全文获取类型
收费全文 | 3334篇 |
免费 | 288篇 |
出版年
2023年 | 10篇 |
2022年 | 32篇 |
2021年 | 44篇 |
2020年 | 32篇 |
2019年 | 49篇 |
2018年 | 57篇 |
2017年 | 38篇 |
2016年 | 70篇 |
2015年 | 150篇 |
2014年 | 190篇 |
2013年 | 183篇 |
2012年 | 260篇 |
2011年 | 248篇 |
2010年 | 127篇 |
2009年 | 130篇 |
2008年 | 190篇 |
2007年 | 194篇 |
2006年 | 179篇 |
2005年 | 177篇 |
2004年 | 183篇 |
2003年 | 172篇 |
2002年 | 153篇 |
2001年 | 47篇 |
2000年 | 39篇 |
1999年 | 49篇 |
1998年 | 48篇 |
1997年 | 42篇 |
1996年 | 35篇 |
1995年 | 33篇 |
1994年 | 28篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 32篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有3622条查询结果,搜索用时 453 毫秒
21.
22.
Cloning and sequencing of the genes encoding the large and the small subunits of the H2 uptake hydrogenase (hup) of Rhodobacter capsulatus 总被引:12,自引:0,他引:12
Michèle Leclerc Annette Colbeau Béatrice Cauvin Paulette M. Vignais 《Molecular & general genetics : MGG》1988,214(1):97-107
Summary The structural genes (hup) of the H2 uptake hydrogenase of Rhodobacter capsulatus were isolated from a cosmid gene library of R. capsulatus DNA by hybridization with the structural genes of the H2 uptake hydrogenase of Bradyrhizobium japonicum. The R. capsulatus genes were localized on a 3.5 kb HindIII fragment. The fragment, cloned onto plasmid pAC76, restored hydrogenase activity and autotrophic growth of the R. capsulatus mutant JP91, deficient in hydrogenase activity (Hup-). The nucleotide sequence, determined by the dideoxy chain termination method, revealed the presence of two open reading frames. The gene encoding the large subunit of hydrogenase (hupL) was identified from the size of its protein product (68108 dalton) and by alignment with the NH2 amino acid protein sequence determined by Edman degradation. Upstream and separated from the large subunit by only three nucleotides was a gene encoding a 34 256 dalton polypeptide. Its amino acid sequence showed 80% identity with the small subunit of the hydrogenase of B. japonicum. The gene was identified as the structural gene of the small subunit of R. capsulatus hydrogenase (hupS). The R. capsulatus hydrogenase also showed homology, but to a lesser extent, with the hydrogenase of Desulfovibrio baculatus and D. gigas. In the R. capsulatus hydrogenase the Cys residues, (13 in the small subunit and 12 in the large subunit) were not arranged in the typical configuration found in [4Fe–4S] ferredoxins. 相似文献
23.
Menzel PT 《Bioethics》1992,6(2):158-165
[In his review essay in this issue of Bioethics,] Julian Savulescu lucidly summarizes and assesses each essay in Strong Medicine. I would like to clarify a few important general points about prior consent as a conceptual framework for the ethical rationing of health care, correct several specific misreadings, and defend my basic claim despite some acknowledged problems. 相似文献
24.
Tina Pallesen Annette Vangsted Lars Drivsholm Henrik Clausen Jesper Zeuthen Håkan Wallin 《Glycoconjugate journal》1992,9(6):331-335
We here report an enzyme linked immunosorbent assay (ELISA) and a scintillation proximity assay (SPA) for detection of the ganglioside FucGM1 in sera from small cell lung cancer (SCLC) patients. The SPA was more sensitive and reproducible than the ELISA. In this assay, monoclonal antibodies specific for FucGM1 were bound to SPA particles and incubated with labelled FucGM1 and 100 µl test-serum overnight, and counted in a -counter. The sensitivity was 0.2 ng. Seven out of twenty sera from SCLC patients were positive, whereas none of twenty sera from healthy individuals were positive for FucGM1. The SPA was more sensitive than the previously reported HPTLC as well as a direct ELISA.Abbreviations MAb
monoclonal antibody
- SPA
scintillation proximity assay
- HPTLC
high performance thin layer chromatography
- SCLC
small cell lung cancer
- FucGM1
Fuc1-2Gal1-3GalNAc1-4(NeuAc2-3)-Gal1-4Glc1-1Cer
- ELISA
enzyme linked immunosorbent assay
- FCS
foetal calf serum
- PBS
phosphate buffered saline 相似文献
25.
