全文获取类型
收费全文 | 32441篇 |
免费 | 1974篇 |
国内免费 | 4789篇 |
出版年
2024年 | 73篇 |
2023年 | 520篇 |
2022年 | 755篇 |
2021年 | 989篇 |
2020年 | 883篇 |
2019年 | 1139篇 |
2018年 | 908篇 |
2017年 | 864篇 |
2016年 | 910篇 |
2015年 | 1132篇 |
2014年 | 1530篇 |
2013年 | 2085篇 |
2012年 | 1496篇 |
2011年 | 1526篇 |
2010年 | 1329篇 |
2009年 | 1625篇 |
2008年 | 1788篇 |
2007年 | 1933篇 |
2006年 | 1973篇 |
2005年 | 1827篇 |
2004年 | 1694篇 |
2003年 | 1589篇 |
2002年 | 1463篇 |
2001年 | 1195篇 |
2000年 | 994篇 |
1999年 | 925篇 |
1998年 | 810篇 |
1997年 | 701篇 |
1996年 | 681篇 |
1995年 | 655篇 |
1994年 | 616篇 |
1993年 | 435篇 |
1992年 | 382篇 |
1991年 | 319篇 |
1990年 | 268篇 |
1989年 | 187篇 |
1988年 | 207篇 |
1987年 | 183篇 |
1986年 | 134篇 |
1985年 | 119篇 |
1984年 | 104篇 |
1983年 | 49篇 |
1982年 | 64篇 |
1981年 | 32篇 |
1980年 | 36篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 16篇 |
1950年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
Purification and properties of theDrosophila zen protein 总被引:1,自引:0,他引:1
Summary The zen protein is encoded by the zerknullt gene required for normal early development inDrosophila. Like many regulatory proteins of this type, zen contains a 60 amino acid homeobox sequence. We have purified the zen protein
and studied its solution behavior and its interaction with DNA. The zen protein exists as a monomer in solution with a molecular
weight of about 40000. It binds specifically to a site about 900 bases upstream from thezen gene. Within this binding site DNase protection experiments indicate that binding is confined to two regions approximately
11 and 14 bases in length that are separated by about 30 base pairs. The protein concentration dependence of the binding curve
suggests that protein binding is non cooperative. 相似文献
112.
Robert Sweetland Patricia C. Sheppard Janice G. Dodd Robert J. Matusik 《Molecular and cellular biochemistry》1988,84(1):3-15
Summary After castration, the rat dorsolateral prostate M-40 mRNA initially decreased then rebounded to precastrated levels. The cellular site of M-40 expression and its renewed expression after castration was defined by in situ hybridization histochemistry. In situ hybridization with either a 32P-labeled or biotin-labeled M-40 cDNA probe demonstrated that M-40 mRNA levels were higher in the lateral than dorsal prostate. A second androgen regulated gene, RWB, also was highly expressed in the lateral prostate. The biotinylated cDNA probes provided microscopic resolution of the expressing cells, revealing two distinct morphologies of lateral epithelium which expressed both the M-40 and RWB mRNA. These morphologies appeared in ducts which contained either epithelial cell sheets that were highly convoluted or thinner epithelial cells with a minimal degree of convolution. The RWB mRNA decreased in both cell populations in response to androgen withdrawal. The decline and reappearance of M-40 mRNA also appeared in both epithelial cell types. These data demonstrated that after castration the M-40 mRNA initially decreased as expected for an androgen sensitive gene and then progressed to a fully inducible state. The mechanism of this progression remains to be elucidated. 相似文献
113.
114.
Abstract. The techniques of molecular biology are being employed to investigate at the gene level the systemically mediated, wound-induced accumulation of two defensive proteinase inhibitor proteins in plant leaves. These techniques have added a new dimension to biochemical and physiological studies already underway to understand the mechanism of induction by wounding. The acquisition of cDNAs from the RNAs coding for the two inhibitors facilitated studies of mRNA synthesis in leaves in response to wounding, and provided probes to obtain wound-inducible proteinase inhibitor genes from tomato ( Lycopersicon esculentum ) and potato (Solarium tuberosum) genomes. Successful transformations of tobacco plants with fused genes, containing the 5' and 3' regions of the inhibitor genes with the open reading frame of the chloramphenicol acelyltransferase ( cat ) gene, have provided a wound-inducible chloramphenicol acetyltransferase (CATase) activity with which to seek cis- and transacting elements that regulate wound-inducibility to help to understand the interaction of cytoplasmic and nuclear components of the intracellular communication systems that activate the proteinase inhibitor genes in response to wounding by insect pests. 相似文献
115.
