | 3725篇 |
2007年 | 3680篇 |
2006年 | 3420篇 |
2005年 | 3337篇 |
2004年 | 2960篇 |
2003年 | 2645篇 |
2002年 | 2444篇 |
2001年 | 1600篇 |
2000年 | 1369篇 |
1999年 | 1458篇 |
1998年 | 1487篇 |
1997年 | 1255篇 |
1996年 | 1015篇 |
1995年 | 1142篇 |
1994年 | 1062篇 |
1993年 | 932篇 |
1992年 | 869篇 |
1991年 | 620篇 |
1990年 | 522篇 |
1989年 | 497篇 |
1988年 | 497篇 |
1987年 | 448篇 |
1986年 | 391篇 |
1985年 | 502篇 |
1984年 | 622篇 |
1983年 | 465篇 |
1982年 | 469篇 |
1981年 | 307篇 |
1980年 | 246篇 |
1979年 | 209篇 |
1978年 | 114篇 |
1977年 | 67篇 |
1976年 | 59篇 |
1975年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 513 毫秒
161.
Spinach-leaf ferredoxin was identified as a calcium-binding protein by 45Ca autoradiography on nitrocellulose membranes and with the cationic carbocyanine dye 1-ethyl-2-[3-(1-ethylnaphtho[1,2-d]thiazolin-2-ylidene)-2-methylpropenyl] naphtho[1,2-d]thiazolium bromide (stains-all). Binding of 45Ca was observed at pH 6.8 and pH 7.8 and in the presence of 5 mM and 20 mM MgCl2. At the higher MgCl2 concentration the Ca2+-binding capacity is reduced. Only micromolar concentrations of LaCl3, however, are required to achieve a similar effect. Both the oxidized and reduced forms of ferredoxin bind calcium.Abbreviations PAGE
polyacrylamide gel electrophoresis
- SDS
sodium dodecyl sulfate
- stains-all
1-ethyl-2-[3-(1-ethylnaphtho[1,2-d]thiazolin-2-ylidene)-2-methylpropenyl] naptho[1,2-d]thiazolium bromide 相似文献
162.
Elizabeth A. Bray Satoshi Naito Nai-Sui Pan Edwin Anderson Philip Dubé Roger N. Beachy 《Planta》1987,172(3):364-370
Soybean (Glycine max (L.) Merr.) seeds contain the storage protein -conglycinin, encoded by a multigene family. -Conglycinin consists of three subunits; , , and . A genomic clone for a -subunit of -conglycinin has been characterized by restriction-enzyme mapping and hybrid selected in-vitro translation followed by immunoprecipitation. In order to determine the developmental regulation of this -subunit gene, its expression was studied in seeds of transgenic petunia (Petunia hybrida) and tobacco (Nicotiana tabacum L.) plants. The -subunit expressed in seeds of petunia and tobacco was recognized by anti--conglycinin serum at a relative molecular mass of 53 000, equivalent to that of the native protein. Separation of the petunia-seed proteins by isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis showed that multiple isoelectric forms of the -subunit were produced. There was approximately a twofold variation in the accumulation of the -subunit protein in the mature seeds of transgenic petunia plants, each containing a single -subunit gene. However, the level of protein accumulation in mature seeds and the amount of -subunit mRNA in developing seeds was not correlated. Accumulation of the -subunit protein in transgenic seeds was less than the -subunit protein that accumulated in transgenic petunia seeds containing a single -subunit gene and less than the amount of the -subunit in mature soybean seeds which contain 8–13 -subunit genes. In transgenic tobacco plants, the accumulation of the -subunit protein in seeds was generally well correlated with the number of genes that were incorporated in the different transformants.Abbreviations kb
kilobase
- kDa
kilodalton
- Mr
relative molecular mass
- SDS-PAGE
sodium dodecyl sulfate polyacrylamide gel electrophoresis 相似文献
163.