Tjakko Abee Jan Knol Klaas J. Hellingwerf Evert P. Bakker Annette Siebers Wil N. Konings 《Archives of microbiology》1992,158(5):374-380
Cells of the purple non-sulphur bacterium Rhodobacter sphaeroides express a high-affinity K+ uptake system when grown in media with low K+ concentrations. Antibodies againts the catalytic KdpB protein or the whole KdpABC complex of Escherichia coli crossreact with a 70.0 kDa R. sphaeroides protein that was expressed only in cells grown in media with low K+ concentrations. In membranes derived from R. sphaeroides cells grown with low K+ concentrations (induced cells), a high ATPase activity could be detected when assayed in Tris-HCl pH 8.0 containing 1 mM MgSO4. This ATPase activity increased upon addition of 1 mM KCl from 166 to 289 mol ATP hydrolysed x min-1 x g protein-1 (1.7-fold stimulation). The K+-stimulated ATPase activity was inhibited approximately 93% by 0.5 mM vanadate but hardly by N,N-dicyclohexylcarbo-diimide (DCCD). These results indicate that the inducible K+-ATPase in R. sphaeroides resembles the Kdp K+-translocating ATPase of Escherichia coli. This Kdp-like transport system is also expressed in R. capsulatus and Rhodospirillum rubrum during growth in media with low K+ concentrations suggesting a wide distribution of this transport system among phototrophic bacteria.Abbreviations
electrical potential difference across the cytoplasmic membrane
- pH
pH difference across the cytoplasmic membrane
- BSA
bovine serum albumine
- PAGE
polyacrylamide gel electrophoresis
- HEPES
4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid
- PMSF
phenyl-methyl-sulfonyl fluoride
- DCCD
N,N-dicyclohexylcarbodiimide
- AIB
2--aminoisobutyric acid
- TMG
methyl--d-thiogalactopyranoside 相似文献
26.
27.
Nigel L. Brown Tapan K. Misra Joseph N. Winnie Annette Schmidt Michael Seiff Simon Silver 《Molecular & general genetics : MGG》1986,202(1):143-151
Summary The DNA sequences of the mercuric resistance determinants of plasmid R100 and transposon Tn501 distal to the gene (merA) coding for mercuric reductase have been determined. These 1.4 kilobase (kb) regions show 79% identity in their nucleotide sequence and in both sequences two common potential coding sequences have been identified. In R100, the end of the homologous sequence is disrupted by an 11.2 kb segment of DNA which encodes the sulfonamide and streptomycin resistance determinants of Tn21. This insert contains terminal inverted repeat sequences and is flanked by a 5 base pair (bp) direct repeat. The first of the common potential coding sequences is likely to be that of the merD gene. Induction experiments and mercury volatilization studies demonstrate an enhancing but non-essential role for these merA-distal coding sequences in mercury resistance and volatilization. The potential coding sequences have predicted codon usages similar to those found in other Tn501 and R100 mer genes. 相似文献
28.
