全文获取类型
收费全文 | 2761篇 |
免费 | 177篇 |
国内免费 | 5篇 |
出版年
2023年 | 25篇 |
2022年 | 52篇 |
2021年 | 99篇 |
2020年 | 79篇 |
2019年 | 127篇 |
2018年 | 120篇 |
2017年 | 79篇 |
2016年 | 98篇 |
2015年 | 119篇 |
2014年 | 164篇 |
2013年 | 193篇 |
2012年 | 235篇 |
2011年 | 212篇 |
2010年 | 111篇 |
2009年 | 98篇 |
2008年 | 142篇 |
2007年 | 136篇 |
2006年 | 86篇 |
2005年 | 92篇 |
2004年 | 68篇 |
2003年 | 95篇 |
2002年 | 79篇 |
2001年 | 41篇 |
2000年 | 35篇 |
1999年 | 30篇 |
1998年 | 17篇 |
1997年 | 21篇 |
1996年 | 19篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1991年 | 20篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 23篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1971年 | 5篇 |
排序方式: 共有2943条查询结果,搜索用时 0 毫秒
11.
Summary The neurosecretory mediodorsal cells that produce a putative growth hormone of the snail Helisoma duryi were studied in fast-growing virgin snails and in slow-growing reproducing snails. There are about 60 mediodorsal cells in clusters on each side of the cerebral commissure of the central nervous system, and they contain dense-cored granules which are 100–200 nm in diameter. The cells of virgin snails have dense Golgi bodies, scattered ER cisternae, and few granules, while those of reproducing snails have pale Golgi bodies, stacked ER cisternae, and numerous granules. Thus the mediodorsal cells of the virgin snails appear to be more active synthetically than those of the reproducing snails. The cells near the endocrine dorsal bodies contain many dorsal body precesses in their membrane interdigitations. There are junction-like interactions between some of the interdigitations. Gap junction-like contacts are seen between mediodorsal cells and glial cells. The axon endings of the mediodorsal cells at the neurohemal area in the labial nerve show more release profiles in virgin snails than in reproducing snails. A daily pattern of release has been observed in reproducing snails, and rates of release are higher in the evening than in the morning. 相似文献
12.
E. coli K12802 cells transformed by multicopy plasmid with phoA gene acquire the ability to oversynthesize alkaline phosphatase, secrete it into the cultural medium, and accumulate the precursor of this enzyme. The dynamics of enzyme production and secretion as well as cytomorphological changes revealed the existence of a mechanism of selective enzyme secretion into the medium. It is characterized by a decrease of enzyme specific activity in periplasm and its increase in cultural medium, appearance of numerous local zones of adhesion of cytoplasmic and outer membranes, formation of large extracellular outer membrane vesicles containing PhoA protein on the cell poles, and their release into the medium. We isolated the vesicles and found that they contain PhoA (in dominating quantity), several other periplasmic proteins, and matrix proteins of outer membranes. By their phospholipid and protein composition, they correspond to the fraction of outer membranes which have the largest density and sedimentation rate and, apparently, contain no lipoprotein. 相似文献
13.
Germinal vesicle migration (GVM) and dissolution (GVD) were studied in goldfish oocytes treated with 17-α,20–β-dihydroxyprogesterone (DHP) and/or demecolcine (DE; a colchicine derivative also known as colcemid) in vitro. DE (100 μg/ml) in the presence of DHP, enhanced steroid-induced GVM, after both 24 and 48 hr of incubation and significantly reduced the DHP ED50 value for GVM. Similarly, administration of DE alone elicited a significant, dose-related increase in GVM after 24 or 48 hr of incubation. The presence of DE, either alone or in combination with DHP, was without effect on GVD. The effect of DE was also tested on ooplasmic viscoelasticity in goldfish follicles subjected to a centrifugal force (160g for 1 min). Preincubation (24 hr) of goldfish follicles in DE significantly influenced the direction and the extent of the centrifugally induced GV movement along the axis of centrifugal force in a dose-related fashion. The present results provide support for the hypothesis that cytoskeletal components, such as microtubules that are sensitive to DE, are involved in the mechanism of GVM in goldfish oocytes. 相似文献
14.
15.
N I Mikhaleva S A Gulevskaia M A Nesmeianova N E Suzina B A Fikhte 《Mikrobiologiia》1984,53(3):432-436
As was demonstrated using the Con-A polymer, membranous fractions prepared by various cell disintegration procedures are a heterogeneous population. The population includes right side out vesicles and inside out vesicles whose proportion depends on the procedure of disintegration. The orientation of these vesicles was studied by electron microscopy, their ATPase activity was assayed by cytochemical techniques, and the morphology of the vesicles was also investigated. The authors discuss the possible effect of Con-A on the reorganisation of membranes and the activity of ATPase. 相似文献
16.
Abidin Bin Hamid John E. Smith 《Journal of industrial microbiology & biotechnology》1987,2(3):137-141
Summary Phenobarbital stimulated aflatoxin biosynthesis byAspergillus flavus and this was paralleled by an increase in microsomal NADPH-cytochromeP-450 reductase and cytochromeP-450 activities. Aflatoxin biosynthesis was inhibited by SKF 525-A, metyrapone and cyanide, inhibitors of the cytochromeP-450 monooxygenase system, further suggesting that aflatoxin biosynthesis byA. flavus could be mediated by a cytochromeP-450 monooxygenase enzyme system. 相似文献
17.
Jacques Hille Frank Verheggen Peter Roelvink Henk Franssen Ab van Kammen Pim Zabel 《Plant molecular biology》1986,7(3):171-176
Summary Plant cells are sensitive to the antibiotic bleomycin, a DNA damaging glycopeptide. A bleomycin resistance determinant, located on transposon Tn5 and functional in bacteria, has been cloned in a plant expression vector and introduced into Nicotiana plumbaginifolia using Agrobacterium tumefaciens. The expression of this determinant in plant cells confers resistance to bleomycin and allows selection of transformed plant cells. 相似文献
18.
19.
Sequence homologies within the 5'' end region of the estrogen-controlled vitellogenin gene in Xenopus and chicken. 总被引:10,自引:2,他引:8
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
P Walker M Brown-Luedi J E Germond W Wahli F C Meijlink A D van het Schip H Roelink M Gruber G Ab 《The EMBO journal》1983,2(12):2271-2279
In oviparous vertebrates vitellogenin, the precursor of the major yolk proteins, is synthesized in the liver of mature females under the control of estrogen. We have established the organization and primary structure of the 5' end region of the Xenopus laevis vitellogenin A2 gene and of the major chicken vitellogenin gene. The first three homologous exons have exactly the same length in both species, namely 53, 21 and 152 nucleotides, and present an overall sequence homology of 60%. In both species, the 5'-non-coding region of the vitellogenin mRNA measures only 13 nucleotides, nine of which are conserved. In contrast, the corresponding introns of the Xenopus and the chicken vitellogenin gene show no significant sequence homology. Within the 500 nucleotides preceding the 5' end of the genes, at least six blocks with sequence homologies of greater than 70% were detected. It remains to be demonstrated which of these conserved sequences, if any, are involved in the hormone-regulated expression of the vitellogenin genes. 相似文献
20.