Summary Fluorescein or rhodamine conjugates of seventeen different lectins were tested for their ability to label the plasma membrane of live plant protoplasts. During the investigation, a strong effect of calcium was observed on the binding of several lectins to protoplasts derived from suspension cultured rose cells (Rosa sp. Paul's Scarlet). The binding of these lectins was increased by elevating the calcium concentration from 1 to 10 mM in the buffer. Other divalent cations had variable, but similar, effects on lectin binding. The mechanism of this effect appeared to involve the protoplast surface rather than the lectins. Although the cell wall-degrading enzymes used to isolate protoplasts had generally no effect on lectin binding, one clear exception was observed. Binding ofArachis hypogaea agglutinin was markedly reduced on protoplasts isolated with Driselase as compared to protoplasts isolated with a combination of Cellulysin and Pectolyase Y-23. Although most of the lectins that labeled protoplasts derived from cultured rose cells or from corn root cortex (Zea mays L. WF9 × Mo17) had specificities for galactose or N-acetylgalactosamine, some differences in protoplast labeling between lectins of the same saccharide specificity were observed. Two different analyses of the interaction betweenRicinus communis agglutinin and rose protoplasts showed that binding was cooperative with an apparent association constant of 7.2 × 105M–1 or 9.8 × 105M–1 with a maximum of approximately 108 lectin molecules bound per protoplast. Treatment of protoplasts with glycosidases which hydrolyze either N- or O-glycosidic linkages of glycoproteins slightly enhanced labeling of protoplasts byRicinus communis agglutinin. Interpretation of these results are discussed.Abbreviations MPR
medium, minimal organic medium (Nothnagel andLyon 1986)
- APA
Abrus precatorius agglutinin
- CSA
Cytisus sessilifolius agglutinin
- ECA
Erythrina cristagalli agglutinin
- GS-I
Griffonia simplicifolia agglutinin
- LcH
Lens culinarus agglutinin
- PNA
Arachis hypogaea agglutinin
- SBA
Glycine max agglutinin
- VAA
Viscum album agglutinin
- VFA
Vicia faba agglutinin
- WGA
Triticum vulgaris agglutinin
- Con A
Canavalia ensiformis agglutinin
- HPA
Helix pomatia agglutinin
- TPA
Tetragonolobus purpureas agglutinin
- RCA
Ricinus communis agglutinin
- DBA
Dolichos biflorus agglutinin
- SJA
Sophora japonica agglutinin
- BPA
Bauhinia purpurea agglutinin
- FITC
fluorescein isothiocyanate
- Ga1NAc
N-acetylgalactosamine
- FDA
fluorescein diacetate
- 2-O-Me-D-Fuc
2-O-methyl-D-fucose
Parts of the work presented here are also submitted in partial fulfillment of requirements for the Ph.D. degree. 相似文献
164.
Dipak Kumar Banerjee 《Journal of biosciences》1987,11(1-4):311-319
Radio-labelled amphomycin (3H-amphomycin) forms a complex with dolichylmonophosphate in presence of Ca2+. Complex formation has also been documented with retinylmonophosphate and perhydromonoeneretinylmonophosphate. Analysis of
the space-filling model suggested both fatty acylated aspartic acid residue at the N-terminus of the lipopeptide and phosphate
head group of dolichylmonophosphate are necessary for the complex formation. The binding ability of amphomycin is then utilized
to localize dolichylmonophosphate in the microsomal membrane. Studies with microsomal membranes from hen oviduct suggested
that dolichylmonophosphate is located in the cytoplasmic side of the membrane. 相似文献
165.
Effect of chemical modification on the binding of gossypol by gossypin (11S protein) and congossypin (7S protein) of cottonseed 总被引:1,自引:0,他引:1
Binding of gossypol by gossypin and congossypin and their succinylated and sulfhydryl group-blocked derivatives has been measured.