Little is known of the selectivity of the blood-brain barrier at birth. Hexoses are transported through the barrier by a facilitating mechanism. To study the capacity of this mechanism to distinguish between analogs of D-glucose, we compared the transport of fluorodeoxyglucose, deoxyglucose, glucose, methylglucose, mannose, galactose, mannitol, and iodoantipyrine across the cerebral capillary endothelium in newborn Wistar rats. Cerebral blood flow, glucose consumption, and the blood-brain permeabilities of the hexoses were 25-50% of the adult values but the ratios between the permeabilities of the individual hexoses were similar to the ratios observed in adult rats. The mannitol clearance into brain was considerably higher than in adult rats (about 10-fold), indicating a higher endothelial permeability to small polar nonelectrolytes. The brain water content was higher in newborn than in adult rats and was associated with a higher steady-state distribution of labeled methylglucose between brain and blood. Hexose concentrations were determined relative to whole blood because the apparent erythrocyte membrane permeability to glucose was as high as in humans and thus considerably higher than in adult rats. The half-saturation concentration of glucose transport across the blood-brain barrier was considerably higher than in adult rats, about three-fold, suggesting that net blood-brain glucose transfer is less sensitive to blood glucose fluctuation in newborn than in adult rats. 相似文献
29.
A method for simultaneous detection of picomole quantities of glutathione (GSH), glutathione disulfide (GSSG), glutathione S-sulfonate (GSSO3H), and cysteine S-sulfonate (CYSSO3H) by high-performance liquid chromatography has been developed. Compounds are separated by anion-exchange chromatography using a citric acid buffer system, and then derivatized postcolumn using o-phthalaldehyde with 2-mercaptoethanol, heated to 70 degrees C, and detected by fluorescence. The compounds elute with retention times of 12.5 min for GSH, 27.5 min for CYSSO3H, 29.8 min for GSSG, and 33.0 minutes for GSSO3H, with detection limits of 10, 200, 10, and 50 pmol, respectively. Recoveries are 103% for GSH, 102% for GSSG, 100% for CYSSO3H, and 96% for GSSO3H. Determination of target compounds in cells is described. 相似文献
30.
Annette Gulik Vittorio Luzzati Mario De Rosa Agata Gambacorta 《Journal of molecular biology》1985,182(1):131-149
We describe in this work the structure and polymorphism of a variety of lipids extracted from Sulfolobus solfataricus, an extreme thermoacidophilic archaebacterium growing at about 85 °C and pH 2. These lipids are quite different from the usual fatty acid lipids of eukaryotes and prokaryotes: each molecule consists of two C40 ω-ω′ biphytanyl residues (with 0 to 4 cyclopentane groups per residue), ether linked at both ends to two (variably substituted) glycerol or nonitol groups. Four lipid preparations were studied; the total and the polar lipid extracts, and two hydrolytic fractions, the symmetric glycerol dialkyl glycerol tetraether and the asymmetric glycerol dialkyl nonitol tetraether, as a function of water content and temperature, using X-ray scattering techniques. The main conclusions from the study of the four lipid preparations can be summarized as follows. (1) As with other lipids, a remarkable number and variety of phases are observed over a temperature-concentration range close to “physiological” conditions. The possibility is discussed that this polymorphism reflects a fundamental property of lipids, closely related to their physiological rôle. (2) As in other lipids, two types of chain conformations are observed: a disordered one (type α) at high temperature; at lower temperature, a more ordered packing of stiff chains, all parallel to each other (type β′). At temperatures and degrees of hydration approaching the conditions prevailing in the living cell, the conformation is of type α. (3) In all the phases with chains in the α conformation, the unsubstituted glycerol headgroups, whose concentration is high in these lipids, segregate in the hydrocarbon matrix, away from the other polar groups. This property may have interesting biological consequences: for example, the chains of a fraction of the bipolar lipid molecules can span hydrocarbon gaps as wide as 75 Å. (4) Two cubic phases are observed in the total and the polar lipid extracts, which display a remarkable degree of metastability, most unusual in lipid phase transitions involving structures with chains in the α conformation. This phenomenon can be explained by the interplay of the physical structure of the cubic phases (the two contain two intertwined and unconnected three-dimensional networks of rods) and the chemical structure of the lipid molecules: the two headgroups of most molecules being anchored on each of the two networks of rods, the migration of the lipid molecules is hindered by the two independent diffusion processes and by the entanglement of the chains. The possibility is discussed that this phenomenon may reflect an evolutionary response to a challenge of the natural habitat of these archaebacteria. 相似文献