全文获取类型
收费全文 | 5251篇 |
免费 | 600篇 |
国内免费 | 1篇 |
出版年
2022年 | 54篇 |
2021年 | 90篇 |
2020年 | 58篇 |
2019年 | 56篇 |
2018年 | 91篇 |
2017年 | 89篇 |
2016年 | 150篇 |
2015年 | 264篇 |
2014年 | 276篇 |
2013年 | 309篇 |
2012年 | 382篇 |
2011年 | 423篇 |
2010年 | 265篇 |
2009年 | 231篇 |
2008年 | 332篇 |
2007年 | 336篇 |
2006年 | 309篇 |
2005年 | 229篇 |
2004年 | 209篇 |
2003年 | 216篇 |
2002年 | 202篇 |
2001年 | 91篇 |
2000年 | 80篇 |
1999年 | 76篇 |
1998年 | 53篇 |
1997年 | 43篇 |
1996年 | 39篇 |
1995年 | 35篇 |
1994年 | 25篇 |
1993年 | 28篇 |
1992年 | 67篇 |
1991年 | 43篇 |
1990年 | 45篇 |
1989年 | 34篇 |
1988年 | 40篇 |
1987年 | 42篇 |
1986年 | 34篇 |
1985年 | 34篇 |
1984年 | 38篇 |
1983年 | 30篇 |
1982年 | 24篇 |
1980年 | 23篇 |
1979年 | 16篇 |
1978年 | 26篇 |
1977年 | 21篇 |
1975年 | 21篇 |
1974年 | 22篇 |
1973年 | 16篇 |
1972年 | 23篇 |
1971年 | 15篇 |
排序方式: 共有5852条查询结果,搜索用时 375 毫秒
81.
Preamylopectin Processing: A Mandatory Step for Starch Biosynthesis in Plants 总被引:20,自引:2,他引:18
下载免费PDF全文
![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mouille G Maddelein ML Libessart N Talaga P Decq A Delrue B Ball S 《The Plant cell》1996,8(8):1353-1366
It has been generally assumed that the [alpha]-(1->4)-linked and [alpha]-(1->6)-branched glucans of starch are generated by the coordinated action of elongation (starch synthases) and branching enzymes. We have identified a novel Chlamydomonas locus (STA7) that when defective leads to a wipeout of starch and its replacement by a small amount of glycogen-like material. Our efforts to understand the enzymological basis of this phenotype have led us to determine the selective disappearance of an 88-kD starch hydrolytic activity. We further demonstrate that this enzyme is a debranching enzyme. Cleavage of the [alpha]-(1->6) linkage in a branched precursor of amylopectin (preamylopectin) has provided us with the ground rules for understanding starch biosynthesis in plants. Therefore, we propose that amylopectin clusters are synthesized by a discontinuous mechanism involving a highly specific glucan trimming mechanism. 相似文献
82.
Steven Szarka Melanie Fitch Santiago Schaerer Maurice Moloney 《Plant molecular biology》1995,27(2):263-275
In order to investigate the role of cell division in plant development, we isolated several plant genes which encode homologues of animal and yeast cell cycle regulators known as cyclins.Through the use of degenerate primers and the polymerase chain reaction (PCR) we isolated a Brassica sequence which showed homology to the cyclin box functional domain found within cyclin proteins. Southern blot analysis indicated that Brassica napus has a large number of genes containing cyclin box-related sequences. This was further supported by the isolation of cyclin box sequences from six different genomic clones. In addition, we have isolated two different cyclin cDNA clones, BnCYC1 and BnCYC2, from a Brassica napus shoot apical cDNA library. Both of the cDNA clones contain a destruction box regulatory domain similar to animal mitotic cyclins.Northern blot analysis using BnCYC2 shows mRNA levels which correlate well with the level of cell division in various tissues. Messenger RNA abundance was highest in 1–3 mm leaves, root tips and shoot apices. The mRNA detected using BnCYC1 was restricted to young leaves and the shoot apex, suggesting divergent, organ-specific roles for cyclin family members. The results demonstrate that the plant cyclin gene family is more extensive than previously demonstrated and consists of genes expressed in all dividing tissues as well as a subset of developmentally specific members. 相似文献
83.
