全文获取类型
收费全文 | 4727篇 |
免费 | 457篇 |
国内免费 | 1篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 88篇 |
2021年 | 150篇 |
2020年 | 81篇 |
2019年 | 77篇 |
2018年 | 122篇 |
2017年 | 107篇 |
2016年 | 162篇 |
2015年 | 292篇 |
2014年 | 293篇 |
2013年 | 342篇 |
2012年 | 385篇 |
2011年 | 392篇 |
2010年 | 268篇 |
2009年 | 211篇 |
2008年 | 290篇 |
2007年 | 291篇 |
2006年 | 264篇 |
2005年 | 185篇 |
2004年 | 189篇 |
2003年 | 182篇 |
2002年 | 163篇 |
2001年 | 49篇 |
2000年 | 44篇 |
1999年 | 52篇 |
1998年 | 41篇 |
1997年 | 22篇 |
1996年 | 18篇 |
1995年 | 24篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有5185条查询结果,搜索用时 15 毫秒
21.
Molecular organisation of the quinic acid utilization (QUT) gene cluster in Aspergillus nidulans 总被引:9,自引:0,他引:9
Alastair R. Hawkins Heather K. Lamb Melanie Smith John W. Keyte Clive F. Roberts 《Molecular & general genetics : MGG》1988,214(2):224-231
Summary The functional integrity of the QUTB gene (encoding quinate dehydrogenase) has been confirmed by transformation of a qutB mutant strain. The DNA sequence of the contiguous genes QUTD (quinate permease), QUTB and QUTG (function unknown) has been determined and analysed, together with that of QUTE (catabolic 3-dehydroquinase). The QUTB sequence shows significant homology with the shikimate dehydrogenase function of the complex AROM locus of Aspergillus nidulans, and with the QA-3 quinate dehydrogenase and QA-1S (repressor) genes of Neurospora crassa. The QUTD gene shows strong homology with the N. crassa QA-Y gene and QUTG with the QA-X gene. QUTD, QUTB, and QUTG, QUTE form two pairs of divergently transcribed genes, and conserved sequence motifs identified in the two common 5 non-coding regions show significant homology with UAS
GAL
and UAS
QA
sequences of the Saccharomyces cerevisiae and N. crassa Gal and QA systems. In addition, conserved 5 sequences homologous to the mammalian CAAT box are noted and a previously unreported conserved 22 nucleotide motif is presented. 相似文献
22.
23.
24.
We have found and characterized an antigen associated with crystal-containing cells in the stomium and connective tissue of the anthers of Nicotiana tabacum L. (tobacco). The antigen, defined by the monoclonal antibody NtF-8B1, localizes to subcellular regions surrounding the crystals. At the light-microscope level, the antigen is detectable just after the first appearance of crystals in the connective tissue of the anther, and at approximately the same time as the appearance of crystals in the stomium. The antigen is not detectable on a Western blot, and gave inconclusive results on a test of periodate sensitivity. It is not the crystals themselves, nor is the presence of the crystals required for antibody recognition. The antigen is sensitive to heat and protease treatment, indicating that it is a protein. The antigen is not tightly membrane-bound, in spite of its localization closely surrounding the crystals. Chemical tests indicate that the druse crystals in the stomium are calcium oxalate.Abbreviations ELISA
enzyme-linked immunosorbent assay
- FITC
fluorescein isothiocyanate
This research was supported by a National Science Foundation postdoctoral fellowship to B.L.H., by National Science Foundation grants DMB-87-15799 and to W.E.F. BSR-88-18035, and by U.S. Department of Agriculture grant GAM-89-01056. The authors thank Phillip T. Evans (Louisiana State University, Baton Rouge, USA), Wilma L. Lingle, Harry T. Horner, Jr. (Iowa State University), and A. Jack Fowler, Jr., for advice and helpful discussions. 相似文献
25.
