全文获取类型
收费全文 | 8209篇 |
免费 | 630篇 |
国内免费 | 8篇 |
专业分类
8847篇 |
出版年
2023年 | 44篇 |
2022年 | 88篇 |
2021年 | 177篇 |
2020年 | 121篇 |
2019年 | 128篇 |
2018年 | 215篇 |
2017年 | 176篇 |
2016年 | 258篇 |
2015年 | 440篇 |
2014年 | 421篇 |
2013年 | 548篇 |
2012年 | 720篇 |
2011年 | 630篇 |
2010年 | 414篇 |
2009年 | 323篇 |
2008年 | 479篇 |
2007年 | 448篇 |
2006年 | 431篇 |
2005年 | 411篇 |
2004年 | 415篇 |
2003年 | 387篇 |
2002年 | 309篇 |
2001年 | 97篇 |
2000年 | 71篇 |
1999年 | 75篇 |
1998年 | 80篇 |
1997年 | 47篇 |
1996年 | 53篇 |
1995年 | 50篇 |
1994年 | 51篇 |
1993年 | 35篇 |
1992年 | 51篇 |
1991年 | 51篇 |
1990年 | 31篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 45篇 |
1984年 | 35篇 |
1983年 | 30篇 |
1982年 | 24篇 |
1981年 | 25篇 |
1980年 | 30篇 |
1979年 | 27篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1976年 | 31篇 |
1975年 | 25篇 |
1974年 | 19篇 |
排序方式: 共有8847条查询结果,搜索用时 0 毫秒
91.
The aerial parts of Passiflora serratodigitata yielded 5,7-dihydroxy-4-phenylcoumarin, its 7-β-glucoside and the known C-glycosylflavones 2″-xylosylvitexin, 2″-xylosylisovitexin, vitexin, isovitexin, a vicenin, and orientin. The known flavone chrysin was also isolated. This is the first report of neoflavonoids in the family Passifloraceae. 相似文献
92.
Marie Kselíková Tomáš Mařík Bedřich Bíbr Jaroslav Lener 《Biological trace element research》1980,2(1):57-64
This study describes the interaction of molybdenum with blood components. Molybdenum-99 was added to blood, and after four
washings, 3% of the total radioactivity was found in red cells. More specifically, the radioactivity was determined to be
associated with the cell membrane.
Molybdenum-99 in the +VI form did not interact with the human erythrocyte membrane; however, Mo(V) forms did interact. Of
five different compounds, the highes uptake was observed with a brown Mo(V)-ascorbate complex generated from Mo(VI) and ascorbic
acid in the molar ratio 1∶20. A membrane suspension of Mo-ascorbate-treated human erythrocytes was prepared and the solubilized
proteins were separated on a polyacrylamide gel in the presence of sodium dodecyl sulfate (SDS). Molybdenum-99 binding to
spectrin was demonstrated, as well as some minor interactions with membrane hemoglobin and bands 6 and 8. 相似文献
93.
94.
Samuel B. Jones Jr. William C. Burnett Jr. Nancy C. Coile Tom J. Mabry M. F. Betkouski 《Oecologia》1979,39(1):71-77
Summary Sesquiterpene lactone glaucolide-A from Vernonia, incorporated in the rearing diets of five species of Lepidoptera, significantly reduced the rate of growth of larvae of the southern armyworm, Spodoptera eridania; fall armyworm, S. frugiperda; and yellowstriped armyworm, S. ornithogalli. Quantitative feeding tests demonstrated that decreased feeding levels and reduced growth resulted from ingestion of a sesquiterpene lactone. Ingestion of glaucolide-A increased the number of days to pupation in four of the species. In the southern armyworm, it significantly reduced pupal weight. Glaucolide-A decidedly reduced percentage of survival of southern and fall armyworms. Yellow woollybear, Diacrisia virginica, and cabbage looper, Trichoplusia ni, larvae were essentially uneffected by the ingestion of the sesquiterpene lactone. Sesquiterpene lactones adversely affect growth rate and survival of certain insects that feed upon plants containing them. They apparently function as defensive products, screening out a portion of the potential herbivores.Vernonieae: Compositae 相似文献
95.
Using, as an example, the susceptibility of 437 bacterial strains (belonging to nomenspecies of the genera,Pseudomonas andXanthomonas) to 86 bacteriophage preparations, this study describes how sequential removal of the more distinctive emerging clusters (or selected groups of elements with prior knowledge of their taxonomic relationships) in a principal components analysis can be employed to analyze, the affinities among the remaining original numerical units. The initial, well-defined clusters had a constraining impact on other elements. This constraint was eased upon successive removal from the data matrix of initially distinctive clusters, thereby enabling clearer views of the relationships among the remaining elements. This procedure (sequential principal components analysis) might be used to evaluate the impacts of individual taxa in a numerical classification. 相似文献
96.
