全文获取类型
收费全文 | 685篇 |
免费 | 50篇 |
专业分类
735篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 25篇 |
2014年 | 28篇 |
2013年 | 31篇 |
2012年 | 41篇 |
2011年 | 53篇 |
2010年 | 37篇 |
2009年 | 35篇 |
2008年 | 48篇 |
2007年 | 37篇 |
2006年 | 40篇 |
2005年 | 47篇 |
2004年 | 46篇 |
2003年 | 32篇 |
2002年 | 39篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1969年 | 1篇 |
1963年 | 1篇 |
1957年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有735条查询结果,搜索用时 15 毫秒
1.
G Gradwohl A Mazen G de Murcia 《Biochemical and biophysical research communications》1987,148(3):913-919
The interaction between highly purified poly(ADP-ribose) polymerase from calf thymus and different topological forms of pBR322 DNA has been studied by gel retardation electrophoresis and electron microscopy. We show that: (i) in the absence of nicks on DNA the enzyme has a marked affinity for supercoiled (form I) DNA, (ii) in the presence of single stranded breaks poly(ADP-ribose) polymerase preferentially binds to form II, (iii) in all cases enzyme molecules are frequently located at DNA intersections, (iv) a cooperative binding of the enzyme on DNA occurs. 相似文献
2.
A Mazen J Menissier-de Murcia M Molinete F Simonin G Gradwohl G Poirier G de Murcia 《Nucleic acids research》1989,17(12):4689-4698
By Energy Dispersive X-ray fluorescence we have determined that calf thymus poly(ADP-ribose) polymerase binds two zinc ions per enzyme molecule. Using 65Zn (II) for detection of zinc binding proteins and polypeptides on western blots, we found that the zinc binding sites are localized in a 29 kd N-terminal fragment which is included in the DNA binding domain. Metal depletion and restoration experiments proved that zinc is essential for the binding of this fragment to DNA as tested by Southwestern assay. These results correlate with the existence of two putative zinc finger motifs present in the N-terminal part of the human enzyme. Poly(ADP-ribose)polymerase fingers could be involved in the recognition of DNA strand breaks and therefore in enzyme activation. 相似文献
3.
Gideon W. Schaeffer F. T. Sharpe Jr. H. L. Carnahan C. W. Johnson 《Plant Cell, Tissue and Organ Culture》1986,6(2):149-157
Rice, Oryza sativa, plants regenerated from anther culture with and without in vitro selection pressure were evaluated for chalky seed. Progeny evaluated included 21 spontaneously doubled haploids selfed 4 times, progeny from plants regenerated from S-aminoethylcysteine resistant callus selfed 4 times and backcrosses of both types to the parental type. All lines with in vitro histories had higher seed chalkiness than the controls both in the intensity of chalkiness and in the number of seeds expressing the character. The full range of intensity and amount of chalkiness was expressed in the progeny. The average intensity of anther/tissue culture-derived progeny was 4–5, based on a scale of 1 (translucent) to 10 (fully opaque), and the average amount of chalkiness within plants sampled was 50–75 percent. The chalky characteristic is transmitted from parent to offspring into a range of identifiable F2 segregants.
Disclaimer statement Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of other products that may also be suitable. 相似文献
4.
The six species of the sectionFoenum-graecum ofTrigonella have the same chromosome number, 2n = 16.T. gladiata andT. cariensis have fairly symmetrical karyotypes, while those ofT. foenum-graecum, T. berythea, T. macrorrhyncha andT. cassia are asymmetrical. C-bands are present in all six species but the number of bands and their positive vary considerably among the species. The karyotype evidence suggests that none of the available species of theFoenum-graecum section can be considered as the wild progenitor of fenugreek. 相似文献
5.