Stephen W. Ball 《Biology & philosophy》1995,10(2):129-180
Gibbard's theory of rationality is evolutionary in terms of its result as well as its underpinning argument. The result is that judgments about what is rational are analyzed as being similar to judgments of morality — in view of what Darwin suggests concerning the latter. According to the Darwinian theory, moral judgments are based on sentiments which evolve to promote the survival and welfare of human societies. On Gibbard's theory, rationality judgments should be similarly regarded as expressing emotional attachments to behavioral norms which originate and function to coordinate social interaction. Consequently, Gibbard's theory of rationality might be used to illuminate Darwin's theory of morality, and vice versa. Additionally, as argued in the present essay, both can be further elaborated, and defended, by developing related themes in philosophical ethics: viz., connected with Hume and 20th-century emotivists. The main problem is that this general Darwinian approach faces widespread opposition nowadays, not only in ethics but in philosophy of science. The purpose of this essay is to analyze Gibbard's theory, critically and constructively, with emphasis on the pertinent commonalities in Darwin, Hume and the emotivists, while also critically addressing their common enemies. The pervasive methodological orientation is to relate this analysis to (philosophy of) science in general, and biological science in particular. 相似文献
84.
Effects of manipulation of food supply on estuarine meiobenthos 总被引:1,自引:0,他引:1
A comparative mesocosm experiment was carried out to determine the effects of natural foods of different quality and quantity on the structure of natural meiobenthic communities collected in undisturbed sediment from the polluted Westerschelde and the comparatively undisturbed Gironde estuaries. Nematode communities are more diverse and species rich in the latter estuary. The organic matter or foods used were phytoplankton, green alga, salt marsh plant detritus and leaf litter detritus which were added at three dose rates including a high dose. There was no change in community structure in response to the treatments in either of the estuarine meiobenthic communities. Analysis of all the results from this experiment indicate that the food quantity manipulations had almost no effect on the deposit feeding meiofauna. It may be that the reserves of organic matter within the sediment were sufficient to satisfy their dietary requirements for the duration of the experiment. The abundance of diatom/epigrowth feeding nematodes which were initially dominant in the Gironde, declined substantially suggesting that they may have been food limited since diatoms were not among the sources of organic matter added to the mesocosm. There was no specific response to the five different types of organic matter added to the mesocosm 相似文献
85.
Colin V. Beechey Simon T. Ball K. M. Stuart Townsend Janet Jones 《Mammalian genome》1997,8(4):236-240
Mouse Chromosome (Chr) 7 distal to band F3 on the physical map is known to be subject to imprinting, maternal duplication
(MatDp) of the region leading to a late embryonic lethality, while paternal duplication (PatDp) causes death in utero before
11.5 dpc. Using a new mouse reciprocal translocation T(7;11)65H to produce MatDp for distal Chr 7, we have mapped the region
subject to imprinting more precisely to bands 7F4/F5 on the cytogenetic map. Fluorescence in situ hybridization (FISH) studies
on mitotic and meiotic chromosomes of a T65H heterozygote show that the imprinted gene Igf2 is located in the same region. This was confirmed by the finding that embryos with MatDp of bands 7F4/F5 did not express
Igf2. We suggest that other members of the imprinted domain containing Igf2, namely Mash2, H19, Ins2, and p57
K1P2
, are also located in 7F4/F5 and that some or all of these genes may be responsible for the two imprinting lethalities seen
with MatDp and PatDp for this region.
Received: 13 October 1996 / Accepted: 8 December 1996 相似文献
86.