The binding by gossypin and congossypin is characterized by weak interaction. Succinylation of gossypin decreases the binding
affinity whereas that of congossypin increases it. Blocking of sulfhydryl groups of both the proteins does not significantly
affect gossypol binding, Succinylation dissociates gossypin and causes conformational changes whereas it does not dissociate
congossypin but causes conformational changes. Sulfhydryl group blocking does not dissociate gossypin or congossypin, nor
does it cause any conformational changes. 相似文献
166.
On binding toVicia faba lectin, the fluorescence of 4-methylumbelliferyl-α-D-glucoPyranoside was quantitatively quenched showing that the interaction
of 4-methylumbelliferyl-α-D-glucoPyranoside took Place in a binding environment. The binding of the fluorescent sugar was
saccharide sPecific as evidenced by the reversal of 4-methylumbelliferyl-α-D-glucoPyranoside fluorescence quenching by D-fructose.
The association constant,K
a, values for the 4-methylumbelliferyl-α-D-glucoPyranoside was determined by comPetition study emPloying reversal of fluorescence
quenching of 4-methylumbelliferyl-α-D-glucoPyranoside by D-fructose. TheK
a value obtained for D-fructose was 1.07 ±0.03 X 104 M-1 and for 4-methylumbelliferyl-α-D-glucoPyranoside was 1.60 ±0.05 X 104 M-1 at 15°C. TheK
a values of 2.51 ±0.06 X 104M-1, l.26 ±0.02 X 104 M-1 and 0.56 ±0.01 X 104M-1, resPectively at 10°, 20° and 30°C were obtained from the ChiPman equation. The relative fluorescence quenching, ΔF
a, at infinite concentration of the free saccharide sites ofVicia faba lectin [P′] was 93.5% at 30°C and the binding constant for 4-methylumbelliferyl-α-D-glucoPyranoside lectin interaction as derived by
Yank and Hanaguchi equation was 0.63 ±0.01 X 104M-1. 相似文献
167.
168.
Lead mining in Wales originated before the Roman Occupation. The main active period was from 1750–1900 when zinc and copper were also mined and during this period only simple and inefficient ore processing methods were available. Consequently large amounts of copper, lead and zinc compounds were lost to the environment and have since become incorporated in sediments and soils. Locally, pollution may still occur from drainage from abandoned mines and by mobilization of mine tailings. This paper describes the present state of Welsh rivers and reviews the distribution of contaminants in sediments and soils. The uptake of heavy metals by plants and the consequences for human health are alto discussed. 相似文献
169.
170.
Summary Phloridzin-insensitive, Na+-independentd-glucose uptake into isolated small intestinal epithelial cells was shown to be only partially inhibited by trypsin treatment (maximum 20%). In contrast, chymotrypsin almost completely abolished hexose transport. Basolateral membrane vesicles prepared from rat small intestine by a Percoll® gradient procedure showed almost identical susceptibility to treatment by these proteolytic enzymes, indicating that the vesicles are predominantly oriented outside-out. These vesicles with a known orientation were employed to investigate the kinetics of transport in both directions across the membrane. Uptake data (i.e. movement into the cell) showed aK
t of 48mm and aV
max of 1.14 nmol glucose/mg membrane protein/sec. Efflux data (exit from the cell) showed a lowerK
t of 23mm and aV
max of 0.20 nmol glucose/mg protein/sec.d-glucose uptake into these vesicles was found to be sodium independent and could be inhibited by cytochalasin B. TheK
t for cytochalasin B as an inhibitor of glucose transport was 0.11 m and theK
D for binding to the carrier was 0.08 m.d-glucose-sensitive binding of cytochalasin B to the membrane preparation was maximized withl- andd-glucose concentrations of 1.25m. Scatchard plots of the binding data indicated that these membranes have a binding site density of 8.3 pmol/mg membrane protein. These results indicate that the Na+-independent glucose transporter in the intestinal basolateral membrane is functionally and chemically asymmetric. There is an outward-facing chymotrypsin-sensitive site, and theK
t for efflux from the cell is smaller than that for entry. These characteristics would tend to favor movement of glucose from the cell towards the bloodstream. 相似文献