Summary The ability of alkalophilic bacteria to remove iron, gallium and aluminium from culture media is reported. Of six bacterial strains grown in the presence of iron, gallium or aluminium (10 M), five were able to accumulate iron or gallium, but only two depleted the aluminium stock. A comparison of gallium removal under low (< 1 gmM) or high (10 gmM) iron conditions showed that two isolates accumulated gallium only under low-Fe conditions. One isolate, a coryneform bacterium, was able to grow in the presence of 1, 10 and 100 mg gallium/l, but growth and siderophore production were affected at high gallium concentration. Similar concentrations of gallium were accumulated from cultures initially containing 1 or 100 mg gallium/l.
Offsprint requests to: D. J. Gascoyne 相似文献
26.
Cholinergic processes were measured in motor cortex, hippocampus, and striatum of cats in the terminal stages of GM1 gangliosidosis and compared to those of control cats. The greatest difference observed was elevation in the rate of K+-stimulated release of acetylcholine (ACh) from brain slices prepared from affected cats. The K+-stimulated release of endogenous ACh was increased by 31-43% and of newly synthesized ACh by 19-80% in brain slices from different brain regions. All regions that were examined were affected but the greatest effects occurred in cortex. The rate of synthesis of ACh was elevated in cortical and hippocampal slices. Choline acetyltransferase activity in brain regions of cats with GM1 gangliosidosis was not significantly different from that in controls, whereas high-affinity choline transport in cortical synaptosomes was elevated. Muscarinic receptor binding sites were reduced in the cortex, hippocampus, and striatum of GM1 mutant cats, whereas the apparent affinity was not altered. These results indicate that there are major alterations of cholinergic function in the brains of cats with GM1 gangliosidosis. 相似文献
27.
V. K. Agarwal W. Schutte J. M. Greenberg J. P. Ferris R. Briggs Steven Connor C. P. E. M. Van de Bult F. Baas 《Origins of life and evolution of the biosphere》1985,16(1):21-40
A simulation of the organic layer accreted onto interstellar dust particles was prepared by slow deposition of a CO:NH3:H2O gas mixture on an Al block at 10K, with concomitant irradiation with vacuum UV. The residues were analyzed by GC-MS, HPLC, and near IR; a reaction pathway leading from NH3 to complex alcohol, fatty acid, and amide products in 27 stages is postulated. The astronomical relevance and significance of the observations are discussed. 相似文献
28.
Summary Intracellular ethanol concentrations inSaccharomyces cerevisiae were measured using a high cell density fermentation technique which permits samples to be fixed for analysis in less than two seconds. No accumulation of intracellular ethanol was detected, regardless of the stage of fermentation. The technique eliminates artifacts associated with concentrating the cell sample and provides a reliable means for detecting whether other fermentation products accumulate intracellularly. 相似文献
29.
Effects of placental malaria on mothers and neonates from Zaire 总被引:1,自引:0,他引:1
D Anagnos L O Lanoie J R Palmieri A Ziefer D H Connor 《Zeitschrift für Parasitenkunde (Berlin, Germany)》1986,72(1):57-64
Of one hundred placentas collected consecutively in the Ubangi district, Zaire, 64 had falciparum malaria. Mothers and infants of the 64 malarious and 36 non-malarious placentas were compared. The malarious placentas had no consistent relationship to infant length or head circumference, APGAR score, birthweight, maternal anemia, splenomegaly or hydramnios. The rate of hydramnios, in fact, was higher in the mothers with non-malarious placentas. Mothers with malarious placentas were younger (means 24) than mothers with non-malarious placentas (means 29). Mothers with fewer pregnancies were more likely to have malarious placentas than older multiparous mothers. There were 7 stillbirths, 4 from mothers with malarious placentas. Infants born to mothers with malarious placentas averaged 100 g less than those from mothers with non-malarious placentas. This study shows that mothers with falciparum malaria from the Ubangi district deliver normal and apparently unaffected infants. 相似文献
30.
The electroplax of the electric eel Electrophorus electricus is the most abundant source of the calcium-binding protein calmodulin. The electroplax has 250 times the amount of calmodulin and its mRNA than eel skeletal muscle. Our data suggest that there is no major difference in gene copies, the degree of methylation, or genome rearrangement of the calmodulin gene in DNAs from eel electroplax and muscle. Differences in the calmodulin-binding proteins in electroplax and muscle suggest a differential role for the functional expression of calmodulin in cellular regulation. 相似文献