Cariillo M.Belen; Milner Caroline M.; Ball Simon T.; Snoek Margriet; Campbell R.Duncan 《Glycobiology》1997,7(7):975-986
The Neu1 locus, in the S region of the murine histocompatibility-2complex, regulates the sialic acid content of several liverlysosomal enzymes. Three alleles, Neu1a, Neu1b, and Neu1c, havebeen described on the basis of differential sialylation of theenzyme liver acid phosphatase. The Neu1a allele occurs in asmall number of mouse strains, e.g., SM/J and is associatedwith sialidase deficiency. We recently described G9, a sialidasegene in the human major histocompatibility complex (Milner etal. (1997) J. Biol. Chem., 272, 45494558), and we nowreport the characterization of the equivalent gene in mouse.The protein product of the murine G9 gene is 409 amino acidsin length and is 83% identical to its human orthologue. Expressionof the murine G9 protein in insect cells has confirmed thatit is a sialidase, with optimal activity at pH 5. To elucidatethe basis of sialidase deficiency in mouse strains carryingthe Neu1a allele, we have sequenced the G9 coding regions frommice carrying the three Neu1 alleles and hence defined the aminoacid sequence characteristic of each allotype. Of particularinterest is a Leu-209 to Ile mutation that is unique to theNeu1a allotype and is associated with reductions in sialidaseactivity of 68% and 88% compared to the Neu1b and Neu1c allotypes,respectively, when these three protein variants are expressedin insect cells. Additional factors, such as differential expression,may also influence the activities of the Nen1 allotypes in vivo.We have observed that the level of G9 mRNA is substantiallyreduced in mice carrying the Neu1a allele compared to the Neu1b(8595% reduction) and Neu1c (70% reduction) alleles. H2 complex MHC Neu1 sialidase 相似文献
87.
Epiphyses of the proximal tibiae of 7-week-old normal and homozygous recessive brachymorphic mice (bm/bm) were immunostained
using a monoclonal antibody to basic fibroblast growth factor to determine its expression in growth plate cartilage, osteoblasts
on the surfaces of the primary spongiosa and articular cartilage. In the normal growth plate, the immunoreactive factor was
present in chondrocytes of the proliferating and upper hypertrophic zones but absent from lower hypertrophic chondrocytes.
Immunostaining was present only in the territorial extracellular matrix immediately adjacent to the chondrocytes of the proliferating
and upper hypertrophic zones. Osteoblasts of the primary spongiosa stained heavily in normal mice. Strong staining was observed
in intermediate zone articular chondrocytes. Cells in the superficial layer of articular cartilage were unstained. The extracellular
matrix of the articular cartilage was completely free of immunostaining. In contrast, the reduced size of bm/bm growth plates
was accompanied by significantly reduced staining intensity in proliferating and upper hypertrophic chondrocytes, and staining
was absent from the territorial extracellular matrix of all zones of the bm/bm growth plate. Osteoblasts of the primary spongiosa
of bm/bm mice stained less than those of normal mice. Articular cartilage chondrocytes in the intermediate zone stained with
less intensity in bm/bm mice, and the cells of the superficial layer were unstained. The extracellular matrix of bm/bm articular
cartilage was completely free of staining. Brachymorphic epiphyseal growth plate and articular chondrocytes, and osteoblasts
in the primary spongiosa, express reduced amounts of immunoreactive fibroblast growth factor-2. This phenotypical characteristic
may be associated with abnormal endochondral ossification and development of bone in brachymorphic mice 相似文献
88.
89.
Lysozyme-promoted association of protein I molecules in the outer membrane of Escherichia coli.
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Incubation of whole envelopes prepared from sonically oscillated Escherichia coli K-12 cultures with lysozyme in vitro resulted in the appearance of a protein species with an apparent molecular weight double that of outer membrane protein I. Similar dimers were also detected in purified outer membranes and whole envelopes from lysozyme-induced spheroplasts of E. coli K-12. This was confirmed by two-dimensional electrophoresis in which the dimers were resolved in the second dimension to run as single polypeptides of protein I. Formation of dimers was correlated with peptidoglycan degradation, but the ability of protein I molecules to associate may vary between strains of E. coli, since dimers were found only in outer membranes from E. coli W7. We suggest that extensive degradation of peptidoglycan leads to nonspecific formation of protein I aggregates, but that these aggregates do not occur in vivo. 相似文献
90.