A role for haemoglobin in all plant roots? 总被引:4,自引:2,他引:2
Abstract. We have found haemoglobin in plant roots whereas previously it has been recorded only in nitrogen fixing nodules of plants. Haemoglobin occurs not only in the roots of those plants that are capable of nodulation but also in the roots of species that are not known to nodulate. We suggest that a haemoglobin gene may be a component of the genome of all plants. The gene structure and sequence in two unrelated families of plants suggests that the plant haemoglobins have had a single origin and that this origin relates to the haemoglobin gene of the animal kingdom. At present we cannot completely rule out the possibility of a horizontal transfer of the gene from the animal kingdom to a progenitor of the dicotyledonous angiosperms but we favour a single origin of the gene from a progenitor organism to both the plant and animal kingdoms. We speculate about the possible functions of haemoglobin in plant roots and put the case that it is unlikely to have a function in facilitating oxygen diffusion. We suggest that haemoglobin may act as a signal molecule indicating oxygen deficit and the consequent need to shift plant metabolism from an oxidative to a fermentative pathway of energy generation. 相似文献
116.
The comparison of primary structures is extended to 22 cytochromesb orb
6, 12 cytochromesc
1 orf, and 8 Rieske FeS proteins. Conclusions are drawn as to their phylogenetic relationship as well as on conserved, functionally important amino acids and secondary structures. The results are in favor of two independent quinone binding sites at opposite surfaces of the membrane, topping one of the two hemes of cytochromeb each. 相似文献
117.
Jürgen M. Schmitt Christine Michalowski Hans J. Bohnert 《Photosynthesis research》1988,17(1-2):159-171
Mesembryanthemum crystallinum responds to high salinity in the soil by shifting the mode of carbon assimilation from the C3 mode to Crassulacean acid metabolism (CAM). Several enzymes of carbon metabolism have increased apparent activities in the CAM mode, including phosphoenolpyruvate carboxylase (PEPcase) and pyruvate orthophosphate dikinase (PPDK). We have identified cDNA clones for PEPcase and PPDK by immunological screening of a cDNA library constructed in the protein expression vector lambda gt11. The clones were characterized by immunoblotting and RNA blotting techniques. RNA blotting showed that during CAM induction the steady-state level of mRNAs for both PEP case and PPDK increased.Abbreviations IPTG
isopropyl thiogalactoside
- PEP
phosphoenolpyruvate
- PEPcase
phosphoenolpyruvate carboxylase
- PPDK
pyruvate orthophosphate dikinase
- Xgal-5
bromo-4-chloro-3-indolyl-beta-D-galactopyranoside 相似文献
118.
The light-harvesting complex of photosystem II (LHC II) contains one major (LHC IIb) and at least three minor chlorophyll-protein components. The apoproteins of LHC IIb (LHCP) are encoded by nuclear genes and synthesized in the cytoplasm as a higher molecular weight precursor(s) (pLHCP). Several genes coding for pLHCP have been cloned from various higher plant species. The expression of these genes is dependent upon a variety of factors such as light, the developmental stage of the plastids and the plant. After its synthesis in the cytoplasm, pLHCP is imported into plastids, inserted into thylakoids, processed to its mature form, and assembled into LHC IIb. The pathway of assembly of LHC IIb in the thylakoid membranes is currently being investigated in several laboratories. We present a model that gives some details of the steps in the assembly process. Many of the steps involved in the synthesis and assembly are dependent on light and the stage of plastid development.Abbreviations PS
Photosystem
- LHC II
Light-harvesting complex of PS II
- LHCP
Apoproteins of LHC IIb
- pLHCP
Precursor of LHCP
- PAGE
Polyacrylamide gel electrophoresis 相似文献
119.
120.