Using a number of intrafamilial PLTs raised against identical HLA haplotypes it has been possible to construct a model in an informative family defining the HLA-D region as a genetic system. This system consists of at least two regions separated by a recombination between HLA-D and GLO. In relation to the site of recombination, a minimum of one centromeric and three telomeric components can be identified per haplotype.—Fourteen PLTs raised and defined within the family were subsequently tested in a Caucasian population (n=84) and in 13 unrelated, complete families.—It is concluded that the hypothetical model proposed for the HLA-D region as a genetic system of linked loci, coding at the cell surface for associated but distinct components (at least four per haplotype), allows for typing of the components of the HLA-D system of any given haplotype. Serological typing of HLA-D components should, in the near future, provide a more convenient way of establishing component phenotypes than the present use of primed lymphocyte typing reagents. Among the components isolated, some have a high association with the classic alleles defined either by homozygous typing cells or DR serology. Others form the basis of cross-reactivity but their presence does not interfere with standard typing. Others, however, seem by their mere presence to be responsible for false assignments.—The concept of HLA-D as a genetic system clarifies many of the inconsistencies observed with a one-locus system.Research scientists from INSERM.Research Fellow from the Danish Medical Research Council.Central Blood Bank — Marseille 相似文献
97.
98.
Norio Ogawa Tom Thompson Henry G. Friesen Joseph B. Martin Paul Brazeau 《The Biochemical journal》1977,165(2):269-277
A soluble somatostatin-binding protein was detected in the cytosol fractions of various rat, human and bovine tissues. Maximum binding occurred at pH8.0-8.5 and was Ca(2+)-dependent. The specific binding of somatostatin per 10mug of cytosol protein from 12 rat tissues ranged between 36 and 15%, and 3% for peripheral blood cells. There was also substantial binding in cytosol from human anterior pituitary and liver, and bovine anterior pituitary. The specific binding in rat and human plasma in the presence of EDTA was only 1%. Gel filtration suggested a molecular weight of approx. 80000 for the somatostatin-binding protein from several sources. Exposure of the binding protein to trypsin eliminates somatostatin-binding activity but ribonuclease and deoxyribonuclease have no effect. The binding protein is thermolabile, ethanol-precipitable, and not completely specific for somatostatin. Bound (125)I-labelled [Tyr(1)]somatostatin is not easily displaced by excess of unlabelled somatostatin. The effects of dithiothreitol and mercaptoethanol on the binding of (125)I-labelled [Tyr(1)]somatostatin to the binding protein suggests that binding involves two sequential steps, first loose binding, then disulphide linkage. Since semipurified somatostatin-binding protein causes a dose-related inhibition of the binding of (125)I-labelled [Tyr(1)]somatostatin in radioimmunoassays for somatostatin, estimates of somatostatin content of tissue extracts by radioimmunoassay in some cases may be spuriously high. It is not yet clear whether the binding protein is a true cytosol protein or an easily solubilized membrane protein. 相似文献
99.
The aim of this work was to discover the pathway of starch breakdown during thermogenesis in the club of the spadix of Arum maculatum. The conventional α-amylase of higher plants could not be demonstrated in extracts of clubs although such extracts did exhibit considerable hydrolytic activity towards starch. This activity had an action pattern characteristic of an endo-amylase, was destroyed by heating to 70°, and was not inhibited by either 7 mM ethylenediaminetetra-acetic acid or 100 mM N-ethyl maleimide. Measurements of this hydrolytic activity, and of the maximum catalytic activities of starch phosphorylase, phosphoglucomutase and hexokinase, were made at different stages of club development. These measurements were compared with estimates of the rate of starch breakdown at thermogenesis. This comparison indicates that phosphorolytic cleavage does not play a large role in such starch breakdown, and that this process is mediated, mainly, by the hydrolytic activity, described above, and by hexokinase. 相似文献
100.
The aim of this work was to establish the pathways of carbohydrate oxidation used in the dark by leaves of Pisum sativum and Triticum aestivum. Segments of young and mature leaves of pea released the carbons of glucose-[14C] as 14CO2 in the order 3,4 > 1 > 2 > 6 whereas in segments of young and mature leaves of wheat the order was 3,4 > 1 > 6 > 2. The detailed labelling of the constituents of mature leaves of wheat by glucose-[1-14C], -[2-14C], -[3,4-14C], and -[6-14C] was determined and showed that the high yield of CO2 from C-6 relative to that from C-2 was due to release of C-6 during pentan synthesis. Estimates were made of the maximum catalytic activities of phosphofructokinase and glucose-6-phosphate dehydrogenase in pea and wheat leaves of three ages. The results of all the above investigations strongly indicate that both pea and wheat leaves in the dark oxidize carbohydrate via glycolysis and the pentose phosphate pathway with the latter accounting for no more than a third of the total. No evidence was obtained of any major change in the relative activities of the two pathways during the development of either type of leaf. 相似文献