Gideon Bach Elizabeth F. Neufeld 《Biochemical and biophysical research communications》1983,112(1):198-205
The biosynthesis of arylsulfatase A was studied in cultured fibroblasts by pulse-chase labeling with [2-3H]mannose; the enzyme was isolated by immunoprecipitation and denaturing polyacrylamide gel electrophoresis. In normal fibroblasts, and in fibroblasts from a patient with multiple sulfatase deficiency, the enzyme was synthesized as a glycoprotein of apparent molecular weight of 59,000; half of it was processed over a period of 4 days to Mr= 57,000. The precursor chain of Mr= 59,000 was secreted in the presence of 10 mM NH4Cl. An immunoprecipitable glycoprotein of normal size was synthesized by fibroblasts from two unrelated patients with metachromatic leukodystrophy, but this material disappeared within twenty hours. In fibroblasts from an individual with pseudodeficiency of arylsulfatase A, the immunoprecipitable precursor glycoprotein was smaller (Mr= 56,000). The synthesis of cross-reactive proteins with altered properties supports the concept of allelic mutations as the genetic basis of metachromatic leukodystrophy and of arylsulfatase A pseudodeficiency. 相似文献
6.
Abstract. The natural Mediterranean maquis and forest vegetation of Israel is commonly considered to be composed mainly of four, roughly equal components: Pinus halepensis, deciduous oak, evergreen oak, and Ceratonia - Pistacia communities. They represent the past climax and subclimax of this region. Evidence accumulated from pollen analysis and wood remnant research in geological and archaeological excavations, as well as from written historical sources, shows that this view is wrong: the ancient vegetation in this area was dominated by Quercus calliprinos. 相似文献
7.
All-trans retinoic acid is well known as a modulator of positional specification in vertebrate development. A similar mechanism may operate in molluscan development. Molluscan development is characterized by an invariant pattern of cell divisions, which allows the study of individual cells in the developing organism. Low concentrations of exogenous retinoic acid applied during gastrulation affect the cell division pattern in the early larval stage of the molluscLymnaea stagnalis. A few cells from the apical plate, a larval organ consisting of seven large cleavage-arrested cells, were induced by retinoic acid to resume cell division. They typically formed an area of proliferating small cells that resembles the adjacent areas of precursor cells of adult ectoderm. The identification of individual cells that are transformed by retinoic acid may provide new insights into the mechanisms underlying positional specification within the embryo. 相似文献
8.
Gideon Ladizinsky 《Economic botany》1993,47(1):60-64
The current views on lentil domestication are based on biological attributes of the wild progenitorLens culinaris ssp. orientalis and on assumptions which have never been tested. Seed dormancy, a major factor in the adaptation of ssp.orientalis to its natural habitat, makes it inappropriate for cultivation, because poor germination causes seed yield following cultivation to be equal to the amount of sown seeds. Higher yield, resulting from the evolution of a non-dormant type can be obtained only after five or six cycles of unprofitable cultivation. It is doubtful that incipient farmers would have undertaken such an endeavor without preexisting knowledge that non-dormant types could eventually be obtained. Experiments involving the sowing of wild lentil would have been much more successful if the non-dormant types were present in appreciable quantities in the seed stock. Establishment of that type in the natural population would have required a period of seven to eight years with favorable growing conditions allowing the non-dormant type to become widespread in the population, followed by massive predation by man reducing the hazard of a population explosion. The close similarity between isozyme profiles of the cultivated lentil and its wild progenitor indicates that lentil cultivation was attempted with seeds derived from different populations and in different areas. 相似文献
9.
Shirley P. Tolley Gideon J. Davies Mark O'Shea Mark I. Cockett Andrew J. P. Docherty Gillian Murphy 《Proteins》1993,17(4):435-437
A nonglycosylated (N30QN78Q) form of the human tissue inhibitor of metalloproteinases, TIMP-1, has been prepared and crystallized in a form suitable for X-ray diffraction analysis. Small single crystals have been grown using sodium tartrate as a precipitant. The crystals are in space group P21, with cell dimensions a = 35.28, b = 53.95, c = 48.56, and β = 96.0°. There is a single molecule of TIMP-1 in the asymmetric unit. The crystals diffract to at least 2.3 Å resolution. Complete data have been collected to 2.9 Å and a search for heavymetal derivatives is in progress. © 1993 Wiley-Liss, Inc. 相似文献
10.